bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation of High-Quality CuInSe2 Thin Films by Molecular Beam Epitaxy
Authors: Tseng B. H. , Lin S. B. , Yang D. J. 
Published: April 2011

AbstractCuInSe2 epitaxial films having superior luminescence properties were prepared by using (001) GaAs substrates and then by thermal annealing in the presence of a Se-beam flux. We also found that exciton emission became dominant when the film composition was very close to the stoichiometry.
In-Situ Investigation of Cu-In-Se Reactions by Thin Film Calorimetry
Authors: Wolf D. , Müller G. 
Published: April 2011

AbstractStudies of the reaction path during annealing of Cu-In-Se thin films for solar cell absorbers have been limited up to now to ex-situ analyses of the phase composition by X-Ray Diffraction (XRD) after processing by a specific temperature-time program. As an indirect method, the application of ex-situ XRD is not sufficient for the determination of reaction temperatures and reaction times for setting up a general model of CIS-formation.We show in this paper that the use of a calorimetric method (Thin Film Calorimetry, TFC) offers the advantage of a direct (in-situ) observation of thin film reactions. Special care is taken to use film thicknesses of practical interest for industrial application (1.5 – 3 μm). In a first step we show results of binary reactions in the Cu-In, In-Se and Cu-Se systems. Their knowledge is necessary for understanding the processes involved in the ternary CIS-layers. It turned out that thin Cu-In and Cu-Se films react already at room temperature and behave as predicted by the bulk equilibrium phase diagrams during heating. In-Se thin films show prominent exothermic reactions starting with the melting of In. The first phase to be formed is generally In2Se which is then converted to more Se-rich compounds. In ternary Cu-In-Se films (Cu/In = 1.00) we observe transitions of the Cu-Se-system which can be attributed to the decomposition of CuSe2 and CuSe. Consequences for the model of improved CIS-growth by a Cu-Se flux agent are discussed.
Several Efficiency Influencing Factors In CdTe/CdS Solar Cells
Authors: Li K. , Feng Z. C. , Wee A. T. S. , Chou H. C. , Lin J. Y. , Kamra S. , Tan K. L. , Rohatgi A. , Zhou L. , Li S. F. Y. 
Published: April 2011

AbstractSeveral efficiency influencing factors in MOCVD-grown CdTe/CdS solar cells, including preferential crystal orientation of CdTe layers, CdTe grain size and surface roughness, interfacial mixing, and surface and interface geometrical morphology, are studied. X-ray diffraction (XRD) shows that polycrystalline CdTe/CdS solar cells with higher efficiencies tend to have more (111) planes of CdTe parallel to the macro-surface. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis reveal the relationship between the grain size/surface roughness and cell efficiency. Secondary ion mass spectroscopy (SIMS) and Auger electron spectroscopy (AES) depth profiling show that the interfacial geometrical morphology has a significant influence on the efficiency of CdTe/CdS solar cells. Finally it is shown that interfacial mixing reduces the number of interfacial states and recombination centers and the energy loss due to internal reflectance, enhancing the performance of the solar cells.
The Perspectives Of High-Rate Low Frequency a-Si:H Films Deposition: Solar Cell Application And Stability Control
Authors: Budaguan B. G. , Aivazov A. A. , Meytin M. N. , Radosel'Sky A. G. 
Published: April 2011

AbstractThe perspectives for solar cell application of structural inhomogeneous a-Si:H films deposited at high growth rates (∼10–20 Å/s) from 100% SiH4 in low frequency (LF) 55kHz glow discharge plasma have been investigated. In this case the influence of structural inhomogeneity on dark dc and photoconductivities and light-induced defect generation kinetics (Staebler-Wronski effect, SWE) in a-Si:H films have been studied. The microstructure of films was investigated by IR spectroscopy analysis. Microstructural parameter R=[SiH2]/([;SiH]+[SiH2]), was used for the quantitative characterization of structural inhomogeneity in the material bulk.It was found that Fermi level position is fixed by deep defect states and does not depend on microstructure parameter R. The comparative analysis of photoconductivity modeling and ESR measurements have shown that recombination in a-Si:H films is controlled by neutral dangling bonds and doesn't depend on parameter R. Meanwhile it was found that the kinetics of light-induced defect generation was controlled by SiH2 or clustered SiH groups content. Thus, the above results allow to perform an independent control of stability and electronic properties of a-Si:H films deposited in LF glow discharge plasma.
Grain Enhancement of Polycrystalline Silicon Films Aided by Optical Excitation
Authors: Sopori B. L. , Chen W. , Alleman J. , Matson R. , Ravindra N. M. , Tan T. Y. 
Published: April 2011

AbstractA new technique for making large-grain thin Si films is described in which optical excitation is used to enhance the grain growth. Grain sizes much larger than the film thickness can be obtained at low temperatures and in short process times. This method is well suited for making thin-film Si solar cells on low-temperature substrates.
Index of Refraction and Strain Induced Birefringence of Pseudomorphic Si1−xGex
Authors: Mailhot S. , Baribeau J. M. , Bruce D. M. , Delâge A. , Janz S. , Jessop P. E. , Lafontaine H. , Robillard M. , Williams R. L. , Xu D. X. 
Published: April 2011

AbstractThe index of refraction of pseudomorphic layers grown on Si has been determined at wavelengths λ=1330 nm and λ= 1550 nm, for Ge concentrations between x=0.01 and x=0.1. The refractive index values were obtained from mode profile measurements on a series of Si1−xGex waveguides. The index of refraction is significantly larger for light polarized parallel to the growth direction than for light polarized in the plane of the epilayer. This birefringence is consistent with the anisotropic index change predicted using photoelelastic theory, given the biaxial strain present in the pseudomorphic Si1−xGex layers.
Strong Blue and Violet Light Emission from Silicon- and Germanium-Implanted Silicon-Dioxide Films
Authors: Rebohle L. , Tyschenko I. E. , Von Borany J. , Schmidt B. , Grötzschel R. , Markwitz A. , Yankov R. A. , Fröb H. , Skorupa W. 
Published: April 2011

AbstractPhotoluminescence (PL) and electroluminescence (EL) from Si+- and Ge+-implanted SiO2 layers thermally-grown on a Si substrate were studied. The PL spectra were recorded after annealing at temperatures in the range of 400° to 1200°C. Single-peak PL at 460 nm and doublepeak PL at 420 and 385 nm due to Si+-implanted and Ge+-implanted oxide layers, respectively, reached a maximum following heat treatment at 500°C for 30 min. The EL spectra from the Gerich oxides after annealing at 1000°C correlated very well with the PL signal, and showed a linear dependence on the injection current. The EL emission was strong enough to be readily seen with the naked eye, and the EL efficiency was estimated to be about 5×10−4. High-resolution transmission electron microscopy (HRTEM) analysis showed that the formation of nanocrystals in the implanted oxide layers occurred at annealing temperatures in excess of 800°C. The observed light emission is attributable to the presence of-≡Si-Si≡, ≡Si-Ge≡ and ≡Ge-Ge≡ centres in SiO2.
High Quality Germanium Photodiodes on Silicon Substrates Using an Intermediate Chemical Mechanical Polishing Step
Authors: Samavedam Srikanth B. , Currie Matthew T. , Langdo Thomas A. , Ting Steve M. , Fitzgerald Eugene A. 
Published: April 2011

AbstractGermanium (Ge) photodiodes are capable of high quantum yields and can operate at gigahertz frequencies in the 1–1.6 μm wavelength regime. The compatibility of SiGe alloys with Si substrates makes Ge a natural choice for photodetectors in Si-based optoelectronics applications. The large lattice mismatch (≈4%) between Si and Ge, however, leads to the formation of a high density of misfit and associated threading dislocations when uniform Ge layers are grown on Si substrates. High quality Ge layers were grown on relaxed graded SiGe/Si layers by ultra-high vacuum chemical vapor deposition (UHVCVD). Typically, as the Ge concentration in the graded layers increases, strain fields from underlying misfit dislocations result in increased surface roughness and the formation of dislocation pile-ups. The generation of pile-ups increases the threading dislocation density in the relaxed layers. In this study the pileup formation was minimized by growing on miscut (001) substrates employing a chemical mechanical polishing (CMP) step within the epitaxial structure. Other problems such as the thermal mismatch between Si and Ge, results in unwanted residual tensile stresses and surface microcracks when the substrates are cooled from the growth temperature. Compressive strain has been incorporated into the graded layers to overcome the thermal mismatch problem, resulting in crack-free relaxed cubic Ge on Si at room temperature. The overall result of the CMP step and the growth modifications have eliminated dislocation pile-ups, decreased gas-phase nucleation of particles, and eliminated the increase in threading dislocation density that occurs when grading to Ge concentrations greater than 70% Ge. The threading dislocation density in the Ge layers determined through plan view transmission electron microscopy (TEM) and etch pit density (EPD) was found to be in the range of 2 × 106/cm2. Ge p-n diodes were fabricated to assess the electronic quality and prove the feasibility of high quality photodetectors on Si substrates.
Near Infrared Light Detectors Based on Uhvcvd Epitaxial Ge on Si (100)
Authors: Colace L. , Masini G. , Galluzzi F. , Assanto G. , Capellini G. , Di Gaspare L. , Palange E. , Evangelisti F. 
Published: April 2011

AbstractIn the present work we investigate photo-detectors based on thick relaxed Ge layers, epitaxially grown on silicon after insertion of a low-temperature-grown Ge buffer layer. By using this procedure it was possible to grow films having thicknesses comparable with light penetration depth in the 1.3–1.6μm spectral range. The films exhibited flatness on the atomic scale. Two kinds of detectors were investigated: vertical heterojunction diodes and a planar Metal-Semiconductor-Metal structure.
The detectors show a good responsivity at normal incidence at both 1.3 and 1.55μm. The photocurrent increases with the voltage applied, reaching a maximum responsivity of 0.24 A/W at 1.3μm under a bias of IV. A complete optoelectronic characterization of the fabricated devices is performed. The results confirm the feasibility of the proposed approach for the fabrication of 1.3–1.55μm near infrared photodetectors integrated on silicon chips.
Practical Nanoscale Silicon Light Emitters
Authors: Fauchet Philippe M. 
Published: April 2011

AbstractImpressive advances have been made over the last few years in teaching silicon how to emit light. Recently, light-emitting devices made of porous silicon and other forms of nanoscale silicon have been demonstrated with specifications that start to make them attractive for commercial applications. This paper reviews the state-of-the-art in the materials science and device properties of nanoscale silicon-based LEDs, including their integration with microelectronic circuits.
Structural Band Gap Engineering
Authors: Demkov Alexander A. , Sankey Otto F. , Fuentes M. 
Published: April 2011

AbstractIn this paper we discuss a novel approach to the band gap engineering of semiconductors Si, Ge, GaAs and AIN. We suggest that nanoporous polymorphs of these materials may exist which would offer a significant variation of the electronic band gap. Structurally, nanoporous semiconductors are related to the zeolitic nets, and a systematic procedure of generating these structures from the (4;2) nets is described. We use the ab initio total energy quantum molecular dynamics method Fireball96 to investigate the energetics and the electronic properties of these nanoporous or “expanded” semiconductor phases.
Study of the Si/ZnS Multilayer System for Optoelectronic Applications
Authors: Voon L. C. Lew Yan 
Published: April 2011

AbstractThe suitability of the (001) Si/ZnS system for optoelectronic applications is theoretically investigated and compared to the Si/Ge system. The band-structure calculations show that Si/ZnS is superior to Si/Ge in a number of respects: directness of band gap can be easily obtained; and optical intersubband transitions fall within the important 1.3–1.6 μm window.
Membrane Curvature Induced by Sugar and Polymer Solutions
Authors: Döbereiner H.-G. , Lehmann A. , Goedel W. , Selchow O. , Lipowsky R. 
Published: April 2011

AbstractWe monitor the effect of transversal membrane asymmetry on the morphology of giant uni-lamellar vesicles in sugar and polymer solutions. The shapes of fluid lipid vesicles are governed by the bending elasticity of their membrane which is characterized by the bending modulus and the spontaneous curvature of the bilayer. We present a recently developed technique for the measurement of the spontaneous curvature using quantitative phase contrast microscopy. Different mechanisms for elastic membrane asymmetry and the role of the bending energy concept for the morphology of cellular organelles are discussed.
Synthesis and Characterization of Supported Bioactive Lipid Membranes
Authors: Winger Theodore M. , Chaikof Elliot L. 
Published: April 2011

AbstractSingle and multicomponent membrane-mimetic surfaces of DPPC and synthetic lipid-peptide conjugates were formed on an alkylated glass surface by a process of vesicle fusion. Correlative atomic force microscopy and radiochemical titration techniques confirmed the generation of a single substrate supported monolayer and predictable deposition of defined concentrations of lipopeptide. Mixed systems were stable for periods exceeding 1 month if stored at room temperature in phosphate buffered saline.
Fine-Scale Oscillatory Banding in Otoliths from Arctic Charr (Salvelinus Alpinus) and Pike (Esox Lucius)
Authors: Meldrum A. , Haldent N. M. 
Published: April 2011

AbstractTransmission electron microscopy of otoliths from the inner ear of arctic charr and pike has revealed the presence of fine banding on the scale of several nanometers. The thickness of the bands was observed to vary in different portions of the sample, and some areas were not banded. EDS analysis could not detect chemical differences within the bands, but electron diffraction showed that the crystallographic orientation of the bands is related by a lattice mismatch indicative of a twinning relationship. Previously, banding on the scale of 50 to 100 microns was observed by SEM in otoliths from arctic charr and was attributed to seasonal variations in growth. The fine-scale twinning observed in this study, however, is unlikely to be nucleated through daily variations. Electron diffraction from the pike samples shows that the material is composed of CaCO3 having the both the vaterite and aragonite structure, and hydrous CaCO3 was also observed.The interaction of the electron beam with the sample material was investigated by conducting several electron-irradiation experiments. The electron beam was observed to interact strongly with the sample and caused the precipitation of cubic CaO from the calcium carbonate matrix. Bright-field imaging showed the development of fine grained (∼ 5 nm) randomly-oriented crystallites which accumulated with increasing electron dose. These initial results suggest that the precipitation of GaO is not driven by electron-beam heating. Previously, a similar phase-change phenomenon has been observed in hydroxyapatite from dental enamel. Other Ca-bearing biominerals may therefore also be expected to be sensitive to electron irradiation.
A Model For Diffusion and Competition in Cancer Growth and Metastasis
Authors: Pescarmona G. P. , Scalerandi M. , Delsanto P. P. , Condat C. A. 
Published: April 2011

AbstractA master equation formalism is used to model the growth and metastasis of a tumor as a function of the diffusion and absorption of a nutrient. Healthy and cancerous (C-) cells compete to bind the nutrient, which is allowed to diffuse starting from a prescribed region. Two thresholds are defined for the quantity of nutrient bound by the C-cells. If this quantity falls below the lower threshold, the cell dies, while if it increases above the upper threshold, the cell divides according to a predefined stochastic mechanism. C-cells migrate when they record a low concentration of free nutrient in the local environment. The model is formulated in terms of a coupled system of equations for the cell populations and the free and bound nutrient. This system can be solved by using the Local Interaction Simulation Approach (LISA), a numerical procedure that permits an efficient and detailed solution and is easily adaptable to parallel processing. With suitable parameter variation, the model can describe multiple tumor configurations, ranging from the classical spheroid with a necrotic core favored by mathematicians to very anisotropic shapes with inhomogeneous concentrations of the various populations. This is important because the nature of the anisotropy may be crucial in determining whether and how the cancer metastasizes. The effects of stochasticity and the presence of additional nutrients or inhibitors can be easily incorporated.
Tactoidal Granules in Concentrated Actin Gels: A Solidlike State of Protein Filaments
Authors: Tang Jay. X. , Oldenbourg Rudolf , Allen Philip G. , Janmey Paul A. 
Published: April 2011

AbstractWe report here the first observation and microscopic characterization of tactoidal granules of actin in concentrated gels of actin filaments (F-actin). Phase contrast microscopy shows these stable tactoids of densely packed F-actin to be of various sizes on the order of 10 μm. The background gel of F-actin is optically birefringent, indicating orientational order of the filaments consistent with theoretical predictions. In contrast, no birefringence is detected through the tactoids, suggesting very distinct yet undetermined packing of the filaments inside. The tactoids demonstrate elastic response upon micromanipulation. The microscopic segregation of F-actin into two states of different protein concentrations is consistent with a first order phase transition between a nematic gel of lower concentration on the order of ten mg/nl and a highly packed, possibly columnar state of protein filaments. In addition to the excluded volume effects which are known to drive thermodynamic phase transitions as a function of particle concentration, additional molecular forces must also play important roles since the formation was found to be irreversible upon dilution.
Computer Simulation of Thermomigration Process
Authors: Gershanov V. Yu. , Garmashov S. I. , Minyaev A. R. , Beletskaya A. V. 
Published: April 2011

ABSTRACTMathematical model of thermomigration of liquid inclusions through a crystal under stationary and non-stationary thermal conditions is presented. It is assumed that the mass-transfer is provided by diffusion only, the crystallization and dissolution processes are carried out in accordance with the diffuse interface mechanism for atomic-rough (non-singular) interfaces and screw-dislocation or two-dimension nucleation mechanisms for singular interfaces.The package of computer programs based on this model enables simulation of the evolution of the cross-sectional shape of cylindrical liquid inclusions. It is possible to simulate the cases of various inclusion sizes, various relationship between the interface and volume mass-transfer restrictions, various liquid phase composition, thermal gradient under stationary and non-stationary thermal conditions as well. The main results of the simulation are presented.
Modelling Analysis of Oxygen Transport During Czochralski Growth of Silicon Crystals
Authors: Egorov Yu. E. , Makarov Yu. N. , Rudinsky E. A. , Smirnov E. M. , Zhmakin A. I. 
Published: April 2011

ABSTRACTGlobal model of oxygen transport in the melt and inert gas is proposed which is based on coupled two-dimensional stationary modeling of global heat transfer, laminar flow of inert gas and turbulent flow in Si melt, and transport of dissolved oxygen in the melt and SiO vapor in the gas. The model allows to study effects of process parameters like flow rate and pressure of inert gas, and rotation of the crucible on incorporation of oxygen into Si crystal.
Demonstration of Improved Quantitative Mobility Spectrum Analysis (i-QMSA)
Authors: Vurgaftman I. , Meyer J. R. , Hoffman C. A. , Redfern D. , Antoszewski J. , Faraone L. , Lindemuth J. R. 
Published: April 2011

ABSTRACTWe discuss an improved quantitative mobility spectrum analysis (i-QMSA) of magnetic-field-dependent Hall and resistivity data, which can determine multiple electron and hole densities and mobilities. A fully automated computer implementation of i-QMSA is applied to a variety of synthetic and real data sets. The results show that the new algorithm increases the information available from a given data set and is suitable for use as a standard tool in the characterization of semiconductor materials and devices.
Tight-binding calculations of electronic structure and resistivity of liquid and amorphous metals
Authors: Bose S. K. 
Published: April 2011

ABSTRACTWe discuss various aspects of calculating the electronic structure of liquid and amorphous metals using the recursion method and the tight-binding linear muffin-tin orbitals (TB-LMTO) basis. Resistivity calculations for such systems based on the Kubo-Greenwood formula and the TB-LMTO-recursion method are presented and compared with similar calculations based on the linear combination of atomic and atomic-like orbitals (LCAO) and the chemical pseudopotential approach. Results for amorphous Fe and Co and liquid Hg, Pd, and some 3d transition metals are presented. Sources of error in the calculation and ways to improve upon the present calculations are discussed.
A Selfconsistent-Charge Density-Functional Tight-Binding Scheme
Authors: Elstner M. , Porezag D. , Jungnickel G. , Frauenheim Th. , Suhai S. , Seifert G. 
Published: April 2011

ABSTRACTWe present an extension to the tight-binding (TB) approach to improve total energies, forces and transferability in the presence of considerable long-range Coulomb interactions. We derive an approximate energy expression in terms of charge density fluctuations δn at a reference (input) density n0, which is a second order approximation to the total energy expression in density functional theory (DFT). With the choice of n0 as a superposition of densities of neutral atomic fragments, we can define a repulsive potential as in standard TB theory, which is pairwise, short ranged and transferable. The zero order terms in the total energy expression are recoverd as the standard terms of our density-functional based tight-binding (DF-TB). For the second order terms, the charge density fluctuations δn are approximated by the total charge fluctuation Δqα at atom α, which is qualitatively estimated by employing the Mullikan charge analysis. Within this approximations the total energy expression contains new parameters, which are related to ab-intio DFT calculations. Finally, by introducing localized basis functions and applying the variational principle we arrive at the Hamilton matrix elements, wich themselves depend on the charge fluctuations and, therefore, the general eigenvalue problem has to be solved self-consistently. To obtain forces for efficient geometry relaxation and molecular-dyamics, we calculated analytical derivatives of the total energy with respect to the atomic sites. In order to demonstrate the strenghts of our self-consistent-charge tight-binding (SCC-TB), we calculated reaction energies, geometries and vibrational frequencies for a large set of molecules and compare the results to semi-empirical methods, density-functional calculations and experiment.