Capacitive energy storage is distinguished from other types of electrochemical energy storage by short charging times, long cycle life and the ability to deliver significantly more power than batteries. A key limitation to this technology is its low energy density and for this reason there is considerable interest in exploring pseudocapacitive charge storage mechanisms which offer the tantalizing possibility of bridging the performance gap between batteries and double layer capacitors. In this paper we review our recent studies on nanostructured materials and mesoporous transition metal oxide films which exhibit increased levels of pseudocapacitance and enhanced energy storage properties.

Our studies with nanoscale anatase TiO₂ show that pseudocapacitive contributions become increasingly important for crystallite sizes below 10 nm, leading to greater amounts of total stored charge without compromising kinetics. Mesoporous films of TiO₂ maintain the high capacitive charge storage properties of the isolated nanoparticles. These architectures, prepared by the co-assembly of block co-polymers with either metal oxide precursors or metal oxide nanoparticles, facilitate electrolyte access to the redox-active walls via the interconnected mesoporous network. Moreover, the nanoscale morphology of the oxide framework ensures that pseudocapacitive contributions dominate the charge storage. Mesoporous films of iso-oriented MoO₃ and Nb₂O₅ exhibit even higher levels of pseudocapacitive charge storage because of an additional contribution associated with lithium ions being inserted into preferentially oriented crystalline layers. The enhanced pseudocapacitive response exhibited by mesoporous transition metal oxide films represents a very promising direction for designing electrochemical capacitors that can achieve increased energy density while still maintaining high power density.

We have synthesized and characterized hybrid nanomaterials capable of enhancing the specific capacitance of thin film supercapacitors. Integration of supercapacitors into the renewable energy grid is critical for efficient use of periodic and transient sources such as solar, wind, and tide. We use combinations of single walled and multiwalled carbon nanotubes as the matrix. The nanotubes are functionalized by novel ruthenium coordination complexes at very low atomic percent. At only a 3% Ru complex functionalization the specific capacitance of our thin films increased by 250%. We will also present our results from our SWCNT- NiO nanoplate composite films. The NiO nanoplates were synthesized by a high-throughput, high-yield microwave process. All of the materials are characterized spectroscopically, electrochemically, and structurally by SEM, TEM, and DLS. Surface area and porosity are measured by BET and BJH methods. CV, CD, and EIS of the resultant thin films will be presented. The composite thin films also display interesting electrochromic and photovoltaic response. Computation studies on these hybrid nanomaterials will also be presented.

MnO₂ as a pseudocapacitive electrode material for electrochemical capacitors have been intensively investigated due to its low-cost, non-toxicity, and high theoretical specific capacitance. For practical application, electrospun nanofiber (NF) network can be the best candidate due to its porous structure with high surface area, facile mass/charge charge transfer, and enabling high mass-loading. However, MnO₂ phase of electrospun NF was hard to be obtained because lots of oxygen is consumed during the combustion of the organics. In this study, we fabricated electrospun MnO₂ NF electrode using novel method: sequential procedure of oxygen partial pressure controlled calcination and electrochemical activation to oxidize low valence MnO_x (x < 2) NFs. Also, the effect of initial phase (Mn₃O₄ and Mn₂O₃) and CNT incorporation on the degree of electrochemical oxidation and capacitance was analyzed.
Electrospun MnO_x NFs were fabricated from solution consist of Mn(acac)₃, PVP, and DMF with a DC voltage of 12 kV. As-spun fibers were calcined at 300 ^oC in air and O₂ ambient to combust organics. MnO_x NF-based electrodes (MnO_x NF (80 %) + carbon black or CNT (10 %) + PVDF (10 %), 1~1.5 mg/cm²) were assembled into 3-electrode cell. Electrochemical oxidation was conducted at constant current density of 1×10² mA/cm². Cyclic voltammetry (CV) was performed under 1 M Na₂SO₄ with a potential sweep range of 0 ~ 0.9 V vs. SCE.
The phases of MnO_x NF calcined under air and O₂ ambient were hausmannite-Mn₃O₄ and bixbyte-Mn₂O₃, respectively. Both NFs have an average width of 120 nm composed of nanocrystal with a size of 17 nm. After electrochemical oxidation, both NFs were transformed to layered birnessite-MnO₂, but capacitance and degree of transformation were quietly different. The capacitances of electrochemically-oxidized Mn₃O₄ and Mn₂O₃ NFs were ~ 200 and 80 F/g, respectively, and loss of capacitance during 1000 cycles of oxidized Mn₃O₄ NFs was much smaller than that of Mn₂O₃ NFs. Mn₃O₄ NFs exhibited superior transformation activity than Mn₂O₃ NFs: oxidation charge of Mn₃O₄ NFs was measured to be 10 times greater than that of Mn₂O₃ NFs approximately, and increase of average oxidation state during oxidation process measured from XPS (Mn 3s core level) for Mn₃O₄ and Mn₂O₃ NFs were 1.2 and 0.3, respectively. This is due to strong Jahn-Teller distortion of octahedral Mn³⁺ subunit in Mn₃O₄ which easily transformed to other stable oxidation states. Based on degree of transformation and the ratio of Q_OX/Q_RED measured from CV as a function of cycle, it was founded that low capacitance and poor cyclability of oxidized-Mn₂O₃ NFs was caused from cathodic dissolution of Mn ions from huge amount of untransformed Mn₂O₃. It is also demonstrated that capacitance and cyclability is significantly enhanced by replacing carbon black to CNT due to low charge transfer resistance and strong binding effect.

Nanocrystalline MnO₂ shows multiple redox states making it attractive for pseudocapacitive charge storage via fast redox reactions for use in supercapacitor energy storage. However, low electrical conductivity of MnO₂ nanoparticles and agglomeration which reduces surface area and lowers materials utilization limits specific capacitance to~350 F/g, far lower than ~1370 F/g possible theoretically. To increase electrochemical activity, integration of MnO₂ with structured carbon to prevent MnO₂ agglomeration and tap the double layer capacitive effect has been tried. Composites of conducting polymers with MnO₂ nanoparticles have also been studied; but since these methods lack control of the MnO₂ nanoparticle size and dispersion, combined advantage of pseudocapacitive properties are not fully availed.
In this work, supercapacitor electrode having a three dimensional (3D) network of MnO₂ nanoparticles dispersed within branched molecular chain structure of polypyrrole (PPy) conducting polymer with nanoscale connectivity is prepared on graphite substrate. Nanocomposite electrode with integrated MnO₂ nanostructure was synthesized by electro-polymerization of pyrrole in the presence of Mn²⁺ ions derived from MnSO₄ in an aqueous medium by sequential ultra-short (10ms) anodic current pulses. This results in anodic oxidative growth of two different chemical entities polypyrrole by polymerization and anodic oxidative deposition of MnO₂ nanoparticles which become electro-embedded within the growing polypyrrole polymeric chain structures. Effect of electro-synthesis parameters, current pulse density and Mn²⁺ ions concentration on nanostructure and oxidation state of MnO₂ is investigated by SEM and XPS. MnO₂ nanoparticles coexist in the hydrated Mn(II) and Mn(IV) states and undergo valence state change contributing to system pseudocapacitance. Detailed electrochemical study of nanocomposite electrode in the supercapacitor configuration is carried out using cyclic voltammetry (CV), impedance spectroscopy (IS), and sequential capacitive charge discharge (CD) techniques. Increasing the density of sequestered MnO₂ nanoparticles in PPy significantly improves specific capacitance from 200 to 620 F/g. MnO₂ nanoparticle distribution is affected by the open porous polypyrrole polymer microstructure modified by pulsed current density. CD characteristic show stable and electrochemical capacitance retention with high Coulomb efficiency for ~5000 cycles with an initial fading of ~8% in performance.
In conclusion, in this work synergic increase in pseudo-faradic charge by combining optimized contribution from both electro-active components, conducting polymer PPy and sequestered MnO₂ nanoparticles is realized and supercapacitors with high specific capacitance and stable operation are described.

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Dye-sensitized solar cells (DSSCs) containing nanowire (NWs) arrays could significantly increase the amount of electricity converted from sunlight by using nanostructured surfaces as more effective light absorbers. These same nanomaterials are combined with plastic electronics to develop semiconductor polymer photovoltaics and they are especially advantages for their lightweight and flexible properties. Effort has been devoted to the study of electrolytes that allow light-to-electrical power conversion for DSSC applications. Several attempts have been made to substitute the liquid electrolyte in the original solar cells by using (2,2&’,7,7&’-tetrakis (N,N-di-p-methoxyphenylamine)-9-9&’-spirobi-fluorene (spiro-OMeTAD) that act as hole conductor [1]. Although efficiencies above 3% have been reached by several groups, here the major challenging is the limited photoelectrode thickness (2 µm), which is very low due to electron diffusion length (Ln) for spiro-OMeTAD (4.4 µm) [2].
In our primary innovation recipe, we successfully overcome limited photoelectrode thickness by fabricating 3-D Transparent Conducting Oxide (TCO) using tin-doped indium oxide (ITO) nanowire (NWs) arrays composed single crystal oriented [100] via a vapor transport method [3] and mesoporous TiO2 nanoparticle (NP)-based photoelectrodes using doctor blade method. Controlled ITO NWs length in the range of over 2 µm are synthesized and has been characterized using field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM) and X-Ray diffraction (XRD). Also to compare the charge collection properties of conventional NPs based solid-state DSSCs with ITO NWs based solid-state DSSCs, we have studied intensity modulated photovoltage spectroscopy (IMVS), intensity modulated photocurrent spectroscopy (IMPS) and transient open circuit voltages. As a result, above 4 µm thick ITO NWs based photoelectrodes with Z907 dye shown the best performing device, exhibiting a short-circuit current density of 6.29 mA cm-2 under simulated solar emission of 100 mW cm-2 associated with an overall power conversion efficiency of 2.98%. Finally we have developed a method of fabricating light-weight and easily bent flexible polymer PV cells with a low sheet resistance using mesoporous TiO2 nanoparticle (NP)-based photoelectrodes coated ITO NWs array on UV curing polymer materials with the optimized photoelectrode thickness. It is our believed that this new class of efficient nanowire based flexible polymer PV cells technology is the next step up.

Nowadays preparation of metal nanoparticles dispersed in polymer nanofiber film prepared by electrospinning has drawn great attention because this kind of composites combines the unique properties of metal nanoparticles (e.g., catalytic activity) with the outstanding characteristics of polymer nanofibers (e.g., the high specific surface area, high electrical conductivity with real perspective for scale-up). Therefore, these metal oxide nanoparticle-loaded carbon nanofiber (MO-NFs) electrodes are expected to enhance the electrochemical reaction (i.e., oxygen and electron transfer processes) in the vanadium redox flow battery (VFB). Here, It was prepared several MO-NFs (i.e. M= Fe,Cu, Mn, Co, ect) electrodes by electrospinning in combination with thermal treatment and these electrodes have been applied to VFB system for the first time. The structural and morphological characterization of these electrodes was carried out by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The electrochemical characterization using electrochemical impedance spectroscopy and cyclic voltammetric techniques has been applied in order to evaluate the electrocatalytic activity towards each half-cell reaction of the VFB system. The novel electrodes synthesized shows a higher reversibility, higher current collection and lower oxidation potential peaks that the conventional electrodes used, leading step forward in VFB scale -up. Finally, a small-scale cell prototype of VRFB has been designed in order to verify these findings.

Complex metal oxides are unique type of materials where they can be used for both energy generation and storage. The stability of the oxides at high temperatures, low toxicity and cost, and chemical stability make them very attractive candidates for commercial applications. In thermoelectrics, complex metal oxide-based materials have faced drawbacks in having high thermal conductivity and low power factor, in turn affecting the thermoelectric figure of merit (ZT). Hence, research was never heavily concentrated on oxides. Our approach to solving the problem of their high thermal conductivity and low power factor has been through nanostructuring, where the three important properties - thermal conductivity, electrical conductivity and Seebeck coefficient become quasi-independent of each other. We have researched on a unique of phase of calcium cobalt oxide (Ca9Co12O28), which is a misfit layer oxide. This phase has hardly been researched in literature because of its high thermal conductivity, thus limiting its use in thermoelectric devices. Through a unique single source precursor based technique, we have been able to synthesize porous nanowire structures of Ca9Co12O28 at temperatures much lower than conventional solid state techniques. Significantly improved ZT has been observed in our nanowire system up to 700K due to reduced thermal conductivity and enhanced Seebeck coefficient compared to the literatures. Same synthetic approach has also been used to prepare porous nanowires of lithium cobalt oxide (LiCoO2). The battery electrode based on these porous nanowires showed the capability to maintain their rate capabilities and accelerated Lithium ion diffusion compared to micron sized particles for high energy demanding (180 cycles at 1C charging/discharging current without degradation).

Silica/magnetite core-shell magnetic nanoparticles have been studied using Ultra Small Angle X-ray Scattering (USAXS) technique. The assembly of these hybrid nanostructured particles is found to be dependent on the strength of external magnetic field. The magnetic field was applied orthogonal as well as parallel to the X-ray beam. These experiments shed light on the stimuli responsive assembly of colloidal nanoparticles. The dipolar chains formed of magnetic nanoentities arrange themselves into 2 dimensional magnetic sheets. The investigation of core-shell nanoparticles using scattering techniques suggest that the lattice parameters of a colloidal crystal can be tuned by varying the strength of external magnetic field.

In this report, we have investigated the dependence of the UV response on the carrier density in Ohmic-type ZnO nanowire (NW) devices. Interestingly, giant enhancement in UV response can be observed as the carrier density in ZnO NW was controlled to be nearly depleted, strongly implying that a great sensitivity of ZnO NW can be obtained at the operation condition of low-current state. Moreover, more than four orders of magnitude changes in ZnO NW conductivity can be apparently measured upon 365 nm light illumination with low power density of few uW/cm^2. Here, we have proposed an operation method by controlling the carrier density to achieve a low-power consumption and ultrasensitive UV nanosensor for optoelectronics applications and optical switching.

Direct conversion of external stimuli to mechanical motion at the micro to nanoscale is of vital importance in advanced technologies including micro- and nano-electromechanical systems, micro-robotics, and biomimetics. A wide range of materials featuring different stimuli-responsive properties are used for the actuation. On the inorganic side, differential thermal expansion, piezoelectric ceramics, and shape memory alloys are typically utilized. The relative size changes (strain) in thermal expansion and piezoelectric systems are usually low, on the order of 0.0001~0.001 even at strong stimuli such as large temperature change or high operating voltage. Consequently, they typically output small displacements far shorter than the actuator length, even with magnification mechanisms such as assembled in a bimorph structure. On the other side, actuators based on polymers or carbon nanotubes exhibit high flexibility and huge size change, but their intrinsically low response speed, weak force output, and incompatibility with present microfabrication processes present severe limitations. Therefore, it is much desired to develop micro- and nano-actuators that can deliver simultaneously high amplitude and strong force at high speed by using conventional microfabrication techniques.
Here we demonstrate a set of microactuators fabricated by a simple microfabrication process, showing simultaneously high performance by these metrics, operated on the structural phase transition in vanadium dioxide responding to diverse stimuli of heat, electric current, and light. In both ambient and aqueous conditions, the actuators bend with exceedingly high displacement-to-length ratios up to 1 in the sub-100 micrometer length scale, over a small temperature rise of 15 Celsius degree, and at frequencies up to 6 kHz. The large normalized actuation amplitude (D/L) directly benefit from the giant strain across the phase transition, as well as the nanoscale thickness of the devices. Even if the length of the bimorph actuator scales down to 1 micrometer, its tip would still displace by more than 10 nm. The work density reaches as high as 0.63 joule per cubic meter. As a comparison, the work density would be ~ 0.001-0.01 joule per cubic meter for the differential thermal expansion actuators (deltaT = 10K) and typical piezoelectric actuators. Therefore, our microactuators offer not only large displacement, but also high work output; consequently, a high actuation force is expected without being compromised by the large displacement. The functionalities of actuation can be further enriched with integrated designs of planar as well as three-dimensional geometries. Combining the superior performance, high durability, diversity in responsive stimuli, versatile working environments, and microscale manufacturability, these actuators offer potential applications in micro-electromechanical systems, microfluidics, robotics, drug delivery, and artificial muscles.

Nanostructured metal oxides have been the subject of great attention in the field of nanotechnology both from a fundamental and industrial point of view. For example, their peculiar electrical properties make them suitable as active sensing materials in resistive sensors, with enhanced performance with respect to bulk materials. Pure ZnO is an n-type semiconductor with a wide bandgap and it is one of the most promising materials due to its use in a wide range applications in various fields, including short wavelength light-emitting diode and room temperature ultraviolet (UV) lasing diode, solar cell, UV-absorber, transparent conductor, gas sensor, etc.. 2, 9, 16, 23-tetranitrophthalocyanine copper (II) (TNCuPc)/zinc oxide nanorod and plate structures were synthesized by solvothermal method. After calcination of TNCuPc/zinc oxide nanorod and plate structures, copper oxide nanopaticles decorated zinc oxide nanorods and plates were successfully synthesized. The results showed that the copper oxide nanoparticles were successfully grown on the zinc oxide nanorods and plates substrates. The materials were characterized structurally using X-ray diffraction and morphologically using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The gas sensing properties of the ZnO based sensors to carbon monoxide (CO) in air were analyzed.

Recently, nanoscale and multi-functional nanowires (NWs) have attracted extensive attention due to their unique electronic, chemical composition, and optical properties. Among the various of NWs, the ternary oxide NWs, Zn2GeO4, are considered since the good thermal stability and ideal optoelectronic property.
In this work, Zn2GeO4 NWs have been successfully synthesized by using Germanium and Zinc powders with gold as catalyst through chemical vapor transport (CVT) method. The diameters of the NWs are in the range of 40-100 nm with high aspect ratio (more than 100). The x-ray diffraction (XRD) reveals that the NWs is Rhombohedral Zn2GeO4. High resolution transmission electron microscopy (HRTEM) indicated that the NWs are single-crystalline with <110> growth direction. Furthermore, the atomic resolution EDS mapping in scanning transmission electron microscopy (STEM) based on energy-dispersive x-ray spectroscopy shows where the atoms actually located.
We also fabricated the Zn2GeO4 nanowires device and which exhibited excellent optoelectronic property under UV (254 nm) illumination. The results show that Zn2GeO4 NWs can serve as the building blocks for UV photodetectors.

Tuning of electric properties by chemical doping has been a key concept in the current semiconductor-based electronics. In case of strongly correlated transition-metal-oxides (TMO), the chemical doping reconstructs their electronic structure and leads to a lot of intriguing physical phenomena, such as high-Tc superconductor, colossal magnetoresistance, and Mott transition. In this presentation, we report on our optical spectroscopic study on the low dimensional confinement of chemical doping in strongly correlated system. Superlattice samples composed of the stacking of insulating SrTiO3 (STO) and metallic La-doped SrTiO3 (LSTO) layers were chosed for this study. As the dimensionality is varied from three to two dimensions by changing the thickness of the SrTiO3 layers, phase transition from metal to insulator occurred through interplay of charge, spin, orbital, and lattice degrees of freedom. We detail our spectroscopic ellipsometry results on the STO/LSTO superlattices, and compare them with other transport, structural, and band calculation analyses.

A nanocomposite capable of showing a resistance switching behavior has been prepared employing novel nanofillers which are conductive nanowires coated with conformal passivation layer of metal oxide to effectively gate electron flows delivered through the conductive core. The nanocomposite prepared by simple mixing of the resistance switchable nanowires with polymer matrix successfully exhibited a resistance switching behavior of highly enhanced reliability and resistance On/Off ratio, along with flexibility due to the presence of nanowires of tiny amount. The advantages of our approach include simple and low cost fabrication procedure along with sustainable performances suitable to resistance switching memory application.

Nanostructures of oxide semiconductors, particularly TiO2 and ZnO, have been widely studied as promising candidates for optoelectronic applications including sensors, solar cells, and energy storage devices. As an effective method for generating nanostructures over large areas, nanostructures of block copolymers have been intensively investigated because they self-assemble into periodic nanostructures, the size and morphology of which can be easily controlled by the molecular weight and composition of copolymers. For instance, nanostructures of block copolymers can be utilized as etching masks or templates to make patterns of functional materials. Cylindrical and lamellar nanostructures of block copolymers in thin films on substrates can be perpendicularly oriented to the plane of the films by neutralizing the substrates. We first fabricated perpendicularly oriented cylindrical and lamellar nanostructures of PS-PMMA diblock copolymers on transparent conductive oxides which were directly neutralized with self-assembled monolayers, or by transferring the block copolymer thin film which was initially fabricated on SiO2 substrates. After the removal of PMMA blocks, PS nanostructures were used as templates for the growth of oxide semiconductors including TiO2 and ZnO. By controlling the size and shape of nanostructures in the template, we were able to control the nanostructures of TiO2 and ZnO synthesized. We applied the nanostructured oxide semiconductors for practical applications including nanoelectrodes in photovoltaic devices.

The interplay among degrees of freedom - lattice, charge, orbital and spin - at the interfaces of strongly correlated oxides generate unique electronic phases and cause many intriguing phenomena, such as 2 dimensional electron gas at the LaAlO3-SrTiO3 hetero-interface and the electrical conduction at the domain walls (homo-interface) in ferroics. In order to search for new types of complex oxide interfaces, we found that the tubular oxide interfaces in self-assembled hetero-epitaxial nanostructures, which form spontaneously during the growth process due to competition of the surface energies, have not been explored yet. We adapted the BiFeO3 (BFO)-CoFe2O4 (CFO) as a model system to carry out the systematic study on the BFO-CFO vertical interface.
In order to investigate the electrical properties of the tubular oxide interface, we have performed conductive atomic force microscopy at different temperatures. The local conduction was found at the BFO-CFO vertical interface and the origin of the conduction is identified as a result of the oxygen vacancies accumulating at the interface. In addition, we have observed that this conduction can be modulated with a DC bias. This phenomenon can be understood owing to the movement of oxygen vacancies driven by the applied bias. The bias cause the oxygen vacancies either accumulate or deplete to the metal contact tip, which in turn affect the resistance at the tubular interface deciding the whether current can pass or not. Such a behavior is very close to a memristor, which can be used to design new practical devices. Our findings suggest the tubular oxide interface can not only be the medium to the coupling between phases, but also be a new state of the matter, which demonstrates a novel concept on oxide interface design and opens a pathway alternative for the explorations of diverse functionalities in complex oxide interfaces.

Recently, there has been much interest in the creation of 3D networks of nanowires. One possible way to do this is to encase the nanowires inside transparent polymer matrices since there is also a demand for obtaining conducting transparent composites. If the filler of the composite is made from a strongly conducting material, the degree of connectivity of the networked nanowires can be tested by measuring its conductivity. Though much work has been done with ITO (Tin-doped indium oxide), little has been done with the chemically similar, but cheaper, ATO (Antimony-doped tin oxide).
In this study, ATO nanoparticles were added into a polystyrene matrix and simultaneously pressed and heated so that a 3D network of the nanoparticles would form. The effecti veness of the conducting pseudo-nanowire networks was measured as the concentration of ATO in polystyrene was varied. Another variable utilized was the temperature at which the samples were pressed. The optical transmittance of the composites was also measured in order to quantify their transparency. It was found that, once the nanowire networks had percolated at a concentration of about 1.25 PHR, the conductivity and, consequently, the coherence of the networks increased at a decreasing rate as the concentration was increased. The effect of the pressing temperature was complex and required many additional sets of specimens to understand. Samples pressed at the highest temperature had the least coherent networks, as the polystyrene became too fluid and disrupted the ATO networks while at lower temperatures the opposite occurred. The optical transmittance dropped sharply as the concentration of ATO reached and surpassed 1.0 PHR. Nanowire networks were, indeed, formed through this process using these materials, but use as a conducting transparent composite in the visible range is unlikely as the percolation threshold occurs at a concentration greater than that of the optical transmittance drop, creating a trade-off between conductivity and transparency. The resistivity did drop as much as six orders of magnitude and may be useful for other applications.

The electronic structure of vanadium sesqui-oxide (V2O3) in different phases has been calculated by the screened exchange hybrid functional. After 40 years of experimental and theoretical investigation, V2O3 is still the subject of intense discussion because of the complicated phase transitions [1]. V2O3 is a canonical Mott-Hubbard insulator at low temperature, and can undergo several metal-insulator transitions by varying the temperature, pressure or doping. Here, different transitions have been examined by the screened exchange (sX) hybrid functional. This functional mixes a Thomas-Fermi screened Hartree-Fock exchange into the local-density approximation (LDA) to correct the band gap and localisation error of density functional theory [2]. As a generalised Kohn-Sham functional, sX can be used for energy minimisation and structural relaxation. This allows a single shot calculation of structure and electronic structure of systems in which bond length variations may contribute to the metal-insulator transition or to other complex phenomena such as multiferroic behavior. This contrasts with perturbative methods such as GW or dynamic mean field theory (DMFT) which only operate on a pre-defined structure. Here, we show that sX can reproduce the paramagnetic metal phase of V2O3 in the corundum structure, the antiferromagnetic insulating phase in the monoclinic structure, and the paramagnetic phase via Cr doping, without adjustable parameters. The electronic structure of the high temperature metallic phase and the low temerature insulating phase is in good agreement with the photoemission spectra [3]. Furthermore we have relaxed a Cr-doped V2O3 corundum structure supercell to realize the doping induced paramagnetic insulating phase with a 0.15eV energy gap from first principle calculation for the first time. We show that the metal insulator transition induced by crystal structure change and doping could be explained in the framework of band theory. The hybrid sX functional can describe the electronic structure change when the Hubbard correlation energy is comparable to the band energy.
[1] S. Lupi, et al., Nat Commun 1, 105 (2010). S. Y. Ezhov, V. I. Anisimov, D. I. Khomskii, and G. A. Sawatzky, Phys. Rev. Lett. 83, 4136 (1999)
[2] S J Clark, J Robertson, Phys. Rev. B 82 085208 (2010).
[3] S. K. Mo, et al., Phys. Rev. B 74, 165101 (2006). H. Fujiwara, et al., Phys. Rev. B 84, 075117 (2011).

The reported magnetic properties of SrRuO3 shows a wide range of values, both from experimental and theoretical studies. From theoretical perspective it is not clear what is the most sound methodology. In this study we have performed an extensive test of the ability of LDA/GGA, LDA+U and LDA+DMFT to describe the properties of SrRuO3. We investigate the dependence of the magnetic moment on both methodology, on-site Hubbard U and double counting correction. Further we compare the impact of the impurity solver on the quasi particle weight Z. Effects of spin-orbit coupling is studied, allowing for determination of spin- and orbital moment easy axes and its dependence upon structural parameters. In the orthorhombic phase the orbital moments are found to be tilted with respect to the spin-moments, emphasizing the importance of taking into account the distortion of the oxygen octahedron.

N-type bulk SnO2 semiconductor has a wide band gap of 3.6 eV at 300 K. One-dimensional SnO2 nanostructures have been attractive to researchers in recent years due to their application in gas sensors and optical devices due to their high surface to volume ratio, chemical stability, remarkable resistivity variation in a gaseous environment, and high exciton binding energy of 130 meV. Much progress has been achieved in the synthesis and structural characterization of 1D SnO2 nanostructures in literature. In this study, Au ions have been implanted into the different substrates and SnO2 single crystal nanowires have been grown using Chemical Vapor Deposition (CVD). We have performed characterizations on optical, electrical and thermal properties of the grown SnO2 nanowires.

Due to the introduction of more stringent regulations governing air-pollution, it becomes important to focus research on the development of low-cost gas sensors in order to access applications where the use of conventional analytical systems is prohibitively expensive. Strontium titanate (ST) has been extensively explored as gas sensors. This material is widely studied due the facility to incorporate different ions in its structure. The substitution of Sr or Ti atoms by monovalent or trivalent ions affect directly its physical and chemical properties leading improve its characteristics of interest. The aim of this study is the synthesis and characterization of LaxSr1-xTi1-yFeyO3 (0 le; x le; 0.05; y = 0.0 le; x le; 0.25, %mol) verifying the effect of the lanthanum and iron in the properties of the material, in the powder form and thin film. First, the nanopowders samples were obtained, this samples were characterized by termogravimetric analysis (TG) and differential thermal analysis (DTA) from where has been obtained the temperature of total elimination of the organic compounds. After heat treatment, the crystalline powder was characterized by X-ray diffraction (XRD) showed that all compositions present only a single cubic phase similar to the SrTiO3 compound. Through scan electronic microscopy (FEG-SEM) we found that the agglomeration of particles and any change of morphology with addition of dopants. The preliminary results for thin films concerning the gas sensor behavior of SrTi1-xFexO3 thin films with 0.0 le; x le; 0.25 obtained by using an electron beam evaporation technique with thickness between 70 and 300 nm. The electrical characteristics of the thin films as a function of sample composition and temperature were evaluated regarding the response to different gases. The best results concerning gas sensibility was observed when thin films were exposed to O3 gas at 260 oC. The thin films doped with lanthanum and iron, will be tested to the same gases and expect an improvement in the electrical response in the presence of O3.
Work supported by FAPESP, CAPES, INCTMN-CNPq.

Thin film transistor (TFT) based circuits that are fabricated on flexible and transparent substrates have great potential for applications such as flexible active matrix liquid crystal displays (AMLCDs), active matrix organic light emitting diodes (AMOLEDs) and radio frequency identification (RFID) tags. Many efforts have been devoted to the development of reliable n-type and p-type semiconductor films for TFTs, demonstrating acceptable field effect mobility and stability. Currently, amorphous silicon (a-Si) and polycrystalline silicon are the dominant materials used for n-type thin film transistors. However, their application in emerging transparent and flexible TFTs is limited due to their relative opacity and difficulties related to fabrication on flexible substrates particularly arising from high temperature processing. Organic semiconductors and oxide semiconductors are promising substitute semiconductors for TFTs due to their low temperature fabrication process and transparency. This paper presents radio frequency sputtered zinc oxide and a solution processed organic semiconductor, namely THOTA, as n-type and p-type TFT materials, respectively, to realize transparent complementary thin-film transistor (CTFT) inverter. The device performance properties such as mobility, ON/OFF ratio are extracted from systematic measurements and related to fabrication and material properties. The performance of CTFT is demonstrated by fabrication of inverter circuits on both glass and polyethylene terephthalate (PET) substrates, indicating the potential of the device for fabrication on rigid as well as light flexible transparent substrates.

This talk will focus on the elaboration of ordered nanomaterials obtained from inorganic liquid crystalline solution and on the ability of such materials to induce an anisotropic response of their properties. The formation of liquid crystalline phases requires very anisotropic particles, free from aggregation. Nanostructured materials can be obtained from the nematic phase of nanoparticle by spin coating or by polymerization of the suspension. We will present two main results concerning oriented film of rutile (i) and PHEMA-goethite hybrid materials (ii).
i) Anisotropic rutile particles are obtained using an original method based on seeding with shorter rod-like particles in very acidic solution. Using this growth process, pure rutile nanorods are elongated enough to organize into a nematic phase when dispersed in water at large volume fractions (phi > 12%). This nematic phase is thermodynamical stable, shows usual nematic textures in polarized-light microscopy and displays typically nematic SAXS patterns. Rutile nanorods were further used to produce dense anisotropic films. UV-light linearly polarized along the crystallographic c (quadratic) axis of the nanorods was more efficient to induce the photodecomposition of methylene blue. In order to have a better understanding of this effect, the electrical resistance of aligned rutile nanorod films has been investigated in the dark and under UV-light irradiation. (ii) Hybrid ordered material is obtained by mixing goethite nanorods with 2-hydroxyethyl methacrylate (HEMA) and a few weight percent of an initiator, followed by UV irradiation. When the polymerization occurs under an applied magnetic field (which orients the nanorods) the resulting material preserves its anisotropy even after removing the field, as revealed by its optical birefringence. Spin-coating the mixture onto glass surfaces yields uniform and homogeneous coatings, whose mechanical properties are superior to those of the undoped polymer and depend on the order degree of particles.

Amorphous Indium Gallium doped zinc oxide (IGZO) of various thickness (25-150 nm) are deposited onto flexible polyethylene napthalate (PEN) substrates by sputtering at room temperature. The films are subsequently annealed in vacuum, forming gas and O2 environments and the optical and electrical properties are compared against the as-deposited samples. The structural, optical and electrical properties of the multilayers are measured by scanning electron microscopy, UV-Visible spectrophotometry, Hall measurement and four point probe. The resistivity decreased from 40 x 10-3 ohm-cm to 2 x 10-3 with increase in the film thickness while the mobility can be as high as 19 cm2 /V-s for 150 nm IGZO thickness. The film has been optimized to obtain a sheet resistance of ~100 #8486;/sq and an average optical transmittance of 80 % around 500 nm for 75 nm thickness IGZO film. The IGZO films shows best electrical properties when annealed in forming gas.

Multilayer structures of Nb2O5/Ag/Nb2O5 have been deposited onto flexible substrates by sputtering at room temperature to develop indium free composite transparent conductive electrodes. The optical and electrical properties of the multilayers are measured by UV-Visible spectrophotometry, Hall measurement and four point probe and the effect of Ag thickness has been studied. The critical thickness of Ag to form a continuous conducting layer is found to be 9.5 nm and the multilayer stack has been optimized to obtain a sheet resistance of 7.2 #8486;/sq and an average optical transmittance of 86 % at 550 nm. The Haacke figure of merit (FOM) has been calculated for the films, and the multilayer with 9.5 nm thick Ag layer has the highest FOM with 31.5 x 10-3 #8486;/sq, which is one of the best FOM reported till date for room temperature deposition on flexible substrates. The multilayered samples are annealed in vacuum, forming gas and O2 environments and the optical and electrical properties are compared against the as-deposited samples.

For the first time, a hybridized epoxide assisted/colloidal crystal templating method has been used to prepare three dimensionally ordered macroporous metal oxides (3DOMs) of aluminum, yttrium, iron, and nickel. Highly ordered arrays of poly(methyl methacrylate) (PMMA) spheres were infiltrated with a precursor solution of metal salt and epoxide and permitted to gel in the interstitial spacing. After complete gelation, the materials were calcined to remove the polymer template while simultaneously forming the metal oxide inverse replicas. These hierarchical structures are composed of hexagonal close packed macroporous voids enclosed by a crystalline (or amorphous), mesoporous metal oxide wall. The materials were characterized by powder x-ray diffraction (PXRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and N2not; adsorption/desorption techniques to probe the structural integrity. X-Ray diffraction analysis revealed by that the prepared 3D frameworks were single-phase, polycrystalline structures with grain sizes between 5-27 nm. Thermal analyses confirmed the full decomposition of the PMMA template. Gas-sorption measurements of the 3DOM materials confirmed the materials exhibited surface areas as high as 89 m2g-1, with average mesopore diameters up to 33 nm. Due to the materials intrinsic properties we expect them to be ideal candidates for applications in heterogeneous catalysis, separations, adsorption, and sensors.

Copper oxide (Cu₂O) encapsulation layer is formed on silver after annealing Ag-17 at. % Cu alloy thin film inside a microwave cavity. The temperature during this process is 70 °C which make microwaves an efficient low temperature processing tool. During the annealing process, Cu segregates to the surface and forms a thin copper oxide layer as confirmed by Rutherford Backscattering Spectrometry and X-ray photoelectron spectroscopy measurements. X-ray diffraction shows identifies the (111) plane for both Ag and Cu₂O. Four point probe measurements suggest the resistivity is controlled by the residual Cu present in the alloy films.

The growing demand for advanced electronic devices based on nanomaterials has motivated efforts to produce nanoscale building blocks with designed functions. Transparent conducting oxide nanocrystals are particularly promising for the development of such devices. In recent decades, many researchers have concentrated on developing methods to process Antimony-doped Tin Oxide (ATO) thin films on plane substrates and have achieved significant results in terms of electrical properties and processing techniques. However, most of these methods are limited to thin film processing, which restricts the use of the material for other applications such as conductive molecular composites and gas sensors. This work describes an investigation on charge transport mechanisms at antimony-doped tin oxide (ATO) ultrathin films (40, 45 and 71 nm) obtained from highly conducting nanocrystals prepared via a nonaqueous sol-gel route in the size range of 4-6 nm. The antimony composition was chosen to be 8.8 mol% and the lowest resistivity (1.1x10-1 and 1.83x10-3 Omega;cm, respectively) was observed at room temperature. The samples were evaluated by XRD, SEM and resistivity measurements were taken in the four-probe mode in the temperature range of 13-300K. The results show a good data fitting on Mott&’s two-dimensional (2D) non-interacting variable range hopping. The results show highly homogeneous deposition, influence of thickness on the transport properties and low resistivity for an ultrathin film. The preparation of crystalline ATO nanoparticles fully re-dispersible in organic solvents consists in one pot reaction under solvothermal treatment of tin (IV) chloride and antimony (III) chloride in benzyl alcohol at 150 oC for 48h. The ATO nanocrystals were collected by centrifugation and washed twice with THF, and placed in a concentrated THF dispersion. The nanoparticles were kept into organic media (20g.L-1) and not dried before the re-dispersion. Electrical measurements were taken of 41, 45 and 71 mn thick films annealed at 500 oC for 2h. The thin film deposition consists of three steps: first step is the quartz substrate functionalization, the second step is the deposition itself and finally the third step is the thermal treatment. First, a hydrophilic substrate is treated at 80 oC with oleic acid. By doing this, the hydrophilic characteristic of the substrate is changed to hydrophobic, very thin oleic acid layer. Then, the functionalized substrate is immersed, using a dip-coater, in a stable colloidal dispersion of ATO nanocrystals in order to promote the interaction of the nanoparticles with the substrate surface (oleic acid). At this moment the nanocrystals self-organize onto the substrate surface. The substrate is pulled off from the colloidal dispersion at controlled rate. The thin film is heated at 500 oC for two hours in order to remove the organic contaminates and to obtain a homogeneous layer.

High resolution nanopatterning of metal oxide materials using low cost and high throughput processes is necessary for the ongoing development of electronic and optical devices. In this work, we demonstrate the fabrication of a sub-50 nm ZrO2 nanomesh structure by size reduction induced volume shrinkage that accompanies microwave assisted annealing. The effect of microwave annealing time on pattern dimension variations such as hole size, wall thickness, and pattern depth are investigated. The evolution of the crystallinity as well as optical properties of the ZrO2 thin films, including the refractive index and transmittance, is studied as a function of annealing time. Interestingly, the pure tetragonal crystalline phase of ZrO2 can be obtained within minutes by rapid microwave-assisted annealing. We believe that the nanopatterning of inorganic oxide materials using the size reduction effect and rapid crystallization capability of microwave annealing is very useful in the field of nanoscale patterning and for applications involving nanoscale oxide materials.

In this study, we deposited PdO thin films on the SiO2/Si substrates by reactive sputter deposition, and investigated CO sensing response of the PdO thin film. The thin film has a flake-like nanostructure with a large surface area and, therefore, it provides a large amount of adsorption sites for CO molecules. Moreover, because of the ultrathin thickness of the nanoflake, the space charge region induced by oxygen and CO adsorption can occupy most part of the nanoflake volume, resulting in a very sensitive change in the electrical conductance of the thin film upon CO adsorption. The gas sensing experiment was performed at atmospheric pressure. The PdO thin film has very different CO sensing behaviors in three temperature regimes, which span over a temperature range from 25oC to 300oC. At the low temperature regime (25-100oC), the CO sensing behavior of the thin film is governed by the replacement of pre-adsorbed oxygen by CO. The lowest CO concentration at which the PdO sensor produces obvious sensing response is 1000 ppm at 25oC and <500 ppm at 50oC. When the temperature is higher than 100oC, the PdO thin film shows a CO sensing response dramatically different from that in the low temperature regime. At temperatures around 150oC, the PdO thin film exhibits an oscillatory sensing behavior. According to x-ray photoelectron spectroscopy and temperature programmed desorption spectroscopy, both PdO reduction by CO and oxidation of metal Pd in dry air become active around 150oC. The oscillatory response can be ascribed to alternative reduction and oxidation reactions occurring on the PdO thin film that is exposed to a CO/dry air gas mixture. The oscillatory response disappears at temperatures higher than 150oC. It seems that, in the high temperature regime, the PdO surface preferably reacts with CO molecules during the CO exposure, and the surface is reoxidized by the dry air after the CO gas is switched off. The CO detection limit of the PdO sensor is smaller than 250 ppm at temperatures higher than 200oC.

Localized surface plasmons originating at metal - dielectric interfaces can enhance linear and non linear optical responses of materials located in their vicinity [1]. The present study aims at optimizing the interaction between gold nanoparticles and luminescent ions to enhance optical amplification processes in optical fibers doped with rare earth ions.
The emission enhancement requires the surface plasmon resonance and the quantum emitter absorption band to be well matched in wavelength. It also depends highly on the distance between the rare earth ion and the gold core. For distances around one nanometer, the luminescence is mainly quenched due to non-radiative decays. However, with a 5 to 20 nm spacer, the radiative decay rate may be amplified by several orders of magnitude [2]. To precisely control the distance between the gold nanoparticle and the luminescent ions, an original multilayer nanostructure has been specifically developed.
Monodisperse gold nanospheres (diameters from 5 to 50 nm) and gold nanorods (aspect ratios of 3) were first obtained by reduction of a gold salt in water. The multi-step coating process developed by Liz-Marzán [3] was then optimized to get homogeneous silica shells with controlled thicknesses and rare earth ion doping rates. The silica shells have thicknesses adjustable from 2 to 50 nm with 5 to 10 nm steps, and can be doped with up to 2 x 1020 rare earth ions per cm3 of silica. These nanoparticles were then incorporated into sol-gel silica composites with high optical quality in order to study their luminescent properties. Particular care was given to the preparation and characterization of the silica matrix in order to limit the luminescence quenching coming from the silica matrix defects, such as organic residues. Photoluminescence emission studies allowed us to determine the optimum distance between the gold core and the rare earth ions to get the maximum emission enhancement. These results could be compared with calculations based on a dipole model approach.
References
[1] M. Fukushima, N. Managaki, M. Fujii, H. Yanagi, S. Hayashi, J. Appl. Phys. 98, 024316 (2005).
[2] P. Anger, P. Bharadwaj, L. Novotny, Phys. Rev. Lett. 96, 113002 (2006).
[3] L. M. Liz-Marzan, M. Giersig, P. Mulvaney, Langmuir 12, 4329 (1996).

Structural defects in uranium dioxide (UO2) strongly affect the thermal transport properties during burn-up. Here we analyze the results of molecular dynamics simulation of void formation in UO2 in the bulk and close to a grain boundary. Specifically, we construct a bicrystal UO2 containing a (310) Σ5 tilt grain boundary, with various densities of vacancies. Above 2500 K the vacancies migrate to form voids. The void formation mechanism is determined from analysis of mean square displacement, defect and energetics. The grain boundaries act as sinks or sources for vacancies; as a result void formation at and near grain boundaries is very different from in the interior of grains.
This work was supported by the DOE-NE Nuclear Energy University Program 10-2258.

Nanosize templates are a low-cost and promising approach for deposition of low-dimensional nanomaterials or transfer of nanopatterns onto a substrate without using costly lithography equipments. Among them, anodic aluminum oxide (AAO) membrane is one of the most attractive nanopore materials due to its highly ordered structure, high pore density and tunable pore size, which make them potentially for a variety of applications. The pore size and interpore distance of AAO membranes are linearly dependent on the applied voltage during the anodization process. In the conventional constant voltage method, the AAO membranes with a large pore size of 300~400 nm could be obtained using an anodizing voltage of 150~195 V. When applying a high voltage over 150 V, however, the burning phenomenon, which would cause structural damages, usually appears owing to the high current flows concentrated at the some weak areas.
In this study, we have developed a constant current method for fabrication of AAO membranes with a large interpore distance in order to avoid the burning phenomenon. Before anodization, the pure aluminum foil was electropolished in a mixed solution of perchloric acid and sulfuric acid. Then, the anodization voltage was increased in phosphoric acid at a constant current density. From our preliminary results, the growth rate of AAO membranes increases form 3mu;m/hr to 6mu;m/hr and the burning phenomenon could be totally avoided at a relatively high anodizing voltage. The surface and cross-sectional morphologies of the AAO membranes were analyzed by field-emission scanning electron microscopy. The effect of current density on the growth rate and burning phenomenon will be systematically investigated.

Feature size of few nanometers can be created by self-assembly of block copolymer (BCP) thin films. Diblock copolymer self-assembly at interfaces enables the generation of nanoscale structures in a parallel, scalable, bottom-up fashion with vast applicability in the nanofabrication industry at low cost and can accomplish rapidly [1]. The high Flory-Huggins parameter (chi; ~0.18) of PS-b-P4VP at room temperature makes it an ideal BCP system for self-assembly and template fabrication in comparison to other BCPs. Herein we have reported the microdomain orientation of lamellar PS-b-P4VP BCP thin films on silicon substrates without the aid of any chelating agents such as 3-pentadecylphenol (PDP). Such high chi; BCP system requires precise fine-tuning of interfacial energies achieved by surface treatment and that improves the wetting property, ordering, and minimizes defect densities. Substrates were molecularly functionalized with ethylene glycol and polystyrene brushes of various molecular weights in a simple quick reproducible way. The BCP solutions prepared in toluene, tetrahydrofuran and their mixture were deposited on modified and unmodified silicon substrates, and subsequently were solvent annealed in various solvents and their mixtures. The surface treatment improved the wetting property of the BCP, pattern ordering and coverage with sub-15nm features of the BCP. We further investigated the effect of experimental conditions such as film thickness; annealing solvents, time, temperature; etc., on self-assembly. Graphoepitaxial directed self-assembly shows promising results with high degree of translational alignment within topographic patterns. The BCP nanopatterns were transferred to the underlying silicon by controlled inductively coupled plasma etches to generate silicon nanoscale patterns with high aspect ratio and greater fidelity.

In this communication we describe a method of synthesis of nanocoral ZnO structures using reactive magnetron sputtering of porous Zn and its subsequent thermal oxidation. This material combines the unique optical and electronic ZnO properties (wide band gap of 3,4 eV and a high exciton binding energy of 60 eV) with an enhanced surface area making it a potential candidate for an array of opto-electronic devices operating based on the absorption of particles, biological material, light, etc.
We report recent progress in the stabilization and functionalization of this material for applications in resistive detectors for alcohol sensing, biomaterial detectors and photoelectrochemical cells.
The nanocoral structures were prepared on glass and silicon (111) substrates by sputtering of a Zn target in an oxygen-argon mixture with a subsequent in-situ annealing in an oxygen flow at 600oC. Ohmic contacts for the resistive detectors were sputter deposited Ti/Al bilayers and for the biosensors on silicon a Ni back contact was used. In order to protect the ZnO surfaces from the adverse pH of the solutions used in the biosensing applications, a sulphur passivation scheme was used.
The polycrystalline character of the nanocoral films was evidenced by X-ray diffraction measurements and the morphology of the films was studied using scanning electron microscope imaging. The internal crystalline structure of the nanocorals as well as of the passivation layer was unveiled through high-resolution transmission electron microscopy and selected area electron diffraction. The nanocoral structures exhibited strong luminescence under He-Cd laser excitation in the near-band-edge (NBE) region as well as in the green deep level emission (DLE) region. Temperature dependent photoluminescence studies showed a splitting of the NBE line into donor-bound and free exciton lines, along with phonon replicas at pumped He temperatures. The structures are hydrophobic and wettable by alcohols.
The bio detectors were fabricated in the extended gate bio-FET configuration, where the nanocoral ZnO was used as the gate electrode susceptible to biomaterial absorption. Bovine serum albumin was the detected species, with control measurements made using buffer solutions.
This study was partially supported by the European Union within European Regional Development Fund, through grant Innovative Economy (POIG.01.01.02-00-008/08 "Nanobiom").

Functional cellular metal oxide bulk materials with precisely controlled architectures, compositions, and densities provide many new opportunities in various energy related fields including green catalysis and energy storage. However, realization of specific combinations of properties (composition, density, morphology, and surface functionality) by traditional, self-organization and self-assembly based synthetic approaches remains to be challenging despite enormous progress that has been made in recent years. Here, atomic layer deposition (ALD) offers a unique opportunity for rapid on-demand materials development by applying the principles of surface engineering and templating to material systems for which robust synthesis strategies have already been developed.
Specifically, I will summarize the progress made in synthesis and characterization of ALD-based nanotubular alumina and titania bulk materials in which composition, density, and feature size can be independently controlled with nm precision. The nanotubular metal oxide bulk materials are obtained by removing the Au core of a metal/metal-oxide core-shell structure intermediate. The resulting material has a unique nanotubular morphology with a narrow, unimodal pore size distribution which makes the material stronger and stiffer than traditional aerogels with similar densities. In case of titania, both anatase and rutile structures have been realized by a post deposition annealing procedure. We discuss several emerging applications of both the intermediate metal/metal-oxide core-shell structure and the final nanotubular metal oxide bulk material. The approach is universal and can be extended to any metal oxide ALD process that uses sufficiently volatile ALD precursors.
Work at LLNL was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344.

The interest in Zinc Oxide (ZnO) doped with transition metal has been attracted much attention in the last years since it was predict a long range magnetic ordering above room temperature in such systems [1]. In spite of the extensive studies on Co-doped ZnO, the origin of its magnetic properties still remains a controversial issue. Some recent theoretical and experimental results have been shown that magnetic ordering depends on defects, such as oxygen vacancies, created during the sample preparation [2, 3].
Nanostructured Co-doped ZnO systems were synthesized via microwave-assisted hydrothermal route with different Co molar concentrations of 1, 3 and 5%. The crystal structures of the samples were characterized using X-ray diffraction (XRD). The microstructure and composition distributions were characterized by transmission electron microscopy (SEM) and energy dispersive X-ray (EDS) measurements. RAMAN scattering was used to study of the incorporation of dopants and the resulting lattice disorder of the host lattice. Co K-edge x-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) was used to determine the valence state and to evaluate the environment of Co in the ZnO lattice. Changes in the density of defects were estimated by RAMAN and Photoluminescence (PL) measurements. Magnetic characterizations were performed using a superconducting quantum interference device (SQUID) magnetometer.
The conjugated different techniques confirmed the Zn replacement by Co ions in the wurtzite ZnO structure, which retains a high crystalline quality. No segregated secondary phases neither Co-rich nanocrystals were detected. Defect mediated magnetic coupling between the Co atoms under the scope of the d0 model is used to interpret the observed magnetic properties.
[1] T. Dietl et al., Science 287, (2000) 1019.
[2] En-Zuo Liu et al., Appl. Phys. Lett. 93, (2008) 132506.
[3] M. Ivill et al., New. J. Phys 10, (2008) 065002.

This paper proposes an alternative technology of direct printing for fabricating metal mesh as invisible electrode by an electrohydrodynamic (EHD) jet printing technique. Induced electrostatic repulsion force could allow continuous nano-fiber ejection using high viscosity liquid up to 50,000 cP. The nano-fiber ejection could be dependent on the polymer property and concentration with conductive filler in paste and we investigated. The resultant pattern could be achieved below 4um line width and aspect ratio is around 0.2 using nano-fiber solution. That pattern has straight and reliable, uniform lines regardless of non-conductive substrate. The EHD jet printed Ag-grid has the sheet resistance of 7 Ohm/square and the tranmittance of 85 % with substrate was cured at 140C under near-infrared(NIR) heater. This nano-fiber solution could be a new alternative to replace the ITO or conductive polymer materials. And we could apply to hybrid tranparent electrode even on a flexible substrate.

We investigated Hf addition effects on solution-processed NiO based resistive random access memory (RRAM) devices. The Hf was introduced to control the amount of oxygen vacancies in NiO thin film as the depletion and accumulation of oxygen species determine the switching characteristics and stability of the RRAM device. To analysis the relationship between Hf content and oxygen vacancies in NiO, the X-ray photoelectron spectroscopy (XPS) was employed. The portion of O2- ions related peak at relatively lower binding energy increased from 65.4 to 73.4% as the Hf content increase. On the other hand, non-stoichiometric oxygen species related portion decreased from 34.6 to 26.5%. These distinct variations of oxygen species imply the electrical characteristic transformation including resistive switching mode. In fact, the NHO based (Ni:Hf =1:0.5) RRAM showed bipolar driving mode while NiO RRAM showed unipolar driving mode. This operation mode transformation can be understood in terms of redox induced resistive switching. The NHO RRAM with Al/NHO/Pt structure showed relatively low set voltage of ~2 V, reset voltage of ~ -1.8 V, and high resistive state ratio over ~10^3. Moreover, NHO RRAM also demonstrated stable switching behavior over 100 cycles and long retention time over ~10^3 seconds.

Metal and metal oxide electrodes play a significant role in many state-of-the-art technologies including photonics, sensing, electrochromics, Li-ion batteries and photovoltaics. Tailored nanostructured interfaces enable modification and tunability of the optical transparency, band gap, carrier concentration and mobility. Smart structures using a combination of semiconductor transparent conducting oxides (TCO) and plasmonic metals with low and high free carrier concentration, respectively, have been proposed for nonlocal plasmonic interactions. These new structures have made possible a novel class of metamaterials with unique tunable optical and enhanced electrical properties. This contribution presents a summary of our recent work on such multilayer large area nanostructures. Various different combinations of plasmonic metals such as silver and gold with TCO materials such as indium tin oxide (ITO) and indium zinc oxide has been fabricated and characterized. In addition, by systematic variation of dimensions enabled by a novel nanoimprinting technique we have shown that the carrier concentration, resistivity, optical band gap and transmission can be suitably changed. With 80-85 % transmission within the visible regime these electrodes are suitable for various photovoltaic and light harvesting applications . Optical properties of these samples were effectively modeled using multiple Lorentz oscillators and the Drude model in Cauchy type dispersion, combined with Bruggeman effective medium theory. Lorentz oscillators are used to be able to fit the sharp features typical in the ellipsometry spectra of these samples and relate to the interband transitions of the electrons. Infrared absorption of the nanostructured samples are dominated by the transverse mode and short interpillar distance, in-line with a Mie scattering type scenario. Optical band gap (Eg) values of the structures have been calculated using both ellipsometry and UV-Vis absorption measurement. Eg tends to decrease in nanostructures compared to the bulk Eg of the material. Detailed optical spectroscopy, ellipsometry and electrical measurements have confirmed that efficient tenability of electrical and optical properties can be achieved in multilayer nanostructured ITO - Ag - ITO compared to just ITO and Ag electrodes. These studies along with complete fabrication technique, and characterization of these novel smart structures will be presented.

Metal-Organic Frameworks (MOFs) are not inorganic oxides in the traditional sense, but are nanoporous, hybrid materials composed of metal ions typically linked to an oxygen-containing organic group. MOFs offer unprecedented opportunities to couple specific interactions between molecules adsorbed in their pores with a transduction mechanism that enables chemical sensing. A key advantage of using these materials in sensing applications is their potential to exhibit physical properties that are altered by very minor perturbations. MOF thermal stability also enables sensor regeneration and many display long-term stability under ambient conditions. In addition, their chemical selectivity is determined by framework topology and the structure of the organic linker, which can be varied easily by synthetic design. We integrated more than a dozen MOFs with various MEMS sensing platforms such as Quartz Crystal Microbalances and Surface Acoustic Wave (SAW) devices. These devices can be used to detect a wide range of small molecules, including water, hydrocarbons, ketones and alcohols. Sensitivity to sub-ppm water vapor concentrations using a MOF-coated SAW device is competitive with state-of-the-art commercial sensors. Our synthetic effort is guided by atomistic modeling, which shows that ultra-high sensitivity and selectivity can be achieved by tuning the size and chemical environment of the MOF pore. We will also describe a new coating design based on multilayered MOF thin films that holds the potential for selective detection in the presence of interfering gases such as water vapor. Overall, our results highlight that MOF-based sensors can exhibit similar performance in terms of working temperature and response intensity to some commercially available sensors and possess much greater synthetic versatility than traditional nanoporous materials such as zeolites.

An ordered channel-array of anodic Ti-Mo alloy oxide was fabricated by anodizing Ti-10Mo (90 wt.% Ti +10wt.% Mo) alloy. The metal substrates were first through electro-polishing (EP). The EP conditions involved a platinum sheet as a cathode, metal substrates as an anode, 5 vol.% perchloric acid (HClO4) + 53 vol.% ethylene glycol monobutylether (HOCH2CH2OC4H9) + 42 vol.% methanol (CH3OH) as an electrolyte. TiO2-MoO3 nanotubes (NTs) growth were achieved using electrolyte of 0.5 wt.% ammonium fluoride (NH4F, 99.9%) + 2 wt.% H2O in ethylene glycol (C2H4(OH)2) solvent with anodization at a constant voltage of 60V for 2 h. SEM images showed that TiO2-MoO3 NT film including (a) porous film and net film, (b) larger pore on TiO2-MoO3 NT top, (c) smaller pore on TiO2-MoO3 NT bottom, (d) barrier layer on TiO2-MoO3 NT bottom. The ordered NT structure has a 120 nm pore diameter, a 140 nm inter-pore distance, a 20 nm-thick pore wall, pore density about 4.5×109 pores cm-2, a 5~10 nm gap between each NTs. Larger open pores are on the top side (51% porosity), while smaller closed pores and barrier layer in a hexagonal pattern are on the bottom side (9% porosity).

The change in surface structure and the characteristics of corrosion caused by plasma and heat were studied with respect to the sealing time (0, 10, 30, 60 minutes) of Anodic Aluminum Oxide (AAO) which is applied to equipment used for vacuum processing. When the film is treated with a sealant, a boehmite layer is formed by the reaction between the water molecules that are present in the pores of the surface. The longer the sealing time, the more the pores are blocked by boehmite. With 60 minutes of sealing time, smute, a condition of oversealing, was formed.
In terms of electrical characteristics, the sealed film had reduced leakage current while an improved breakdown voltage and permittivity. Particularly, the most efficient improvement in characteristics occurred with a sealing time of 10 minutes, which was approximately 35% and 23.8%, respectively. In addition, the evaluation of resistance to plasma and heat was also conducted. The plasma resistance was best with a sealing time of 10 minutes. If sealed for 30 or 60 minutes, cracks formed in the plasma environment, which reduced the dielectric properties. The sealing time of 10 minutes was the optimal condition that effectively improved the insulation properties while minimizing the formation of cracks and generation of contamination particles by high plasma resistance.

Atomic layer deposition (ALD) of complex oxides is a significant method to adjust the composition and microstructure of the thin films. Multiferroic BiFeO₃ thin films were proved to have ultra-high ferroelectric property and good magnetoelectric (ME) effect, thus it is promising to study and prepare nano-scaled BFO films by ALD to increase memory density and optimize multiferroic properties.
In this work, BFO thin films were synthesized by deposition Bi₂O₃ and Fe₂O₃ ALD monolayers with sequences of Bi-O-Fe-O and Fe-O-Bi-O. The precursors used were β-diketonates that tris(2,2,6,6-tetramethyl-3,5-heptanedionato) bismuth (Bi(thd)₃), tris(2,2,6,6-tetramethyl-3,5-heptanedionato) iron (Fe(thd)₃) and Ozone (O₃). The as-deposited materials were amorphous but crystallized into perovskite structure after annealed at 650^oC. The polarization properties of the BFO films found in the P-V measurements were promising and strongly affected by the ALD sequence which dictates the composition and structure of the BFO thin films.
Ultra-thin BFO films were observed and studied by scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Polarization voltage (P-V) measurements. Piezoresponse force microscopy (PFM) and Superconducting quantum interference devices (SQUID) measurement is underway and so far the promising results indicate ALD enables the synthesis of a BFO composite with magnetoelectric coupling effect and potential in memory applications.

Resistive random access memory (RRAM) has emerged as one of the most promising candidates for future memory technologies due to its excellent performance such as high-speed operation, low power consumption, good switching endurance, long retention time and outstanding scalability. Several theories have been proposed to explain the resistive switching mechanism, which can be classified as: 1) metal-oxide interfacial effect models such as Schottky barrier, FN tunneling and space charge limited current (SCLC); 2). filament model such as the formation and rupture of metallic filament or oxygen vacancy current path; 3). trap-assistant model such as Pool-Frankel emission in the bulk of the transition oxide materials. An appropriate explanation of resistive switching mechanism for different RRAM structures is still a challenge due to the different properties of the resistive change material and various interfaces.
In this paper, a fully CMOS compatible AlOx/WOx bilayer RRAM cells are fabricated in commercial CMOS foundry. The cell electrical characteristics of both the DC and AC are measured and analyzed. To investigate the switching mechanism of this type RRAM cell, the current density (J) versus applied voltage (V) are measured at various temperatures from 300 K to 480 K for the initial resistance states (IRS), the high resistance states (HRS), and the low resistance states (LRS). In the temperature-dependent measurements, cells at IRS and HRS expose semiconductor behavior, while the LRS exhibit a weak metallic behavior. Meanwhile, the complex impedance is measured at frequencies varied from 1 kHz to 5 MHz. The frequency-dependent measurement results showed that LRS conductance (G) has significant different relation with frequency (f) in comparison to HRS and IRS.
The stacked AlOx/WOx resistive switching cells also showed some unique properties, such as the symmetry of J-V curves in positive and negative directions, distinct resonance point in IRS, HRS and LRS. Based on measured electrical performance of RRAM cells at different temperature and frequency, a metal filament forming/rupture and oxygen vacancy combination model is established to explain the switching behavior for this AlOx/WOx bilayer RRAM cell.

The time required for gas evacuation before the introduction of discharge gases into the panel is one of the major problems in the production of AC-plasma display panels (AC-PDPs). The long outgassing time of PDP, is mostly related to the magnesium oxide (MgO) layer. MgO thin films are often used as protective layers of the dielectrics in AC-PDPs to improve their discharge characteristics and lifetime. In this study we investigated the surface morphology, preferential crystal orientation, chemical species, and outgassing impurities of protective MgO thin films, along with the manufacturing steps of an AC-PDP, by photoelectron spectroscopy in air (PESA) and Kelvin probe force microscopy (KPFM). We prepared MgO thin films on SiO2/Si substrates, then a surface potential was induced on the films by ultraviolet (UV) light irradiation. KPFM showed that a very high surface potential exists, probably due to the high secondary electron emission from the MgO surface induced by UV light irradiation. An increase in the secondary electron emission from the MgO surface was observed, that was due to the removal of the Mg(OH)2 thin film formed on the MgO layer by UV light irradiation. In this study, we used a commercially available atomic force microscope (AFM) to perform Kelvin probe force microscopy (KPFM) measurements to obtain the secondary electron emission coefficient. Our proposed method of evaluation by KPFM in ultraviolet (UV) light is demonstrated before and after UV light irradiation. KPFM measurements of different materials have been performed for the first time using an AFM. This instrument has both a high resolution for KPFM measurements (better than 0.1 mV) and a high lateral resolution and allows the topography to be imaged during KPFM measurements. Images of gold, and magnesium oxide surfaces, taken in air and vacuum, exhibit a large contrast in the surface potential difference and demonstrate the basic concept of KPFM. This study demonstrates the utility of KPFM for visualizing negative charges which can be used to determine the relationship between electrical properties and the MgO structure through the comparison of surface potential and topographic maps. To clarify this point, we investigated the emission of electrons from the MgO surface during UV irradiation and its relationship with various parameters using a specially designed system for performing photoelectron spectroscopy in air (PESA). This system provides a very high S/N ratio, which makes it possible to detect the emission of electrons from the surface. To illustrate the mechanism of the photoelectron-induced reaction, it is important to focus on the surface potential due to the emission of electrons from MgO thin films before and after UV light irradiation.

MgO has multiple useful characteristics and is expected to be applied in various fields. In this study, Co nanoparticles were deposited on a substrate in an island pattern using an arc plasma gun (APG). Then, a MgO thin film was formed on this substrate by metal organic decomposition (MOD), which enables the formation of films in atmosphere, thus yielding a double-layer structure. The MgO thin film on Co nanoparticles deposited using the APG with 500 pulses of arc discharge exhibited improved crystallinity and a photoelectron emission that was at least threefold higher than that of the MgO thin film without Co nanoparticles. Although the transmittance of the specimen, formed by depositing Co nanoparticles on a Si substrate with 500 pulses of arc discharge, was 30% or lower, it increased to higher than 90% after the formation of a MgO thin film on the substrate and the dispersion of the Co nanoparticles within the MgO thin film during heat treatment at 900 °C. Thus, a highly transparent film was obtained. It was clarified that the characteristics of MgO thin films are markedly improved by depositing Co nanopaticles before forming the films on them. We successfully established a bottom-up process that requires no ion injection by dispersing Co nanoparticles within the MgO thin film during heat treatment. Moreover, high-quality ultrathin films of Co nanoparticles were formed on a substrate in an island pattern in vacuum in a short time to form seed crystals and promote the growth of MgO crystals. Co nanoparticles (lattice parameter; a-axis, 4.95566 Å) are well lattice-matched to MgO (lattice parameter; a-axis, 4.2126 Å). MgO is currently used for cathodes of PDPs because of its high photoelectron emission. Here, we measured the photoelectron emission of the MgO/Co thin films using a photoelectron yield spectroscopy (PYS) system. The photoelectron emission of the MgO/Co thin films is higher than that of the MgO thin film without Co nanoparticles, which was formed by the MOD method, owing to the deposition of Co nanoparticles. In particular, the photoelectron emission of the MgO/Co thin film formed with 500 pulses is at least threefold higher than that of the MgO thin film without Co nanoparticles. The dispersion of Co nanoparticles within the MgO thin film is considered to result in the increase in photoelectron emission. Originally, metals show high photoelectron emission, and photoelectrons are emitted from Co components injected into the MgO thin film as well as from those on the MgO film surface, resulting in the increased photoelectron emission. Because the MgO/Co thin film is an insulator, the ionization potential of MgO will be decreased; hence, power consumption can be reduced by using this film for the cathodes of PDPs.

The synthesis of high quality ZnO nanowire (NW) arrays on a range of conventional conductive substrates has important applications in LEDs, nanogenerators and piezotronics. In this paper, using ammonium hydroxide as the reactant, together with zinc nitrate hexahydrate, ZnO NW arrays have been grown on various patterned metal layers, such as Au, Ag, Cu and Sn, without predepositing a seed layer. The mechanism for this novel synthesis route has been discussed and the effect of parameters such as ammonia concentration and solution/container volume ratio on the nanowire growth has also been investigated. Preferentially selective nucleation
and the subsequent growth of ZnO NW arrays was demonstrated on patterns of different metals without a ZnO seed. Electrical characterization was subsequently performed to reveal the characteristics of the contacts formed between the ZnO NWs and the underlying metal layer . Further demonstration of the as-fabricated ZnO NW arrays on flexible substrates as an electromechanical switch in response to externally applied strain exhibits the potential applications of the demonstrated seedless synthesis of patternedZnO NW arrays in areas ranging from sensing, and energy harvesting to interfacing piezotronics with silicon based technologies.

The lead zirconate titanate (PZT) morphotropic phase boundary (MPB) composition is the principal piezoelectric material used for electronic devices. Several researches study means to improve the piezoelectric properties, including the rare earth modified PZT (RE-PZT). However, the usual synthesis methods to prepare these materials decrease the piezoelectric properties. A new wet-chemical method called oxidant peroxo method (OPM), developed by Camargo and Kakihana, is characterized by the fundamental oxy-reduction reaction between lead (II) ions and several water-soluble titanium peroxo complexes, leading to the formation of an amorphous and reactive precipitate free of all the contaminants commonly found when synthesized by other chemical routes. In this study, highly reactive nanosized powders of pure PZT in 52/48 of Zr/Ti and RE-PZT (RE=La, Pr, Nd) were synthesized by OPM route. The PZT amorphous precipitate was heat-treated at different temperatures from 500 to 900 °C for 0.5-2 h, in order to find the best condition to obtain smaller grain size. These materials were analyzed by X-ray diffraction (XRD) and Raman spectroscopy at room temperature and transmission electron microscopy (TEM) to structural and morphological determination. The OPM method was efficient in the pioneer synthesis of Pr-PZT, which was successfully prepared with high reproducibility. It was observed that the temperature and time of heating influences the morphology of the nanosized particles, resulting in larger particles, from 50 nm for powders calcined at 600 °C to approximately 200 nm for those treated at 900 °C, forming sintered aggregates with presence of necks. The results incated that the best calcination condition was at 600 °C/0.5 h, since crystalline powders were obtained with smaller grain size, which is evidence of premature sinterization. At this condition, PZT and La-PZT grain size were smaller than in previous research [2] and also the powders present less necks formation. Despite of Pr-PZT grain size was similar to La-PZT, the Pr-PZT showing other secondary phases on XRD when calcined at 600 °C/0.5 h.

Tin (IV) dioxide, SnO2, is a semiconductor material central to many applications involving interfacial charge transfer such as transparent conductive oxide glass, lithium ion batteries, excitonic solar cells, field effect transistors, heterogeneous catalysis and gas sensing. We demonstrate here a general and straightforward synthesis of SnO2 nanostructures with controllable predominant {10-2} and {11-3} facets, and simultaneous Sn2+ self-doping. The doping resulted in tunable sub-bandgap oxygen vacancy states and the corresponding shifting in the semiconductor Fermi levels. Combined with the facets control, the increased density of states gives rise to enhanced charge transfer responsible for NO2 gas sensing. Our work highlights the possibility of simultaneous engineering of surface energetics and electronic properties of SnO2 based materials.

Oxide nanostructures of various dimensions, morphologies, and sizes have been widely designed, produced, investigated, and subsequently applied in a variety of fields in the past decades. Among these researches, controlled synthesis of novel one-dimensional nanostructures has become the most important and interesting topic from both academic and industrial viewpoints since it is the gateway to exploring distinct physical and chemical fundamentals and corresponding advanced applications. In most cases of the solution-based syntheses, the formation of one-dimensional V₂O₅ nanostructures requires the presence of various surfactants and reductants due to the high redox-activity of vanadium oxides. In this work, to further enhance the gas sensing performance, highly aligned V₂O₅ nanowires (an average diameter of 10minus;50 nm and hundreds of micrometers in length) with extremely porous surfaces have been successfully and uniformly synthesized via a facile hydrothermal method with the absence of any surfactants, reductants or templates at 180 °C. The innovative sensing platforms of porous V₂O₅ nanowires demonstrated excellent response and recovery speeds as well as stable H₂-concentration-dependent sensitivities.

The advantages of metal oxide nanoparticles for thin-film transistors are regularly discussed in the literature, with the main promise being the reduction of the annealing temperature compared to precursor systems. Despite their advantages nanoparticles intrinsically inherit several problems: Among other disadvantages, they exhibit a large surface area, hence they tend to form aggregates. The latter observation makes it difficult to process nanoparticles from solution. One approach to circumvent that problem is to find a suitable functionalisation, e. g. a shell of hydrocarbon chains covalently bound to the surface.
The ZnO nanoparticles for this study were synthesized according to a modified recipe by controlled desomposition of Zinc 2-ethylhexanoate using octylamine as the source for the ligands. The resulting nanoparticles show a monodisperse size distribution around 5 - 7 nm. A dispersion of these nanoparticles in organic solvents is stable for months and they offer the possibility to generate homogenous films by spin coating.
The research during this study is focussed on the removal of the ligand shell in functionalised ZnO nanoparticles. A common approach is to anneal the resulting films at higher temperatures in order to remove the capping agents. This method, however, contradicts the promise of low temperature processability. Therefore a method needs to be developed to support the removal of ligands by non-thermal methods. Several approaches were investigated and their effect on the electronic properties in thin-film transistors was studied. The following techniques - and combinations thereof - lead to distinct improvements in the device performance: UV irradiation is applied before annealing in order to decompose the capping molecules; vacuum treatment[2] after annealing supports the removal of the ligand shell; and chemical bath technology (before annealing) helps to chemically remove the functionalisation. Naturally, the effect of the studied methods is most dominant in the low temperature regime (Tanneal = 150 - 250 °C).
By applying these non-thermal methods it is possible to obtain films of ZnO nanoparticles with extraordinary performance: Samples with a maximum process temperature of 250 °C, hence suitable for plastic substrates, show field effect mobility values of more than 0.1 cm2/Vs.

Tools to measure sub-nN forces are becoming increasingly important as the development of nanotechnology progresses. While atomic force microscopy and optical traps have become the standard for mechanical characterization at this level, these techniques can be slow, challenging to multiplex, and it is difficult to generate large statistical datasets with these instruments. Here we investigate a new system that leverages light-matter interactions in the decaying optical field of nanofiber waveguides to measure distances and forces normal to the direction of light flow. Plasmonic nanoparticles embedded in the evanescent field are used as the transducers and their scattering intensity can be monitored as a function of force. The strong dielectric-plasmonic coupling combined with the decaying near-field allows sharp modulation in the scattering intensity when the nanoparticle-waveguide separation changes by distances as small as an angstrom. By integrating the waveguides into microfluidic devices and carrying out experiments and simulations, we systematically study the nanoparticle transducers and their ability to quantify fluidic forces and velocities. These results pave the way for new high-throughput in situ nanomechanical diagnostics and instruments as well as microscopy applications.

Inkjet printing provides an interesting technology for electronic devices, as it is a versatile minimum-waste cost-effective technique for direct writing on almost every surface without need of masks or high temperature. Among the fields in which it has been tested, transparent and flexible electronics offer a variety of applications ranging from large-area roll-to-roll (such as OLEDs for lightning or solar cells) to small low-consumption biocompatible devices such as biosensors.
This work aims to present some recent advances in the field of semiconductors synthesized by inkjet. Chemical routes are used to obtain suitable inks, based on salts of Ga, In, Zn, Cu and Sn and solvents as methoxyethanol and isopropylic acid. Inkjet printing provides thin layers 20-300nm thick, with morphology strongly depending on the organic solvents. Different thermal treatments are tested, and some chemical and optical characterization of the obtained layers allows to optimize the technology for each material.
The effectiveness of the inks and the technique is demonstrated by the electronic behavior of thin-film transistors fabricated by the proposed technology. The different devices are compared, suggesting the properties of the different materials analyzed, as a step ahead in the development of a complete logic for such promising applications of the transparent flexible electronics.

Ceramic coatings prepared by thermal spraying process are now widely used in industry for corrosion or wear resistance. Microstructure of the coating determines its properties. In this paper, nanostructure Al2O3-13%TiO2 coating was prepared by plasma spraying process. The parameters for retaining a fraction of the nanostructure were investigated. The forming mechanism and microstructure characteristics of the coating were studied detailedly. Compared with conventional Al2O3-13%TiO2 coating, the structure characters of the nano-coating are quite different. Al2O3 amorphous phase was detected in the coating by selected-area electron diffraction, which formed mainly because of the rapid cooling velocity after thermal spraying. The microhardness of the nano-coating is lower than that of the conventional coating and appears two kinds of distribution form. Study shows that nano Al2O3-13%TiO2 coating possesses the excellent wear abrasion property. Wear mechanism of the coating was also discussed in this article.

The cubic perovskite SrTiO3 is an important semiconductor oxide with a band gap of 3.2 eV. It has a wide variety of applications such as: dielectric materials, photoluminescent devices, and in photocatalysis. It is conventionally obtained by the classic solid state synthesis (SS), in which TiO2 and SrCO3 react for several hours at temperatures as high as 1200 °C. Besides the high energy demand, SS is not useful for the control of physical characteristics, such as particle size and morphology, which has become essential for some of its applications.
It is known that many soft and green routes can produce SrTiO3. Among them, the hydrothermal (HT) and sol-precipitation (SP) methods, as well as the molten salt synthesis (MS) are interesting not only due to their low cost and energy use, but also because of the possibility of particle size and shape control. This study compares the size and morphology of the SrTiO3 particles obtained by these three synthetic pathways. Scanning electron microscopy (SEM) was used to compare particle size and morphology, and X-ray diffraction (XRD) was used to confirm the perovskite formation as well as to determine the Scherrer&’s particle size.
MS synthesis was carried out in a KCL/NaCl flux at 1073 K for 4h, using amorphous titania (obtained from the hydrolysis of titanium tetraisopropoxide - TTIP - at pH 7) and strontium carbonate as the precursors; SP synthesis was carried out by adding a TTIP solution in acetic acid to a strontium nitrate solution followed by stirring at 333 K for 3h; HT synthesis was carried out in an autoclave, where a mixture of strontium nitrate and amorphous titania in 0.5 mol/L KOH was kept at 358 k for 20h.
Morphologically, HT synthesis led to irregular shaped SrTiO3 particles with wide size distribution. The nanometric average grain size estimated by Scherrer&’s formula was 30 nm, although aggregates observed by SEM achieved several micrometers in size. MS method also produced a wide size distribution of particles, but in this case they showed a cubic-like morphology. Scherrer&’s grain size was 40 nm. Oppositely, the SP route produced a narrow distribution size of cubic-like particles. A distribution histogram showed that the particles had an average size of 270 nm. Scherrer&’s crystallite size of this material was 49 nm.
All three MS, HT and SP routes proved useful for producing SrTiO3 with different particle sizes and shapes. Among them, SP and MS lead to cubic-like particles, and SP clearly leads to smaller and uniform particles.

Synthesis of tailored coatings with controlled wettability is a key step toward the realization of several cutting-edge applications such anti-fogging coatings, self-cleaning surface and enhanced membranes for water purifications, to name a few [1, 2]. In particular, synthesis of super-hydrophilic coatings requires both a hydrophilic material and a greatly enhanced surface roughness [1]. Although, several methods have demonstrated to result in temporary super-hydrophilicity of the substrate surface [1], maintaining this property over time is particularly challenging. With respect to the chemical and thermal stability, inorganic materials and in particular nanoceramics offer superior performances and thus are a promising candidate for the synthesis of long-term stable super-hydrophilic films and membranes. Obtaining highly rough/porous nanoceramic coatings at low temperature is very challenging as it usually results in mechanically unstable morphologies [2] that may easily disintegrate over time [3]. Here, we propose a novel approach for the fabrication of highly porous films of hydrophilic TiO2 nanocrystals featuring extremely high porosity and enhanced mechanical stability. The performance of these films as anti-fogging coatings is assessed in realistic conditions for long-term utilization.
[1] F. C. Cebeci, Z. Z. Wu, L. Zhai, R. E. Cohen, M. F. Rubner, Langmuir 2006, 22, 2856.
[2] A. Tricoli, M. Righettoni, S. E. Pratsinis, Langmuir 2009, 25, 12578.
[3] A. Tricoli, M. Graf, F. Mayer, S. Kühne, A. Hierlemann, S. E. Pratsinis, Adv. Mater. 2008, 20, 3005.

Versatile nano-structures with enhanced scattering and suppressed reflection have emerged to improve the photon absorption and the optoelectronic conversion efficiency. The nano-roughened surface scattering induces reflected Haze and depolarization, which were known to play an important role on improving the photovoltaic cell efficiency. Although the nano-roughened anodic aluminum oxide (AAO) structures have been considered to serve as an antireflective coating in the application of solar cells, the relationship between geometric scale of the nano-porous AAO and the reflected Haze as well as the depolarization properties has rarely been addressed. In this study, the depolarization factor and the reflected Haze ratio of nano-porous AAO thin-film with different aspect ratios are investigated.
In experiment, the high-purity aluminium (99.99%) with a film thickness of 200 nm was deposited on p-type silicon wafer by employing a thermal evaporater at a working pressure of 5×10minus;6 Torr for 2 hours. By using a two-step anodization under the electrochemical voltage ranged from 40 to 60 V at room temperature, the nano-porous AAO thin-film was prepared. The appearance of nano-porous AAO thin-film with different aspect ratios were observed by FE-SEM. The pore-size increases and the pore-density decreases with increasing bias from 40 to 60 V is observed, ascribing that the violent migration of Al3+ and O2minus; ions affects the alumina to cause a combination of adjacent pores. The porosity of AAO thin-film increases from 15.7% to 62.2% with thier pore-size broadened from 12.96 to 50.76 nm as the applied voltage increases from 40 to 60 V. The field polarization analysis of the nano-porous AAO surface reveals that the TE-mode incidence suffers a more serious depolarization from the spatially confined nano-porous surface, whereas the TM-mode incident laser beam falls within the vertically aligned nano-porous to slightly release the mixed substrate effect. By increasing the porosity from 15.7 % to 62.2%, the depolarization factor gradually increases from 0.45 to 0.75 for the TE-mode incidence and from 0.36 to 0.72 for the TM-mode incidence. To investigate the effect of nano-porous properties on the surface nonlinear scattering, the divergent angle of the reflected beam from the nano-porous AAO thin-film and the flat alumina film on p-type silicon wafer under TE and TM-mode incidences are observed. With the nonlinear scattering is enhanced by nano-porous surface, the reflected Haze ratio gradually saturates at larger porosity. The reflected Haze ratio increases from 4% to 19% under TE-mode incidence and from 2 % to 18 % under TM-mode incidence with the porosity of AAO increasing from 15.7 % to 62.2%. The TE-mode scattering strongly correlates with the porosity of AAO, whereas the TM-mode scattering is significantly affected by the laser incident angle. The premier observation on the direct proportionality between the Haze/depolarization and the AAO porosity is reported.

We demonstrate a small, low-cost, low-power, highly sensitive, and selective nanomaterials-based gas sensor. A network of tungsten oxide nanoparticles is heated by an on-chip microhotplate while the conductance of the network is monitored. The device can be heated with short pulses, thereby drastically lowering the power consumption, without diminishing the sensor response. The sensor shows high sensitivity to hydrogen sulfide and does not have significant cross sensitivities to hydrogen, water, or methane, gases likely to be present in operation. A sensing mechanism is proposed, and its effect on electronic properties is discussed.

Transition metal ferrites have attracted a lot of sustained interest due to their many potential applications in areas including optoelectronics, magneto-optics, high density data storage, etc. In particular, iron oxides (Fe₃O₄ and -γ Fe₂O₃) are also well suited for biomedical applications. We have studied aqueous solutions of Fe₃O₄ nanoparticles that are of the same nominal size (10 nm) but have differing saturation magnetization. We have employed Faraday Rotation (FR) at He-Ne wavelengths (633 nm) to characterize the magnetic response of these systems. Faraday rotation measures the rotation of the polarization vector of light as it interacts with a magnetic field in a medium. Unlike the traditional DC field setup, we have employed a highly sensitive AC field setup that allows reliable determination of the key parameter, the Verdet constant, for these systems. While the work presented focuses on the magnetic response of the nanoparticle system, details of the experimental apparatus and measurement analysis are also presented to highlight the sensitivity and reliability of the measurement.
In addition to investigating the magnetic response of the particles as a function of saturation magnetization, we have carried out measurements with different volume concentrations of the nanoparticles that allow us to investigate the aggregation behavior of these nanoparticles. To better understand the dynamics of the nanoparticle aggregates, we have also measured FR as a function of frequency (800 Hz to 13.9 kHz). Our results point to a consistent picture where these variables (saturation magnetization, volume concentration, and oscillation frequency) affect the magnetic response in an interesting and predictable manner. Results from FR are supplemented with x-ray diffraction measurements, transmission, and ellipsometry measurements that allow us to propose a model that describes the observed dependences.

A gas sensor is an important device applied in broad fields, such as security, vehicle installation and environmental monitoring. In the future, it is expected that gas sensor is also mounted in handheld device, such as a mobile phone and a smart phone. It is necessary to miniaturize, low power consumption, and high functionality for improvement of the portability.
The needle crystal of Cu-Sn nanowire like a nano tree was synthesized by electrolytic plating. It is the three-dimensional structure that the perpendicularly needlelike crystal grew from core nanowire. Although it was known that Cu-Sn grow up to be a tabular dendrite in film forming by electrolytic plating, nanowire trees of Cu-Sn prepared by controlling the conditions of plating. The nano trees of the porous structure and the large surface area can give many reaction sites for sensors. Therefore, the oxide of this nano tree can expect the application to a gas sensor.
The precise results of the procedure and the properties will be presented by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDS), and X-ray diffraction (XRD) at the conference.

The use of composites of polymers has been the subject of numerous studies due to the successful combination of materials with different properties into a common matrix. Within this approach the use of organic-inorganic hybrid materials has been highlighted due to their mechanical, thermal, optical and electrical. The combination of inorganic materials such as zinc oxide to semiconducting polymers can enhance their physicochemical characteristics. Organic materials such as conjugated polymers can be made electrically conductive due to the insertion of H + ions along the polymer chain. Nanoparticles of zinc oxide used as sensors, biosensors, photodetectors have a great application potential in the areas of electronics and environmental engineering. This work studied composites with different ratios of mass of zinc oxide in the polymer matrix. From the anisidine and aniline monomers were synthesized semiconducting polymers polyaniline (PAni) and poly (o-methoxyaniline) (POMA). To obtain a homogeneous mixture solubility test was performed with different polymers. These polymers were mixed in different masses of nanoparticles of zinc oxide deposited on rigid substrates using the technique of scattering surface. Due to the difference in the physicochemical characteristics of the solvents was investigated dispersion of nanoparticles using techniques viscosity and optical microscopy. With these results it was possible to choose the most suitable solvent, obtaining more homogeneous composites and flexible. Preliminary results using the technique of UV-Vis show an absorption band around 374nm indicating the presence of zinc oxide in the composites. Electrical impedance measurements showed that the composites adhere to a system jumps (Random Barrier Model Free Energy), which conductors systems to evolve increases with the amount of zinc oxide in the polymer matrix. These results corroborate the measurements of optical microscopy indicating that the addition of semiconductor islands POMA increases the distance of hops between the charge carriers. This work was supported by MEC / SESu / DIFES, PRONEM / FAPEMIG, Nanobiomed / CAPES, INEO / CNPq and CNPq.

Nanostructured complex metal oxides with ATiO3 perovskite structure have been of great interest during last decade. Among these perovskite materials, self-assembled SrTiO3 nanostructures are considered as a promising candidate for various applications such as photo-electrochemical and biological applications. A crucial step toward the realization of such materials in functional systems is the development of controlled growth and assembly of these nanostructures into ordered or complex architectures. The focus of this work is on detailed investigation of the formation of SrTiO3 nanotube arrays during a controlled two-step anodization and hydrothermal process. Starting from the TiO2 nanotube structure, the microstructural changes at the nanoscale is investigated through doping of the TiO2 nanotubes with strontium toward formation of the complete SrTiO3 structure. Synthesis, functional characterization and growth mechanism of SrTiO3 nanotube arrays are investigated using a field emission scanning electron microscopy (FESEM), glazing angle x-ray diffraction (HT-GAXRD), and high-resolution transmission electron microscopy (HRTEM) and x-ray photoelectron spectroscopy (XPS). As a promising part of this work, transfer of such self-assembled SrTiO3 nanotube arrays onto silicon substrate is also shown.

Three dimensional (3D) nanowire arrays, sharing similar structures with mammalian olfactory array receptors, are attracting more attention recently for sensor fabrication. In our former work, we mimicked the biological olfactory receptor array and demonstrated that both noble metals and metal oxides coated 3D ZnO nanowire arrays are capable of performing as highly sensitive and selective sensors for different gas detections. Recently, we found several factors could strongly influence the performance of our gas sensor, such as length, spacing of nanowires, etc, therefore, it is essential to optimize the parameters to further improve the sensor performance. With e-beam lithography technique, spacing and length of the nanowires arrays can be tuned. By controlling the growth conditions and shell thickness, the gas sensors based on metal oxide core/shell structures were further investigated.

Several techniques have been used for the preparation of heterogeneous catalysts based on metal nanoparticles inserted into high-area oxide supports. These preparative routes aim to maximize the active phase dispersion, optimize the size and shape of the metal particles and enhance the interaction strength between the metal nanoparticle and the oxide support. The use of mesoporous materials has become a general strategy to increase the total surface-area of the support. However, the achievement of highly dispersed nanoparticles and strong metal-support interactions in these structures remain as challenging tasks.
In the present work we use a modified sol-gel method[1] for the preparation of gold nanoparticles embedded in mesoporous TiO2 which can be accessible for catalysis. Our synthetic approach to incorporate the nanoparticles into titania accessible networks is based on the use of organic spacers, such as aromatic carboxylates derivatives[2]. Two sets of samples were prepared, a set of pure TiO2 mesoporous structures and a set of Au@TiO2 mesoporous structures. These materials were characterized by BET measures and TEM, XRD and TG analysis. Also the catalytic behavior of these materials on the CO oxidation at 423 K was followed by using in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) coupled to on-line mass spectrometry (MS) analysis. The catalytic behavior and the observed surface species determined from DRIFT-MS were related to results obtained from CO catalytic oxidation tests, temperature-programmed desorption, thermogravimetric and differential scanning calorimetry analysis.
References
[1] G. Budroni, A. Corma. Angew. Chem. Int. Ed. 2006, 45, 3328 -3331
[2] M.Sabo, W.Böhlmann, S.Kaskel. J. Mater. Chem. 2006, 16, 2354-2357

MLCC(Multi-Layer Ceramic Capacitor) is a typical and common passive component for all electronic products. In the MLCC, the thick film process of submicron is adapted by the control of ceramic nano particles. However, in order to apply nano-BaTiO3 particles in the MLCC, control of grain size is an important element during sintering. In particular, it is difficult to get a standard of sintering process, because there isn't enough research of dielectric properties in nano-grain. In addition, the composition of high dielectric constant, high reliability and high break down voltage has not been reported in the sintering of the dielectrics using nano particles. In particular, it is important in the industry of electronic component. In this study, we observed the microstructure with the change of additives in the sintering of nano BaTiO3. As a result, the dielectric properties of the sintered body were investigated with the controlled microstructure. As additives, metal ions of Mn, Mg, Dy, Cr, Si and Ca were selected. These additives were coated on the surface of the nano BaTiO3 particles by wet coating process. As the source material, metal-nitrates which were soluble in ethanol and D.I. water were used. According to the variation of additives, we evaluated the grain size and tried to explain the relationship between grain size and the dielectric properties. In particular, the break down voltage which is an important requirement in the ultra-thin MLCC was evaluated.

Due to the surging demand for a high-density, high-speed and low-power non-volatile memory device, Resistive Switching Random Access Memory (RRAM) has a high potential for being the next-generation memory device. But, one of the difficulties faced currently with these memory devices is the understanding of the true mechanism that leads to this unique behavior. In this contribution, we present an approach which involves combining AFM-based characterization and simulation models to expose the true nano-scale mechanism that leads to such unique switching behavior.
Our experiment involves fabrication of oxide-based RRAM using Atomic Layer Deposition (ALD) of titanium dioxide (TiO2). We started by sputtering platinum on a Si/SiO2 wafer followed by deposition of a very thin layer of TiO2 (40-60 nm) and another layer of platinum sputtered on top.
Considering that most characterization of resistive switching (RS) behavior has relied on electrical measurements, direct electrical access to the area of interest is essential for nano-scale characterization. For this reason, atomic force microscopy (AFM) comes as the initial choice because it provides a nano-scale electrode. But, this set up was customized to study the temperature and gas environment (oxygen partial pressure) dependencies on the resistive switching behavior as well as to reveal the mechanisms in more detail. The I-V sweeps and ac impedance measurements under various temperature showed that oxygen reduction/evolution reaction at the interface and resulting Schottky-like interface switching behavior has dominant influence on the RS behavior.
Data accumulated through the electrical measurements and chemical/phase mappings were systematically analyzed and summarized. From the accumulated data showing specific temperature, gas pressure, and electrical bias dependencies, we suggest a simplified model, which fits well with the obtained data.

Interfaces and topological boundaries in complex oxide materials, such as domain walls, have recently received increasing attention due to the fact that their properties, which are linked to the inherent order parameters of the material, its structure and symmetry, can be completely different from that of the bulk material. I will present recent results on electronic and optical properties of ferroelectric domain walls in multiferroic BiFeO3 and ErMnO3. The origin and nature of the observed electrical conductivity at certain wall types is probed using a combination of conductive atomic force microscopy, high resolution transmission electron microscopy and first-principles density functional computations.

TiO2 nanotubes have recently attracted increasing interest due to their excellent biocompatibility and photocatalytic properties. Various applications are currently being developed: biomedical devices, sensors, solar cells... A research field that has yet to be fully investigated is the use of TiO2 nanotube arrays as membranes for biofiltration or cellular immunoisolation. Such inorganic membranes could prove useful in the development of an artificial pancreas to cure type 1 diabetes: these membranes present very narrow pore size distributions coupled to a high pore density while being robust and biocompatible.
The fabrication of TiO2 nanotubes is usually carried out by anodization of a metallic Ti foil in an organic electrolyte solution, using a Pt foil as counter electrode. The impact of experimental conditions on the structural parameters of TiO2 nanotubes has already been thoroughly investigated. After the anodization process, each TiO2 nanotube presents an open top end and a closed bottom end (barrier layer in between the tube and the underlying metallic Ti).
In order to produce self-standing membranes, the nanotubes have to be detached from the Ti foil and their bottom ends need to be opened. Despite many different techniques reported so far, these steps are still difficult to realize in practice (especially for large area membranes) and usually involve corrosive and hazardous chemicals.
A new and facile fabrication technique is reported here to produce TiO2 nanotubular membranes with through-hole morphology without the use of any harsh chemical etchant. It consists in a 3-step anodization procedure. A Ti foil is first pre-anodized (80V, 1h) in an ethylene glycol solution containing NH4F and H2O. The produced layer of TiO2 tubes is then removed from the Ti foil by sonicating the sample in a diluted HCl aqueous solution. This results in a dimpled Ti surface that is anodized again (80V, 24h) in the electrolyte solution. After rinsing with water and ethanol, a post-anodization procedure is carried out using a fresh electrolyte solution and a much higher voltage (180V). After a few (3-10) minutes, the TiO2 layer starts to detach from the underlying Ti. It is then easy to recover the whole membrane in one single piece with a scalpel. SEM studies permitted us to conclude that a very thin layer of tubes grown in between Ti and TiO2 during the post-anodization step causes the detachment of the final TiO2 membrane.
SEM characterization of these membranes highlights their through-hole morphology. The pores present a conical shape across the membrane thickness ranging from ~140 nm at the top to ~60 nm at the bottom. These membranes have already been tested for diffusion of glucose, insulin and IgG and show promising results.

Atomic layer deposition (ALD) is a thin film deposition technique based on self-terminating surface reactions. In difference to similar methods like chemical vapor deposition (CVD) or physical vapor deposition (PVD), the ALD process ideally results in the deposition of single atomic layers conformably coating the entire surface regardless of topography. Typically the process is split in two half reactions in which sequentially a metal followed by an oxidizer precursor is injected into the reaction chamber. Each precursor is specifically designed to react with the previously deposited layer, which enables precise thickness control. A wide variety of precursor gasses is available making it possible to deposit multifaceted materials.
The presented results discuss (1) the implementation of an ALD reactor into an UHV photoemission spectroscopy chamber to enable the determination of the electronic band lineup of ALD thin film interfaces without exposing them to the ambient, and (2) the use of this set-up for the measurement of the electronic structure and stoichiometry of Al2O3 thin films of various thicknesses. The measurements were performed with x-ray and ultraviolet photoemission spectroscopy (XPS, UPS) as well as with inverse photoemission spectroscopy (IPES) without breaking the vacuum between deposition and characterization. This enabled measurements unaffected by ambient contamination.

Nanowires have been the subject of intense research the last years due to their optimal characteristics acting as a a sensing element due to their reduced size and high volume / surface ratio, and their well-controlled physical and chemical properties [1].
Reliability and homogeneity of nanodevice properties are relevant requirements for large scale production devices. Integration of nanowires or nanostructures in general into electronic and functional devices is a challenging issue because of the handicaps presented in their handling and assembly steps.
Manipulation and preparation of nanomaterials for sensor purposes often is divided in several phases, where the nanostructure synthesis stage is separated from the contacting one. This assembly approach implies following a high time-consuming process and adds uncertainty factors to the fabrication process. A strategy to achieve a more reliable and reproducible nanomanipulation method would be to perform the synthesizing and contacting processes in one step, reducing fabrication stages.
With this objective, here we present the localized growth of tin oxide nanowires on top of CMOS compatible micromembranes with incorporated heater in order to provide the thermal energy necessary to synthesize the nanowires.
An Au film is deposited on top of the microhotplate surface in order to use Au as nucleation seed of the metal oxide nanowires. The growth is performed by chemical vapor deposition (CVD), using the molecular precursor [Sn(OtBu)4] [3] and the high temperature required for growing metal oxide nanowires (above 925K) is provided by the heater. HRTEM analysis showed monocrystalline tin dioxide nanowires, with predominant [101] direction of the tetragonal SnO2 phase, showing the same cristalline quality as nanowires of large area deposition.
The device has been proven to be effective as gas sensor, as a direct application of the one-step nanodevice fabricated. Nanowires have been tested towards NO2 and CO pulses in a synthetic air atmosphere on a constant gas flow, showing a high response to low concentrations of toxic gas species. Moreover, the grown nanowires have been operating for more than two months, keeping its gas response at high values and demonstrating high robustness and durability.
The here presented strategy can be extended to other chemistries and paves the way to a new fabrication route to nanodevices.
[1] S. Barth, et al. Prog. Mater. Sci. (2010) 55 563
[2] S. Barth et al. Chem. Comm., (2012) 48 4734
[3] S. Mathur et al., Small 1 (2005) 713.

Over a few decades, remarkable advancements have been made for synthesis of functional metal oxide nanomaterials [1-5]. The fabrication of undoped as well as transition metal doped ZnO nanostructures remains unabated due to their advanced applications in optoelectronic, sensing and spintronics devices. In this we paper we demonstrate structural transition in 1-10% Ni doped ZnO nanostructures (say Ni:ZnO NS) synthesized by a chemical precipitation route. The structural, optical, electronic and magnetic properties of prepared nanostructures were extensively investigated. The formation of hexagonal phase of ZnO for all the Ni doped ZnO nanostructures is evident through their characteristic X-ray diffraction patterns [1]. The average crystallite size for 1-10% Ni:ZnO was estimated to be 9.3-27.9nm. An XRD reflection from NiO (200) plane was observed only for 7% and 10% of Ni:ZnO NS [2]. The occurrence of a prominent Raman line at 115cm-1 for all the Ni:ZnO NS further confirmed single phase formation [3]. No additional vibrational modes due to NiO/Ni were detected in the Raman spectra [4]. In agreement with XRD results, HR-TEM images of 1-7% of Ni:ZnO NS vividly exhibit 20nm size particles. Interestingly, formation of nanorods initiates with 7% Ni doping and for 10% Ni:ZnO complete structural transformation takes place resulting in the formation of nanorods (diameter: 21-50nm, length: 215-375nm). FTIR analysis elucidates that incorporation of Ni in Zn lattice and formation of Zn-O-Ni linkages lead to anisotropic growth of nanorods [3, 5].
References:
[1] N. Goswami and D.K. Sharma, Physica E, 42, 1675-1682 (2010).
[2] N.M. Ulmane, A. Kuzmin, I. Steins, J. Grabis, I. Sildos and M. Pars, J. of Phys.: Conf. Series, 93, 012039-012043 (2007).
[3] R. Elilarassi, G. Chandrasekaran, Mats. Chem. and Phys, 123, 450-455 (2010).
[4] R. Bacsa, Y. Kihn, M. Verelst, J. Dexpert, W. Bacsa, P. Serp, Surf. Coat. Tech., 201, 9200-9204 (2007).
[5] N. Goswami and A. Sahai, Mater. Res. Bull., Accepted (2012).

A new technology has recently emerged which uses sensors based on liquid crystals (LC) to gain analytical information about the environment. The key feature of these sensors is that they require little or no power to function, yet they are simple to operate, robust, cheap and chemically specific. The basic design of such devices exploits the change in the anchoring of a LC on a given substrate,(typically a metal oxide insulator) in response to the presence of a specific analyte. This change, in turn, determines an optical response which can be easily detected with a polarized microscope [1]. In this work we investigate the molecular organization of LC at the interface with a metal oxide insulator (that is, amorphous and crystalline SiO2) by means of atomistic molecular dynamics simulations [2,3]. We address the problem of the relationship between the morphology of the substrate and the underlying LC phase, for the specific case of a nematic LC, 4-n-pentyl-4'-cyano biphenyl (5CB), supported on different forms of silica. We also consider the case of 5CB supported on an amorphous silica substrate chemically functionalized with octadecyltrichlorosilane (OTS). The analysis of our simulations reveals that changes in both the anchoring orientation and the degree of order of the LC depend not only on the chemical nature of the substrate, but also on its morphology (e.g surface roughness) [4].
References:
[1] R.R. Shah and N.L. Abbott, Langmuir 19, 275 (2003).
[2] G. Tiberio et al., ChemPhysChem 10, 125 (2009).
[3] A. Pizzirusso et al., C., Chem. Sci., 3, 573 (2012).
[4] O.M. Roscioni et al., submitted to Langmuir (2012).

Magnetic particles have potential applications in position sensing, ultrahigh density magnetic storage media, clinical diagnosis and treatment, biological labeling, and separation applications. Janus particles exhibit an asymmetric magnetization making them suitable building blocks for directed three-dimensional assembly under in external magnetic fields.
Iron oxide capped Janus particles are prepared via physical vapor deposition of nanometer thin iron films onto a polystyrene or silica particle monolayer in an oxygen/argon atmosphere. Subsequently, the aqueous suspension of Janus particles is exposed to a magnetic field and monitored for 30 min. Three assembly behaviors are observed: (i) staggered chains, (ii) double chains, or (iii) no assembly. Parameter that may affect the assembly behavior such as deposition rate, iron oxide cap thickness, particle volume fraction, and assembly time are studied. A deposition diagram has been developed relating deposition rate and assembly behavior. The cap materials are determined by the physical properties of the iron oxide thin films as follows: Fe1-xO leads to staggered chains, Fe3O4 leads to double chains and α-Fe2O3 shows no assembly. More recently, we have focused on determining the mechanism of Janus particle chain formation and contraction in parallel electric and magnetic fields.
In our experiments, the AC electric field is introduced first to assist formation of staggered Janus particle chains. Subsequent application of a strong external magnetic field contracts the staggered chains into a double chain structure. We have studied the relation between the viscosity of the surrounding solution and the iron oxide Janus particle chain dynamics as a function of particle size and chain length. The solution viscosity is adjusted by addition of specific amounts of glycerol to our aqueous system. We observe that chain dynamics are strongly correlated with the viscosity of the solution thereby pointing to the potential application of these Janus particle chains as in situ micro-viscometers.

Growing demands for new emerging biomaterials aimed at introducing wound healing materials. Specialglass filaments has been shown in an initial human trial to speed wound healing (with little scarring) in diabetic patients. A wide field of applications — from burns to battlefield injuries — may bein store for this biocompatible material. However, new bioactive glasses based on borate and borosilicate compositions have shown the ability to enhance new bone formation, borate glass introduced via boric acid with nontraditional processing. The introduction of borate glass into hybrid aluminum matrix composite is established through direct metal oxidation DIMOX and rheocasting. Direct metal oxidation, DIMOX, is applied on recycled Al-alloy that has been prompted to redesign production processes to more cost efficient. Aluminum alloy (scrap) is heated at different temperatures, 1000oC, 1050oC and 1100oC for holding time (10 to 30 minutes) and then poured into metallic mold. Boric acid is applied to the melt for the same holding time at 2, 5, 10 and 20 wt. %. The kinetic of formation of hybrid composite is introduced with the effect of alloying elements addition (boric acid). Ceramic alumina, intermetallic as well aluminum borosilicate is introduced as different reinforcements in residual aluminum metal matrix composite. The material may be introduced as a new implant with dispersed bioactive borate glass. The effect of alloying elements segregation and the solubility limit produce multifunction biomaterials with different compositions. Scanning electron microscopy with energy dispersive X-ray spectroscopy EDX is utilized for micro-structural characterization. Besides, 3-point test is applied for mechanical characterization. This application is dominant for dispersed bioactive glass in a hybrid composite implant. The structure may be critical to numerous applications for bone regeneration, and the healing of soft tissue wounds.

The percolation threshold in a ceramic composite depends on the processing conditions used to fabricate them along with the size and shape of the filler used. In this study, borosilicate glass microspheres of various sizes were used as the matrix material and nanosized antimony tin oxide (ATO) particles were used as the filler. The microsphere/ATO composites were fabricated by hot pressing at temperatures in the range between the glass transition temperature and the softening temperature of the glass in order to control the viscosity. The pressure and temperature applied allowed the ATO to be confined to the spaces between certain glass particles, forming percolating networks at low volume fractions of the ATO. By adjusting the particle size ratios of the glass and ATO, along with having multiple size distributions of the glass, composites with specific electrical and optical properties were developed. Even though apparently very similar microstructures were made using different processing parameters, the percolation and conductivity showed noticeably different response. The differences can be attributed to the interaction between the segregated ATO particles with one another. The electrical properties were examined using ac impedance spectroscopy along with current AFM, which allowed for valuable insights into the structure-property-processing relationships in these materials. In addition to determining the percolation threshold under specific conditions, the measurements facilitated the interpretation of the behavior of the insulator and conductor interfaces between the glass and the ATO nanoparticles as well as the ATO-ATO interfaces.

Recently, strain effects of ZnO nano-/micro-structures are intensively studied due to their tunable electronic and optical properties via strain engineering, which is a useful route to tune the band structure and physical properties of nano-/micro/structures. Since the strain induced by externally applied forces significantly affects the physical properties of ZnO, information about the strain distribution within it plays an important role in great potential applications for the stretchable and wearable device systems utilizing their deformation. Until now, however, the strain effects simply bent ZnO nano-/micro-structures have been reported. We have investigated strain effects in a ZnO microwire(MW) with wavy geometries using cathodoluminescence (CL) measurements. The MW was laterally bukled using elastomeric substrate of polydimethylsilane (PDMS). The variations in peak positions and full width at half maximums (FWHMs) of near-band-edge (NBE) emission in CL spectra along the length of the wavy wires were measured at room temperature. Curvature sections of the wavy MW showed significantly lower photon energy of NBE emission and broadened FWHM as compared with straight sections. The observed variations indicate that the local strains in the wire led to the local changes of the band gap of the ZnO MW.

Many ternary metal oxide semiconductors have remained less explored in the context of energy applications of current interest in spite of their interesting chemical, physical and optoelectronic properties. Herein we report synthesis of one such optoelectronically interesting metal oxide; Copper Bismuth Oxide (CuBi₂O₄) by a one-step, low temperature and high yield wet chemical method with significant process control on morphological features. We study the optoelectronic and photocatalytic properties of the synthesized forms for energy harvesting applications. Apart from being a metal oxide of earth abundant metals, CuBi ₂O₄ shows good potential for photoelectrochemical (PEC) and photovoltaic applications because of its unique set of properties, namely a narrow bandgap (Eg ~1.4 eV), p-type semiconducting character, and high absorption over the entire visible spectrum of solar energy. In the present synthesis method, most striking is the significant and interesting evolution of material morphology with processing temperature over a small range from 40 ⁰C to 75 ⁰C. Thus, unisotropic nanopods are obtained at 40 ⁰C, isotropic nanoballs at 60 ⁰C and hierarchical nanofloweres at 75 ⁰C. We study and report the phase and microstructural evolution in detail by X ray diffractometry and electron microscopy (SEM/TEM) techniques to understand the driving mechanism.
Furthermore, we probe the optical and electronic properties of CuBi₂O₄ in detail to determine its energy band structure and charge transport, mobility, and recombination behavior, which are crucial in the context of the energy harvesting applications. These studies include measurements of UV-Visible absorption, cyclic voltammetry, and current-voltage/capacitance-voltage (Mott Schottkey) characteristics.

Titanium dioxide (TiO2) nanowires are assembled randomly via spray deposition to form nanowire networks. Networks are contacted electrically over device (<5 mu;m) and material (>5 mu;m) length scales. Despite the relatively simple fabrication technique, the semiconductor oxide nanowire networks display rich & complex electrical properties, due to the coupled movement of oxygen vacancies and electrons within the network and the evolving connectivity of the network [1]. By applying a voltage across the device oxygen vacancies, acting effectively as n-type dopants in TiO2, can be shunted through the TiO2 film to create conductive channels within the oxide. This coupled motion between dopants and electrons is believed to produce resistive switching and memristive phenomena observed in thin solid films of TiO2 [2]. In this work, we report the unique memristive behaviour observed in randomly assembled Titania networks and describe how this behaviour changes as the network is heated and stimulated with UV light irradiation. Device reliability/lifetime, material properties, and potential applications in non-volatile memory storage are also discussed.

The use of microwave irradiation is a promising alternative heat source for the synthesis of inorganic materials such as perovskite oxides. The method offers massive energy and time savings as compared to the traditional ceramic method.
As compared to synthesis techniques where heat is transferred by convection, the reactions in microwave techniques are orders of magnitude faster. Microwave-assisted synthesis of perovskites in the solid state is often limited to “simple” compositions (ternary) but the possibility of combining microwaves with other methods such as hydrothermal synthesis, sol-gel, or combustion allows for better stoichiometric control of complex doped phases. In particular, combining microwave heating with solvothermal synthesis may result in metastable phases and novel morphologies. Single-mode microwave synthesis allows separating the magnetic and electric components and provides an accurate control of the temperature together with much shorter reaction and processing times.
The synthesis of a wide range of perovskite oxide materials is feasible by microwave techniques, where such materials include superconducting, ferromagnetic, ferroelectric, dielectric and multiferroic perovskite systems.

Smart sensors, offering real-time analysis of gaseous chemical analytes, are essentials for environmental emissions monitoring, fossil fuel combustion control, medical diagnosis, artificial olfaction and homeland security. Simplicity in operation, low cost, flexibility in production and small size constitute the main advantages of chemoresistive-type semiconductor chemical sensors based on metal oxides over electrochemical, optical, acoustic and other types of chemical sensors.
One of the top design priorities for semiconductor chemical sensors is developing simple, low-cost, sensitive and reliable nanosensors. However, the need to implement heating elements in sensor devices, and the resulting high power consumption, remains a major obstacle for the realization of miniaturized and integrated chemoresistive thin film sensors based on metal oxides. Here we fabricate structurally simple but extremely efficient chemoresistive sensors with ~90% transmittance at visible wavelengths.
Pronounced self-heating in nanocolumnar metal oxide thin films on glass substrate with indium-tin oxide electrodes enables ultrahigh response to nitrogen dioxide and volatile organic compounds with detection limits down to sub-ppb levels and power consumption of a few tens of microwatts. Superior performance of the self-heated nanocolumnar thin film sensors paves new ways for the fabrication of highly sensitive chemical sensors with ultralow power consumption on various substrates. High transparency at visible wavelengths creates opportunities for their use in transparent electronic circuitry and optoelectronic devices with avenues for further functional convergence.

Yttrium Titanate belongs to a family of compounds called pyrochlores with significant properties such as ionic conduction, optical non-linearity and radiation tolerance that have resulted in applications thermal barrier coatings, high-permittivity dielectrics, solid electrolytes in solid-oxide fuel cells, and materials for safe disposal of actinide-containing nuclear waste, and hydrogen storage material. The application of these materials in ODS ferritic steels have been recently evaluated. In recent years, it has also been shown to have higher activity than TiO2 for photocatalytic water splitting and a more efficient host material than TiO2 for Er3+ luminescence. The calculated band gap for yttrium titanate is 2.84 eV as compared to 3.12 eV for TiO2. Since Y3+ and Er3+ have similar ionic radii, crystal structural and lattice constants, Er can easily replace Y3+ to form Er doped yttrium titanate. The Y3+ and Er3+ are indistinguishable and as a result Er3+ does not cluster, thereby reducing concentration quenching. Additionally, Y2Ti2O7 has low phonon energy (<712 cm-1) which reduces the possibility of ron radiative recombination and enhances PL intensity. ErxY2-xTi2O7 thus has tremendous applications in fiber amplifiers, integrated optical devices and selective emitters for thermophotovoltaic applications. Since 1-D nanostructures are deemed to be important building blocks for future optical and optoelectronic nanodevices, we have used electrospinning methods to synthesize nanofibers and freestanding, non-woven nanofibers membranes of single phase yttrium titanate and ErxY2-xTi2O7 ( x= 0 -10 %) with diameters less than 150 nm and have characterized the physical, thermal and optical properties. We have demonstrated that such fibers can be synthesized at a relatively low cost and high production volume with a narrow diameter range. No clear phases are observed up to a calcination temperature of 700 oC and pyrochlore phase appear at 725 oC which are also confirmed by the TGA. Single pyrochlore phase is observed at temperatures greater than 900 oC. No other oxide phases are present.

Transparent conducting oxides (TCOs) have revolutionized our modern devices such as displays, light emitting diodes (LEDs), thin film photovoltaics (PV) and smart-windows. Among the TCOs, Sn-doped In2O3 (ITO) and F-doped SnO2 have mostly been commercially exploited because of their excellent visible transparency and conducting properties. The increasing demand for new performing materials with specific optical properties, lower cost and earth abundant elements is driving new investigations of these materials. Furthermore, TCO nanocrystals (NCs) exhibit distinctive near infrared (NIR) optical properties, including absorption due to electronic carriers that can be either plasmonic or polaronic in nature. Thus, these NCs offer a new opportunity to manipulate light, stimulating a new way of photophysical investigation and novel devices such as transparent electrochromics.
However, the effective introduction of aliovalent dopants during the synthesis of colloidal NCs can be challenging. For instance, we have recently demonstrated that aluminum can be incorporated into zinc oxide by carefully balancing reaction kinetics through selection of the coordinating ligands of the aluminum and zinc precursors. Now, we have significantly extended synthetic control of NC growth to other TCO compositions that allow us to investigate shape effects on the NIR optical properties of these novel materials. For instance, we will present a new colloidal synthesis of TiO2 anatase NCs that permits doping with Nb by including a Nb5+ precursor in the reaction flask. Nb-doped TiO2 NCs of around 9-15 nm in size with control over the Nb content are obtained. The incorporation of the dopant leads to the appearance of a tunable broad absorption peak spanning from visible to IR region as an effect of the free carriers generated by the substitutional Nb5+. Increasing the amount of Nb precursor the Nb-TiO2 crystals also systematically varied their shape from tetragonal to “peanut” like elongated structures. Meanwhile, we also developed a synthesis for shape-controlled tungsten bronze NCs, specifically Cs-WO3. Manipulating the mixture of organic reagents, we varied the shape between rods, spheres, and disc-like hexagonal prisms. In this case, two distinct NIR absorption bands are present, which evolve systematically with the shape of the NCs. Together, these two new doped oxide NC systems significantly expand our understanding of free carrier generation through doping in NCs and the resulting optical properties.

Vanadium dioxide (VO2) is a strongly correlated material that displays a metal-to-insulator transition at 68°C. When VO2 is doped with approximately 4% Tungsten (W), the transition temperature approaches room temperature. Here we investigate single crystalline VO2 nanobeams, where the lateral material dimension is smaller than the characteristic metallic domain size, with a graded W dopant profile. Through the use of scanning photocurrent microscopy, which measures photocurrent as a function of the local photo-injection position, and Kelvin probe microscopy, we were able to provide a direct mapping of this W distribution. This mapping included the stress associated with the introduction of W, along with the characterization of any doping induced internal electrical fields. Our results may shed light on the band structure and charge dynamics in strongly correlated materials providing valuable insight into the eventual design of Mott field effect transistors.

The influence of particle shape on localized surface plasmon resonance in tungsten bronzes has been unexplored. Given the high transmittance of visible light and high absorption of near infrared light in tungsten oxides, the potential to use such materials in electrochromic devices and other plasmonic constructs drives the need to understand the role of particle shape on SPR properties. Using varying ratios of oleylamine to oleic acid allows the synthesis of Cs0.29WO3 nanocrystals in three distinct shapes: hexagonal prism, truncated cube, and pseudo-sphere. We rationalize shape effects by systematically correlating the number of faces for an idealized nanocrystal with the plasmon resonance characteristics. Comparing the synthesized shapes, as the number of faces in the idealized polyhedra progresses from eight to ten to infinity, the larger number of surface faces correlates with broader plasmon resonance features and fewer distinct resonances.

Metal (Au, Pt, Au@Pt) and metal oxide (TiO2) nanoparticles are synthesized with colloidal techniques and subsequently used as nanocrystal inks for thin films deposition. The optical properties of Au colloids are strongly influenced by both Pt and TiO2 interfaces: while platinum causes a damping and a blue-shift of the Au Surface Plasmon Resonance (SPR) peak as a consequence of the metal-metal interaction, the anatase matrix is responsible for the red shift of the plasmon frequency due to the increased refractive index. By a careful tailoring of the nanoparticles synthesis, high quality, scattering-free films composed of an anatase matrix embedding Au, Pt and Au@Pt colloids are deposited at room temperature and stabilized at 200 °C. Room temperature exposure of these films to hydrogen leads to optical changes. In the case of Au, there is a slow blue shift of the surface plasmon band, resulting in a wavelength dependent optical response. Much faster but smaller optical changes occur for titania films containing Pt. When both metals are present, the optical response of the gold is much faster. This is attributed to spillover of hydrogen atoms from platinum to gold. This synergy enables enhanced optical sensing of hydrogen at room temperature by combining the low temperature dissociation of H2 on Pt with the intensive surface plasmon response of the gold nanocrystals.

Controlled growth of nanostructures has long been regarded as one of the biggest obstacles to their commercial applications. Herein we demonstrate the feasibility of controlling growth of ZnO nanotubes and nanowires by floating substrates on the surfaces of reacting solutions with different concentrations, a key factor for differential growth. These slim ZnO nanotubes with outer diameters of 26.6+-12.2 nm and inner diameters of 8.3+-6.2 nm (confidence level of 95%) are a recently discovered new class of nanostructures whose growth is driven by screw dislocations (S. A. Morin et al., Science 2010, 328, 476-480). Concentrations of precursors below 0.5 mmol L-1 adequately allow the slow relocation of solute clusters and spontaneous formation of the single crystal tube while the concentrations above 15 mmol L-1 induce high-speed deposition of newly forming solute clusters and fast growth of nanowires; therefore the concentration plays a crucial role in determining the morphology of one dimensional (1D) ZnO nanostructures. The newly discovered enhanced wettability properties of ultrathin ZnO nanotubes are suggested to be caused by coupling the morphology and size effects of the nanostructured surface. These ultrathin nanotubes with low density and small dimension form a wet-hair-like hierarchical morphology, which shows a further improved superhydrophobic property with an 8.6+-1.6 larger contact angle than that of ZnO nanorods due to the morphology effect. In addition, owing to the large surface to volume ratio and increased effective UV-irradiated area of the ultrathin tubular structure, the ZnO nanotubes exhibit 5 times faster superhydrophobicity to superhydrophilicity conversion speed than nanorods under 254 nm UV illumination. Furthermore, UV light with a wavelength of 254 nm exhibits 40 times faster wettability conversion speed for nanotubes than that of 365 nm, which is suggested to be a result of the band gap shift at the nanoscale. The underlying mechanism is fully discussed in this work. The combined advantages of enhanced superhydrophobicity, improved sensitivity, and faster conversion speed by coupling morphology and size effects of these ZnO nanotubes should give them broad applications in self-cleaning surfaces and wettability switches.

Super-hydrophobic materials have been studied from their great potential in wide practical applications. Self-cleaning effect is one of the most famous and useful property of super-hydrophobic materials. Many methods have been used to fabricate super-hydrophobic materials including chemical deposition, photocatalysis, lithography, template methods and ion bombardment. These methods have difficulties to fabricate self-cleaning films because of their opacity of aging effects.
In this present work a transparent and super-hydrophobic films having self-cleaning effect are fabricated by simple method. Anodization and polymer replication technique was used to make nanofiber structure on the films. Because nanofiber structure have important role in hydrophobic and transparent property, effect of nanofiber structure on hydrophobic and transparent was also studied. These two properties are inverse proportion according to the length of the nanofibers. With these results, optimum fabrication condition for transparent self-cleaning films was found from the transmittance and contact angle measurement. Self-cleaning test was also performed to compare the transparent super-hydrophobic film with other films.
Industrial aluminum surface was elctropolished to smooth the surface and anodized in oxalic acid. Anodized aluminum surface has nanoscale pores on the surface. After widening process using phosphoric acid, AAO template was coated by PDMS. TPT polymer solution was painted on the template and the template with PET film was covered. To increase hydrophobic property, we took silane process on the film. And finally transparent super-hydrophobic films were fabricated. Contact angle and transmittance tests were performed to obtain contact angle and transparency of the films. The results show that contact angle and transparency are inversely proportional. The anodizing condition to fabricate transparent super-hydrophobic surface was decided from the results. Self-cleaning test was also performed. Water drop test was conducted on to the four types of dusted samples: the smooth TPT polymer film and the transparent TPT super-hydrophobic film, TPT film treated by silane, TPT film without silane treatment and glass. All films were tilted 10° to observe self-cleaning effect. It was found that large contact angle makes for good self-cleaning, and the transparent TPT super-hydrophobic film had the best self-cleaning performance because of the contact angle. Transmittance before and after the test were almost identical.
The resulting transparent super-hydrophobic film is simpler to fabricate than earlier methods and fabrication time and cost are therefore smaller. And because of its flexibility, it can be applied various industrial field like a self-cleaning window.

Large area, crystalline metal oxide thin films on plastics are strongly demanded in flexible electronic device technologies as well as by those who aim at replacing glasses by lightweight plastics. Many of the active functions of oxide thin films emerge in their crystalline states, and high bulk densities or small porosities are preferred. Crystallization as well as densification, however, is driven in principle by atomic diffusion at high temperatures where plastics cannot survive. This is why great efforts have been made for over thirty years to develop "low-temperature" deposition techniques, where people have focused on how to crystallize and densify the films "without firing." Here we propose a totally different route, where (i) a polymer release layer is deposited on a silicon substrate, (ii) a precursor gel film is deposited on the release layer by spin-coating, (iii) the gel film is fired into a crystalline metal oxide film, and (iv) the fired film is transferred onto a plastic substrate by melting or softening the substrate surface. The crystalline oxide thin films thus transferred onto plastic substrates were crack-free and had smooth surface. Transparent, 60 nm thick anatase thin films with high optical reflectivity could be prepared on PMMA and polycarbonate (PC) substrates. Transparent, electrically conductive, 660 nm thick ITO thin films on a PC substrate are another example. Patterned ITO thin films could also be prepared on plastics by using a mother silicon substrate with periodic grooves. The technique is significant in that the crystallization and densification, which are key factors for superior functionalities, are guaranteed for the films by the firing process, and that the principle of the technique allows any kinds of crystalline metal oxide thin films to be fabricated on any kinds of plastic substrates.

Superhydrophilic and superhydrophobic surface have been studied due to their special surface wetting properties. The superhydrophilic and superhydrophobic surfaces can be produced by modifying surface roughness and surface energy. These surfaces both need enhanced roughness, such as micro/nano-structured hierarchical structures. The surface wetting properties depend on their surface energy, if the surface has fully developed roughness. The surface energy is should be higher than that of water for superhydrophilicity and lower for superhydrophobicity. Diverse methods have been developed to get the special wetting properties. However, conventional methods cannot produce arbitrary three-dimensional surface and involve complex and time-consuming processes. It brings limitation of applications in industrial fields.
Here, we present fabrication method of three-dimensional superhydrophilic and superhydrophobic surface by single-step anodization. This method is based on self-aggregated aluminum oxide nanowires and hierarchical micro/nano-structure was formed by the nanowires. Formation process of the hierarchical structure is as follows. Anodization is performed on industrial Al (99.5%) in 0.3 M oxalic solution at a constant voltage of 65 V. At first, nanohole structures were formed on the Al substrate. However, these nanoholes were gradually etched and widened. So the walls of nanoholes become thinner. Some parts of the nanoholes have been completely etched away. The remaining nanoholes on the top surface have entirely vanished and the walls enclosing the nanoholes are transformed into nanowires. Finally, the upper part of alumina nanoholes is entirely transformed to nanowires with the hierarchical micro/nano-roughness by self-aggregation. The formation occurred within 10 min. The fabricated surface has superhydrophilicity due to surface roughness and surface energy of the alumina nanowires. The superhydrophobic surface was fabricated on the superhydrophilic surface using a hydrophobic polymer with low surface energy. n-Hexane and heptadecafluoro-1,1,2,2-tetrahydrodecyl trichlorosilane(HDFS) mixed 1000:1 in volumetric ratio and dipped the superhydrophilic surface in the mixing solution for 10 min. After wash the specimen, the surface has superhydrophobicity by surface energy of HDFS. Contact angle of the surface is higher than 150°.
However, the surface topography was not changed because the HDFS coated with monolayer. The self-aggregated alumina nanowires are formed not only plane surface but also complex three-dimensional surface. The HDFS coating also can apply arbitrary shape. Therefore, we can easily fabricate complex three-dimensional superhydrophilic and superhydrophobic surface mentioned above our method. It can widen the applications filed in industrial area.
We believe the findings will be of great interest to surface scientists generally, and particularly to researchers working on fluidics, water drag reduction, and self-cleaning.

Aluminum oxide (Al2O3) demonstrated an excellent surface passivation for both n-and p-type c-Si solar cells due to the presence of high negative fixed charges (Qf ~1012 cm-2) in combination with low density of interface states (Dit ~ 1011 eV-1.cm-2). However, during the high-temperature (~ 800C) annealing step in the fabrication of the solar cell, unwanted blisters appear on the surface of the film, which in turn degrade the surface passivation effect. Our study aims to understand the mechanisms of blister formation and to control its growth rate. For this, we have carried out experiments to show the dependency of blister growth under the influence of different atmospheric and annealing conditions.
Al2O3 films were deposited on Monocrystalline <100> silicon substrate by RF (13.56 MHz) magnetron sputtering, using an Al (99.99% purity) target. A mixed gas of argon and oxygen was used for sputtering, and the oxygen flow ratio was varied to obtain the stoichiometry of Al2O3. The thickness of the deposited films was 35 nm. After the metal oxide deposition process all the samples were annealed in nitrogen atmosphere at an initial temperature (T0 = 430C) for 30 minutes to activate the passivation mechanism. The analysis of blistering effect was performed at four different temperatures (T1=600C, T2=700C, T3=800C, T4=900C) under two different atmospheric conditions (nitrogen and oxygen) for 90 sec. After each annealing steps (from T0 to T4), electronics properties of the interface was characterized using Capacitance-Voltage measurements on Metal Insulator Semiconductor capacitors to extract the effective charges and the interface states density. In addition, lifetime measurements of minority carrier were performed to evaluate the effective Surface Recombination Velocity (SRV). In parallel, the structure, the stoichiometry and the diffusion at the interface between silicon and metal oxide were examined by Secondary Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Secondary Ion Mass Spectroscopy (SIMS).
We observed blister formation only takes place for samples annealed at temperatures above 700C in nitrogen atmosphere, whereas no blisters were seen under oxygen atmosphere. The dependency of minority carrier lifetime was correlated to the blister density. Moreover, the presence of oxygen in the atmosphere during annealing avoids the aluminum diffusion in silicon and reduced the interface state density (chemical passivation). Cross-sectional study of the blister on 800C sample under nitrogen condition shows that the adhesive nature of Al2O3 with silicon surface is being lost. Temperature above 800C leads to a structural change from amorphous to polycrystalline.
To obtain an excellent surface passivation without blister formation at temperature greater than 800C, we have shown that oxygen atmospheric condition is mandatory. At this specific processing conditions surface recombination velocity (SRV) less than 10 cm.s-1 was achieved.

In recent years, many researchers are interested in transparent thermal insulating materials (TIM) for many potential desires in the various fields of industry. Particularly, solar control coatings for transparent TIM are transparent at UV-visible range and effectively reflecting at Near-Infrared (NIR) range. The various nanoparticles have been investigating the continuous and new methods to reduce solar heat as it ensures a potentially low-cost and high-productivity solution. A promising materials group to achieve the purpose is represented by the nanoparticles of transparent oxide conductors such as tin doped indium oxide (ITO) and antimony doped tin oxide (ATO). They are known to provide highly transparent solar filters to absorb infrared light by possibly activating surface Plasmon polaritons of free electrons, as typically resulted in gold and silver particles. Similarly, hexaboride based lanthanum types, a violet-black material as a nanoparticle, has also been demonstrated to be one of the commercial materials serving as an NIR shielding with high visible light transmittance. For practical applications, however, optical properties of a stronger and wider-band NIR absorption with high transmittance in visible region are in high needs. At this point, tungsten trioxide (WO3) is well known that exhibits the transparent property in the visible and NIR ranges. Additionally, WO3-based electrochromic devices are mainly being researched for smart film applications with changeable modulations in optical spectra. A metallic conductivity and strong NIR absorption can be induced when free electrons are introduced into crystals by either decreasing the oxygen content or by adding ternary elements. Until now, study on the synthesizing WO3 with different morphologies and properties has been widely reported. In the other hand, MoO3 has a wide band gap of 3.2 eV5 and is well known metal oxide materials used in gas sensing, catalytic, photochromic, and electrochromic research fields due to the similar physical and chemical characteristics to the WO3 and is studying the various applicability in the field of industry at the same time. Nevertheless, there is limited work reported on the synthesis and heat-shielding properties of molybdenum oxides nanoparticle.
In this work, the MoO2 for control over size and morphology of nanostructures were synthesized by a solid state reaction using changing temperature, additive, and air condition. The structure and sizes of MoO2 particles was observed XRD and PSA spectrometer, the optical properties of their films were investigated by UV/VIS, NIR spectrometer. Synthesized particles typically formed cubic structure for good absorption of NIR, size observed as being 50~100 nm. Especially, remarkable absorption of NIR wavelength ranges makes ceramic composite films good candidate for use as a heat shielding window, it clearly shows useful for applications where heat shield is required.

Fe2O3 is of great interest due to its various applications such as photoelectrochemical water splitting, Li-ion batteries, pigments and chemical sensors. For these applications, since the device performance largely depends on the surface-to-volume ratio of the Fe2O3 electrodes or catalysts, tremendous efforts have been devoted to synthesize Fe2O3 nanomaterials with large specific surface areas.
Among them, Fe2O3 nanotubes have attracted great interest owing to the facile synthesis of them using anodic oxidation processes. Most of studies on Fe2O3 nanotubes were based on anodization of Fe or Fe-alloy foils, which results in Fe2O3 nanotubes on thick metal substrates. For high-quality chemical sensors or solar water splitting cells, the separation and transfer of Fe2O3 nanotube arrays from the metal substrates onto Si or glass substrates are needed. However, using the synthesis-and-transfer method, obtaining vertical Fe2O3 nanotubes on the Si or glass substrates is challenging because Fe2O3 nanotubes are very fragile and thus the separation of large-area Fe2O3 nanotubes is difficult. Alternatively, vertically synthesis of Fe2O3 nanotubes on Si or glass substrates have been reported, but the quality of the Fe2O3 nanotubes fell far behind those from anodization of Fe foils.
Here we report synthesis-in-place of vertically aligned Fe2O3 nanotubes. By anodizing Fe films on Si or glass substrates, we could obtain vertical Fe2O3 nantubes on the substrates. The orderness of the Fe2O3 nanotubes is unparalleled with those of the previously reports. Furthermore, the vertically synthesized Fe2O3 nanotubes on the Si or glass substrates could be used as chemical sensors and without additional processes. The experimental results reveal that the chemical sensors based on the high-quality Fe2O3 nanotubes exhibits ultra-sensitive gas sensing properties to flat Fe2O3 thin films. In addition, it will be shown that the Fe2O3 nanotubes are very promising as high-quality solar water splitting for hydrogen production.

MnO2 have attracted enormous attention of scientific community due to its physical and chemical properties and their applications in super capacitors, Li batteries and as a catalysts, etc. MnO2 exist in α, β, γ and lambda; type crystallographic structures and it can be synthesized in different forms such as nanowire, nanorod and nano particles. Existence of MnO2 in different forms and structures is responsible for their excellent properties. Synthesis in particular structure and the improved properties of MnO2 has been the interest of materials scientists for several years. In the present case, we report on synthesis of MnO2 nanowires and nanorods employing hydrothermal process and investigation of their magnetic characteristics and explore some distinct magnetic behavior. In a typical α-MnO2 nanorods (nanowires) synthesis, Mn(CH3COO)2.4H2O and Na2S2O8(NH4)2S2O8 for nanowires) were dissolved at room temperature (RT) with a molar ratio of 1:1 in40 mL of distilled water by magnetic stirring.40 ml of 1-octanol was added to the above solution mixture. The mixed solution was transferred to a 100 mL Teflon-lined stainless steel autoclave and heated at 120 °C for 12 h (140 °C for 12 h) in a preheated electric oven. After the reaction, the final precipitated products were washed sequentially with deionizedwater and ethanol to remove the sulfate ions and other remnants by filtration. The obtained powder was subsequently dried at 100 °C for 12 h in air. Magnetization measurements were carried out at RT employing vibrating sample magnetometer. The saturation magnetization values of MnO2 nanorods and nanowires at RT are found to be 0.193 and 0.095 emu/g respectively. The coercivity values MnO2 nanorods and nanowires are found to be 29 and 48 Oe respectively. Coupling between Mn ions in the Mn4+-O-Mn4+configuration leads to the observed RT ferromagnetism. Dielectric property measurements of nanowires and nanorods at various frequencies and temperatures are in progress and will be presented in the conference.

The Mg interstitials promote formation of vacancies surrounded by oxygen atoms that are expected to develop a net spin. An active defect is believed to interact with another closely situated active defect, and this eventually may lead to long range ferromagnetic ordering if the defects couple ferromagnetically. Recently we have reported ferromagnetic ordering in MgO thin films [1] produced by rf/dc sputtering on Si substrates. It was found that magnetic moment averaged over film volume (saturation magnetization) increases almost linearly with increasing film thickness, and starts to decrease after reaching a maximum at a finite thickness. In sufficiently thick films room-temperature ferromagnetic ordering is completely suppressed and the expected diamagnetism appears. At least three effects leading to destruction of ferromagnetic order may appear as the films are grown thicker. The first one is related to the increasing cation defects as the thickness of the material increases which when saturated results in a maximum of the effective magnetization beyond which the defects tend to coalesce leading to decrease of magnetization of the film. The second one is related to the strain effects in the film which relaxes with increasing film thickness. The third effect is the expected changes in the intermittent distance between closely situated defects. If the second and third effects are dominant the regions of strongly coupled magnetic moment surrounded by noninteracting medium should appear, leading to the appearance of superparamagnetic-like state before the films exhibit the expected diamagnetic bulk behavior. We have tested the above expectations in Mn doped MgO films deposited on Si substrates by co-sputtering from metallic Mn and Mg targets in (Ar+O₂) atmosphere. Field and temperature dependences of dc-magnetization as well as ac-magnetic susceptibility were studied in temperature range between 2 and 300 K and in dc magnetic field up to 7 T. The appearance of superparamagnetic-like state at the cost of ferromagnetic one was found for the films with thickness exceeding 80 nm. Films thicker than 120 nm show only diamagnetism.
References:
[1] Mukes Kapilashrami et al. APL 96, 232505 (2010)

Metal oxide field effect transistor (FET)-based biosensors have attracted more and more interest because of its advantages encompassing direct transduction, amplified signal and high reliability. Our research group previously described solution-processed oxide thin-film transistor (TFT) devices as alternative deoxyribonucleic acid (DNA) biosensors for the first time [1]. For a further study, we suggest solution-processed In-Ga-Zn-O (IGZO) TFT with multi-stacked active layers (MAL) for a new detection method of DNA. Enhanced sensing ability and stable electrical performance of TFT were attained through the use of MAL structure in consequence of improved film quality. As-fabricated IGZO TFT had a turn-on voltage (Von) of -0.8 V and a sub-threshold swing (S.S) value of 0.48 V/decade. For investigation of sensing ability, artificial double-crossover DNA nanostructures were immobilized on the IGZO surface after a dry-wet method. After attaching, an anomalous hump effect was observed accompanying a significant decrease of Von (-13.6 V) and degradation of S.S (1.29 V/decade). This sensing behavior was ascribed to the middle interfaces of the MAL and the negatively charged phosphate groups on the DNA backbone, which generated a parasitic path in the IGZO active layer. Consequently, these results redeem conventional FET-based DNA sensors favorably with remarkable sensitivity and stability.
[1] S. J. Kim, B. Kim, J. Jung, D. H. Yoon, J. Lee, S. H. Park, and H. J. Kim, Appl. Phys. Lett. 100, 103702 (2012).
Keyword: DNA biosensor, InGaZnO, thin-film transistors, multi-stacked active layer

Viral diseases such as HIV, A(H5N1), A(H1N1), and hepatitis viruses are dangerous diseases. To avoid this infection, one should find suitable vaccines. For this purpose, highly concentrated virus soup is required because only very dilute virus soup is obtained after the cultivation of these viruses. Although a traditional method (for instance, the ultracentrifugation) could be used, it is a very time consuming and batch type process. To solve this disadvantage, we prepared hierarchically self-assembled nanoporous membrane by different anodizing conditions on anodize aluminum oxide membrane. This membrane has larger pores at the bottom side, which facilitates mainly the flux. On the other hand, the upper part has very small size of pores suitable the filtration of the virus from the mother soups.

Doped-SrTiO3 is a wide-band gap semiconductor with remarkable electronic properties ranging from metallic-like electron mobility to superconductivity. It has also emerged as a model platform for the discovery of two-dimensional electron gases (2DEG), and 2D superconductivity at the interfaces between various titanates. For substitutional doping of SrTiO3 elemental niobium is typically used: Nb substitutes for Ti, allowing n-type conductivity. Despite intense research efforts, however, the epitaxial growth of conductive thin-film Nb-doped SrTiO3 still remains challenging. The “nature of dopants”, which is the key for tuning electronic properties of doped-SrTiO3, remains controversial, in particular, in studies of the interface physics of SrTiO3-based Mott insulators.
We showed that under certain growth conditions not only substitutional but also interstitial Nb is present in SrTiO3 film. Analyses of scanning transmission electron microscopy (STEM) images and electron energy loss spectroscopy (EELS) data indicate that the interstitial Nb is strongly coupled with strain in the lattice. Additionally, the x-ray energy dispersive spectroscopy (EDX) results from Nb-doped SrTiO3 film, obtained using high-efficiency EDX available on new generation aberration-corrected S-TEMs, revealed that there are distinct regions in the film where higher concentration of Nb can be observed and these regions exhibit higher intensity in annular dark-field (ADF) signal and lower Ti content. Considerably more Nb atoms than absence of Ti atoms in these regions indicate that Nb atoms often go not only into Ti sites to substitute Ti but also into interstitial sites of the lattice. Analysis of Ti L2,3- and O K-edges indicates that unlike substitutional Nb, interstitial Nb appears to be electronically inactive. Based on quantitative EDX analyses, precise multislice STEM simulations were conducted to elucidate the strain and high resistivity in Nb-doped film. Additionally, we systematically studied the effects of ionization level of Nb dopants on lattice strain in Nb-doped SrTiO3 film.

Vanadium dioxide (VO2) is a strongly correlated oxide exhibiting a first-order metal-insulator transition (MIT) that is accompanied by a structural phase transition from a low-temperature monoclinic phase to a high-temperature rutile phase. For the VO2, the compositional variation can significantly influence the electronic states and phase transition properties, and subsequently affect the charge injection phenomena and the work function. However, comprehensive studies for the deeper understanding on vanadium oxide systems with strong coupling among the phase transition, the compositional variation, and electronic properties are still lacking. Therefore, we investigate a morphotropic phase transformation in the VO2 nanobeams annealed in high-pressure hydrogen gas, which leads to the stabilization of metallic phases. Structural analyses show that the reduced VO2 nanobeams are hexagonal-close-packed structures with roughened surfaces at room temperature unlike as-grown VO2 nanobeams in monoclinic. Quantitative chemical examination reveals that the hydrogen significantly reduces oxygen in the nanobeams depending on the annealing time. Interestingly, the work function and the electrical resistance of the reduced nanobeams follow a similar trend to the compositional variation due mainly to the oxygen-deficiency-related defects. The electronic transport characteristics also show that the reduced nanobeams are metallic state over a large range of temperatures.

We have investigated the effects of inductively coupled plasma (ICP) on the electrical and optical properties of indium tin oxide (ITO) source/drain (S/D) electrode for ZnO-based thin-film transistors. The sheet resistance and the optical transmittance of 50nm-thick ITO thin film were 110 ohm/sq and 75.3% (at 550nm), respectively. However, in case of ITO deposited with optimized RF power of ICP, the sheet resistance of 70ohm/sq and optical transmittance of 76.5% (at 550nm) have been achieved caused by higher plasma density and higher ionization yield. We also fabricated ZnO-based bottom-gate thin-film transistors (TFTs) with using the ITO S/D electrodes deposited with/without ICP. The oxide TFTs having ITO S/D deposited with ICP show higher mobility and smaller subthreshold swing(SS), which might be due to the improved interface quality between ITO S/D and channel as well as the improved electrical property of ITO S/D itself.

A new precursor and process for ALD of thin film, crystalline iron oxides Fe3O4 and α-Fe2O3 will be discussed. The deposition proceeds at 120 °C with growth rates of 0.6 and 0.9 Å/cycle, respectively, and uniform film thicknesses were observed for aspect ratios of ~30:1. This result is remarkable not only for the crystallinity of the films but also for the control over iron oxidation state. The precursor is in the 2+ state and we achieve selective oxidation of ½ the Fe with peroxide, all with O3. Furthermore, virtually no growth is observed with H2O. These results indicate that the well-defined surface chemistry between the precursor and various oxygen source controls the iron oxidation state and crystalline phase. The low temperatures employed in this process method are further relevant to applications beyond traditional high temperature processing. Finally, we highlight the applicability of the α-Fe2O3 films to solar water splitting through the testing of photoelectrochemical devices and the coating of high surface area substrates. Studies of the deposition mechanism and the effect of vapor precursor ligand substitution will be discussed as time allows.

Dihydrogen sulphide (H2S) is a dangerous pollutant released in fossil combustion processes. In this contribution, p-CuO (particle) / n-SnO2 (nanowire) heterostructures were evaluated as selective H2S sensors, and the working principle behind their good performance was qualitatively modelled. It was concluded that the sensing mechanism was dissimilar to standard redox reactions typical of simple metal oxide devices, but ascribable to the sulphurisation of CuO and the consequent variation of the pn-junction band structure at the CuO-SnO2 interfaces. Experimental data showed that these H2S sensors suit well for alarm applications with extremely high selectivity and sensitivity to this gas for concentrations between 1 ppm and 10 ppm.

The Zinc-oxide(ZnO) has been widely used in fabrication of NO2, CO or Oxygen detecting gas sensor. Basically, ZnO is n-type semiconductor which has a wide band gap, about 3.3eV. Nowadays, research on ZnO nano-wire characterization is very actively performed because it is able to realize a micro-sensor array with conventional Silicon processing. However, it isn&’t easy to characterize physical and chemical properties of single or bundle of ZnO nano-wire. To achieve a high-performance of gas-sensor with ZnO, we have to verify a resistance variation that is result from the ionosorption effect in different reacting gas(CO, O2) concentration ambient. In this study, we employed conductive AFM system to measure the resistance of single ZnO nano-wire which had been grown on the Au thin film by a thermal process. By using the AFM probing technique, Au coated conducting cantilever can approach a single ZnO nano-wire in nano scale and get the I-V curves with sweeping applied voltage between Au electrode and cantilever. And during measure the I-V curves, we controlled concentration of reacting gas(CO, O2) in measuring chamber to change the ionosorption rate. Also, we employed Kelvin Force Microscopy(KFM) system to measure the potential change of a single ZnO nano-wire and get the surface potential images as the ratio of gas ionosorption changes with oscillating AC bias between Au electrode and cantilever. From the results of such experiments, we verified reacting gas detecting ability of single ZnO nano-wire which would be necessary for the realization of micro-sensor array.

Practical stress scenarios in large area electronics such as simultaneous thermal and bias stress as are replicated in the reliability and performance tests of low temperature deposited indium-zinc oxide (IZO) thin film transistors (TFTs). Temperature dependence on failure is determined by considering different operation temperatures of 20, 50, and 80 °C. Concentration of acceptor-like and donor-like trap charges increases with time and deteriorates the TFT switching properties by increasing subthreshold swing and increasing leakage currents. Post-fabrication anneals are performed at low temperature of 150 °C for time periods of 12, 24, 36, 48 and 60 hr. The 48 hr annealed TFTs exhibit good switching properties with a I_on/I_off ratio of ~ 10⁸ maintaining high stability under prolonged kinetic stresses (positive bias at high operating temperature). The improved stability with anneal time is correlated with the density of acceptor-like and donor-like trap states by developing a mathematical model which suggests over a 50% reduction in trap density with 12 hr anneal, and to insignificant numbers with consecutive anneal times.

Mixed oxide thin film transistors (TFTs) with indium gallium zinc oxide (IGZO) as the channel layer were deposited at low temperatures and annealed post deposition in reducing ambients vacuum followed by forming gas (5% H₂ in N₂) at 150 °C. Vacuum anneals are found to induce additional defects and vacancies; however, forming gas anneal compensates by reducing defect density and increasing the concentration of hydrogen atoms. The distinctive role of hydrogen as donor in IGZO has been explored as one of the newest studies by examining TFT characteristics. All TFTs are subjected to reliability stress tests under bias and photonic energies. Vacuum annealed samples show larger hysteresis than as-fabricated TFTs, and recover to low hysteresis of 0.2 V post forming gas anneal. Forming gas annealed TFTs also display lower leakage currents and higher I_on/I_off ratio. TFTs demonstrate better subthreshold swing post forming gas anneal than vacuum anneal. The influence of hydrogen as a donor atom has been verified, and mechanisms causing improved stability post forming gas anneal have been investigated. Elastic recoil spectrometry and Hall measurements have been performed to correlate the H concentration with increased carrier concentrations enhanced TFT performance.

This study extensively reports the instability of indium gallium zinc oxide (IGZO) thin film transistors (TFTs) under standalone and combined bias and visible light stresses. Defects and failure causing mechanisms have been identified under all conditions. Oxygen vacancy ionization and defect excitation was attributed to wavelengths of light below 532 nm. Although positive gate stress of 20 V contributes majorly towards charge trapping, a negative voltage bias stress with 410 nm light illumination drives the device into failure due to excessive hole trapping. The design enhancements made to the fabrication of the TFTs such as intermetal dielectric deposition are responsible for higher I_on/I_off ratio under stresses. The post-fabrication of the TFTs in vacuum, forming gas, and oxygen anneal ambient demonstrates varying trends in stability performance under bias and optical stresses, and provides ample information on the vacancies/donor formation (hydrogen/oxygen) states. While vacuum anneal cannot enhance the performance under photonic stresses, oxygen anneal induce maximum stability under extended stress.

Antimony tin oxide (ATO) nanoparticles from Alfa Aesar were redispersed in water using tetramethylammonium hydroxide (TMAH) as a dispersing agent and deposited onto glass substrates by spin coating. Films of one to five layers were made. These thin films were characterized using impedance spectroscopy and ultraviolet-visible spectroscopy to obtain their resistances and optical transmittance, respectively. The films displayed resistances around 108-109 Omega; and optical transmittance in the near infrared to near ultraviolet range above 95%. Resistance measurements on the films were also taken a month after fabrication. These resistances were found to be about an order of magnitude greater than the original resistances measured. This indicates that the ATO
films are unstable in air and may be interacting with oxygen, causing them to become more resistive. Thermogravimetric analysis (TGA) in various atmospheres will be conducted to further investigate the stability of the ATO nanoparticles. TGA results will be used to optimize the film properties by adjusting deposition parameters and determining suitable annealing temperatures.

The modification of TiO2 - anatase surfaces with organic and organometallic molecules are key to the high energy conversion efficiency of dye-sensitized solar cells. The interfacial characteristics are of paramount importance for the charge injection efficiencies. Despite the widespread use of anatase surfaces, however, there has been little work investigating the structural and electronic properties of adsorbed dye molecules at the single molecule level. We report on a combined experimental and theoretical study of the structural and electronic properties of the photosensitizer N3 (cis-bis(isothiocyanato)bis(2,2&’-bipyridyl-4,4&’-dicarboxylato)-ruthenium(II)) adsorbed on TiO2 anatase (101). In situ electrospray ionization deposition combined with scanning tunnelling microscopy and spectroscopy studies in ultra high vacuum at low temperature provide direct access to the dye-substrate interface at the atomic scale. Our experiments probe the local electronic structure revealing mutual interactions between dye molecules as well as interactions with the oxide support with single molecule sensitivity.

The increasing concern over climate change and exhausting fossil fuels have seen great effort being directed towards the development of new energy generation /conversion systems. Innovative materials for energy conversion hold the key for renewable energy production. The ability to design these nanomaterials with tailored structures and functionalised properties is an important challenge that researchers strive to meet. Aimed at developing new nanostructures for efficient photocatalytic and photo-electrochemical solar energy conversion, we have been focusing on the structural design and band-gap modification of several types of semiconducting metal oxides including TiO2 nanocrystals, layered titanate, tantalates and niobate-based pervoskites. The resultant innovative material systems exhibited efficient visible light active photocatalytic performance, which underpin a number of important solar-energy conversion applications including water/air purification, solar fuel production, and low cost solar cells.

Dye sensitized solar cells (DSSCs) have been gathering a lot of interest due to their low cost, high efficiency and facile fabrication routes. The development of a photoanode composed of various types of nanostructures to get a large surface area for higher dye loading is one of the main issues in the DSSC research field. Among nanomaterials for DSSCs, TiO2 still shows highest power conversion efficiency and 1-D crystalline nanostructures such as nanowires revealed promising properties providing direct pathways for electrons to the electrode. In this presentation, we introduce densely-packed hierarchical TiO2 nanoforest. Highly dense and all-directional TiO2 nanobranches were successfully grown on the backbone nanowires. The overall light-conversion efficiency of the densely-branched TiO2 nanoforest DSSCs were almost 4 times higher than the efficiency of DSSCs constructed by the non-branched TiO2 nanowires.

A key factor for the success of new generation PV technologies is the ability to design low-cost, low-temperature, scalable and roll-to-roll compatible fabrication methods. In recent years progressive development of batch type vacuum-free ALD technologies has taken place with novel systems capable of working in the open atmosphere being presented. The key to atmospheric ALD (AALD) is that precursors are separated in space rather than in time (as opposed to conventional ALD, which has a sequence of pulse-purge steps), thus allowing orders of magnitude faster deposition rates and low precursor wastage, while keeping the advantages of conventional ALD. We have developed an AALD system for the deposition of solar cell components and which is compatible with roll-to-roll processing. We will illustrate its potential with several examples, namely, ultrafast deposition of high quality amorphous TiO2 and ZnO blocking layers for inverted bulk heterojunction solar cells; low temperature deposition of high conductivity Cu2O films and it use in back-surface-field (BSF) designs for low-cost inorganic solar cells; deposition of doped TiO2 and ZnO films for application in solar cells; and deposition of In-free transparent conducting oxides.

Lithium-ion batteries store electrical energy in the form of chemical potential, the same as that in primary batteries; however, the charge-discharge process in lithium-ion batteries is more complex as it involves not only Faradaic reactions at the interface between electrodes and electrolyte, but also is accompanied with mass and charge transport and volume change of the electrodes that commonly possess low electrical conductivity. Electrodes away from thermodynamic equilibrium include nanostructures with high surface energy, poor-crystalline materials, and materials with significant surface or bulk defects. Such materials are in higher energy state and, thus, easier for phase transfer and nucleation; such materials also have less closely packed structure, permitting faster mass transport and accommodating more lithium-ions as well as tolerating more volume change. This presentation will take vanadium pentoxide and lithium titanate as two model materials to illustrate the influences of doping, surface defects and carbon coating, and nanostructures on the lithium-ion intercalation properties.

The beneficial effect of addition of Multi-Walled Carbon Nanotubes (MWCNTs) in traditional photoanodes of Dye Sensitized Solar Cells (DSSCs) composed of anatase TiO2 nanoparticles has been systematically investigated. The composite MWCNT / TiO2 have been prepared via a simple and fast route to exploit the beneficial effects of MWCNTs in terms of charge transport and collection, with the aim of enhancing the photo-conversion efficiency in dye sensitized solar cells. The presence of MWCNTs can favour electron collection during solar cell operations, inhibiting the recombination processes which lead to loss of photo generated charges and are the main responsible for reduced photo-conversion efficiency. Low MWCNT concentration does not affect transparency of the photoanode, which is almost equal to bare TiO2 without MWCNTs addition. At concentrations above 0.015% in weight CNTs start affecting the transparency of the layers, which is detrimental in terms of light harvesting in operating devices. The photoanodes have been dye sensitized using the commercial Ru-based N719 molecules. The main effect of MWCNTs on the functional properties of the cells is to increase the short circuit photocurrent and the fill factor, while the effect on the open circuit photovoltage is of minor importance. Overall photo-conversion efficiency from 7.0% in bare TiO2 to 9.0% in optimized photoanodes (0.002% wt. MWCNTs) has been obtained. The Excess in MWCNTs results in dramatic drop of the functional properties of the solar cells. Impedance spectroscopy and transient photovoltage decay clearly indicate enhanced electron lifetime in optimized photoanodes, which is the most direct evidence of the beneficial effect of MWCNTs on the electron transport properties of the photoanodes. Photoanodes with the highest MWCNTs loading present quite bad transport properties, probably due to unwanted excess of dye uptake. These results represent a simple and viable route to improve photo-conversion efficiency in dye sensitized solar cells.

In this work, graphene nanosheets uniformly decorated with ultra-small Fe3O4 nanparticles were synthesized via a facile hydrothermal method for lithium ion batteries anode application. The average size of electrochemically active Fe3O4 particles was well controlled to be less than 5 nm so that extremely short lithium pathways were provided, thus enhancing the rate capability of such composite. Furthermore, graphene nanosheets provided large, conductive supports for Fe3O4 nanoparticles anchoring, thus effectively preventing the aggregation of nanoparticles during charge/discharge process and enhancing the cyclic performance of such composite. The morphology of this composite was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The average size of Fe3O4 nanoparticles was measured under TEM and confirmed by applying Scherrer equation on X-ray diffraction (XRD) data. The electrochemical performance of such obtained Fe3O4-based anode was tested for a total cyclic number of 2120: rate capability test with current densities ranged from 90 to 7200 mA g-1 for 920 cycles, followed by a cycling test at 1800 mA g-1 for 1200 cycles. During the rate capability test, steady reversible capacities were delivered under each current density with last reversible capacities of 1177, 1096, 833, 488, 242, and 146 mAh g-1 at 90, 180, 900, 1800, 3600, 7200 mA g-1, respectively. The subsequent cyclic test demonstrated the superior cyclic stability of such composite and delivered a reversible capacity of 437 mAh g-1 at the 2120th cycle.

Ba doped SrCu2O2 (SCO) thin films were synthesized on glass substrates by the conventional annealing of Sr-Cu-O films composed of SrCO3 and CuO deposited by Metal-organic Chemical Vapor Deposition (MOCVD) technique. The optimal annealing conditions for the stabilization of the SCO phase at room temperature are mainly based on a rapid cooling of the sample. The K and Ca doped SCO have been reported so far, however, a promising improvement in the electro-optical properties has not been achieved. As they appear to reduce the bandgap and increase the electrical conductivity a little bit. Ba doping was found important in a sense that it simultaneously improves the electrical conductivity and optical transparency which is very essential for transparent conductive applications. Optical characterization of these Ba-SCO films shows an average transparency of 75% in the visible range at 550 nm, a bandgap of 3.26 eV and their average electrical conductivity was measured to be 4.3x10-2 S cm-1.

Metal oxide nanostructures with hetero-contacts and phase boundaries offer unique platform for designing materials architectures for sensing applications. Besides the size and surface effects, the modulation of electronic behaviour due to junction properties leads to modified surface states that promote selective detection of analytes. The growing possibilities of engineering nanostructures in various compositions (pure, doped, composites, heterostructures) and forms (particles, tubes, wires, films) has intensified the research on the integration of different functional material units in a single architecture to obtain new sensing materials. In addition, new concepts of enhancing charge transduction by surface functionalization and use of pre-concentrator systems are promising strategies to promote specific chemical interactions, however the challenge related to reproducible synthesis and device integration of nanomaterials persist.
This talk will present how chemically grown metal oxide nanostructures can be transformed into advanced material technologies for energy and sensoric applications.

We report the creation of two-dimensional electron gas (2DEG) and three dimensional electron slabs (3DES) by tailoring the polarization effect in polar ZnMgO/ZnO heterostructure. The observation of Shubnikov-de Haas oscillations and quantum Hall effect provide clear evidence of quantization of high mobility carriers in 2DEG. Our analysis shows that 2DEG exhibits a large zero-field spin-splitting energy. We also demonstrate that the carriers can be distributed in a 3DES which constitutes a compositionally graded heterostructure while still maintaining the characteristic of high mobility. The characteristics of 3-D spreading electrons are evidenced by the capacitance-voltage profiling and the quantization of 3D Fermi surface in magneto-transport measurements.

Although well known due to its capability to exist in many different shapes,1 ZnO is living a new era, thanks to the possibility to apply it as a functional material in several diverse applications.
Herein, we report hierarchically self-assembled structured ZnO films to be applied as functional material in two critical applications, namely dye sensitized solar cells (DSCs) and gas sensors (GSs). In particular, application of engineered ZnO photoanodes in DSCs is exploited for the enhancement of photoconversion efficiency, based on three main concepts: (i) high optical density of the sensitized layer, allowing complete light absorption in the spectral range of the dye; (ii) high light scattering of the absorbing layer, enhancing the residence time of light inside the sensitized film and improve light absorption; (iii) inhibition of back reaction, which causes electron recombination between the conducting layer at the anode and the electrolyte. The films are prepared by the simple, cheap and large area scalable spray pyrolysis method and are composed of polydispersed ZnO aggregates consisting of nanosized crystallites. The aggregates are submicrometer-sized thus acting as efficient light scattering centers, while the nanoparticles deliver the mesoporous structure and the high specific surface area needed for high dye loading. A ZnO compact buffer layer is formed between the conducting substrate and the layer composed of polydispersed aggregates, which efficiently acts as a blocking layer for the back reaction. Optimized structure led to high light absorption, efficient electron transport and collection, inhibition of back reaction electron recombination, and resulted in unprecedented overall photoconversion efficiency up to 7.5%.2
On the other hand, a simple and fast wet chemistry technique delivers hierarchical microstructures composed of interconnected nanosheets, able to significantly improve ZnO performances as gas sensors even at relatively low temperatures, thanks to a self-assembled microstructure.
The chance to obtain complex self-assembled structures, ranging from micro- to nano-sizes, by applying cheap and fast approaches, thus avoiding the use of both high-vacuum and inert atmosphere techniques, could reliably pave the way toward scale-up and industrial exploitation of ZnO-based devices.
1. C. Woll, Progress in Surf. Sci., 2007, 82, 55
2. N. Memarian, I. Concina, A. Braga, S.M. Rozati, A. Vomiero, G. Sberveglieri, Angew. Chem. Int. Ed., 2011, 50, 12321

Chemorestistive gas sensors are usually based on modified metal oxides (SnO₂, TiO₂, WO₃,hellip;) with highly dispersed transition metals (Fe, Cr, V,hellip;) or noble metals (Pt, Pd,hellip;) to enhance the sensor response. The sensing mechanism can follow different pathways, depending on the interaction of the target gas with the oxide surface. In fact, chemoresistive gas sensors is an application of heterogeneous catalysis field, where the reaction to the target gas is followed by a change of the resistance of the catalyst. For instance, in the case of the ethanol sensing, if the role of the sensing layer is just to provide chemisorption sites to the target gas to react without electron transfer (dehydration reaction) the sensor response is much lower than if the metal oxide plays a much active role promoting reactions involving charge transfer (dehydrogenation or oxidation). The aim of this work is to extend the knowledge from the heterogeneous catalysis field to metal-oxide based gas sensors. A well known catalyst system is titania-supported vanadium pentoxide, which is known to promote various oxidative reactions. The kind and distribution of vanadium-related species is still not completely understood, nevertheless the hypothesized species all point to a surface modification of the titania support. Hence, our question was whether it was possible to conceive a modification of titania support with vanadium oxide species in the processing of gas-sensing devices. The leading idea was the preparation of active surface species based on vanadium oxides that could favor the electronic exchange between the gaseous analyte and the titania support. The potential of nanocrystalline oxides in enhancing the sensing performance of metal oxide-based chemical sensors is well accepted, hence we focused our attention on nanocrystalline titania. In this paper we describe the successful deposition of vanadium oxide species onto the surface of titania nanocrystals by sol-gel processes, and the investigation of the related gas-sensing properties. Amorphous TiO₂ nanoparticles were prepared by sol-gel processing in dodecylamine of solutions prepared from TiCl₄. The amorphous nanoparticles were crystallized in the TiO₂ anatase phase by solvothermal treatment at 250 °C in oleic acid, as confirmed by X-ray diffraction. A V-containing solution, prepared from methanolysis of VCl₄, was added to the TiO₂ suspension before the crystallization step. The resulting materials were characterized by X-ray diffraction, Transmission electron microscopy, Fourier transform infrared, NMR and Raman spectroscopy. It was shown that V was deposited onto the resulting TiO₂ nanocrystals, without forming discrete V oxide species. The surface modified TiO₂ nanocrystals were used to prepare promising chemoresistive gas-sensors to ethanol, which could be latter extended to other target gases.

Metal oxide nanowires are interesting materials for many advanced applications such as chemoresistive and optical gas sensors, excitonic solar cells, thermoelectrics, field emitters. Their high surface to volume ratio brings out their surface-related properties such as the ones governing chemical sensing transduction principles or charge separation and injection in dye sensitized solar cells. Their single crystalline assembly reflects in stable functional properties over long term operation as required for industrial exploitation of these nanomaterials in real environments. In excitonic solar cells, the enhanced electron mobility due to the single crystalline assembly can significantly reduce the recombination processes affecting charge collection and photoconversion efficiency. Concerning thermoelectric applications excellent durability of metal oxides at high temperatures in air should be advantageous for high-temperature applications. Beside it has recently been shown that nanowires achieve extremely large enhancements in thermoelectric efficiency due to a reduction in thermal conductivity produced by increased phonon-boundary scattering.
Metal oxides in form of nanobelts, nanowires and nanorods have been first prepared via vapor phase methodologies [Science, 2001 291,1947]. We have thoroughly studied the growth of single crystal structures using evaporation and condensation from powder in controlled environment and different experimental set up. Metal oxide nanowires were integrated as chemical sensors in functional devices and then tested towards a wide range of chemicals, including odorous molecules such as ammonia, hydrogen sulfide. To further gain selectivity, innovative gas-sensor architectures, based on surface ionization mechanism and magnetic field activation, have been investigated and will be presented. Furthermore one dimensional oxidic structures were applied in new photoanodes for excitonic solar cells. Optimized structures are based on a compromise between the electronic transport (guaranteed by single crystalline nanowires) and the optical density of the photoanode, guaranteed by the presence of nanoparticles. Finally, combining n-ZnO and p-CuO nanowire based elements, a planar thermoelectric device has been proposed, fabricated and experimentally characterized, confirming feasibility of fabricating planar thermoelectric devices based on metal-oxide nanowires.

Tin oxide (SnO2) represents a major fraction of research for developing solid state gas sensors. Nevertheless, a detailed insight into the chemical-to-electrical transduction mechanisms between ammonia (NH3) molecules and this metal oxide is still limited. In this contribution, the adsorption of NH3 onto SnO2 was examined by Density Functional Theory (DFT) calculations and confronted to experimental data obtained with individual nanowire devices. It was concluded that under real working conditions non-lattice oxygen (O5c) adsorbed on SnO2 exhibit a more basic character than lattice bridging oxygens (O2c) and consequently, they play a key role in the dehydrogenation of NH3 onto SnO2, with N2 and H2O as the main resulting products. The sensing process of ammonia onto tin oxide nanowires involves not only physical mechanisms but has a concomitant chemical nature that requires two molecules of NH3 for the reaction to take place. Our theoretical modelling reveals why ammonia sensing is competitive to the adsorption of water molecules. As a result, interfering effects in monitoring traces of NH3 intrinsically occur in humid conditions.

Nanostructures such as nanowires, nanorods, and nanoparticles are attractive for fabrication of gas, humidity, and light sensors, since they offer higher surface-to-volume ratios, and subsequently, higher sensitivity. Metal oxide nanostructures, including zinc oxide (ZnO), are well-known for their sensing properties, due to the presence of surficial oxygen vacancies. ZnO nanostructures are attractive for sensor applications not only due to their morphological diversity (e.g., nanowires, nanorods, and nanoparticles), but also the variety of synthesis methods (e.g., such as chemical vapour deposition (CVD), laser ablation, hydrothermal, and sol-gel process) and the low cost of precursor materials. One of the main obstacles in materialization of commercial devices based on nanostructures is the complexity and cost of fabrication methods used for development of functional and accurate devices. Almost all the techniques used involve sophisticated and expensive patterning using electron beam lithography or have fairly low yield and the resulting devices lack a stable and repeatable performance.
This work presents our results for sketching low-cost, yet accurate sensing devices on paper using ZnO nanostructure inks. The electrodes of the sensor are drawn by hand, using different drawing materials, including custom-made pencils made from graphite nanoparticles as well as silver paint. ZnO nanostructures, synthesized with different morphologies by sol-gel and hydrothermal methods, are utilized as the sensing material. The feature sizes and crystal quality of the nanostructures are examined by transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. The morphology and microstructural properties of sketched ZnO film on paper&’s cellulose fibres are characterized using scanning electron microscope (SEM) and atomic force microscope (AFM). Sensors were fabricated on various types of paper to study the effect of paper properties on the performance of the devices.
The static and dynamic response of the sensors to the intensity and wavelengths of the UV light as well as hydrostatic pressure and pulses of different gasses such as oxygen and carbon monoxide are systematically investigated. The sensors sketched on paper demonstrate excellent performance, manifesting fast, accurate and high sensitivity, and repeatable response to changes in the environment.

Chemical sensors made of tailored ceramic nanoparticles (e.g. wide-band semiconductors) offer excellent miniaturization potential and are able to reproducibly detect trace amounts of important analytes down to ppb concentration [1, 2]. Application of these sensing materials to emerging fields such as non-invasive medical diagnostic by breath analysis has the potential to drastically reduce diagnostic costs while offering better service quality to the patients [3]. State-of-the-art nanoparticle-based chemical sensors still suffer from poor reproducibility from batch to batch preparation, long-term instability of the baseline [4] and limited selectivity against disturbing analytes that may be present in complex gas mixtures such as the breath. This drastically limits their application to more qualitative assessment of an analyte presence within simple gas mixtures. Here, we will present fundamental phenomena controlling the long-term stability of nanoparticle-based chemical sensors and propose new materials and approaches to improve their reliable utilization in breath analysis [5]. In particular, the feasibility of stabilizing the grain size by co-synthesis of a second metal-oxide [5, 6] will be critically discussed focusing on the dynamic shift of their electrical properties during operation at moderate temperatures [7].
[1] A. Tricoli, M. Righettoni, A. Teleki, Angew. Chem. Inter. Ed. 2010, 49, 7632.
[2] A. Gurlo, R. Riedel, Angew Chem Int Edit 2007, 46, 3826.
[3] M. Righettoni, A. Tricoli, J. Breath Res. 2011, 5, 10.1088/1752.
[4] G. Korotcenkov, Sens. Actuator B-Chem. 2005, 107, 209.
[5] M. Righettoni, A. Tricoli, S. E. Pratsinis, Anal. Chem. 2010, 82, 3581.
[6] A. Tricoli, M. Graf, S. E. Pratsinis, Adv. Funct. Mat. 2008, 18, 1969.
[7] A. Tricoli, Biosensors 2012, 2, 221.

The recently developed piezoelectric nanogenerators (NGs) could convert mechanical energy into electricity and have played a key role in self-powered systems. In this regard, the integration of transparency and flexibility characteristics is of dramatic importance in the development of NG, especially for its potential applications in optoelectronics, flexible circuits, artificial skins, and flexible touch screens. Several works on this aspect has been reported by using flexible polymeric substrate and transparent electrode materials like ITO, graphene, and carbon nanotube. However, few works regarding to the high output of the NG (especially high output voltage) were reported; from another point of view, the robustness of the transparent flexible NG as well as its niche applications were rarely considered.
In this work, we fabricated transparent flexible nanogenerators (NGs) by employing flexible polydimethylsiloxane (PDMS) substrate for the growth of ZnO nanowires. The fully packaged NG showed good transparency with a transmittance of 50% to 60% in the visible range. The output voltage and current was 8 V and 0.6 mu;A, respectively, corresponding to an output power density of ~5.3 mW/cm3. The NG also showed excellent robustness and could stably scavenge energy from the motion of a vehicle. Based on this characteristic, we demonstrated its application as a self-powered sensor for monitoring vehicle speed and detecting vehicle weight.

Transition-metal oxide surfaces play an important role in a wide range of applications such as heterogeneous catalysis, photocatalysis and photo-electrolysis. In this talk recent studies on a prototypical model oxide system - the rutile TiO2(110) surface will be presented.
We will address clear-cut identification of surface defects such as oxygen vacancies, hydroxyl groups, and near surface defect such as interstitials. We find that water molecules dissociate both in O-vacancies at subsurface interstitial sites. We show that at temperatures between ~150 K and ~210 K water monomers diffusing along the Ti troughs form stable dimers that diffuse faster than the water monomers. An H-bond-mediated roll-over mechanism operating for the water dimers explains the faster diffusion of the water dimer compared to the diffusion of water monomers.
Finally, we will demonstrate that these results can improve our understanding of the use of TiO2 as photocatalysts. By means of high resolution scanning tunneling microscopy (STM) and temperature programmed desorption/reaction (TPD/TPR) spectroscopy, we have studied the desorption and thermal decomposition of ethanol and ethoxide groups on differently prepared TiO2(110) surfaces (r-, h-, and o-TiO2(110)). The combination of spectroscopic techniques and STM is very informative for clear-cut assignment of site specific reactions. In addition the photoreaction of ethanol on differently prepared TiO2(110) surfaces was studied.

Replacement of precious metal catalysts by commercially available alternatives is of great importance among both fundamental and practical catalysis research. Nanostructured metal-free or covalent metal-free/non-precious metal hybrids demonstrated promising catalytic properties in a wide range of energy generation/storage applications. Specifically engineering graphene with guest atoms can improve its catalytic activity for electrochemical oxygen reduction reaction (ORR) and thus can be considered as a potential substitute for the expensive Pt/C catalyst in fuel cells or metal-air batteries. On such perspective, we have reported a boron and nitrogen dual-doped graphene (B,N-graphene) with a synergistic effect between heteroatoms to further boosts its electrocatalytic activity. Via a newly developed two-step doping method, B,N-graphene had a unique B-C-N bonding configuration with a strong chemical interaction between B and N dopants. Consequently, the oxygen reduction catalytic activity and efficiency of B,N-graphene are comparable with those obtained on the commercial Pt/C catalyst, and significantly higher than those for the solely doped graphene with B or N, and h-BN/graphene hybrid. The new catalyst also shows a complete methanol tolerance and excellent long-term stability, which are much better than those of the commercial Pt/C.
Additionally, direct nucleation, growth, or attachment of nanoparticles/nanocrystals on the surface of these modified graphene sheets can produce various metal-free/non-precious metal hybrids with internal bonding and synergistic coupling effects to further enhance their specific catalytic activities. We used single boron-doped graphene (B-graphene) and nitrogen-doped graphene (N-graphene) substrate respectively to synthesize Ni(OH)2 or Co3O4 nanoparticles as an example to assess the aforementioned synergistic catalysis phenomenon. Due to the reversed electronegativity to C (chi;=2.55), B (chi;=2.04) and N (chi;=3.04), the doped graphene has totally different surface functional groups and electron-donor/acceptor defects, which can significantly influence the morphologies, chemical components, and properties of above non-precious metal catalysts. Consequently, the metal-free/non-precious metal hybrids lead to significantly higher electrocatalytic activity than those of either non-precious metals or graphene alone due to the existence of strong chemical coupling interaction between graphene and non-precious metal nanoparticles. Using these modified graphene with designed electronic structures, the applications of synthesized hybrids can be extended to wide energy-related reactions like hydrogen/oxygen evolution reactions (HER/OER). This study may pave the way toward feasible molecular design and synthesis strategy for the development of a wide variety of advanced cost-effective catalysts for broad commercialization of energy conversion/storage technologies beyond metal-air batteries and hydrogen productions.

Research in the field of metal oxide and mixed metal oxide systems is highly significant in many areas of scientific study and applied technology. In heterogeneous catalysis mixing metal oxides is often found to have a synergistic effect on catalytic activity, selectivity and stability. State of the art microscopy indicates that the formation of a defective nano-structured mixed metal oxide phase, as opposed to a mixture of single oxides, provides the high activity.
Traditionally mixed metal oxide catalysts are prepared by co-precipitation, where metal salts are precipitated from a solution by altering its pH. However, co-precipitation has several fundamental short comings. Use of nitrate metal salts coupled with large volumes of water required to remove alkali impurities from catalysts (introduced in the precipitation step) have a detrimental impact on the environment. The presence of diffusion gradients in the precipitation process results in poor mixing of metals which requires a complex ageing processes to resolve, the mechanism by which is poorly understood. The required calcination temperatures to produce mixed metal oxide phases if often high, resulting in sintering, loss of surface area and nano-structural properties. Mixed metal oxides will form at lower calcination temperatures, unfortunately single oxide phases are also observed.
The use of supercritical carbon dioxide is a promising implementation of green chemistry due to its benign nature and plentiful supply. The preparation of catalyst materials using supercritical anti-solvent (SAS) technology allows for the utilisation of supercritical fluid properties, namely high diffusion rates and zero surface tension between the carbon dioxide anti-solvent and a mixed metal salt solution. SAS produces sub 100 nm particles of exceptional mixed amorphous metal salts. These salts require significantly lower calcination temperatures than co-precipitated materials, and provide a single phase crystalline mixed metal oxide with no single metal oxides observed. The amorphous nature of the precursor imbues defects in the final mixed metal oxide, which is reflected in their exceptionally high catalytic activity.
Example systems investigated include Cu-Mn oxides for use as oxidation catalysts and also Co-Zn-Ti oxide material for Fischer-Tropsch chemistry. Phases have also been produced that are reported to have desirable properties for magnetic applications

Water gas shift reaction (CO+H2Oharr;CO2+H2) is an industrially important reaction, present not only in the methane steam reforming process, but also in the fuel cell technology (power plants and transportation sector). Functional fuel cells are unambiguously related to "mature" WGS catalytic materials. In the present work, Pt nanoparticles (1.0-2.0 nm size) supported on Ce1-xTixO2-δ and Ce1-xLaxO2-δ (x=0, 0.20, 0.50, 0.80, 1) oxide carriers, which were prepared using sol-gel method, were thoroughly investigated in terms of microstructure, morphology, surface chemistry and assessment of catalytic performance towards the WGS reaction in the 200- 400oC range. In the case of Ce1-xLaxO2-δ oxides, the nanocomposite systems of Ce1-xLaxO2-δ/CNT (carbon nanotube) were prepared and critically compared for the reaction at hand. A deep insight into the effect of (a) Ce/M (M: La, Ti) ratio of the oxide support and (b) the oxide coupling with the carbon nanostructure (when applicable), on the catalytic performance of Pt-loaded catalysts was realized after employing N2-physisorption, in situ X-ray diffraction (XRD), High resolution transmission electron microscopy (HR-TEM) and HAADF/STEM, Scanning electron microscopy (SEM), in situ Raman spectroscopy and Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) under different gas atmospheres, H2 temperature-programmed reduction (H2-TPR), and temperature-programmed desorption (NH3- TPD and CO2-TPD) techniques.
Critical reaction parameters such as temperature, feed composition and GHSV (h-1), along with the chemical composition of the oxide (Ce/M atom ratio) and the Pt loading were investigated. The catalytic oxides with Ce0.8M0.2O2-δ composition decorated with 0.5 wt% Pt was found to be profoundly better than the rest of oxides compositions investigated towards WGS reaction. In particular, at 250oC the CO conversion (CO=0.03 bar, H2O=0.1 bar; GHSV=40,000 h-1) over 0.5 wt% Pt/Ce0.8Ti0.2O2-δ was increased by a factor of 2.5 and 2.0 compared to 0.5 wt% Pt/TiO2 and 0.5 wt% Pt/CeO2, respectively. In the case of Ce0.8La0.2O2-δ mixed metal oxide (solid solution), an enhanced WGS activity (by a factor of 1.3-2.0 at 300oC) was exhibited by Pt-loaded materials compared to CeO2 and La2O3 single oxides. Hybridization of Ce0.8La0.2O2-δ with carbon nanostructure led to an 20% increase of the catalytic activity. This can be partially correlated to the Pt-oxide interface altering as unraveled by the band gap change of the material.
The catalytic superiority of Pt/Ce0.8M0.2O2/(CNT) oxides/composite oxides is discussed based on a unique combination of their properties, such as robust morphology, which is preserved after reaction, moderate values for surface acidity, surface basicity and reducibility, significant “coke” resistance and hydrothermal stability. These properties influence the site reactivity of Pt across the metal-(oxide) support interface according to the analysis of kinetic rate results obtained.

The combination of different nanobuilding blocks in a single heterostructure can lead to materials with improved properties by selecting components with the desired characteristics for a specific application. Carbon-based heterostructures containing metal oxides, metals or both are particularly promising for energy and environmental applications. In this work, we describe a novel microwave-assisted synthesis, characterization and application of metal oxides supported on various carbon-based substrates (e.g. reduced graphene oxide CNTs and carbon black).
The synthesis is based on non-aqueous sol-gel chemistry, which showed to be an elegant approach for the fabrication of metal oxide nanocrystals [1] and ordered organic-inorganic hybrid materials [2]. These routes involving the reaction of metal oxide precursors in organic solvents (e.g. benzyl alcohol) at moderate temperature and pressure, offer advantages such as high purity, high reproducibility and the ability to control the crystal growth without the need of using additional ligands. In this contribution, the suitability of such an approach will been highlighted for the fabrication in only one-step of composite materials involving metal oxides and nanostructured carbon substrates [3-4].
The properties of these nanocomposites in view of applications in energy storage, catalysis and sensing will also be discussed.
References:
[1] N. Pinna, M. Niederberger, Angew. Chem. Int. Ed., 2008, 47, 5292
[2] N. Pinna, J. Mater. Chem., 2007, 7, 2769
[3] S. Baek, S.-H. Yu, S.-K. Park, A. Pucci, C. Marichy, D.-C. Lee, Y.-E. Sung, Y. Piao, N. Pinna, RSC Adv. 2011, 1, 1687
[4] P. A. Russo, N. Donato, S. G. Leonardi, S. Baek, D. E. Conte, G. Neri, N. Pinna
Angew. Chem. Int. Ed. 2012, DOI: 10.1002/anie.201204373

Titanium rutile nanorods synthesized by hydrothermal method showed the best performance of the non assisted photoanodes for hydrogen production and also promising results in DSSC&’s. It also has proved to be one of the most promising candidates for taking the leap from the lab to the prototype because of its high reproducibility, low cost production and scaling up availability. However, before this step, it is needed to going further and focusing into the optimization of the electrical, optical and photocatalytic properties of titania rutile nanorods. To date, all works done about titania rutile nanorods have been focused on the applications already known and on demonstrating its better performance compared to the ones previously published. However, there is a lack of knowledge and thoroughness in many ways of the whole process of synthesis and post-treatment of the samples. This knowledge is crucial for understanding the post-treatment needed to improve the samples performance and the first step to bring these devices to the level of sophistication achieved, for example, in PV devices.
In this work, we show an in depth study on the electrical and photocatalytic properties of titania rutile nanorods grown by hydrothermal process for its optimization on PEC applications, such as solar water splitting. We employed EIS as a diagnostic tool and a theoretical model is presented in terms of fundamental electronic processes occurring in the photoelectrochemical device. Based upon the results obtained on XPS and EIS measurements, we demonstrated that the presence of residual chlorine based products from the synthesis affects negatively in both, conduction and charge transfer from the electrolyte to the photoanode. We demonstrated that these chlorine residual products can be completely removed by an appropriate annealing process.

Due to their unique properties, nanostructured materials have shown great promise for use in thermoelectric energy conversion devices. Specifically, if the nanowire diameter is between the respective mean free paths of electrons and phonons, decreased thermal energy propagation without diminished electrical transport can be achieved. While this type of structurally-determined decoupling of transport properties has been shown to increase thermoelectric performance, even greater enhancements can be achieved if the electrically properties can also be affected beneficially via nanostructuring, as oppose to not being affected at all. Theoretically, a strongly confined 1-D system can demonstrate this simultaneous enhancement, but nanowires with such small diameters (< exciton bohr radius) are practical for neither property measurement nor device implementation. Conversely, nano-sized features within the nanowire can positively affect electric transport while still limiting thermal propagation via large phonon surface scattering provided intrinsically by the nanowire morphology. This approach may provide a more robust avenue towards enhancement of all thermoelectric properties.
This study explores the creation and subsequent effects of nanostructured inclusions on both thermal and electrical transport in ZnO. We employ a simple diffusion scheme to create controllable polytypoid M2O3(ZnO)n (M = In, Ga) nanowires, wherein single atomic inclusion layers of In form in the ZnO nanowire. The inclusion spacing is controlled by varying the amount of metal precursor and annealing conditions to achieve average distances of 2 - 40 nm. Thermal and electrical measurements on single In2-xGaxO3(ZnO)n nanowires reveal modified transport properties, where the Seebeck coefficient, electrical conductivity, and carrier mobility all increased while thermal conductivity simultaneously decreased. Using aberration-corrected transmission electron microscopy and spatially resolved electron dispersive X-ray spectroscopy, we were able to fully analyze the M2O3(ZnO)n structure, as well as the ZnO-M2O3 interface. Insight into the structural features provides mechanistic understanding of the affects nanostructuring has on both electric and phononic transport. The relations obtained here can help design principles for future nanostructured materials applicable in next generation thermoelectric devices.

High temperature stable ordered mesoporous metal oxides were prepared from a silica hard template. The stabilization of the compounds is based on achieving the self-limited grain growth regime within the hard template. The self-supported replicas maintain the periodic mesoporous structure and a high surface area only showing a slight reduction of the long-range order of the pore channels.
The stability of the nanostructure at temperatures as high as 1100C is shown in terms of a self-limited grain growth dominant regime. The proposed route has low dependency on the material to prepare allowing its use for synthesizing a wide variety of mesostructures based on metal oxides.
Mesoporous nickel based cermets were synthesized and characterized by using this approach. Finally, fuel cell tests were carried out using an electrolyte-supported SOFC and a mesoporous layer working as anode. A maximum value of power density of 346 mW/cm2 was achieved at 700C in 5%H2. Moreover, virtually no degradation of the microstructure and the electrochemical performance was demonstrated for the cermet after more than 200h of test at 800C in a water satured 5%H2 in argon atmosphere.
This methodology could represent a step forward towards the implementation of mesostructures in applications where high thermal stability is required such as solid oxide fuel/electrolysis cells, gas separation membranes or high temperature catalysis.

New catalyst materials with higher activity and durability are critical to achieving widespread commercialization of PEM fuel cells. The incorporation of metal oxide materials as durable supports into cathode catalysts offers a promising route to address these challenges. In this work, we develop novel support materials based on tungsten oxide nanoparticles tailored to increase the performance of the oxidation reduction reaction (ORR) by enhancing the Pt stability and activity and reducing corrosion. We will describe the synthetic methods and the functional characteristics of incorporating tungsten oxides into cathode catalysts.
We have previously demonstrated the controlled growth of 5-100 nm crystalline WO₃ nanoparticles by hot-wire chemical vapor deposition (1). Synthetic methods to control the metal oxide crystal structure, particle size and the oxidation state to highly substoichiometric WOx will be discussed. Atomic layer deposition (ALD) utilizing an organometallic precursor and O₂ as a reducing agent is employed to deposit Pt particles on the WO₃ substrate. Pt deposited using ALD on the WO_x support was characterized for electrochemical area and oxygen reduction activity using rotating disk electrodes (RDEs). The mass activity of ~50wt% Pt/WO_x was found to be higher than that of the lower Pt wt% catalysts; the addition of a graphitized carbon to the Pt/WO_x increased the mass activity to ~65% of the activity of baseline Pt/C (2,3,4).
The conductivity of the metal oxide support is critical to the performance of the catalyst. The correlation of the crystal structure and conductivity of the metal oxide has also been investigated. Various approaches to increasing the conductivity of the Pt/WO_x material will be discussed.
(1) S.-H. Lee, R. Desphande, P.A. Parilla, K.M. Jones, B. To, A.H. Mahan, A.C. Dillon. Adv. Mater. 2006, 18, 763.
(2) H. A. Gasteiger, S. S. Kocha, B. Sompalli and F. T. Wagner, Appl. Catal. B-Environmental, 56, 9 (2005).
(3) I. Takahashi and S. S. Kocha, J. Power Sources, 195, 6312 (2010).
(4) Y. Garsany, O. A. Baturina, K. E. Swider-Lyons and S. S. Kocha, Anal. Chem., 82, 6321 (2012).

Multiphoton excited luminescent nanomaterials such as semiconductor quantum dots (QDs) or gold nanorods (GNRs) are emerging as useful tools in diagnostic medicine and therapeutics. These nanomaterials are excited with near-infrared (NIR) light mitigating some of the drawbacks associated with the use of UV light as the excitation source. NIR light is silent to tissues thus minimizing autofluorescence, possesses greater tissue penetration capabilities and does not incur damage to the sample. However, these nanomaterials require femtosecond (fs) excitation light to induce the multiphoton excited luminescence.
It is in this regard that there has been an ever-increasing interest in lanthanide (Ln³⁺)-doped upconverting nanoparticles (UCNPs) as an alternative to more common multiphoton excited nanomaterials. With UCNPs, it is possible to obtain UV/visible/NIR emissions using a single NIR excitation source (typically 980 nm) via a process known as upconversion. Upconversion is a multiphoton excitation process, however, unlike conventional multiphoton excited materials where the absorption is simultaneous, the multitude of long-lived “real” electronic energy states of the Ln³⁺ ions (from the partially filled 4f shell) allow for sequential absorption of multiple NIR photons eliminating the need for complex and expensive optical excitation.
Here, we present the synthesis of upconverting Ln³⁺-doped UCNPs and demonstrate how they can be used in biological applications. However, before these biological studies can be performed, the surface of the UCNPs must be modified, first to impart water dispersibility and second to attach chemically and/or biologically relevant molecules. Furthermore, we will show how these UCNPs can be used as building blocks towards developing a multi-modal nanoplatform for the biological imaging and nanothermometry of malignant cancer cells.

Nanostructured titanium dioxide (TiO₂) materials combine the special electrical, optical and chemical sensitivity properties of bulk titania with a high surface-to-volume ratio, therefore opening the possibility to design electrochromic, photochemical and photoconductive devices with an enhanced coupling to the environment. In this context the coupling between TiO₂ and selected dopants has been the key to the development of hybrid TiO₂-based active materials leading to devices such as optimized photovoltaic solar cells [1] or photochromic paper [2]. Both are based in a nanostructured TiO₂ matrix doped either with a dye or Ag nanoparticles, respectively. In addition, TiO₂ is an excellent host for trivalent rare-earth ions that show intense light emission both in the infrared and the visible adequate for the development of light emitting devices [3].
In a previous work we have studied the preparation and linear optical response of Er-doped TiO₂ films by electrophoretic depositon using the low cost and large scale colloidal sol-gel technique [4]. In the present work, we study the conditions to obtain efficient infrared light-emission for Er-doped TiO₂ nanoparticulate materials prepared by colloidal sol-gel. Sols with Er concentrations ranging from 0.5 to 6 mol% were prepared. The average nanoparticle sizes lies in the range from 5 nm to 8 nm. Structural characterization techniques and optical spectroscopy techniques have been used to monitor their properties upon annealing treatments up to 900 ^oC. It is observed that the anatase to rutile phase transition temperature increases as a function of the Er content. All the samples annealed above 300 ^oC show the characteristic and well defined Er photoluminescence spectra with a maximum intensity around 1.5 microns. It has been found that the samples with concentrations below 1 mol% show the highest emission efficiency (photoluminescence intensity and lifetime) and have promising properties for the development of integrated gain devices in the infrared. For higher concentrations Er-Er energy transfer processes take place, leading most likely to up-conversion processes that have potential applications for solid-state lighting devices in the visible. The influence of the Er ions concentration and of the anatase-rutile phase on the photoluminescence response will be discussed.
[1] I. Chung, B. Lee, J. He, R. P. H. Chang and M. G. Kanatzidis, Nature 485, 486 (2012).
[2] Y. Ohko, T. Tatsuma, T. Fujii, K. Naoi, C. Niwa, Y. Kubota and A. Fujishima, Nat Mater 2, 29 (2003).
[3] W. Luo, C. Fu, R. Li, Y. Liu, H. Zhu and X. Chen, Small 7, 3046 (2011).
[4] M. Borlaf, M. T. Colomer, F. Cabello, R. Serna and R. Moreno, J. Phys. Chem. B (2012) DOI: 10.1021/jp304044w.

Highly bright and efficient inverted quantum dot (QD) light emitting diodes with low turn-on voltage were fabricated by using double electron transport layers (ETL) of metal oxides. By investigating the device characteristics for various ETLs such as zinc oxide (ZnO)nanoparticles, tin oxide (SnO2) nanoparticles, and ZnO/SnO2 double layers, we found that the device with the ZnO/SnO2 ETL exhibits significantly enhanced device performance (i.e., low turn-on voltage down to the bandgap of QDs, high external quantum efficiency (E.Q.E) of about 7%) compared to the devices with ZnO or SnO2 single layer. The improved performance can be attributed to better electron injection into the QD emissive layer. The double layer of ZnO nanoparticles and SnO2 nanoparticles enhances electron injection into the QD layer owing to the improved energy-level matching. Based on these results, we can fabricate red, green, blue and white quantum dot light-emitting diodes with low turn-on voltage and high efficiency.

Current trend towards the development of smart materials with enhanced switching properties may be a relevant approach for realizing higher functional densities per unit area and per unit mass for the next generation of switching and/or tunable devices. In this context, transition metal oxides present potential electrical and optical properties making them very promising for many applications in electronic and optical devices. Among these materials, vanadium dioxide (VO2) is particularly interesting because of its sharp reversible Metal-to-Insulator Transition (MIT) that occurs near room temperature (TMIT asymp; 68 °C) on ultrafast timescales (<10-12 s). This MIT is associated with a structural transition from a high-temperature tetragonal phase to a low-temperature monoclinic phase, and is characterized by significant changes of electrical and optical properties in response to external stimuli such as temperature, electric field and/or optical control signal. The production of high-quality VO2 films remains a challenging task, due to the existence of several stable vanadium oxide phases other than VO2. Therefore, it is important to develop reliable experimental methods to synthesize VO2 thin films and to avoid other undesirable vanadium oxide phases.
Reactive pulsed laser deposition (RPLD) is a powerful method for growing a variety of materials in the form of thin films or nanomaterials. In particular, in the case of VO2, through a thorough optimization process of the laser parameters, we were able to synthesize high-quality thin films exhibiting a metal-to-insulator transition at a temperature of 68oC with an excellent reproducibility. We have also shown that the transition temperature can be lowered towards room temperature by doping VO2 with donors, such as W or Mo. Moreover, the MIT temperature can be tailored over a wide range of temperature by doping the VO2 films with a mixture of donors and acceptors (such as Ti or Al). The RPLD-deposited VO2 films present optical switching properties within a large dynamic range (i.e. tunability) in both near infrared and middle infrared ranges. Therefore, VO2 is an excellent candidate for applications including a variety of ultrafast IR shutters, modulators, uncooled micro-bolometers, smart windows, etc. With that respect, we have also conducted studies to demonstrate the potential of these VO2 films for advanced applications such as i) spatial light modulators (SLMs) in near and middle infrared ranges, and ii) smart radiator devices (SRDs) for a passive thermal control of spacecrafts. In this presentation, we will review the synthesis and the characterization of VO2 thin films as well as their application to photonic and smart radiator devices.

Understanding the nature of the metal-oxide semiconductor interface and modifying it to achieve desired device characteristics are crucial for their application in junction based devices like resistive memory, solar cells and light emitting diodes. In this study, nanotechnological route of modifying the Titanium metal- Copper oxide interface by incorporating a monolayer material has been investigated. Due to the 2-dimensional nature and possibility of modifying the electronic nature, hexa-peri-hexabenzocoronene and graphene are ideal interface layers. Effect of conductivity type of the organic layer, hexa-peri-hexabenzocoronene (p-type, HBC) and hexafluoro - HBC (n-type, 6F-HBC) and electronic properties of the oxide layer (CuO and Cu2O) on the structural and electronic properties of the resulting interfaces has been investigated. In interface between CuO (p type) and HBC (p type), spectroscopic ellipsometry investigations show the formation of hybrid interfacial layer (about 4 nm thick) with absorption features related to Cu-C bonding, modified HBC valence states, and Cu(2+) - O electron interaction. X-ray photoelectron spectroscopy analysis carried out on CuO-HBC bilayers show the appearance of an additional C1s peak at lower energy due to Cu-C interaction. The change in the electronic properties of monolayer materials (p type HBC to n type 6F-HBC) results in large changes in terms of ohmic and rectifying junctions along with drastic modifications from unipolar to bipolar resistive switching of the metal-oxide interface. Conductive atomic force microscopy techniques have been used to probe the underlying organic monolayer-oxide interface (after removing the top metal contact using FIB) maintained in different ON and OFF states during resistive switching. Effect of incorporation of graphene layer on the structural and electronic properties of metal-semiconductor interface has also been investigated. The area dependence of macroscopic and nanoscale electronic properties of metal-oxide interface with and without graphene layers has been studied to understand the nature of graphene- oxide interface. This study shows that nature of metal-semiconductor contact can be modified by using monolayer materials having different electronic and structural properties.

A colloidal route to vanadium sesquioxide (V2O3) nanocrystals with a metastable bixbyite crystal structure has recently been developed. In addition to being one of the first reported observations of the bixbyite phase in V2O3, it is also one of the first successful colloidal syntheses of any of the vanadium oxides, which are studied for their unique catalytic, electrochemical, and structural properties. V2O3 is known to undergo a property-altering phase transformation from monoclinic to rhombohedral phase at 170 K. Last year a new V2O3 polymorph with a bixbyite-type crystal structure was discovered, however the structure could not be isolated as a pure phase and reverted to VO2 upon exposure to ambient conditions. In contrast to this finding, our nanocrystals are pure bixbyite and retain structural stability in air. The bixbyite structure was examined by x-ray diffraction and an aminolysis reaction pathway was determined by Fourier transform infrared spectroscopy. The nanocrystals, measuring 5 to 30 nanometers in diameter, possess a flower-like morphology which densify into a more spherical shape as reaction temperature is increased. A direct band gap of 1.3 eV was calculated from optical data. This value is slightly higher than the theoretical value reported earlier this year, indicating that quantum size effects may alter electronic properties. The onset of the irreversible transformation to the thermodynamically stable rhombohedral phase occurs at 500°C in argon. The transformation proceeds without particle sintering, suggesting that the existence of the metastable phase cannot be attributed to surface energy effects alone, in contrast to most other reported metastable phases at the nanoscale.

Recently, various oxide nanoassemblies have been highlighted as promising candidate materials for gas sensing applications due to the extremely porous configuration and the desired sizes. However, the relatively high operating temperature is always a critical issue even for modern oxide nanosensors. A room-temperature sensor system could simplify device design by eliminating the heater component, save electrical power, be assembled on flexible polymer substrates, and most importantly, avoid triggering explosion in an explosive environment. To date, data related to the room-temperature oxide nanosensors are extremely lacking and most of the previously reported cases require the presence of catalytic nanoparticles for assisting sensing reactions. In this work, a series of spherical hollow V₂O₅ nanoassemblies with various diameters (~ 1 mu;m) has been successfully synthesized by a facile polyol method for manufacturing porous gas sensors. In contrast to the conventional oxide nanosensors working at much higher than the room temperature, the present one-dimensional nanoblocks as well as the extremely high surface to volume ratio (356.33 m²g^minus;1) of the assemblies, which provide not only accessible channels for targeted molecules inwardly diffusing but the tiny V₂O₅ sites for the self-catalytic mechanisms, evidently contribute to the high sensing performance on various gases observed at room temperature.

This paper focuses on the manufacturing and electrical characterisation of multi-layer structures. These include metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS), which show rectification properties in their I-V characteristics. MIM/MIS multi-layer structures are promising devices for concealed object detection, THz wireless data transmission [1], replacement for transistors in electronic circuits, resistive memory devices and light detection [2]. In particular these structures find application in rectifying antenna (Rectenna) devices. The properties which make these multilayer structures ideal for such applications are their high cut-off frequency (low series resistance and capacitance) and low cost manufacturing potential compared with other THz solutions.
The rectenna device, which shows promise for energy harvesting, converts electromagnetic energy propagating through space to direct current. It regards light for its wave nature, as opposed to solar cells where light is harvested by a quantum physical approach, which is limited by the band-gap of the active material. A rectenna can harvest light of all frequencies up to the cut-off frequency of the device and hence maximising this frequency is desirable. The device is composed of an antenna to collect the energy from light, after which, a rectifier (the MIM or MIS structures in our case) converts the input signal to a DC current. This technology is proven to work with 70% efficiency on the micro-wave frequency scale [3].
We have manufactured MIM and MIS devices based on Si-SiO2, Al-Al2O3, Ni-NiO, Nb-Nb2O5, Cr-Cr2O3 and Mo-MoO3 metal-oxides with various top metal electrodes. The thin native oxide layers are formed by dry oxidation of the materials to ensure an ultra-thin insulating layer for the MIM/MIS structure. The suitability of these multilayer structures for rectenna applications is discussed in terms of their rectification properties and cut-off frequency.
[1] Electronic Letters 48, 10 (2012)
[2] IEEE Transactions on Nanotechnology 2012. 11(2): p. 346-351.
[3] IEEE Antennas and wireless propagation letters, 2007, vol. 6

Silica thin films with vertically oriented cylindrical 2D hexagonal close packed (HCP) pores have numerous potential applications in areas including membrane separations, sensors and catalysis due to the well-defined short diffusion paths for reactants and charge carriers provided by their accessible cylindrical pores1. Conventional techniques to synthesize small molecule surfactant-templated silica thin films with 2D HCP well-ordered channels on ordinary substrates (glass slides or silicon wafers) leads to cylindrical channels parallel to the substrate due to the preferential interaction between the polar head groups of surfactants and the hydrophilic substrate.2 This pore orientation makes the majority of the pores inaccessible to reactants or bulk phases in contact with the silica film. Strategies have been described to orient pores in films prepared with block copolymers (drawing upon analogous strategies in the block copolymer literature), but there are few reports in the literature of oriented silica films prepared with small molecule templating. The pores templated with conventional small-molecule surfactants not only provide small pores (on the order of 2-5 nm), but they are also valuable for specific applications; for instance, in our group we are using mixtures of cationic and carbohydrate-based surfactants to move towards preparing mesoporous materials with molecular imprinting of the surface to impart selectivity towards target carbohydrates.
Here we describe a very simple, inexpensive and universal technique to synthesize vertically oriented mesoporous silica films by modifying the surface of the substrate with a random poly(vinyl alcohol-co-ethylene) copolymer. This copolymer provides a random distribution of polar hydroxyl and non-polar methyl functionality on the surface, which is hypothesized to provide equal interactions with polar and non-polar components of surfactants so that 2D HCP micelles will align perpendicular to the substrate. The templates that we use in this proof-of-concept study are mixtures of cationic (hexadecyl trimethylammonium bromide) and carbohydrate (e.g. n-octyl-beta-D-glucopyranoside) surfactants that are of interest to us for simultaneous pore templating and surface imprinting. A combination of x-ray diffraction and TEM will be used to show that hydrophilic substrates such as glass slides and silicon wafers can be readily modified using poly(PVA-co-PE) to induce vertical alignment of the small 2D HCP cylindrical mesopores found in cationic / sugar co-templated silica films. The relationship between the structure of the random copolymer and the surfactant composition will be discussed.
References
1. Thuc-Quyen Nguyen, Junjun Wu, Vinh Doan, Benjamin J. Schwartz, Sarah H. Tolbert; Science,288,652(2000).
2. Yunfeng Lu, Rahul Ganguli, Celeste A. Drewien, Mark T. Anderson, C. Jeffrey Brinker, Weilang Gong, Yongxing Guo, Hermes Soye, Bruce Dunn, Michael H. Huang & Jeffrey I. Zink; Nature,389,364(1997).

Microelectronic technology in radiation sensors has been using metal-oxide-semiconducters (MOSs) because of their high-sensitivity and linear performance, real-time response and low noise. New types of radiation dosimeter systems need these responsible characteristics. In this study, the effects of gamma irradiation on p-type Al2O3 MOS capacitors have been investigated. The MOS capacitors were fabricated on p-type silicon (100) substrate with a nominal resistivity 10 Omega;-cm and Al2O3 insulator layer with a thickness of 250 nm were grown by sputtering in a clean room environment. MOS capacitors were irradiated by using Co-60 gamma source from 2 Gy to 4 Gy. As a result of ionizing radiation passing through to MOS structure, electron-hole pairs were created. The electrons are much more mobile than the holes, so electrons swept out from oxide layer by external applied electric field. Consequently, charge collection occurs in oxide layer and in interface of MOS capacitor. This affects flat band shifts. In order to study the gamma radiation effects on Al2O3 MOS capacitors, the capacitance-voltage (C-V) measurements were performed. Results shows that the Al2O3 MOS capacitors can be used for low dose radiation detections.

A combined conformal coating and gas/solid reaction process has been used for the first time to convert porous anodic alumina templates into robust, freestanding, multi-wall titania nanotube (MWTNT) arrays that resist appreciable nanotube bundling upon drying. A sol-gel infiltration process was first used to apply a thin conformal titania coating to the alumina templates. After selective etching to generate a gap between the template and the titania coating, exposed alumina was converted into nanocrystalline titania via reaction with titanium tetrafluoride gas and then with humid oxygen. After selective dissolution of residual aluminum-bearing phases and drying, freestanding, non-agglomerated, well-aligned MWTNT arrays were generated (i.e., with coating-derived inner titania tubes resting inside reaction-derived outer titania tubes). When incorporated as aligned electrodes in dye-sensitized solar cells, the dye loading and power conversion efficiencies were higher by factors of 2.2 and 1.8, respectively, than for solar cells with single-wall titania nanotube array electrodes. By controlling the conditions used for alumina template formation, sol-gel coating, and gas/solid reaction, this hybrid process may be used to generate robust, uniformly-aligned MWTNT arrays with dimensions and functional chemistries tailored for a variety of electrical, optical, chemical, or biochemical applications.

Ceria (CeO₂) has earned intensive interest in the past decade because it plays a vital role in emerging technologies for environmental and energy-related applications, such as fast-response gas sensors, ultraviolet ray detector, environmental-friendly pigments, and gamma radiation dosimetry, and as an oxidation catalyst. In the work presented here, Ce_0.97Cu_0.03O₂ nanoparticles were synthesized by a microwave-assisted hydrothermal method under different synthesis temperatures. The microwave-assisted hydrothermal method combines the advantages of both hydrothermal and microwave-irradiation techniques such as very short reaction time, production of small particles with a narrow size distribution and high purity which might be attributed to fast and homogeneous nucleation of the mixture. The obtained nanoparticles were tested as catalysts in preferential oxidation of CO to obtain CO-free H₂ (PROX reaction). The samples were characterized by X-ray diffraction, transmission electron microscopy (TEM), electron paramagnetic resonance spectroscopy (EPR) and temperature-programmed reduction (TPR). X-ray diffraction measurements detected the presence of pure cubic CeO₂ for all synthesized samples. TEM images of the Ce_0.97Cu_0.03O₂ nanoparticles revealed that samples synthesized at 80^oC are composed mainly of nanospheres with an average size of 20 nm. The formation of some nanorods with an average diameter of 8 nm and 40 nm in length, and the size reduction of the nanoparticles from 20 to approximately 15 nm is observed with increasing synthesis temperature. EPR spectra indicated that copper is found well dispersed in sample synthesized at 160^oC, located predominant in surface sites of ceria. For samples synthesized at 80 and 120^oC, the species are less dispersed than in the other one, resulting in the formation of Cu²⁺minus;Cu²⁺ dimmers at the surface of ceria. TPR profiles presented two reduction peaks, one below 400^oC attributed to the reduction of different copper species and a second peak around 800^oC attributed to the reduction of Ce⁴⁺ → Ce³⁺ species located in the volume of the nanoparticles. The peak related to the reduction of copper species shifts to lower temperatures with increasing synthesis temperature, i.e., the sample synthesized at 160^oC is more easily reduced than the ones synthesized at 120 and 80^oC. The nanoparticles showed active as catalysts for the CO-PROX reaction. The microwave-assisted method revealed efficient for the synthesis of Ce_0.97Cu_0.03O₂ nanoparticles with copper species selective for the CO-PROX reaction, which reaches CO conversions up to 92% for the sample synthesized at 160^oC.
Work supported by FAPESP, CAPES, INCTMN-CNPq.

Plasmonic noble metal nanoparticles are known to enhance efficiency of semiconductor-based photocatalytic water splitting. Most of the times the enhancement is associated to the charge transfer from the semiconductor to the metal nanoparticles, acting as cocatalyst. However it is only recently that more focus is being put on developing an understanding of the precise nature of the contribution(s) of such metal nanoparticles in the photocatalytic or photoelectrochemical (PEC) performance of different materials. Thus far most of the work regarding plasmonic enhancement of PEC water splitting has been reported on single junction TiO₂-Au or Fe₂O₃-Au systems.
In the present work we introduce the notion of Au nanoparticles influence on a functional hetero-interface; highlighting the effects of a concurrent action of a band-matched hetero-interface for charge separation and optical enhancement effects of Au nanoparticles. For this we took up an unexplored heterojunction of ZnFe₂O₄ (ZFO) and ZnO nanorods as photoanode and deposited plasmonic gold nanoparticles on the surface of ZFO. By doing so, we obtain a dramatic improvement in the overall PEC performance as compared to the pristine ZnO electrode (12 times) or ZFO/ZnO hetero- structure (4 times). Along with the microstructural and optoelectronic characterization, the enhancement is analyzed in detail using PEC current-voltage and incident photon to current conversion measurements. The peculiar combination of metal (Au)/narrow bandgap (ZFO)/wide bandgap semiconductor (ZnO) offers a synergistic effect of electric field intensity and plasmon energy transfer due to Au nanoparticles; better charge separation at Au-ZFO (plasmonic resonance energy transfer) and ZFO/ZnO interfaces, light harvesting due to ZnO nanorods and better charge transport due to high aspect ratio of ZnO nanorods. The materials properties of Au/ZFO/ZnO complement each other remarkably well in the configuration proposed in terms of their optical, electronic and photocatalytic properties.

An array of nanowires on glass is fabricated in which a gold core nanowire is encapsulated within a hemicylindrical shell of δ-phase manganese dioxide, using the lithographically patterned nanowire electrodeposition (LPNE) method. The specific capacitance, Csp, of arrays of gold:mp-MnO2 nanowires is measured using cyclic voltammetry with a potential window from -0.4V to +0.5V with respect to mercurous sulfate electrode(MSE). For a mp-MnO2 shell thickness of 68 ± 3 nm, core:shell nanowires produce a Csp of 1020 ± 100 F/g at 5 mV/s and 450 ± 70 F/g at 100 mV/s. The cycle stability of this Csp, however, is extremely limited in aqueous electrolyte, decaying by >90% in 100 scans, but after oven drying and immersion in dry 1.0 M LiClO4, acetonitrile, dramatically improved cycle stability is achieved, characterized by the absence of Csp fade for 1000 cycles at 100 mV/s. The scanning potential window is further increased from 0.9V to 1.6V, which improves the charge storage by a factor of 2. The energy density increased from 5.5 Wh/kg to 91.7 Wh/kg with power density of 25 kW/kg. By fabricating four gold contacts onto the MnO2 nanowires, the resistance is measured as high as a few G Omega;, however, after lithium ion doping in LiClO4 electrolyte, the resistance drops by 2 orders of magnitude.

Photovoltaic (PV) schemes often encounter a pair of fundamentally opposing requirements on the thickness of PV semiconductor layer: a thicker semiconductor PV layer provides enhanced optical density for effective light harvesting, but inevitably elongates the charge transport path length in the PV layer, while a thin PV layer shortens the transport length but, at a cost of optical density. We tackle this challenge by transforming the traditional flat 2-D TCO to 3-D TCO nanoarchitectures, followed by coating a conformal thin layer of PV materials uniformly on all surface of the 3-D TCO. As such, the thickness of PV layer can be significantly thinned to shorten the transport distance while still retaining the large surface area of PV materials for sufficient light harvesting.
Herein, we report a set of wet chemistry-based synthesis of highly conductive 3-D fluorinated tin oxide (FTO) electrodes including 3-D nanoscale photonic crystal inverse opal FTO electrodes, FTO nanoparticle electrodes, hollow FTO nanobeads electrodes, and nanoporous sponge-like FTO electrodes. Using atomic layer deposition method, an ultrathin TiO2 layer is conformally coated on all surfaces of these 3-D FTO nanostructured electrodes to serve as the photoanodes in dye-sensitized solar cells. PV performance of the resulting cells was further studied, showing significantly enhanced electron extraction in the 3-D nanostructured FTO electrodes due to the largely reduced transport distance in the PV layer.

Bismuth-doped anatase titanium dioxide nanofibers (Bi-doped TiO₂ NFs) were synthesized and applied in flexible composite films that are easy to handle and recycle after use. Bismuth doping can decrease the band gap of TiO₂ and show photodegradation of organic dyes with photons of the visible spectrum. The potential advantage of using nanofibers instead of nanoparticles becomes conspicuous in film-type photocatalyst applications. In this study, bismuth-doped titanium dioxide nanofibers were obtained in a multi-step procedure. First, bismuth-doped sodium titanate nanofibers were prepared from TiO₂ nanoparticles and bismuth precursor (Bi(NO₃)₃) through the alkali hydrothermal method. Then, bismuth-doped sodium hydrogen titanate nanofibers were made by washing the bismuth-doped sodium titanate nanofibers in HCl solution. Finally, the bismuth-doped sodium hydrogen titanate nanofibers were transformed to Bi-doped TiO₂ NFs by calcination at 600 ^oC for 12 hours in air. The photocatalytic activity of Bi-doped TiO₂ NFs with different Bi-doping concentration were evaluated and compared to a TiO₂ nanoparticle catalyst by decomposing methyl orange in aqueous solutions. 0.5 wt% Bi-doped TiO₂ NFs shows almost the same photocatalytic activity as Degussa P25. The microstructure of composite films and the morphology of individual nanofibers were studied by field-emission scanning electron microscopy equipped with an EDX-analyzer, transmission electron microscopy and by X-ray diffraction. Since composites of nanofibers with cellulose enable mechanically strong structures, after some optimization, such catalyst films/membranes might be good candidates in large-area coatings and freestanding films produced in large volumes. The composite films made from the nanofibers exhibit better mechanical integrity than those of the nanoparticle-cellulose composites.

In terms of deposition area, SnO2 doped with F or Sb is the most widely used transparent conductive oxide (TCO) material for many energy generation and electronic applications due to its low cost. In thin film solar cells (TFSCs), TCOs are commonly used as electrodes both above and below the solar absorbing region. Currently, high quality SnO2 requires a processing temperature of ~450C, which limits its applications in amorphous Si (a-Si) and copper indium gallium selenide (CIGS) TFSCs. Furthermore, it would be highly desirable to further improve its electrical conductivity and light-trapping capability simultaneously.
In this paper we demonstrate a novel nanostructured Sn-rich SnO TCO material with significantly reduced processing temperature, higher electrical conductivity, and enhanced light-trapping capability compared to conventional SnO2 TCO. The Sn-rich SnO was fabricated by co-sputtering Sn and SnO2 with a molar ratio slightly larger than 1:1. The as-deposited film was amorphous with a thickness of ~100 nm. After regular furnace annealing in an N2 environment above 225C, crystalline needle-like SnO nanostructures were formed, as revealed by scanning electron microscopy (SEM) and X-ray diffraction. These self-assembled SnO nano-needles are approximately 100nm wide and 500nm long and they propagate horizontally throughout the thin film in random orientations. Alternatively, rapid thermal annealing (RTA) was used to quickly grow SnO nano-needle crystals—XRD results indicate complete crystallization after RTA at 300C for 30s. Since the SnO was Sn rich, XRD analysis further shows that Sn nanocrystals were formed after annealing due to Sn segregation according to the Sn-O phase diagram. The surface texture introduced by the SnO nano-needles and the plasmonic scattering from the Sn nanocrystals both enhances the light trapping capability of the Sn-rich SnO TCO layer. The electrical conductivity of the crystallized Sn-rich SnO was found to be ~10^4S/cm, even better than the best F or Sb doped SnO2 obtained at 450 C (1.6×10^3S/cm). Reflectivity measurements of the nanostructured Sn-rich SnO thin film show a low reflectance <15% in the wavelength range of 520nm to 800nm without thickness optimization, making SnO needle-like nanostructures a potential candidate for an antireflection (AR) coating as well.
With its low processing temperature, high electrical conductivity, , enhanced light trapping capability, and anti-reflection properties, the nanostructured Sn-rich SnO demonstrated in this work has the potential to serve the function TCO layer, light-trapping structure and the AR coating simultaneously on solar cells. This multifunctional nanostructured metal oxide thin film could further improve the performance and reduce the cost of TFSCs.

Pure-phase β-MnO2 nanobelts and nanowires were synthesized through an economic hydrothermal method. The electrochemical properties and photodegradation of the methyl blue (MB) under UV and visible-light illumination were investigated. The MnO2 nanobelts show effective activities for the degradation of MB, and high sensitivities to the H2O2. The results showed that the degradation of MB reached near 65% and 90% in 100 min under visible and UV light illumination, respectively. And with the concentration of H2O2 was increased, the reduction peak at CVs appeared stronger. The Mn3O4 nanowires were also obtained through calcining of the MnO2 nanowires in vacuum at 773K for 2h. The hysteresis loop of Mn3O4 was also studied and it exhibited weak characteristic of ferromagnetism.

Flexible Dye sensitized solar cells (FDSSCs) are light weight, thin, bendable and inexpensive which enable them to be integrated in to portable, mobile and wearable applications. Indium tin oxide (ITO) coated plastic electrodes (usually polyethylene terephthalate (PET)) has been widely used as substrate for flexible electrodes. However ITO is expensive and relatively rare thereby increases the overall price of the device. Graphene with its unique features such as high mobility, high transparency, high theoretical value of specific surface area which reaches to 2630 m2/g, high transparency (88.8%) over whole solar spectrum and flexibility can be a very promising alternative to ITO based electrodes. A major challenge for making DSSCs on plastic substrates and Graphene is the temperature limitation of substrates in producing working electrodes and chemical inertness of Graphene. We report on fabrication of ZnO nanostructure over Graphene/PET substrates to be used as photoelectrodes for FDSSCs.
We employed a novel seed layer-free sonochemical technique to synthesize ZnO nanostructures on Graphene/PET. Sonochemistry is a low temperature, catalyst free process which is done at atmospheric conditions, making it environmental friendly. Graphene was grown by thermal chemical vapor deposition (CVD) Graphene has been transferred on to PET via chemical process. The presence of Graphene and ZnO is confirmed by Raman Spectroscopy. Comparative study of structural and electrical characteristics by SEM, XRD, TEM, transparency and conductivity measurements for ZnO nanorods grown directly on Graphene/PET and PET/ITO as photoanode is presented. The effect of Graphene on dye loading and on efficiency of FDSSC is quantitatively investigated. The effect of mechanical bending on the output characteristics is also measured. The results prove the feasibility of our method to synthesize ZnO nanorods on Graphene/PET at room temperature in an environmentally benign manner as well as promising characteristics of ZnO nanostructures over Graphene/PET as photoanode for flexible dye sensitized solar cells.

Indium tin oxide (ITO) nanostructures may improve performance in transparent conductor and optoelectronic applications. One such application is organic photovoltaic devices (OPVs) where a nanostructured electrode may improve charge collection, and allow decoupled optical absorption and charge extraction [1]. While ITO nanowires can be fabricated by self-catalyzed vapour-liquid-solid (VLS) growth, this method limits the available morphologies. A recently developed technique combines the VLS growth of ITO with the geometrical shadowing control of glancing angle deposition (GLAD) [2]. This technique, known as VLS-GLAD, significantly enhances control over ITO nanowire branching, feature size, and number density [3]. Unique hybrid structure morphologies suitable for three-dimensional electrodes can be produced; the flexibility of VLS-GLAD may enable structural optimization for applications such as OPVs. Optical and electrical properties of VLS-GLAD ITO structures demonstrate high quality transparent conducting properties. Additionally, OPV devices have been fabricated incorporating branched ITO nanowires as three-dimensional electrodes. Non-optimized device efficiencies of VLS-GLAD ITO electrode P3HT:PCBM bulk heterojunction OPVs demonstrate the utility and performance of nanostructured ITO electrodes.
[1] D.A. Rider et al., Nanotechnology 22 (2011) 085706
[2] A.S. Alagoz and T. Karabacak, Mater. Res. Soc. Symp. Proc. 1350 (2011)
[3] A.L. Beaudry et al., Nanotechnology 23 (2012) 105608

With the increase in the energy demand, interest on alternatives to PV technology such as the direct conversion of solar energy into storable fuels has arisen. However, the efficiency is still low. Nano-structured metal oxides with high-aspect ratios have shown attractive performances in water splitting. There are a variety of synthesis techniques for nanostructured metal oxides including wet-chemistry and plasma-based methods. In this work, we propose a novel processing technique based on surface treatment of metal (W, Mo, Fe) samples by high-fluxes of low-energy helium ions. This synthesis technique provides an efficient route for the formation of porous metallic nanostructures.
Exposing the metal surface to a high flux of low energetic He ions creates bubbles in the subsurface of the metal and following the coalescence of these bubbles the surface expands to form fibreform nano-structures, with filament diameters smaller than 20nm [1,2]. The helium-induced nano-structure provides a high level of porosity which makes the surface ideal for light absorption across the whole solar spectrum. The size of the structures can be controlled in the range 20-1000 nm by the surface temperature while the thickness of the nanostructured layer depends on the processing time [1,3]. By this processing techniques, similar surface modifications can be obtained on various metal (W, Mo, Fe, Al) surfaces.
Tungsten was chosen as a case study due to its effective photocatalytic activity of its oxide (WO3) in the monoclinic phase. Nanostructured tungsten samples were oxidized through an optimized 2-step oxidation procedure. The good photoresponse (above 1mA.cm-2 at 1.7 V vs. RHE) obtained through this approach, demonstrates the potential of the helium-assisted processing of metals.
References
[1] M.J. Baldwin and R.P. Doerner, Nucl. Fusion 48 (2008).
[2] S. Kajita, W. Sakaguchi, N. Ohno, N. Yoshida, and T. Saeki, Nucl. Fusion 49, 095005 (2009).
[3]G. De Temmerman et al., J. Vac. Sci. Technol. A, 30 041306 (2012).

In this presentation, we report the use of a microwave-assisted hydrothermal method to synthesize MnO2 nanostructures with well-controlled morphology and crystallinity in high uniformity and purity. The use of microwaves to drive solution-phase reactions offers many advantages in comparison with conventional heating processes, for example, prompt start-up, uniform temperature distribution in reaction solutions, efficient energy conversion and delivery, easy control over reaction conditions, and possible scaling up. By appropriately controlling the reaction conditions, we successfully synthesized uniform δ-MnO2 microflowers consisting of assemblies of nanosheets, α-MnO2 nanowires, and α-MnO2 nanotubes with open ends. The detailed morphological and crystalline evolutions have been studied at the atomic resolution with time-dependent x-ray diffraction, transmission electron microscopy, and controlled synthesis. The as-synthesized MnO2 nanostructures have been incorporated into air cathodes in lithium-air batteries to serve as catalysts for facilitating the electrochemical processes involving oxygen reduction and evolution reactions. The results indicate that the morphology and crystallinity of the MnO2 nanostructures indeed influence the performance of the lithium-air batteries and the α-MnO2 nanotubes represent the best in terms of energy capacity and stability.
Reference: T. T. Truong, Y. Liu, Y. Ren, L. Trahey, Y. Sun, ACS Nano 2012, 6, 8067.
Use of the Center for Nanoscale Materials and Advanced Photon Source at Argonne National Laboratory was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract No. DE-AC02-06CH11357.

Sensitive measurement of proteins is one of critical demands for early diagnosis of disease. Electrochemical immunoarray, as a selective, sensitive, portable and low-cost analysis method, is more favored in clinical immunoassays. In sandwich-type immunoassay, the secondary antibody molecules are usually labeled by signal tags, such as redox-active probes, enzyme, or semiconductor nanoparticles. Thus, the amount of the secondary antibody always influences the sensitivity of the electrochemical immunosensor to a great extent.[1] Besides, increasing the upload of antibody in sandwich-type immunoassay is an alternative method to amplify the detection signal, which could result in more target analytes and recognition elements captured onto electrodes. This strategy usually requires electrode with a large real surface area and sufficient space.
Since the formation of self-organized arrays of TiO2 nanotubes (TiNT) by electrochemical anodization of Ti was reported by Zwilling and co-workers in 1999,[2] TiNT have generated much interest.[3] In this study, we proposed a novel signal-amplified electrochemical immunosensor by using TiNT layer as the platform. Due to the distinct tubular features - large surface area, high pore volume and good electrochemical conductivity, TiNT based electrodes showed excellent signal-amplified effects.[4] Gold nanoparticle (AuNP) was further utilized to bind horseradish peroxidase (HRP) tagged antibodies as recognition elements. Compared to immunosensors based on either flat electrode, the immunosensor using TiNT layer as electrode shows high amplified electrochemical signals from the catalytic reaction of the carried HRP relative to hydrogen peroxide (H2O2). Under optimal conditions, the proposed immunosensor exhibited a good electrochemical behavior to antigen in a concentration range from 0.1 ng mL-1 to 105 ng mL-1 with a detection limit of 0.01 ng mL-1. Using TiNT arrays as platform may provide lots of potentials for development of ultrasensitive electrochemial immunosensor for the diagnosis and monitoring of carcinoma and its metastasis.
Acknowledgements: This work was supported by the National Natural Science Foundation of China (No. 21005012, 21275026, 11004025, 11174046), the financial support from New Century Excellent Talents in the University of China (NCET-10-0305 for Y. Y. Song), and the Fundamental Research Funds for the Central Universities (N110805001, N110705002).
References:
[1] Matschulat, D., Deng, A., Niessner, R., Knopp, D., 2005. Analyst 130, 1078-1086.
[2] Zwilling, V., Darque-Ceretti, E., Boutry-Forveille, A., 1999. Electrochim. Acta 45, 921-929.
[3] Ghicov, A., Schmuki, P., 2009. Chem. Comm. 20, 2791-2808.
[4] Song, Y. Y., Zhuang, Q. L., Li, C. Y., Liu, H. F., Cao, J., Gao, Z. D., 2012. Electrochem. Comm. 16, 44-48.

The bulk nanostructures of Co3O4 recently draw great attention as a peroxidase-like catalyst in environmental applications. However, they suffer the degradation of the peroxidase-like activity due to the agglomeration of particles. Herein, we report a facile method to synthesize the “agglomeration-free Co3O4 nanoparticles-carbon nitride nanotube hybrids” (Co3O4 NP-CNNT hybrids) using a thermal-heating-assisted liquid polyol process and heat-treatment in air. Co3O4 NP-CNNT hybrids shows the superior peroxidase-like activity of 18 times higher than that of bulk Co3O4 NPs due to the stronger affinity with substrate molecules (TMB and H2O2) by the larger specific surface area of Co3O4 NPs anchored on CNNTs and an electron-transfer ability of CNNTs. Electron Spinning Resonance (ESR) provides the clue for the peroxidase-like redox role of Co3O4 NP-CNNT hybrids in the presence of TMB and H2O2. First, Co3O4 NPs anchored on CNNTs or CNNTs supply an electron to H2O2, and generates OH radicals from H2O2. Next, TMB is oxidized and generate an electron and generated electron offset the lack of electron of Co3O4 NP-CNNT hybrids.

Semiconducting nanocrystals with tailored shapes have been widely investigated in the past decades because of their many shape-dependent properties. Anatase, a metastable phase of the titanium dioxyde (TiO₂), is one of the most interesting material in many applications, such as photocatalysis, photovoltaics, photo/electrochromics or sensors.¹ Photocatalytic materials must display a relatively high specific surface and a good stacking of atoms constituting the crystalline structure to display high activity. Indeed, defects may act as recombination center between photogenerated electrons and holes and consequently decrease photocatalyst efficiency² In addition to an influence of the nanoparticles size, recent works on the anatase phase demonstrated the effect of the expressed surfaces nature on the nanoparticles photoreactivity.³ With a solid background in oxide nanoparticles tailoring from metallic salts in aqueous solution,⁴ our research group successfully transferred conventional syntheses of titanium dioxide to microwave assisted thermohydrolyses. The brookite phase is often obtained with a classical oven as a by-product, whereas microwave heating is efficiently used for the formation of pure anatase.⁵ Furthermore, conventional heating method is compared with hydrothermal and microwave activated synthesis. The use of organic additive is thus avoided and good photocatalyst with clean surface is consequently more quickly obtained.⁶ Photocatalysts obtained by microwave synthesis were compared to their conventional counterpart in order to check whether significant improvement in Rhodamine B degradation in aqueous solution was observed. Additionally time resolved microwave conductivity (TRMC) was used to probe the crystalline improvement of the materials.

References
1. X. Chen and S. S. Mao, Chem. Rev 107, 2891 (2007),
2. G. Benko, B. Skarman, R. Wallenberg, A. Hagfeldt, V. Sundstrom, and A.P. Yartsev, J. Phys. Chem. B, 2003, 107, 1370.
3. D. Q. Zhang, G. S. Li, H. B. Wang, K. M. Chan and J. C. Yu, Cryst. Growth Des. 10, 1130 (2010)
4. J.-P. Jolivet, C. Froidefond, A. Pottier, C. Chanéac, S. Cassaignon, E. Tronc, and Patrick Euzen, J. Mater. Chem., 2004, 14, 3281
5. A. Pottier, S. Cassaignon, C. Chanéac, F. Villain, E. Tronc, and J.-P. Jolivet, J. Mater. Chem., 2003, 13, 877
6. F. Dufour, S. Cassaignon, O. Durupthy, C. Colbeau-Justin, and C. Chanéac, Eur. J. Inorg. Chem., 2011 submitted.

Fischer-Tropsh synthesis (FTS) has been known as a method for production of hydrocarbons from mixture gas of CO and H2. In particular, high temperature Fischer-Tropsch (or HTFT) reaction has been commercially operated at temperatures of 300°C-350°C by using an iron-based catalyst, mainly producing gasoline and light olefins. Traditionally, the iron-based catalyst has been prepared by various methods such as co-precipitation and wetness impregnation with various supports like carbon, silica, alumina, and so on. In commercial F-T catalysts, some promoters such as Cu, SiO2 and K have been also used to enhance the activity, stability, and selectivity of catalysts. Herein, we newly suggest the iron carbide nanocatalysts which were supported on CMK-3 and activated charcoal catalysts by melt-infiltration process of an iron nitrate hydrate salt at 323K and subsequent ex-situ activation step under CO gas flow at 623K. After acvitation step, the obtained catalysts showed extremely high CO conversion rate as well as high selectivity to gasoline (C5-C12) during the HTFT reaction owing to the uniform particle dispersion with small particle size ranged about 5~10 nm,. In addition, potassium as a basic promoter which was added into the iron carbide/carbon suppoted catalysts by the incipient wetness method affected electronic structure of iron carbide nanoparticles, and could enhance the CO conversion rate and decrease methane selectivity, dramatically.

Transition metal oxides (TMOs) are intensively investigated for electrochemical energy storage applications, including Li-ion battery and supercapacitors. As materials for electrodes, the high resistivity of most TMOs significantly restricts their practical applications. Although nanostructured composites, introducing conductive mediators into oxides, are promising to steer by the resistivity limitation, achieving highly conductive oxide itself is still the fundamental route for the goal of high performance electrochemical electrodes. To this end, we report our study on tuning the conductivity of vanadium oxide by several orders. We also demonstrate its promising potential for supercapacitor application.
In this work, vanadium oxide nanomaterials were obtained with different valence states to tune their conductivity, from a resistivity of ~ 10 Omega;cm down to ~ 10-3 Omega;cm at room temperature. The change of their metal-insulator transition property and the fundamental mechanism of the conductivity variation were investigated. Finally the significant improvement of supercapacitor performance based on the conductive vanadium oxide was also reported.

Abstract:
The high temperature ionic conductivity of yttria-stabilized zirconia made it a promising candidate material for high temperature energy storage applications. However, little efforts have been made to investigate its supercapacitive characteristics. Likewise, clay, the most common minerals, is a composite of several supercapasitive minerals such as iron oxides, alumina, silica etc which have many useful properties, including high specific surface area and excellent adsorptive capacity. Nevertheless, little attention has been paid to exploring its energy storage potentials. Attempt is made in this study to investigate the capacitive properties of yttria-stabilized zirconia-clay composite electrode prepared through powder metallurgy technique. Powder yttria-stabilized zirconia was mixed in a turbula mixer with varying compositions of ultra-fine clay that were previously calcined and mechanically milled in a planetary ball mill. The blended powders were further calcined and compacted into briquettes, and finally fired at 1200oC, 1300oC and 1400oC for one hour. The calcined blends and compacted samples were characterized using ultra-high resolution field emission scanning electron microscope (UHR-FEGSEM) equipped with energy dispersive spectroscopy (EDX), and X-ray diffractometry (XRD). Electrochemical characteristics of the sinter composites in sulphuric acid environment were performed by cyclic voltammetry, potentiodynamic polarization, chrono-amperometry, and Electrochemical Impedance Spectroscopy (EIS) in a three-electrode system.

As McGehee and coworkers described a number of years ago [K.M. Coakley et al. MRS Bull. 2005 30, 57], a hole carrying conducting polymer (such as P3HT), when loaded into titania thin films with HCP cylindrical nanopores, is hypothesized to give better photovoltaic performance as compared to a disordered or bicontinuous cubic nanopore arrangements. Confinement in cylindrical nanopores is expected to provide isolated, regioregular “wires” of conjugated polymers with tunable optoelectronic properties, which have been shown to improve hole conductivity over that in bicontinuous cubic structure [M.D. McGehee, MRS Bull. 2009, 34, 95]. Here, we describe the synthesis of surfactant-templated titania thin films with vertically aligned cylindrical pores with a size amenable to P3HT loading and compare the photovoltaic performance of such films with interconnected globular pores and lamellar pores of comparable dimensions.
The mesoporous titania thin films have been synthesized by evaporation-induced self-assembly with Pluronic surfactant P123 as the template. P123 is a triblock copolymer surfactant with average structure (EO)20(PO)70(EO)20 where EO represents an ethylene oxide polymer unit and PO represents a propylene oxide polymer unit. Depending upon the molar ratio of P123 to titania precursor (M), films with lamellar, hexagonal or cubic mesostructure are observed. Films with the desired 2D hexagonal close packed (HCP) columnar mesopore phase are obtained for M ratios of 0.012-0.015. For higher M ratio, a lamellar microstructure is observed. HCP structures cast onto hydrophilic oxide surfaces (such as those of titania or fluorinated tin oxide that might be present in bulk heterojuction materials) usually align parallel to the surface. To provide vertical alignment of the pores, surface modification of substrates with crosslinked surfactant P123 has been used to provide a surface that is chemically neutral towards the PEO and PPO blocks. Conditions are found giving vertically aligned, 2D HCP titania films with pores near 10 nm in diameter, which are precisely the structures expected to provide short carrier diffusion length and high hole conductivity required for an efficient bulk heterojunction solar cell. For comparison, comparable films have also been prepared with F127, which has structure (EO)106(PO)70(EO)106, in an effort to further expand the pore size. The pores of the materials will be filled with P3HT by spin coating followed by thermal and solvent annealing, and the resulting photovoltaic performance as a function of pore structure, symmetry and orientation will be discussed.

Anodically grown TiO2 nanotube arrays are the focus of intense research due to their excellent performance in a variety of applications including but not limited to excitonic solar cells, water photoelectrolysis and photocatalysis, hydrogen sensors, glucose sensors, stem-cell differentiation, biomarker assays and drug delivery. However, several applications in nanoelectronics, energy harvesting and sensing require nanostructures which possess more morphological complexity. Multipodal nanotubes are branched nanotubes possessing three or more ‘pods&’, formed by the process of nanotube combination [1]. Multilayer nanotubes are a closely related architecture where the potential-step induced electrochemical branching of nanotubes is used to create connected bilayer films with nanotubes of two different pore diameters. Using simulations and experiments, we show that multilayer nanotube arrays enable active layer photon management in excitonic solar cells and photocatalysts. Obtained multilayer nanotube arrays are shown to increase the light absorption which can be beneficial for some of the aforementioned applications such as solar solar cells and photocatalysis. Small diameter nanotubes provide a larger surface area for the attachment of sensitizing dyes/quantum dots while on the other hand, large diameter nanotubes with diameters comparable with the wavelength of the incident light, are strong Mie scatterers, which in turn increases the re-absorption probability of the scattered light. Thus, the simultaneous utilization of large and small diameter nanotubes in multilayer films increased light absorption and photocurrents in solar cells. Such enhanced light absorption is particularly important in the near-infrared region of the solar spectrum in which most excitonic solar cells and visible-light responsive photocatalysts suffers from poor quantum efficiencies. Multilayer nanotube arrays afforded us a nearly 50 % improvement in photocurrent over single layer nanotube array films of the same thickness for N-719 sensitized Gratzel cells. Both multipodal and multilayer nanotubes enable the construction of a type of broadly absorbing tandem solar cells connected optically in series, wherein each component cell absorbs a different band of the solar spectrum and contributes to photocurrent while generating the same open circuit photovoltage. Multipodal nanotube structures also offer the promise of sorting and handling quantum dots, in building three-terminal nanodevices, and in multiplexed sensing applications by different surface functionalization of the individual legs.
1. A. Mohammadpour, P.R. Waghmare, S.K. Mitra and K. Shankar, “Anodic Growth of Large-Diameter Multipodal TiO2 Nanotubes”, Acs Nano, Vol. 4, No. 12, Dec, 2010, pp. 7421-7430.

In order to meet the world&’s energy requirements in an environmentally sustainable way, current carbon intensive sources must be progressively replaced with renewable ones. PEC water splitting seems like a suitable approach to this great challenge provided that the photoactive electrode materials satisfy the stringent band gap, band edge position and stability criteria to enable technically and economically feasible production of hydrogen. Copper tungstate is a promising electrode material for the oxygen evolution reaction in PEC water splitting, as reported by Gaillard et al (2011, 2012) (i-ii). Here we describe a simple method to synthesize CuWO4 by hot-wire chemical vapor deposition and the characterization of films thereof. Incandescent tungsten and copper filaments were used as metal sources in a low-pressure oxygen atmosphere to produce films on gold-sputtered stainless steel and FTO glass substrates. Uniform polycrystalline CuWO4 films were identified by XRD, SEM and EDAX. The as synthesized materials are p-type semiconductors with a direct band gap of around 2.3 eV. Three electrode PEC testing in basic aqueous solution shows that the films are active for water splitting with a current density of 15 mu;A cm-2 at +1 V (vs. Ag/AgCl) and a flat band potential of -0.1 V. Despite the material high crystallinity, low conductivity and poor carrier transport remain to be solved. Ongoing research is aimed at eliminating junction rectification in equilibrium by comparing performance in different substrates. Future research direction includes band gap engineering of BixCu(1-x)W2O8 alloys.
__________________________________________________________________________
References:
i. Chang, Y., A. Braun, et al. (2011). "Effect of Thermal Treatment on the Crystallographic, Surface Energetics, and Photoelectrochemical Properties of Reactively Cosputtered Copper Tungstate for Water Splitting." The Journal of Physical Chemistry C 115(51): 25490-25495.

ii. Gaillard, N., Y. Chang, et al. (2012). "Copper Tungstate (CuWO4)-Based Materials for Photoelectrochemical Hydrogen Production." MRS Online Proceedings Library 1446.

Titanium dioxide (TiO2), thanks to its interesting properties as nontoxicity, low cost and high chemical stability, has been extensively investigated for several application in which, following light absorption, the generated charges can be usefully applied, as for photovoltaic applications or for photocatalytic devices. However, due to the wide intrinsic energy gap of TiO2 (between 3.0 and 3.2 eV, depending on the crystalline structure), only a small fraction of the solar spectrum can be used to promote the light absorption. In the photocatalytic devices one of the most important goal of the recent research is to be able to prepare photocatalyst which can be active by absorbing the visible light, in order to increase the application of TiO2-based system in poor regions (where it could be difficult to use UV light sources) or to reduce the application cost. In order to increase the fraction of the solar spectrum that can be absorbed, different approaches have been used, mainly by doping TiO2 with metals or anions.
In this paper we will show the photocatalytic results obtained depositing metal-doped TiO2 nanofibers (NF) prepared by electrospinning technique (ES) for the photo-degradation of a pollutant-model (Rhodamine 6G) in water under visible light irradiation. The ES preparation technique allows a quick deposition of fibers on wide surfaces using a cost-effective system.
TiO2 NFs were doped with different metals: iron, copper, tungsten. The NFs have been characterized by using X-ray photoemission spectroscopy (XPS), X-ray diffraction (XRD) and Secondary Electron Microscopy (SEM). The photocatalytic properties have been studied recording the variation of the optical absorption of R-6G when the sample is illuminated by an fluorescent lamp (visible spectrum).
All the metal doped NFs show higher photocatalytic activity than the undoped ones and the best effect is observed when a very low metal concentration (less than 0.01%) is used.

Facet-dependent activities of nano-materials have long been the focus of researchers. Ag2O microcrystals with different facets exposed exhibit distinct photocatalytic activities. Ammonium ions can easily complex with the Ag+ to form [Ag(NH3)2]+ complexing ions, which can release Ag+ slowly in the presence of OH-. The formed AgOH quickly decompose to be the Ag2O nucleus. This process is quite important to slow down the growth rate of Ag2O microcrystals and create favorable conditions for anions to adsorb onto the given facets of Ag2O particles. Five morphologies of Ag2O microcrystals cubic ({100}), octahedral ({111}), rhombic dodecahedral ({110}), polyhedra with 18 faces ({100}+{110}) and rhombicuboctahedral ({100} + {110} + {111}) are obtained via this simple kinetic method. The photocatalytic activities of the Ag@Ag2O photocatalysts with different morphological structures are evaluated by the degradation of methyl orange dye solution under visible light irradiation. Due to the highest surface energy of the {100} facet, the larger difference value between the weighted average of the effective mass of holes and electrons along the <100>direction, and the suitable redox potentials of the (100) surface; the cubic Ag@Ag2O with {100} facets exposed displays higher photocatalytic activity than other structures with {110}, {111} or multi-facets exposed.

The plasmonic photocatalyst Ag@AgCl(Br) which has high photocatalytic activity under the irradiation of visible light, has been a hot spot in photocatalytic researches. The crystalline and morphological structures of AgCl(Br) have great influence on the photocatalytic activity of Ag@AgCl(Br). The novel near-spherical AgCl(Br) microcrystals with convex surface are synthesized by using ionic liquid C16MimCl(Br) as halides source and stabilizer during hydrothermal process. With series of high-index facets exposed on the convex surface, the near-spherical AgCl(Br) has high surface activity which results in the high photocatalytic activity of the near-spherical Ag@AgCl(Br). Kinetic controlling method is also a pathway to control the crystal growth of AgCl. The generation of Ag+ is controlled by using a wet chemical oxidization method in the NaCl solution. With the insufficient supply of Ag+, Ag+ is priority to react with the Cl- absorbed on corners (<111>) and edges (<110>) of cubic seeds. And the AgCl concave cubes with preferential overgrowth along <111> and <110> direction are obtained. The growth rates along <111>, <110> and <100> directions of cubic seeds can be tuned by changing the generation rate of Ag+ and the concentration of NaCl in the growth process. And a novel 3D AgCl hierarchical superstructures are obtained with the fast growth along <111> directions and slight growth along <110> and <100> directions of cubic seeds. Due to the high-index facets exposed on the surface of AgCl concave cubes and hierarchical superstructures, both structures have high activity in oxygen generation of water oxidization under irradiation by UV/vis light.

As an important functional material, n-type semiconducting binary oxides indium oxide (In2O3) with a wide band-gap (3.5-3.7 eV), has attracted much interest for several decades due to its high electrical conductivity and good optical transparency. There are three crystal structures reported for In2O3: cubic bixbyite-type (c-In2O3) at ambient conditions, hexagonal corundum-type (h-In2O3) under high pressure and temperature, and orthorhombic Rh2O3(II)-type structure under higher pressure and temperature. Therefore, the In2O3 system is a good model for the fundamental studies of phase transformation in solid state due to its polymorphic, allowing the control of its functional properties by structural manipulation. H-In2O3 shows some novel and enhanced properties, such as stable conductivity and high sensitivity to gases, compared to the thermodynamically stable c-In2O3. However, the studies of the production h-In2O3 were relatively rare because of the difficult conditions of the synthesis. However, Therefore, it still remains a great challenge to find a high yield, straightforward, less hazardous, and environmentally benign method for the synthesis of h-In2O3 at ambient condition.
In this work, large scale hexagonal corundum-type indium oxide (h-In2O3) was synthesized via structural transformation from initial cubic indium oxide directly using high-energy ball milling approach at room temperature. The structural transformation was attributed to the rearrangements of InO6 octahedra unit by deformation and large defect concentrations during milling.Importantly, the as-synthesis h-In2O3 exhibited enhance reversible capacity and good cycling performance in lithium ion batteries compared to the initial c-In2O3, indicating that it is hold great promise as lithium ion battery materials.

Multiferroic materials have recently received considerable attention in both areas of photocatalytic and photovoltaics (PV) due to their interesting optical characteristics. As an intensively studied multiferroic material, BiFeO3 has also been recognized as a perspective material for potential photovoltaic and visible-light photocatalytic applications due to its small band gap (sim;2.2-2.8 eV) and good chemical stability. Recently, the utilization of one-dimensional (1D) semiconductor for solar water splitting has attracted growing attention. In comparison with bulk materials, photocatalysts in the form of 1D nanostructures such as nanowires (NWs), nanobelts and nanotubes have shown enhanced efficiencies for photocatalytic water splitting activity.
Gold nanoparticles (AuNPs), which can strongly absorb visible light because of the localized surface plasmon resonance (LSPR) from the collective oscillation of conductive electrons and do not undergo corrosion under photocatalytic conditions, have been used to combine with semiconductor photocatalysts to enhance the water splitting performance. Among all the methods for synthesizing AuNPs, pulsed laser ablation in liquid phase (PLAL) on a Au bulk target offers an exciting way to produce relatively “bare and clean” AuNPs, which are anticipated to facilitate catalytic reactions because the reactive sites on the NPs surface are mostly exposed and readily accessible for reactants during catalytic reactions. As a result, AuNPs prepared by laser ablation technique are expected to act as highly efficient catalysts.
We have demonstrated the potential for solar water splitting with a novel hybrid Au/BiFeO3 photocatalysts synthesized by a simple and functionalization-step-free solution process. An enhancement of ~ 30 times in photocatalytic activity for oxygen generation under visible light was observed when minute amount of Au (1.0 wt %) was added on the surface of BiFeO3 nanowires. Their superior catalytic activity is due to the plasmonic effect as well as the unique surface-chemistry features of the PLAL-AuNPs. The synthesis, characterization of the BFO NWs and their photocatalytic properties will be presented.

Nanowire based photovoltaic devices have potential advantages over conventional planar devices by decoupling the light absorption length and photo-generated carrier collection length, thus enabling efficient charge collection in low-cost absorbers. However, controlling the geometry and alignment of a nanowire structure over large device areas has proven challenging, and previous attempts typically result in non-ideal device structures. Herein, we describe a potentially scalable method to manufacture Earth-abundant zinc oxide (ZnO) nanowire-based solar cells, with demonstrated performance benefits over comparable planar junction devices.
In this work, we present a scalable fabrication method to spatially control vertical ZnO nanowire arrays for photovoltaic applications. We use colloidal lithography to enable hexagonal alignment of the ZnO nanowire array. ZnO nanowires are grown by parallel hydrothermal reaction at the nucleation sites defined by self-assembled polystyrene nanospheres, a technique potentially adaptable to high-throughput, large-area manufacturing. We control the spacing between nanowires and their geometry by varying the nanosphere diameter. Using the ZnO nanowire array, we develop cuprous oxide (Cu₂O) - ZnO heterojunction thin-film solar cells with enhanced light-absorption. We report the strong enhancement of photo-generated carrier collection by incorporating ZnO nanowires in the device. We perform an optical simulation using three-dimensional finite-difference time-domain method to analyze optical effects of ZnO nanowires in the device. We also find that the heterojunction based system provides an additional benefit of amplified light absorption at specific regions by the photonic crystal effect, due to the refractive index difference between ZnO and Cu₂O.

Recent study on one dimensional (1D) metal oxide nanowires have drawn great attention due to their great application potentials in various fields such as electronics, optics and photonics. Among them, indium oxide (In2O3) nanostructure-based transistors, memory devices and gas sensors have been demonstrated. In2O3 has a wide band gap about 3.6-3.8 eV, and the as-prepared In2O3 nanostructures present in general n-type conductivity mainly due to the existence of oxygen vacancies. There are lots of applications of indium oxide nanowires. Here, we demonstrate In2O3 nanowires as the anodes of lithium ion battery.
In this work, we report the synthesis of highly conductive In2O3 nanowire arrays by chemical vapor deposition (CVD) method. The morphology, structure, and composition of the In2O3 nanowires were studied by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), and X-ray photoelectron spectroscopy (XPS). The battery performance of indium oxide nanowires grown on a stainless steel substrate for lithium-ion battery anodes was studied. The anode system possesses a high capacity of 500 mAhg-1 at 1C and excellent cycling stability (>500 cycles) when cycled in the range, 0.01-3.0V. The high cycling stability of In2O3 is outstanding among metal oxide anodes reveals the great stability of the assembly. It shows the great potential of In2O3 for application in the lithium ion battery field.

Solar hydrogen generation has attracted considerable interest since it promises clean, environmentally friendly energy generation. The first report of photoelectrochemical decomposition of water into hydrogen used an n-type semiconductor in photoelectrochemical cell under UV illumination and application of an external bias. Development of a hydrogen generation system that does not require an external voltage is critical for efficiently exploiting solar energy. Hydrogen generation from water without applying an external voltage requires p- and n-type semiconductor electrodes that can respectively decompose water into hydrogen and oxygen when illuminated by light. There have been many studies of high-efficiency n-type semiconductor photoanodes, however a few reports on high-efficiency, stable photocathodes for generating hydrogen. Therefore it is important to develop p-type semiconductors in order to build an efficient p- and n-type double electrode photoelectrochemical cell. In this study we demonstrate fabrication of p-type ZnO photocathode on transparent conductive electrode substrate. Until now various shapes of 1D n-type ZnO nanostructures (nanorods, nanowires, etc) have been fabricated in recent years by different techniques such as catalyst assisted thermal evaporation, solvothermal/hydrothermal route. However, the fabrication of high quality p-type ZnO nanostructures remains one of the challenges for the development of ZnO-based nano-devices. Arrays of n-type ZnO have been synthesized on FTO glass by solvothermal/hydrothermal techniques. The single crystalline ZnO nanorods have a diameter of ~120 nm and a length of ~2.0mu;m. Crystal structure and morphology of as prepared nanorods were investigated by XRD, FESEM and TEM. Photocatalytic properties, such as photocurrent and IPCE were examined under the one sun condition in the photoelectorchemical cell.

Photocatalysis has gained significant attention in the area of environmental cleaning and clean energy generation. NaTaO3 (band gap Eg = 4.01 eV) is a highly efficient photocatalyst for water splitting reaction under UV radiation. To utilize the visible radiation, a novel solid solution photocatalyst NaTaO3-LaFeO3 was developed, by doping LaFeO3 (up to 8%) into NaTaO3. The photocatalyst was characterized with various experimental techniques and its performance was tested for hydrogen evolution. Additionally hybrid DFT calculations were carried out to understand the origin of the photocatalytic activity.
Fe doped NaTaO3 and La-Fe co-doped NaTaO3 were prepared by solid state route. Fe doping induced intense visible light absorption (up to 550 nm) in NaTaO3 while La-Fe co-doping extended the visible light spectra up to 450 nm. Co-doping of La-Fe led to a compound with unique crustal structure and microstructure. The crystal structure studies showed that LaFeO3 and NaTaO3 formed a solid solution, as they share the same space group (SG No. 62, Pbnm) and have lattice parameters close to each other. TEM and FESEM studies indicated that the solid solution photocatalyst had surface nano-steps of 20-50 nm size. Although both photocatalysts showed visible light absorption, only co-doped NaTaO3 powders (i.e. solid solution) showed visible light driven hydrogen evolution upon Pt co-catalyst loading, under visible light radiation. The photocataytic activity of Fe doped NaTaO3 samples was found to be insignificant. In order to understand the origin of the photocatalytic activities, hybrid DFT calculations were carried out. These calculations provided an accurate description on the band structure of the mono-doped and co-doped NaTaO3. DFT studies showed that the visible light absorption originates on account of Fe 3d induced electronic states in both the cases. In the case of Fe mono-doping, the mid-gap states are unoccupied and thus electronic transitions from VB to mid gap states occur which gives rise to intense visible light absorption but it is not suitable for photocatalytic hydrogen reaction. On the other hand, La-Fe co-doping improves the band structure, by producing occupied mid-gap states close to the VB. The electronic transition from mid-gap states to CB is likely in this case, which is suitable for photocatalytic reactions. The optical properties from the experimental findings and DFT calculations agree well with each other. The results of DFT calculations and experimental findings on relevant doped NaTaO3 powders are presented in detail. The present study shows that modified NaTaO3 materials have promise to develop photocatalysts working under solar radiation. Further, the experimental and computational studies together contribute to the understanding of the doped photocatalysts.

Recently, many developments have occurred in the field of thin film solar cells with efficiencies enhanced by nanoscale light trapping. A variety of nanoparticles with wide band gap have been investigated, serving as antireflection, plasmonic enhancement in solar cells 1,2. Among them, zinc oxide (ZnO) is an ideal material with large band gap (3.3eV), making it transparent in both visible and near-infrared regime. ZnO nanoparticles with sizes comparable to the wavelength of the utilized solar spectrum could be used as broadband antireflective coating and light scattering layers for solar cells. In addition, nanoparticle films can be solution processed from precursor inks, enabling the use of simple, highly scalable fabrication process compatible with flexible substrates.
In this work, we coat a ZnO nanoparticle layer on top of Gallium Arsenide (GaAs) solar cell using pneumatic spray deposition. The spray coated ZnO nanoparticle film enhances GaAs solar cell efficiencies by strong antireflection and light scattering effects. The optical properties are characterized by absorption and transmission measurements over the spectrum from 350 nm to 900 nm. A ZnO coated cell shows over 30% absorption enhancement at wavelengths from 400 nm to 600 nm and near 20% enhancement from 700 nm to 900 nm compared to a control cell without coating. This light scattering effect is illustrated by the transmission measurement of ZnO coated glass with the same coating conditions as for GaAs solar cells. The haze factor is as high as 0.84 at 470 nm and above 0.5 in the near-infrared region. The spectral response of the solar cells was determined by the external quantum efficiency (EQE) measurement over a bandwidth of 350 nm - 900 nm. The ZnO coated cell has higher EQE from 400 nm to 900 nm compared to planar cell. This result is consistent with light absorption measurement. To optimize the sprayed ZnO nanoparticle film properties, three different surface densities on the top of GaAs solar cells are fabricated and characterized. The optimized structure shows a 16.3% short circuit current improvement and a 10.3% overall energy conversion efficiency improvement.
In conclusion, the highly scattering ZnO nanoparticle coating results in a broadband enhancement of the GaAs solar cell performance. The optimized nanoparticle coating results in a maximum efficiency improvement 10%. Moreover, this spray coating process can be used for a variety different kinds of fairly large band gap material particles, and can be also applied to other types of solar cells.
1. Jeong, S., McDowell, M. T. & Cui, Y. ACS Nano 5, 5800-5807 (2011).
2. Chen, C.-P. et al.. Nanotechnology 21, 215201 (2010).

Herein we present a simple synthetic method of 2-dimensional iron-oxide/carbon nanocomposites. Using iron oleate complex as the precursors for both iron oxide and carbon, highly monodisperse iron oxide nanoparticles and carbon materials were synthesized simultaneously via simple heat treatment. The iron oleate complex was prepared by “Heating-up” method.[1] Using sodium sulfate salt powder as template, 2-D nanostructure of the nanocomposite was created. Initially, highly ordered 2-D assembly of iron oxide nanoparticles embedded in carbon matrix was formed on the surface of salt particles during the heat treatment. Subsequently, the nanocomposite was easily separated by dissolving salt in water. We also prepared 2-D manganese-ferrite/carbon nanocomposite and 3-dimensional agglomerated iron-oxide/carbon nanocomposite which was prepared by not using a sodium sulfate salt as template. Crystalline structure and particle size of iron oxide nanoparticles could be controlled by the heating rate and temperature of heat treatment.
These nanocomposite materials were investigated their electrochemical properties as anode material for Li-ion secondary battery. The 2-D hybrid nanocomposites exhibited good cycling stability compare to the 3-D nanocomposite which is attributed to their unique thin-layered composite structure. Furthermore, even at a very high density of 5000 mA g-1, the capacity of the 2-D nanocomposites were retained as high as 81.5 % of the initial capacity. These results can be ascribed to merit of morphology for relaxation of the volume change and diffusion of lithium ion during the electrochemical discharge/charge reaction. The iron oxide nanoparticles maintained the shape and size in the 2-D iron-oxide/carbon nanocomposite electrodes during the charge/discharge cycling test.
The synthetic procedures are not only easily scalable for mass production but also extensible to various 2-dimensional metal-oxide nanoparticle/carbon nanocomposites which are potentially applied to practical energy storage and conversion devices, and catalyst such as fuel cells, solar cells, and electrochemical capacitors.
[1] Park, J.; An, K.; Hwang, Y.; Park, J.-G.; Noh, H.-J.; Kim, J.-Y.; Park, J.-H.; Hwang, N.-M.; Hyeon, T. Nat. Mater. 2004, 3, 891.

Three types of liquid, gel, and solid EC glass devices were made. The EC glasses have the same electrochromic electrode of WO3 film, and the same counter electrode of NiO film; but with difference ion layer of (a) 1M LiClO4-PC, (b) 1M LiClO4-PC + 2,2-Diethoxyacetophenone, and (c) Ta2O5 layer that divide devices into liquid, gel, and solid EC glass. The basic EC glass has a configuration of glass/ITO/WO3/ion layer/ ITO/glass. The ion layers for the liquid, gel, and solid type EC glasses were 1M LiClO4 + Propylene-carbonate, 0.1wt.% 2,2-Diethoxyacetophenone + 1M LiClO4 + Propylene-carbonate, and 50nm thickness of Ta2O5 layer on the EC electrode, respectively . For the liquid and gel types EC glasses, the two electrodes (EC electrode and counter) were assembled into a sandwich-type cell and sealed with hot-melt film, and electrolyte of ion layer were injected into the space between the two electrodes with a syringe. For the solid type EC glass, the EC electrode (WO3) with ion layer (Ta2O5 ) coating was first absorbs lithiun ions (Li+) in the 1M LiClO4 + Propylene-carbonate electrode under 5 voltage applied and used platinum (Pt) plate as counter then deposited NiO and ITO film to obtain a completely solid EC glass.

This work shows the synthesis and characterization of an environmental-friendly material, tungsten oxide-based nanowires (WO_x-based NWs), and its application for low-cost heterojunction solar cells. The heterojunction solar cell was fabricated by using WO_x-based NWs as a p-type material for full spectrum absorption. The nanostructure of WO_x-based NWs could be utilized to increase the contact area of p-type and n-type layer. The power conversion efficiency (PCE) of solar cells would be optimized by tuning carrier concentration, band gap, morphology, and crystallinity of WO_x-based NWs. The morphology and structure of WO_x-based NWs were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). The crystallinity of WO_x-based NWs was also measured by X-ray diffractometer (XRD). The band gap and absorption spectra were analyzed by UV-visible optical absorption spectroscopy and the PCE of heterojunction solar cells was measured by I-V measurement and solar simulator.

Fast charge transport in the TiO2 network is essential for effective charge collection, particularly in solid state cells where recombination is very fast. In order to increase the electron mobility, substantial efforts have been focused on developing one dimensional (1-D) TiO2 (polycrystalline nanotube and single-crystalline nanowire) electrode materials for solar cells application. However, there is little experimental evidence of substantially enhanced electron transport in these 1D nanostructure-based solar cells. For example, there is not much difference in electron transport between 1-D TiO2 nanotube and NP-based DSSCs. (e.g. K. Zhu, N. R. Neale, A. Miedaner, A. J. Frank, Nano Lett. 2007, 7, 69.) Herein, a rapid solvothermal approach was used to synthesize aligned 1D single crystal rutile TiO2 nanowire (NW) arrays on transparent conducting substrates as electrodes for dye-sensitized solar cells. Using these NW films, we demonstrate that the electron diffusion coefficient of single crystal rutile TiO2 NWs is more than two orders of magnitude higher than that of rutile NP films at the same photoelectron density. In light of these results along with good stability and high refractive index of rutile TiO2, constructing aligned arrays of 1D single crystal rutile TiO2 represents an attractive approach for solar cell and other optoelectronic applications, which, on the other hand, has not been paid much attention over the past several decades. The data presented here also suggest that it may be possible, by using proper texture and crystal orientation, to significantly improve the electrical transport properties of other oxide materials that currently have limited utility in solar cell and related applications because of their low carrier mobility.

Discovering new methods of forming organic-inorganic interfaces facilitate the development of improved photovoltaic and photocatalytic devices. Using XPS, FTIR, and AFM we have shown that it is possible to thermally graft uniform monolayers of aryl and benzyl halides to TiO2 surfaces with the loss of a halogen leaving groupnot;. This approach can be used as an alternative method for linking pi-conjugated molecules such as molecular dyes to TiO2 with a direct linkage between the metal oxide surface and the molecular aromatic system. NMR characterization of equivalent solution-based reactions indicates that the reactivity seen on the metal oxide surface is unique to the surface and does not occur in the solution phase. Currently, focus lies on understanding the interactions occurring between the molecule and the surface that allow this reaction to take place. FTIR, XPS, and density functional theory calculations provide new insights into how the structure of the surface and the nature of the molecule allow for this unique and unexpected reactivity seen at the metal oxide surface.

Solar Photoelectrochemical (PEC) water-splitting is a process of semiconductor-assisted decomposition of water into hydrogen and oxygen in the presence of sunlight. Several materials systems have been and are being examined in this context but the current drive is towards the use of non-silicon, earth-abundant nanostructured materials in the interest of cost effectiveness. Among various nanostructures, quasi 1D nanostructures (nanorods, nanowires, nanotubes) have been attracting quite an attention recently because they provide a direct pathway for efficient and confined charge transport along with more surface accessibility for the electrolyte, which is useful for efficient PEC cell.
Cuprous oxide (Cu2O), a p-type semiconductor, is currently attracting attention of researchers as a photocathode material in PEC cell. Cu2O has many advantages such as its proper band gap (~2 eV) for the absorption of visible light, favourable conduction band position (~0.7 V negative of hydrogen evolution potential) etc. We have thus synthesized cuprous oxide nanoneedles by simple anodization method followed by controlled annealing directly on copper substrate. The Cu2O nanoneedles film is then studied for PEC application. The as-prepared Cu2O nanoneedles show excellent performance with current of ~1.2 mA/cm2 at 0 applied bias Vs reversible hydrogen electrode (RHE) under AM1.5 illumination (100 mW/cm2) in the presence of aqueous 50 mM Na2SO4 electrolyte. The major drawback of Cu2O as a photocathode for water splitting is its instability in aqueous solutions under illumination. To decrease this instability, we have developed a strategy to modify its surface by using a simple chemical technique. By this method, we have observed that the performance of the p-Cu2O photocathode also improves further. These interesting set of data will be presented and discussed.

Since Gratzel and coworkers reported dye-sensitized solar cells (DSCs) in 1991, three-dimensional networks of TiO2 nanoparticles were most frequently used as DSCs photoanodes. The networks of TNPs offer a high internal surface area for anchoring large quantities of dyes for maximizing light harvesting, but this nanoporous film have numerous sites of recombination recations during electron diffusions, and these recombinations is one of major factors limiting device performance. On the other hand, aligned TiO2 nanotubes (TNTs) provide an alternative electron transport material that reduces charge recombination and increases electron collection relative to conventional disordered TNPs channels. Anodized TNTs on Ti foil are most frequently employed as photoanodes, but opacity of the Ti substrate, it requires back-side illuminations which decreased light harvesting. Several reports have suggested the preparation of freestanding TNTs membrane, but most reports described fabrication of one-side closed TNTs membrane, and only few reports are introduced making both open-ended TNTs, but these methods have some problems in fabricating process and hard to follow. In this study, we describe a simple selective etching method that produces noncurling, freestanding, large-area, aligned TNTs with both ends opened. The novel selective etching process only removed the thin 2nd bottom layer from the physically and chemically stable thick amorphous 1st top layer under thermal treatment at 250°C, yielding ordered doubly open-ended TNTs that could be easily transferred to an FTO substrate for the fabrication of front-illuminated dye sensitized solar cells (DSCs). The TNT-DSCs yielded a higher PCE (8.6%) than was observed from TiO2 nanoparticle-based DSCs (7.3%), for comparable film thicknesses of 16 micro meter, despite the use of 20% less dye. Intensity-modulated photocurrent and photovoltage spectroscopy (IMPS and IMVS, respectively) revealed that the TNT-DSCs exhibited electron lifetimes that were 10 times longer than those of TNP-DSCs, which contributed to high device performances
References
1) J. Choi et al., Chem. Commun. 2012, 48(70), 8748-8750.

Manganese dioxide (MnO2) is considered to be a promising transition metal oxide for the next generation of supercapacitors because of its ideal capacitor performance (1370 F/g), environmental friendliness, and high-power density. However the poor electric conductivity (10-5 ~ 10-6 S/cm), and the brittle property of the MnO2 limits the high power performance and flexibility of the device. We introduce a highly flexible and high power maintaining supercapacitor by fabricating a thin MnO2 coating on multiwall carbon nanotube (MWNT) yarn by thermal decomposition method. It exhibited high electrochemical performance with energy density and power density. The MnO2/MWNT yarns also retain their capacitance and resistance value after bending and overhand knot since the yarn exhibits good tensile strength These results represent that the MnO2/MWNT yarn can be a promising work for the lightweight and micro sized energy storage application.

We have demonstrated charge transport and recombination properties of dye-sensitized solar cells (DSSCs) based on 3D TiO2 inverse opal electrodes. The 3D TiO2 inverse opal structures were fabricated using a TiO2 nanoparticles in polystyrene colloidal crystals template. Their morphology, crystalline and surface states of the 3D TiO2 inverse opal structures were characterized by SEM, TEM and XPS analysis. The charge transport and recombination properties of DSSCs for conventional nanoparticles TiO2 electrode and TiO2 inverse opal electrode were studied by the intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS) measurement. The 3D TiO2 inverse opal electrodes showed enhancement of transport times and recombination in comparison with TiO2 nanoparticles electrodes. The recombination times of 3D inverse opal electrodes was remarkably longer by 4.3 ~ 6.2 times, indicating that the 3D inverse opal based DSSCs have 10% higher charge collection efficiency than the DSSCs for nanoparticles. Although, the 3D inverse opal structure have less dye adsorption due to their macro pores, the 3D TiO2 inverse opal based DSSCs showed a comparable JSC and conversion efficiency compared to the TiO2 nanoparticles based DSSCs due to higher charge collection efficiency and light scattering properties.

Bismuth ferrites crystallites were synthesized by a polyvinyl alcohol (PVA) modified hydrothermal method using Fe(NO₃)₃#9679;9H₂O and Bi(NO₃)₃#9679;5H₂O as starting materials with NaOH as the mineralizer. The phase evolution of bismuth ferrites between sillenite Bi₂₅FeO₄₀, perovskite BiFeO₃ and orthorhombic Bi₂Fe₄O₉ in the process of hydrothermal reactions was controlled by adjusting the process parameters, such as initial Bi:Fe ratio, NaOH concentration, reaction temperature and duration time et al. X-ray diffraction (XRD) analysis indicates that the pure phase of BiFeO₃ could be synthesized under the reaction temperature of 200 °C for 24 h with C_NaOH of 5.0 mol#9679;L^-1 and the initial Bi:Fe ratio of 1:1. Meanwhile, Bi₂₅FeO₄₀ could be obtained with C_NaOH of 2.0 mol#9679;L^-1 and Bi₂Fe₄O₉ could be obtained with increasing C_NaOH of above 10 mol#9679;L^-1 under the same reaction conditions. As the reaction temperature and duration time were tuned, there would also be a similar phase evolution of bismuth ferrites. With addition of PVA, the individual Bi-Fe oxides could be existed in a more wide range of processing parameters. The mechanism of forming different bismuth ferrites in the hydrothermal process was investigated and discussed. Moreover, photocatalytic properties of the bismuth ferrites crystallites were explored as well. The results showed that they had a bandgap of about 2.2 eV and performed a good degradation effect at visible light region.

Flexible and lightweight energy storage systems have received tremendous research interest recently due to their potential applications in wearable electronics, roll-up displays and other devices. To manufacture such systems, flexible electrodes with desired electrochemical and mechanical properties are critical. Here we present a novel method to fabricate flexible electrodes for asymmetric supercapacitors based on the nanocomposites made with electroactive oxide materials and carbon nanotubes and/or graphene. The proper combination of the unique properties of each nanomaterials enable highly flexible and mechanically strong films that can serve as electrodes directly without using any current collectors or binders. Specifically, the electrodes fabricated with graphene, nanotubes and MnO2 exhibited outstanding mechanical properties (tensile strength of 48 MPa) and superior electrochemical activity that were not achieved by any of these components alone. The combined effects from nanotubes and graphene ensure high active material loading (~ 71wt% MnO2), areal density (8.80 mg/cm2) and high specific capacitance (372 F/g). Similarly, the electrodes made with carbon nanotubes and activated carbon also exhibited strong mechanical strength and improved electroactivity under high mass loading densities and high current conditions. Employing a roll-up approach and using flexible MnO2 electrodes as the positive electrodes and the flexible activated carbon electrodes as the negative electrodes , asymmetric supercapacitors with 2 V working voltage were successfully fabricated. The fabricated device showed excellent rate capability, demonstrating 78% of the original capacitance when the scan rate was increased from 2 mV/s to 500 mV/s. Owing to the unique composite structure, these supercapacitors were able to deliver high energy density (24 Wh/kg) under high power density (7.8 kW/kg) conditions. These features could enable supercapacitor based energy storage systems being very attractive for a variety of critical applications, such as the power sources in hybrid electric vehicles and the back-up powers for wind and solar energy, where both high energy density and high power density are required.

Bismuth ferrite, BiFeO3, (BFO), in its polycrystalline and thin film forms, is probably the most intensively studied functional oxide in the past few years in view of its very interesting multiferroic properties. However, it is beginning to be realized that the material could display many interesting application-worthy properties by appropriate doping and chemical manipulation, especially on the nanoscale. Here, we present results of photoelectrochemical activity studies on calcium doped bismuth ferrite nanoparticles with nominal composition Bi1-xCaxFeO3, where x=0 and 20%. The nanoparticles were synthesized via sol gel route. The powders were annealed in two steps; 400C in three separate runs and further annealed at 550C for 30 minutes. X-ray diffraction showed the formation of pure BFO phase and the appearance of Fe3O4 and Bi6Ca4O13 phase was noted above the solubility limit. Diffuse reflectance spectra were measured and converted into absorption readings using the K-M method. It showed that all the samples in the Ca doped BFO series have direct band gap and can absorb light in the visible region, the value for pure BFO being 2.22 eV reducing down to 2.12 at 20 % Ca doping content. the photoelectrochemical activity of BFO and BCFO was measured by cyclic voltammetry performed in 0.5M NaOH under simulated solar radiation as well as in dark. It shows photo current of 397 µA/cm2 at -0.38 v for pure BFO increases to 839 µA/cm2 for 20% Ca content with respect to Ag/AgCl reference electrode. Ca doping showed significant enhancement of BFO photocatalytic activity and decomposition of organic dyes. The current results along with previous reports indicate that BFO and BCFO could be promising materials for photoelectrode, photocatalytic and water splitting applications.

ZnO nanotetrapod (ZnO-TP) photoanodes have been fabricated by a simple thermal evaporation method followed by characterization of their morphological, structural, optical and photoelectrochemical properties. The reaction time was found to be a critical factor in the synthesis of well-defined tetrapod nanostructures. The crystallinity of the grown tetrapods was investigated using X-ray diffraction as well as Raman spectroscopy. The photoluminescence (PL) spectra of the fabricated ZnO nanostructures showed two peaks; a near-band-edge (NBE) emission in the UV region and a broad deep-level emission (DLE) in the green emission region. Used as photoanodes to photoelectrochemically split water, the 90 min-treated ZnO-TP electrodes showed a photocurrent density of 0.4 mA/cm2 under AM 1.5G illumination (100 mW/cm2, 0.5 M Na2SO4), a significantly greater photocurrent than the bulk ZnO counterpart electrodes. The transient photocurrent measurements revealed exceptional stability of the as-fabricated ZnO-TPs.
References:
Hassan, N. K.; Hashim, M. R.; Allam, Nageh K., 2012, Chemical Physics Letters, Volume 549, p. 62-66.

The nanostructures of Fe2O3, Co3O4 and NiO possess physical properties that have aroused increasing attention as they have potential applications in many fields, for example NiO is a useful semiconductor and antiferromagnetic material, used in gas sensing and catalysis. The high chemical reactivities of nanoparticulate metal oxides towards adsorbates can be attributed not just to high surface areas, but also to unusually reactive morphologies. The reactivity and selectivity of catalysts have a large dependency on the arrangement of surface atoms and the number of dangling bonds on various crystal planes. Nanocrystal catalysts of various shapes with different uniform crystal planes exposed therefore, are important in the investigation and enhancement of catalytic properties. The use of biotemplates to encourage growth of specific morphologies has become a useful tool in the development of highly active catalysts.
We studied the effect of a chitosan template on the growth of the oxides Co3O4, Fe2O3 and NiO. Chitosan (2-amino-2-deoxy-β(1→4)-D-glucan) is produced through the deacetylation of chitin and has the ability to preferentially sequester transition metal ions from aqueous solutions. This sequestering effect is one of the properties which make biological templates attractive: high porosity and surface chemistry are also attractive features of biopolymers. We have demonstrated successfully the synthesis of these metal oxides using the biotemplated approach and High resolution TEM revealed the active (111) face of Co3O4 was over-expressed by this synthesis. Average particle sizes of 100nm, with an octagonal morphology were produced, with exposed interplanar angles of 135°. The NiO crystals synthesized had a cuboid morphology with crystal sizes of 25 - 40 nm. Metal oxides were synthesized both in the presence and absence of biotemplate.

Fe3O4 due to its high specific capacity, is known as a material of choice for lithium-ion battery anodes. But it has drawbacks such as low conductivity and poor cyclic performance etc. To address these limitations, free-standing Fe3O4/Graphene/Carbon nanotube(CNT) films were prepared via hydrothermal reaction methods. The synergistic effect of graphene and CNTs provide a flexible matrix for Fe3O4. A series of experiments were performed to determine important processing factors such as composition, annealing treatments that affect the overall performance of the electrodes. Currently the best film had a sheet resistance of 23 Omega;/sq and a BET surface area of 132 m2/g. In addition, the lightweight films were directly tested as lithium-ion battery anodes without using a current collector or a binder, eliminating unnecessary weight in the overall devices. The discharge capacity was found to reach 880 mAh/g at 200 mA/g current density and 580 mA/g at 400 mA/g. The rate capability tests (from 200 mA/g up to 1200 mA/g) also indicated that the lab prepared Fe3O4 loaded films have much better performance as compared to the samples made by using commercial Fe3O4. The metal oxide to graphene ratio was optimized for both high specific capacity and excellent cyclic stability. The details of the processing method with a promising path for flexible energy storage devices will be discussed.

There is a critical need for improved methane-oxidation catalysts to both reduce emissions of methane, a green-house gas that will soon be regulated, and significantly enhance the efficiency of power generation in gas turbines. Presently available, emissions-control catalysts are notoriously ineffective at reducing CH4 in exhaust streams. High-temperature combustion also results in the emission of toxic nitrogen oxides (NOx) and CO. Combustion of CH4 promoted by heterogeneous catalysts could utilize the available energy of methane at lower temperatures, increasing efficiency and limiting emissions by drastically reducing the required temperatures. Materials for this application must also be catalytically and mechanically stable at high reaction and flame temperatures. PdOx is recognized as one of the best catalysts for catalytic CH4 oxidation. Unfortunately, Pd-based catalysts tend to deactivate, both due to the loss of active surface by sintering and due to the transformation into the less active but thermodynamically favored metallic Pd phase at temperatures above 600 °C. Although alumina is a commonly employed support, both experimental and theoretical studies reveal that ceria (CeO2) can improve the catalytic activity of supported Pd due to the stabilization of PdOx species. Materials that could simultaneously enhance the performance of Pd-based catalysts at low temperatures and limit deactivation at elevated temperatures would greatly improve the viability of catalytic CH4 combustion processes.
In this contribution, we report on a novel, hierarchical design of core-shell type catalysts that is inspired by the concepts of supramolecular chemistry. Two active building blocks, Pd and CeO2, are prepared separately, then self-assemble and organize in solution to form supramolecular core-shell structures held together by metal ion-ligand coordination chemistry. We exploit the pre-organization of the functionalized Pd@CeO2 core-shell structures to disperse single units onto a modified, catalytically inert alumina carrier. Transmission Electron Microscopy (TEM) investigations demonstrate that it is indeed possible to deposit single structures where the metal-promoter interaction is maintained even after severe thermal treatments at temperatures up to 850 °C. The special configuration of the hierarchical catalyst gives rise to exceptionally high and stable performance for the catalytic combustion of methane with reduced amounts of Pd and ceria. The particular geometry appears to stabilize the active phase of the catalyst, not only preventing agglomeration of palladium oxide particles during the catalytic reaction but also preventing the PdOx from being transformed to Pd at its usual transition temperature.

This research is to achieve a solid-state ultracapacitor based on alumina nanotube (AAO NT) with large surface to deposits high-k dielectric and metal electrodes. Unlike type of wet type capacitor which requires electrolyte connecting to operate, and multilayer ceramic capacitor (MLCC) which requires multiple fabrication processes, the solid-state ultracapacitor offers high capacitance, light weight, lost-cost, simple process, mass-production, and thermostable advantages. The approach is to explore the high capacity and thermostable solid-state ultracapacitor. The approach is expects to provide both light weight but large active surface area to significantly boost the achievable the capacitance. The electrochemical processes of anodization, electro-deposition, electroless-deposition, and sol-gel depostion will be investigated to fabricate a thin film solid-state ultracapacitor under ambient conditions, thereby enabling low-cost and mass production of the capacitor. We will also characterize the solid-state capacitor to achieve a high capacitance and thermostable properties.

A graphene sheet is an excellent electron-acceptor with superior conductivity due to its two dimensional (2D) π-conjugation structure. The wrapping of a 1D graphene sheet around an inorganic nanofiber is still unexplored, and its predicted extraordinary properties (such as superior electron transfer abilities) are unconfirmed. In this work, we report a facile method for fabricating a new nanocable structure consisting of reduced graphene oxide (RGO) wrapped anatase TiO2 nanofibers by UV-light photocatalytic reduction. The nanocable was prepared by injecting 0.8 g/L aqueous graphene oxide colloid into 0.8 g/L electrospun TiO2 nanofibers in ethanol, followed by a mild UV light irradiation for 20 h. The conformal wrapping of RGO is a result of noncovalent interactions (van der Waals and electrostatics). The RGO walls of the nanocables exhibited a uniform thickness of ~5 nm. Half of the oxygen groups were removed and the partially reduced RGO was favored to be well dispersed in water. The thickness of the RGO nanowalls could be precisely controlled between 3 and 5 nm by simply adjusting the concentration of the GO, while the reduction degree of the RGO was found to be inversely proportional to such concentration. The invariability of the ID/IG ratio of the D to G bands in Raman spectra proposed the presence of a “defect-repair” process in the reduction. We further demonstrated the enhancement of photoinduced electron transfer and depression of electron combination by integrating the RGO/TiO2 nanocables into TiO2 photoanodes. The enhancement of photocurrent in the photoanodes integrated with an optimized 5 wt% RGO/TiO2 nanocables results in longer electron lifetime and a 2/3 reduction of the charge transfer resistance (Rct). Their excellent electrical characteristics prove the nanocable to be a good candidate for the collection and transport of electrons in electrodes. The synthesis strategy presented here should be applicable to other RGO wrapped 1D nanostructures with different compositions and diameters, and allows for a range of photovoltaic devices and energy storage applications.

Akaganeite is an iron oxy-hydroxide (β-FeOOH) that forms as a bundled cluster of nanotubular crystals. Under select growth conditions, these nanocrystal assemblies form particles shaped like small grains of orzo pasta. These unique nanoporous materials offer potential utility as pigments, catalysts, even elements of electrochemical energy storage systems. Naturally, the ability to control the size, shape, and nanoscale morphology of these crystals stands to dramatically impact their potential applicability. We explore here the influences of organic acids, such as citric acid, on akaganeite crystal growth. Because akaganeite grows as an aligned assembly of nanocrystal tubules, modifying the size and shape of these particles involves controlling multiple stages of crystal nucleation and growth. In the present work, we show that citric acid is particularly well-suited to akaganeite modification and can be used to control both elongation of growing nanocrystalline tubules and secondary formation of nanotube bundles. We describe the synthesis and characterization of these modified materials and explore the mechanistic interactions between citric acid and these complex crystalline nanostructures. Investigating the complex organic-inorganic interfaces in this modified akaganeite system may provide key insights into controlling crystal growth in additional materials systems.
Sandia National Laboratories is a multi program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

ZnO has been considered a promising material for gas sensors, solar cells, UV light-emitting diodes, field emission devices, piezoelectric nanogenerators, and nanopiezotronics. During the last years, advancements in preparation methods improved the electrochemical and electrophysical parameters of ZnO. Investigations have shown that the variations of shape and size of nanostructured ZnO enlarged its application. Therefore it is very important to control the size and the shape formation of nanostructured ZnO during the growth.
We have developed a new chemical route for ZnO nanostructures preparation that combines electrochemical anodization and thermal annealing in a very convenient technique to obtain crystalline nanostructures on stiff (alumina, silicon and glass) and flexile (Kapton®) substrates. The preparation parameters like the type and the concentration of electrolyte, the anodization voltage and the current have been tailored to obtain the nanosized ZnO structure. The structures are composed by nanoparticles forming elongated aggregates with chain-like morphology. The diameter of particles is ranging from 15 to 70 nm and length of chains is more than 1 µm. The optical properties of ZnO nanostructures have been studied by continuous wave PL at room temperature: all samples exhibited typical ZnO emission spectrum composed of exciton UV peak and defect band in the visible range. By increasing the annealing temperature from 350 to 400°C we observed an increased ratio of UV to visible peak thus indicating better quality of the treated ZnO nanostructure for sample with smaller structures. The chemical sensing characteristics of the structures have been tested towards ethanol, acetone, carbon monoxide and nitrogen dioxide. The sensor response is quite high and the recovery of the signal is almost complete.
These preliminary results have shown that ZnO nanostructures are interesting for chemical sensing, the low temperature process allow preparation on many types of substrates, even flexible ones. The prepared nanostructures also could have novel applications in optoelectronics and biomedical science.

ZnO is a group II-VI semiconductor with a large band gap, exciton binding energy at room temperature and unique properties such as high thermal stability, near band emission, piezoelectricity, transparent conductivity, natural abundance and non-toxicity. Such properties make ZnO a potential candidate for a variety of applications including optoelectronic devices, chem-bio and gas sensors, solar cells, field emission devices, transistors and lasers for room temperature operation. However, due to the difficulties in the realization of reproducible p-type ZnO, it is challanging to fabricate stable high quality ZnO based homojunctions, which are essential for designing various optoelectronic devices. In this work, high aspect ratio vertically oriented micro-scale one-dimensional (1D) pillars and two-dimensional (2D) walls were fabricated on a p-type silicon (Si) wafer using the top down fabrication processes. These structures are then conformally coated with a dense array of n-ZnO NWs (~300 nm in length and 50-80 nm in diameter) subsequent to a thin film pre-coating of aluminum-doped-ZnO (AZO) on the Si structures via a hydrothermal growth technique. The resulting three-dimensional (3D) heterostructures of n-ZnO/p-Si were characterized and compared with their planer counterparts for varieties of applications including solar cells, chem-bio sensors, photodetectors and field ionization gas sensors.

New and unexpected physical properties that are absent in their individual bulk constituents have triggered intensive research interest in polar oxide heterostructures. Recent technical advances in the fabrication of atomically abrupt oxide interfaces enable the formation of high mobility two-dimensional electron gases (2DEG) at ZnMgO/ZnO polar oxide interface. The significant results promise potential application of polar oxide interfaces in new generation of electronics. The mechanism of interface conduction was reconciled by the polar discontinuity at interface and the carriers were originated from the surface states. In this work, we investigated the modulation of UV irradiation and solvent polarity on carrier dynamics and transport properties at ZnMgO/ZnO heterointerface. Firstly, we demonstrated the presence of negatively charged excitons at ZnMgO/ZnO interface. Distinct features between the neutral donor bound exciton and free exciton are detected both in time-resolved photoluminescence and photoluminescence excitation spectra and it is identified to be the radiative recombination related to two dimensional electron system at the heterostructure interface. Moreover, the UV photo-response properties have been investigated based on the Pd/ZnMgO/ZnO Schottky structure. The devices exhibit a different gain enhancement at reverse and forward bias, which is related to the transport of minority carriers at metal-semiconductor interface and 2DEG channels. In addition, we also demonstrated the modulation of polar solvent on transport property of Pd/ZnMgO/ZnO Schottky diode. The experimental facts exhibited that when the polarity of solvent on the unprotected ZnMgO surface area increased, the current at reverse bias of diode increased exponentially, and the rectifying characteristics will be recovered as the solvent adsorption was dried out. The reversible modulation of conductivities and diode features by the adsorption of polar solvent molecules can be understood in the view point of effective barrier height reduction and chemical interaction of surface charges. The interesting results suggested such a fascinating interface system can be used for high-performance UV photodetectors and smart sensors of polar liquids.

ZnO nanowires (NWs) have in recent years attracted considerable research interest as a promising material system for novel functional devices. Moreover, when alloyed with transition metals (TMs) such as Ni, Cr, Mn, etc, ZnO exhibits ferromagnetic properties at and above room temperature. This makes it a promising candidate for future devices with spin-enabled functionality, e.g. spin-polarized light sources. However, doping with TMs often degrades intensity of near-band-edge (NBE) emissions in ZnO and hence hinders this material from photonic applications. In this work we suggest to circumvent this degradation by coating ZnO NWs with TM particles with the purpose to enhance their radiative efficiency by utilizing the interaction of light due to excitonic emission in ZnO and surface plasmons (SP) arising from collective electron excitations in the TM coating.
We show that coating ZnO NWs with a transition metal, such as Ni, increases efficiency of light emission at room temperature. Based on time-resolved photoluminescence measurements, this enhancement is attributed to energy transfer between near-band-edge emission in ZnO and surface plasmons in the Ni film which leads to an increased rate of the spontaneous emission. It is also shown that the Ni coating leads to an enhanced non-radiative recombination via surface states, which becomes increasingly important at low measurement temperature and in annealed ZnO/Ni NWs. Our results provide a direct proof that SP-mediated enhancement of light emission can be achieved in the ZnO/TM system which is promising for future efficient light emitters with spin-enabling functionality.

Metal oxide-based hetero-structures such as metal oxide/CNTs find important applications in gas sensing and electrocatalysis. Atomic Layer Deposition (ALD) has proven to be an elegant approach for the homogeneous and conformal coating of flat surfaces as well as complex and high surface area nanostructures with a thickness control at the atomic scale.
ALD is therefore ideally suited for the fabrication of functional hetero-structures.1, 2 Film growth is based on subsequent gas-surface reactions and requires anchoring sites for the growth initiation. Depending on the density and nature of functional surface species principally two ALD growth modes can be expected, i.e. a 2D growth mode and a 3D, few-layer island growth mode.3 Depending on the film thickness, intermediate cases can be observed when the growth mode switches from an initial island growth to a 2D growth once the islands have coalesced to form a continuous layer. Hence, the controlled tailoring of the type and density of the functional groups used as nucleation sites and anchoring points for the oxide during ALD, would enable to tune the growth mode and therefore the ALD coating, i.e. from uncoated to selectively decorated up to a fully coated substrate.
In a previous work, J.P. Tessonnier et al. demonstrated that thermal treatment permits the control of the degree of graphitization of the tube walls and that the carbon nanotubes (CNTs) surface graphitic character influences the type and density of surface groups created during functionalization by nitric acid treatment.4 Based on this work, using a non-aqueous sol-gel approach to atomic layer deposition,5 we demonstrated that the controlled tailoring of the type, degree and density of functionalization of the CNTs surface allowed us to tune the coating from selectively decorated up to fully coated CNTs.6 This is of interest for designing functional heterostructured CNT based materials.
Here we will report the tailored deposition of various metal oxides on carbon based nanostructures, by controlling their surface functionalization. Furthermore, we will demonstrate the application of this approach to the functionalization and coating of electrospun carbon fibers, which allows tuning the electrocatalysts activity. Finally, the properties of gas sensors made of metal oxide-coated CNTs will be also presented.
References:
1. M. Knez, K. Niesch and L. Niinisto, Adv. Mater., 2007, 19, 3425-3438.
2. C. Marichy, M. Bechelany and N. Pinna, Adv. Mater., 2012, 24, 1017-1032.
3. R. L. Puurunen, Journal of Applied Physics, 2005, 97, 52.
4. J.-P. Tessonnier, D. Rosenthal, F. Girgsdies, J. Amadou, D. Begin, C. Pham-Huu, D. Sheng Su and R. Schlogl, Chem. Commun., 2009, 7158-7160.
5. E. Rauwel, G. Clavel, M. G. Willinger, P. Rawel and N. Pinna, Angew. Chem.-Int. Edit., 2008, 47, 3592-3595.
6. C. Marichy, J.-P. Tessonnier, M. C. Ferro, K.-H. Lee, R. Schlögl, N. Pinna and M.-G. Willinger, J. Mater. Chem., 2012, 3, 7323-7330.

For good performance of photonic devices whose working principle is based on the enhancement of electromagnetic fields obtained by confining light into dielectric resonators with dimensions in the nanometre length scale, a detailed knowledge of the optical mode structure becomes essential. However, this information is usually lacking and can only be indirectly obtained by conventional spectroscopic techniques. Here we unraveled the influence of wire size, incident wavelength, degree of polarization and the presence of a substrate on the optical near fields generated by cavity modes of individual hexagonal ZnO nanowires by combining scanning near-field optical microscopy (SNOM) with electrodynamics calculations within the discrete dipole approximation (DDA). The near-field
patterns obtained with very high spatial resolution, better than 50 nm, exhibit striking size and spatial dispersion effects, which are well accounted for within DDA, using a wavevector-dependent dipolar interaction and considering the dielectric anisotropy of ZnO. Our results show that both SNOM and DDA simulations are powerful tools for the design of optoelectronic devices able to manipulate light at the nanoscale.

ZnO is a II-VI semiconductor with a wide direct bandgap of 3.37 eV and an exciton binding energy of 60 meV. These properties make it potentially a more thermally stable optical emitting material at room temperature than the widely used semiconductor GaN, which has an exciton binding energy of 25 meV.
Room temperature photoluminescence (PL) spectra of ZnO show two primary emission peaks: one peak centered at 3.37 eV attributed to band-edge exciton recombination, and a broader peak centered around 2.3 eV due to superposition of donor-acceptor-pair recombination from near conduction-band electron states to hole states in oxygen vacancies and Zn interstitials. By coupling luminescent centers in the ZnO to nearby plasmonic elements in the form of metal nanoparticles or rough metal films, these emission bands can be variously enhanced or quenched. Many studies on the effects of plasmons on the photoluminescence of ZnO have examined ZnO in a two-dimensional films or quantum wells. However, much recent interest has focused on ZnO in one-dimensional nanowire assemblies.
Here we present recent experimental results on plasmon-mediated-photoluminescence in ZnO-MgO core-shell nanowire structures. Arrays of vertically-oriented ZnO nanowires are grown by a modified vapor-solid method inside a vertical furnace on a crystalline ZnO template. The sides of the ZnO nanowires are then coated with a shell or spacer layer of MgO via electron-beam evaporation using a glancing-angle deposition apparatus; functionalization of the core-shell structures occurs by depositing Ag nanoparticles in the same apparatus. Electron microscopy confirms the uniformity of the core layers, making it possible then to study the strength of exciton-plasmon coupling by varying the thickness of the MgO shell while measuring its effects on ZnO photoluminescence.
Photoluminescence studies were carried out using a He-Cd laser (325 nm) as the excitation source. In PL studies of the Ag-functionalized core-shell nanowires, strong quenching occurs for the visible emission independent of the MgO thickness. In contrast, the band-edge emission displays a nearly linear increase in enhancement factor of as much as 20 as the nominal thickness of the MgO spacer is increased from 10 to 60 nm. The PL enhancement is consistent with the Purcell mechanism assuming dipole-dipole coupling between excitons and the Ag localized surface plasmons.
Nanowires without Ag were also studied to decouple plasmonic effects from potential optical cavity effects due to the MgO shell. Without the Ag nanoparticles, the PL of the core-shell nanowires shows an oscillation in enhancement with increasing shell thickness, with a surprising and still unexplained minimum in the PL enhancement at a shell thickness of 30-40 nm.
Through this research, it will be possible to effectively tailor the emission properties of ZnO for optoelectronic applications such as light-emitting diodes, nanowire lasers and sensors.

Discovery of photovoltaic effect in multiferroic material explores an alternative way of photovoltaic research. Without the need a conventional p-n junction, this perovskite structured material is able to separate the photogenerated charge carrier. The non-centrosymmetric behavior makes this material polarized and this spontaneous in built polarization is responsible for charge separation. However, the reported external power conversion efficiency of some promising material such as BiFeO3 (BFO) and Bi2FeCrO6 (BFCO) till now is quite low. The crystal structure and quality of as prepared material is basically sensitive to these PV properties. Besides, notion of heterostructure in multiferroic material comes from common compound semiconductor gives an order of flexibility of tuning PV properties. Preliminary results revealed that BMO thin films exhibit pronounced power conversion efficiencies under 1.5 AM light illumination. Here in this report, we will represent in particular, the epitaxial growth, electrical, and optical properties of Bi-Mn-O thin film system together with the synthesis of heteroepitaxial BiMnO3 (BMO) and BFO structure and their optical properties deposited by pulsed laser deposition on single crystal substrate.

We present a study of the electronic properties, relevant to hole-transporting materials in solar energy conversion applications, of NiO synthesized by a new ALD process. The accepter concentration, flat band potential, and valence band position were determined by electrochemical Mott-Schottky analysis of impedance data for films less than 100 nm in thickness . The effects of post-deposition annealing and film thickness reveal oxidation of the NiO at temperatures as low as 300 C in 1 atmosphere of oxygen. Films annealed at 400 oC and above in Ar exhibited signs of thermal decomposition. Thinner films were found to have a higher carrier concentration. A p/n heterojunction diode was fabricated from transparent ALD TiO2 and NiO layers with the structure that show rectifying behavior.

Over the past few decades, the excellent luminescence of Eu-doped yttrium oxide (Y2O3:Eu3+) powder phosphors has lead to their widespread use as red components in plasma display panel and fluorescent light [1, 2]. 2D (Two-dimensional) PCL (photonic crystal layer) have been applied to various light emitting devices incorporating luminescent film materials in an attempt to enhance their extraction efficiency [3]. Recently, we have reported 2D TiO2 nanoparticles PCL on Y2O3:Eu3+ phosphor films [4]. This method can enhance the extraction efficiency, which is limited to approximately 7.0% in Y2O3:Eu3+ phosphor films by the total internal reflection (TIR). In this study, we examined the height effects of 2D ZrO2 nanoparticles PCL on the photoluminescence properties of annealed Y2O3:Eu3+ phosphor films fabricated by sol-gel method [4].
The 2D ZrO2 nanoparticles PCL-assisted Y2O3:Eu3+ phosphor films were fabricated using two successive processes, preparation of the Y2O3:Eu3+ phosphor film and fabrication of the 2D ZrO2 nanoparticle PCL. The Y2O3:Eu3+ phosphor films were prepared by Pechini-type solution-based material process and spin-coating method. The 2D hexagonal-lattice hole patterns of ZrO2 nanoparticles PCL were generated on the Y2O3:Eu3+ phosphor films by one step reverse nano-imprint lithography. The trimethylolpropane propoxylate triacrylate (TPT)/Polydimethysiloxane (PDMS) reverse nano-imprint stamp was replicated from a quartz master mold that was patterned using nanosphere lithography (NSL). The TPT/PDMS stamp filled with ZrO2 nanopartices was then reverse-imprinted onto the Y2O3:Eu3+ phosphor film substrate with a pressure of 10 atm at 100 dgree celsius for 25min. After detachment of TPT/PDMS stamp, sub-micron size PCL patterns of the ZrO2 nanoparticles were formed directly on top of the Y2O3:Eu3+ phosphor film. The sizes of the ZrO2 nanoparticles used in patterning ~ 580 nm were 20 ~ 40 nm. We controlled the height of the ZrO2 nanoparticle patterns by varying the height of master mold, and the height of 2D ZrO2 nanoparticle hole patterns were in the range 200 ~ 370 nm.We observed the effects of 2D ZrO2 nanoparticle photonic crystal patterns on the light extraction efficiency of phosphor films. This simple process results in a 2D ZrO2 nanoparticles PCL (h = ~ 370 nm), where the extraction efficiency was improved by 6.87 times compared to the conventional Y2O3:Eu3+ phosphor films.

Today, organic light emitting diodes (OLEDs) and displays have achieved commercial relevance due to their unique contrast and low power consumption. While most state-of-the-art OLEDs for OEM applications are deposited in vacuum, science and industry work hard on solution processable and hence potentially low-cost fabrication alternatives. The main objectives are to overcome solvent limitations during the deposition of multi-layer devices and to enhance the lifetime of the devices. The latter is often limited by intrinsic defects in polymers, so that is wise to omit polymers whenever possible.
One material class that was proven to be very beneficial for (vacuum deposited) OLEDs are transition metal oxides. In this work we use a variety of metal oxide precursors in order to fabricate charge carrier transport layers from MoO3, WO3, V2O5 and others for OLEDs from solution. The respective layers are transparent to visible light and become insoluble to most solvents enabling the subsequent deposition of almost any emitters. In particular we have focused on processes that can be carried out at moderate temperatures to be suitable for roll-to-roll fabrication on flexible plastic substrates. While most precursors require oxygen to be converted into a metal oxide, we investigated processes that can be carried out under nitrogen atmosphere and hence are beneficial for the device lifetime. By using metal oxides with very high work function, we were able to fabricate efficient blue emitting OLEDs from solution as holes could easily be injected into the low HOMO of the emitter matrix.
The very same fabrication techniques and considerations can also be applied to the fabrication of organic solar cells. The insolubility of the metal oxide precursors allows for building very advanced device stacks with high power conversion efficiencies.

The design of functional organic/inorganic materials (bottom-up method) combined with printing technology (top-down) is a very powerful approach for fabricating functional coatings and for building complex 2 and 3 dimensional nanostructures [1]. Especially, the patterning of optical films with high refractive index promises the development of novel applications based on nanophotonics. We demonstrate here an efficient strategy for direct imprint of inorganic films at very high resolution [2] and tune of the optical properties of the patterned nanostructures for device fabrication.
A specific imprint resist based on hybrid organic/inorganic TiO2 resist was synthetized for crack free films with very high resolution patterns. Sub-10 nm resolution was achieved and defines state of the art for patterning functional films [2]. The imprinting process is performed by UV light at low pressure. Furthermore, post-imprint thermal annealing allows optical property tuning over a wide range of values. For instance, a refractive index higher than 2.0 and an extinction coefficient close to zero can be achieved in the visible wavelength range.
The proposed approach promises to drastically simplify the fabrication of photonic devices and the development of novel nanophotonic structures, which are very difficult to achieve by conventional nanofabrication processes. Examples of nanophotonic structures patterned by direct imprinting of TiO2 material will be presented and their optical characterization will be discussed. The present method opens an original route for fabricating novel printable photonic devices at low cost and high throughput.
[1] Y. Ofir, I. W. Moran, C. Subramani, K. R. Carter, V. M. Rotello, Advanced Materials 22, 3608, (2010).
[2] C. Pina-Hernandez, V, Lacatena, G. Calafiore, S. Dhuey, S. Cabrini, C. Peroz, submitted to Nanotechnology (2012).

GaN-based light emitting diodes (LEDs) are attracting great interest as candidates for next generation lighting sources due to low power consumption and long life time. However, the light extraction efficiency of conventional LEDs are still low due to the total internal reflection at the interface between GaN (=2.4) and air(=1.0). To improve the light extraction efficiency, patterned sapphire substrate (PSS) has been widely used in LEDs. The general PSS leads to irregular reflection at the interface between PSS and GaN, suppressing the total internal reflection. Although the general PSS makes irregular reflection contributing to improve the light extraction efficiency, some of photons generated at active layer pass through the interface between PSS and GaN.
In this work, we employed MgO nano-facet structure on the bottom of patterned sapphire to further increase the light extraction efficiency by Lambertian reflection at interface between sapphire and Ag reflector. If the bottom surface of sapphire has flat plane, light propagating inside the sapphire could be wave-guided in sapphire. However, if interface at the sapphire and reflector has accurate roughness, Lambertian reflection occurs at the interface. As a result, light propagating inside the sapphire can be out-coupled into free space, which can lead to additional improvement in light extraction efficiency of LEDs.
We simulated how light extraction efficiency of LED is affected by the refractive indices of inter-layer between sapphire and Ag reflector. When the refractive index of inter-layer is same as that of sapphire(=1.77), light extraction efficiency shows the maximum value. Here, MgO is employed as an inter-layer since MgO(=1.73) has the similar value of refractive index with that of sapphire. In addition, the nano-facets of MgO are formed during growth due to anisotropic properties of MgO between crystal orientations, resulting in the enhancement of light extraction efficiency. We fabricated lateral-type LEDs with MgO nano-facet layer between bottom of sapphire and Ag reflector. LEDs with MgO layer of 0.2 um showed 12.9 % increase of the light output relative to the conventional ones originated from the Lambertial reflection at the interface between MgO and Ag reflector.

The giant photochromism has been reported for MgSnO thin film. It was speculated that electron traps are formed by valence band excitation. The rechargeable battery using the electron traps of MgSnO is now under development. The purpose of this study is to realize the vapor phase synthesis of phptochromic ZnSiO crystals.
ZnSiO crystals are synthesized by a plasma enhanced CVD method. The surface measurement with AFM reveals that the ZnSiO nanocrystals are deposited on a substrate at room temperature. Their peak diameters are between 60-120 nm. Since a substrate is at room temperature during the CVD process, it is considered that the ZnSiO nanocrystals are grown in a vapor phase reaction. It is demonstrated that the ZnSiO nanocrystals show the photochromic transition by the excitation of valence electrons.
Photo induced structural changes were identified for hydrogenated amorphous silicon (a-Si:H) and chalcogenide As2S3 glass. In a-Si:H, atom migrations around point defects create dangling bonds, leading to the reduction of photoconductivity. In the case of As2S3, on the other hand, structural changes in a medium range order changes band structure, leading to the red shift of photo absorption. The photochromism of ZnSiO nanocrystals observed in this study is based on the different mechanism from these well-discussed cases: electron traps are formed by the valence band excitations as well as MgSnO thin film.
The detailed properties of phorochromic transition of ZnSiO nanocrystals will be discussed in the presentation.

Total energy consumption by commercial and residential buildings in the US nears 40 Quads. Approximately 1/3 of that energy use is due to space heating and cooling. Recent analysis of materials that comprise the building envelope would benefit from smarter windows that more effectively managed heat. We will describe recent efforts in using doped metal oxide nanocrystals in electrochromic windows to manage solar heat gain in buildings. These nanocrystals show switchable absorption properties in the IR due to their dynamically tunable surface plasmon resonances. We will describe the impact of different mesoscale nanocrystal architectures on the switching, optical properties, etc - which are controllable by block copolymer-directed assembly. Strategies for infiltrating the architectures with both gel and solid polymer electrolytes will also be discussed.

Physical and chemical properties and stability of nanostructured metal oxides are highly dependent on the morphology of the materials. In templated porous oxides the morphological features may be controlled at multiple length scales by the use of hard templates or soft templates and combinations of these. These length scales include those of pores, surrounding walls, and length scales defining the external particle morphologies. In this presentation, we will focus on interactions between single or multiple templates and precursor species that allow control of both pore architecture and external shapes of the particles. In particular, we will demonstrate that with Pechini sol-gel precursors for multicomponent oxides and colloidal crystal templates, it is possible to form either macroporous microspheres with low polydispersity or more extended, hierarchically structured macroporous solids. The former are obtained by limiting specific precursor components in the reaction mixture to control nucleation and growth of porous microspheres during step-growth polymerization. The latter materials are produced by spinodal-decomposition of mixed phases in the precursor, similar to a mechanism described in some non-templated sol-gel systems. Average microsphere diameters can be controlled through the stoichiometry of the precursor mixture. The distribution of phases in multicomponent systems obtained by combined colloidal-crystal and surfactant templating will also be discussed. All of these features are relevant for a variety of energy conversion and storage applications, including solar thermochemical conversions and lithium ion batteries.

Semiconducting metal oxide nanowires have potential applications ranging from gas sensors to photoanodes for solar water splitting. Realizing such applications requires a fundamental understanding of metal oxide nanowire growth mechanisms. In order for nanowire growth asymmetric material deposition must occur. Crystallographic defects are possible sources of such anisotropic growth. Herein I report a study of the defect driven growth mechanisms of tungsten oxide nanowires.
Tungsten oxide nanowires are synthesized in a multi-zone horizontal tube furnace with WO3 source powder and a sputtered W film on a silicon substrate. The temperature difference between the source and substrate controls the supersaturation and thus the driving force for transport and deposition. An inlet gas manifold allows the mixture of argon and oxygen gases to determine the effect of oxygen partial pressure on nanowire growth. The tungsten-oxygen system can contain a variable amount of oxygen vacancies which result in a large array of compositions. Oxygen vacancies in tungsten oxides form ordered defect planes through the material. The W film partially reduces tungsten oxide source vapor species, resulting in an oxygen deficient point of nucleation. Introducing oxygen gas into the reactor prevents the formation of these defects and an inhibition of nanowire growth is observed. Similarly, if the W film is oxidized, thereby removing the reductive power of the film, nanowire growth is repressed. Radial imaging of single nanowires using high resolution transmission electron microscopy (HRTEM) show planar defects oriented along the growth axis. Additionally, focus ion beam milled nanowire cross sections were also characterized using HRTEM. Selected area electron diffraction patterns contain streaking orthogonal to the growth direction, further indicating planar defects parallel to the nanowire growth direction.

Other semiconducting metal oxides such as those of titanium and niobium also exhibit ordered defects due to oxygen deficiency. The defect driven mechanism reported may be of general importance for the control of morphology in other oxide nanowires.

Zinc oxide (ZnO) nanowires (NWs) exhibit UV-induced photoelectricity and high sensity to surface adsorbates, enabling a variety of applications ranging from photodetectors and photogenerators to chemical and biological sensors. However, because ZnO NWs (ZNWs) are typically grown as isolated structures or thin films on surfaces, it remains challenging to build functional macroscopic architectures. One attractive strategy is to fabricate nanostructures such as ZNWs on scalable conductive frameworks. This provides a means to make electrical contact to a large number of functional nanostructures in parallel, and to amplify the NW-driven signal intensity above ambient noise levels.
In particular, multi-wall (MW) carbon nanotubes (CNTs) are an attractive framework due to their excellent electrical conductivity and structural robustness. As-synthesized CNTs can be manipulated to form horizontally aligned (HA) CNT sheets, 3D micro-features, and indefinitely long yarns. It has been shown that ZNWs can be directly grown on CNTs via a low-temperature vapor-solid (VS) growth mechanism, where Zn is supplied by evaporation of Zn metal. This process was adapted to build hybrid 3D architectures comprising ZNWs on HA-CNT sheets fabricated by mechanical rolling of patterned CNT forests.
Here we present a systematic investigation of the UV-photoelectric characteristics of hybrid thin films of ZNWs directly grown on HA-CNTs. Due to the distributed electrical contact provided by the CNT backbone, this architecture exhibits a large photocurrent of µA-mA, compared to ~nA levels measured for individual ZNWs at comparable illumination intensity. Further, the high conductivity of CNTs connected to ZnO through Ohmic contact over the conformal atomic interface enables rapid transport of photogenerated electrons from the semiconducting ZnO structures to the metallic CNTs. As a result, the ZnO-CNT hybrid architecture can provide much rapid (i.e., sub-second) photoresponse dynamics upon pulsed illumination. The ZnO-grown HA-CNT films show anisotropic photoconductivity depending on whether the electrons flow along the aligned CNT axes (i.e., parallel configuration) or hop across CNT-CNT junctions (i.e., perpendicular configuration). Higher conductivity and larger photocurrent are achieved in the parallel configuration, while the contribution of ZnO photoconductivity is more dominant in perpendicular configuration as the nanoscale ZnO contacts significantly reduce the contact resistance between CNTs. The built-in potential generated in the direction across ZnO-CNT heterojunctions competes with the externally applied bias to control the photocurrent amplitude and direction. By tuning the anisotropic conductivity of the CNT network and the morphology of the ZnO, further high-performance optical and chemical sensing properties could be achieved.

One-dimensional (1-D) nanostructures of metals and metal-oxides are currently the subject of intense research both in order to discover fundamental science at the nanoscale as well as for their potential as sensing, catalytic, and other electronic applications. Furthermore, the development of MEMS microfabrication techniques and nanotechnology has significantly generated cost savings in materials used or savings in the time it takes to perform a process. Here, I report the facile synthesis method of alternatively driven nanowires arrays with air-bridge structure on a single substrate produced by a chemical vapor deposition, followed by the fabrication of junction type (n-n, p-p, and n-p junction) sensor arrays based on CuO and ZnO nanowires. The sensor were tested for their ability to distinguish three gases (hydrogen, carbon monoxide, and nitric dioxide), which they were able to do unequivocally when the data was classified using a linear discriminant analysis (LDA). It was attributed to the modulation of the sensor resistance due to potential barrier at nanowire/nanowire junctions as well as the surface depletion region of each nanowire and the various catalytic processes occurring on the metal nanoparticles on the semiconducting nanowires.

Nanotechnology is offering unprecedented tools to medicine over the last few years. The extensive use of nanoparticles for therapy and/or diagnostics has unveiled a new generation of nano-biomaterials for medical applications. The general trend is towards the development of bioactive rather than bio-inert materials, with materials directly triggering or participating to cellular reaction pathways. Nanostructured metal oxides play also an important role in this scenario, and not only as inert materials as one would expect. Mesoporous particles are proposed as vectors for drug delivery, while magnetic oxide nanoparticles are studied for magnetic-induced hyperthermia and diagnostics/imaging.
Recently redox-active metal oxide nanoparticles have been shown to directly interact with cells. In particular, cerium oxide nanoparticles (nanoceria) have been recently reported to show outstanding biomedical activity, acting as well tolerated anti-age and anti-inflammatory agents, and potential pharmacological applications due to redox changes in the Ce oxidation state (Ce4+/Ce3+) that trigger the abatement of intracellular reactive oxygen species (ROS), hindering the oxidative stress cytotoxic effects. This is especially important, since the etiology or development of many serious diseases imply oxidative stress, and the search of reliable and effective antioxidant therapy is a focus of current pharmacological research. Nanoceria are redox-active owing to the co-existence of Ce3+ and Ce4+ oxidation states and to the fact that Ce3+ defects, and the compensating oxygen vacancies, are more abundant at the surface. However, the comprehension of the biological antioxidant mechanisms of nanoceria is at an early stage and controversial results are reported in the literature.
This talk will summarize our recent studies on the antioxidant effects of nanoceria. Studies were performed on a model of two human leukocyte cell lines, the monocytic U937 and the T lymphocytic Jurkat, focusing on the mechanisms through which nanoceria affect the oxidative status and proneness to apoptosis induced by a set of cell damaging agents. It was found that nanoceria reduce the oxidative status and the extent of damage-induced apoptosis, including DNA-damaging agents, metabolic inhibitors, X-ray exposure, UV irradiation and oxidations. The mechanisms of interaction of nanoceria with different antioxidant and pro-oxidant enzymes will be also presented as a function of defect engineering introduced by Sm doping.

Many past studies have examined the response of fluorite structured oxide to a variety of irradiations, including ions, electrons, and gamma-rays, mostly motivated by the use of UO2 as a nuclear fuel material, while CeO2 being the chemically closest non-radioactive simulant material. However, as these studies concentrated on bulk or thin film materials, the damage pattern is complex, as atomic effects (knock-on damage and radiolysis) are superimposed to wide-area effects, such as formation and propagation of dislocations, defect cluster formation, amorphisation and recrystallization.
In the present work we concentrate on the irradiation of CeO2 nanoparticles using electron beams in TEM&STEM at various level of beam diameters, ranging from homogeneous unfocussed irradiation of particle-assemblies, to the fully focused irradiation of a sub-nm sized region with aberration corrected condenser lens. Major findings include:
(i) CeO2 nanoparticles are resistant against focused beam hole drilling in the sense of perforation at any dose and dose rate achievable in modern TEM. Some local amorphisation is observable.
(ii) However, focusing onto corners or edges leads so significant materials ablation, hinting to the importance of free surfaces for oxygen extraction and Ce ablation
(iii) Medium focused electron beams can merge and recrystallize neighbouring touching nanoparticles, as well as spontaneously turn one well-facetted nanoparticle into a sphere, a kind of quasi-melting phenomenon.
(iv) As a reference, cubic zirconia nanoparticles are found to perforate with fully focused nanobeams, proving that the fluorite structure is beneficial but not sufficient as an explanation for ceria resistance, and the unique ability of Ce to change oxidation states to accommodate oxygen vacancies must be the key-factor.
The motivation and impact of the study is twofold, firstly small nanoparticles allow to better separate damage mechanisms, as particles are single grain and do not normally hold dislocations, and can therefore help to advance understanding of traditional radiation damage; secondly, there is correlation between surface-induced damage and surface activity for e.g. catalytic or biomedical applications of nano-ceria, and we aim at developing the electron beam as a nanoscale probe for testing particle shapes and various facet orientations for oxygen extraction from ceria powders.

Over a past few decades, the field of metal oxide nanostructures embodies an interesting and assorted class of materials whose properties cover the extremes from super-conducting metals, metals, semiconductors to non-conducting insulators. Here we demonstrate a novel facile technique that is promising for fabrication of pure metal oxide nanostructures in large quantities. The method of Exploding Wire Technique (EWT) adopted by us for synthesis of nanomaterials, demonstrates a general method for the synthesis of various transition metal oxide nanocrystals in high yield [1, 2]. In this paper, we report synthesis and characterization of copper oxide nanocrystals. Due to several reasons nanostructures of copper oxides are widely reported. For example, their p-type semiconducting behaviour, that acts as a benchmark for industries based on solar electronics, nanodevices, nanophotonics and plasmonics [3, 4]. Moreover, thermoelectric, catalytic and superconducting doped oxides based on copper are of immense significance due to their large excitonic binding energy (140meV) [5]. The issues related to synthesis of pure phase and mono-disperse nanomaterials remain unabated. To address these issues of fabrication and characterization of copper oxide nanostructures, we devised the method of EWT to synthesize nanocrystals of copper oxide. The Cu/Cu2O nanocrystals prepared by our novel method were characterized through various techniques. The XRD analysis for structural identification and phase quantification via Rietveld simulations was carried out to check the simulated and experimentally estimated lattice parameters. TEM/SPM revealed the real space images of prepared nanostructures. The stoichiometry and oxidation states for prepared sample could be ascertained through EDAX and XPS spectroscopies. The optical properties probing the quantum confinement and band structure alterations were performed through UV-Visible and fluorescence spectroscopy. The study of vibrational modes and identification of local bonds in composition of CuO/Cu2O was carried out through Raman and FTIR spectroscopy.
References:
[1] A. A. Ashkarran, J. Clust Sci., 22, pp.233-266 (2011).
[2] P. Sen, J. Ghosh, A. Abdullah, P.Kumar and Vandana, Proc. Indian Acad. Sci. (Chem. Sci.), 115(5-6), pp 499-508 (2003).
[3] M. Yin, C.-K. Wu, Y. Lou, C. Burda, J. T. Koberstein, Y. Zhu and S. O&’Brien, J. Am. Chem. Soc., 127, pp.9506-9511 (2005).
[4] K. P. Rice, Jr. E. J. Walker, M.P. Stoykovich and A. E. Saunders, J. Phys. Chem. C, 115 (5), pp. 1793-1799 (2011).
[5] S. Deki, K. Akamatsu, T. Yano, M. Mizuhata and A. Kajinami, J. Mater.Chem., 8, pp.1865-1868, (1998).

Metal-organic frameworks (MOFs) constitute a peculiar class of porous compounds and are currently being investigated for a great variety of applications such as gas separation and storage, catalysis or drug delivery. However, until now efforts to exploit the unique structural features of these compounds for battery materials are very rare.
Herein we report the targeted fabrication of nanoscale transition metal oxide@carbon composites by a controlled thermal treatment of metal-organic frameworks. We employed copper- and iron containing frameworks with different topologies including commercially available as well as in-house prepared structures. The obtained composites exhibit very high electrochemical capacities that approximate the theoretically possible values of the respective metal oxides while being exceptionally reversible. For example, nano-sized iron oxide FexOy@carbon composite obtained from Basolite® F300 shows an initial specific capacity of 904 mAh/g retaining 94% of its initial capacity after fifteen cycles. It is also shown that by impregnating with different metal salts using the incipient wetness technique prior to the thermal treatment it is possible to tune the cycling stability of the resulting material while merely reducing the capacity.
Furthermore we present a detailed microstructural characterization using X-ray diffraction, transmission electron microscopy and depth profiling Auger electron spectroscopy in order to rationalize the exceptional performance of these new materials. It is shown that during the decomposition of the MOF precursor small metal oxide clusters are formed that are surrounded by amorphous carbon which can cushion the volume expansion of the active material during lithiation and delithiation. In addition due to the microporosity of the metal organic templates the added metal salts are finely dispersed throughout the matrix leading to very well intermixed metal oxides @ carbon composites with very good capacity retention. This is also a direct result of the precursor structure which represents a perfect mixture of the respective metal bound to oxygen and carbon as a spacer between those entities.
We consider this novel synthesis route a distinguished example for the potential of MOFs as precursors for electrode materials as well as a major step towards the application of conversion-type materials in next generation lithium-ion batteries.

One of the fundamental recent breakthroughs has been the recognition that surface electron and spin states are intimately linked to the chemical reactivity of metal oxide surfaces [1], opening novel avenues for optimized catalytic devices based on oxides. In particular, it has been found that the orbital occupancy of 3d states in perovskite oxides is directly related to the chemical activity in the oxygen evolution reaction. Interestingly, among oxides, manganites with AMnO₃ composition are considered to be one of the forefront candidates for this kind of catalysts. Although an important activity has been directed towards the comprehension of the evolution of the character of electronic states at manganite interfaces and surfaces with strained epitaxial structures [2,3], there are important knowledge gaps to be bridged in relation with the surface chemical/catalytic properties. Interestingly, although it is well known that oxide surface have a pivotal role on surface reactivity, is a lack of basic knowledge relating the electronic character of e_g-symmetry states (dz² versus dx²-y² occupancies) at manganite surfaces and the efficiency of specific relevant catalytic processes related to the oxygen evolution reaction. To investigate the electronic orbital occupancy at the surface, we have carried out x-ray linear dichroism at the Mn L_2,3 edge, from which we have shown that the surface electronic structure of manganites is given by the interplay between surface and strain [4]. For that purpose, epitaxial thin films of various thicknesses were grown on a variety of single crystalline substrates creating distinct tensile or compressive strains. The systematic analysis of the dichroic data allowed us determining how the band filling changes with strain. In agreement with theoretical predictions [5] and earlier data [2], it is found that tensile (compressive) strain favors x²-y² (3z²-r²) occupancy. Strikingly, we also observe an additional contribution that is found to favor the 3z²-r² occupancy and thus unbalancing (in some cases overriding) the strain-related contributions. This additional contribution is attributed to the presence of free surfaces and can be explained by symmetry breaking of the MnOx coordination octahedral [5]. These conclusions are reinforced by our observation that the atomic surface termination also modifies the dz²/dx²-y² occupancy ratio at manganite surfaces. The present findings offer new prospects to dynamically adjust the surface-related reactivity via electric fields and strain. Recent progresses using voltage-controlled strain or orbital filling may be combined to reach active control of relevant surface electronic states.
[1] J. Suntivich et al, Nature Chemistry 3, 546 (2011);
[2] A. Tebano et al., Phys. Rev. Lett. 100, 137401 (2008); Phys. Rev. B 74, 245116 (2006).
[3] M. Huijben et al., Phys. Rev. B 78, 094413 (2008)
[4] D. Pesquera et al., Nat. Comms., in press
[5] M. Calderon et al., Phys. Rev. B 60, 6698 (1999)

Transition metal oxides have been one of the target of primary research due to their tremendous potential for practical applications such as non-volatile memories, magnetic recording media, solar cells, chemical catalyst and so on. Recently, oxide nanocrystals have gradually caught significant attention as results of their fascinating physical properties. Since functional oxide nanocrystals possess interesting magnetic, electric, and optical properties than other scales, a combination of two or more different nanocrystals would deliver a new pathway to design the material systems in nanoscale.
In this study, monodispersed epitaxial oxide nanocrystals with one covering the other have been successfully created by utilizing the instable characteristics of bismuth-based complex ternary oxides[1]. This method takes advantage of both the virtues of traditional core-shell nanostructures and the epitaxial supported nanostructures, showing the control of facet and interface of core-shell nanocrystals. Here, we fabricated nanocrystals combined with rock-salt structure of antiferromagnetic CoO and spinel structure of ferrimagnetic Fe3O4, where we could manipulate one through the other easily. Our results show that the magnetic properties such as the magnetic anisotropy, the coercivity, and the magnetization are tunable and can be precisely controlled by the size, thickness, orientation, interface and the role of core or shell at room temperature. In addition, a large exchange bias has been observed due to the strong magnetic interaction of the core and shell magnetic nanocrystals.
This approach can be expanded into all sorts of bismuth-containing oxide and then demonstrates different epitaxial core-shell metal oxide nanocomposite easily. Based on the novel structure and their possibility of convenient control of physical characteristics, this study provides us a new opportunity to understand the fundamental properties of nanoscopic metal oxides and the potential to design more desirable functional devices in the future.
[1]K. Bogle, V. Anbusathiah, M. Arredondo, J. Y. Lin, Y. H. Chu, J. M. Gregg, M. Castell and V. Nagarajan, “Synesis of Epitaxial Metal Oxide Nanocrystals via a Phase Separation Approach”, ACS Nano 4, 5139 (2010).

The realization and characterization of mixed-valence lanthanum manganite (La_1-xSr_xMnO₃) based nanoscale features remains a challenge towards their implementation in real devices such as magnetic sensors, magnetic memories or magnetic tunnel junctions. While intense research has been devoted to the generation of good quality thin films, there is considerably less reported on the fabrication and performance of La_0.7Sr_0.3MnO₃ (LSMO) nanoislands and very little work done regarding bottom-up nanostructuring approaches. In this work we present self-assembled ferromagnetic LSMO nanoislands (thickness ~10-40nm and lateral size ~50-200 nm) chemically grown using a very simple bottom-up methodology and we provide a comprehensive characterization of the system concerning its structural and magnetic properties.
LSMO nanoislands were obtained following the chemical solution deposition (CSD) route on (001)-YSZ single crystal substrates. Square-based (001) nanoislands (~80% of the total population) coexist with a minority (~20%) of triangle-based (111) nanoislands. These nanoislands appear strain-relaxed and exhibit the (001)LSMO[110]//(001)YSZ[100] and (111)LSMO[-112]||(001)YSZ[100] epitaxial relationship respectively, as measured through X-ray diffraction and TEM. SQUID magnetometry experiments have evidenced bulk-like magnetic performance of the nanoisland ensemble with Tc ~350 K. Magnetic Force Microscopy (MFM) analysis of the magnetic structure of individual nanoislands revealed three different magnetic configurations (low contrast, vortex and multidomain) which appear correlated to the nanoisland size and which could not possibly be deduced from the macroscopic magnetic study. The chemical composition and the magnetic structure of individual LSMO nanoislands are explored using Photoemission Electron Microscopy (PEEM). X-ray absorption spectra (XAS) provide separate information of the surface and the bulk composition of the nanoislands and give evidence of Mn²⁺ present on the surface of otherwise stoichiometric nanostructures. Ferromagnetic domains less than 70 nm are resolved using X-ray magnetic circular dichroism (XMCD), which allows for the detection of magnetic vortex states in both (001)LSMO square and (111)LSMO triangular manganite nanoislands. The evolution of single nanostructures under in-plane magnetic field is seen to depend on the specific nanoisland size and geometry.
We acknowledge the financial support from MICINN (MAT2008-01022, Consolider NANO-SELECT) and Generalitat de Catalunya (Catalan Pla de Recerca 2009 SGR 770 and XaRMAE). J.Z. and P.A. acknowledge FPU PhD grants from Spanish MICINN and J. G thanks CSIC for a JAE-post.