bluuebunny/crossref_metadata_2025 huggingface dataset:
High-Dielectric-Constant All-Organic/Polymeric Composite Actuator Materials
Authors: Huang Cheng , Su Ji , Zhang Q.M.
Published: April 2011

Among various electroactive polymer (EAP) actuator materials developed recently, the class of EAPs whose responses are stimulated by external electrical fields (often known as the field type EAPs) is especially attractive due to their high strain level and elastic energy density. However, for most field type EAPs, dielectric constant is low, generally less than 10. Consequently, these polymers usually require high electric fields (>100 V/μm) to generate high elastic energy density which limits their applications. In this paper, we will investigate some avenues to significantly raise the dielectric constant and electromechanical response in field type polymeric materials. By exploiting an all-organic composite approach in which high-dielectric-constant organic particulates were blended with a polymer matrix, a polymeric-like material can reach a dielectric constant higher than 400, which results in a significant reduction of the applied field to generate high strain with high elastic energy density. An all-polymer high-dielectric-constant (K>1,000 @1 kHz) percolative composite material was fabricated by the combination of conductive polyaniline particles (K>105) within a fluoroterpolymer matrix (K>50). These high-K polymer hybrid materials also exhibit high electromechanical responses under low applied fields. In addition, a three-component all-organic composite was designed and prepared to improve the dielectric constant and the electromechanical response, as well as the stability of the composites, in which a high-dielectric-constant organic dielectric phase and an organic conductive phase were embedded into the soft dielectric elastomer matrix.
High Performance P(VDF-TrFE-CFE) Terpolymer for BioMEMs and Microfluidic Devices
Authors: Xia Feng , Klein Rob , Bauer Francois , Zhang Q. M.
Published: April 2011

BioMEMs and microfluidic devices have gained a lot of attention in recent years due to their emerging applications in biochemical analysis, medical diagnosis, chemical analysis and synthesis, drug discovery and drug delivery, biosensing and biomimetic systems. The materials requirements for bioMEMs are biocompatible, chemically modifiable, easy to fabricate, economic, compliable and smart. Among various materials, the electroactive polymeric materials can best meet these requirements. Recently, we developed a group of poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) based terpolymers which have very high strain level and high energy density. The longitudinal and transverse strain of these materials can reach about –7% and 4.5%, and the elastic energy density is around 1.1 J/cm3, which are very attractive for the development of polymeric pump, valve and other microfluidic components for all polymer-based bioMEMs and microfluidic integrated system. This paper reports on the recent efforts on the optimization of the terpolymer performance and development of microfluidic components using the electroactive terpolymers for bioMEMs.
Effects of Electrode Configurations on Internal Stress Distribution of Multilayer Actuators
Authors: Lee Dong-Kyun , Choi Ji-Won , Han Deuk-Young , Kim Hyun-Jai , Yoon Seok-Jin
Published: April 2011

The internal stress distribution in multilayer actuator was analyzed by a numerical simulation. Around the edge of conventional inter-digital electrodes, the non-uniform electric field generated the stress concentration, which caused the ceramic to crack. Various electrode configurations were presented to decrease this stress concentration. Especially the float electrode type is a promising design because this can be fabricated using almost the same process as the conventional multilayer actuator, and the simulated results indicted that the float electrode type decreased the stress concentration of inter-digital type in approximately 1/3.
Crack Initiation and Growth in a Notched NiTi Shape Memory Alloy Sheet
Authors: Tong Wei , Tao Hong , Zhang Nian
Published: April 2011

An experimental investigation was carried out to study the crack initiation and growth in a single-edge notched NiTi shape memory alloy sheet under tension. It is observed that a crack initiated at the tip of a V-shape notch before the peak axial load was reached and it grew steadily across the width of the NiTi sheet until final fracture. In-plane crack-tip deformation fields at various stages of the crack growth were measured based on an image correlation technique and the crack-tip opening displacement (CTOD) and crack-tip opening angle (CTOA) were subsequently determined. The fracture surface of the NiTi sheet was dimpled based on scanning electron microscopy examinations.
Charge Transfer Dynamics in Single-Wall Carbon Nanotubes Mat: In Situ Raman Spectroscopy
Authors: Gupta S. , Hughes M. , Windle A.H. , Robertson J.
Published: April 2011

Carbon nanotubes-based actuator has been investigated using in situ Raman spectroscopy in order to understand the actuation mechanism and to determine associated parameters. We built an actuator from a sheet of single-wall carbon nanotubes (SWNT mat) and studied in several alkali metal (Li, Na, and K) and alkaline earth (Ca) halide solutions. Since Raman can detect changes in C-C bond length: the radial breathing mode (RBM) at ∼190 cm-1 varies inversely with the nanotube diameter and the G band at ∼1590 cm-1 varies with the axial bond length, the variation of bonding was monitored with potential. In addition, the intensities of both the modes vary with either emptying/depleting or filling of the bonding and antibonding states due to electrochemical charge injection. We discuss the variation of intensity/frequency providing valuable information on the dynamics of charge transfer on the SWNT mat surface. We found the in-plane microscopic strain (∼ -0.25%) and the charge transfer per carbon atom (fc ∼ -0.005) as an upper bound for the electrolytes used. It is demonstrated that though the present analyses does comply with the proposition made earlier, but the quantitative estimates of the associated parameters are significantly lower if compared with those of reported values for carbon nanotubes. Moreover, the extent of variation (i.e. coupled electro-chemo-mechanical response) does depend upon the type of counter-ion used. The cyclic voltammetry (CV) is also described briefly.
Development of fundamental components for amplification of magneto-surface-acoustic-waves in highly magnetostrictive metal films by means of electron bunching
Authors: Kawahata Takeshi , Obata Naohisa , Nishimura Kazuhiro , Uchida Hironaga , Inoue Mitsuteru
Published: April 2011

In a magneto-surface-acoustic-wave (MSAW) device, phase velocity is controlled by an external magnetic field. We proposed amplification of MSAW with a hybrid structure of FeB amorphous film / InSb semiconductor thin film / LiNbO3 substrate, which is expected to compensate the attenuation of MSAW caused by eddy current loss. In the fabricated MSAW device having the FeB amorphous film with low coercivity and high magnetostrictive, the phase retardation of about 600 degree/cm at magnetic fields of ±300 Oe was obtained. The InSb thin film with a mobility of about 3.5×103 cm2/Vs was obtained by using annealing process. The results show possibility of the MSAW amplification.
Conductance transient comparative analysis of ECR-PECVD deposited SiNx, SiO2/SiNx and SiOxNy dielectric films on silicon substrates
Authors: Castán H. , Dueñas S. , Barbolla J. , Del Prado A. , San Andrés E. , Mártil I. , González-Díaz G.
Published: April 2011

A study of metal-insulator-semiconductor (MIS) structures based on SiNx, SiO2/SiNx and SiOxNy films deposited on silicon by electron cyclotron resonance plasma-enhanced chemical vapour deposition (ECR-PECVD) is presented. Interface trap densities measured by deep level transient spectroscopy (DLTS) are higher for silicon oxynitride-based MIS capacitors than for silicon nitride and silicon oxide-silicon nitride-based ones. However, conductance transient analysis demonstrated that Al/SiNx/Si devices exhibit the highest disordered-induced gap states (DIGS) density, whereas the lowest one corresponds to Al/SiNx/SiO2/Si, and silicon oynitride-based MIS capacitors show an intermediate behaviour. In addition, thermal treatments applied to Al/SiOxNy/Si samples reduce DIGS densities to values even lower than those corresponding to Al/SiNx/SiO2/Si devices.
The band alignment problem at the Si-high-k dielectric interface
Authors: Demkov A.A. , Fonseca L.R.C. , Tomfohr J. , Sankey O.F.
Published: April 2011

We investigate the use of the complex band structure of high-k gate dielectrics to estimate their charge neutrality levels, and compute band offsets to Si. Results of these model calculations are then compared to those obtained with direct electronic structure methods and available experiment. It appears that charge neutrality levels thus obtained indeed provide a consistent picture. However, the uncertainty in the conduction band position inherent in the local density approximation may render the theory inadequate for the engineering support. Despite this limitation, linear re-scaling of the charge neutrality levels based on the experimental band gaps has shown excellent agreement with experimental data.
Substrate/oxide interface interaction in LaAlO3/Si structures
Authors: Busani T. , Devine R.A.B.
Published: April 2011

Amorphous lanthanum aluminate films (LaAlO3) were deposited on Si substrates at room temperature using rf sputtering in pure Ar or an Ar/O2 mixture with a stoichiometric target. The film composition was analyzed using XPS and EDX. The evolution of the material resulting from annealing at temperatures in excess of 900 °C was studied using infrared spectroscopy, XPS profiling and AFM. We obtain clear evidence for in-diffusion of Si from the substrate into the dielectric film. FTIR analysis showed only one peak centered at 747 cm−1 with an FWHM of 185 cm−1 for as-deposited samples indicating an amorphous structure. Annealed samples showed very narrow absorptions at 483–510, 607, 695–720 and 811 cm−1. No evidence for SiO2 peaks at ∼1060 cm−1 was observed suggesting that the LaAlO3 structure tends not to reduce into a mixture of SiO2 and a silicide. Short time annealing at 1000 °C results in a broad band at 905 cm−1 which can be interpreted in terms of the formation of a layer rich in Si-O-La bonds. Nitridation of the substrate before oxide deposition and annealing slows the degradation process but does not suppress it. X-ray diffraction analysis of the annealed films indicates a very oriented crystalline structure, yet unidentified, whose direction depends upon the orientation of the Si substrate. The dielectric constant in both annealed and as-deposited films was measured to be less than 14 and the leakage current density was very low. Some mobile charge was detected. This dielectric constant is substantially less than the value ∼ 25 anticipated from bulk, single crystal measurements.
Flat-band Voltage Shift of MOS Capacitors with Tantalum Nitride Gate Electrodes Induced by Post Metallization Annealing
Authors: Kadoshima M. , Yamamoto K. , Fujiwara H. , Akiyama K. , Tominaga K. , Yamagishi N. , Iwamoto K. , Ohno M. , Yasuda T. , Nabatame T. , Toriumi A.
Published: April 2011

We have investigated the flat-band voltage (VFB) shifts of tantalum nitride gate MOS capacitors prepared by two methods. One is CVD-tantalum nitride (CVD-TaN) deposited by the chemical vapor deposition technique using Ta[NC(CH3)2C2H5][N(CH3)2]3 as a precursor, and the other one is sputtered tantalum nitride (sp-TaN) electrodes deposited by reactive DC magnetron sputtering. In the case of the CVD-TaN electrodes, the effective work function estimated from the relationship between VFB and the equivalent oxide thickness (EOT) of the MOS capacitors was about 4.4eV after post metallization annealing (PMA) at 400°C, and shifted to the mid-gap after PMA at 950°C. Moreover, the VFB values of MOS capacitors with sp-TaN electrodes also showed the same behavior after PMA. This shift is mainly dependent on the PMA temperature, regardless of the deposition method used. Similar VFB shifts induced by PMA were also observed in sp-TaN/ Al2O3/ SiO2/ p-Si and sp-TaN/ TaOx/ SiO2/ p-Si capacitors. However, in the case of the sp-TaN/ TaOx/ SiO2/ p-Si capacitors, the VFB shift was also observed when the PDA temperature after the TaOx deposition was 800°C and the PMA temperature after the TaN deposition was only 400°C. These results strongly suggest that this VFB shift caused by the PMA originates from a thin interfacial oxide layer between the TaN gate electrode and the dielectrics. Therefore, the maximum processing temperature after gate electrode deposition is important in order to control the threshold voltage of tantalum nitride gate MOSFETs.
Progress in Developing Nerve Agent Sensors Using Combinatorial Techniques
Authors: DiCesare John C. , Parker Jennifer , Horne Starr N. , Kita Justin , Earni Raghu , Peeples Christopher
Published: April 2011

Development of a sensor capable of selective detection of specific nerve agents is imperative in today’s atmosphere of terrorism. The sensor needs to be inexpensive, portable, reliable, absent of false positives and available to all military and first responders. By utilizing the techniques of molecular imprinting, combinatorial chemistry, silica sol-gel synthesis and lanthanide luminescence, a sensor for the detection of the hydrolysis product of the nerve agent soman is being developed. There are many parameters that require investigation in order for the sensor to become a reality. These parameters include 1) the selection of a chelate that can bind to the lanthanide and anchor the nerve agent simulant during the formation of the molecularly imprinted polymer, 2) the determination of the environment best suited for this complex formation, 3) the formation, as well as modification of the silica sol-gel for molecular imprinting to take place, and 4) the proper quantity and ratios of monomers used to create the three dimensional imprint. Key to the success of optimizing these parameters is the development of a combinatorial assay that allows for the synthesis and testing of tens of thousands of combinations of parameters. Work on the development of the combinatorial assay has lead to a method of preparing thin film polymers capable of analyzing the presence of nerve agent simulants. Current work is underway to validate the combinatorial assay and to synthesize and evaluate a library of sensor materials selective for nerve agents.
Nanorods Produced on the Surface of Thin Films of TiOx by Surface-Imprinting
Authors: Roberts M. Joseph , Johnson Scott K.
Published: April 2011

Worldwide, there is great interest in new processes for production of nanoscale features in materials surfaces. Our recent work explores imprinting of nanosized objects into thin films. In this paper, we present results from surface imprinting of TiOx sol-gel films with anodized alumina. Scanning Probe Microscopy provides evidence for the quality of the imprinting process.
Seeded and Non-Seeded Methods to Make Metallic Nanorods and Nanowires in Aqueous Solution
Authors: Sau Tapan K. , Murphy Catherine J.
Published: April 2011

Gold and silver nanorods/wires of different dimensions were obtained by wet-chemical seeded and non-seeded growth methods.
Highly Efficient Formation of TiO2-XNX–Based Photocatalysts - Potential Applications For Active Sites in Microreactors, Sensors, and Photovoltaics
Authors: Gole James L. , Burda Clemens , Fedorov Andrei , Prokes S. M.
Published: April 2011

We have produced nitrogen doped, stable, and environmentally benign TiO2-xNx photocatalysts whose optical response can be tuned across the entire visible region using a nanoscale exclusive synthesis route, performed in seconds at room temperature. This synthesis, which can be simultaneously accompanied by metal atom seeding, that can be accomplished through the direct nitration of anatase TiO2 nanostructures with alkyl ammonium salts. Tunability throughout the visible spectrum depends on the degree of TiO2 nano- particle agglomeration and the influence of metal seeding. The introduction of a small quantity of palladium, in the form of the chloride or nitrate, promotes further nitrogen uptake, appears to lead to a partial phase transformation, displays a counter ion effect with the acetate, and produces a material absorbing well into the near infrared. The nitridation process also induces the formation of oxygen hole centers. Silver introduced as the nitrate into a TiO2 or TiO2-xNx nanostructure framework, forms seeded AgxO - TiO2 or TiO2-xNx nanostructure mixtures which can be induced to self-assemble and to agglomerate into nano-needle and planar arrays using select metal probes. Surprisingly, no organics are incorporated into the final TiO2-xNx products. These visible light absorbing photocatalysts readily photodegrade methylene blue and when used to create photocatalytic sites on a surface based microreactor induce ethylene oxidation with visible light. They can be transformed from liquids to gels and placed on the surfaces of sensor and microreactor based configurations to 1) facilitate a photocatalytically induced solar pumped sensor response, and 2) provide a possible means for the catalytically induced disinfection of airborne pathogens. In contrast to a process which is facile at the nanoscale, we find little or no direct nitridation of micrometer sized anatase or rutile TiO2 powders at room temperature. Thus, we demonstrate an example of how a traversal to the nanoscale can vastly improve the efficiency for producing important submicron materials.
Influence of the Network Geometry on Electron Transport in Nanoparticle Networks
Authors: Benkstein K. D. , Kopidakis N. , van de Lagemaat J. , Frank A. J.
Published: April 2011

Computer simulations are applied to understand the influence of network geometry on the electron transport dynamics in random nanoparticle networks, and the predicted results are compared with those measured in one class of random nanoparticle networks: dye-sensitized nanocrystalline TiO2 solar cells. The model is applicable to all classes of random nanoparticle networks, such as highly disordered quantum dot arrays. The random nanoparticle networks are simulated by the step-wise condensation of a diffusion-limited aggregate. The fractal dimension of the nanoparticle films was estimated from the simulations to be 2.28, which is in quantitative agreement with gas-sorption measurements of TiO2 nanoparticle films. Electron transport on the computer-generated networks is simulated by random walk. The experimental measurements and random-walk simulations are found to be in quantitative agreement. For both a power-law dependence of the electron diffusion coefficient D on the film porosity P is found as described by the relation: D ∝ | P -Pc |μ. This power-law relation can also be derived from percolation theory, although only qualitatively. The critical porosity Pc (percolation threshold) and the conductivity exponent μ are found to be 0.76 ± 0.01 and 0.82 ± 0.05, respectively. It is estimated that during their respective transit through 50 and 75% porous 10-μm thick films as employed in the dye-cell, the average number of particles visited by electrons increases by 10-fold, from 106 to 107.
Spectroscopy Studies of InP Nanocrystals Synthesized Through a Fast Reaction
Authors: Furis Madalina , MacRae David J. , Lucey D. W. , Sahoo Yudhisthira , Cartwright Alexander N. , Prasad Paras N.
Published: April 2011

We present spectroscopic characterization of InP nanocrystals grown through a fast reaction in a non-coordinating solvent. The photoluminescence (PL) spectra collected from these nanocrystals exhibit a sharp feature associated with the band-edge emission and a broad infrared feature associated with deep level surface trap emission. The emission efficiencies of the as-grown nanocrystals vary between 0.3% and 1% from sample to sample. After undergoing an HF etching process, the emission efficiency increases to 18% and the emission associated with surface states is eliminated from the PL spectrum. Time-resolved photoluminescence (TRPL) experiments conducted at room temperature on the as-grown and HF-etched nanocrystals show that before etching the PL intensity decay is multi-exponential, with a fast (3ns) component independent of wavelength, associated with the non-radiative recombination processes. The etching process effectively eliminates the non-radiative component and the post-etching PL decay can be fitted with a single exponential decay characterized by long (45ns) lifetimes. We tentatively associate these long lifetimes with the recombination of carriers from spin-forbidden states. This assignment is supported by the observation of a significant redshift of the feature associated with band-edge recombination in the PL spectrum with respect to the lowest energy feature in the photoluminescence excitation (PLE) spectrum.
Deposition of Functionalised Gold Nanoparticles by the Layer-by-Layer Electrostatic Technique
Authors: Paul S. , Palumbo M. , Petty M. C. , Cant N. , Evans S. D.
Published: April 2011

Intensive research is currently underway to exploit the intriguing optical and electronic behaviour of nano-sized particles. The basis of the unique properties of these particles is the smallness of their size; dimensions on the nanometre scale can result in interesting quantum mechanical phenomena, such as Coulomb blockade. There are currently a number of ways by which the nanoparticles can be deposited onto solid substrates. Here, we report on the use of the layer-by-layer electrostatic method, which has shown much promise in the context of deposition of thin films of certain organic materials. In this technique, layers of oppositely charged materials are generated by dipping an appropriate substrate into solutions of polyelectrolytes. For example, the polybases poly(ethyleneimine) (PEI), when adsorbed on a substrate, produce a positively charged surface. We have deposited carboxylic acid (-COOH) derivatised gold nanoparticles onto a PEI-coated silicon substrate and an amine funtionalised silicon substrate. The distribution of the gold nanoparticles was compared using atomic force microscopy.
Magnetic Characterization of CoFe2O4 Nanoparticles
Authors: Lawes G. , Naughton B. , Clark D. R. , Ramirez A. P. , Seshadri R.
Published: April 2011

We have synthesized CoFe2O4 nanoparticles with length scales ranging from 3.5 nm to 14.2 nm. We have characterized the magnetic properties of these samples using both DC and AC magnetization, and find some slightly anomalous behavior in two of the samples. We tentatively attribute these features to interactions between the magnetic nanoparticles.

There is a great deal of interest in understanding the physical basis for the magnetic properties of nanoparticles in order to facilitate their incorporation into a wide range of commercial applications. By studying the magnetic characteristics of CoFe2O4 nanoparticles using bulk measurement techniques, we are able to probe the properties of both the individual nanoparticles and interactions in these systems. In this report, we discuss our magnetic characterization of a series of CoFe2O4 nanoparticles grown using an aqueous co-precipitation technique. In addition to DC magnetization at fixed fields and temperatures, we also investigated the magnetic properties using AC susceptibility measurements. The long term goal of this research is to understand interparticle interactions in magnetic nanoparticles.
Turbostratic Disorder in [(Bi2Te3)x(TiTe2)y] Superlattices
Authors: Harris Fred R. , Standridge Stacey , Feik Carolyn , Johnson David C.
Published: April 2011

A family of metastable [(Bi2Te3)x(TiTe2)y] superlattices (where × and y denote the number of layers of each of the two components) was prepared by annealing modulated elemental reactant precursors at temperatures below 280°C. Structural analysis by traditional XRD shows the superlattice structures are highly aligned to the substrate with many orders of diffraction peaks from the c direction of the superlattice. Off-axis diffraction techniques presented in this paper suggest that the order between the layers in the a-b direction of these superlattice structures is turbostratic. In this type of behavior, the quasi two-dimensional crystals of Bi2Te3 and TiTe2 that comprise the superlattice structure lie like a deck of cards thrown in disarray on a surface. An analysis of the diffraction data leading to this conclusion is given.
High-Temperature PbTe Thin Films for Use in Cascade Thermoelectric Power Generation
Authors: Posthill J.B. , Caylor J.C. , Crocco P.D. , Colpitts T.S. , Venkatasubramanian R.
Published: April 2011

PbTe-based thin films were deposited by thermal evaporation at temperatures ranging from ambient temperature to 430°C on different vicinal GaAs (100) substrates and BaF2 (111). This materials system is being evaluated as a potential candidate thermoelectric material for a mid-temperature stage in a cascade power generation module. Pure PbTe, PbSe, and multilayer PbTe/PbSe films were investigated. All films deposited on different vicinal GaAs (100) substrates were found to be polycrystalline when deposited at 250°C or lower. A subtle effect of substrate orientation and multilayer periodicity appears to contribute to the more randomly oriented polycrystallinity, which also lowers the thermal conductivity. These results are compared with PbTe epitaxial results on BaF2 (111).
Synthesis and thermoelectric properties of Ce(Ru0.67Rh0.33)4Sb12.
Authors: Staneff Geoff D. , Asimow Paul D. , Caillat Thierry
Published: April 2011

Exotic filled skutterudite compositions show promise for thermoelectric applications. Current work was undertaken with a nominal composition of Ce(Ru0.67Rh0.33)4Sb12 to experimentally verify its potential as an n-type thermoelectric material. Nominal electroneutrality was expected at 0.89 cerium filling and fully filled materials were expected to be strongly n-type. Filled precursors of the nominal composition were synthesized using straightforward solid state reaction techniques, but standard synthesis routes failed to produce a fully-filled homogenous phase. Instead, the filled thermoelectric Ce(Ru0.67Rh0.33)4Sb12 was synthesized using a combination of solid state reaction of elemental constituents and high pressure hot pressing. A range of pressure-temperature conditions was explored; the upper temperature limit of filled skutterudite in this system decreases with increasing pressure and disappears by 12 GPa. The optimal synthesis was performed in multi-anvil devices at 4–6 GPa pressure and dwell temperatures of 350–700 °C. rutheniumThe result of this work, a Ce(Ru0.67Rh0.33)4Sb12 fully filled skutterudite material, exhibited unexpected p-type conductivity and an electrical resistance of 1.755 mΩ-cm that increased with temperature. Thermal conductivity, Seebeck coefficient, and resistivity were measured on single phase samples. In this paper, we report the details of the synthesis routeand measured thermoelectric properties, speculate on the deviation from expected carrier charge balance, and discuss implications for other filled skutterudite systems.
Effect of High Valence Metal Doping on Thermoelectric Properties of [Ca2CoO3-δ]0.62CoO2
Authors: Fujie K. , Horii S. , Matsubara I. , Shin W. , Murayama N. , Shimoyama J. , Kishio K.
Published: April 2011

We report the synthesis and thermoelectric properties of high valence metal-doped [Ca2Co1-xMxO3-δ]0.62CoO2 (M = Re, Mo or Nb) compounds. Approximately 10% M-doping for Co sites in block layer was found to be effective for dramatic suppression of oxygen nonstoichiometries. Seebeck coefficients were systematically enhanced with M-doping levels (x), and however, electrical resistivities also increased with x for conventionally sintered bulk samples. On the other hand, magnetic alignment and/or densification were remarkably effective for reduction of the resistivity. In the case of Mo-doped (x = 0.1) sample, a highly c-axis aligned and densified sample showed 1–3 times larger power factor at 1100K (5.3 μ WK−2cm−1) than the non-doped one. Moreover, these high valence metal doped Ca349 compounds exhibited the oxygen nonstoichiometry suppressed dramatically.
Thermoelectric Properties of Semiconducting Intermetallic Compounds: FeGa3and RuGa3
Authors: Amagai Y. , Yamamoto A. , Lee C. H. , Takazawa H. , Noguchi T. , Obara H. , Iida T. , Takanashi Y.
Published: April 2011

We report transport properties of polycrystalline TMGa3(TM = Fe and Ru) compounds in the temperature range 313K<T<973K. These compounds exhibit semiconductorlike behavior with relatively high Seebeck coefficient, electrical resistivity, and Hall carrier concentrations at room temperature in the range of 1017- 1018cm−3. Seebeck coefficient measurements reveal that FeGa3isn-type material, while the Seebeck coefficient of RuGa3changes signs rapidly from large positive values to large negative values around 450K. The thermal conductivity of these compounds is estimated to be 3.5Wm−1K−1at room temperature and decreased to 2.5Wm−1K−1for FeGa3and 2.0Wm−1K−1for RuGa3at high temperature. The resulting thermoelectric figure of merit,ZT, at 945K for RuGa3reaches 0.18.
The effects of passivation layer and film thickness on the mechanical behavior of freestanding electroplated Cu thin films with constant microstructure
Authors: Xiang Yong , Vlassak Joost J. , Perez-Prado Maria T. , Tsui Ting Y. , McKerrow Andrew J.
Published: April 2011

The goal of this paper is to investigate the effects of film thickness and the presence of a passivation layer on the mechanical behavior of electroplated Cu thin films. In order to study the effect of passivating layers, freestanding Cu membranes were prepared using standard silicon micromachining techniques. Some of these Cu membranes were passivated by sputter depositing thin Ti films with thicknesses ranging from 20 nm to 50 nm on both sides of the membrane. The effect of film thickness was evaluated by preparing freestanding films with varying thickness but constant microstructure. To that effect, coatings of a given thickness were first vacuum annealed at elevated temperature to stabilize the microstructure. The annealed films were subsequently thinned to various thicknesses by means of chemical mechanical planarization (CMP) and freestanding membranes were prepared both with and without Ti passivation. The stress-strain curves of the freestanding Cu films were evaluated using the bulge test technique. The residual stress and elastic modulus of the film are not affected significantly by the passivation layer. The elastic modulus does not change with film thickness if the microstructure keeps constant. The yield stress increases if the film is passivated. For passivated films, yield stress is proportional to the inverse of the film thickness, which is consistent with the formation of a boundary layer of high dislocation density near the interfaces.
The Thermal Annealing Effect On The Residual Stress And Interface Adhesion In The Compressive Stressed DLC Film.
Authors: Choi Heon Woong , Moon Myoung-Woon , Kim Tae-Young , Lee Kwang-Ryeol , Oh Kyu Hwan
Published: April 2011

We studied on the thermal annealing effect on the residual stress and the mechanical properties in thin compressive stressed diamond-like carbon film on Si substrate. Annealing experiments were carried out with Rapid Thermal Procedure system at 200–600 °C, and the stress change with annealing temperature was investigated by in-situ stress measurement system. The apparent stress reduction occurred with minimal structure changes. In order to measure the change of chemical structure of diamond-like carbon film by annealing, we used Raman spectrometer. The adhesion deterioration in interface has been detected as annealing temperature increased. In the compressive stressed DLC film, we observed the dramatic evolution of interface delamination at certain high temperature using in-situ heating stage built in Environment SEM. The quantitative change of adhesion affected by annealing process was also measured with scratch testing. For exploring the interface structure affected by the thermal annealing process at high temperature, the cross section of annealed film has been observed with HR TEM.
Investigation of Structural and Mechanical Properties of UV and Microwave-Irradiated Al2O3 / ZrO2 Multilayers by Sol-Gel Coating
Authors: Phani A. R. , Haefke H.
Published: April 2011

Thin film multilayers of Al2O3 / ZrO2 have been deposited on quartz and AISI 440C steel substrates at room temperature by sol-gel dip coating technique followed by annealing at different temperatures ranging from 200°C to 800°C for 5h. Prior to annealing the deposited films have been exposed 10 min to ultraviolet radiation (248 nm wavelength) and microwave (2.45 MHz at 800 W power) respectively. Unlike conventional annealing methods, microwave heating is generally quite faster, simpler, and very energy efficient. The lower temperature and shorter time with microwave irradiation might be ascribed to the activating and facilitating effect of microwave on solid phase diffusion. X-ray diffraction (XRD) and scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analyser techniques have been employed to characterize structural, morphological and elemental composition of the thin films. Adhesion strength failure measurements on films have shown critical loads up to 35 N. Nanohardness indentation tests of the films exposed to microwave have shown hardness of 10 GPa with elastic modulus of 85 GPa compared to the annealed films hardness of 4.5 GPa with elastic modulus 57 GPa.
Interdiffusion in Coherent Si0.90Ge0.10/Si0.95Ge0.05 Superlattices
Authors: Aubertine D. B. , McIntyre P. C.
Published: April 2011

We present the use of x-ray scattering from Si1-XGeX/Si1-YGeY superlattices as a tool for measuring the concentration dependence of interdiffusivity in Si/SiGe epitaxial thin films. Although x-ray scattering from compositionally modulated films is an ultra-high-sensitivity technique for measuring interdiffusion in a variety of systems, the concentration dependence of Si/SiGe interdiffusion complicates its interpretation. We show that these complications can be avoided using Si1-XGeX/Si1-YGeY superlattices with a small compositional modulation. This strategy is assessed using numerical simulations of both interdiffusion and dynamical x-ray diffraction. We demonstrate its effectiveness by measuring the activation enthalpy and exponential prefactor for interdiffusion in compressively strained Si0.925Ge0.075. The results are 4.38 ± 0.05 eV and 36 ± 9 cm2/s respectively.
Nanoindentation Behavior of Gold Single Crystals
Authors: McCann Martha M. , Corcoran Sean G.
Published: April 2011

Nanoindentation is an increasingly used tool to investigate the mechanical properties of very small volumes of material. It is usually a very consistent measure of the elastic response of material and plastic response to point contact loading. Nanoindentation experiments on gold single crystals display tremendous variation in the residual deformation. The depth of penetration, which is vital in hardness determination, can differ by as much as 100%. This large variability of the load-depth data is usually explained by surface differences such as crystal orientation, oxide thic kness, presence of multiple solid phases, or contamination layers. None of these reasons apply to the variation observed in the gold system. The onset of plastic deformation is observed at a stress level on the order of the theoretical yield strength. The difference in depth of penetration is independent of this elastic -plastic transition. This paper reports on attempts to correlate the depth of penetration to surface feature size and surface preparation procedures.
Experimental Measurements of Surface Residual Stress Caused by Nano-scale Contact of Rough Surfaces
Authors: Wang J. , Shrotriya P. , Yu H. H. , Kim K.-S.
Published: April 2011

A previous dislocation model analysis predicts that nano-scale contacts of surface steps induce nucleation of dislocations leading to pro-load and anti-load dislocation segregation near the contact surface. Such dislocation segregation generates a sub-layer of tensile residual stress in a much thicker layer of compressive residual stress near the surface. The sub-layer thickness is expected to be about 50 to 100 times the step height. In order to verify the predictions of the model analysis, experiments are carried out on polycrystalline aluminum surface to determine the existence of the tensile sub-layer. The variation of the residual stress along the thickness direction is measured using a newly developed high sensitivity curvature-measurement interferometer. The interferometer measures the curvature change of the back surface of a plate specimen of about 1.9 mm thickness while the contact-loaded front surface is chemically etched. The residual stress distribution measured with sub-nanometer spatial resolution is compared with analytical predictions.
The fabrication of p-Ge/n-Si photodetectors, compatible with back-end Si CMOS processing, by low temperature (< 400 °C) molecular beam epitaxy and electron-beam evaporation
Authors: Bandaru Prabhakar , Sahni Subal , Yablonovitch Eli , Kim Hyung-Jun , Xie Ya-Hong
Published: April 2011

We report on the low temperature growth, by molecular beam epitaxy (375 °C) and electron-beam evaporation (300 °C), of p-Ge films on n-Si substrates for fabricating p-n junction photodetectors, aimed at the integration of opto-electronic components with back-end Si CMOS processing. Various surface hydrogen and hydrocarbon removal treatments were attempted to improve device properties. We invoke Ge diffusion and growth modes as a function of deposition temperature and rate to correlate structural analysis with the device performance.
Strain Modulation of β-FeSi2 by Ge-Segregation in Solid-Phase Growth of [a-Si/a-FeSiGe]n Multi-Layer
Authors: Murakami Y. , Kenjo A. , Sadoh T. , Yoshitake T. , Itakura M. , Miyao M.
Published: April 2011

Strain modulation of β-FeSi2 by Ge doping was investigated. By solid-phase growth of [a-Si/a-Fe0.4Si0.5Ge0.1]n layered structures, the [a-SiGe/β-FeSi2-xGex]n multi-layered structures (n=1, 2, 4) were formed after annealing at 700 °C. From the analysis of the x-ray diffraction spectra, it was found that β-FeSi1.3Ge0.7 strained by 0.4–0.5 % was formed for the sample with n=1. This value corresponded to the band gap modulation of 30 meV based on the theoretical calculation. The strains decreased with increasing n, which was due to that segregation of Ge atoms from the a-Fe0.4Si0.5Ge0.1 layers to the a-Si layers became significant with increasing n. After annealing at 800 °C, agglomeration of β-FeSi2 occurred, and nanocrystals of relaxed β-FeSi2 and c-Si0.7Ge0.3 were formed. These new structures are useful for formation of opto-electrical devices.
Reduction of dark current in AlGaN/GaN Schottky barrier photodetectors with a low-temperature-grown GaN cap layer
Authors: Chi G. C. , Sheu J. K. , Lee M. L. , Kao C. J. , Su Y. K. , Chang S. J. , Lai W. C.
Published: April 2011

AlGaN/GaN-based ultraviolet (UV) Schottky barrier photodetectors (PDs) with and without the LT GaN cap layer were both fabricated. It was found that we could achieve a lower leakage current from sample A. With incident light wavelength of 320 nm and a –1 V reverse bias, the measured responsivity was around 0.03 A/W and 0.015 A/W for samples with and without the LT GaN cap layer, respectively. The response speed of the sample A was also found to be faster.
Evidence of strong indium segregation in MOCVD InxGa1-xN/GaN quantum layers
Authors: Maciejewski Grzegorz , Jurczak Grzegorz , Kret Sławomir , Dłużewski Paweł , Ruterana Pierre
Published: April 2011

An investigation of 1–5 nm in diameter indium rich clusters in MOCVD InxGa1-xN/GaN quantum well is carried out. To this end, quantitative High Resolution Transmission Electron Microscopy (HRTEM) is coupled with the Finite Element Method (FEM) for the calculation of thin foil relaxation and for image simulation. The measurement of the tetragonal distortion from HRTEM images is a useful tool for the determination of chemical composition in heterostructures. However, for a correct interpretation of the measured lattice distortion on HRTEM images, one needs to take into account the strain averaging across TEM sample and inhomogeneous relaxation of the sample. As a first step, 3D FEM simulation of the relaxation process as a function of the position of indium rich cluster relative to the foil surface is performed. Next, the calculated 3D displacement field is used to simulate the HRTEM images. The results clearly show that the magnitude of the strain field depends on the cluster position. It is concluded that the HRTEM images of indium rich clusters can differ even for the same indium content due to different positions of the clusters.
Growth of non-polar a-plane and cubic InN on r-plane sapphire by molecular beam epitaxy
Authors: Lu Hai , Schaff William J. , Eastman Lester F. , Cimalla Volker , Pezoldt Joerg , Ambacher Oliver , Wu J. , Walukiewicz Wladek
Published: April 2011

Growth of non-polar III-nitrides has been an important subject recently due to its potential improvement on the efficiency of III-nitride-based opto-electronic devices. Despite study of non-polar GaN and GaN-based heterostructures, there are few reports on epitaxial growth of non-polar InN, which is also an important component of the III-nitride system. In this study, we report heteroepitaxial growth of non-polar InN on r-plane sapphire substrates using plasma-assisted molecular beam epitaxy. It is found that when a GaN buffer is used, the following InN film appears to be non-polar (1120) a-plane which follows the a-plane GaN buffer. The room temperature Hall mobility of undoped a-plane InN is around 250 cm2/Vs with a carrier concentration around 6×1018 cm-3. Meanwhile, if InN film is directly deposited on r-plane sapphire without any buffer, the InN layer is found to consist of a predominant zincblende (cubic) structure along with a fraction of the wurtzite (hexagonal) phase with increasing content with proceeding growth.
Non-Equilibrium Acceptor Concentration in GaN:Mg Grown by Metalorganic Chemical Vapor Deposition
Authors: Gong Y. , Gu Y. , Kuskovsky Igor L. , Neumark G. F. , Li J. , Lin J. Y. , Jiang H. X. , Ferguson I.
Published: April 2011

It is shown that the high p-type conductivity in GaN:Mg, grown by metal-organic chemical vapor deposition followed by post-growth annealing, is due to non-equilibrium acceptor concentrations. A series of samples cut from a single GaN:Mg wafer, which initially had undergone rapid thermal annealing (RTA) after growth, has been investigated. The samples were annealed at various temperatures in nitrogen ambient for over 12 hours, and temperature-dependent Hall effect measurements were performed. For samples annealed at temperatures higher than 850 °C, the hole concentrations decrease by at least an order of magnitude, compared with the original sample. This behavior is explained by an Mg acceptor concentration in excess of its equilibrium solubility limit in the original sample; thus, at high enough temperatures, in the absence of hydrogen, Mg acceptors diffuse either to form electrically inactive precipitates or are eliminated. It is worth noting that the acceptor activation energy remains the same for all samples.
Thermally stimulated current spectroscopy of carbon-doped GaN grown by molecular beam epitaxy
Authors: Fang Z-Q. , Look D. C. , Armitage R. , Yang Q. , Weber E. R.
Published: April 2011

Deep traps in semi-insulating (SI) or high-resistivity C-doped GaN grown by metal-organic chemical-phase deposition or molecular-beam epitaxy have been studied by thermally stimulated current (TSC) spectroscopy. Incorporation of carbon in GaN introduces CNacceptors, resulting in compensation and formation of SI-GaN; however, as [C] increases in the GaN samples, both resistivity and activation energy of the dark current decrease. In the GaN samples with low [C], we find at least six TSC traps: B (0.61 eV), Bx(0.50 eV), C1(0.44 eV), C (0.32 eV), D (0.23 eV), and E (0.16 eV), all of which are very similar to electron traps typically found in n-type GaN by deep level transient spectroscopy (DLTS). However, in the GaN sample with the highest [C], both traps E and B are suppressed, and instead, trap Bxappears. Based on DLTS studies of electron-irradiated and plasma-etched GaN samples, we believe that traps E, D and C are related to VN, and that trap B is probably related to VGa, in the form of complexes such as VGa-ON. As [C] increases, CGadonors become more favorable, and the transition of trap B to trap Bxmay suggest that CGarelated complexes are forming. In comparison with lightly C-doped GaN, heavily C-doped GaN sample exhibits very strong PPC at 83 K. We show that the PPC in both cases can be simply explained by the thermal emission of carriers from shallower traps.
Time Resolved Photoluminescence of Si-doped High Al Mole Fraction AlGaN Epilayers Grown by Plasma-Enhanced Molecular Beam Epitaxy
Authors: Furis Madalina , Cartwright Alexander N. , Hwang Jeonghyun , Schaff William J.
Published: April 2011

We report on detailed temperature dependent, time-resolved photoluminescence (TRPL) studies of Si-doped AlGaN epilayers. In these samples, the Al concentration varies from 25% to 66%. The samples were found to exhibit metallic-like temperature-independent conductivity. The deep level “yellow” emission, whose presence would indicate the existence of a large number of defects associated with growth, Si incorporation, and/or alloy formation, is absent. In addition to emission corresponding to the donor-bound exciton, the PL spectrum exhibits features associated with transitions involving localized carriers. This assignment of the emission mechanisms is based on the activation energies extracted from the temperature dependent photoluminescence (PL) quenching. Specifically, at room temperature the PL spectrum is dominated by transitions involving localized states. The localization energy varied from sample to sample and was observed to be between 115 meV to 200 meV. The PL intensity decay in the lower Al mole fraction epilayers exhibits a slow component associated with the presence of donor-bound excitons.
Anisotropic Dielectric Properties of GaN Epilayers on Sapphire
Authors: Rowell N. L. , Yu G. , Lockwood D. J.
Published: April 2011

Polarized infrared reflectance from 300 to 1200 cm-1 at different incidence angles was measured at room temperature for sapphire and GaN/sapphire samples. A film of GaN was grown approximately 1.5 μm thick on c-plane sapphire by MOCVD with a thin GaN buffer layer. Because of the hexagonal structure of sapphire and GaN, their uniaxial optical properties are anisotropic. In the p-polarized reflective spectrum, we observed the mixed effect between the distinct infrared-active modes with dipole-moment oscillation perpendicular (E-mode) and parallel (A-mode) to the c axis. The contribution of the A-mode increased with increasing incidence angle. Therefore, we were able to obtain simultaneously the infrared dielectric functions parallel and perpendicular to the c axis, by fitting simultaneously three polarized reflectance spectra at three different incident angles with a suitable model. In the procedure, we adopted a new fitting technique, i.e., fitting the first numerical derivative of the polarized reflectance spectra to improve the accuracy of the phonon parameters and to overcome the inconsistency between the model and measurement in the whole frequency range. Excellent agreement has been obtained between the measured and fitted first derivative reflectance spectra for both the sapphire and GaN/sapphire samples. The dielectric information thus obtained for sapphire and GaN is of greater accuracy than those reported previously.