Ferroelectric (FE) thin films and nanostructures find a wide range of applications in capacitive elements, non-volatile memories, micro- and nano-electromechanical system (MEMS/NEMS) sensors, actuators and transducers, as well as actively tunable photonic and phononic crystals, and energy harvesting nano- and micro-generators. With the drive towards miniaturization, multiple intrinsic and extrinsic factors need to be leveraged in order to increase and/or maintain the high dielectric and piezoelectric response of ferroelectric materials and reduce size effects. Additionally, patterning ferroelectric materials at the nanoscale poses a continuous challenge for manufacturing methods that need compatibility, in terms of alignments and user-defined shapes, with the device creation requirements. Chemical solution deposition provides a very flexible approach for processing of short and high-aspect ratio ferroelectric nanostructures, as well as thin and ultrathin ferroelectric films with controlled crystallographic orientation and enhanced dielectric and piezoelectric response on a variety of substrates. Low aspect ratio (1D and 2D), ferroelectric nanostructures were processed through thermochemical nanolithography, local crystallization of precursor sol-gel films deposited on silicon, glass and plastic substrates. High aspect ratio (3D) ferroelectric nanostructures were processed through soft-template infiltration of precursor sol-gel solutions, followed by thermal treatment leading to removal of organic template and crystallization of the 3D ferroelectric nanostructures. Both methods allow a high resolution control of the created shapes in terms of location (alignment) and dimensions. Superlattice-like ferroelectric thin films were processed on platinized Si substrates by leveraging the thermodynamic drive for the B-site cation gradient formation in PbTiO3-based solid solutions, leading to an enhancement of the piezoelectric response through processing-induced phase boundaries. Ferroelectric size effects were observed in all the processed ferroelectric structures. Specifically, critical size, and impact of lateral and substrate-induced constraints on the extrinsic contributions to the piezoelectric response in the polycrystalline, ferroelectric nanostructures and thin films will be discussed.

Through selection of a adhesion layer that forms a low energy interface with platinum for SiO₂/Si substrates, improved dielectric and ferroelectric responses of solution deposited BaTiO₃ and Pb(Zr,Ti)O₃ (PZT) thin films has been observed. PZT films deposited on substrates with ZnO adhesion layers have 35% and 21% percent enhancements over traditional titanium adhesion layers in remanent polarization and permittivity, respectively, with values of 32 µC cm-1 and 1950 measured. A 300% increase in room temperature permittivity of BaTiO₃ is measured on ZnO-buffered substrates compared to titanium-buffered, with values approaching 1400 measured. Chemical mapping via scanning transmission electron microscopy and energy dispersive spectroscopy and secondary ion mass spectroscopy revealed nearly completely homogeneous films deposited on the ZnO-buffered platinized silicon substrates while films on traditional substrates possessed titanium and zirconium concentration gradients. The improvements in electromechanical response have been ascribed to significantly improved chemical homogeneity in the oxide films by eliminating titanium diffusion through the platinum films. Sandia is a multiprogram laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Thin film ferroelectrics are important for fully-integrated, low voltage applications ranging from decoupling and charge storage capacitors to FERAM. While solution deposition offers several advantages for the fabrication of these types of devices, it is accompanied by many challenges as well, including precise control of film stoichiometry, chemical homogeneity, microstructure development during crystallization, as well as yield and reliability at the wafer lever. Such issues are of increasing importance as dielectric layer thicknesses shrink below 50nm and as multilayer structures and/or features with nanoscale lateral dimensions are investigated. Reliable and robust use of such nanofeatures at extremely high operating electric fields requires a fundamental understanding and, ideally, mitigation of potential defect origins at every stage of fabrication. This talk describes recent advances in characterizing and controlling the evolution from liquid solution to ceramic film, with a focus on the role of electrode interactions and related phase and interface development in film structure and properties, and the resulting effects on ferroelectric performance and reliability. 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.

Isothermal (700 oC) ultraviolet annealing (UVA) processing of crystallized Ba0.60Sr0.40TiO3 (BST) thin films for exposure times up to 225 min films has been studied. The BST films, grown on PtSi wafers via the metalorganic solution deposition (MOSD) technique, were crystallized via conventional furnace annealing (CFA) prior to UVA treatment, and the effects of UV annealing time on the structural, dielectric and insulation properties were evaluated. The experimental results demonstrated significantly improved structural, dielectric and insulation properties for the UVA films. Specifically, lattice parameter contraction (toward that of bulk BST60/40) and a 20% reduction in loss were observed for the UVA treated films with respect to the CFA/control film. Leakage current characteristics were found to be the most sensitive characterization technique to access material property modification as a result of UVA exposure time. Specifically, the 225 min UVA exposure time resulted in a three-order of magnitude reduction in leakage current density compared to the CFA film, and the lowest value observed was 1.06 x10-7 A/cm2 at E=300 kV/cm. The useable tunability (tunability value at the maximum acceptable leakage current, 500 pA) was found to be elevated by a factor of two with respect to that of the CFA/control BST film (52.31%/UVA film vs. 18.5%/control film). It is suggested that the improved material properties are due to the mitigation of unwanted oxygen vacancies within the film after UV-annealing. A mechanistic model is presented and discussed.

In a modern world, size of electronic deviceâ?Ts shrinks drastically with time. Fabricating a small scale device with flexible structure as well as high electromechanical coupling has numerous applications in sensors and actuators. In this paper, we are demonstrating a simple phenomenon of increased effective piezoelectric co-efficient (d₃₃) by exploiting flexoelectric effect in two forms of non-piezoelectric, semi-crystalline polyvinylidene fluoride (PVDF) films by reducing its size proportionally. PVDF has been classified into four major molecular conformation based on its repeated arrangement of [-CH2-CF2-]_n unit cell in the amorphous region^[3]. Of the four groups, only alpha phase is non-polar, other three groups are polar in nature. In our experiment, first one is a alpha phase (α) PVDF film^[2] which is transparent in nature and second one is a mixture of alpha and beta phase (α₁) PVDF film ^[1] which is milky white in color and micro pores are randomly arranged within them. Both the PVDF films are fabricated using free radical polymerization technique under different physical condition. The molecular conformations of both PVDF films are in minimum energy state because they are neither stretched nor poled using any external method which results in increased life of polymer film. The tensile stretching experiment is performed in trapezoid shape polymer film; because application of uniform load in non-uniform shape will lead to generation of strain gradient, and the net effect is due to flexoelectricity. The experiment is performed in both (α) and (α₁) phase PVDF films separately. As the size of trapezoid shape PVDF film is proportionally scaled down from its original size to a ratio of 0.4, we observed an increase of 1.8 times and 2.74 times in the effective d₃₃ response of (α) phase and (α₁) phase respectively. The results suggest that these films can generate huge effective piezoelectric response if its size is reduced to micrometer range. The fabricated low cost film can be attached to any flexible surface for micro-level sensor or actuator application with an enhanced performance. REFERENCE:1. S. Baskaran, N. Ramachandran, X. He, S. Thiruvannamalai, H. Lee, H. Heo, Q. Chen, and J. Y. Fu, Phys. Lett.A 375, 2082 (2011). 2. S. Baskaran, X. He, Q. Chen, and J. Y. Fu, Appl. Phys.Lett. 98, 242901 (2011). 3. A.J. Lovinger, Science, 220, 4602 (1983).

The ability to pattern piezoelectric thin films without damage is crucial for the development of microelectromechanical systems (MEMS). Many of the available patterning techniques can degrade crystallinity or stoichiometry, with deleterious effects on the piezoelectric properties and potential long-term consequences in reliability. Here, direct patterning of complex oxides through microcontact printing was explored as an alternative. This process utilizes an elastomeric stamp to transfer a chemical solution precursor of a piezoelectric material directly onto a substrate in a desired pattern. Two routes were utilized to improve the wetting of the 2-methoxyethanol-based PbZr_0.52Ti_0.48O₃ (PZT) solution â?oinkedâ? onto the surface of the stamp: composite polyurethane/polyethylene glycol diacrylate monolithic stamps and multilayer polyurethane/polydimethyl siloxane stamps. PU-based stamps were used to deposit patterned PZT layers over the thickness range from ~75 nm to 1 μm. The lateral feature sizes attained varied from 1 cm to 5 μm. On crystallization, the patterned features formed phase-pure perovskite PZT. The printed features have comparable electrical and electromechanical properties to those of continuous PZT films of similar thicknesses. For example, 1 μm thick PZT features had a permittivity of 1050 and a loss tangent of 0.02 at 10 kHz. The hysteresis loops are well formed, without pinching of the loops; the remanent polarization was 30 μC/cm², and a coercive field of 45 kV/cm. Measurements of the Rayleigh behavior and first order polarization reversal curves demonstrate that the films patterned by microcontact printing show properties which are indistinguishable from the blanket films.

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~50-150 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. These nanoislands appear strain-relaxed and exhibit an epitaxial relationship (001)LSMO[110]//(001)YSZ[100] as measured through X-ray diffraction and TEM. SQUID magnetometry and Ferromagnetic Resonance experiments have evidenced bulk-like magnetic performance of the nanoisland ensemble with Tc~350 K and a biaxial in-plane anisotropy with the easy axis parallel to the [110]LSMO direction. Besides, 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 production of low cost, long length YBa2Cu3O7-δ (YBCO) coated conductors is one of the main prerequisites for spreading the use of superconductivity in power applications. Currently, a promising coated conductor design is based on a metallic Ni-5%W tape (RABiTS) coated with a La2Zr2O7 â?" CeO2 buffer structure, and a superconducting YBCO top layer. Up to now, vacuum techniques have resulted in the best properties for high temperature superconductor (HTSC) thin films. However, to reduce production costs and improve scalability, a shift towards chemical solution deposition (CSD) conditions would be preferred. The main advantages are the lower investment, faster deposition with higher yield, ease of stoichiometric composition control and modification, and processing under ambient pressure, enabling completely continuous production. In this research, we combine the use of Drop-on-Demand (DOD) ink-jet printing with completely water- based inks as a novel approach to the CSD process for coated conductors. This method holds the promise of improved scalability due to lower ink losses, continuous processing and a drastically increased precursor lifetime due to the prevention of solvent evaporation and dust incorporation. Moreover, ink-jet printing has the potential to switch quite easily from continuous coatings to a multi-filamentary pattern, which is particularly important for alternating current (AC) or field applications of coated conductors. The fluid properties, often expressed with dimensionless constants, like the Reynolds and Weber numbers, for printable liquids were determined. For proof-of-concept, single crystals of SrTiO3 with a low mismatch towards YBCO, were used as substrates. La2Zr2O7 (LZO) and CeO2 â?"buffered Ni-W tapes were used as well for some tests on coating behaviour.

Metallates based on group 5 and 6 elements, among which yttrium orthovanadate YVO4, exhibit an undeniable interest as host lattices of lanthanide-doped luminescent materials, which justifies the search for developing simple and easy preparation routes, either as powders or as thin films. Next to quite sophisticated techniques such as Direct Current or Radio-Frequency magnetron sputtering, chemical vapour deposition, pulsed laser deposition, and soft-lithography, solution techniques based on sol-gel, Pechini processes, polymer-assisted deposition techniques, and a microwave-assisted chemical solution deposition process have been reported so far. The present work deals with the development of a not expensive and comparatively soft chemistry route chemical route based essentially on stoichiometrically well-defined and water-soluble coordination complexes that make the process easy, perfectly controlled and widely applicable to other related formulations. Y2O3, V2O5, YVO4 and luminescent Eu-doped YVO4 films were deposited on quartz substrates by spin coating of an aqueous solution of EDTA compounds, then dried and calcined under appropriate but rather soft conditions, when comparing with other routes. The addition of (hydroxypropyl)methyl cellulose (HPMC) in the spin coated solution, as a viscosity-modulating agent, was implemented for a series of samples and was shown to influence the structural and morphological properties of the films. In most cases, the polymer allows the formation of more uniform films. As expected, the spin coating rate is confirmed to be a crucial parameter influencing the morphology and homogeneity of the films prepared by this route. Significant modifications of crystal structures of the complexes appear in the films compared with the bulk structures, that are attributed to the presence of water molecules. This spin coating route induces a preferential orientation of crystallites within the films for V2O5 and YVO4 with or without HPMC. This work emphasizes on one side the poorly explored potential of EDTA-complexes as molecular precursors for the preparation of films of pure and Eu-doped yttrium vanadate, and on the other side, the positive role played by the cellulosic derivative HPMC as additive inside a hybrid precursor for the same objective. It provides a detailed analysis of the potentialities of this quite simple chemical route, in aqueous medium, and at comparatively moderate temperatures, for the synthesis of such materials that are most often obtained under more severe or sophisticated conditions.

Due to the wide range of applications in electronics, transparent amorphous semiconducting oxides have been attracting considerable attention by research groups around the globe but also by the industry. This interest is fueled by the high mobility that these transparent semiconducting materials exhibit despite of their amorphous morphology. An example of these semiconducting oxides is the wide band gap n-type semiconductor zinc tin oxide (ZTO), which reaches in its amorphous state a mobility of up to 40 cm²/Vs. Furthermore, it is desirable to fabricate these amorphous thin films at low temperatures and with techniques that are compatible with a large-scale production. One way to accomplish these two goals is the usage of a sol-gel based fabrication of the semiconducting layer. I will show that we are able to fabricate fully functional high-mobility field-effect transistors with a sol-gel processed ZTO channel. In addition, I will present temperature dependent FET characteristics from which the temperature-dependent mobility and consequently information about the nature of the charge carrier motion in these devices is obtained. Furthermore, data will be shown for devices where, in addition to the ZTO, also the dielectric is sol-gel processed. These devices, based on the dielectric zirconium dioxide, exhibit even higher mobilities.

Many inorganic materials have been attracted for future electronics devices from their fascinating electrical, magnetic, and optical properties. In many cases, oxide materials are incorporated in electronic devices as thin films. There are two main issues for film growth methods for future applications: (1) Efficient fabrication for lower cost, and (2) low temperature operation for substrates which cannot withstand high temperatures (T > 500 °C). From such demands, the polycrystalline and epitaxial growths by means of UV laser irradiation for various oxide materials have been investigated. An excimer laser-assisted metal organic deposition (ELAMOD) is one of the photo-induced crystal growth methods: this is a combination process of chemical solution deposition (CSD) and pulsed UV laser irradiation. Oxide films are crystallized from deposited amorphous matrix by means of excimer laser irradiation instead of high temperature furnace heating. We have demonstrated a mechanism for epitaxial growth of oxide films on single crystal substrates in the ELAMOD process, and we revealed that not only a photothermal heating effect but also a photochemical reaction at growth interface plays a quite important role for crystal growth of oxide films under pulsed UV laser irradiation in the CSD process [1]. In a polycrystalline growth, a photothermal effect is an essential factor since a first crystal nucleation in amorhous films without a preferential nucleation site has no choice but to depend on the sufficient photothermal heating. We have revealed that the threshold of effective annealing time (in which the temperature at the film surface increases over the effective temperature for the nucleation and crystal growth) for the first crystal nucleation is about 60 ns in the case of perovskite oxide films [2]. Based on these growth mechanisms, we have developed a new facile fabrication process for high quality uniaxial oriented grown Dion-Jacobson perovskite (DJP) thin films on amorphous substrates by means of the ELAMOD [3]. The obtained DJP thin film showed perfect uniaxial oriented growth on glass substrates owing to the strong gradient heating realized by pulsed laser irradiation, and the film surface had atomically flat terraces. We have confirmed that these characteristics of the obtained DJP thin films functioned very well as a seed layer for the fabrications of various perovskite oxide thin films with high orientation quality, and in addition, epitaxial strains from the grain surface of seed layers can control the physical property of the oriented grown upper perovskite oxide films. Thus, we have revealed that the photo-assisted CSD process can prepare various oxide films at very low temperature, and the crystal quality is highly controllable. [1] T. Nakajima et al., Chem Mater. 20 (2008) 7344. [2] T. Nakajima et al., Appl. Phys. Express 2 (2009) 023001. [3] T. Nakajima et al., Cryst. Growth Des. 10 (2010) 4861.

Chemical solution deposition is a competitive technique to obtain epitaxial films, and in our group we are involved in its use in a reproducible and scalable way to produce magnetic functional oxides with good performances. Taking into account the new requirements concerning environmental safety and energy saving we need the use of new designed solutions. Looking at these objectives we will present here our work in the preparation of eco-friendly precursor solutions with reduction of fluorine content, which should be adapted to the requirements of Superconducting YBCO layers production with enhanced single thickness deposition, leading to high production rates with optimal performance. In this context, SC films with good properties based in solution approach can be performed by using additives in the preparation of the YBCO precursor solutions. Moreover, the introduction of inkjet printing, a useful and competitive deposition procedure, makes necessary the use of starting solutions with very well controlled rheological properties. Some examples for the preparation of useful LSMO and YBCO precursors to be used in inkjet deposition will be presented. Changes in solvent and use of inorganic salts and polymers produce changes in the rheological properties of the solution improving the thickness and homogeneity of the final layers. Besides, a deep understanding of the thermal decomposition processes, represents a powerful tool to produce ceramic layers with improved structural properties. It is also described a new approach to nanostructured YBCO layers. Preparation of colloidal solutions of oxide nanoparticles adapted to form stable solutions with Yttrium, Barium and Copper salts will be presented. The results of the use of this â?oex-situâ? approach to the formation of YBCO-nanocomposite layers will be discussed.

Chemical Solution Deposition (CSD) is a flexible, low cost and scalable methodology for the fabrication of epitaxial thin films for electric, electronic, magnetic or superconducting applications. In particular we have studied the preparation of CSD CeO₂ thin films on yttria-stabilized zirconia (YSZ) single crystals as buffer layer for high temperature superconductors. Previous studies on the epitaxial growth mechanism and microstructure evolution of CSD- CeO₂ films demonstrated that doping ceria with Gd³⁺ or Zr⁴⁺ can strongly enhance grain boundary mobility promoting epitaxial growth and resulting in a much improved film crystallinity and generation of terraced-like surface morphology. However, porosity is an important property of CSD films that is not easily removed and can be detrimental for some applications. Atomic Layer Deposition (ALD) has attracted much attention to deposit conformal thin films with atomic layer control over flat surfaces or nanometer 3D features. This technique is unique for its self-limiting nature of surface reactions, hence fine tuning of the chemical reactions between different precursors and the surface reactive sites becomes a key parameter to nanoengineer film structure and properties. For the first time, we obtained highly epitaxial and dense CeO₂ ultrathin films on YSZ with surface roughness down to 1nm. These films have been characterized by X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy and transmission electron microscopy. Optical characterization by spectroscopic ellipsometry has been carried out to assess film thickness and porosity and correlated with chemical solution deposited (CSD) CeO₂. Conformal coatings of ALD- CeO₂ have been demonstrated on complex 3D nanostructures suggesting that a combination of CSD and ALD could be employed as a potential strategy to close porosity of solution deposited films.

Zinc oxide (ZnO) has attracted increasing attention due to its remarkable electrical properties, such as wide band gap energy (~3.37eV at 300k) and large free exciton binding energy (60meV). In this study, we fabricated ZnO film by a novel solution process named â?~Spin-Sprayâ?T [1]. Spin-spray enables to deposit crystallized ZnO films by spraying source solution of Zn ions and reaction solution including oxidizing agent and pH buffer like ammonia. It has several advantages for fabricating ZnO films to other processes like sputtering, chemical vapor deposition (CVD) and pulsed laser deposition (PLD), such as high deposition rate, low environmental load and low initial cost for apparatus [1]. In this study, we fabricated ZnO film by changing pH during the deposition and investigated their difference in structural and crystallographic properties. Before the deposition, the glass substrate was ultrasonically cleaned in de-ionized water (D. I. water) and ethanol for 10minutes each to remove impurities on the surface followed by air plasma treatment for 10minutes to enhance the hydrophilic property. The source solution was prepared by dissolving 10mM of zinc nitrate hexahydrate (Zn(NO3)2 6H2O) in 1.00L of de-ionized water. And the reaction solution was prepared dissolving ammonia (NH3) and 10mM trisodium citrate (C6H5Na3O7) in same amount of de-ionizes water. We controlled from pH 6 to 12 by changing the concentration of ammonia. ZnO film was fabricated by spraying these solutions on to glass substrates fixed on rotating disk. The spin-sprayed ZnO films subjected to UV illumination to decrease their resistivity by decomposing citrates remained in films. Here, the effect of solution pH to the change of structural, optical and electrical properties of fabricated ZnO films were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV-VIS spectrometry, and four prove method, respectively. Spin-sprayed film at pH lower than 6.6 were not crystallized and that at pH 9.4 had zinc hydroxide peaks in XRD. On the other hand, all of as-sprayed film at pH higher than pH 9.6 had ZnO peaks (JCPDS card No. 36-1451). There were structural changes to sprayed ZnO films surfaces by changing pH in during spraying. The film had porous surface up to pH 9.4, while that deposited at higher than 9.6 had dense and smooth surface.

ZnO is a wide-band gap, n-type semiconductor with numerous applications in piezoelectric resonators, light-emitting devices, and photovoltaics. Polycrystalline ZnO is routinely made using techniques such as chemical spray pyrolysis, sol-gel synthesis, screen printing, and electrochemical deposition. Most of these techniques can be done at low temperatures and are high throughput processes. However, high quality epitaxial films are required for optoelectronic applications, and epitaxial films have been nearly impossible to achieve using these techniques. Heteroepitaxial films of ZnO, while challenging, have been obtained on various substrates â?" including sapphire, GaN, CaF₂, ScAlMgO₄, Si, and GaAs â?" using expensive high temperature, vacuum processesâ?" such as pulsed laser deposition, chemical vapor deposition (CVD), metal-organic CVD, molecular-beam epitaxy, and sputtering. We report on the rather remarkable epitaxial growth of ZnO on the (111) surface of single crystal Au microplates. Despite the 13% lattice mismatch between (0001) ZnO and (111) Au, we are able to grow ZnO in an aqueous solution at 90°C onto single crystal Au microplates, which are also made through simple chemical synthesis. We present evidence of epitaxy through electron backscatter diffraction, high resolution transmission electron microscopy, and electron diffraction. We also assess the optoelectronic quality of the ZnO films by presenting photoluminescence spectra. Further, we separate the ZnO film from the Au microplate to produce ZnO membranes suitable for the creation of nanophotonic structures like microdisk resonators and suspended 2D photonic crystal structures. Finally, we will discuss the possible applications of epitaxial growth of ZnO on single crystal gold microplates, which will range from better electrical contacts to enhanced light extraction in light-emitting diodes and possibly improved oxide-metal interfaces for plasmonic devices and metamaterials.

We have developed a new solution route for the deposition of thin films. This innovative technique uses aqueous solutions in which metals are bound to a water soluble polymer. Unlike typical sol-gel processes, the solutions remain stable for months to years and the metals remain protected from reactivity while bound to the polymer. The solution may then be applied to any type of surface in a variety of ways including spin coating, dip coating, insipient wetness or ink jet printing. Thermal treatment then removes both water and polymer at as low as 450 C. Further annealing yields epitaxial, crack-free films. We have made a wide variety of stable solutions of over 40 metals that allow for the preparation of a wide variety of materials in which stoichiometry of the films is readily controlled by simply mixing solutions. We will present results on the deposition of a range of materials from complex oxides to nitrides to carbides. We will demonstrate the ability to control both phase and oxidation state of the metal based on lattice engineering. Deposition of a wide range of materials from actinide oxides to YBCO to germanium metal to gallium nitride and titanium carbide will all be discussed in terms of epitaxy surface roughness and performance of the thin films. As a solution technique, there are no limitations of line-of-sight growth. Conformal coatings are obtained on a variety of surfaces including complex porous structures such as photonic crystals. We will present results showing the coating of phosphors onto porous alumina discs and photonic crystals with thin films of Eu:YVO4. Complex composites with nanoparticles can also be produced. We will show results of incorporation of silica nanoparticles into crystalline films that show epitaxy on all sides of the nanoparticle.

Metal organic precursors are widely used for the production of functional oxide thin films. After spreading and evaporating a solution containing the precursor salt, the film is pyrolyzed to remove the organic ligands, leaving the desired oxide film on the substrate. The process parameters (heating rate, temperature, atmosphere) rely on the information delivered by thermal analysis experiments (notably, thermogravimetry and mass spectrometry) done on precursor powders. In this communication, we will give a number of examples showing that the thermal behaviour of powders may differ greatly from that of thin films. The general reason for this difference relies on the higher surface to volume ratio of films that facilitates gas and heat exchange between the precursor and its surroundings (substrate and atmosphere). It will be shown that films tend to decompose at lower temperatures than powders do [1], that their decomposition is much more sensitive to traces of oxygen in the atmosphere and that formation of undesirable intermediate products, like carbonates, can be reduced. Since, owing to the higher mass of powders, their thermal analysis is much easier than on films, we will try to give some general rules that indicate when a different behaviour is expected and, consequently, when the thermal analysis of thin films is not necessary. In contrast with the high expectation recently created [2], several examples together with numerical simulations will be given to highlight the great difficulty (or impossibility) of inducing self-combustion on films. Finally, the implications of our findings for the present search of low-temperature routes for film production from metal organic precursors will be discussed. [1] P. Roura et al. Thin Solid Films (2011) doi:10.1016/j.tsf.2011.09.058. [2] Myung-Gil Kim et al. Nat. Mater. 10 382 (2011).

Expeditious development of macroelectronics such as flat panel displays, sensor arrays, and flexible circuitry will require low-cost, large-area compatible, high-throughput fabrication methods, and materials offering appropriate combinations of high charge carrier mobility, high electrical conductivity, large dielectric constants, mechanical flexibility, and optical transparency. Recent advances in oxide thin films indicate great promise for realizing the desired properties, and high-throughput solution processing of oxide films on flexible substrates offers the potential to reduce costs and minimize capital-intensive growth equipment. Nevertheless, current generation oxide solution processing techniques typically require high annealing temperatures (T_anneal >400 ^oC) which are incompatible with flexible polymeric substrates. We demonstrate here that the combustion processing, chemical reaction route based on intense exothermicity, can be a general strategy for the solution growth of diverse metal oxide films (In₂O₃, a-Zn-Sn-O, a-In-Zn-O, ITO) at annealing temperatures as low as 200 ^oC. With the low annealing temperature of combustion processing, the optically transparent transistors were fabricated on flexible plastic substrates.

ZnO is a promising material for short-wavelength optoelectronics and thin film transistors. To realize ZnO-based CMOS-type circuits, it is essential to fabricate both high quality n-type and p-type films with a low cost process. Nevertheless, fabrication of p-type ZnO remains a major challenge due to its asymmetric doping limitations. Compared with the conventional thin film deposition techniques, such as physical vapor deposition and chemical vapor deposition, the sol-gel technique has advantages of easy control of the chemical composition and lower process costs. These characteristics make the sol-gel technique a very attractive approach, especially for the co-doping of ZnO thin films. In the last few years, several researches have been devoted to the study of sol-gel derived p-type ZnO. However, the p-type ZnO films prepared by non-toxic sol-gel processes have not been reported to date. In this paper, we report that In-N co-doped p-type ZnO thin films were achieved through a sol-gel spin coating method with both non-toxic solvent and stabilizer. The resistivity of p-type ZnO films is 4.43 Ω cm with the carrier concentration of 1.36 Ã- 10¹⁸ cm^-3 at room temperature. X-ray photoemission spectroscopy (XPS) shows that the binding energy of In 3d_5/2 (444.7 eV) and In 3d_3/2 (452.2 eV) are in good agreement to the typical signals of indium in the In-N bond, which indicates that indium atoms tend to bond to nitrogen atoms in In-N co-doped ZnO films. Thus, the repulsive interactions between N acceptors can be effectively reduced, leading to the enhancement of N incorporation as p-type dopants in ZnO. The N 1s core level were also measured via XPS with Al Kα photon lines from the undoped and In-N co-doped ZnO films to identify the nitrogen contents in the In-N co-doped ZnO film. For the undoped ZnO film, no obvious peak related to nitrogen is observed. That is, the signal of N 1s core level is not interfered by the Auger electrons of Zn atoms when Al Kα is selected as the X-ray source, which can not be achieved with Mg Kα photon lines. However, for the In-N co-doped ZnO sample, an apparent peak corresponding to N 1s core level is detected at around 399 eV, which is close to the Zn-N bond. It is believed that N and In existed in ZnO are mostly in the states of In-N and Zn-N bonds. Moreover, the co-doped ZnO film with the thickness of 200 nm has a high transparency about 90% in the visible region. The calculated optical band gap reveals a red-shift from 3.27 eV for the undoped ZnO film to 3.22 eV for the In-N co-doped ZnO film, which is presumably due to near-band-edge defects and the narrow band gap of InN (0.7 eV) and (ZnN)^- (0.8 eV). Secondary ion mass spectroscopy depth profiles not only confirm the nitrogen contents in the In-N co-doped films, but also indicate the uniform doping of nitrogen into the ZnO film. This study successfully demonstrates the development of p-type ZnO films via the non-toxic sol-gel spin coating method.

Semiconductor nanowires (SC-NWs) have potential applications in diverse technologies from nanoelectronics and photonics to energy harvesting and storage due to their quantum-confined opto-electronic properties coupled with their highly anisotropic shape. Here, we explore new approaches to an important solution-based growth method known as solution-liquid-solid (SLS) growth. In SLS, molecular precursors are reacted in the presence of low-melting metal nanoparticles that serve as molten fluxes to catalyze the growth of the SC-NWs. The mechanism of growth is assumed to be similar to that of vapor-liquid-solid (VLS) growth, with the clear distinctions of being conducted in solution in the presence of coordinating ligands and at relatively lower temperatures (<300 C). The resultant SC-NWs are soluble in common organic solvents and solution processable, offering advantages such as simplified processing, scale-up, ultra-small diameters for quantum-confinement effects, and flexible choice of materials from group III-V to groups II-VI, IV-VI, as well as truly ternary I-III-VI semiconductors as we recently demonstrated. Despite these advantages of SLS growth, VLS offers several clear opportunities not allowed by conventional SLS. Namely, VLS allows sequential addition of precursors for facile synthesis of complex axial heterostructures. In addition, growth proceeds relatively slowly compared to SLS, allowing clear assessments of growth kinetics. In order to retain the materials and processing flexibility afforded by SLS, but add the elements of controlled growth afforded by VLS, we transformed SLS into a flow based method by adapting it to synthesis in a microfluidic system. By this new methodâ?"so-called â?oflow-SLSâ? (FSLS)â?"we have now demonstrated unprecedented fabrication of multi-segmented SC-NWs, e.g., 8-segmented CdSe/ZnSe defined by either compositionally abrupt or alloyed interfaces as a function of growth conditions. In addition, we have studied growth rates as a function of catalyst size/SC-NW diameter and shown for the first time that SLS is governed by Gibbs-Thomson effects. Lastly, from an applications standpoint, we report growth of SC-NWs from a range of substrates, including ITO-coated glass for fabrication of hybrid photovoltaic devices, comparing these to their quasi zero-dimensional quantum-dot counterparts.