bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cayley Tree Random Walk Dynamics
Authors: Katsoulis Dimitrios , Argyrakis Panos , Pimenov Alexander , Vitukhnovsky Lexei 
Published: April 2011

AbstractWe investigate diffusion on newly synthesized molecules with dendrimer structures. We model these structures with geometrical Cayley trees. We focus on diffusion properties, such as the excursion distance, the mean square displacement of the diffusing particles, and the area probed, as given by the walk parameter SN, the number of the distinct sites visited, on different coordination number, z, and different generation order g of a dendrimer structure. We simulate the trapping kinetics curves for randomly distributed traps on these structures, and compare the finite and the infinite system cases, and also with the cases of regular dimensionality lattices. For small dendrimer structures, SN approaches the overall number of the dendrimer nodes, while for large trees it grows linearly with time. The average displacement R also grows linearly with time. We find that the random walk on Cayley trees, due to the nature ot these structures, is indeed a type of a “biased” walk. Finally we find that the finite-size effects are particularly important in these structures.
Spatial Fluctuations and the Flipping of the Genetic Switch in a Cellular System
Authors: Metzler Ralf 
Published: April 2011

Abstract– It has been realised that noise plays an important rôle in cellular processes where fluctuation induced number fluctuations of certain messenger molecules become non–negligible, due to the small total number of these molecules within one cell. In the following, it is argued that spatial fluctuations of such molecules and their impact on genetic switches should be considered as well.
Transport Properties in Ionic Media
Authors: Rollet A.-L. , Jardat M. , Dufrêche J.-F. , Turq P. , Canet D. 
Published: April 2011

AbstractTransportcoe[ ]cients in charged media exhibit strong variations, according to the conditions of displacement of the particles. Electrical transport, characterized by the simultaneous displacement of positive and negative charges in opposite directions obeys Ohm's law, but its variation with concentration (non-ideality), depends on several types of interactions, whose time of establishment varies from picosecond to nanosecond. Several diffusion processes can occur: mutual diffusion, where ions move simultaneously in the same direction, keeping local elec- troneutrality, and self diffusion where individual ionic particles move separately. The variation of diffusion coefficients with concentration dependson non-ideality factors analogous to those occuring in conductance, and their experimental evidence is facilitated b y the availability of experimental tec hniquesowing different characteristic times of observation. This phenomenon is particularly noticeable for self-diffsuion coefficients, where the dynamical processes can be observed from the picosecond range (neutron quasi-elastic scattering), to millisecond (NMR) and to hour scale (radiactive tracers). The results are especially enhanced for porous charged media like ion exchanging membranes (nafions).Those results are be explained here theoretically in the framework of contin uous solv en t model theories (brownian dynamics) and experimentally in the study of self-diffusion in nafion membranes.
Grain Orientation of Aluminum Titanate Ceramics during Formation Reaction
Authors: Ohya Yutaka , Nakagawa Zenbe-e , Hamano Kenya , Kawamoto Hiroshi , Kitaoka Satoshi 
Published: April 2011

ABSTRACTA microstructural change during the formation reaction of aluminum titanate from a mixture of rutile and corundum powders has been studied. The characterization was carried out using a polarization microscope, a scanning electron microscope and a micro-focus X-ray diffractometer. The formation of aluminum titanate was controlled by a nucleation step. The formation reaction proceeded to form spherically oriented regions of aluminum titanate grains among the matrix of rutile and corundum. At the end of the reaction, the specimen was entirely filled with the oriented region of consisting several hundred micrometers. The oriented region was composed of primary aluminum titanate grains of several micrometers and pores. Large cracks due to a thermal expansion anisotropy were formed at the boundaries of the orientated regions. The formation of the oriented region was caused by a small change in free energy, increasing elastic energy, and the endothermic nature of the reaction.
Interference Effect between Electron and Ion Flows in Semiconducting Fe3−δO4
Authors: Hong Jeong-Oh , Yoo Han-Ill 
Published: April 2011

ABSTRACTThe effective valence, zFe–αFe*, of mobile Fe-ions (Fe2+, Fe3+) in semiconducting Fe3O4was determined at elevated temperatures via the electrotransport experiment in association with the literature data on the cation diffusivity and total electrical conductivity. It has been found that the value for zFe–αFe* varies systematically from below 2 up to 3 with oxygen partial pressure at a fixed temperature. The effective valence is determined not only by the mobility difference of Fe2+and Fe3+ions (zFe), but also by the cross effect between the cations and electrons upon their transfer (αFe*). A value of zFe–αFe* between 2 and 3 may be attributed to the mobility difference between Fe2+and Fe3+ions even in the absence of the cross effect, but the values of zFe–αFe* < 2 clearly indicate that the cross effect is in play in Fe3O4.
Transport Properties And Crystal Chemistry Of Ba-Sr-Bi Oxides
Authors: Gökçen Oya A. , Meen James K. , Jacobson Allan J. , Elthon Don 
Published: April 2011

ABSTRACTRhombohedral (R) phases of the binary systems AE-Bi-O (AE = Ca, Sr, Ba) have low temperature (β2) and high temperature (β1) polymorphs and the β1 polymorph is a good oxygen ion conductor. In a previous study, we showed that in the ternary system Ba-Sr-Bi-O, conductivities of polycrystalline R samples are unaffected by Ba:Sr, whereas temperature ranges of the β2↔β1 polymorphic transition are. Recently, we proved that the conductivity of both polycrystalline and single-crystal R samples is sensitive to spatial direction. For single crystals, the conductivity is highest perpendicular to the c-axis. Along the conduction plane, the conductivities are significantly higher than those of polycrystalline R samples; perpendicular to that plane they are significantly lower. The BaBiO3 perovskite (P) phase, predominantly an electronic conductor, has conductivities of 10 to 102 S/cm at 350-800°C in air. Conductivity measurements of the R-P assemblages with different R:P showed that percolation threshold is around 35 volume % P.
Effect of Polymerization of Precursor Solutions on Crystallization and Morphology of Ce0.9Gd0.1O1.95 Powders
Authors: Wang Shuqiang , Awano Masanobu , Maeda Kunihiro 
Published: April 2011

ABSTRACTSynthesis of Ce0.9Gd0.1O1.95 (CGO) powders from polymeric precursor solutions formed by mixing nitrates and ethylene glycol at 60-85 was investigated with emphasis on the effect of the polymerization of the precursor solution on the crystallization and morphology of the derived intermediate and the resultant oxide powders. It was revealed by FTIR that the molecular structures of the polymeric precursor solution change from aldehyde or ketone groups to carboxylic acid and carboxylate groups with increasing heating time. TG-DTA analyses demonstrated the temperature shifting and the disappearance of the exothermic reactions of the derived powders with different heating times of the polymeric precursor solutions. Furthermore, it was identified by XRD, SEM and TEM that the derived powders can be changed from well crystallized organic formates of Ce1-xGdx(HCOO)3 with dendritic growth to loose agglomerated cubic CGO powders with grain sizes below 10 nm.
NO Decomposition Property of Lanthanum Manganite Porous Electrodes
Authors: Matsuda Kazuyuki , Kanai Takao , Awano Masanobu , Maeda Kunihiro 
Published: April 2011

ABSTRACTThe NOx decomposition activity of electrochemical cells composed of YSZ solid electrolyte and La1−xCaxMnO3 porous electrodes was examined. La1−xCaxMnO3 powders were prepared by solid-state reaction using corresponding metal oxides and carbonates. The powders were dispersed in polyethylene glycol and screen-printed on both sides of the electrolyte pellet. The electrochemical decomposition of NO was carried out in the temperature range from 973 to 1173 K by passing a mixed gas of 1000 ppm NO and 2% O2 in He through the cell. When the DC voltage was applied to the cell, NO was directly decomposed to N2 and O2 in the oxidizing atmosphere. The cells composed of the La0.8Ca0.2MnO3 electrodes showed a higher NO decomposition ratio and current efficiency than that of other La1−xCaxMnO3 electrodes.
Technology transfer challenges in the manufacturing of a-Si tandem solar cells
Authors: Carlson D. E. , Ganguly G. , Lin G. , Gleaton M. , Bennett M. , Arya R. R. 
Published: April 2011

ABSTRACTBP Solar started commercial production of amorphous silicon tandem solar cells in Toano, Virginia in 1997. The scale-up process has involved overcoming technology challenges in several areas. It was necessary to develop high speed, multiple-beam laser scribing systems that could pattern photovoltaic modules over an area of 0.8 square meters with close dimensional tolerances. In addition, the deposition rate of amorphous silicon was doubled while production was being ramped up, and the deposition system was modified to meet capacity requirements. The utilization of the germane feedstock gas was increased by about 25% in order to reduce material costs. In addition, the dimensional tolerances of the deposition system geometry were determined and controlled in order to assure uniform deposition of the amorphous silicon alloys. Effects of contaminants (such as pump oils and residual dopants) on device performance were quantified. Sources of debris that could cause shunts and shorts in the devices were identified and minimized. Current research efforts are focused on further increases in the amorphous silicon deposition rate, improvements in device performance and the development of in-situ diagnostic tools to monitor and control the manufacturing process.
Diffusion and Solubility of Hydrogen in Amorphous and Microcrystalline Si:H Films
Authors: Beyer Wolfhard 
Published: April 2011

ABSTRACTHydrogen diffusion and solubility effects in hydrogenated amorphous and microcrystalline silicon films are reviewed. Various diffusion-related effects have been observed which need to be considered in models of hydrogen diffusion. Hydrogen solubility is found to affect hydrogen incorporation and hydrogen transport.
Laplace-transform Transient Photocurrent Spectroscopy as a Probe of Metastable Defect Distributions in Hydrogenated Amorphous Silicon
Authors: Gueorguieva Mariana J. , Main Charlie , Reynolds Steve 
Published: April 2011

ABSTRACTThree Laplace transform methods for recovering the density of electronic states from transient photocurrent data are evaluated through a study of light-induced defect creation in PECVD a-Si:H films. A mathematically approximate method is shown to be sufficient to resolve the deep defects, whose density is estimated to increase by a factor of five from the annealed state after 3 hours' exposure to simulated AM1 illumination. An exact method, and a method employing Tikhonov regularisation, are found to give very similar results, provided the current-time data are smoothed beforehand in the former case. The increased resolution available is, however, unnecessary here, and these methods are shown to be more suited to the study of discrete levels or narrow distributions.
Electrical Stability of a-Si:H TFTs Fabricated at 150°C
Authors: Gleskova H. , Wagner S. 
Published: April 2011

ABSTRACTWe investigated the electrical stability of amorphous silicon thin-film transistors (a-Si:H TFTs) fabricated on 51 μm thick polyimide foil at 150°C. Gate dc-voltage bias stressing caused an increase in threshold voltage and subthreshold slope, and a minor decrease in mobility. Annealing in H2+N2 substantially improved the stability of the TFTs. In annealed TFTs the threshold voltage shift exhibited a power law dependence on time with the exponent γ depending on gate bias Vg. For Vg = 20 V, γ = 0.45, while for Vg = 80 V, γ = 0.27. The threshold voltage shift also exhibited a power law dependence on Vg with the exponent β depending slightly on stress duration. β = 2.1 for t = 100 sec and 1.7 for t = 5000 sec. These values fall into the range experimentally observed for a-Si:H TFTs fabricated at the standard temperatures of 250-350°C.
Generation- Recombination Noise in Amorphous Semiconductors
Authors: Main Charlie , Reynolds Steve , Badran Rashad I. 
Published: April 2011

ABSTRACTWe examine different approaches to the analysis of noise in amorphous hydrogenated silicon associated with trapping and generation – recombination processes, which appear to predict very different noise spectra. In one approach the broad noise spectrum observed is assumed to be composed of a distribution of Lorentzian noise spectra, each associated with traps at a given energy depth, with appropriate weighting according to the energy distribution of characteristic time constants. This latter weighting is taken to mirror the energy distribution of states in the gap. This represents a linear superposition of the (weighted) contribution from individual trapping levels, each with its own characteristic time constant. This approach thus assumes that each trap level is an independent source of fluctuation in free carrier number, unaffected by the presence of other traps in the material. At first sight this assertion seems plausible, since in the multi-trapping situation envisaged, cross-correlation effects must be very small. However, the presence of several groups of traps, or, in the limit, a continuum, results in a distribution of characteristic time constants, which is not a simple linear superposition of the time constants for each level. Thus the assertion that a flat density of states, or a region which is flat, such as the top of a broadened level, results in a region of 1/f slope in the noise spectrum, may not be valid. We present an alternative model in which the distribution of time constants is appropriately incorporated, and compare the predictions of this model with the ‘superposition’ approach, using computed noise spectra.
Silicon Thin Film Deposition on Nano-Structured ZnO Substrates
Authors: Könenkamp R. , Chu V. , Conde J. , Dloczik L. 
Published: April 2011

ABSTRACTAmorphous and micro-crystalline Si films have been deposited by the hot-wire technique on deeply structured columnar ZnO films. It is found that nearly perfect conformal deposition occurs for amorphous films, similar to what was previously found for rf-plasma deposited films. Micro-crystalline films deposited by the hot wire technique are less conformal since deposition occurs preferentially on protruding features of the substrate, while films deposited by rf-plasma CVD exhibit high conformality.
Electromechanical properties of amorphous and microcrystalline silicon micromachined structures
Authors: Gaspar J. , Boucinha M. , Chu V. , Conde J.P. 
Published: April 2011

ABSTRACTElectrostatic actuation of bridge and cantilever structures is studied. The structures are composed of bilayers of amorphous or microcrystalline silicon and aluminum fabricated using surface micromachining on glass substrates. The structures are actuated by applying the sum of a DC and a low-frequencyAC voltage. The resulting AC deflection is detected optically. The dependence of this deflection upon theapplied voltages and the bridge length is studied and compared with the predictions of an electromechanical model. The deflection amplitude can be electrostatically controlled and detected with a precision estimated to be better than a nanometer.
Films and Devices Deposited by Hwcvd at Ultra High Deposition Rates
Authors: Mahan A. H. , Xu Y. , Iwaniczko E. , Williamson D. L. , Beyer W. , Perkins J. D. , Vanecek M. , Gedvilas L. M. , Nelson B. P. 
Published: April 2011

ABSTRACTThe structure of a-Si:H, deposited at rates in excess of 100Å/s by the hot wire chemical vapor deposition (HWCVD) technique, has been examined by x-ray diffraction (XRD), Raman spectroscopy, H evolution, and small-angle x-ray scattering (SAXS). As the film deposition rate (Rd) is increased, we find that the XRD, Raman and the H evolution peak curves are invariant with Rd, and exhibit structure consistent with state-of-the-art, compact a-Si:H films deposited at low Rd. The only exception is the SAXS signal, which increases by a factor of ∼100 over that for our best low Rdfilms. We relate changes in the film electronic structure (Urbach edge) to the increase in the SAXS signals. We also note the invariance of the saturated defect density versus Rd, and discuss possible reasons why the increase in the SAXS does not play a role in the Staebler-Wronski Effect for this type of material. Finally, device results are presented.
Properties of Nano-crystalline n-type Silicon Films Produced by Hot Wire Plasma Assisted Technique
Authors: Ferreira I. , Fernandes F. Braz , Vilarinho P. , Fortunato E. , Martins R. 
Published: April 2011

ABSTRACTIn this work, we present the properties of n-type silicon films obtained by hot wire plasma assisted technique produced at different rf power and gas flow rate. The films were produced at a filament temperature of 2000°C and the rf power was varied from 0W to 200W while gas flow rate was varied from 15 to 100sccm keeping rf power at 50W. In this flow rate range, the growth rate of the films varied from 5Å/s to 250Å/s and the corresponding electrical room dark conductivity varied from 10−2 to 10(Ωcm)-1. On the other hand, we observed that the electrical conductivity increased from 2 to 6(Ωcm)-1, and the Hall mobility from 0.1 to 2cm2/V.s as rf power change from 0W to 200W. The infrared, EDS and XPS analyses revealed the existence of oxygen incorporation, which is not related to post-deposition oxidation. The X-ray diffraction and [.proportional]Raman data show the presence of Si crystals in the films structure and the SEM micrographs reveal a granular surface morphology with grain sizes lower than 60nm.
High-rate deposition of a-SiNx:H films for photovoltaic applications
Authors: Kessels W.M.M. , Assche F.J.H. van , Hong J. , Moschner J.D. , Lauinger T. , Schram D.C. , Sanden M.C.M. van de 
Published: April 2011

ABSTRACTThe feasibility of the new ‘Expanding Thermal Plasma’ technique for the deposition of a-SiNx:H at high deposition rates (typically ∼20Å/s) has been investigated. The structural film properties of the a-SiNx:H are reported for various process conditions and the application of the material as antireflection coating on (multi)crystalline silicon solar cells is studied. Furthermore, the performance of the material for surface and bulk passivation is investigated.
Nanostructured silicon films produced by PECVD
Authors: Martins R. , Águas H. , Silva V. , Ferreira I. , Cabrita A. , Fortunato E. 
Published: April 2011

ABSTRACTThis paper presents the process conditions that lead to the production of nanostructured silicon films grown by plasma enhanced chemical vapour deposition close to the so-called gamma regime (powder formation), highly dense and with low density of bulk states. Thus, the powder management is one important issue to be addressed in this paper. As a general rule we observed that high quality films (low density of states and high μτ products) are obtained when films are grown under low ion bombardment at high hydrogen dilution and deposition pressure conditions, to allow the proper surface passivation and surface activation.
Growth Monitoring of Cu-Poor Prepared CuInS2 Thin Films
Authors: Luck Ilka V. , Alvarez-Garcia Jacobo , Calvo-Barrio Lorenzo , Werner Axel , Perez-Rodriguez Alejandro , Morante J. R. , Bräunig Dieter 
Published: April 2011

ABSTRACTThe CuInS2 thin film formation from a Cu/In precursor stack in the presence of elemental sulfur using a rapid thermal process under Cu-poor conditions has been studied. The process has been aborted at appropriate stages and the corresponding samples were investigated by XRD, Raman spectroscopy and SEM. The sulfurisation starts from elemental Cu and CuIn2. Elemental In and the binary phases Cu11In9 and Cu7In3 appear as intermediate phases. At the end of the sulfurisation the sample contains the ternary phases CuInS2 and CuIn5S8. CuS and β-In2S3 are detected by Raman spectroscopy at the sample surface and at distinct stages of the sulfurisation only. A difference in CuInS2 crystal quality is observed between the surface and the bottom of the samples.
Growth of Co-evaporated Cu(In,Ga)Se2 – The Influence of Rate Profiles on Film Morphology
Authors: Bodegård M. , Kessler J. , Lundberg O. , Schöldström J. , Stolt L. 
Published: April 2011

ABSTRACTThe influence of the evaporation rate profiles on the microstructure of co-evaporated Cu(In,Ga)Se2, (CIGS), is discussed. The influence of Cu excess in the beginning of the CIGS growth has been investigated. In addition, the Ga rate has been varied in order to create bandgap grading in the CIGS film. By studying CIS and CGS films separately and as CGS/CIS stacks results on interdiffusion of In and Ga interdiffusion have been obtained. The resulting thin films are investigated mainly using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). Solar cell devices were prepared and IV measurements performed on samples with varying CIGS deposition parameters.
Ion beam assisted deposition of Cu(In,Ga)Se2 films for thin film solar cells
Authors: Lippold Gerd , Neumann Horst , Schindler Axel 
Published: April 2011

ABSTRACTWe report on a novel ion beam selenization process. The reactive chalcogen component Se and a significant part of the thermal energy needed for CIGS formation is delivered directly into the growing surface by a low energy Se ion beam from a broad beam ion source. This highly controllable technique with respect to ion energy, dose and uniformity and with scale- up capabilities can be used in two ways either for selenization of metallic Cu/(In,Ga) thin film stacks or in co-deposition. In the case of co-deposition the CIGS growth temperature can be reduced to < 400°CBesides the description of the method we present results of Se ion beam analysis and properties of CIGS thin films, produced by the novel selenization process.
Electronic Properties of Cu-In-S Solar Cells on Cu-Tape Substrate
Authors: Konovalov Igor , Penndorf Jürgen , Winkler Michael , Tober Olaf 
Published: April 2011

ABSTRACTThin film solar cells obtained by the “CIS on copper tape” technique are investigated. This technique promises a high throughput capability, but the efficiency of the cells is still about 5 % only. The model of the band structure of the absorber has been introduced into the model of the whole cell. Parameters of the model were determined experimentally by use of quantitative EBIC profiling, C-V doping profiling, Hall measurements, and AFM. The structure has been simulated using SCAPS-1D software. Results of the simulation show a good correlation to the measured I-V and DSR data of the cell. The benefits and drawbacks of the cell structure as well as factors limiting its efficiency are discussed.