bluuebunny/crossref_metadata_2025 huggingface dataset:
A Comparative Analysis of Iridium Oxide Nanowires in Electrical Detection of Biochemical Reactions
Authors: Venkatraman Vinu , Reddy Ravikiran , Zhang Fengyan , Evans David , Hsu Sheng-Teng , Ulrich Bruce , Prasad Shalini
Published: April 2011

Pt, Ir, Au and few other precious metals have highly conducive electrical and chemical properties; hence have been widely used in pH sensors and bimolecular sensing applications. The chief objective of this research is to highlight and demonstrate the advantages that Iridium Oxide (IrOx) nanowires offer over these competing metals in improving the performance metrics of biomolecular sensing. Iridium oxide has very good conductivity and very high charge storing capacity, and hence has an ability to detect very small changes in the surface charge. Nanowires have an ideal morphology to crowd protein molecules and highly increase the surface area of interaction. Higher area of interaction along with iridium oxide's high intrinsic physical adsorption rate, strongly enhance the rate of immobilization of biomolecules and hence enabling high sensitivity detection. Inflammatory protein, C-Reactive protein (CRP) that is a biomarker for cardiovascular disease was used as the model biomolecule for this study.
Experimental Research on Thermal Energy Storage of a New Type of PCM Heat Exchanger
Authors: Xiaoqin Zhu , Jin Hu , Nanjing Li , Panpan Wang , Jiansheng Lu , Ben-Abdallah Noureddine
Published: April 2011

Thermal energy storage with phase change materials is one of the most efficient means of storing available energy because of its advantages such as providing higher thermal storage capacity, lower storage temperature, isothermal operation and less storage space. Thermal energy storage property of a new type of PCM heat exchanger was investigated, in which its main body is based on the traditional structure of a shell-and-tube heat exchanger, and is full of PCMs (CaCl2·6H2O) in the tubes. The hot air at the temperature of 40° was selected as a flow medium, and the temperature measurements of the test points were carried out at the inlet and outlet of this kind of PCM heat exchanger. The experimental results showed that this kind of PCM heat exchanger could store thermal energy from the hot fluid by means of PCMs in the tubes. Its prospect in engineering applications such as the recovery and utilizations of industrial afterheat or waste heat etc was also analyzed and forecasted.
Review on Development and Investigations of Phase Change Materials in Thermal Energy Storage
Authors: Xiaoqin Zhu , Jin Hu , Zhaosheng Cao , Jiansheng Lu , Jialin Sun , Ben-Abdallah Noureddine
Published: April 2011

Thermal energy storage with phase change materials is one of the most efficient ways of storing available energy because of its advantages such as providing higher heat storage capacity, lower storage temperature, isothermal operation and less storage space. This paper reviews the development and investigations of phase change materials in thermal energy storage systems of various engineering applications. There are many phase change materials that melt and solidify at a wide range of temperatures, making them attractive in a lot of applications. Various categories of phase change materials suitable for thermal energy storage are introduced, and the investigations on their important enhancement techniques are also discussed.
High Conducting Heterovalent Substituted NASICON-like Phases in ScPO4-Na3PO4Quasibinary System
Authors: Potapova Anna , Zhuravleva Mariya , Smirnova Irina , Spiridonov Felix , Zimina Galina , Novoselov Andrey
Published: April 2011

Phase equilibria in quasibinary system ScPO4-Na3PO4 and formation of heterovalent Zr-substituted solid solutions (up to 10 mol%) for Sc3+ in Na3Sc2(PO4)3 complex phosphate were studied by ceramic technique at 1050°C. Obtained samples were investigated with X-ray powder diffraction and impedance spectroscopy. Zr-substituted (10 mol%) Na3Sc2(PO4)3has ionic conductivity of 3.18.10-1 S/cm at 300°C.
Carbon Nanoparticles for Counter Electrode Catalyst in Dye-Sensitized Solar Cells
Authors: Joshi Prakash , Xie Yu , Mwaura Jeremiah , Ropp Mike , Galipeau David , Qiao Qiquan
Published: April 2011

We report dye-sensitized solar cells using low cost carbon nanoparticles as an alternative to platinum as a counter-electrode catalyst for triiodide reduction. The counter carbon-electrode was deposited onto fluorine-doped tin oxide (FTO) by spin coating from an aqueous colloidal suspension of the blend of carbon nanoparticles and TiO2 nanocrystals. DSSC devices were fabricated using a stable Ru complex dye (Z-907) as the sensitizer. The cells based on carbon-nanoparticle counter electrode were made and then compared with those cells from platinum counter electrode at similar fabrication conditions. The results have shown that the device performance in terms of short circuit current density (Jsc), open circuit voltage (Voc) and energy conversion efficiency (η) from the cells based on carbon nanoparticle counter electrode were comparable to those from platinum counter-electrode devices. The carbon nanoparticle based cells have achieved an overall energy conversion efficiency of 5.55% under one sun AM 1.5 illumination (100 mW/cm2). The carbon nanoparticles showed significant potential as a low cost alternative to the current widely-used platinum.
Phosphorous and Boron Doped Colloidal Silicon Nanocrystals in Conjugated Co-polymers
Authors: Svrcek Vladimir , Fujiwara Hiroyuki , Kondo Michio
Published: April 2011

One-way to improve organic solar cell efficiency is blending conjugated polymer with a second nanocomposite. We report on blending of freestanding boron- and phosphorous-doped environmental friendly silicon nanocrystals (Si-ncs) with two conjugated polymers i.e. (poly(3-hexylthiophene) (P3HT) and poly[methoxy-ethylexyloxy-phenylenevinilene] (MEH PPV)). The electrochemical etching and pulverization of doped porous silicon films are used for fabrication of photesensitive Si-ncs/polymers blends. Processing of Si-ncs dispersed in polymers allows simple tuning of the Si-ncs concentrations in the blends. The blends with high Si-ncs concentrations are prepared and opto-electric properties are compared and discussed. Both types of polymers containing doped Si-ncs showed a photoconductivity response under illumination AM1.5 at ambient temperature and atmosphere.
Thermoelectric High Power Generating Module Made by n-Ba8AlxSi46-x Clathrate
Authors: Munetoh Shinji , Arita Makoto , Makiyama Hideki , Motooka Teruaki
Published: April 2011

We have developed a new thermoelectric power-generating module composed of 72 pieces of n-type Ba8Al18Si28 clathrate elements made by arc melting. The Seebeck coefficient, specific electric resistance and thermal conductivity of Ba8Al18Si28 clathrate were 250 μV/K, 1.9 mΩcm and 3.1 W/mK at 500 °C, respectively, and the thermoelectric figure of merit (ZT) was 0.8. The new thermoelectric module was constructed using only n-type thermoelectric elements connected in series with hook-shaped electrodes. The open-circuit voltage of the module increased with hot-side temperature up to 1.8 V at 500 °C and generated 0.24 W. The module was successfully used to charge lithium-ion batteries for mobile phones.
Actinide Selective Systems for Environmental Extraction and Sensing Applications
Authors: Wu Xianghong , Bharara Mohan Singh , Tate Brandon K , Tonks Stephen A , Vilseck Jonah Z , Gorden Anne Elizabeth Vivian
Published: April 2011

The potential environmental and health concerns surrounding actinides and the use of nuclear fuels limits the acceptance of nuclear power by the public. This in turn, hinders the capability of this country to take advantage of nuclear power. Expanding our fundamental knowledge of actinide coordination chemistry will allow for the development of improved actinide sensors, new separations methods, or new means of radioactive waste remediation. We have designed and optimized a solution-phase parallel method for the synthesis of a library of symmetrical 2-quinoxalinol salens, Schiff-base type ligands with a 2-quinoxalinol incorporated into the salen backbone. This combines the rigid salen coordination framework with the quinoxaline properties that impart properties for use in colorimetric or fluorescent sensors. These have now been incorporated into organic soluble resins for metal extraction.
The Role and Management of Free Water in the Production of Durable Radioactive Waste Products Using Hydraulic Cements
Authors: Angus Michael J. , Butcher Ed , Godfrey Ian H. , Milestone Neil B.
Published: April 2011

Water is a necessary component in the production of encapsulated wastes based on hydraulic cements which are widely used for immobilization of intermediate and low level waste (ILW) and (LLW). Apart from providing the fluidity required to readily transport slurry wastes, it plays an essential role in hydrating the cement. Too low a water content prevents homogeneous mixing of the cement binder and waste and does not provide the fluidity needed for effective infilling of solid wastes. The water left after hydration creates a porous network that allows egress of gaseous corrosion/radiolytic degradation products such as hydrogen. A broad envelope (i.e. range) of acceptable water/binder ratios is essential for effective process control, particularly for the encapsulation of slurry wastes which have widely varying water contents.

Nevertheless, the presence of large amounts of free water in the pore system of the hardened matrix allows easy transport of soluble ions such as hydroxide, which can lead to metal corrosion, and the increased permeability of the system increases the leachability. Therefore effective management of the ‘free’ water content of a waste product will allow optimisation of both the encapsulation process and the product quality and durability.

This paper describes a range of innovative approaches to ‘water management’, including the use of alternative hydraulic cements, modification of powder characteristics and use of superplasticised composite OPC grouts and examines the contribution of 1H NMR relaxometry in providing improved understanding of the distribution of water within the pores of the hardened cement matrix.
High-Efficiency HIT Solar Cells for Excellent Power Generating Properties
Authors: Kinoshita Toshihiro , Ide Daisuke , Tsunomura Yasufumi , Taira Shigeharu , Baba Toshiaki , Yoshimine Yukihiro , Taguchi Mikio , Kanno Hiroshi , Sakata Hitoshi , Maruyama Eiji
Published: April 2011

In order to achieve the widespread use of HIT (Hetero-junction with I etero-Intrinsic T ntrinsic Thin-layer) solar cells, it is important to reduce the power generating cost. There are three main approaches for reducing this cost: raising the conversion efficiency of the HIT cell, using a thinner wafer to reduce the wafer cost, and raising the open circuit voltage to obtain a better temperature coefficient. With the first approach, we have achieved the highest conversion efficiency values of 22.3%, confirmed by AIST, in a HIT solar cell. This cell has an open circuit voltage of 0.725 V, a short circuit current density of 38.9 mA/cm2and a fill factor of 0.791, with a cell size of 100.5 cm2. The second approach is to use thinner Si wafers. The shortage of Si feedstock and the strong requirement of a lower sales price make it necessary for solar cell manufacturers to reduce their production cost. The wafer cost is an especially dominant factor in the production cost. In order to provide low-priced, high-quality solar cells, we are trying to use thinner wafers. We obtained a conversion efficiency of 21.4% (measured by Sanyo) for a HIT solar cell with a thickness of 85μm. Even better, there was absolutely no sagging in our HIT solar cell because of its symmetrical structure. The third approach is to raise the open circuit voltage. We obtained a remarkably higher Voc of 0.739 V with the thinner cell mentioned above because of its low surface recombination velocity. The high Voc results in good temperature properties, which allow it to generate a large amount of electricity at high temperatures.
Dielectric Function and Defect Structure of CdTe Implanted by 350-keV Bi Ions
Authors: Petrik Peter , Fried Miklós , Zolnai Zsolt , Khánh Nguyen Q. , Li Jian , Collins Robert W. , Lohner Tivadar
Published: April 2011

In this work we have developed optical models for the ellipsometric characterization of Bi-implanted CdTe. We have characterized the amount and nature of disorder using Rutherford Backscattering Spectrometry combined with channeling (RBS/C). Samples with a systematically varying degree of disorder were prepared using ion implantation of Bi into single-crystalline CdTe at an energy of 350 keV with increasing doses from 3.75×1013 cm-2 to 6×1014 cm−2. The motivation for use of the high atomic mass Bi ions was that previous studies using lighter ions revealed damage at a low level, even for doses several times higher than the amorphization threshold estimated by simulation [P. Petrik et al., phys. stat. sol. (c) 5, 1358 (2008)]. In contrast, Bi ions create sufficient disorder for investigation of the changes in dielectric function critical point (CP) features in a wider variety of structures from single-crystalline to the disordered state. The CP features can be described by numerous methods starting from the standard CP model, through the parameterization of Adachi [Adachi et al., J. Appl. Phys. 74, 3435 (1993)], and finally to the generalized CP models. The standard CP model has been demonstrated to be a reliable approach for polycrystalline CdTe characterization used in photovoltaic applications [Li et al., phys. stat. sol. (a) 205, 901 (2008)].
MOCVD Growth of High-Hole Concentration (>2×1019 cm−3) P-Type InGaN for Solar Cell Application
Authors: Yu Hongbo , Melton Andrew , Jani Omkar , Jampana Balakrishnam , Wang Shenjie , Gupta Shalini , Buchanan John , Fenwick William , Ferguson Ian
Published: April 2011

InGaN alloys are widely researched in diverse optoelectronic applications. This material has also been demonstrated as a photovoltaic material. This paper presents the study to achieve optimum electrically active p-type InGaN epi-layers. Mg doped InGaN films with 20% In composition are grown on GaN templates/sapphire substrates by MOCVD. It is found that the hole concentration of p-type InGaN depends strongly on the Mg flow rate and V/III molar ratio and hole concentration greater than 2×1019 cm−3 has been achieved at room temperature. The optimum activation temperature of Mg-doped InGaN layer has been found to be 550-600°C, which is lower than that of Mg-doped GaN. A solar cell was realized successfully using the InGaN epi-layers presented here.
Properties of P(VDF-TeFE) thin film formed by annealing process with electric field
Authors: Jeong Jong-Hyeon , Kimura Chiharu , Aoki Hidemitsu , Okuyama Masanori , Sugino Takashi
Published: April 2011

In order to apply P(VDF-TeFE) piezoelectric polymer to micro-generator as a membrane, the polymer is deposited on a substrate by spin-coating method. In this process, some changes of properties and quality of the film are caused by a solvent which was used to dissolve the polymer granule. Since a solvent affects the film properties and surface stability, we have carried out the thermal process at a temperature higher than melting point. However, this thermal process due to a temperature higher than Curie point of the polymer causes a falling-off in electrical properties. In this paper, we have studied a method to prevent a falling-off in electric properties of P(VDF-TeFE) film even though the film is annealed at a temperature higher than Curie point.
Informatics for Quantitative Analysis of Atom Probe Tomography Images
Authors: Suram Santosh K , Rajan Krishna
Published: April 2011

An informatics based approach to extract further refinements on the crystallographic information embedded in the Spatial Distribution Maps (SDMs) has been developed. The data mining based methods to generate and interpret spectra that de-convolute the SDMs are discussed. This work has resulted in a method to generate SDMs that can map three-dimensional crystallographic information as opposed to existing methods that map structural information on only one atomic plane at a time. The broader implications of this work on enhancing the interpretation and resolution of structural information in atom probe tomography studies is also discussed.
Characterization of the Crack Propagation in the API X-52 and API X-65 Steels into Cathodic Protection
Authors: Aguilar A. , Esparza R. , Gil M.A. , Cuahutitla L.F. , Rubio-Rosas E. , Rodríguez-Lugo V. , Perez R.
Published: April 2011

Cathodic protection has been applied for many years as the best method to prevent the corrosion in systems which transported hydrocarbon pipelines. However, it has found the presence of stress corrosion cracking (SCC) in steel pipelines with high concentrations of carbonates and bicarbonates with pH final (9 to 11). The resistance to the stress corrosion cracking of the API X-52 and API X-65 steels was evaluated on compact modified wedge opening specimens (WOL). The specimens were loaded of 95% of the yield strength. The resistance of crack propagation and the corrosion rate were evaluated with different applied potentials (-850 and -650 mV), this with respect to a saturated copper/copper sulfate reference electrode. The used electrolytes were simulated soils (carbonate-bicarbonate solution). Evidence of crack propagation of the API X-52 and API X-65 steels were carried out by scanning electron microscopy. The obtained result showed susceptibility to SCC on specimens with cathodic protection. The cathodic protection applied (-850 mV vs Cu/CuSO4 electrode) decreases considerably the corrosion rate on the evaluated steels. In this work the loaded stress showed to be a very important variable on the susceptibility to SCC.
Critical Indicator of Slip-Prone Clayey Soils Due Rainfall in Teziutlán-Puebla-México Zone: Yield Stress Determination by Slump Tests
Authors: Méndez-Sánchez Arturo. F. , Nieto Zepeda Karen E. , Pérez-Trejo Leonor , Paniagua-Mercado Ana M.
Published: April 2011

The yield stress evaluation as a function of water content for slip-prone clayey soils due to rainfall is studied in this work, particularly, the clayey soil from the region Teziutlán-Puebla-México. Yield stress was calculated as a function of water content using the slump test in cylindrical geometry. Results show a critical point of water content where yield stress decreases dramatically, and those values were related to the historical daily rain data. It was found a maximum precipitation millimeters that triggers the landslide, but still is low compared with the historical reported data.
Phase-separation in ZnxCd1-xSe/C Core/shell nanocrystals studied with cathodoluminescence spectroscopy
Authors: Estrin Yevgeni , Rich Daniel H , Moshe Ofer , Bhattacharyya Sayan , Gedanken Aharon
Published: April 2011

ZnxCd1-xSe/C core/shellnanocrystals with 31-39 nm diameter semiconductor cores and 11-25 nm-thick carbon shells were synthesized from solid state precursors. Transmission electron microscopy showed striations on a scale of ˜1 – 5 nm in the nanocrystals that are indicative of a composition modulation, and reveal a chemical phase separation and possible spinodal decomposition within the nanocrystals. Such a composition modulation within the ternary nanocrystals represents a rarely reported phenomenon that could lead to additional applications. The optical properties and carrier relaxation kinetics of the nanocrystals were examined with variable excitation cathodoluminescence (CL). As the excitation level is increased, carrier filling in two-dimensional (2D) phase-separated Cd-rich regions leads to a partial saturation of states before the onset of carrier filling in the higher bandgap homogenous Zn0.47Cd0.53Se regions. In order to model the state filling using Fermi-Dirac statistics for non-interacting carriers, a random quantum well model was used to determine the electron and hole eigensates in the Cd-rich regions of the nanocrystals.
Acetaldehyde Photocatalytic Decomposition over Nanostructured TiO2 Sol-Gel Catalysts
Authors: Castillo S. , Camposeco R. , Carrera R. , Mujica M. , Ángel P.Del , Montoya J.A. , Vázquez A.L. , Morán-Pineda M. , Goméz R.
Published: April 2011

TiO2nanoparticles were synthesized by the Sol-Gel method by using 2-propanol as solvent in acid medium (pH1). The samples were annealed at 200 and 500°C and were characterized by BET, XRD-Rietveld refinements, TEM and FTIR. The activity was evaluated by the acetaldehyde photodecomposition in an isolated chamber with an initial concentration of contaminant of 300 ppmv with oxygen (2%) assisted with a 365-nm UV lamp. The test results were compared with those obtained with a commercial catalyst (P25). Improved photoactivity (≍100 % of acetaldehyde in 150 min) was obtained with catalysts annealed at 200°C (TiO2-P-200°C), that showed nanoparticles (≍7 nm) and abundant anatase phase (≍ 63 %) coexist with the brookite phase (≍ 37 %), as well as irregular equiaxial morphology. The samples annealed at 500°C (TiO2-P-500°C), showed an increment in nanoparticles (≍22 nm), different ratio and phase composition (anatase-brookite-rutile), and therefore less activity (≍80 %). This high activity could be explained by the special ratio of anatase-brookite and the dimension of nanometric crystal size. The aforementioned characteristics could be useful in the degradation of reactive organic gases like acetaldehyde either in confined spaces or in the open air.
Improved Quality of Bulk II-VI Substrates for HgcdTe and HgZnTe Epitaxy
Authors: Sen Sanghamitra , Stannard John E.
Published: April 2011

Single crystals of CdTe or dilute alloys of Cd1−yZnyTe (y≤0.04) and CdTe1−zSez (z ≤0.04) with low defect density, high purity and large single-crystal area (>30 cm2) are required as substrates for high-quality epitaxial Hg1−xCdxTe thin films in the infrared (IR) detector industry. Bridgman or gradient freeze is the most common technique used for commercial production of these materials because of its success in producing large area substrates of good quality and reproducibility. For epitaxial growth of Hg1−xZnxTe, which has been of considerable interest in recent years as an IR detector material, the substrate of choice has been Cd0.80Zn0.20Te, for lattice matching with long wavelength Hg1−xZnxTe epitaxial layers (x = 0.13–0.14). The primary focus of this paper is on CdZnTe which is currently the preferred substrate material and most widely used for both HgCdTe and HgZnTe epitaxy. This paper reviews the current status of bulk substrate technology for IR detector applications, highlighting critical issues and essential research areas for further improvement of these materials.
Twinning Effects in Hg1−xCdxTe(x˜0.2) Grown by THM in the 〈111〉 Direction
Authors: Weiss Efiezer , Kedar Ehud , Mainzer Nili
Published: April 2011

Hg1−xCdxTe crystals with x˜0.2 were grown by the traveling heater method (THM), in either the [111]A or [111]B directions, using oriented CdTe seeds. Twins are sometimes formed during the growth of these crystals. In crystals grown in the [111]A direction the twins, of orientation [511]B, are constantly growing at the expense of the original [111]A oriented grain. Growth in the [111]B direction, on the other hand, suppresses the growth of the twin domain. Photodiodes and capacitors realized on the (111)A plane are markedly superior to those on the twin plane, [511]B. The difference is due to higher fixed charge and larger fast surface state densities in the case of the [511]B plane. These effects are explained by the lattice structures in the {111} and {511} planes and their possible influence on surface reactivity.
Buffer Layers for Ferroelectric-Based Infra-Red Detectors on Si Grown by a Novel CVD Method
Authors: Stauf Gregory T. , VanBuskirk Peter C. , Kirlin Peter S. , Kosar Walter P.
Published: April 2011

Ferroelectrics such as PbTiO3 and BaSrTiO3 are promising candidates for pyroelectric infrared detector materials. Integration of ferroelectric thin films on Si will permit fabrication of low-cost infrared detector arrays, but a buffer layer will be required to reduce interactions with the substrate. For this reason we have investigated MOCVD of MgAl2O4 and yttria-stabilized zirconia (YSZ) buffer layers on both Si and MgO. A single source molecule, magnesium dialuminum isopropoxide (Mg[Al(OCH(CH3)2)4]2), was used for deposition of the MgAl2O4, the first time to our knowledge that well characterized multi-metal oxide films have been deposited by CVD from a single-source compound. Both EDAX and RBS showed film stoichiometries consistent with the elemental ratio in the source. A novel liquid solution-based flash vaporization technique was used to transport the organometallic sources into the reactor, providing both excellent reproducibility and ease of stoichiometry control and deposition rate. Highly oriented [100] MgAl2O4 was grown on MgO, and [100] YSZ was grown on MgO and Si. Degree of preferred orientation of the YSZ was found to be dependent on oxygen partial pressure, both for the MgO and Si substrates.
Structural Relaxation and Structural Memory at Amorphous Silicon Dangling Bonds
Authors: Branz Howard M. , Fedders Peter A.
Published: April 2011

We examine the energy and time scales of configurational relaxation around the dangling bond defect, D, in hydrogenated Amorphous silicon (a-Si:H). After D captures or emits charge, its bond angle, electron energy eigenvalues and local structural environment all change. This determines the measured electronic energy levels; we use previous theoretical results and experimental data to estimate the density of gap states in the different atomic configurations of D. We also describe D relaxation effects observed in experiments, including the very slow relaxations found in recent transient capacitance measurements. To explain the unusual T-independent kinetics of transient capacitance carrier emission, we propose a model of “structural memory” in a-Si:H. After carrier capture, neighbors of D retain memory of their pre-capture configuration for seconds at 300K. The rate-limiting step to carrier emission is an effectively one-dimensional random walk of these neighbors through their configuration space and back to the pre-capture configuration. The final, activated, step of emission is very rapid. We describe analytic and monte Carlo calculations that support the structural memory Model and propose possible microscopic Mechanisms.
New Approaches to Molecular Dynamics Simulations of a-Si:H
Authors: Li Qiming , Biswas R. , Soukoulis C.M.
Published: April 2011

A new tight-binding molecular dynamics approach for Si-H systems is developed using the valence orbitale of Si and H for calculation of atomic forces. Previous tight-binding models are not able to describe formation energies of different charge states of H in c-Si and new physics is introduced in our model to describe both effects of charge transfer and varying atomic environments. The Si-H Model was developed by fitting to silane, and ensuring that the formation energies of different charge states of H in c-Si were correctly described. This new model also describes well vibrational properties of SiHn configurations, and the structural and electronic properties of a-Si:H Models. The new molecular dynamics utilizes quantum mechanical forces, incorporating important electronic effects, and is robust enough to simulate hundreds of atoms as would be needed in realistic a-Si:H systems.
Comparison of Dark and Light-Induced Annealing of Metastable Defects in a-Si:H
Authors: Gleskova Helena , Nakata M. , Wagner S.
Published: April 2011

We propose a rate law that unifies the dark and light-induced annealing of metastable defects in hydrogenated Amorphous silicon (a-Si:H). Its form is dN/dt ∼ - C Naf (T), where N is the defect density, C the concentration of free electrons (holes), f (T) a dispersive function, t the time, and T the temperature. Special dark and light-annealing experiments, designed to keep the free electron density constant, were conducted to eliminate C from the rate law. We find that f (T) for the dark annealing process differs from that for light-annealing. We calculated the thermal activation energies for the decay of N to 1/e of its initial value. They are 1.56±0.2 eV for dark annealing and 0.91±0.2 eV for light-induced annealing.
Metastability Under High-Intensity Light of Device-Quality He-Diluted, H2-Diluted and Standard a-Si:H Films Deposited Between 50°C and 350°C
Authors: Morin P. , Roca i Cabarrocas P.
Published: April 2011

We report the results of a study of the metastability under illumination by high intensity red light of device quality a-Si:H thin films deposited using a wide range of deposition conditions. The process variables included substrate temperature, pressure, rf power, and dilution of silane by He or H2. In-situ Monitoring of the sample conductivity and defect density during light-soaking provides the kinetics of the degradation of the electronic properties of the films. We observe equilibration of the photoconductivity and of the defect density. The characteristic time of equilibration τse of the defect density varies by more than an order of magnitude, dividing the samples into two groups: one group with a τse on the order of 103 seconds, the other with a τse on the order of 104 seconds. Low steady state defect densities combined with high ημτ products are observed for “standard” a-Si:H deposited between 100°C and 250°C and He-diluted films deposited above 250°C.
Charge and Current Transient Measurements on N-Type Hydrogenated Amorphous Silicon in the Relaxation Regime
Authors: Paschen Uwe W. , Kwon Daewon , David Cohen J.
Published: April 2011

Junction capacitance measurements were employed to study the thermal emission of electrons after application of a voltage filling pulse on a 80 Vppm PH3 doped a-Si:H sample on p+ c-Si substrate. We show that these data can be explained in terms of the relaxation Model. In addition, the time dependence of the charge flow into the depletion region during the filling pulse is investigated by current transient Measurements. Finally, we present charge transient data for a 9 Vppm a-Si:H sample on n+ c-Si substrate and compare the results to those obtained on samples on p-type substrates.
Switching Effects, Current Fluctuations and Lateral Photovoltage - The Electrical Appearance of A-Si:H/Metal Multilayers
Authors: Panckow Andreas N. , Drüsedau T.P. , Schmidt U.
Published: April 2011

Multilayer systems (MLS) consisting of hydrogenated Amorphous silicon (a-Si:II) and a transition Metal (Mo, Ti) were prepared by alternating dual magnetron sputtering. In this study we investigate the electrical performance of multilayer films containing discontinuous metal sublayers separated by a-Si:H sublayers of 80 nm thickness. A voltage of typical 8 V applied to the coplanar electrodes switches the samples from a semiconducting to a metallic state. The switching effect, which is reversible by thermal annealing, is accompanied by chaotic current oscillations. The temperature dependence of the conductivity in the metallic state is described by Inσ α T−1/2. The asymmetric illumination of the interelectrode spacing in coplanar configuration resulted in a generation of a lateral photovoltage.
A Basic Study of the GeH4 + H2 RF Discharge
Authors: Wickboldt Paul , Pang Dawen , Paul William
Published: April 2011

Extensive studies were made of GeH4+H2 and SiH4+H2 rf discharges used in depositing a-Ge:H and a-Si:H films. Residual Gas Analysis (RGA) Measurements were made of the gaseous species generated by these discharges. Data from the measurements of SiH4 + H4 discharges were entirely consistent with the generally accepted models of silane discharge chemistry and a-Si:H film deposition. Identical experiments for GeH4 + H2 discharges show that the chemistry for these discharges cannot be interpreted using a model similar to that proposed for silane. A review of the literature reveals differences between the stability of GeH2 and SiH2 radicals. These differences, usually overlooked by other workers, can account for the observed differences in the RGA results, as well as offer an explanation as to why it is difficult to deposit structurally homogeneous a-Ge:H.

Other RGA Measurements and electrode potential measurements are compared to the properties of a-Ge:H films that are deposited under different deposition conditions. Overall, the results strongly suggest that the chemistry which is beneficial for homogeneous film growth is promoted by a high electron temperature in the discharge. This conclusion is shown to be consistent with the results summarized above.
Influence of Substrate Temperature on the Properties of A-Si:H P-Layers Obtained from Trimethylboron
Authors: Puigdollers J. , Asensi J.M. , Bertomeu J. , Andreu J. , Delgado J.C.
Published: April 2011

a-Si:H p-layers doped by trimethylboron (TMB) were obtained by PECVD in a monochamber reactor with a rotating substrate holder. The influence of the substrate temperature (Ts) on the film properties was systematically studied for two different doping gas concentrations. The incorporation of boron, hydrogen and carbon was studied by Secondary Ion Mass Spectrometry (SIMS). Optical properties were determined by means of Photothermal Deplection Spectroscopy (PDS) and optical transmission. Dark conductivity (aj and activation energy (Eact) were measured electrically. Our results show that Σd has a marked dependence on substrate temperature, although boron atom concentration depends only slightly on Ts. The optical gap for samples obtained at the higher concentration also depends on Ts and its dependence is related to the hydrogen content, as boron content does not change. P-i-n diodes were obtained with the p-layer deposited from TMB.
1/f Noise Measurements of Hydrogenated Amorphous Silicon-Carbon Alloys
Authors: Dyalsingh H. M. , Khera G. M. , Kakalios J. , Tsai C. C. , Street R. A.
Published: April 2011

Measurements of the optical, electronic and 1/f noise properties for a series of n-type doped hydrogenated amorphous silicon carbide thin films with varying gas phase concentrations of CH4 are described. The increase in the optical absorption edge of the n-type a-SiCx:H films with the addition of carbon is slower than in p-type films. Studies of the variation in the non-Gaussian statistics which characterize the 1/f noise indicate that the disorder at the mobility edge is greater for films with higher carbon concentrations.
Understanding of Thin Film Transistor Electrical Measurements in the Light of the Defect Pool Model
Authors: Deane S.C. , Powell M.J.
Published: April 2011

Recently we described a new computer program which used a defect pool model of the density of states in a thin film transistor. With this model we modelled the effects of thermal bias annealing on the field effect characteristics of amorphous silicon thin film transistors, and used these results to determine key defect pool parameters. Here we use this program to provide new insight into other features of thin film transistor properties, such as activation energies of conduction as a function of gate bias, details of the subthreshold slopes, Movement of the apparent flat band voltages, and contact effects including current crowding. These effects are all successfully modelled and explained with our first principles defect pool Model, and compared with experimental results on a variety of material systems. In particular we show how measurements of the apparent flat band voltage produce potentially misleading results, and explain the inconsistency between observations of much less current crowding in contacts compared to predictions based on observed bulk defect densities and conventional Models.
High Performance A-Si:H Thin Film Transistors, TFTs: The Importance of Nitride Dielectrics with no Detectable Si-Si Bonding
Authors: He S.S. , Lucovsky G.
Published: April 2011

This research addresses silicon nitride dielectrics for a-Si:H TFTs. Si-Si bonds in these films detected by AES have been identified as the major factor that degrades the performance of the TFTs. With no detected Si-Si bonds in the silicon nitride and a relatively low concentration of Si-NH bonds, the TFTs show optimized performance.
Dependence of Field-Effect Mobility on Deposition Conditions in a-Si:H TFT
Authors: Chida Y. , Kondo M. , Ganguly G. , Matsuda A.
Published: April 2011

High electron Mobility (over 3 cm2/Vs) thin film transistors (TFTs) have been fabricated using a-Si:H on thermally oxidized crystalline Si substrate. The procedures for fabricating the high performance TFTs are presented and the possible reasons for the high mobility are discussed.
Improvement of Brightness & Threshold-Current in Visible-Light a-Sic:H Thin Film Led by Using Metal Sheet Substrate
Authors: Boonkosum Wirote , Kruangam Dusit , Panyakeow Somsak , DeLong Bancherd
Published: April 2011

An effort has been made to improve the brightness of the a-SiC:H Thin Film LED (TFLED) by using highly-thermal conductive Metal (SUS) sheet substrates instead of glass substrates. The structure of the TFLED is metal substrate/n a-SiC:H/i a-SiC:H/p a-SiC:H/ITO. The results from the preliminary examination show that at room temperature; 1) the threshold current necessary for the observation of the emission for the TFLED deposited on a SUS substrate is half of that for a glass substrate, 2) the highest brightness is about 5 cd/m2 for a SUS substrate while about 1 cd/m2 for a glass substrate.
High Performance Metallization Issues for Ulsi
Authors: Rosenberg Robert
Published: April 2011

The microelectronics industry is accelerating towards increasingly sophisticated circuit technology to interface with and drive a wide spectrum of products from low power to supercomputation systems. The base Si CMOS technology will span the applications such that optimization must be achieved by personalized wiring for each industry sector. As the feature size decreases to 0.25/µm or less, the interconnect metallization becomes a dominant technological challenge as circuit speeds, reliability and manufacturing costs are directly affected. The label "high performance" must now be defined in the context of the application. For example, as scaling proceeds for increased density and circuit speed, current density increase will impact lifetime by electromigration. Methods of simulation of fundamental degradation modes and design software tools must be developed and used in concert with performance simulation to optimize interconnect metallization ground rules early in the development cycle. Availability of such tools for interconnects is practically nonexistent, spurring significant focus on this direction by the materials community.
Interfacial Reactions of Co and Si/Co Films on GaAs
Authors: Kwak J. S. , Baik H. K. , Lee J. I. , Noh S. K. , Shin D. W. , Park C. G.
Published: April 2011

Interfacial reactions of Co and Si/Co films on GaAs have been investigated using X-ray diffraction(XRD), Auger electron spectroscopy(AES), cross-sectional transmission electron microscopy(XTEM), microdiffraction, and energy dispersive spectroscopy(EDS). Cobalt starts to react with GaAs at 380°C by formation of ternary phase, most probably Co2GaAs. At 420°C, CoGa nucleates at the Co and Co2GaAs interface and grows with Co2GaAs. At higher temperature, Co2GaAs disappears and CoGa/GaAs layer structures are formed. Annealing of the layer-deposited Si/Co films at 380°C results in the formation of Co2GaAs. At 420°C, the entire layer of Co is consumed, while Co2Si transforms to CoSi, and binary phases, CoGa and CoAs, are formed on top of the ternary phase beneath the CoSi layer. In the subsequent reaction, CoSi grows at the expense of the decompositions of CoGa and CoAs at 460°C. At 600°C, ternary phase is decomposed, and CoSi forms interface with GaAs. This finding can be understood from the calculated Si-Co-Ga-As quaternary phase diagram.
Interfacial Reactions and Phase Stability in the Ni/InP System
Authors: Mohney Suzanne E. , Austin chang Y.
Published: April 2011

Nickel is widely used in electrical contacts to InP, especially in NiAuGe ohmic contact to n-type InP. Several researchers have even suggested that the reaction of Ni with InP plays an important role in the ohmic nature of Ni-based contacts. However, numerous discrepancies are found in the literature concerning the Ni/InP reaction. In this study, an examination of the phase equilibria in the Ni-In-P system aids in an interpretation of bulk and thick film diffusion couples, and many of the apparent discrepancies in the literature are clarified. Finally, minor variations in the processing of the contacts (changes in the annealing gas and substrate cleaning procedure) are found in this study to have a less important role in altering the Ni/InP reactions than previous researchers have suggested.
Composition and Structure of as-Deposited and Oxidized Dcs-Based Cvd WsiX Films
Authors: Moinpour Mansour , Moghadam Farhad , Cham Johnny , Lu Wen-Juei
Published: April 2011

CVD WSix films have been widely employed for ultra thin gate and bit-line applications. Recently, for sub 0.5 μm technologies based on CVD WSix polycide gates and interconnects, efforts have been made to replace the silane-based deposition chemistry with that based on dichlorosilane (DCS) reduction of tungsten hexafluoride (WF6). Fluorine-contaminated gate oxides and poor film adhesion and cracking (especially after high temperature annealing/oxidation) are main characteristics of silane-based WSix which could be detrimental for fine geometries of sub 0.5 |im technologies. In this paper, the composition and structure of DCS-based CVD WSix films were studied. WSix films were deposited on 200 mm, implanted polysilicon substrates; silicide film thickness ranging from 60 to 200nm. A high temperature furnace anneal and oxidation cycle was used to examine post-oxidation film properties. SIMS, RBS and X-ray diffraction (XRD) were used to determine film composition profile, structure and texture on both as-deposited and annealed/oxidized films. Si/W uniformity through the depth of the film, for both W-rich and Si-rich interfaces, and its impact on film adhesion and cracking were studied. Also, WSix step coverage for sub 0.5 μm polycide topographies were examined.
Titanium Carbide Films Deposited by Laser Reactive Ablation
Authors: Barucca G. , Leggieri G. , Luches A. , Majni G. , Mengucci P.
Published: April 2011

Titanium carbide films were deposited on silicon wafers by laser reactive ablation. A pure titanium target placed inside a methane (CH4) atmosphere was irradiated by a XeCl excimer laser with a fluence of 5 J/cm2 and a repetition rate of 8 Hz. Experiments were performed at different values of the ambient pressure in order to investigate the influence of the deposition parameters on the film properties. Results show that at low pressure values (p< 10-5 mbar) the deposited layers are mainly constituted of metallic titanium whereas for pressure ranging from 10-5 to 10-1 mbar they are formed of titanium carbide (TiC) with small amount of oxides. The stoichiometry and thickness of the titanium carbide films can be controlled by the partial pressure of the atmosphere and the number of laser pulses, respectively.
On the Forward Conduction Mechanisms in SiC P-N Junctions
Authors: Pelaz Lourdes , Vicente J. , Jaraiz M. , Bailon L. , Barbolla J.
Published: April 2011

ABSTRACT:In SiC junctions, it is usual to find the ideality factor n=2 (or slightly higher) in 6H-SiC and n>2 and temperature dependent for 3C-SiC. However, the recombination current yields an ideality factor no higher than 2. This value can be slightly increased by considering the Poole-Frenkel effect (PFE), so that the 6H-SiC junction characteristics can be properly fitted. On the other hand, 3C-SiC junction characteristics, which are quite different from the ideal ones, cannot be satisfactorily explained on the basis of this model and the multitunnel capture-emission mechanism is proposed as the responsible for this behavior.
Interaction of Hyperthermal Hydrogen with the Diamond Surface
Authors: Haggerty David , Bandis Christos , Pate Bradford B.
Published: April 2011

A mass-selected low kinetic energy (1–50 eV) ion source is used to expose the diamond (111) surface to ionized atomic hydrogen (H+) at controlled impact kinetic energy. We report the result of 20 eV and 50 eV kinetic energy exposures as measured by ultraviolet photoelectron spectroscopy (UPS). UPS is found to be a useful probe of hydrogen adsorption on diamond.
Thermally Annealed GaN Nucleation Layers And The MOCVD Growth Of Si-Doped GaN Films On (00.1) Sapphire
Authors: Wickenden D. K. , Miragliotta J. A. , Bryden W. A. , Kistenmacher T. J.
Published: April 2011

The effect of epitaxial growth temperature in the range 985 – 1050°C on the preparation of device quality Si-doped GaN layers on self-nucleated (00.1) sapphire has been explored. Not unexpectedly, several device-related properties monotonically improve with increasing growth temperature, including: (a) carrier density; and, (b) volume fraction of heteroepitaxial domains. However, a number of equally important device-related properties show a local maximum or minimum and include: (a) optical second-harmonic generation intensity; (b) structural coherence; and, particularly (c) surface morphology. The antecedents of the first class is found in an increase in surface and bulk diffusion and a reduction in film defect incorporation and stress at the GaN/GaN (nucleation layer)/α-Al2O3 heterointerface (even for overlays with thicknesses near 1 μm). The second class apparently stems from the limited range over which the thermally annealed GaN nucleation layer stimulates pseudo two-dimensional growth of the overlayer.
Recombination Processes of the Broadband And 1.681 Ev Optical Centers in Diamond Films
Authors: Bergman L. , Mcclure M. T. , Glass J. T. , Nemanich R. J.
Published: April 2011

Micro- and Macro-photoluminescence techniques were employed in this research to investigate the role of nitrogen-doping on the optical spectra of chemical vapor deposited diamond films and to determine whether the origin of the broadband luminescence is due to vibronic interaction of the nitrogen centers. The temperature behavior of the broadband PL and of the 1.681 eV silicon related optical center were analyzed. The intensity of the broadband was found to exhibit a temperature dependence characteristic of optical emission from a continuous distribution of gap states while the temperature dependence of the 1.681 eV band followed the Boltzmann quenching process.
Properties of the Heteroepitaxial AIN/SiC Interface
Authors: Benjamin M. C. , Wang C. , Kern R. S. , Davis R. F. , Nemanich R. J.
Published: April 2011

This study presents the results of surface investigation of the heteroepitaxial AIN/SiC interface. The analytical tools employed included UPS, XPS, Auger spectroscopy, and LEED. The surface electronic states were characterized by uv photoemission obtained at surface normal. Conclusions drawn from this study are that the AIN/SiC structure results in a negative electron affinity surface which is extremely sensitive to defect density. The surface Fermi level is found to be near the middle of the AlN gap, and a possible band alignment between the AlN and SiC is presented.
Arsenic Incorporation in InP Epilayers and Arsenide/InP Heterostructures Grown by Chemical Beam Epitaxy
Authors: Rossignol V. , Bensaoula A. H. , Freundlich A. , Bensaoula A. , Neu G.
Published: April 2011

Low levels of arsenic contamination have been previously reported (∼0.01%) in CBE grown InP by different groups. The level of As incorporation in InP is usually enhanced when arsenide(InGaAs, InAsP) / InP heterostructures are grown.

In this work, optimal growth conditions to minimize the non-intentional As contamination during the growth of these heterostructures are discussed. The red shift of band-edge excitons in the low temperature photoluminescence spectra as well as the analysis of high resolution X-ray diffraction patterns of InAsP/InP multi-quantum wells suggest the presence of As in InP barriers. This contamination is consistent with the ratio of As/P partial pressure (As residual in the chamber: 10-9-10-8 Torr) and the As/P incorporation rates. We have studied the influence of the growth temperature, the group-V/III flux ratio and the growth rate on the level of the As incorporation.