Symposium Organizers
Junqiao Wu University of California-Berkeley
Anderson Janotti University of California-Santa Barbara
Weiqiang Han Brookhaven National Laboratory
Ho-Cheol Kim IBM Almaden Research Center
V1: Complex Oxide Nanostructures
Session Chairs
Tuesday PM, April 14, 2009
Room 3001 (Moscone West)
9:00 AM - V1.1
Size Dependent Ferroelectric Polarization in BaTiO3 Nanocrystals Probed by Electron Holography.
Gil Markovich 1 , Daniel Szwarcman 1 , Yossi Lereah 2 , Martin Linck 3 , Hannes Lichte 3
1 Chemistry, Tel Aviv University, Tel Aviv Israel, 2 Department of Electrical Engineering-Physical Electronics, Tel Aviv University, Tel Aviv Israel, 3 Triebenberg Laboratory, Institute of Structure Physics, Technische Universität Dresden, Dresden Germany
Show AbstractIn bulk ferroelectric crystals and thin films, the paraelectric to ferroelectric phase transition is accompanied by the formation of polarization domains to minimize the system energy with respect to the depolarization field and mechanical strain . While experimental data is available for thin perovskite films, only few studies address the electric polarization properties of ferroelectric nanocrystals. Hence, it is yet to be established, what is the minimal nanocrystal (NC) size and geometry that could support the ferroelectric crystal phase in the absence of external support such as a substrate, metal electrodes or adjacent high dielectric constant material. It is not established experimentally whether a small isolated NC exists as a single ferroelectric domain, or that its high depolarizing field causes other forms of ferroelectric order. In this work we obtained images of ferroelectric polarization in isolated BaTiO3 NCs with nanometer resolution using off-axis electron holography, above and below the Curie temperature. It is found that the polarization magnitude within 20-55 nm NCs is size dependent, forming complex configurations in the larger nanocrystals with polarization values surpassing the bulk values quoted in the literature. In addition, the polarization appears to decay or re-orient near free NC surfaces to minimize the depolarization energy.
9:15 AM - V1.2
Atomic–Scale Imaging of Multiple Phase Transformation in LiFePO4 Nanocrystals for Advanced Li-Ion Batteries.
Sung-Yoon Chung 1 2
1 Materials Sci. & Eng., Inha University, Incheon Korea (the Republic of), 2 , Nalphates, LLC, Wilmington, Delaware, United States
Show AbstractOlivine-type lithium metal phosphates have attracted a great deal of attention over the last decade as an alternative cathode material in Li-ion batteries. In particular, to improve the electrochemical performance of LiFePO4, numerous investigations have been made in addition to many studies of the intrinsic ionic and electronic properties and the thermodynamic phase equilibria. The achievement of remarkable high-rate capability and outstanding thermochemical stability in LiFePO4 during the intercalation reaction (S.-Y. Chung et al., Nature Mater., 1, 123 (2002)) have resulted in the recent success of the application as a safe power source adopted for power tools and potentially for hybrid electric vehicles as well (Nature, 444, 16 (2006)).Among a variety of factors that govern the electrochemical cycling behavior in this class of compounds, control of the particle size and its distribution is recognized to be of great significance for charge and discharge reactions at high rates. Considering the one-dimensional nature of Li ion diffusion in the lattice based on previous studies, synthesis of the nanostructured phosphates is necessary to minimize the effective diffusion length of Li ions as well as to maximize the surface area of the particles for the enhancement of the mass and charge transport across interfaces for a limited time. Therefore, understanding of the exact mechanism of nanocrystal formation and relevant phase transformation in these olivines is a crucial step toward the achievement of a higher power density with a sufficient energy density in the electrochemical cells. By utilizing in-situ high-resolution electron microscopy (HREM) along with a hot-stage specimen holder, the initial stage of nucleation and growth of LiFePO4 nanocrystals at high temperatures in real time are directly observed (S.-Y. Chung et al., Nature Phys. (in press)). More details for atomic-scale probing of crystallization and resulting nanocrystal formation in LiFePO4 will be presented.
9:30 AM - **V1.3
Photoelectrochemistry of Complex Oxides for Dye-Sensitized Solar Cells.
Mario Alpuche-Aviles 1 , Yiying Wu 1
1 Department of Chemistry, Ohio State University, Columbus, Ohio, United States
Show AbstractComplex oxides have been used for applications such as the transparent conductive oxides, dye sensitized solar cells and photocatalysis. For these applications, it is fundamentally important to investigate their band structures and the oxide/electrolyte interfacial properties. However, these studies for complex oxides are scarce, and the results are often contradictory. In this talk I will use zinc stannate (Zn2SnO4) as an example and talk about our systematical study on the energetics of the conduction band and valence band of zinc stannate (Zn2SnO4) nanoparticles by optical, electrochemical and photoelectrochemical methods combined with a comprehensive characterization of the material by SEM, XRD and ICP-MS. We have established the band gap of Zn2SnO4 and the energy of the conduction band edge in both aqueous and nonaqueous MeCN solutions. In MeCN solution, which simulates the dye-sensitized solar cell electrolyte, we demonstrate the dependence of the conduction band edge on the electrolyte composition. This opens the possibility of keep increasing Voc by using interfacial interactions to shift the ECB to higher energies. Moreover, from CV the Zn2SnO4 has a much lower recombination rate near the ECB. This will avoid the problem normally associated with TiO2, of lower η at higher VOC due to e and I3- recombination losses at traps below the CB. These results and methods reported are valuable to the developments of new materials for photovoltaics and photocatalysis.
10:00 AM - **V1.4
Domain Wall Nanoelectronics.
Ramamoorthy Ramesh 1
1 , UC Berkeley, Berkeley, California, United States
Show AbstractOur recent work is focused on understanding the properties of domain walls in ferroelectrics and multiferroics. We are using the multiferroic, BiFeO3 as a model system. Using a combination of experimental and theoretical approaches we are exploring the electronic structure and transport in domain walls. We observe electronic transport that is 5-6 orders of magnitude higher at the domain walls compared to the bulk. The nature of transport is also dependent on the type of domain wall. In this talk, I will discuss our results and possible ideas for using such domain walls in nanoelectronic devices
10:30 AM - V1.5
Strain Engineering of Metal-Insulator Domains in Single-Crystal VO2 Micro- and Nanowires
Jinbo Cao 1 2 , Joanne W. L. Yim 1 2 , Simon Huang 1 , Wen Fan 1 3 , D. Frank Ogletree 4 , Junqiao Wu 1 2
1 Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 2 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Department of Thermal Science and Energy Engineering, University of Science and Technology of China, Hefei China, 4 Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractMany transition metal oxides exhibit spatial coexistence and ordering of different phases on the sub-micron scale. The origin of this phase inhomogeneity is under debate, and is believed to be either due to intrinsic properties of strong correlated electrons or extrinsic effects arising from chemical disorder and lattice strain. Free standing, single-crystal oxide nanostructures offer the possibility of continuously tuning the lattice strain to modulate the phase transition at the sub-micron scale. VO2 undergoes a metal-insulator transition at ~340 K. We synthesized single-crystalline VO2 micro- and nanowires using the vapor transport method. By bending or axially stressing the wire, we established coherent strain in the wire. The wire responds to the local strain field by creating regular, sub-micron scale metal-insulator domains, which we investigated in situ using optical and electron microscopies. In addition, a new, “superlattice” structure with a period of ~ 100 nm was observed within the insulator domains, which may indicate the stabilization and ordering of new phases in VO2.
11:30 AM - V1.7
Low Temperature Solution Phase Syntheses of Perovskite and Semiconductor Oxide Nanocrystals.
Richard Brutchey 1
1 Department of Chemistry, University of Southern California, Los Angeles, California, United States
Show AbstractCurrent solution phase synthetic methods typically require combinations of high temperature, high pressure, and/or extreme pH conditions; however, there is a need to rationally develop new methodologies for the synthesis of functional oxide nanocrystals under low temperature conditions, much in the same way that organic chemists have developed a very extensive and diverse toolbox of bench-top reactions. Moreover, it is becoming increasingly important to develop more environmentally friendly, safer, and less energy intensive synthesis methods for nanocrystals that are also scalable, high yielding, and which avoid toxic or caustic reagents. Ultimately, such issues will be of extreme importance in the context of developing large-scale technologies based on nanocrystals. Our research program is directly addressing these issues by developing low temperature routes to two classes of technologically important and functional oxide nanocrystals – perovskites and semiconductor oxides. The rational chemical design behind the synthetic methodologies and the resulting properties of the nanocrystals will be discussed.
11:45 AM - V1.8
Nonhydrolytic Synthesis and Shape Control of BaTiO3 Nanocrystals.
Jun Wang 1 , Zhiqun Lin 1
1 Department of Materials Science and Engineering, Iowa State University, Ames, Iowa, United States
Show AbstractWe report the synthesis of barium titanate (BaTiO3, BTO) nanocrystals via a nonhydrolytic thermal decomposition approach, using a commercial available Ba-Ti precursor. Oleic acid was used as the surface capping ligand, and the shape of the BTO nanocrystals was found to be highly dependent on the concentration of oleic acid. The effect of oleic acid concentration on the shape of BTO nanocrystals was systematically studied. By varying the concentration of oleic acid in the reaction solution, BTO nanoparticles, nanorods and nanowires were obtained. X-ray powder diffraction, TEM and EDX analysis were used to characterize the crystalline structures and chemical compositions of as-synthesized BTO nanocrystals.
12:00 PM - V1.9
Tuned Strain In Complex Oxide Nanocomposites Grown From Metal-Organic Solutions
Anna Llordes 1 , J. Gazquez 1 , P. Abellan 1 , A. Pomar 1 , F. Sandiumenge 1 , S. Ricart 1 , T. Puig 1 , D. Grebille 2 , D. Chateigner 2 , X. Obradors 1
1 , ICMAB-CSIC, Bellaterra (Barcelona) Spain, 2 , CRISMAT-ENSICAEN , Caen France
Show AbstractNanocomposite thin films represent a new class of materials with special properties due to their size-dependent phenomena. In addition, chemical solution methodologies have been successfully applied to the growth of a high diversity of functional oxides nanocomposites, with low production costs and high versatility. Solution-derived nanocomposites have shown a large variety of possibilities where the assembling of nanoparticles (NP) can either show an epitaxial relationship with film matrix or not [1]. Nanocomposite functionality is governed both by the assembling of NP and interfacial energy, which are related to NP crystalline orientation and structure as well as to the strained epitaxial matrix. Therefore, microstructural analysis is a crucial issue in order to correlate the disorder parameters to the new functionalities.We present two XRD-methodologies of general validity and complementary to local TEM technique, to evaluate and quantify the strain-anisotropy and epitaxial NP fraction in nanocomposites thin films. The first procedure is based on simultaneous refinement of structural and microstructural disorder parameters using the Rietveld method combined with Fourier analysis for broadened peaks, in which case, anisotropic models are also applied when strain-size anisotropy effects need to be considered. The second procedure determines and quantifies the NP polycrystalline and epitaxial fractions, which does not require any Rietveld refinement procedure. This second strategy is based on the simultaneous out-of-plane measurement of textured and polycrystalline NP signals in a XRD area detector. The quantification of the volume fractions is attained by applying the integrated intensity expression of a single crystal and a powder sample with an angular correction. Results obtained with this second procedure are seen to be in agreement with those obtained by Rietveld and TEM observations which evidence its application to other complex oxides systems.We have applied these methodologies to epitaxial YBa2Cu3O7-x (YBCO) thin films with homogeneous distributed oxide NP (BaZrO3 or Y2O3), in which the distorted YBCO crystalline structure is governed either by randomly oriented NP (BaZrO3) or by epitaxial NP (Y2O3). The control of disorder lattice parameters, strain-size anisotropy and NP orientations will be discussed in terms of final nanocomposite superconducting properties. We emphasize that YBCO-BaZrO3 nanocomposites show the most efficient vortex pinning mechanisms reported so far in high temperature superconductors [1]. The key parameter relies on the resulting isotropically and strongly modified faulted structure of YBCO at the nanoscale level. [1] J.Gutiérrez, A. Llordés, et al., Nat Mater.,6, 367 (2007)We acknowledge the financial support from MEC, FPU, FPI and RyC, Generalitat de Catalunya (Pla de Recerca SGR-0029 and CeRMAE), and EU (HIPERCHEM, NESPA)
12:30 PM - V1.11
Strain Effects on Relaxor Ferroelectric Properties of PbSc0.5Nb(1-x)/2Tax/2O3 Thin Films and Nanoceramics.
Margarita Correa 1 , Ashok Kumar 1 , Ram Katiyar 1
1 Physics, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractPbSc0.5Nb(1-x)/2Tax/2O3 (PSNT for x = 0.3, PST for x= 1) nanoceramics and thin films were prepared by high energy ball mill with solid state reaction technique and pulse laser deposition (PLD) respectively. A comparative study of the microstructure, dielectric properties, and polarization of PSNT and PST thin films and nano ceramics were carried out over a wide range of temperature (100 K-600 K) and frequency (100 Hz to 1 MHz). High Resolution Transmission Electron Microscopy (HRTEM) image of PSNT and PST thin films indicate the presence of small polar nano regions (PNRs) and long range ordered regions in crystal lattice plane respectively. PST nanoceramics (PST-N) showed normal ferroelectric behavior where as its thin film form (PST-F) illustrated relaxor behavior. PSNT nanoceramics (PSNT-N) and its films (PSNT-F) demonstrated weak frequency dispersion and strong frequency dispersion in dielectric spectra respectively. A shift in dielectric maximum temperature (Tm) towards lower temperature side i.e. 65 K and 85 K were observed for PSNT-F and PST-F compare to their nanoceramices indicates greater role of substrate-electrode-interface strain on dielectric properties. Well behaved hysteresis at room temperature for PSNT-F point toward strong competition between short range order and long range order. A weak slim hesteresis for PST-F were observed at room temperature suggesting the existence of polar nano regions far above dielectric maximum temperature.
V3: TiO2 Nanostructures
Session Chairs
Wednesday AM, April 15, 2009
Salons 1 - 7 (Marriott)
8:00 PM - V3.1
Solution Processed Titania Nanostructures.
Ho-Cheol Kim 1 , Oun-Ho Park 1 , Sang-Min Park 1 , Robert Miller 1
1 , IBM Almaden Research Center, San Jose, California, United States
Show AbstractTitania is a wide band gap semiconductor and has been studied extensively due to its promising opto-electric properties for a variety of applications. It is common that to introduce nanoarchitectures improves the performance of titaina. In particular, specific length scales of nanostructures of titania are required depends on the material combinations for photovoltaic applications. Numerous approaches have been explored to create well-defined nanostuctures of titania. However, challenges are still remained for developing a simple and low-cost method of substrate non-selective preparation of supported titania nanostructures. In this presentation, we report our progress in creating titania nanostructures based on solution processes. We focus on creating supported nanostructures of titania on substrates (typically conductive substrates such as ITO) from a solution of of titania precursor. We employed a commercially available organic titanate as the precursor of titania after chelating. A N-butyl polytitanate, n-C4H9O-[Ti-(O-n-C4H9)2O]n-n-C4H9 with molecular weight of ~ 1250 g/mol, and a benzoylacetone were used as the precursor and the chelating agent, respectively. For a sol-filling method, we used a nanoscopic scaffold generated from plasma etching process using a block copolymer etch mask. This approach gives nanopillars of titania of approximately 25 nm in diameter and 100 nm in height on substrates. A microtransfer molding method using a sacrificial template was used to create titania nanostructures as well. The transfer molding method provides nanostructures of feature sizes ranging from 130 nm to 250 nm. The limitations and challenges of materials and fabrication methods will be addressed in this presentation.
8:15 PM - V3.2
Preparation and Properties of Titanium Oxide Nanodots Formed by Phase Separation-induced Assembly.
Wenjian Weng 1 , Ming Luo 1 , Ge Shen 1 , Chenlu Song 1 , Gaorong Han 1
1 Materials, Zhejiang University, Hangzhou, Zhejiang, China
Show AbstractAs an important metal oxide, titanium oxide (TiO2) is strongly attractive and has been investigated intensively due to its widespread applications in solar energy conversion, gas sensors, catalysis and environmental pollution remediation. Nanosized TiO2 materials can demonstrate remarkably higher performances. In this work, uniform titanium oxide (TiO2) nanodots were prepared on substrates through phase separation-induced assembly. Marangoni effect is adopted into the present preparation of TiO2 nanodots on a substrate. Here, titanium tetrabutoxide (TBOT) and polyvinyl pyrrolidone K30 (PVP K30) are selected as the two phases. The average dot size can be effectively adjusted by changing the concentration of titanium alkoxide or PVP in ethanol solution. X-ray diffraction (XRD) patterns show the formation of anatase phase for TiO2 nanodots. A representative transmission electron microscopy (TEM) image and selected-area electron diffraction (SAED) pattern confirm that each freestanding nanodot shows polycrystalline characteristic. The as-prepared TiO2 nanodots exhibit intense room temperature ultraviolet (UV) luminescence and low-field electron emission, which promise its potential applications as tunable short-wavelength devices and field-emission-based flat panel display.
8:30 PM - **V3.3
Sol-Gel Bio-Templating of Titanium Dioxide Photonic Band Gap Structures
Michael Bartl 1 , Jeremy Galusha 1
1 Department of Chemistry, University of Utah, Salt Lake City, Utah, United States
Show AbstractBiological systems have developed a wealth of cuticular photonic structures optimized to strongly interact with visible light. In particular, many butterflies and beetles obtain their striking iridescent coloration from exoskeleton photonic crystals with lattice morphologies far more complex than what is attainable by current synthetic photonic structure engineering at visible length scales. For most photonic applications, however, these bio-polymeric low-dielectric lattices must be converted into high-dielectric structures. In this talk, we will present a sol-gel double-imprint bio-templating route to replicate the diamond-based cuticular photonic crystal structure found in a Brazilian weevil into the high-dielectric compound titanium dioxide (titania). We will discuss the key parameters that must be fine-tuned for a successful bio-templating process, including minimal shrinkage of the overall structure to ensure the lattice constant of the diamond-based structure remains within the range of visible light; controlling the filling fraction of the titania framework, while keeping its structural integrity; creating a highly-crystalline and dense titania framework to increase its dielectric constant/refractive index for efficient light interaction.
9:00 PM - V3.4
Solution-Grown TiO2 Nanowire Arrays Vertically Oriented on Glass Substrates.
Curtis Berlinguette 2 1 , Ruohong Sui 2
2 Department of Chemistry, University of Calgary, Calgary, Alberta, Canada, 1 Institute for Sustainable Energy, Environment & Economy, University of Calgary, Calgary, Alberta, Canada
Show AbstractThe task of aligning linear TiO2 nanostructures orthogonal to a support (e.g., ITO glass) is a relatively difficult task to achieve. While a variety of techniques are able to do this, the need for exotic reagents or templates, multiple reaction steps and or energy-intensive procedures limit the scalability of many of these methods. Sol-gel chemistry represents one of the more promising avenues for overcoming these obstacles; however, no such route has been documented in the absence of a template or electrochemical potential. This talk will outline a facile self-assembly approach we have developed for generating TiO2 arrays on ITO glass from solution using readily available reagents.
9:15 PM - V3.5
Formation of Nanowires of TiO2
Deepa Khushalani 1
1 Dept. of Chemical Sciences, TIFR, Mumbai, MH, India
Show AbstractOver the last few years, extensive work has been devoted to formation of TiO2 nanowires, nanorods and/or high aspect ratio fibres of this ubiquitous material. One of the main applications for such structures has been due to their immense demand as components of a solar cell where an organic moiety, such as a light-absorbing dye, is set to be incorporated as a sensitizer to aid in the conduction of the excited electrons. Presented here, are two simple yet separate strategies that have been developed to form nanowires of TiO2 whose widths are 5-10nm and lengths are on the orders of microns. These synthetic pathways are based on simple solution based techniques and provide a route by which large scale production can be readily obtained. The phase of the oxide can be easily controlled to anatase polymorph and moreover, results involving formation of dye-sensitized solar cells will be presented where the photocurrent efficiency obtained is 5%.
9:30 PM - V3.6
Synthesis and Characterization of Nanocarbon-Supported Titanium Dioxide.
Marcus Worsley 1 , Joshua Kuntz 1 , Octavio Cervantes 1 , T. Yong-Jin Han 1 , Peter Pauzauskie 1 , Joe Satcher 1 , Theodore Baumann 1
1 Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractTitanium dioxide is a widely researched material with applications ranging from photocatalysts to electrodes to hydrogen storage materials. However, issues such as absorption limited to the ultraviolet range, high rates of electron-hole recombination, and relatively low surface areas have limited commercial use of titanium dioxide. Recent efforts have focused on combining titanium dioxide with various materials to address some of these issues. Titanium dioxide in the presence of carbon (e.g. activated carbon, graphite, and carbon nanotubes) is currently among the most attractive combinations. While recent work has shown some improvements, surfaces areas and photocatalytic activity is still limited. Achieving surface areas well over 1000 m2/g, and higher electrical conductivities, one could envision charging-discharging rates and photoefficiencies significantly higher than currently possible. Here, we describe our efforts in fabricating a variety of new nanocarbon-supported titanium dioxide structures that exhibit such surface areas and improved electrical conductivities. Nanocarbons consisting of single-walled carbon nanotubes and carbon aerogel nanoparticles were used to support titanium dioxide particles and produce monoliths with densities as low as 80 mg/cm3. Electrical conductivities of >100 S/m and BET surfaces areas >1500 m2/g were observed. In this presentation, we will describe the synthesis of these nanostructures (which can be generalized for other metal oxides), as well as the characterization of structural and electrical properties.
9:45 PM - V3.7
Hydrogen and Carbon Dioxide Sensors Based on Transparent Titania Nanotube Array Films for Non-invasive Medical Application.
Oomman Varghese 3 1 , Maggie Paulose 1 , Kefeng Zeng 3 , Thomas LaTempa 2 1 , Somnath Roy 1 , Lei Mei 2 , Craig Grimes 2 1
3 , SentechBiomed Corporation, Boalsburg, Pennsylvania, United States, 1 Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania, United States, 2 Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractGases evolved from the human body have been routinely used as a means to diagnose various diseases and patient conditions. Earlier we developed an integrated resistive sensor system operating at room temperature for monitoring transcutanous hydrogen in lactose intolerant patients. The sensing element was comprised of a micron length (hydrogen sensitive) titania nanotube array film upon a titanium foil base. We have recently developed low temperature carbon dioxide sensors by performing a surface treatment on the same nanostructure. While nanotube arrays grown on titanium foil offer easy fabrication they suffer from a fragile nature, being easily broken. Furthermore, the oxide layer formed on the foil, underneath the nanotubes, during the annealing-crystallization step results in a high base resistance and hence the need of sophisticated electronics for resistance monitoring. We have successfully fabricated micron length transparent nanotube arrays on FTO coated (conductive) glass. These films are robust and offer flexibility in varying the base resistance of the sensor. Evaluation and performance of the room temperature hydrogen and carbon dioxide sensors fabricated using micron length transparent nanotube arrays will be presented.
10:00 PM - **V3.8
Semiconducting Oxide Nanowires: Synthesis, Transparent Electronics and sensing Applications
Chongwu Zhou 1
1 Ming-Hsieh Department of Electrical Engineering , University of Southern California, Los Angeles, California, United States
Show AbstractSemiconducting metal oxide nanowires have attracted great research efforts due to their unique properties and a wide variety of applications in transparent electronics, chemical sensors and bio-sensors. They can also be used as active materials for next generation displays and portable electronics. In this presentation, we will present our recent achievements in the synthesis and device applications based on metal oxide nanowires. We developed a laser ablation method for the synthesis of different metal oxide nanowires, including In2O3 nanowires, SnO2 nanowires and some doped In2O3 nanowires. Besides, we are also able to get complicated metal oxide nanowires, such as In2O3 nanowire network, bundled In2O3 nanowires.With the capability of synthesizing high-quality nanostructured materials, we fabricated high performance transparent thin film transistors (TTFTs) using both pristine In2O3 nanowires and doped In2O3 nanowires. The In2O3 nanowire TTFTs were made on glass and PET substrates using Al2O3 as gate insulator and ITO as both source and drain electrodes. These devices showed a transparency of about 80% and n-type transistor performance. A subthreshold slope of 0.2 V/dec, a current on/off ratio of 106, and a field-effect mobility of 514 cm2V-1S-1 were fulfilled on these nanowire TTFTs.Besides, with incorporations of Arsenic dopants into In2O3 nanowires, As-doped In2O3 TTFTs were also fabricated, which exhibited a subthreshold slope of 0.2 V/dec, a current on/off ratio of 106, and a field-effect mobility of 1,342.8 cm2V-1S-1 without any post-treatment. In addition, we successfully integrated In2O3 TTFTs with organic light emitting diodes (OLEDs) to make an active matrix organic light emitting diode (AMOLED) display, and thus enabled to show an animation in the display by controlling nanowire TTFTs.Moreover, we will talk about our recent work in electronic nose and bio-sensing study. Through an integration of different nanostructured materials in a chemical sensor array, including In2O3 nanowires, ZnO nanowires, SnO2 nanowires, and carbon nanotubes, a senor array successfully detected important industrial gases including ethanol, carbon monoxide, and hydrogen with good selectivity. In bio-sensing, by conjugating peptide aptamers with In2O3 nanowires, the In2O3 nanowire biosensors can detect syndrome coronavirus (SARS-CoV) nucleocapsid (N) protein down to 600 pM. These sensors have great potential to be applied in both cancer therapy and disease diagnosis.
Symposium Organizers
Junqiao Wu University of California-Berkeley
Anderson Janotti University of California-Santa Barbara
Weiqiang Han Brookhaven National Laboratory
Ho-Cheol Kim IBM Almaden Research Center
V6: Poster Session: Electrical, Optical Properties
Session Chairs
Wednesday PM, April 15, 2009
Salon Level (Marriott)
9:00 PM - V6.1
Gas Sensors Based on Polymerized Acrylonitrile/ZnO Nanobelts.
Chih Ho 1 , Cheng-Ying Chen 1 , Jr-Hau He 1
1 , National Taiwan University , Taipei Taiwan
Show Abstract Hybrid nanomaterials can combine the features of different nanomaterials and tailor the properties to achieve the desired material performance. Due to the ultrahigh surface-to-volume ratio and reduced dimensionality of the active area in the one-dimensional nanostructures, chemical sensing based on these nanostructures has attracted enormous attention. Moreover, the unique structural and electrical properties of ZnO nanostructures [1-4] have encouraged scientists to develop ZnO nanostructured gas sensors since the device responds to the change in the electrical conductance occurring in the surface-surrounding atmosphere [1, 5-6]. However, the high-temperature operation of unmodified ZnO nanostructured sensors not only consume energy but also deteriorate the structure of the sensing layers, causing instability in the response. As a result, it is worth investigating whether it is possible to utilize other functional nanomaterials to enhance properties of gas sensing at low working temperature. The concept of the sorption of gas in the polymer has been utilized in mass-sensitive resonant frequency sensors [7], in which transduction involves measuring mass changes, volume changes, conductance changes, or capacitance changes, induced by sorption of gaseous analytes in the polymer. Typically, the sensitivity of these sensors does not exceed 10-100 ppm for common analytes [7]. Reaching a level below 10 ppm is seen only in some cases [8]. Accordingly, the sorbent polymer-coated ZnO nanostructures may exhibit a substantial improvement in the sensitivity of the gas sensor performance compared with unmodified ZnO nanostructures. In this work, we present a bilayer polymer/ZnO gas sensor based on ZnO NBs and plasma polymerized acrylonitrile (PP-AN) nanoscale surface coating with better oxygen-sensing response than unmodified ZnO NBs due to oxygen sorption in PP-AN. We also demonstrate that UV light illumination can enhance the oxygen sensing of PP-AN/ZnO NBs significantly by modifying the surface potential since the effects of oxygen desorption and adsorption of the polymer on the electron depletion region of the ZnO is significant under UV light. The sensing results obtained using this prototype sensor of the bilayer nanomaterial demonstrate encouraging performance aspects including reduced operating temperature, reduced power consumption, and enhanced sensitivity.References[1]Wang Z L 2004 Annu. Rev. Phys. Chem. 55 159-96[2]Pan Z W, Dai Z R and Wang Z L 2001 Science 291 1947-9[3]He J H, Hsin C L, Liu J, Chen L J and Wang Z L 2007 Adv. Mater. 19 781-4[4]He J H, Lao C S, Chen L J, Davidovic D and Wang Z L 2005 J. Am. Chem. Soc. 127 16376-7[5]Fan Z Y, Wang D W, Chang P C, Tseng W Y and Lu J G 2004 Appl. Phys. Lett. 85 5923-5[6]Sberveglieri G 1995 Sens. Actuators B: Chem. 23 103-9[7]Grate J W 2000 Chem. Rev. 100 2627-48[8]Thomas S W and Swager T M 2006 Adv. Mater. 18 1047-50
9:00 PM - V6.10
Influence of the Internal Stress on the Phase Transitions in Y2O3 Thin Films Induce by Thermal Annealing and Ion Implantation.
Fabien Paumier 1 , Bertrand Lacroix 1 , Michael Jublot 2 , Jerome Pacaud 1 , Rolly Gaboriaud 1
1 Laboratoire de Physique des Matériaux (PHYMAT), University of Poitiers, Chasseneuil Futuroscope France, 2 LETI MINATEC , CEA, Grenoble France
Show AbstractOxides with fluorite-related structure as pyrochlore or rare earth oxide with bixbyite structure (Ia3) Re2O3 have been recently an active area of researches because of their high radiation damage tolerance. Yttrium oxide, Y2O3, has also several physical properties particularly relevant for MOS devices and optical applications in the fields of luminescence (high dielectric constant and high refractive index). The physical properties of these materials deposited as a thin film strongly depend on their microstructure and thus on the elaboration conditions. Y2O3 thin films were deposited by Ion Beam Sputtering (IBS) on different substrates. The IBS deposition technique promotes a very particular structure with different and controlled nonstoichiometry or defects concentration due to a strong perturbation of the oxygen vacancy network induced by argon bombardment during the growth (atomic peening effect). By combining RBS, X-Ray Diffraction and Transmission Electron Microscopy it is shown that oxygen stoichiometry can be accommodated either by a local disorder of the pre-existing oxygen vacancy network of the cubic-C Re2O3 structure (a disordered fluorite-like structure) or, in a strong nonstoichiometric case (the unique valence state of Yttrium cation do not allow a charge compensation), by extended defects (aggregation of oxygen vacancies into a disc across which the crystal collapses to create prismatic dislocation loops). Both types of defects, oxygen vacancy network disorder and dislocations, induce an important elastic strain field and leads to a very high compressive stress in thin films.This work shows two major results leading to establish a strong relationship between internal stress and the phase transformations induced by annealing or ion implantation: - The study of stress relaxation under thermal annealing is performed by in situ quantitative X-ray diffraction (KJMA’s theory). It is clearly shown that the process occurs by complete recrystallization via nucleation and growth of a new cubic-C structure with a low density of defects with activation energy depending on the initial compressive stress. - For ion implantation, experiments were performed at cryogenic temperature with xenon ions in a range of fluence of 1.10^11 – 1.10^16 ions/cm^2, and at different energies (70-380 keV). Two dissimilar structural transitions were evidenced, depending on the implantation energy and on the initial compressive stress in the films. In the case of Y2O3 which exhibits the highest density of defects and dislocations (high compressive stress), partial nano crystallization (amorphization?) occurs for energies below 180 keV. Above 180 keV, a transition from cubic to monoclinic structure is observed. The elastic strain stored in thin film (before implantation) turn out to be a driving force for the structural transformations induced by ion implantation and can explain the dependence with the deposited energy.
9:00 PM - V6.11
Investigation of MgAlON Films on Electron Emission Properties.
Mikihiko Nishitani 1 2 , Masahiro Sakai 2 , Masaharu Terauchi 1 , Yukihiro Morita 1
1 Co-operation Laboratory of Panasonic, Osaka university , Suita Osaka Japan, 2 Image Devices Development Center, Panasonic Corporation, Moriguchi Osaka Japan
Show AbstractMgO is put to practical use as a protective film of the plasma display with Ne/Xe discharge gas, since MgO is transparent, and sputtering characteristics-resistant are high, and the secondary electron emission coefficient (γ) for the Ne ion which is necessary for the low voltage of the electric discharge is high. It will be more necessary to design the material with the high secondary electron emission coefficient for Xe ion to realize the electric discharge which is low voltage with high efficiency in plasma display. So far, it was suggested CaO, SrO, BaO or the composite materials of those. However, due to the ionicity of those materials, surface reaction of hydration / carbonate proceeds in the atmosphere quickly, and it is difficult to control the secondary electron emission coefficient (γ) . As a result, the oxide of the alkaline-earth metal does not reach practical use. On the other hand, we think that we may manufacture a film which has high secondary electron emission coefficient (γ) with surface satability, using MgO-AlN system. That system can be controlled the energy differences from a vacuum level to a fermi level (a work function) with the use of NEA (Negative Electron Affinity) of AlN. And, the instability of the surface of MgO may change with the covalency of AlN. In this study, we try to design the material with MgO-AlN system to meet the demand of the plasma display which can expect high electron emission by the Xe ion irradiation with the surface stability. The film of MgO-AlN system was manufactured by the conventional magnetron sputtering with MgO sintering target and Al or AlN sintering target and MgO granules. As for the film which we made, a lot of content of the oxygen is observed, and it is thought that the composite films consist of MgO - AlN - Al2O3 . We also observed that a fermi level could be raised by letting AlN composition increase, which were confirmed by ultraviolet photon energy dependence of the electronic emission. We studied with XPS that the surface reaction, such as surface hydration / carbonate of MgO, could be controlled in addition of AlN. The electric discharge characteristics were evaluated from the minimum pressure that an RF electric discharge produced. As let Al/ (Mg+Al) increase by the evaluation that used Ar gas for, an electric discharge characteristic is improved,; but, the dependence of the electric discharge characteristic changes around Al/(Mg+Al) ~ 0.7. We are going to carry out a more detailed analysis by film structure and the most surface measurement that are on an electronic state.
9:00 PM - V6.12
Development of a Chemiresistor Sensor for Polypropylene Degradation Products.
Shawn Dirk 1 , Patricia Sawyer 1 , Robert Bernstein 1 , James Hochrein 2 , Cody Washburn 1 , Stephen Howell 3 , Darin Graf 4
1 Organic Materials, Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 Materials Reliability, Sandia National Laboratories, Albuquerque, New Mexico, United States, 3 Rad Hard CMOS Technology, Sandia National Laboratories, Albuquerque, New Mexico, United States, 4 Advanced Sensor Technologies, Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractRecently we have examined the use of cross-linked assemblies of nanoparticles as a chemiresistor-type sensor for the detection of degradation products from the oxidative and radiation induced degradation of polypropylene. We have developed a simple method that uses a silica matrix to fabricate a chemiresistor-type sensor that minimizes the swelling transduction mechanism while optimizing the change in dielectric response. These sensors were exposed with the use of a gas chromatography system to three previously identified polypropylene degradation products including 4-methyl-2-pentanone, acetone, and pentanone and the limits of detection (LoD) were determined for each analyte. Recent results using other bridged polysiloxane precursors and plasticizers will also be discussed. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin company, for the United States Department of Energy under contract DE-AC04-94AL8500.
9:00 PM - V6.13
Piezoelectric Diode Based Switches.
Jun Zhou 1 2 , Peng Fei 1 3 , Yudong Gu 1 3 , Wenjie Mai 1 , Yifan Gao 1 , Rusen Yang 1 , Gang Bao 2 , Zhong Lin Wang 1
1 School of Materials Science and Engineering, Georgia Institute of technology, Atlanta, Georgia, United States, 2 Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, United States, 3 Department of Advanced Materials and Nanotechnology, Peking University, Beijing China
Show AbstractA flexible, optically transparent, water proof and well packaged device was fabricated by using a two-end bonded ZnO piezoelectric-fine-wire (PFW) (nanowire, microwire) on a flexible polymer substrate. The study of electromechanical properties of the device was carried out in atmosphere at room temperature. The strain induced change in I-V transport characteristic from symmetric to diode-type has been observed [1]. When the devices were under compressive strain, as the strain was increased, the currents both under positive bias and negative bias were suppressed. Finally a diode-like I-V behavior is received. Statistic study showed that the ratio of the devices, which exhibited downward and upward diode-like I-V behavior under compressive strain, is nearly 1:1. This phenomenon is attributed to the asymmetric change in Schottky-barrier heights at both source and drain electrodes as caused by the strain induced piezoelectric potential-drop along the PFW, which have been quantified using the thermionic emission-diffusion theory. Based on this study, a new type piezotronic switch device with an “on” and “off” ratio of ~120 has been demonstrated. Our studies also provide solid evidence about the existence of piezoelectric potential in the ZnO wire although it has a moderate conductivity. This means that the free carriers can partially screen the piezoelectric potential/charges, but they cannot completely neutralize the charge. The existence of the piezoelectric-semiconductor coupling process not only supports the mechanism proposed for nanogenerators and piezotronics, but also can be used to fabricate a new type of piezoelectric diodes and switches, which are highly-sensitive, cost-effective, versatile and fully packaged for a wide range of applications.[1] Piezoelectric-potential-controlled polarity-reversible Schottky diodes and switches of ZnO wires, J. Zhou, P. Fei, Y. D. Gu, W. J. Mai, Y. F. Gao, R. S. Yang, G. Bao, Z. L. Wang, Nano Letters, 2008, on line.[2] For more information: http://www.nanoscience.gatech.edu/zlwang/
9:00 PM - V6.14
Effect of the Interface Roughness on the Performance of Nanoparticulate Zinc Oxide Field-Effect Transistors.
Koshi Okamura 1 , Norman Mechau 1 , Donna Nikolova 1 , Horst Hahn 1
1 , Institute of Nanotechnology, Forschungszentrum Karlsruhe, Karlsruhe Germany
Show AbstractField-effect transistors (FETs) based on nanocrystalline materials have been attracting great interests as a promising candidate for printable electronics. The nanocrystalline FETs mostly work in the n-channel enhancement mode, which has rarely been accomplished by organic FETs. Furthermore, the FETs can be fabricated in solution-processes such as chemical bath deposition, spin-coating solution of precursor followed by postannealing, or spin-coating suspension of nanocrystals. Spin-coating suspension of nanocrystals has the advantage over the other two solution-processes in terms of low temperature and high throughput processing, leading to low-cost and large-area device fabrications. However, the critical parameter of such FETs is the interface roughness between the nanocrystalline semiconductor and the insulator. Because the nanocrystalline semiconducting layer consists of nanocrystals and their agglomerates in the range of a few tens of nm, it is expected that the interface roughness thicker than or comparable to the thickness of the carrier accumulation has a significant influence on the FET characteristics. Therefore, nanoparticulate zinc oxide (ZnO) FETs are taken as a model system of nanocrystalline FETs, and the effect of the interface roughness on the field-effect mobility is investigated in conjunction with the film roughness and the capacitance analyses.ZnO nanoparticles were dispersed in 2-methoxyethanol with a small amount of copolymeric stabilizer, and were processed by ultrasonic treatments. The agglomerate sizes were changed by the duration of the process, so that the resulting films have different roughness at the interface to the insulating layer. The FETs in the bottom-gate configuration were fabricated from the suspensions, consisting of a lightly doped p-type Si substrate, a thermally grown SiO2 layer of 200 nm, a spin-coated nanoparticulate ZnO layer, and resistively evaporated top Al source and drain electrodes. The FET with the lowest average roughness of 47.4 nm showed the best mobility of 8.4x10-3 cm2/Vs. In contrast, the FET with the highest roughness of 70.6 nm showed two orders of magnitude lower mobility of 8.7x10-5 cm2/Vs. These results indicate that the roughness at the interface between a nanoparticulate layer and an insulating layer is a key parameter for the performance of nanoparticulate FETs.
9:00 PM - V6.15
Characterization of Bicontinuous Double Gyroid TiO2 Thin Films
Marleen Kamperman 1 , Edward Crossland 2 , Marc Hillmyer 3 , Ullrich Steiner 2 , Ulrich Wiesner 1
1 Materials Science & Engineering, Cornell University, Ithaca, New York, United States, 2 Department of Physics, University of Cambridge, Cambridge United Kingdom, 3 Department of Chemistry, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractWe have developed bicontinuous double gyroid hybrid solar cells using block copolymer templates. In principle, the double gyroid structure should be close to ideal for functioning photovoltaic devices since the monodisperse pore diameters and fully interconnected channels provide continuous connectivity of all electronically active phases to the device electrodes. However, in order to establish structure-cell performance relationships it is crucial to fully characterize the symmetry, order and orientation of the materials. In this presentation a full account of the characterization on the TiO2 thin films is given.Transmission small angle X-ray scattering was used to elucidate the morphological behavior of diblock copolymer poly(4-fluorostyrene)-b-poly(D,L-lactide) (PFS-b-PLA), which served as the template. Experimental and simulated grazing incidence small-angle X-ray scattering (GISAXS) patterns combined with experimental and simulated scanning electron microscopy (SEM) images were used to determine the order and orientation of the films at each processing step towards the TiO2 replica. Grazing incidence wide-angle X-ray scattering (GIWAXS) and high resolution transmission electron microscopy (HRTEM) studies were performed to determine the crystal structure and crystallite size in the final TiO2 structure.
9:00 PM - V6.16
Investigating the Structure and Morphology of Electrochemically Synthesized Titania Nanotubes via Cross-Sectional TEM and Micro-XRD.
Que Anh Nguyen 1 , Yash Bhargava 1 , Thomas Devine 1 , Velimir Radmilovic 2
1 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 2 National Center for Electron Microscopy, Lawrence Berkeley Labs, Berkeley, California, United States
Show AbstractTitania nanotubes have emerged as an exciting new material with a wide array of applications such as sensors, dye sensitized solar cells, and batteries due to their semi-conducting nature, high surface area, and distinct morphology. Their use in devices however, requires a clear understanding of the nanotubes' structure (micro and macroscopic) and properties, as well as their growth optimization via control of the synthesis parameters. In this work we examine the structure and morphology of electrochemically synthesized titania nanotubes via scanning electron microscopy (SEM), cross-sectional transmission electron microscopy (TEM), and micro-diffraction techniques. The nanotubes are grown via anodization of Ti in a fluoride-containing electrolyte. The tube diameter, length, and organization are controlled by synthesis parameters such as anodization voltage and time, and electrolyte chemistry. To our knowledge, this is the first time cross-sectional techniques have been implemented for the study of titania nanotubes. Cross-sectional TEM can provide information on the structure of the nanotubes at the atomic level, and allow for an evaluation of the tube morphology and defect crystallography. TEM analysis also gives an intimate view of the structural relationship between individual nanotubes, as well as between the nanotubes and the oxide barrier layer that serves as the interface between the nanotubes and the metal substrate. Microdiffraction, on the other hand, allows for structural analysis with high spatial resolution (1mmx1mm spot size), and provides a unique opportunity to investigate the crystal structure of the barrier layer. In addition, we probe the identity of the different oxide layers using energy dispersive spectroscopy (EDS). Because TiO2 is a highly functional material, a comprehensive appreciation of the atomic structure and properties of the nanotubes will enable materials engineering and optimization for specific device applications.
9:00 PM - V6.17
High Mobility Low-Voltage Oxide Semiconductor Transistors and Circuits.
Paul Wobkenberg 1 , Aneeqa Bashir 1 , Jeremy Smith 1 , James Ball 1 , Donal Bradley 1 , Thomas Anthopoulos 1
1 Department of Physics, Imperial College London, London United Kingdom
Show AbstractElectronics based on metal oxide semiconductors is an emerging technology that aims to demonstrate transparent microelectronics for use in existing but also new applications spanning from optical displays and logic circuits to improved renewable energy sources such as photovoltaics. Only five years since their first demonstration, oxide transistors have already managed to outperform other competing materials technologies such as organic semiconductors and amorphous silicon. Despite the immense progress, however, the promise of transparent semiconductors and devices as an enabling, or even disruptive, technology is only likely to be realised when a combination of simple processing and high-performance can be achieved.The aim of our work is twofold. First, we address the issue of simple manufacturing and second we address the issue of the high operating voltages typical for state-of-the-art oxide transistors. In particular, we demonstrate the use of a simple deposition technique, namely spray pyrolysis (SP), for the fabrication of high carrier mobility low-voltage oxide electronics. Despite the widespread use of this technique in other conductive oxide application areas, this is the first time that SP is employed for the fabrication of oxide transistors.To demonstrate the potential of this alternative deposition method we fabricate high mobility electron-transporting transistors based on zinc oxide (ZnO) deposited at different substrate temperatures. Film deposition is performed entirely in ambient atmosphere without any special precautions. It is established that as-deposited ZnO films are smooth with excellent uniformity. Transistors based on these ZnO films show strong electron transport with maximum mobility of 10-15cm^2/Vs. Threshold voltages and current on-off ratios are between 10-20V, and 10^4 - 10^6, respectively. The derived electron mobility is found to depend strongly on the substrate temperature during film deposition as well as on the transistor architecture employed. For example, in terms of electron mobility, bottom-gate, bottom-contact transistors are found to perform worse than bottom-gate, top-contact devices by a factor of 5 to 6.Another key finding of this work is the compatibility of SP with a number of solution processible self-assembled monolayer molecules that can be utilised as nanometre-thin gate dielectrics. By combining spray pyrolysis with solution processible phosphonic acid based self-assembled monolayer nanodielectrics, we are able to demonstrate high mobility (>10cm^2/Vs) ZnO transistors operating below 1.5V. Using these transistors, we have fabricated unipolar inverter circuits with excellent operating characteristics such as low-voltage (<2V) and negligible operating hysteresis. Our proposed method is simple and compatible with a wider range of precursor materials and could even enable incorporation of suitable dopants without the need for demanding conditions typically required by other deposition methods.
9:00 PM - V6.18
Structural, magnetic and transport properties of Co:ZnO:N.
Verena Ney 1 , S. Ye 1 , T. Kammermeier 1 , A. Ney 1
1 Experimentalphysik, Universität Duisburg-Essen, Duisburg Germany
Show AbstractFor spintronic applications it would be adjuvant to develop semiconductor materials which exhibit a controllable magnetization and conductance. Approaches with 10%Co doped ZnO have shown that films with high quality show a purely paramagnetic behaviour [1,2], which turns to be superparamagnetic as soon as clusterformation starts. For reactive magnetron sputtering these properties can be tuned by changing the oxygen content of the sputter gas. The resistance of the n-type films decreases with decreasing oxygen content – clusters emerge. One of the most important steps towards practical applications is the development of p-type ZnO which has been tried especially with co-doping of nitrogen. We investigated the influence of nitrogen on the structural, magnetic and transport properties of 10%Co:ZnO. These films were prepared by substituting O2 with N2 in the sputter gas, which was done in the range of (Ar:O2:N2) 10:1:0 to 10:0.3:0.7. The presence of nitrogen enhances the structural quality of the films. Up to 10:0.5:0.5 the films stay purely paramagnetic - the usual onset of clustering is shifted towards lower oxygen contents. First transport measurements reveal an even further increased sheet resistance of more than 100 GΩ at RT for high N-contents. [1] A. Ney et al, Phys. Rev. Lett. 100, 157201 (2008)[2] T. C. Kaspar et al, New J. Phys. 10, 055010 (2008)
9:00 PM - V6.19
Co-doped ZnO: From an Anisotropic Paramagnet to a Phase Separated Superparamagnet.
Andreas Ney 1 , S. Ye 1 , T. Kammermeier 1 , K. Ollefs 1 , V. Ney 1 , F. Wilhelm 2 , A. Rogalev 2 , T. Kaspar 3 , S. Chambers 3
1 Experimentalphysik, Universitaet Duisburg-Essen, Duisburg Germany, 2 , European Synchrotron Radiation Facility, Grenoble France, 3 Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractThe hope of discovering a dilute magnetic semiconductor (DMS) with ferromagnetic order up to room temperature (RT) still motivates research on suitable material combinations. One candidate is Co:ZnO, which has been widely studied in the past years, but with contradicting results. We recently reported the absence of intrinsic ferromagnetic interactions in pulsed laser deposited (PLD) Co:ZnO films with a high structural perfection as measured by x-ray linear dichroism (XLD) [1]. On the other hand, clustered material and defects were considered to be the major source for the ferromagnetic-like behavior [2]. To study the magnetic properties in greater detail, we prepared a series of Co:ZnO-films on c-plane sapphire by reactive magnetron sputtering. The structural and electronic properties are readily tuned by the Argon-to-Oxygen ratio of the sputter gas. The structure was characterized using x-ray diffraction (XRD) and XLD, revealing that for optimized oxygen-rich preparation conditions Co:ZnO grown by sputtering as well as PLD samples are devoided of phase separated material and the Co:ZnO films behave paramagnetic with single-ion anisotropy in agreement with [1] and [3]. If the preparation conditions are altered to oxygen-deficient ones, the magnetic behaviour changes significantly: SQUID magnetometry and magnetic resonance studies reveal that such samples behave like a blocked superparamagnetic ensemble with blocking temperatures up to room temperature. In this regime, phase separated Co and/or CoO clusters can be detected by XRD. In the intermediate regime XLD studies reveal that a large fraction of the Co dopant atoms are not located on Zn-substitutional sites and indications of metallic Co can be found in the x-ray absorption spectra. In the entire range of preparation conditions we find no sign of intrinsic ferromagnetism for the homogeneous Co-doped ZnO system without other co-dopants if phase separated Co and/or CoO are absent. The influence of n-type doping will be briefly addressed.[1] A. Ney et al., Phys. Rev. Lett. 100, 157201 (2008).[2] T. C. Kaspar et al., Phys. Rev. B 77, 201303(R) (2008).[3] P. Sati et al., Phys. Rev. Lett. 96, 017203 (2006).
9:00 PM - V6.2
Correlation of Electronic Properties with Ferromagnetism in Cu-doped ZnO.
Chang Oh Kim 1 , Sung Kim 1 , Ji Sun Nam 1 , Hyoung Taek Oh 1 , Suk-Ho Choi 1 , Yun Son 2
1 College of Electronics and Information, Kyung Hee University, Yongin, Kyungkido, Korea (the Republic of), 2 Quantum-functional Semiconductor Research Center, Dongguk University, Seoul Korea (the Republic of)
Show AbstractStructural, optical, and magnetic properties of Cu-doped ZnO (ZnO:Cu) films grown on Si (100) at 400 oC by RF magnetron sputtering have been studied by SEM, XRD, PL, XPS, and SQUID. Cu concentration (nCu) is varied from 0 to 3 mol % and the film thickness is ~ 100 nm. The XRD peak observed dominantly at about 34o is attributed to the ZnO (002) plane, and its intensity decreases with increasing nCu, consistent with the nCu-dependent change of the near-band-edge PL intensity. At nCu=3 mol %, not only the ZnO phase but also metallic Cu and Cu2O phases are observed in the XRD patterns, whilst only the ZnO (002) peak is visible at nCu < 3 mol %. This could indicate that the thermal solubility limit of Cu in ZnO is below 3 mol %. The XPS intensities of Zn 3d, Zn 3p, and Zn 3s states decreases gradually as nCu increases from 0 to 3 mol %, also consistent with the PL intensity variation with nCu. The Fermi level up-shifts from the VB maximum (VBM) when nCu ≤ 1 mol %, but when nCu ≥ 2 mol %, it down-shifts. The Fermi level of undoped ZnO is located at ~ 1.83 eV with respect to the VBM, and moves up to ~ 3.21 eV at nCu = 1 mol %. The M-H curves shows that ZnO:Cu films exhibits a transition from paramagnetism to ferromagnetism (FM) as nCu increases from 0 to 1 mol %. When nCu ≥ 2 mol %, the FM character of ZnO:Cu films is weakened. These results suggest that the nCu-dependent change of magnetization in ZnO:Cu films is closely correlated to their electronic properties. The M-T curves under zero- and nonzero- field-cooling conditions shows that the Curie temperature is higher than 300K. Possible physical mechanisms are discussed to explain the experimental results.
9:00 PM - V6.21
Unconventional Semiconducting ZnO Thin Films.
Jelena Buha 1 , Igor Djerdj 2 , Zoran Djuric 1
1 , IHTM- Institute of Microelectronic Technologies and Single Crystals , Belgrade Serbia, 2 , Department of Materials, Swiss Federal Institute of Technology (ETH), Zürich Switzerland
Show AbstractThe development of nanosized electronics is becoming more and more important to modern society. Nowadays the need for nanoscale devices that can process data at high speed and store information with high density is widely recognized.[1] The successful development of nanotechnology depends on the ability of researchers to efficiently manufacture structures smaller than 100 nm. Traditional optical lithography and etching techniques used in semiconductor industry are impractical for structures smaller than 100nm since their resolution is limited by the wavelength of the light used (Top-Down approach). Therefore, there is a need of nanosized electronic components that can be addressed by traditional optical lithography and etching techniques. Furthermore, it is desired that visible light will have little or zero influence on the device. Therefore, the semiconductor band gap must be sufficiently large (>3 eV) so that exposure to visible light does not cause an inter-band transition. A material that is capable of yielding a high mobility, low carrier concentration, and high band gap is ZnO. Zinc-oxide-based nanoparticles can be formed from the reaction of zinc acetylacetonate in acetonitrile, via solvothermal nonaqueous routes, as reported before.[2] Here we report a method to produce a zinc-oxide thin film semiconductor by spin coating a colloidal solution of zinc-oxide nanoparticles on a glass or silicon substrate, at temperatures of 300° C or less. The nanoparticles have an average primary size of 20 up to 100 nm and are stabilized in the colloidal solution. A high ion concentration might lead to aggregation and poor dispersion. After the particle formation, the level of ions is reduced by washing in order to obtain a stable dispersion. Therefore repeated washings are necessary, allowing thus the inorganic ion level to reach the desired concentration below 1 mM. After the stable nanoparticle colloidal solution is produced, a layer of zinc-oxide-based nanoparticles is applied by spin coating and subsequently annealed for 1-5 min at temperatures between 130°-300° C in the ambient environment. The resulting films with various thicknesses are further characterized by AFM and TEM techniques, whereas their electronic properties are successfully proved. This type of materials show promising applications in fields such as semiconductor channels of thin film transistors, display backplanes, portable computers, memory elements in transaction cards, and identification tags.[1] Nanotech: Special Issue: Sci. Am. 2001, September[2] Crystal Growth & Design; 7 (1); 113-116; 2007
9:00 PM - V6.22
Isotype n-ZnO/n-(Al)GaN Heterostructures and Field-effect Transistors.
Yahya Alivov 1 3 , Zhaoyang Fan 1 , Daniel Johnstone 2 , Xiao Bo 3 , Qian Fan 3 , Hadis Morkoç 3
1 Nano Tech Center and Department of Electrical and Computer Engineering, Texas Tech University , Lubbock, Texas, United States, 3 Depatment of Electrical Engineering, Virginia Commonwealth University, Richmond, Virginia, United States, 2 , SEMETROL, Chesterfield, Virginia, United States
Show AbstractElectrical properties of isotype n-ZnO/n-GaN and n-ZnO/n-AlGaN heterostructures obtained by rf-sputtering of ZnO films on III-nitride layers have been studied using temperature dependent current-voltage (I-V-T), deep-level transient spectroscopy (DLTS), capacitance-voltage (C-V), and photocapcitance methods. Highly rectifying behavior of n-ZnO/n-(Al)GaN diodes have been observed with forward to reverse currents ratios ~10(5)-10(6) at ±5 V. Current-transport properties as well as point defect structure of the grown n-ZnO/n-(Al)GaN heterostructures have been analyzed. From C-V profiles existence of high density electron gas at the n-ZnO/n-GaN interface has been observed that is consistent with measured band alignment of these structures. Arrhenius plot using I-V-T data revealed activation energy 0.125 eV for the reverse bias leakage current path, and 0.62 eV for the ZnO/GaN band offset from forward bias measurements. Field effect transistors with ultrathin ZnO layers (30-100 nm) on such n-GaN and n-AlGaN layers have been fabricated and the performance has been studied as a function of ZnO thickness and doping.
9:00 PM - V6.23
Work Function Effects of Nano Structured ZnO Thin Film on the Acetone Gas Sensitivity.
Seung Hyun Jee 1 , Soo Ho Kim 1 , Young Soo Yoon 1
1 Ceramic Engineering, Yonsei University , Seoul Korea (the Republic of)
Show AbstractWe deposited various nano structured ZnO thin films on a polycrystalline aluminium substrate to fabricate an acetone gas sensor at below 200 degree C. Even though ZnO thin film shows relatively high sensitivity for acetone gas, the operation temperature and detectable minimum acetone gas concetration are still high when we consider the real commercial application of ZnO thin film based gas sensor. It is very well known large effective surface area of ZnO thin film gives positive effects on gas sensitivity. In order to increase the surface area of ZnO thin film, nano structured ZnO thin film with nano rod or nano wall is very effective, since the electron transfer reacion occurred on surface of ZnO thin film. The electron trnasfer on surface depends on work function. However, influence of work function of ZnO thin film on acetone gas sensitivity has not been reported yet. In this study, Zno thin films with various nano structures were deposited by a r.f. sputtering method on aluminium substrate with micro heater and sensing electrode. In order to control the work function intentionally, different deposition conditions were used. In conclusion, we suggested that the sensitivity strongly depends on the work function of the as-deposited nano structured ZnO thin film.
9:00 PM - V6.25
Evolution of the textural, structural and morphological properties of freeze- dried Ag-TiO2 nanoparticles tailored by temperature.
Marcelo Viana 1 , Nelcy Mohallem 1
1 Química, Universidade Federal de Minas Gerais, Belo Horizonte Brazil
Show AbstractTiO2 appears to be a promising and important prospect for use in environmental purification due to its strong oxidizing power, photoinduced hydrophilicity, non-toxicity and long-term photostability. Nanocomposites formed by titania and silver have potentials applications since silver particles can act as electron traps aiding electron–hole separation. This serves the purpose of mediating the electrons away from the TiO2 surface, hence preventing them from recombining with the holes.Titanium isopropoxide (IV) and silver nitrate solution was used as starting of Ag-TiO2 nanoparticles. After precipitation at room temperature, this material was freeze-dried and annealed at various temperatures between 200 and 1200οC. The precipitate was characterized by thermogravimetry-differential thermal analysis (TGA-DTA). FTIR and XRD were used to investigate the structural evolution of the nanoparticles, the anatase–rutile phase ratio and the dependence of crystallite size with the annealing temperature. The morphology changes were investigated using SEM and TEM. Textural characteristics of the materials as specific surface area, porosity and pores distribution were investigated by nitrogen gas adsorption. The nanocomposites showed interesting textural and morphological characteristics and potential application in photocatalytic and bactericidal devices.
9:00 PM - V6.26
Nickel Oxide and Polymer Composite Electrodes for Tunable Charge Storage.
Michael Brumbach 1 , Dave Wheeler 1 , Bonnie McKenzie 1 , Todd Alam 1 , Bruce Bunker 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractElectrochemical capacitors are high power devices where charge is either stored at the electrical double layer at the solid/electrolyte interface or via redox processes within the solid/electrolyte near-surface, i.e. pseudocapacitance. These charge storage mechanisms can be reversed quickly leading to fast discharge rates and thereby differentiating them from battery performance. Several metal oxides are known to act as effective capacitor and/or battery electrodes, such as RuO2, NiOOH, and MnO2. However, either electrical conductivity and/or cation diffusivity are often poor in these materials. The addition of conducting polymers has been shown to create a synergistic effect thereby increasing conductivity and capacitive properties. In this work pseudocapacitive properties are evaluated by creating NiOOH/Ni(OH)2 electrodes with nanoscale architectures to: 1) maximize interfacial contact area with electrolyte, 2) increase solution access to electroactive material, and 3) decrease diffusion distances for charge compensating cations. Electrodeposition, codeposition, and evaporation induced synthesis were utilized to create nanoscale architectures of the nickel oxide. Composite electrodes will be discussed where monomeric precursors to conducting polymers were used in the synthesis of the metal oxide thin film to aid in directing the formation of nanoscale features and/or to infiltrate the film with conducting material upon polymerization. Monomeric components (including benzothiadiazoles) were also chosen to selectively tune the redox potential in order to obtain a greater voltage window for a pseudocapacitive response. Cyclic voltammetry and impedance were used to evaluate electrode compositions and the efficacy of certain nanoscale architectures for increasing electrochemical capacitance. Mechanisms for the increased capacitance were investigated using materials characterization including XRD, SEM, and NMR.
9:00 PM - V6.27
Heteroleptic Osmium(II) Terpyridyl Sensitizers for Application in Dye-Sensitized Solar Cells.
Anthony Onicha 1 , Felix Castellano 1
1 Chemistry & Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio, United States
Show AbstractA series of novel dyes of mixed denticity based on Os(II) bearing modified terpyridine ligands have been designed and synthesized. The compounds have been structurally characterized and investigated photophysically, electrochemically and photoelectrochemically in operational dye sensitized solar cells. Dye-sensitizers based on Os(II) offer comparable performances relative to those based on Ru(II) with the added advantage of extended absorption properties into the red and near-infrared region of the electromagnetic spectrum and superior chromophore stability to extended light soaking. Certain modified terpyridine ligands lead to higher extinction coefficients and light-harvesting properties that extend to lower energy regions of the spectrum. Dye-sensitized solar cells based on these dyes have been fabricated and studied alongside the benchmark molecule N3, Ru(dcb)2(NCS)2, to standardize performance comparisons.
9:00 PM - V6.28
Electrical and Optical Characteristics of Tin-Doped Indium Oxide Nano-Columns Prepared by Glancing Angle Deposition with Nitrogen.
Min-Hsiang Hsu 1 , Chia-Hua Chang 2 , Peichen Yu 2 , Ming-Shin Su 3 , Kung-Hwa Wei 3
1 Department of Physics, National Tsing Hua University, Hsinchu Taiwan, 2 Institute of Electro-Optical Engineering, National Chiao-Tung University, Hsinchu Taiwan, 3 Department of Materials Science and Engineering, National Chiao-Tung University, Hsinchu Taiwan
Show AbstractTin-Doped Indium Oxide (ITO) has been widely employed as a transparent conductive thin film for a variety of applications, such as organic and semiconductor light emitting diodes, flat panel displays, and thin-film solar cells. The unique transparent and conductive properties of ITO arise from both the wide bandgap of indium oxides and the incorporated oxygen vacancies, and therefore facilitate the injection-current spreading for light emitting diodes and photogenerated-carrier collection for solar cells. However, the conversion efficiencies of optoelectronic devices are still limited by the transmission loss due to the ITO film and a finite carrier life time. Over the past few years, multiple studies have been made on the enhanced transmission using sub-wavelength structured (SWS), anti-reflective surfaces, based on the zero-grating effect. The SWS surfaces have several advantages over the conventional dielectric anti-reflective coatings, such as omnidirectional and broadband responses, polarization insensitivity, and reliability in harsh and abrasive environments. It is therefore very advantageous to investigate ITO nanostructures that could not only offer broad angular and spectral anti-reflective characteristics, but also improve carrier collection due to increased surface areas of electrodes.In this work, the synthesis of uniformly-oriented ITO nano-columns is successfully demonstrated using glancing-angle electron-beam evaporation. The characteristic column formation, assisted by the incident nitrogen flux, involves either catalyst-free or self-catalyst vapor-liquid-solid (VLS) growth mechanisms. The nano-column material exhibits broadband and omnidirectional antireflective characteristics (<6%), up to an incidence angle of 70° for the 300 nm-900 nm wavelength range for both s- and p- polarizations. Moreover, the sheet resistances that can vary from tens of ohms per square to a few hundred ohms per square are dependent on the nitrogen flow rate. The material and structural properties, such as the surface morphology and crystallinity of ITO nano-columns are also discussed for various growth conditions. Since the conductive ITO nano-columns prepared by glancing-angle deposition are fully compatible with current technologies, the novel material can offer a viable solution to boosting efficiencies of light emitting diodes and solar cells.
9:00 PM - V6.29
Microstructure and Electrical Properties of Nanocrystalline Ce0.8Sm0.2-xDyxO2-δ (0≦x≦0.15) for Intermediate Temperature Solid Oxide Fuel Cells.
J. Choi 1 , M. Heo 1 , S. Nam 1 , Kyeongsoon Park 1
1 , Sejong University, Seoul Korea (the Republic of)
Show AbstractSolid oxide fuel cell (SOFC) has attracted considerable attention because of its high-energy conversion efficiency and environmental friendship. Ce0.8Sm0.2-xDyxO2-δ (0≦x≦0.15) nanopowders for use as electrolyte of SOFC have been successfully synthesized by solution combustion method. The calcined Ce0.8Sm0.2-xDyxO2-δ nanopowders showed ceria-based single phase with a cubic fluorite structure. The crystallite sizes of the calcined Ce0.8Sm0.2-xDyxO2-δ nanopowders with various Dy contents ranged from 25 to 56nm. The calcined nanopowders were isostatically cold-pressed under 150MPa to prepare pellets. The electrical conductivity of the sintered pellets was measured in the temperature range of 400-800°C in air by using four-point DC method. We discussed the influence of Dy content on the microstructure and electrical properties of the nanocrystalline Ce0.8Sm0.2-xDyxO2-δ.
9:00 PM - V6.3
Strong Enhancement of Near-band-edge Photoluminescence from Carbon Nanotubes/ZnO Hybrid Structures.
Dong Hee Shin 1 , Sung Kim 1 , Sung Won Hwang 1 , Chang Oh Kim 1 , Suk-Ho Choi 1
1 College of Electronics and Information, Kyung Hee University, Yongin, Kyungkido, Korea (the Republic of)
Show Abstract100 nm ZnO films were fabricated on n-type Si (100) wafer by radio-frequency magnetron sputtering and subsequently annealed in a rapid thermal annealing system at 900oC for 3min in O2 ambient. Single-wall carbon nanotubes (CNTs) of 3 to 120 nm thickness (t) were then deposited on top of ZnO films by spin coating and vacuum filtration. Structural and optical properties of the CNT/ZnO hybrid structures were studied by using field emission scanning electron microscopy (FE-SEM), photoluminescence (PL), and cathodoluminescence (CL). The coverage of CNTs on the surface of ZnO increases with t, and their diameter ranges from ~ 0.8 to ~ 2 nm, as confirmed by FE-SEM. Near-band-edge (NBE) PL from ZnO is observed at ~ 385 nm for the hybrid structures as well as for a ZnO single layer. The NBE-PL intensity of the hybrid structures is larger than that of the ZnO single layer for all t values, and in particular, at t = 10 nm, the PL intensity is almost 9 times enhanced by the hybridization. The NBE-PL peak of the hybrid structures blue-shifts with respect to that of bulk ZnO for all t values. CL mapping shows that stronger luminescence comes from the ZnO region covered with CNTs. Based on these experimental results, possible luminescence mechanism is discussed.
9:00 PM - V6.30
Effect of Sintering Temperature on the Electrical Properties of Dy-doped Nanocrystalline Ce0.8Dy0.2O2-δ.
M. Heo 1 , J. Choi 1 , S. Nam 1 , Kyeongsoon Park 1
1 , Sejong University, Seoul Korea (the Republic of)
Show AbstractCeria-based oxide electrolytes with high ionic conductivity have attracted much attention for application in intermediate temperature solid oxide fuel cells. We successfully synthesized Ce0.8Dy0.2O2-δ nanopowders by solution combustion method. The Ce0.8Dy0.2O2-δ green bodies were sintered at various temperatures, ranging from 1300-1400°C. The nanocrystalline sintered bodies were characterized by XRD, TEM, and field emission scanning electron microscopy (FE-SEM). The crystal structure of the calcined Ce0.8Dy0.2O2-δ nanopowders and the sintered pellets belonged to a cubic fluorite structure. Higher sintering temperature resulted in enhanced grain growth and microstructural densification. Four-point DC method was used to measure the electrical conductivity at 400-800°C in air for the sintered nanocrystalline pellets. The correlation between the microstructure and electrical transport properties of the nanocrystalline Ce0.8Dy0.2O2-δ was discussed, depending on sintering temperature.
9:00 PM - V6.31
Improvement of Electrical Properties of Sputtered Zinc Oxide Thin Films by Using Zinc Doped Indium Oxide Seed-layer.
Zhiyong Qiu 1 , Pangpang Wang 2 , Ri-ichi Murakami 2 , Takashi Ishiguro 1
1 Faculty of Industrial Science and Technology, The Tokyo University of science, Noda, Chiba, Japan, 2 Department of Mechanical Engineering, The university of Tokushima, Tokushima, Tokushima, Japan
Show Abstract It is well known that un-doped ZnO thin films behave high transmittance and intrinsic n-type semi-conductive. But the intrinsic carrier concentration, from the oxygen vacancies, is not high enough to make ZnO thin films good electrical conductive. Doping some different elements (such as Al, Ga, etc.) is considered as the normal device to improve the electrical properties of ZnO thin films. Unfortunately, the doping of impure element will collapse the crystal structure of ZnO, and the impurity ions will also strongly scatter free electrons which make the carrier mobility falling. Therefore, obtaining high conductivity and good crystalline at same time is nontrivial. In this work, glass covered with 10nm thick indium doped zinc oxide (IZO) seed-layer, was used as substrate to prepare ZnO thin film by a magnetron sputtering system. IZO was selected as the seed-layer for the following reasons. First, the IZO have similar constitution and structure to the ZnO which can be expect to improve the crystallinity of ZnO films. Second, IZO film behaves high carrier concentration, which may charge ZnO layer to increase the carrier concentration of it. And the high transmittance of IZO film will not greatly affect the optical properties of ZnO/IZO bilayer thin films. As the result shows that the IZO seed-layer plays a very important role in improving the conductivity of the ZnO films. The IZO/ZnO bilayer thin films exhibit high electronic mobility and carrier concentration with high transmittance compared to undoped ZnO films deposited directly onto glass substrates. The best IZO/ZnO bilayer thin films obtained low resistivity of 3.2*10^–3 Ohm*cm with mobility of 20.3 cm^2/V*s, and carrier concentration of 9.6 *10^19 cm^–3, which are marked better than undoped ZnO monolayer films deposited under the same conditions (2.6*10^–2 Ohm*cm for resistivity, 8.5 cm^2/V*s for carrier mobility and 1.2*10^19 cm^–3 for carrier concentration). The simulated transmittance of the IZO/ZnO bilayer thin films of 200 nm in thickness was about 90%, which is good enough for use in most optical applications. The ZnO in bilayer thin films behave a 100 preferred orientation, with a sharp peak in XRD data. It was attributed the improvement of carrier mobility to the crystallinity improvement of ZnO, which affected by the IZO seed-layer, and the free electrons supplied by IZO seed-layer may be the most important reason of the increasing of carrier concentration. The detail mechanism was also discussed in this work. As the IZO seed layers used are as thin as 10 nm, this represents an economic choice to substitute ITO as transparent conducting oxide (TCO) films. It was also demonstrated that the IZO/ZnO structure can be stacked and still retain good electrical and optical properties. Furthermore, this technique is expected to be suitable for doped ZnO films such as aluminum-doped (AZO) films and gallium-doped zinc oxide (GZO).
9:00 PM - V6.32
Investigation of Plasma-induced Emission Properties of Large Area ZnO Nanorod Array Cathodes.
Qingliang Liao 1 , Junjie Qi 1 , Liansheng Xia 2 , Yunhua Huang 1 , Ya Yang 1 , Yue Zhang 1 , Huang Zhang 2
1 Department of Materials Physics, University of Science and Technology Beijing, Beijing China, 2 Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang China
Show AbstractHigh intensity electron emission cathodes based on well-aligned ZnO nanorod array were fabricated. An investigation of the high-intensity electron emission properties of the ZnO nanorod array cathodes was presented. Intense current electron beams were obtained from the cathodes. At electric field of 7-8 V/μm and pulse duration of ~100 ns, the highest emission current density reached 73-78 A/cm2. The production mechanism of the electron beams was the plasma-induced emission. The plasma expanded at a velocity of about 10.9 cm/μs during the pulse interval. Whether the emission currents are high or low, the plasma on the cathode surface were always distributed uniformly. The ZnO nanorod array cathodes are expected to be applied to high power vacuum electronic devices as electron beam sources.
9:00 PM - V6.33
Own Oxide Films on Cleaved Surface of Layered InSe Single Crystals Under Humidity Conditions.
S. Drapak 1 , S. Gavrylyuk 2 , Z. Kovalyuk 1
1 , Frantsevich Institute of Material Sciences Problems, National Academy of Sciences of Ukraine, Chernivtsi Ukraine, 2 , Chernivtsi National University, Chernivtsi Ukraine
Show AbstractIndium selenide InSe belongs to the wide group of layered semiconductors and is a prospective material for formation on its base of various optoelectronic devices. Investigations on the composition and structure of the transparent conducting oxide films formed on an InSe surface at different temperature and time regimes (XRD studies, Raman spectra, etc) of semiconductor substrate oxidation are widely presented in a number of publications. The interest to investigations of InSe own oxide (Ox) is caused by the possibility of using Ox-InSe structures as solar cells, radiation stable photodiodes for visible and near IR regions of spectral diapason, polarization-sensitive photodetectors, phototransistors, etc. As follows from these investigations the Ox formed at T > 320-360°C on surface of InSe can consist of In2Se3, In2(SeO4)3 or In2O3 (depending on heat treatment conditions of InSe). According to literature data the thermal oxidation at T < 320-360°C does not lead to oxide phase’s formation on the InSe surface.In this research on the base of XRD measurements and AFM investigations we have shown for the first time that Ox formed on InSe surface at T < 100°C consists of selenium selenate (insulating matrix) with the inclusions of In nanoparticles. The possibility to use In-Ox-InSe structures and indium selenide’s Ox as relative humidity (RH) sensors is under consideration. It is established that the surface resistance of Ox linearly decreases with increasing RH. It is shown that a long term keeping of Ox in open-air atmosphere with RH ≈ 100% (over 9-10 weeks) leads to changing of Ox elemental composition. In this case the Ox consists of In2O3, In(OH)3 and In2(SeO3)3*2H2SeO3*H2O. The surface resistance of such the Ox films also demonstrates a linear dependence on RH, but the Ox surface resistance increases with increasing RH.
9:00 PM - V6.34
Cobalt Oxide as an Electrode for Dye Sensitized Solar Cells.
Tsu-Heng Weng 1
1 Material Science and Engineering, National Tsing Hua University, Hsinchu Taiwan
Show AbstractThis work shows a new substitution, cobalt oxide nanostructures, for the typical TiO2 electrode in the dye sensitized solar cell (DSSC). With superior surface area, the cobalt oxide nanostructures can capture more dye molecules. The cobalt oxide nanostructures were synthesized on indium tin oxide (ITO) glasses by the hydrothermal method in reflux system at 85°C. The morphology and band gap of the cobalt oxide nanostructures were characterized by scanning electron microscopy (SEM, Hitachi S4700), high-resolution transmission electron microscopy (TEM, JEOL JEM-2010), UV-Vis absorption spectroscopy (Hitachi U3010), and cyclic voltammetry (CV). The DSSCs were fabricated by cobalt oxide nanostructures as an electrode combined with the use of ruthenium-complex dye and I-/I3- electrolyte. The incident-photon-to-current efficiency (IPCE) of the DSSCs was measured by a solar simulator and their electrical properties of the devices were also characterized.
9:00 PM - V6.35
Semiconductor-metal Phase Transition in Doped Ion Beam Synthesized VO2 Nanoclusters.
Helmut Karl 1 , Johannes Dreher 1 , Bernd Stritzker 1
1 Institute of Physics, University of Augsburg, Augsburg Germany
Show AbstractWe have synthesized VO2 nanoclusters embedded in 200 nm thick thermally grown SiO2 on 4-inch silicon wafers by sequential ion implantation of the ions V and O with an energy of 100 keV and 36 keV respectively. Under these conditions the maximum of the concentration profiles are located at a depth of approximately 100 nm in the SiO2 thin film. Finally the dopants W and Mo with increasing fluences were implanted. The formation of W and Mo doped VO2 nanoclusters has been obtained by an annealing step in a rapid thermal processor in flowing Ar at 1000°C for 10 min. The structural changes in the VO2 precipitates during the hysteretic semiconductor-metal phase transition have been investigated by temperature dependent Raman spectroscopy. Additionally the optical properties of the nanoclusters were analyzed by spectral ellipsometry in the spectral range of 320 to 1700 nm. It will be shown, that the semiconductor-metal phase transition hysteresis can be systematically controlled by the dopand concentration and discussed in correlation to the observed Raman line shifts during temperature cycling through the transition.
9:00 PM - V6.36
Antimony-doped Tin Oxide Nanocrystals: Synthesis and Solubility Behavior in Organic Solvents.
Rafael Oliveira da Silva 1 , Tiago de Goes Conti 1 , Andre F.de Moura 1 , Daniel Grando Stroppa 2 , Luiz C. G. Freitas 1 , Caue Ribeiro 3 , Emerson R. Camargo 1 , Elson Longo 1 , Edson Roberto Leite 1
1 LIEC-Chemistry Department, Federal University of São Carlos, São Carlos, São Paulo, Brazil, 2 LME-LNLS, Brazilian Synchrotron Light Laboratory, Campinas, São Paulo, Brazil, 3 , EMBRAPA Instrumentação Agropecuária, São Carlos, São Paulo, Brazil
Show AbstractMetal oxide nanocrystals (NC) synthesis via nonaqueous sol-gel is a recent methodology which has been shown to be a suitable and useful method when compared with aqueous systems and hot injection methods. Moreover, soft chemical routes are considered promising ones to fulfill most of the requirements such as high crystallinity, high purity and reproducibility from the molecular precursor to the final product as well as general applicability. This work focuses on the nonaqueous synthesis of antimony-doped tin oxide (ATO) NC in the range of 2-6 nm as well as an investigation of their solubility in organic solvents (CHCl3 and THF) in the presence of amphiphilic molecules (oleic acid and oleylamine). 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 120°C for 24h. The ATO NC were collected by centrifugation and washed twice with THF. The entire product presented a well crystallized structure, revealed by XRD peak width, nanoparticles near spherical shape and an average particle size of 4nm, confirmed by HRTEM images. The synthesis product was stable as a colloid by re-dispersition in THF and CHCl3 assisted by an amphiphilic molecule. In addition, to unravel the underlying processes, a set of molecular dynamics simulations was performed involving the compatibility of oleic acid and oleylamine in mixtures with both CHCl3 and THF. The results showed that it is possible to redisperse metal oxide nanoparticles synthesized via a nonaqueous sol-gel route through a suitable solvent-surfactant combination. In addition, the experimental results showed that three oleylamine molecules per nanocrystal suffice to promote the solubility of ATO NC in THF and chloroform. In general the number of surfactant molecules per NC is in the range of 1000-10000 (considering the synthetics routes where the surfactant is added during the synthesis process). Although, our studies focused on chloroform and tetrahydrofuran, the interaction between amphiphilic molecules and solvents can be predicted by molecular dynamics simulations with very good qualitative agreement. Futhermore, the general conclusions may be applied to other similar low polarity aprotic solvents.
9:00 PM - V6.37
Epitaxial Growth of Multifunctional Metal Oxide Thin Films by Laser Molecular Beam Epitaxy.
Chang Ke 1 , Zhen Yang 1 , Wei Guang Zhu 1
1 EEE6, Nanyang Technological University, Singapore Singapore
Show AbstractThe variety of electronic, optical and magnetic properties offered by metal oxide has driven significant efforts in exploring as thin films for wide applications. High quality epitaxial films have attracted much attention for their superior properties on device applications and fundamental studies. As one of the most versatile approaches for single crystal oxide film growth, Laser Molecular Beam Epitaxy (laser-MBE) technique is used in this work, and in-situ reflection high energy electron diffraction (RHEED), and ex-situ high resolution x-ray diffraction (XRD) measurements are employed to investigate the structure of these thin films. Binary metal oxide (SnO2) ultrathin films have been epitaxially grown on SrTiO3 single crystal substrate, and to the best of our knowledge it is the first attempt of SnO2 grown thin film with perovskite structure. The epitaxial relationships between the film and substrate are found to be[100]//[111]SrTiO3) and [101]SnO2)//{100}SrTiO3), and a minimum FWHM ~0.3° in out plane is obtained under the optimized growth condition. (100) SnO2/(111) Nb-doped SrTiO3 n-n type hetero junction has been fabricated, and the diode-like current behavior is explored. The interface band bending has been studied by electrical transport measurement and x-ray photoemission spectroscopy.
9:00 PM - V6.4
Surface-defects Enhancing Photocatalytic Performance of ZnO Hierarchical Nanostructures Synthesized via a Low-temperature Aqueous Solution Route.
Yanhua Tong 1 , Juan Chen 1 , Guei Gu Siu 1
1 , City University of Hong Kong, Hong Kong China
Show AbstractZnO nanomaterials have recently been widely explored in photocatalytic application because of their high efficiency and eco-friendly feature. To obtain high photocatalytic activity is usually via increasing the effective surface area of ZnO materials. However, enhanced photocatalytic activity of hierarchical ZnO nanostructures in this report may be attributable to high surface defects. The hierarchical ZnO nanostructures were easily to be synthesized and controlled using optimal ratio of Zn<2+> to OH<-> in aqueous solution. The photoluminescence measurement indicates that the ZnO hierarchical nanostructures have more surface defects than ZnO nanopowder. The rate constant of photodegradation of Rhodamin 6G for ZnO hierarchical nanostructures is around 6 times larger than that for ZnO nanopowder, although the surface area of the former (10.56 m<2>/g) is smaller than that of the latter (17.88 m<2>/g). It suggests that the enhanced photocatalytic activity in this report is not related with the surface area but surface defects. Furthermore, the photocatalysts were reused for six times without loss of activity, revealing excellent stability and recyclability.
9:00 PM - V6.5
Investigation of the Electronic Transport Properties in the Nanostructured Porous Films of SnO2.
Samad Bazargan 1 , Tong Leung 1
1 Chemistry, WATLab, University of Waterloo, Waterloo, Ontario, Canada
Show AbstractThin layers of tin oxide were deposited on Corning glass( #0211) substrates by a simple spin coating method followed by annealing under oxygen flow at 100-500oC. The morphology of the films was studied using atomic force microscopy, scanning electron microscopy, and transmission electron microscopy, which shows how the initially uniform and smooth films become rough and particles start to form throughout the film upon increasing the annealing temperature. Crystallographic investigations using x-ray diffraction and transmission electron microscopy indicate that crystalline grains start forming at 350oC and grow in size and volume percent of the total film at higher annealing temperatures. The results of chemical composition studies on films using x-ray photoelectron spectroscopy show that pure films composed of tin and oxygen were synthesized. Optical measurements on the films confirm a transparency of 92-95% in the visible range. The d.c. and a.c. resistivity measurements were performed in the temperature range of 25-300K. Resistivity results indicate the existence of different regions with different thermal activation energies for the charge carriers. The n-type carriers are introduced by tin interstitials, oxygen deficiencies, and other types of defects in the system. Cooling the system below 60K leads to a sudden drop in the resistivity of the system, giving rise to a sharp peak in the resistivity of the film. Further studies including mass spectrometry and Hall measurement are done, and the reasons behind this unexpected resistivity change are discussed.
9:00 PM - V6.6
Tunable Lattice Strain in Vertically Aligned Nanocomposite (BiFeO3)x:(Sm2O3)1-x Thin Films.
Zhenxing Bi 1 , Joonhwan Lee 1 , Judith Driscoll 2 , Quanxi Jia 3 , Haiyan Wang 1
1 Electrical and Computer Engineering, Texas A&M University, College station, Texas, United States, 2 Dept. of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom, 3 Materials Physics and Applications, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractA unique epitaxial two-phase vertically aligned nanocomposite (VAN) (BiFeO3)x:(Sm2O3)1-x thin films were deposited on SrTiO3 (001) substrates by pulsed laser deposition (PLD). The films were characterized by cross-section transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), Energy dispersive spectroscopy (EDX) and X-ray diffraction (XRD). The VAN thin films exhibit a highly ordered vertical columnar structure with high epitaxial quality. We demonstrate that the strains of the two phases in both out-of-plane and in-plane directions can be tuned by the deposition parameters during growth, e.g. deposition frequency and film composition of the nanocomposite. The strain tunability is found to be directly related to film composition and the systematic variation of the column widths in the nanocomposite. This study suggests a promising avenue in achieving tunable strain in functional oxide thin films by using VAN structures.
9:00 PM - V6.7
Rectifying Polarity Switch of Pt/TiO2-x/Pt.
Ni Zhong 1 2 , Hisashi Shima 1 2 , Hiro Akinaga 1 2
1 , Nanotechnology Research Institute (NRI), National Institute of Advanced Industrial Science and Technology (AIST), Japan, Ibaraki Japan, 2 , CREST, Japan Science and Technology Agency, Tokyo Japan
Show AbstractPt/TiO2-x/Pt attracts considerable interest due to the observation of the memoristance switch and field-programming rectification behavior. Most recently, a rectifying polarity switch behavior has been found in the Pt/TiO2-x/Pt, which is considered as a promising candidate for high density electronic logic devices. However, the mechanism of this behavior is still in ambiguous. In the present work, current-voltage (I-V) characteristic of Pt/TiO2-x/Pt has been studied. The Pt/TiO2-x/Pt devices in the initial state exhibit a rectifying I-V behavior. By applying the pulse voltage, the rectifying polarity could be switched. The mechanism of the rectifying polarity switch is proposed as the local drift of defects, such as oxygen vacancies, due to the application of the pulse voltage. In order to prove this assumption, the dependence of the rectifying polarity switch on the device size and applied pulse voltage width has been investigated. The required pulse voltage height for the polarity switch (Vswitch) exhibits a little dependence on the device size, while relates closely to the applying pulse voltage width. With an increase of the pulse voltage width, Vswitch decreases. Moreover, Vswitch shows a strong dependence on the measurement temperature (T), Vswitch exhibits a decrease with increasing T. These results suggest that the rectifying polarity switch in the Pt/TiO2-x/Pt is attributed to a thermal and dynamic dependence process. It agrees well with the proposed model.
9:00 PM - V6.8
Application of Simple Cycloalkylsilanetriols as a Modifier for Surface on Inorganic Particles.
Bok Ryul Yoo 1 , Jung Dong Euy 1 , Joon Soo Han 1
1 Organometallic Chemistry Laboratory, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractSimple cycloalkylsilanetriols RSi(OH)3 [R =c- pentyl (1), c- penteny (2), and c-hexenyl (3)] were synthesized as white powders in 70- 98% isolated yields, respectively, from the hydrolysis of the corresponding trialkoxysilanes with mild acidic water. Silanetriols 1–3 are soluble in water and polar organic solvents such as alcohol, acetone, THF, DMSO, and etc. They undergo condensation reaction under thermal and acidic/basic conditions to afford a variety of polymeric silsesquioxanes. They are useful materials for can be used as surface modifiers for inorganic materials such as silica and titania: 1) silanetriol can interact with hydroxyl groups on inorganic materials through hydrogen bonding, 2) then can undergo condensation by heating about 110 Č above to form M-O-Si covalent bond. In this presentation we will discuss the application of silanetriols as modifier for surface of inorganic materials such as silica and titania particles.
9:00 PM - V6.9
Correlating the Microstructure-Gas Sensing Properties Relationship for Ink-Jet Printed Oxide Nanoparticles on Microhotplate Substrates.
Elvin Beach 1 , Patricia Morris 1
1 Materials Science & Engineering, The Ohio State University, Columbus, Ohio, United States
Show AbstractOne of the major challenge in the wide-spread deployment of gas sensors built with oxide nanoparticles as the gas sensitive component is the ability to reproducibly deposit thin films made from nanoparticles in a reproducible manner. In addition to reproducible deposition the processing technique must be low-cost and capable of high through-put processing for manufacturing. Ink-jet printing allows for deposition of picoliter (pL) droplets with positioning accuracy of on the order of two micrometers and is capable of printing at acceptable speeds for large-scale manufacturing. The work presented here examines how the formulation of oxide-nanoparticle laden suspensions, ink-jet printing operating conditions such as drop speed and size, and heat treatment of the deposited suspension to form a thin film influence the gas sensing properties of oxide nanoparticles deposited on microhotplate substrates. The porosity of the thin films is also tailored using oxide nanoparticle coated latex microspheres to introduce large pores in the oxide film to improve gas diffusion rates. The microstructures are examined using a focused ion beam (FIB) cross-sectioning sample preparation technique followed by transmission electron microscope (TEM) imaging and microanalysis. Variables such as film thickness, primary particle size, secondary particle size, porosity and uniformity are correlated to the gas sensor data collected. The work presented here focuses on two well-known metal oxide materials for gas sensors: tin (IV) oxide and nickel (II) oxide where the former is an n-type material and the latter is p-type. The findings from this research enable a better understanding for further development of ink-jet printing as a tool for rapidly producing gas sensor arrays in both research and manufacturing applications.
Symposium Organizers
Junqiao Wu University of California-Berkeley
Anderson Janotti University of California-Santa Barbara
Weiqiang Han Brookhaven National Laboratory
Ho-Cheol Kim IBM Almaden Research Center
Thursday AM, April 16, 2009
Room 3001 (Moscone West)
9:15 AM - V7.1
A Quick and Economical Method for Growing ZnO Nanowires.
Jeong-Hyun Cho 1 , Elizabeth Cha 2 , David Gracias 1
1 Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2 Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractThe potential applications for ZnO are increasing due to its biocompatibility. On the nanoscale, ZnO structures possess additional electrical, chemical, mechanical and optical properties giving them the capability to improve current devices and aid in the development of new technologies. ZnO nanowires are customarily fabricated via the vapor-liquid-solid (VLS) method which utilizes chemical vapor deposition (CVD). In this approach, a catalytic liquid alloy phase is used to absorb a vapor until supersaturation, creating nucleation sites on the liquid-solid interface for nanowire growth. This liquid catalyst, most often Au, defines the length and diameters of the nanowires. However, while this method is effective, it is also costly and time consuming. Recently, we developed a quick and economical method for growing ZnO nanowires, which utilizes photolithography and thermal evaporation. Photolithography was used to generate a pattern on the silicon substrate, after which thermal deposition was used to create a defined layer of zinc which was patterned through the removal of photoresist. Under atmospheric pressure using a hot plate, heat was then applied initiating nanowire growth for 10 minutes. On the Zn layer pattern, 20 nanometers wide and 10 micrometers long ZnO nanowires were grown. This process gives a simple and cost effective method for growing ZnO nanowires that can be used in a variety of applications.
9:30 AM - **V7.3
Dopants in Bulk and Nanoscale ZnO.
Matt McCluskey 1
1 , Washington State University, Pullman, Washington, United States
Show AbstractZinc oxide (ZnO) is a metal-oxide semiconductor that has attracted resurgent interest as an electronic material for a range of device applications. In our work, we have focused on how defect properties change as one goes from the bulk to the nanoscale. In bulk, single-crystal ZnO doped with hydrogen or deuterium, infrared (IR) spectroscopy and Hall-effect measurements show that hydrogen binds to a host oxygen atom and donates an electron to the conduction band. The IR-active complex is unstable, decaying over a few weeks at room temperature. A more stable hydrogen donor may be substitutional hydrogen, predicted by Janotti and Van de Walle [Nature Materials 6, 44 (2007)].The effect of hydrogen on the conductivity of ZnO nanoparticles has implications for nanoscale optoelectronic devices. In our work, infrared (IR) reflectance spectra of as-grown and hydrogen-annealed ZnO nanoparticles were measured at near-normal incidence. The as-grown particles were electrically semi-insulating, and show reflectance spectra characteristic of insulating ionic crystals. Samples annealed in hydrogen showed a significant increase in electrical conductivity and free-carrier absorption. A difference was observed in the reststrahlen line shape of the conductive sample compared to that of the as-grown sample. The effective medium approximation was applied to model the reflectance and absorption spectra. The agreement between experimental results and the model suggests that the nanoparticles have inhomogeneous carrier concentrations.In addition to hydrogen doping, we successfully doped ZnO nanoparticles with Cu. To probe the electronic transitions of Cu2+ impurities in ZnO nanoparticles, IR transmission spectra were taken at liquid-helium temperatures. Two absorption peaks were observed at energies of 5781 and 5821 cm-1. These absorption peaks arise from internal transitions of Cu2+ ions. Similar absorption lines were observed in bulk ZnO [Appl. Phys. Lett. 81, 622 (2002)]. However, the width of the absorption peaks in our nanoparticles is broader than that of bulk crystals, perhaps due to inhomogeneous strains and/or electric fields.Work supported by the Department of Energy and the National Science Foundation.
10:00 AM - V7.4
Tunability of Aspect Ratio in ZnO Nanowires Through Different Amine Based Structural Agents.
Farah Alvi 1 , Rakesh Joshi 1 , Ashok Kumar 1
1 mechanical engineering, university of south florida, Tampa, Florida, United States
Show AbstractSolution growth method for synthesizing high aspect ratio ZnO nanowires have high potential due to its low cost and easy scalability with great control on growth parameters. Nanowires grown by such methods have been used for solar cell applications. However, the solution methods have not been fully utilized due to the lack of understanding of the interactions between different structural agents and Zn+2 precursors. In this article we describe the growth of ZnO nanowires by using different amine based structural directors to control the orientations of 1D Nano wires.We have used smaller, moderate and longer chain amines in equi-molar ratio with zinc precursors for the nanowire growth.It has been experimentally observed that the amine has a bi-directional role in the solution growth .The Amines not only act as structural directors in regulating the diameter to length ratio of ZnO nanowires but also take part in reactions with precursor.Larger chain amines produce longer and thinner ZnO nanowires while the smaller chain amines lead to thicker and shorter nanowires. Role of different amine agents in solution based ZnO nanowire growth has been determined and presented using several characterizing techniques.
10:15 AM - V7.5
The Effects of Hydrogen in Oxides.
Anderson Janotti 1 , Joel Varley 1 , Chris Van de Walle 1
1 Materials, University of California Santa Barbara, Santa Barbara, California, United States
Show AbstractHydrogen is a very common impurity in many semiconducting oxides, being present in the various growth and processing environments. It is commonly accepted that H incorporates in oxides as an interstitial impurity, forming a strong bond with O atoms. Using density functional calculations we have shown that H can also occupy substitutional sites in oxides. In ZnO, H substitutes for O and bonds equally to all four Zn nearest neighbors, forming a multicenter bond. HO has low formation energy, acts as a shallow donor, and it is stable against dissociation into interstitial hydrogen and oxygen vacancy in n-type ZnO. The formation energy of substitutional hydrogen, and therefore its concentration, explicitly varies with oxygen chemical potential, providing a link between n-type conductivity and oxygen partial pressure in ZnO. The calculated migration barrier indicates that substitutional hydrogen becomes mobile at temperatures near 500°C, consistent with recent experimental observations. Details about the multicenter bond and its consequences for doping control in ZnO and other oxides, such as SnO2 and TiO2, will also be presented.
10:30 AM - V7.6
Patterned Growth of Vertically Aligned ZnO Nanowire Arrays on Inorganic Substrates at Low Temperature without Catalyst.
Sheng Xu 1 , Yaguang Wei 1 , Melanie Kirkham 1 , Jin Liu 1 , Wenjie Mai 1 , Dragomir Davidovic 2 , Robert Snyder 1 , Zhong Wang 1
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 School of Physics, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractVertically aligned ZnO nanowires (NWs) have a variety of astonishing applications in electronics as well as optoelectronic and electromechanical nanodevices. In this presented work, we demonstrate an approach to grow high-quality ZnO NW arrays that can meet the following three criterions. First, the growth is at low temperature so that the NWs can be integrated with general substrates. Second, the NWs are grown following a designed pattern, with a high degree of control in size, orientation, dimensionality, uniformity as well as shape. Finally, the catalyst is eliminated for integration with silicon based technology. Our method combines electron beam lithography and a low temperature hydrothermal method to achieve patterned and aligned growth of ZnO NWs at <100 Celsius degrees on general inorganic substrates. On non-epitaxial substrates (e.g. Si) coated with ZnO seed film, we could grow ZnO NW arrays with one NW on one site by increasing the growth temperature. On epitaxial substrates (e.g. GaN), perfectly aligned highly uniform ZnO NW arrays could be grown with controllable NW size and tunable pattern pitch. It could also be easily scaled up. This approach opens up the possibility of creating patterned, vertically aligned one-dimensional ZnO nanostructures for many applications such as sensor arrays, piezoelectric antenna arrays, two-dimensional photonic crystals, integrated circuit interconnects, and nanogenerators.
11:15 AM - **V7.7
Photoinduced EPR Studies of Native Defects in ZnO and TiO2 Crystals.
Larry Halliburton 1
1 Physics Department, West Virginia University, Morgantown, West Virginia, United States
Show AbstractOptical and electrical properties of wide-band-gap semiconductors are often controlled by native defects. Electron paramagnetic resonance (EPR) provides a sensitive method to monitor these defects. In-situ illumination of a sample during an EPR experiment (photoinduced EPR) provides detailed information since the light at low temperature produces changes in the charge states of the defects. In this talk, a review of EPR spectra from native defects in ZnO and TiO2 crystals is presented. To produce sufficient numbers of both zinc vacancies and oxygen vacancies in a ZnO crystal, an electron irradiation near room temperature with 1.5 MeV electrons was performed. Following the electron irradiation of ZnO, spectra associated with Fe3+ ions, singly ionized oxygen vacancies, nonaxial singly ionized zinc vacancies, neutral zinc vacancies, axial singly ionized zinc vacancies, and zinc vacancies having an OH− ion at an adjacent oxygen site are monitored. Varying the illumination wavelength between 350 and 750 nm shows that the ground state of the neutral oxygen vacancy is deep, approximately 1.3 eV above the valence band, and that the ground state of the singly ionized zinc vacancy is also deep, about 0.9 eV above the valence band. EPR has also been used to monitor photoinduced Ti3+ ions and self-trapped holes in fully oxidized TiO2 crystals. Illumination with 442 nm laser light at 30 K and below produces four electronlike centers and one holelike center in TiO2. Three of the electronlike centers have S = 1/2 and are assigned to a substitutional Ti3+ ion in the otherwise perfect lattice, a substitutional Ti3+ ion adjacent to a Si4+ ion, and a substitutional Ti3+ ion adjacent to an oxygen vacancy. The fourth electronlike center has S = 1 and is assigned to two Ti3+ ions adjacent to one oxygen vacancy. The holelike center has S = 1/2 and consists of a hole shared equally by two adjacent oxygen ions in the otherwise perfect lattice. The behavior of oxygen vacancies in these two oxide semiconductors are strikingly different. Large concentrations of the S = 1 oxygen-vacancy centers are easily produced in TiO2 by heating samples in a reducing atmosphere. This work was supported by NSF Grant No. DMR-0804352.
11:45 AM - V7.8
Fabrication of Phosphorus-doped ZnO Quantum Dots by Metal Organic Chemical Vapor Deposition.
Liping Zhu 1
1 , Zhejiang University, Hangzhou China
Show AbstractDue to numerous unique properties expected in the low dimensional system, nanometer-scale materials promise to be important in the next-generation optoelectronic devices. As a new nanostructure material, ZnO quantum dots (QDs) are attracting considerable attention because of the ultimate quantum confinement[1]. It is well known that acceptor doping is fundamental to controlling the electrical properties of ZnO, however, the lack of stable p-type materials is still the key issue which hinders the development of ZnO-based optoelectronic devices. Phosphorus is a good dopant to realize p-type ZnO suggested by the theory for large-sized-mismatched group-V dopants based on first-principles calculations and phosphorus doped ZnO thin films exhibit good stability and reproducibility[2]. In our previous study, we have developed an effective and reproducible route to prepare phosphorus doped ZnO films by MOCVD with a special thermal evaporator[3]. In this study, we fabricate phosphorus doped ZnO QDs using the similar method.Phosphorus doped ZnO quantum dots (QDs) have been fabricated on Si substrates by metal organic chemical vapor deposition method without using additional thermal activation processes. Single-crystal phosphorus doped ZnO quantum dots (QDs) have the average diamter of 10 nm and show preferred orientation with (001) direction. The incorporation of phosphorus in ZnO QDs was identified by x-ray photoelectron spectroscopy (XPS). The acceptor doping behavior was confirmed by the valence band XPS and scanning tunneling microscopy, which demonstrated the tuned Fermi level and electrical properties for the phosphorus doped ZnO QDs respectively. Quantum confinement effect for the phosphorus doped ZnO QDs is clearly observed from their room temperature photoluminescence spectra.References[1] B. Gil, A. V. Kavokin, Appl. Phys. Lett. 81, 748 (2002)[2] Arnold Allenic, Wei Guo, Yanbin Chen, Michael Brandon Katz, Guangyuan Zhao, Yong Che, Zhendong Hu, Bing Liu, Sheng Bai Zhang, and Xiaoqing Pan, Advanced Materials, 19,3333(2007)[3] J. Jiang, L.P. Zhu, J.R. Wang, X.Q. Gu, X.H. Pan, Y.J. Zeng, Z.Z. Ye, Mater. Lett. 62, 536 (2008).
12:00 PM - V7.9
Characterization of ZnO Thin Films and Nanostructures Grown by Pulsed Laser Deposition.
Christian Weigand 1 , Matt Bergren 3 , Astrid-Sofie Vardoy 1 , Kjetil Valset 1 , David Carey 3 , Cecile Ladam 2 , Per Erik Vullum 2 , John Walmsley 2 , Ragnar Fagerberg 2 , Tom Furtak 3 , Reuben Collins 3 , Jostein Grepstad 1 , Helge Weman 1
1 Department of Electronics and Telecommunications, Norwegian University of Science and Technology, Trondheim Norway, 3 Department of Physics, Colorado School of Mines, Golden, Colorado, United States, 2 Materials and Chemistry, SINTEF, Trondheim Norway
Show AbstractHybrid organic/inorganic solar cells constitute a promising alternative to conventional photovoltaic devices by reducing the cost of electrical power per kWh. Controlling the morphology of the inorganic acceptor (e.g. ZnO, TiO2) is key to achieving efficient charge transfer and improved energy conversion efficiency for such photovoltaic devices. By nanostructuring the inorganic acceptor, the organic/inorganic interface area can be increased, and controlled pathways of charge collection can be facilitated. Pulsed laser deposition (PLD) allows for controlled growth of planar as well as nanostructured oxide thin films. In this work, ZnO planar films and nanostructures were grown by PLD on both silicon and sapphire substrates. Planar films were investigated with x-ray diffraction and atomic force microscopy, whereas the nanostructures were examined by scanning electron microscopy and transmission electron microscopy (TEM). ZnO nanorods were successfully grown using a gold catalyst, at a high substrate temperature of 800°C and an ambient gas pressure of 0.5 mbar (5% oxygen, 95% argon). Preferential formation of planar thin films was observed upon reduction of the overall gas pressure, whereas a change in gas composition to pure oxygen led to the growth of ZnO nanosheets. Similar structures were found when lowering the growth temperature to 600°C for a 5% oxygen:95% argon ambient gas composition. High-resolution TEM data indicate growth of [0001]-oriented defect-free nanorods of wurtzite ZnO on sapphire substrates.
12:15 PM - V7.10
The Electronic Properties of ZnO Nanowires under Different Environments and Diode Characteristics of Hybrid p-type Organic/n-type ZnO Nanostructures.
Jongsun Maeng 1 , Minseok Jo 1 , Seok-Ju Kang 1 , Min-Ki Kwon 1 , Gunho Jo 1 , Minhyeok Choe 1 , Tae-Wook Kim 1 , Hyunsang Hwang 1 , Dong-Yu Kim 1 , Seong-Ju Park 1 , Takhee Lee 1
1 Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of)
Show AbstractZnO nanostructures such as nanowires and nanowalls have attracted great interest due to their unique properties, including a wide direct bandgap of 3.37 eV and large exciton binding energy (~60 meV) for potential applications in optoelectronic devices. In particular, the large surface area to volume ratio of ZnO nanowires has a strong influence on electrical transport by adsorption and desorption of ambient active elements onto and from the ZnO surface. We observed the current decreased and threshold voltage shifted to a positive gate bias direction as the ZnO nanowire field effect transistors (FETs) were swept at slower gate bias sweep rates. These phenomena are attributed to increased adsorption of oxygen on the nanowire surface by the longer gate biasing time [1]. Adsorbed oxygens capture electrons and cause a surface depletion in the nanowire channel. Different electrical trends were observed for ZnO nanowire FETs under different oxygen environments of ambient air, N2, and passivation. In second part of this presentation, n-type ZnO nanowalls synthesized by metal organic vapor deposition were applied into hybrid p-n diode junction with p-type semiconducting polymers (poly(3,4-ethylene-dioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS). Most research in hybrid p-n junctions using ZnO nanowires and semiconducting polymer matrices have been focused on electroluminescence study for photonic applications. In our study, we performed the reverse recovery measurement in order to estimate the minority carrier lifetime in organic/inorganic hybrid p-n junctions [2]. In the bipolar p-n junctions, minority carriers can be stored when the diode is forward biased, and a large transient reverse current is required to extract carriers when the device is switched to reverse bias. Our detail study on the minority carrier dynamics will prove the formation of p-n junctions and enhance understanding the characteristics of p-n junctions. [1] J. Maeng, G. Jo, S.-S. Kwon, S. Song, J. Seo, S.-J. Kang, D.-Y. Kim and T. Lee, Appl. Phys. Lett. 92, 233120 (2008). [2] J. Maeng, M. Jo, S.-J. Kang, M.-K. Kwon, G. Jo, J. Seo, H. Hwang, D.-Y. Kim, S.-J. Park, and T. Lee, Appl. Phys. Lett. 93, 123109 (2008).
12:30 PM - V7.11
Structure and Magnetic Properties of Co-doped ZnO Nanoparticles Produced by Chemical Vapor Synthesis.
Ruzica Djenadic 1 , Tom Kammermeier 2 , Andreas Ney 2 , Guvenc Akgul 3 , Klaus Attenkofer 3 , Markus Winterer 1
1 Nanoparticle Process Technology, Department of Engineering Sciences, and Center for NanoIntegration Duisburg-Essen, CeNIDE , University of Duisburg-Essen, Duisburg Germany, 2 Experimental Physics, and Center for NanoIntegration Duisburg-Essen, CeNIDE , University of Duisburg-Essen, Duisburg Germany, 3 Advanced Photon Source , Argonne National Laboratory , Argonne, Illinois, United States
Show AbstractCo-doped ZnO nanoparticles with the different cobalt concentration were synthesized by chemical vapor synthesis (CVS). Solid anhydrous acetate precursors were evaporated using a laser flash evaporator [Winterer 2007], transported by the helium gas stream into the hot wall reactor where the precursor are decomposed and nanoparticles are formed at 20 mbar and 1100°C. The as-synthesized particles were separated from the gas stream by thermophoresis. The materials were structurally characterized by X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-VIS), electron paramagnetic resonance spectroscopy (EPR), and extended X-ray absorption fine structure spectroscopy (EXAFS). Magnetic properties were investigated using a superconducting quantum interference device (SQUID). The Rietveld refinement of the XRD data shows that nanocrystalline, single phase wurtzite powders were synthesized. The crystallite size is increasing and the lattice constant ratio, c/a, is decreasing slightly with increasing cobalt concentration. EXAFS data analysis shows that zinc is successfully replaced by cobalt. However, no ferromagnetism is observed in as-synthesized Co-doped ZnO powders.[Winterer 2007] M. Winterer, V. V. Srdic, R. Djenadic, A. Kompch, T. E. Weirich, Rev. Sci. Instr., 78 (2007) 123093.
Symposium Organizers
Junqiao Wu University of California-Berkeley
Anderson Janotti University of California-Santa Barbara
Weiqiang Han Brookhaven National Laboratory
Ho-Cheol Kim IBM Almaden Research Center
V10: Sensors, Fuel and Solar Cells
Session Chairs
Friday AM, April 17, 2009
Room 3001 (Moscone West)
9:00 AM - V10.1
Palladium Decorated Zinc Oxide Nanowires for Gas Sensors.
Rakesh Joshi 1 2 , Qiang Hu 1 2 , Ashok Kumar 1 2
1 mechanical Engineering, ENB118, University of South florida, Tampa, Florida, United States, 2 Nanomaterials & Nanomanufacturing Research Center, University of South Florida, Tampa, Florida, United States
Show AbstractGas sensors based on various materials such as metals and metal oxides have been developed for detection of toxic gases. Low selectivity and requirement of high operation temperatures for most gas sensors have prompted the use of traditional materials in nanostructured mode. In this report we present the room temperature detection of 100 ppm carbon monoxide using metal ( Pd) decorated Zinc Oxide (ZnO) nanowires. Zin oxide nanowires were grown via Vapor Liquid Solid method and palladium nanoparticles were prepared by using the solution growth method. Surface of the ZnO nanowires was decorated by Pd nanoparticles using solution method. For this purpose, the ZnO nanowires and palladium nanoparticles were removed from their substrates by sonification in methanol solution and mixed properly using couninous slow stirring for one hr. The final solution containg metal decorated nanowires was dropcasted on the sensor chip with interdigited electrodes. Gas sensing properties of such nanowires were studied at room temperature for various concentrations (100 to 500 ppm CO in synthetic air) of the gas in continuous flow. Enhancement in gas sensing response by Pd decoration on ZnO nanowires was observed. Palladium acts as catalyst in sensitization and improves the reaction and response time. The improvement in gas sensing behavior is attributed to the change in conductivity of the Pd decorated ZnO nanowires on CO exposure due to the donation of electrons resulted from gas oxidation to p type ZnO nanowire surfaces.
9:15 AM - V10.2
Nano Electronic Nose: Nanostructured Sensor Array with Integrated Micromachined Hotplates for Critical Chemical and Explosive Discrimination
Pochiang Chen 1 2 , Saowalak Sukcharoenchoke 1 , Guozhen Shen 1 , Chongwu Zhou 1
1 Ming-Hsieh Department of Electrical Eng., University of Southern California, Los Angeles, California, United States, 2 Mork Family Department of Chemical Engineering and Material Science, University of Southern California, Los Angeles, California, United States
Show AbstractNanowire and carbon nanotube chemical sensors have attracted a lot of attention due to their small size and high surface-to-volume ratios. Our previous studies have shown that high performance chemical sensors based on indium oxide nanowires displayed a good detection of NO2 down to 5 ppb at room temperature. In addition, operating these nanowire sensors at elevated temperatures leads to even better performance and also enable the detection of other technologically important chemicals such as hydrogen and ethanol. However, selectivity is still an important issue in the chemical sensing community.A hybrid chemical sensor array composed of individual metal oxide nanowires, functional metal oxide nanowires, and carbon nanotubes (CNTs) with integrated micromachined hotplates for sensitive gas discrimination was demonstrated. Key features of our approach include the integration of nanowire and carbon nanotube sensors, precise control of the sensor temperature using the micromachined hotplates, and the use of Principal Component Analysis (PCA) for pattern recognition. This sensor array was exposed to important industrial gases, explosives, and chemical warfare, including hydrogen, carbon monoxide, Trinitrotoluene (TNT), and dimethyl methylphosphonate (DMMP) at different concentrations and sensing temperatures. Thus, an excellent selectivity was obtained (ex. TNT ~ 8 ppb in CNT sensors) to build up an interesting “smell-print” library of these gases. The sensing mechanisms of TNT and DMMP were studied with aid of a mass spectrometer and principal component analysis (PCA) of the sensing results was applied in discrimination of these tested chemicals, and in-depth analysis revealed clear improvement of selectivity by the integration of CNT and functional metal oxide nanowire sensors.
9:30 AM - **V10.3
Integrated Approaches in Templated Functional Oxide Materials.
Jochen Gutmann 1 2 , Mine Memesa 1 , Maria Lechmann 1 , Philip Lellig 1 2
1 , Max-Planck-Inst. for Polymer Research, Mainz Germany, 2 , Univ. of Mainz, Mainz Germany
Show AbstractTemplating of functional oxide materials via block copolymers is a technique that currently progresses towards a mature state. While it is therefore readily possible to obtain nanomaterials from functional oxides with are well defined in terms of their structure, morphology and function, it is furthermore possible to integrate a second function into the (hybrid) material. With this approach even mutually orthogonal functions can be integrated into the same material.We have used this integrated templating approach to obtain integrated barrier materials for photo electronic devices as well as functional oxide materials for hybrid solar cells. Doing so, we covered the whole materials science development cycle from chemical synthesis via structural characterization to application. We'll demonstrate why eacvh of these steps is synergistic and how a rational materials design can evolve from basic research.
10:00 AM - V10.4
Improved Response Time in Nanostructured Relative Humidity Sensors with Reactive Ion Etching Process.
Martin Kupsta 1 , Michael Taschuk 1 , Michael Brett 1 2 , Jeremy Sit 1
1 Electrical Engineering, University of Alberta, Edmonton, Alberta, Canada, 2 , NRC National Institute for Nanotechnology, Edmonton, Alberta, Canada
Show AbstractOur group has been studying the relative humidity (RH) sensing properties of nanostructured thin films produced by glancing angle deposition (GLAD). The GLAD technique allows for control of thin film nanostructure and porosity through substrate motion control and feedback from real-time measurements of deposition rates. The films used for the current work are composed of TiO2 columns approximately 100 nm in diameter, several microns high, and are deposited on interdigitated electrode capacitor substrates. Typically, our sensors exhibit a three orders of magnitude change in impedance for changes from 0% to 100% RH, and response times below 500 ms are easily achieved. We have recently demonstrated an ultraviolet treatment which reverses sensor ageing, and increases the device responsivity[1].Response time of our sensors varies with the size and nature of the pores in our sensors, which in turn relies on column properties such as diameter and surface roughness. By growing denser films, it is possible to achieve a higher sensitivity, but at the expense of response time. We have recently developed a 1D numerical diffusion code which includes nanostructure morphology, adsorption and electromagnetic properties of our devices. This modeling indicates that the response time of our devices is limited by surface adsorption. We present here work on application of a post-deposition reactive ion etch (RIE) treatment to produce high diffusivity channels through the film. This treatment allows us to produce sensors which simultaneously exhibit good sensitivity and extremely rapid response times. The post-deposition treatment allows further tailoring of the properties of the RH sensors for increased response time while retaining the high sensitivity offered by denser films. In this paper, we will demonstrate that the RIE treatment improves the response time of high sensitivity films by a factor of 2, while retaining a large sensitivity. We present studies on etch process parameters that optimize the improvement in response time, as well as on the impact of UV treatment in combination with the etch process. Current experimental and numerical results will be presented.[1] M.T. Taschuk, J.J. Steele, A.C. van Popta and M.J. Brett. "Photocatalytic Regeneration of Interdigitated Capacitor Relative Humidity Sensors Fabricated by Glancing Angle Deposition", Sensors and Actuators B 134(2), pp. 666 - 671 (2008)
10:15 AM - V10.5
UV-light Operated Gas Sensors Based On Metal Oxide Nanowires For Room Temperature Applications.
Joan Daniel Prades 1 , Roman Jimenez-Diaz 1 , Francisco Hernandez-Ramirez 2 1 , Albert Cirera 1 , Albert Romano-Rodriguez 1 , Sanjay Mathur 3 , Joan Ramon Morante 1
1 EME/XaRMAE/IN2UB, Department of Electronics, University of Barcelona, Barcelona Spain, 2 , Electronic Nanosystems S.L., Barcelona Spain, 3 Inorganic and Materials Chemistry, University of Cologne, Cologne Germany
Show AbstractMetal oxide materials are used in process control industries and environmental monitoring [1]. Nevertheless, they need to be operated at high temperature (T > 150 C), which is considered a major technical limitation [2]. In this work, we report a viable alternative to activate chemical reactions at the surface of metal oxide nanowires illuminating them with ultra-violet (UV) light and thus, enabling their use as gas sensors even at room temperature. Experimental results demonstrate that responses towards different concentrations of NO2 similar to those obtained with thermally activated sensor surfaces can be achieved by choosing the optimal experimental conditions. A theoretical model capable to describe the influence of the experimental parameters playing a role in these measurements will be presented, such as the photon flux impinging the nanowires; and the advantages and disadvantages of our experimental approach will be discussed in detail. [1] (a) F. Röck, N. Barsan, and U. Weimar. Chem. Rev. 108, 705 (2008).(b) A. Kolmakov, and M. Moskovits. Annu. Rev. Mater. Res. 34, 151 (2004).[2] (a) A. Diéguez, A. Vilà, A. Cabot, A. Romano-Rodríguez, J.R. Morante, J. Kappler, N. Barsan, U. Weimar, W. Göpel, Sens. Actutators B 68, 94 (2000). (b) N. Barsan, D. Koziej, and U. Weimar. Sens. and Actuators B. 121, 18 (2007).
10:30 AM - V10.6
Fabrication of TiO2 Nanotubes with High Sensitivity for Toluene Gas.
Hongyan Yue 1 , Js Huh 2 , Wd Fei 1 , Sl Zhang 2
1 Material Physics and Chemistry, Harbin Institute of Technology, Harbin, Heilongjiang, China, 2 Department of Materials Science and Metallurgy, Kyungpook National University, Deagu Korea (the Republic of)
Show Abstract Low dimentional TiO2 nanostructures such as nanotubes, nanowires and nanobelts have attracted much attention in recent years because they have potential applications in electronics, optics, catalysts and gas sensors. Many methods have been developed to synthesize one-dimensional titania nanotubes of various dimensions. The hydrothermal method is a simple and cost-effective method for the large scale production of titania with small diameters. The performance of metal oxide-based gas sensors is largely dependent on the morpholoy of the sensing layers used. A highly ordered, nanotubular structure with size-dependent and surface area-related properties could further improve gas sensitivity compared with nanoparticles. However, there is no report of TiO2 nanotubes gas sensitivity for organic gas. TiO2 nanopowders with anatase structure were firstly prepared by controlling the pH value of a precursor solution. The prepared TiO2 nanopowders were hydrothermally treated in a sealed teflon-lined stainless autoclave. Then, the samples were washed by DI water or 0.15M HCl to obtain TiO2 nanotubes. The microstructures were observed by Scanning Electron Microscope (SEM) and Transsition Electron Microscope (TEM). The phase composition of the nanotubes was determined by X-ray diffraction (XRD). The gas sensitivity of TiO2 nanotubes for toluene gas was also tested. TiO2 nanotubes with a length of 0.5μm to 5μm and a diameter of approximately 10nm can be prepared by hydrothermal treatment. The morphology of TiO2 nanotubes prepared by 0.15M HCl washing is destroyed to some extent. The TiO2 nanotubes with DI water washing shows better sensitivity than that with 0.15M HCl washing. The reason is that when the sensors are calcined at 500oC for 2h, the nanotubes remain as the nanotubes structure where a lot of Na exist in nanotubes with DI water washing. However, some of nanotubes have been destroyed and become particles in nanotubes with 0.15M HCl washing.
11:15 AM - V10.7
Integration of Self-heated Nanowires In Ultra-low Power Consumption Gas Sensors.
Francisco Hernandez-Ramirez 1 2 , Joan Daniel Prades 2 , Roman Jimenez-Diaz 2 , Albert Romano-Rodriguez 2 , Sanjay Mathur 3 , Joan Ramon Morante 2
1 , Electronic Nanosystems S.L., Barcelona Spain, 2 EME/XaRMAE/IN2UB, Department of Electronics, University of Barcelona, Barcelona Spain, 3 Inorganic and Materials Chemistry, University of Cologne, Cologne Germany
Show AbstractNanowires are considered potential components of new devices and circuit architectures, due to their unique properties derived from their tiny dimensions [1]. In this work, we demonstrate that self-heating in individual metal oxide nanowires induced by current flowing through them can be used to fabricate ultra low consumption gas sensors. This overcomes the requirement of heating the sample and entails a significant saving of energy consumption [2]. Our first proof-of-concept devices exhibit good responses towards different concentrations of reducing (CO) and oxidizing gases (NO2) as function of the applied current. It is noteworthy that their performance is nearly identical to those obtained with an external microheater, demonstrating that energy-efficient metal oxide sensors suitable for mobile devices can be obtained using this intrinsic effect. The here-presented technology represents an important advance in power efficiency and miniaturization, paving the way to the development of functional devices based on nanomaterials [1] Y. Cui, Q. Q. Wei, H. K. Park, and C. M. Lieber, Science 293, 1289 (2001)[2] J. D. Prades, R. Jimenez-Diaz, F. Hernandez-Ramirez, S. Barth, A. Cirera, A. Romano-Rodriguez, S. Mathur, J. R. Morante, Applied Physics Letters 93, 123110 (2008).
11:30 AM - V10.8
A Core-shell Nanocomposite: a Novel Electrolyte for Low Temperature Fuel Cells.
Y. Huang 1 2 3 , Youquan Mi 4 , Shao-Ju Shih 1 , Bin Zhu 4
1 , Harvard University, Boston, Massachusetts, United States, 2 , University of Oxford, Oxford United Kingdom, 3 , Nanyang Technological University, Singapore Singapore, 4 , Royal Institute of Technology (KTH) , Stockholm Sweden
Show AbstractIn this paper, the LiZn-oxide has been successfully coated on the SDC nano-particles (less than 100 nm in size) forming a two-phase nanocomposte thin film, which is distributed over the surfaces of SDC nano-particles uniformally, as proved by EF-TEM. Electrical property measurments show that such a thin layer has significantly enhanced ionic conductivity, which reaches higher than 0.1 S/cm at the temperature of 300°C that is equivalent to the pure SDC at 800°C or YSZ at 1000°C. This enhancement of conductivity is benefited from the interfaces between the nano-particles which is unable to obtain from the conventional single-phase bulk materials. These new materials based on the novel core-shell LiZn-oxide coated SDC nanocomposites have opened a new advanced 300-600ºC SOFC technology and is likely to make a breakthrough in SOFC materials and technology.
11:45 AM - V10.9
Characterization of Nanoscale Electrolytes for Solid Oxide Fuel Cell Membranes.
Cynthia Ginestra 1 , Michael Shandalov 1 , Ann Marshall 1 , Changhyun Ko 2 , Shriram Ramanathan 2 , Paul McIntyre 1
1 Materials Science & Engineering, Stanford University, Stanford, California, United States, 2 School of Engineering & Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractSolid oxide fuel cells (SOFCs) are an interesting energy conversion technology, but a major disadvantage of current SOFCs is their relatively high operating temperatures (600 – 1000 °C). Yttria-stabilized zirconia (YSZ) is the most widely used material for SOFC electrolytes, and reduced operating temperatures may be achieved by making the SOFC electrolyte membrane thinner (from tens of um to tens of nm), thereby reducing Ohmic losses associated with oxygen ion transport across the membrane at lower temperatures. Furthermore, atomic layer deposition can be used to synthesize ultra-thin dense films owing to the nature of layer-by-layer growth. We report on the microstructure and electrochemical properties of nanoscale (20 – 50 nm) yttria-stabilized zirconia synthesized using a nanolaminate approach via atomic layer deposition. Yttria contents between 3 and 12 molar percent were achieved by varying the number of Zr and Y precursor pulses during alloy film growth. Post-deposition annealing enabled layer interdiffusion in the nanolaminate structures and fully crystallized the initially mixed-amorphous/polycrystalline material. We observed columnar, hexagonal grains (diameters 5 – 25 nm) spanning the entire thickness of the nanoscale YSZ films, as well as a tetragonal-to-cubic phase transition occurring at average compositions between 6 and 10 molar percent yttria. Detailed high temperature in-plane electrical conductivity measurements were performed on the nanoscale YSZ films using impedance spectroscopy. Nanoscale YSZ films showed high total conductivity even with low yttria content, comparable to the conductivity of bulk 8YSZ at higher temperatures.
12:00 PM - V10.10
Templated Metal-Oxide Nanocomposites as Electrodes for Next-Generation Electrical Energy Storage.
Erik Spoerke 1 , Erica Martin 1 , Michael Brumbach 1 , Bruce Bunker 1
1 Electronic and Nanostructured Materials, Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractThe need to develop new materials for electrical energy storage has become increasingly important as energy demands continue to grow and technological alternatives to fossil fuels expand. One area of particular interest to the electrochemical community involves the development of new, nanostructured metal oxide electrode materials for incorporation into lithium ion batteries or ultracapacitors. We describe here a materials synthesis strategy that utilizes both organic and inorganic templates to synthesize and assemble mesoporous electroactive oxide nanocomposites with promising electrochemical behaviors. By integrating both organic templates, such as functional amphiphilic molecules, and inorganic templates, such as zinc oxide, we can produce nanostructure electroactive oxides, such as ruthenium oxide or vandadium oxide, with texture and porosity on multiple length scales. This approach also enables us to create mixed, composite oxides, reducing the amount of cost-prohibitive elements such as ruthenium in the material. Electrochemical characterization reveals these templated, functional metal oxides to be promising candidates for incorporation into next generation electrical energy storage applications. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.
V11: Synthesis and Applications III
Session Chairs
Friday PM, April 17, 2009
Room 3001 (Moscone West)
2:45 PM - V11.2
Phase and Interface Development in Integrated Nanoscale Ferroelectrics
Geoff Brennecka 1 , Chad Parish 1 , Jacob Jones 2 , Dan Marincel 3 , Bruce Tuttle 1
1 , Sandia National Labs, Albuquerque, New Mexico, United States, 2 , University of Florida, Gainesville, Florida, United States, 3 , Missouri University of Science and Technology, Rolla, Missouri, United States
Show AbstractFerroelectric materials such as Pb(Zr,Ti)O3 are extremely attractive for integrated applications such as charge storage capacitors and FeRAM, but the feature sizes of ferroelectric-based devices remain considerably larger than those based on other materials technologies. As recent reports—both theoretical and experimental—have demonstrated, only a handful of unit cells are required for the existence of ferroelectricity, so practical size limitations are imposed not by the ferroelectric phenomenon, but by available fabrication, processing, and patterning techniques. We have developed chemical solution-based fabrication technology for nanoscale ferroelectrics that is compatible with both electron-beam and diblock-copolymer-based patterning approaches. In this talk, we discuss the effects of thermal processing on phase and interface development in continuous and patterned nanoscale PZT-based thin films with feature sizes ranging from <10 to 100nm, with a strong focus on interactions with various electrode materials. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL8500.
3:00 PM - V11.3
Effects of Functionalization of Single TiO2 Nanotubes on Electrical Conductance.
Mingun Lee 1 , Dongkyu Cha 1 , Hyunjung Shin 2 , Moon.J. Kim 1 , Jiyoung Kim 1
1 MSEN, University of Texas at Dallas, Richardson, Texas, United States, 2 MSEN, Kookmin University, Seoul Korea (the Republic of)
Show AbstractNanotubular structure has been widely investigated as one of the most promising materials for nanoscale technology applications due to their unique physical properties, which arise from dimensionality and size effects. In particular, one dimensional nanotubes are expected to be a building block for bio- and chemical sensors because of their large surface to volume ratio. Although tubular shape is appropriate for sensor applications, it is still necessary to improve their selectivity and detection limit to identify a certain chemical and biological species. In this presentation, we will discuss functionalization of stand alone TiO2 nanotube transistors in order to enhance their sensing ablities.In this study, we will present that we produce various diameter and wall thickness of TiO2 nanotube with atomic layer deposition (ALD) combining nano-templates method. A local Pt interconnection between a single TiO2 nanotube and pre-patterned Cr/Au probe pads were prepared by focused ion beam (FIB) system. The TiO2 nanotube is expected to be an n-type semiconductor due to oxygen vacancy. Conductance of the TiO2 nanotube is modulated by localized charges at surface, which cause depletion of n-type conductance region. The portion of depletion to conduction areas, which directly affects the sensitivity, can be decided by tube wall thickness and doping level of the TiO2 nanotubes. In this presentation, the oxide nanotube wall thickness is controlled by ALD technique with atomic scale precision. On the other hand, doping concentration, implying stoichiometric value between Ti and O, is varied by moderate annealing (at 300C) in oxidation and reduction ambients. Effects of wall-thickness and doping concentration on sensitivity is investigated using water treatment.Surface modification enables TiO2 nanotube to detect specific chemicals selectively. We treat its surface with various types of chemicals having diverse terminal group such as carboxylic acid, alcohol and ester. However, only improving selectivity is insufficient to produce high performance sensors because it should work under low concentration. To improve detection limit, TiO2 should be more sensible according to environmental changes. We will discuss effect of functionalization of single nanotube sensors in conjunction of their wall thickness and annealing treatment for sensor applications. This research was supported by a grant (code #: M105KO010026-05K1501-02611) from 'Center for Nanostructured Materials Technology' under '21st Century Frontier R&D Programs' of the Ministry of Education, Science and Technology, Korea.
3:15 PM - V11.4
Anodic TiO2-nanotubes: Growth and Modification of Electronic Properties.
Robert Hahn 1 , Felix Schmidt-Stein 1 , Andrei Ghicov 1 , Jan Macak 1 , Julia Kunze 1 , Patrik Schmuki 1
1 Institute for Surface Science and Corrosion, University Erlangen, Erlangen Germany
Show AbstractSelf organized nanotubular structures of transition metal oxides grown on their metallic substrates, especially titanium [1], have attracted great scientific and technological interest due to the possibility to exploit their functional properties (such in photo-catalysis, solar energy conversion, and biology) in a nanotubular morphology. The conventional way to grow anodic TiO2 nanotubes is an optimized electrochemical treatment of Ti in fluoride containing electrolyte (for an overview see [2]).In the first part of the work we report on an entirely novel approach [3], the growth of nanotubes by so-called RBA (rapid breakdown anodization). This nanotube growth-process is in comparison extremely fast (seconds instead of hours) and leads to surface coatings consisting of dense packed bundles of nanotubes with very high aspect ratios (tube length up to 50 micrometer, tube diameter of ~40 nanometer).The second part of the presentation will demonstrate that the electronic properties of these TiO2 nanotubes can be significantly modified by doping with suitable elements (C [4],N) or by stable reduction to form even highly conductive phases [5].Literature:[1] V. Zwilling, M. Aucouturier, E. Darque-Ceretti, Electrochim. Acta, 45, 921 (1999).[2] J.M Macak et al., Curr Opin Solid State Mater Sci 11 (2007).[3] R. Hahn, J. M. Macak, P. Schmuki, Electrochem. Commun.,9, 947 (2007).[4] R. Hahn, A. Ghicov, J. Salonen, V. Lehto, P. Schmuki, Nanotechnology, 18, 105604 (2007).[5] R. Hahn et al. (2008) in preperation.
3:30 PM - V11.5
WITHDRAWN 04/01/09 Uniform and Tunable Nanocatalysts Derived from Polystyrene-b-poly(vinyl pyridine) Templates for Controllable 1D Nanostructure Growth.
Jennifer Lu 1 , Anita Ghia 1 , Qiang Fu 1
1 , University of California at Merced, Merced, California, United States
Show AbstractPolystyrene-b-poly(vinyl pyridine) is an ideal template for small 1D nanostructure growth for substrate-based applications, since nanocatalysts that are less than 5 nm can be derived using this micelle lithography approach. By selecting proper metal compounds, metal species can effectively be localized around VP ligands. Therefore, this template can be used to prepare a variety of metal oxide nanoparticles. Bimetallic and single metallic nanocatalysts with tunable size and periodicity such as Cu/Mo, Au/Mo, Au, Cu, and Fe, have been successfully synthesized, demonstrating that different metal species can be attached to the ligand, PVP. The uniformly distributed nanocatalysts have been able to catalyze high-density, high-quality 1D nanostructure growth over a large surface area. By simply adjusting the spin–coating speed used to disperse this block copolymer-loaded metal micelle solution on a surface, the nanocatalyst density can be varied accordingly, thereby allowing the density of SWNTs to be tuned accordingly. Pseudo epitaxial growth of SWNTs has been observed. Uniform and extremely small nanocatalysts have been shown to be capable of promoting the synthesis of SWNTs and silicon nanowires with narrow size distribution.
3:45 PM - V11.6
Facile Synthesis and Characterizations of Nanocrystalline α-Alumina with Novel Morphology at 1000 °C.
Xiaoxue Zhang 1 , Erkki Levanen 1 , Tapio Mantyla 1
1 , Tampere University of Technology, Tampere Finland
Show Abstractα-Alumina, as one of the most studied ceramic material, is of great importance due to its wide applications as an engineering material, an electronic ceramic and a catalyst. Nanocrystalline α-alumina is believed to have improved mechanical strength and hardness as well as wear and corrosion resistance as compared to the currently available α-alumina materials. However, considerable speculations have been made in the literature claiming that it is impossible to make sub-100 nm nanocrystalline α-alumina; and most of the reported α-alumina has nearly spherical morphology. We have developed a simple route to synthesize nanocrystalline α-alumina with novel morphology without any seeding material by calcining the unusual prepared boehmite flaky powder at 1000 °C for 40 h. The α-alumina nanocrystallites in the size of 5 nm are observed for the first time, and more interestingly the nanocrystallites are formed themselves into nanorods having widths of about 15 nm and lengths of about 50-250 nm. The processing parameters of such nanocrystalline α-alumina are studied and detailed characterizations are carried out in order to study the synthesis mechanism. The transformation to α-alumina cannot be completed at 900 °C even with a very long dwell time of 160 h. At 1000 °C, a dwell time of 40 h is required to complete the phase transformation to α-alumina, however at 1100 °C only 1 h is required to obtain pure α-alumina. The formation scheme of the novel morphology of the nanocrystalline α-alumina is also illustrated and the morphology of the starting boehmite powder plays an important role. The phase transformation mechanism from θ-alumina to α-alumina is finally discussed and the diffusional nucleation model is found to be more reasonable in our study. It is supposed in our study that α-alumina nucleates at the grain boundaries of the θ-alumina grains and grow into the whole grains, forming the so-called primary crystallites. The primary crystallites then grow together into large secondary crystallites, which later agglomerate and aggregate into even larger particles.
4:30 PM - V11.7
Fluorine Doped - Tin Oxide Nanorods Arrays Fabricated by Spray Pyrolysis Deposition.
Doh-Hyung Riu 1 , Cheol-Kyu Song 2 , Chang-Yeol Kim 1 , Seung-Hun Huh 1 , Kwang-Yeon Cho 1 , Eun-Bae Kong 1
1 Nano Materials Application Division, Korea Institute of Ceramic Engineering and Technology, Seoul Korea (the Republic of), 2 , Solarceramic Co., Seoul Korea (the Republic of)
Show AbstractFluorine doped - tin oxide (FTO) nanorod arrays were deposited on a 30 x 30 cm2 glass substrate by ultrasonic spray pyrolysis deposition utilizing a solution mixture of tin chloride pentahydrate and ammonium fluoride. Uniform nanorod arrays of FTO single crystal with thickness of 700 nm – 1500 nm were obtained in-situ without any catalyst and template, whose orientation was along (101) orientation. The nanorods were single crystals whose shape were rectangular and the diagonal was about 50-100 nm depending on the deposition time and temperatures. The sharp tip of pyramidal shape of nanorod can be used as a FED emitter.
4:45 PM - V11.8
Quantitative Investigation of the Factors Affecting the Hydrothermal Growth of Zinc Oxide Nanowires.
Aron Rachamim 1 , Sharvari Dalal 1 , Michael Swanwick 1 , Andrew Flewitt 1 , William Milne 1
1 Centre for Advanced Photonics and Electronics, University of Cambridge, Cambridge United Kingdom
Show AbstractZinc oxide (ZnO) nanowire applications include short wavelength optical devices, transparent semiconductors, biological sensors and piezoelectric devices. An advantage of ZnO nanowires is the potential for solution growth at low temperatures over large areas. However, for these nanowires to be utilised, precise information is needed regarding optimisation of the growth conditions to achieve nanowires of the required densities, widths and lengths. In this work, ZnO nanowires were grown by forming a zinc (sub)oxide seed layer on a substrate which was subsequently immersed in an equimolar aqueous solution of zinc nitrate and hexamine (0.025 M). The seed layer was formed by spin coating the substrate with a 0.01 M solution of zinc acetate dihydrate in 1-propanol followed by annealing at 623 K for 20 min. The substrates and conditions of growth were varied and changes in the nanowire growth rate and morphology observed.It was found that the growth rate on ITO or metal coated silicon substrates was up to three times higher than that on native silicon. Conducting substrates may be growth catalysts by acting as reservoirs for the donation or acceptance of electrons enabling addition of ions more easily to nanowire growth faces.Increasing the density of seeding by repeated spin coating led to an approximately linear increase in the density of subsequently grown nanowires. The effect upon nanowire width and length was more complicated with a non-linear decrease in both these quantities observed, which is attributed to steric hindrance. Nanowire growth is completely linear with time. A growth rate of 3.1 nm min-1 was observed on Si at 353 K in 20 ml of solution over a period of up to 8 hours. This indicates that at least one step in the growth is slow at these temperatures. A linear dependence of growth rate with temperature was observed in the range of 343 K to 373 K, with a constant of proportionality of 0.078 nm min -1 K -1. This suggests that the rate limiting step is not a simple matter of overcoming a chemical activation energy. Also, although the zinc nitrate is consumed in the reaction, the hexamine acts to stabilise the pH which is maintained at a constant level ~6.3.A linear relation exists between solution concentration and nanowire growth rate of 14 nm min-1 M-1 measured at 363 K. Interestingly, whilst varying growth time and temperature led only to small changes in nanowire width, changes in concentration led to quite large changes in nanowire morphology. Increasing the concentration above 0.025 M led to much thicker nanowires being produced, and as the concentration was increased above 0.06 M, the resulting nanorods first became tightly compacted and then sterically aligned vertically before finally becoming fused together into a thin film.
5:15 PM - V11.10
Reversibly UV-light-induced Wettability Transition of Thin Films of Organic-capped TiO2 Nanorods.
Gianvito Caputo 1 2 , Barbara Cortese 1 , Concetta Nobile 1 2 , Marco Salerno 3 , Roberto Cingolani 1 2 , Giuseppe Gigli 1 2 , Athanassia Athanassiou 2 , Davide Cozzoli 1 2
1 , Scuola Superiore ISUFI Università del Salento, Lecce Italy, 2 , National Nanotechnology Laboratory of CNR-INFM, Unità di Ricerca IIT, Distretto Tecnologico ISUFI, Lecce Italy, 3 , Istituto Italiano di Tecnologia-IIT, Genova Italy
Show AbstractNanocrystalline TiO2 is among the most intensively studied semiconductor oxides, owing to its low-cost and environmentally compatible applications in a number of light-assisted catalytic processes.1 More recently, the capability of TiO2 surfaces to rapidly convert under UV illumination from an initially hydrophobic state to a highly amphiphilic one, followed by a slow back-recovery of the starting properties under ambient conditions, has attracted great technological interest.2 In particular, these findings have stimulated the fabrication of “smart” TiO2 -based inorganic surfaces that can exhibit simultaneous bactericide, self-cleaning and antifogging behaviour under suitable light excitation.3,4 However, the understanding of the mechanisms underlying the aforementioned wettability changes remains elusive yet and, consequently, the ability to drive TiO2 surface modifications in a deliberated manner needs to be developed further. Here, we demonstrate the UV-driven reversible wettability of hybrid organic-inorganic nanocrystal-based thin-film coatings composed of close-packed arrays of surfactant-capped anatase TiO2 nanorods5 achieved on either flat or lithographically patterned polymer (SU-8) substrates. Such TiO2 -covered surfaces are characterized by a dual micro-/nano-scale roughness, arising from the overlapping of nanocrystals with the micrometer-sized features of the SU-8 patterns. Under selective laser irradiation, the as-prepared oxide films exhibit a surface transition from a highly hydrophobic to a highly hydrophilic condition, which is reflected by an excursion in the water contact angle value larger than 100°. A mechanism is identified, according to which the UV-induced hydrophilicity correlates with progressive increase in the degree of surface hydroxylation of TiO2 at those sites which are not passivated by the capping surfactants.6,7 A dark storage period allows the initial hydrophobicity to be restored. The influence of geometrical and compositional parameters of the hybrid surfaces has been evaluated within the frame of available theoretical models.8 1.T. L. Thompson, J. T. Yates Jr., Chem. Rev. 2006, 106, 4428.2.I. P. Parkin, R. G. Palgrave, J. Mater. Chem., 2005, 15, 1689. 3.N.Sakai, A. Fujishima, T. Watanabe, K. Hashimoto J. Phys. Chem. B 2003, 107, 1028.4.X. Feng, J. Zhai, L. Jiang Angew. Chem. Int. Ed. 2005, 44, 5115.5.P. D. Cozzoli, A.Kornowski, H. Weller J. Am. Chem. Soc. 2003, 125, 14539.6. G. Caputo, C. Nobile, T. Kipp, L. Blasi, V. Grillo, E. Carlino, L. Manna, R. Cingolani, P.D. Cozzoli, A. Athanassiou J. Phys. Chem. C 2008, 112, 701.7. G. Caputo, C. Nobile, R. Buonsanti, T. Kipp, L. Manna, R. Cingolani, P.D. Cozzoli, A. Athanassiou J. Mater. Sci. 2008, 43, 3473.8. G. Caputo, B. Cortese, C. Nobile, M. Salerno, R. Cingolani, G. Gigli, P.D. Cozzoli, A. Athanassiou Adv. Funct. Mater. 2008, in press.
5:30 PM - V11.11
Picoliter Printing with Oxide Nanoparticles: A Route to High-Performance, Reproducible Microsensor Arrays.
Elvin Beach 1 , Diandra Rollins 1 , Kurt Benkstein 2 , Christopher Montgomery 2 , Steve Semancik 2 , Patricia Morris 1
1 Materials Science & Engineering, The Ohio State University, Columbus, Ohio, United States, 2 Chemical Sciences Division, National Institute of Standards & Technology, Gaithersburg, Maryland, United States
Show AbstractPicoliter drop deposition (PDD), based on the drop-on-demand ink-jet principle, was investigated as a method for fabricating nanostructured metal oxide-based chemiresistor gas sensors on microhotplate substrates. This technique shows promise for reproducible deposition of minute quantities of material with a high level of both placement precision and thin-film microstructure organization, but many interrelated variables must be controlled, including the pre-formed metal oxide nanoparticles and the processing characteristics of the deposition ink itself. First, metal oxide nanoparticles, which are the heart of robust gas sensing devices, were carefully synthesized (including, SnO2, NiO and TiO2) using hydrothermal and solvothermal techniques. Second, the preparation of stable suspensions is of critical importance for generating picoliter drops with consistent size, shape and trajectory. A careful study of oxide nanoparticle-laden suspensions has been carried out to identify how critical variables such as surface tension and solvent evaporation rate influence the PDD process is also described here. Control of the deposition process is important for consistent materials placement; however, it is only the first step in making high performance sensing materials. Drying and annealing to form useful micro/nanostructured films for chemiresistive sensing is equally important. The unique capabilities of microhotplate substrate arrays allows for efficient, almost combinatorial, study on the influence of the heating rate and maximum temperature applied during drying and annealing to microstructural feature formation. In depth investigations of the nanoparticle thin-film microstructures were carried out using cross-sectional electron microscopy. Correlations between the nanoparticle-laden suspension properties, PDD processing parameters and the final thin film microstructure were revealed that led to films with optimal gas sensor performance. Temperature-programmed sensing (TPS) was utilized to determine the operating temperatures that showed the highest level of gas sensitivity for each material and fixed-temperature sensing (FTS) was used to examine the response and recovery characteristics of each oxide film. The sensing results for tin(IV) oxide (SnO2) with particle sizes less than 10 nm in diameter are compared to a newly proposed comprehensive theory regarding the influence of particle size and shape on the sensitivity of metal oxide nanoparticles to various oxidizing and reducing agents.