bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study of Th4(PO4)4 P2O7 and Solid Solutions With U(IV), Np(IV) and Pu(IV): Synthesis, Characterization, Sintering and Leaching Tests
Authors: Dacheux N. , Thomas A. C. , Chassigneux B. , PichotI E. , Brandel V. , Genet M. 
Published: April 2011

AbstractIn the framework of radwaste storage, the thorium phosphate-diphosphate Th4(PO 4)4P 2O7 (TPD) has been synthesized in the ThO2 – P2O5 system. This material is very resistant to aqueous corrosion. In this paper we report the conditions of synthesis of TPD doped with small amounts of trivalent actinides and of solid solutions with uranium (IV), neptunium (IV) and plutonium (IV). Sintered samples of TPD and Th4_xUx(PO4)4P2O7 (TUPD) have been prepared after pressing at 100-800 MPa at room temperature then heating at 1250°C for 10 hours. The corresponding density varies from 87 to 93% of the calculated value from crystal data. Leaching tests of Th4 (PO4)4P2O7 doped with Am3+ or Cm3+ and solid solutions Th4_xUx(PO4)4P2O7 (TUPD) or Th4-xPux(PO4)4P2O7 (TPPD) have been performed in water and in several acidic media at room temperature and at 90'C. The dependence of the leaching rate on the pH has been determined: the partial order related to [H3O+] is in the 0.35 – 0.44 range while the apparent leaching rate is equal to about 1 x 10–5x–4 x 10–5 g/(m2d).
Methodologies for Predicting the Performance of Ni-Cr-Mo Alloys Proposed for High Level Nuclear Waste Containers
Authors: Dunn D. S. , Cragnolino G. A. , Sridhar N. 
Published: April 2011

AbstractFor the geologic disposal of the high level nuclear waste (HLW), aqueous corrosion is considered to be the most important factor in the long-term performance of containers, which are the main components of the engineered barrier subsystem. Container life, in turn, is important to the overall performance of the repository system. The proposed container designs and materials have evolved to include multiple barriers and highly corrosion resistant Ni-Cr-Mo alloys, such as Alloys 625 and C-22. Calculations of container life require knowledge of the initiation time and growth rate of localized corrosion. In the absence of localized corrosion, the rate of general or uniform dissolution, given by the passive current density of these materials, is needed. The onset of localized corrosion may be predicted by using the repassivation and corrosion potentials of the candidate container materials in the range of expected repository environments. In initial corrosion tests, chloride was identified as the most detrimental anionic species to the performance of Ni-Cr-Mo alloys. Repassivation potential measurements for Alloys 825, 625, and C-22, conducted over a wide range of chloride concentrations and temperatures, are reported. In addition, steady state passive current density, which will determine the container lifetime in the absence of localized corrosion, was measured for Alloy C-22 under various environmental conditions.
A Stem Study of P and Ge Segregation to Grain Boundaries in Si1-xGex Thin Films
Authors: Qin W. , Ast D. G. , Kamins T. I. 
Published: April 2011

AbstractThe segregation of phosphorus to grain boundaries in phosphorus implanted Si0.87Ge0.13 films, deposited by chemical vapor deposition (CVD), was directly observed by scanning transmission electron microscopy (STEM) with energy dispersive x-ray (EDX) microanalysis. The segregation was determined to be a thermal equilibrium process by measuring and comparing the average phosphorus concentrations at the grain boundaries in Si0.87Ge0.13 films subjected to 700, 750 or 800°C annealing, following the implantation and 1000°C annealing processes. The measured segregation energy was 0.28 eV/atom. No Ge segregation was found at grain boundaries in phosphorus implanted Si0.87Ge0.13 films by STEM x-ray microanalysis. Neither was evidence shown by STEM microanalysis that Ge segregated to grain boundaries in intrinsic Si1-xGex films with x = 0.02, 0.13 and 0.31. Secondary ion mass spectrometry (SIMS) analysis showed that these intrinsic Si1-xGex films contained 1019 to 4 × 1019/cm-3H, depending on the deposition temperature.
Experimental Verification of a Random Medium Model for the Optical Behaviour of Ultrathin Crystalline Silicon Layers Grown on Porous Silicon
Authors: Stalmans L. , Abouelsaood A.A. , Ghannam M.Y. , Poortmans J. , Bender H. , Caymax M. , Nijs J. 
Published: April 2011

AbstractThe random medium model for porous silicon (PS) is applied to a porous silicon layer to be used as a back reflector in a thin film silicon solar cell realized in an ultrathin epitaxially grown Si layer on PS. Three-layer-structures (epi/PS/Si) have been fabricated by RPCVD of 150-1000 nm epitaxial silicon layers on the porous surface of silicon wafers. The light reflection has been measured in the 300-1000 nm wavelength range. An excellent agreement is found between the experimentally measured reflectance curves and those calculated using the random medium model. The analysis shows that the epitaxial growth has led to an appreciable reduction in the porosity in the intermediate PS layer from about 60% to 20-30%.
Amorphous Silicon Alloy Materials and Solar Cells Near the Threshold of Microcrystallinity
Authors: Yang J. , Guha S. 
Published: April 2011

AbstractOne of the most effective techniques used to obtain high quality amorphous silicon alloys is the use of hydrogen dilution during film growth. The resultant material exhibits a more ordered microstructure and gives rise to high efficiency solar cells. As the hydrogen dilution increases, however, a threshold is reached, beyond which microcrystallites begin to form rapidly. In this paper, we review some of the interesting features associated with the thin film materials obtained from various hydrogen dilutions. They include the observation of linear-like objects in the TEM micrograph, a shift of the principal Si TO band in the Raman spectrum, a sharp, low temperature peak in the H2 evolution spectrum, a shift of the wagging mode in the IR spectrum, and a narrowing of the Si (111) peak in the X-ray diffraction pattern. These spectroscopic tools have allowed us to optimize deposition conditions to near the threshold of microcrystallinity and obtain desired high quality materials. Incorporation of the improved materials into device configuration has significantly enhanced the solar cell performance. Using a spectral-splitting, triple-junction configuration, the spectral response of a typical high efficiency device spans from below 350 nm to beyond 950 nm with a peak quantum efficiency exceeding 90%; the triple stack generates a photocurrent of 27 mA/cm2. This paper describes the effect of the improved materials on various solar cell structures, including a 13% active-area, stable triple-junction device.
Kinetics of Light-Induced Changes in P-I-N Cells with Protocrystalline Si:H
Authors: Koval R.J. , Koh J. , Lu Z. , Lee Y. , Jiao L. , Collins R.W. , Wronski C.R. 
Published: April 2011

AbstractStudies have been carried out on the thickness dependent transition between the amorphous and microcrystalline phases in intrinsic Si:H materials (i-layers) and its effect on p-i-n solar cell performance [1]. P(a-SiC:H)-i(a-Si:H)-n(μcSi:H) cell structures were deposited with the intrinsic Si:H layer thickness and the flow ratio of hydrogen to silane, R=[H2]/[SiH4], guided by an evolutionary phase diagram obtained from real-time spectroscopic ellipsometry. The thickness range over which the fill factors are controlled by the bulk was established and their characteristics investigated with different protocrystalline i-layer materials (i.e., materials prepared near the amorphous to microcrystalline boundary but on the amorphous side). Insights into the properties of these materials and the effects of the transition to the microcrystalline phase were obtained from the systematic changes in the initial fill factors, their light-induced changes, and their degraded steady states for cells with i-layers of different thickness and H2 dilution.
Stability of Amorphous Silicon Thin Film Transistors
Authors: Wehrspohn R.B. , Deane S.C. , French I.D. , Hewett J. , Powell M.J. 
Published: April 2011

AbstractDangling bond defects are created during positive bias stress of amorphous silicon thin film transistors and there is an energy barrier between 0.9 and 1 eV for this process. We have studied how this energy barrier depends on the material parameters of the amorphous silicon, namely hydrogen content, hydrogen bonding, Urbach energy and intrinsic, deposition induced stress. We observe no dependence on the hydrogen content or hydrogen bonding type, but we do observe a clear dependence on the Urbach energy and the intrinsic stress. These measurements support a localized model for defect creation involving Si-Si bond breaking and the switching of a neighboring H atom to stabilize the broken bond. These results suggest that stable amorphous silicon TFTs can be obtained at low deposition temperatures by control of the deposition-induced, intrinsic stress.
Modelling of Drift Mobility Experiments on a-Si:H
Authors: Chen Wen Chao , Hamel Louis-André , Kemp Mathieu , Yelon Arthur 
Published: April 2011

AbstractWe present recent results of a study of the behavior of electronic carriers in a-Si:H, using the model of multiple trapping (MT) in an exponential density of states. In previous publications, using Monte Carlo simulations, we showed that the standard low field MT model gives reasonable agreement with experiment particularly if the Meyer-Neldel effect is included in the model. We report here on the results of including two other effects. First, we have included a simple model of field assisted detrapping, to take account of the effect of high fields. We obtain very good agreement with the results of measurements on both electrons and holes, from a number of laboratories. In addition, we show here that the validity of an effective temperature approach can be checked easily by comparison with experiment. Second, we have presented a simple model of rapid relaxation of trapped carriers. This model offers the possibility of removing the apparent inconsistency between these measurements, and other experiments.
Two Carrier Sensitization as a Spectroscopic Tool for a-Si:H
Authors: Fonseca L.F. , Weisz S.Z. , Rapaport R. , Balberg I. 
Published: April 2011

AbstractIn a recent letter we have reported the first observation of the phenomenon of minority carrier-lifetime sensitization in hydrogenated amorphous silicon (a-Si:H). We find now that combining the study of this phenomenon with the study of the well-known phenomenon of majority carrier lifetime sensitization, in this material, can provide direct information on its density of states (DOS) distribution. This finding is important in view of the limitations associated with other methods designed for the same purpose. We have carried out then an experimental study of the effect of light soaking on the phototransport in a-Si:H. We found that the increase of the dangling bond concentration with light soaking affects the sensitization and thermal quenching of the majority carriers lifetime. Using computer simulations, we further show that the details of the observations associated with the sensitization effect yield semiquantitative information on the concentration and character of the recombination centers in a-Si:H.
Collection Efficiencies Greater Than Unity by Electron Or Hole Gating in a-Si:H p-i-n Diodes
Authors: Zollondz J.-H. , Main C. , Reynolds S. 
Published: April 2011

AbstractWe report measured electron and hole gating in thick a-Si:H (3.5 μm) p-i-n diodes under reverse bias conditions. Previous publications have shown very high collection efficiency values for electron gating (p-side bias, n-side probe) of up to 50 (i.e. 5000%) for measured and simulated data and predictions of up to 400 (i.e. 40000%) from simulations. Reversing the usual sides of illumination for (electron) gating a situation can be created where, by n-side bias and p-side probe illumination, holes can be gated to travel through the sample to be collected at the contact. Even though the holes have much lower mobility, by this process we can still obtain collection efficiencies greater than unity. This measurement is more difficult because of unwanted illumination by stray bias beam photons on the more sensitive p-side, caused by reflections within the apparatus. Simulation of this situation corroborates qualitatively the measured data. A wide ranging study of the gating phenomenon in relation to different incident wavelengths and photon fluxes for bias and probe beam is reported. We present comparisons of electron and hole gating by measurement and simulation and explain the phenomenon for both electron and hole gating in terms of field changes near to the incident bias interface.
Electronic Transitions in Mixed Phase Crystalline/Amorphous Silicon in the Low Crystalline Fraction Regime
Authors: Cohen J. David , Kwon Daewon , Chen Chih-Chiang , Jin Hyun-Chul , Hollar Eric , Robertson Ian , Abelson John R. 
Published: April 2011

AbstractAmorphous silicon films were prepared by dc reactive magnetron sputtering under conditions approaching the phase transition to microcrystallinity. Using TEM imaging these films were found to contain clusters of 5 to 50 nm sized Si crystallites embedded in an amorphous silicon matrix. Photocapacitance and transient photocurrent sub-band-gap optical spectra of this material appear to consist of a superposition of a spectrum typical of amorphous silicon together with an optical transition, with a threshold near 1. 1eV, that exhibits a very large optical cross section. This transition arises from valence band electrons being optically inserted into empty levels lying within the amorphous silicon mobility gap. Using modulated photocurrent methods we have determined that these states also dominate the electron deep trapping in this material. We argue that these states arise from defects at the crystalline-amorphous boundary.
Plasma Etching Conditioning of Textured Crystalline Silicon Surfaces for a-Si/c-Si Heterojunctions
Authors: Rosa R. De , Addonizio M.L. , Chiacchio E. , Roca F. , Tucci M. 
Published: April 2011

AbstractThe development of a hybrid heterojunction fabricated by growing ultrathin amorphous silicon by Plasma Enhanced Chemical Vapor Deposition using temperatures below 250°C offers the potential of obtaining high efficiency solar cells deposited on glassy substrates. The surface preparation represents one of the most critical steps. The first aim of etching is to remove the native oxide layer from the surface of the crystalline wafer, before amorphous layer deposition. The possibility of obtaining this goal with a dry procedure that reduces the exposure of the sample to the environment is not trivial.We performed several dry etching processes but the best results were obtained using an etching process involving CF4/O2 gases. We have found evidence that plasma etching acts by removing the native oxide and the damaged surface of textured silicon and by leaving an active layer on silicon surface suitable for the emitter deposition. SEM analysis has confirmed that it is possible to find plasma process conditions where no appreciable damage and changes in surface morphology are induced. Detailed investigation was performed to find compatibility and optimization of amorphous layer deposition both on flat and textured cast silicon by changing the plasma process parameters. By using this process we achieved on cast silicon for solar applications photovoltaic conversion efficiencies of 12.9% on 51 cm2 and 9.2% on 45 cm2 active areas for amorphous crystalline heterostructure devices realized on monocrystalline and polycrystalline silicon respectively. We also investigated the compatibility of the process with industrial production of large area devices.
Deposition of a-Si:H Devices in a RTR System for Photovoltaic and Macroelectronic Applications
Authors: Scholz M. , Peros D. , Böhm M. 
Published: April 2011

AbstractThis work presents first results of potential manufacturing processes for integrated series connected hydrogenated amorphous silicon (a-Si:H) thin film solar modules and/or pindiode/TFT based macroelectronic circuits on flexible tapes. A RTR (Reel-To-Reel) deposition system on laboratory scale has been built, The system consists of seven metal sealed LIHV stinless steel chambers to obtain ultra high vacuum as a basis for high quality a-Si:H layers, in order to support continuous movement of the tape in the RTR process the chambers cannot be isolated from each other. The necessary pressure difference between the sputtering chambers and the PECVD (Plasma Enhanced Chemical Vapor Deposition) chambers is provided by pressure stages. They are optimized for high molecular flow resistance without any influence on the moving substrate tape. The back metal contacts and the semitransparent TCO (Transparent Conductive Oxide) contacts are deposited by rf magnetron sputtering, the a-Si:H film system is deposited by PECVD. Parallel to the film deposition a Nd:YAG laser patterning system is coupled into one chamber. This allows for instance a total manufacturing of integrated series connected solar modules in one system without breaking the vacuum. Our present investigations focus on the deposition of doped and intrinsic high quality a-Si:H based layers in neighboring chambers. The quality of semiconducting films deposited in adjacent chambers is studied with regard to potential contamination effects.
Thin-Film Transistors based on Hot-Wire Amorphous Silicon on Silicon Nitride
Authors: Stannowski B. , Meiling H. , Brockhoff A. M. , Schropp R. E. I. 
Published: April 2011

AbstractWe present state-of-the-art thin-film transistors (TFTs) incorporating amorphous silicon i-layers deposited by hot-wire chemical vapor deposition. The TFTs are deposited on glow-discharge silicon nitride as well as on thermally-grown silicon dioxide. The devices on silicon nitride have a field-effect mobility above 0.7 cm2/Vs, a threshold voltage around 2 V and a sub-threshold slope as low as 0.5 V/dec. As commonly observed, the TFTs on silicon-dioxide have higher values for the threshold voltage and the sub-threshold slope. In the annealed state the hot-wire TFTs show almost the same properties as TFTs deposited by conventional plasma-enhanced chemical vapor deposition. Nevertheless, the stress-time dependent behavior under prolonged gate-voltage stress at elevated temperature is different from that of the glow-discharge devices. The hot-wire TFTs are clearly more stable than their glow-discharge counterparts. Furthermore, we found differences in the stress behavior of the hot-wire TFTs deposited on silicon nitride and silicon dioxide.
Temperature Dependent Transient Leakage Currents in Amorphous Silicon Thin Film Transistors
Authors: Lemmi F. , Street R. A. 
Published: April 2011

AbstractThe transient response of a-Si:H thin film transistors (TFT) provides information about gap states in the channel and about the TFT conduction mechanisms. We present results of a detailed parametric study of transient leakage currents in TFTs, extending from 10-3 sec to >100 sec and at temperatures up to 400K. The form of the transient decay depends most notably on the off-state gate voltage, which determines the leakage current mechanism and magnitude. The measurements use chains of many TFTs, such that we can measure dc on/off ratios of >1011.In the sub-threshold region (e.g. Vg~-2V) some samples exhibit non-monotonic decay of the drain current, with a minimum followed by a slow increase to a steady state. Typically this effect is barely visible at room temperature due to the extremely low values of the dc current. Higher temperatures enhance the phenomenon, which has activation energy of about 1 eV for the current magnitude and time constant. We attribute the effect to back-channel electron conduction. This explanation is consistent with the form of the TFT transfer characteristics, and the weak drain-source voltage dependence excludes a contact injection mechanism.At more negative gate off-state voltages, some samples exhibit increasing leakage currents, indicative of hole conduction. These samples feature a monotonically decreasing transient decay with a pronounced drain-source voltage dependence, consistent with contact injection being enhanced by a hole-enriched channel in the high field drain region.Effects of on-state gate pulse width and amplitude are also discussed, as well as the effect of high temperature stress on the TFT transients.
High-Performance Damascene-Gate Thin Film Transistors
Authors: Ma Eugene , Wagner Sigurd 
Published: April 2011

AbstractWe report a novel TFT structure where the gate metal is embedded into a SiNx passivation layer. This allows the subsequent gate dielectric layer to be much thinner than in conventional bottom-gate structures. thereby reducing the threshold voltage and the sub-threshold slope. TFTs employing these damascene-gate structures were fabricated with SiNX gate dielectrics as thin as 50 nm. Such devices exhibit threshold voltages of 0.9 V, sub-threshold slopes of 0.1 V/dec, ION/IOFF current ratios of 106 and linear region field-effect mobilities of 0.6 cm2/Vs.
Flexible A-SI Based Solar Cells with Plastic Film Substrate
Authors: Ichikawa Yukimi , Fujikake Shinji , Tabuchi Katsuya , Sasaki Toshiaki , Hama Toshio , Yoshida Takashi , Sakai Hiroshi , Saga Misao 
Published: April 2011

AbstractA flexible amorphous silicon (a-Si) based photovoltaic (PV) module has been developed. The a-Si solar cell fabricated on a heat-resistance plastic film with a thickness of 50μm has a new monolithic series-connected structure named SCAF to obtain a high output voltage required for practical use. Applying a-Si/a-SiGe double-junction structure to 40cm × 80cm SCAF solar cells, we obtained a stabilized efficiency of 9% with an excellent reproducibility. Flexible PV modules fabricated from the SCAF solar cells have been tested in several demonstration sites to study their durability under outdoor conditions.
Optimization of High Efficiency Amorphous Silicon Alloy based Triple-Junction Modules
Authors: Banerjee A. , Yang J. , Guha S. 
Published: April 2011

AbstractA systematic approach has been used to scale up high efficiency 0.25cm2 active-area amorphous Si alloy based triple-junction devices to high-efficiency encapsulated modules of aperture area ~920cm2. In order to analyze the losses involved in the scale-up, intermediate aperture area, 40cm2 and 450cm2, modules have also been fabricated. The best stable active-area efficiency obtained on the small-area cells is 12.9%. The best initial efficiency of a ~920cm2 aperture area encapsulated module is 12.1%. National Renewable Energy Laboratory (NREL) has independently light soaked three of the ~920cm2 modules. They have measured a stable efficiency of 10.5% which represents a new world record. This paper presents various aspects of the large-area module work.
Amorphous Silicon Solar Cells Techniques for Reactive Conditions
Authors: Shimizu Satoshi , Okawa Kojiro , Kamiya Toshio , Fortmann C.M. , Shimizu Isamu 
Published: April 2011

AbstractThe preparation of amorphous silicon films and solar cells using SiH2Cl2 source gas and electron cyclotron resonance assisted chemical vapor deposition (ECR-CVD) was investigated. By using buffer layers to protect previously deposited layers improved a-Si:H(Cl) solar cells were prepared and studied. The high quality a-Si:H(Cl) films used in this study exhibited low defect densities (~1015cm-3) and high stability under illumination even when the deposition rate was increased to ~15A/s. The solar cells were deposited in the n-i-p sequence. These solar cells achieved VOC values of ~ 0.89V and ~ 3.9% efficiency on Ga doped ZnO (GZO) coated specular substrate. The a-Si:H(C1) electron and hole μτ products were ~10-8cm2/V.