bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Properties of Weakly Absorbing Highly Conductive SiC Thin Films Prepared in a TCDDC System
Authors: Martins R. , Willeke G. 
Published: March 2011

ABSTRACTp- and n-type weakly absorbing highly conductive (σ>0.1(Ωcm)-1) SiC thin films with similar structural and optoelectronic properties have been prepared in a TCDDC reactor. These films contain Si microcrystals embedded in an amorphous Si:O:C:H matrix. C is preferentially incorporated as stoichiometric SiC, whereas O is present mainly as suboxide. Absorption coefficients smaller than cr-Si are observed for films containing about 20at% C and 25at% O. From diffraction studies there is no evidence for the presence of SiC crystallites. Photoluminescence studies show a peak at about 1.68eV, similar to gd a-SiC:H of comparable optical properties.
A Semi-Transparent Solar Cell Using a-SiC
Authors: Hanaki Ken-Ichi , Hattori Yutaka , Nakabayashi Hideki , Yamaguchi Shunzo , Hamakawa Yoshihiro 
Published: March 2011

ABSTRACTA review is given of the fabrication technology and applications of a new type of semi-transparent solar cell having the structure p(a-SiC)-i(a- SiC)-n(μ-Si) heterojunction. A series of systematic investigations has been made on the effect of i-layer thickness and the optical energy gap on the photovoltaic performance of p(a-SiC)-i(a-SiC)-n(μ-Si) heterojunction solar cells. The results show that there is an optimum zone in the i-layer properties. For purposes of making cells with sufficient visible light transmission, we adopted an a-SiC active layer whose optical energy gap is in the range from 1.9 to 2.0 eV. In this case, a conversion efficiency of 6.3% with visible light transmittance of more than 25% has been obtained. The rate of light induced degradation has also been checked on this new type of solar cell. This newly developed semi-transparent solar cell, named “SOLAR GLASS,” might open new areas in a wide variety of applications for modern life such as home electronics, automobiles, medical electronics, etc. As an example, an automobile application is demonstrated and discussed.
Advances In High-Efficiency, Multiple-Gap, Multijunction Amorphous Silicon-Based Alloy Thin-Film Solar Cells
Authors: Guha S. 
Published: March 2011

ABSTRACTIt is now well-recognized that multijunction, multi-gap amorphous silicon-based alloy solar cells offer the attractive advantage of obtaining high efficiency with good long-term stability. In this paper we review the progress made in this field. Research directions to further improve the efficiency are discussed.
Direct Measurement of the Mobiuty-Lifetime Product of Holes and Electrons in an Amorphous Silicon P-I-N Cell
Authors: Crandall Richard. S. , Sadlon Kyle , Kalina Jeffrey , Delahoy Alan E. 
Published: March 2011

ABSTRACTDirect measurements of the electron and hole mobility-lifetime products, μτ, on a 10μm thick hydrogenated amorphous silicon (a-Si:H) pi- n solar cell are presented. The μτ products, determined from charge collection using strongly absorbed light are μτ|h = 2.2 × 10−8cm2V−1 and μτ|e = 3.0 × 10−7cm2V−1, for holes,and electrons, respectively. Measurements of the drift length, ld = μτ|e + μτ|h, using uniformly absorbed light and analyzed using the uniform field model,1 give ld = 2.9 × 10−7 cm2 V−1 s−1. These results are the first experimental evidence that the carrier with the larger, μτ product determines the photovoltaic behavior. Evidence for space charge limited transport of photogenerated holes is also be presented.
Linkage of Efficiency and Stability of a-Si Solar cells
Authors: Redfield David , Bube Richard H. 
Published: March 2011

ABSTRACTBy combining the steady-state and transient behaviors of a recently generalized analysis of the kinetics of metastable defects in good amorphous Si:H, it is shown that no treatment can remove all metastable defects. There is always a significant remnant that is proposed to be the observed built-in defects, which are then not a separate species, distinct from the metastable defects. This remnant is due to vibrational breaking of weak bonds in latent defect centers, and cannot be due to recombination of thermally excited carriers. If the stability can be improved by reducing the number of these latent defect centers, this will also reduce the density of built-in defects that control the initial efficiency. Furthermore, there are good reasons to believe that the source of these defects is extrinsic to a-Si:H, so that improvement in both properties may be achievable.
Growth Kinetics for Propagation of Si-Network
Authors: Azuma M , Shirai H , Hanna J. , Shimizu I 
Published: March 2011

ABSTRACTChemical reactions were systematically investigated with regard to the propagation of Si-network in the vicinity of the growing surface by using various precursors, SiHn, SiHnFm, and SiHnCim (n+m≤3) generated by plasma-induced decomposition of SiH4, SiF4, SiH2Cl2 and SiHCl3. Atomic hydrogen was an effective agent to promote the propagation reaction due to its strong chemical affinity for silicon and its ability to diffuse through the Si-network. A preliminary analysis was made of the kinetics of the propagation reactions.
Comparison of Prolonged Light Soaking of Single and Stacked Junction A-SI:H Solar Cells
Authors: Lechner P. , Scheppat B. , Geyer R. , Rübel H. , Gorn M. , Kniffler N. 
Published: March 2011

ABSTRACTLight-induced degradation of a-Si solar cells is dependent on their design. The degradation rate for single cells increases with i-layer thickness. Very thin i-layer devices (d < 100 nm) exhibit a delayed onset of degradation which is accompanied by a severe loss of open circuit voltage at prolonged exposure times. By extrapolating i-layer thickness to zero and therefore separating bulk and interface effects, the latter may account for a substantial loss of stability. The introduction of a SiC buffer layer at the p/i interface results in a considerable higher degradation mainly caused by a loss in fill factor.Double stacked cells, as compared to single cells having similar initial efficiences, show higher stability. The instability at extended exposure times of very thin single cells as used in a tandem configuration did not influence the stacked device.
Optical Degradation and Morphology in a-Si:H
Authors: Nakata Jun-ichi , Miyanishi Atsushi , Shirafuji Junji , Imao Shozo , Fujibayashi Keiji , Inuishi Yoshio 
Published: March 2011

ABSTRACTThe relationship between the optical degradation and the morphology of hydrogenated amorphous silicon (a-Si:H) films was studied through the analysis of the annealing processes. The annealing of optically induced metastable dangling bonds can be explained in terms of the first and the second order reactions with dispersive hydrogen diffusion for the films deposited at lower and higher temperature, respectively. The activation energy of the annealing was estimated to be 0.8 eV with a small distribution in both cases. Optically enhanced annealing was first observed. It was found by DLTS and CT measurements that the density of hole trap located at Ev+0.6 eV was remarkably decreased by the light soaking, accompanied by the simultaneous increase of electron trap at Ec-0.7 ∼ Ec-0.9 eV due to the dangling bonds. These experimental facts support the view that the hole trap corresponds to the weak bonds, which convert to the metastable dangling bonds by light soaking.
SiC Multilayered Photoreceptor for Electrophotography
Authors: Nakayama Y. , Akita S. , Itoh H. , Yajima T. , Nakano M. , Kawamura T. 
Published: March 2011

ABSTRACTNew multilayered photoreceptor consisting of all layers of a-Si1−xCx:H (x=0.1−0.8) has been developed on the basis of a high rate deposition process established using a glow discharge in a mixture of SiH4 and C2H2. This SiC photoreceptor is for negative charging and shows the excellent spectral sensitivity that is high in a short wavelength region and is reduced at the wavelengths longer than 600nm, suitable for the plain paper copier. The charge acceptance more than 40V/μn is achieved for the thickness less than 20μm. The charging characteristics are discussed in terms of deep emission states in the a-SiC:H.
Material Parameters in a Thick Hydrogenated Amorphous Silicon Detector and their Effect on Signal Collection
Authors: Qureshi S. , Perez-Mendez V. , Kaplan S. N. , Fujieda I. , Cho G. 
Published: March 2011

ABSTRACTTransient photoconductivity and ESR measurements were done to relate the ionized dangling bond density and the spin density of thick hydrogenated amorphous silicon (a-Si:H) detectors. We found that only a fraction (∼30–35%) of the total defect density as measured by ESR is ionized when the detector is biased into deep depletion. The measurements on annealed samples also show that this fraction is about 0.3. An explanation based on the shift of the Fermi energy is given. The measurements show that the time dependence of relaxation is a stretched exponential.
Observation of Random Telegraphic Noise in Large Area a-Si:H/a- Si1−x, Nx:H Double Barrier Structures
Authors: Arce R. , Ley L. 
Published: March 2011

ABSTRACTRandom Telegraphic Noise (RTN) with an amplitude of about 1% has been observed in the current through a-Si:H/a-Si1−xNx.:H double barrier structures. The area of the devices, 0.25 mm2, is five orders of magnitude larger than the area of the devices where RTN has previously been observed. The power spectra of the noise can be fitted by a superposition of Lorentzians from which average switching times are deduced. The switching times are thermally activated with activation energies between 0.2 and 0.6 eV and depend on bias voltage. Assuming that the current through these structures is confined to microchannels of cross section area < lμm2 the RTN and its characteristics are explained by the random charging and discharging of individual traps placed in the vicinity of the current channel.
The Effect of Hydrogen Dilution of the Gas Plasma on Glow Discharge a-Ge:H
Authors: Turner W. A. , Jones S. J. , Lee Choochon , Lee S. M. , Li Yuan-min , Paul W. 
Published: March 2011

ABSTRACTA series of films of amorphous hydrogenated germanium has been produced using the r.f. glow discharge technique by varying the H2/GeH4 ratio in the gas plasma from 0 to 50 while keeping all other deposition parameters constant. Electronic, optical, and structural characterization has been performed. No significant changes in optical and electronic properties were observed for this range of dilution, in contrast to repeated reports on the hydrogenated silicon-germanium alloy system. However, small systematic changes in structure are observed using TEM techniques. We conclude that the observed differences are unimportant in determining the optical and electronic properties of this material.
High-Resolution X-Ray Characterization of Amorphous Semiconductor Multilayers
Authors: Persans P. D. , Ruppert A. F. , Abeles B. , Hughes G. , Liang K. S. 
Published: March 2011

ABSTRACTWe discuss high-resolution x-ray diffraction measurements on a-Si:H/a-Ge:H periodic amorphous multilayers. Analysis of the data using the dynamical theory yields information on layer thicknesses and densities, interface and surface roughness, and structural defects such as layer thickness fluctuations.
Low Temperature Optically Induced Esr in a-Si:H and the Presence of Interface States
Authors: Ristein J. , Hautala J. , Taylor P. C. 
Published: March 2011

ABSTRACTComparative studies of low-temperature (T ∼ 30 K) optically induced ESR using above gap red (633 nm) and below gap i.r. (1060 nm) light have been performed on several samples of a-Si:H. Experiments were performed on both films on quartz substrates and on powdered samples which were removed from the substrates. Excitation with red light always yields the well-known light induced ESR (LESR) spectrum which is ascribed to a superposition of two resonances: electrons trapped in conduction band-tail states and holes trapped in valence band tail states in a 1:1 ratio. On the other hand, excitation with i.r. light results in a different LESR spectrum with an enhanced feature overlapping with the signal attributed to trapped band-tail electrons. Although observed on all films studied on quartz substrates, this asymmetry is not observed in a powdered sample where only the band tail electron and hole resonances are observed in the ratio 1:1. This result suggests that interface states are responsible for the excess LESR spin density in the films on quartz substrates. Experiments performed as a function of film thickness confirm this interpretation.
Amorphous Silicon/Silicon Germanium Alloy Superlattices with Periods from 1 to 100 NM
Authors: Conde J. P. , Chu V. , Wagner S. 
Published: March 2011

ABSTRACTThe electron and hole transport perpendicular to the plane of the layers in a-Si:H, F/a-Si, Ge:H, F multilayers is analyzed. We measure the electron dark conductivity σd and its activation energy Ea, d, the photo conductivity σph and its exponent γ, the electron and hole mobility-deep trapping lifetime (μτd)e, h and the hole mobility-recombination lifetime (μτr)h. We identify three regions of barrier thickness ds with very different transport properties: (a) ds≲50Å, dominated by tunnelling between quantum confined states in the bottom of the wells; (b) 50Å ≲ds≲200Å, in which the well acts as the provider of an extra, controllable tail state density; and (c) ds≳200Å, where the individual layers are essentially decoupled.
VHF-GD a-Si:H Films Prepared at Very Low Temperature
Authors: Ziegler Y. , Curtins H. , Baumann J. , Shah A. 
Published: March 2011

ABSTRACTStructural, optical and electrical properties of a-Si:H films prepared with the VHF Glow Discharge system were studied as function of deposition temperature, particularly in the range below 100°C. Usually, this material has poor optoelectronic properties. The a-Si:H material discussed in this work shows a surprisingly low hydrogen content, a low dihydride to monohydride ratio, good optical and electrical properties.
a-Si and μc-Si Grown from SiF4 with High H2 Dilution in a DC Glow Discharge
Authors: Okada Y. , Chen J. , Campbell I. H. , Fauchet P. M. , Wagner S. 
Published: March 2011

ABSTRACTa-Si and μc-Si were grown from SiF4 with H2 dilution in a DC glow discharge. The crystallinity of films deposited over a range of substrate temperatures and SiF4/H2 flow ratios was studied by Raman spectroscopy and the boundary between microcrystalline and amorphous Si was determined. We find that μc-Si can be grown from SiF4 with less H2 dilution than from SiH4. In the SiF4/H2 system, the etching by of F atoms appears responsible for μc-growth; H atoms play an important role in balancing growth and etching reactions.
Microcrystallinity in a-Si & a-SiC Films Made by Hg-Sensitized Photo-CVD
Authors: Saxena N. , Fortmann C. M. , Russell T. W. F. 
Published: March 2011

ABSTRACTA model for the role of H atoms as an etchant specie during deposition of microcrystalline (μc) films of Si:H and SiC:H is explored. Growth rates and etch rates of films made by Hg-sensitized photo-CVD have been measured as a function of reactor pressure (between 5 and 0.5 torr) and H2 dilution (up to 30:1). Gas phase reactions and diffusion to the substrate of depositing and etching species, have been modelled. It is found that high H radical flux (not necessarily high H2 dilution) promotes μc film growth. There are two surface etching reactions by H radicals: (i) selective etching of uncoordinated Si surface atoms (amorphous phase) from the film, leaving behind the more etch-resistant μc phase; (ii) in SiC:H alloy systems, a selective etching of C species, causing a decrease in C incorporation into the growing microcrystalline film. Films with increasing carbon content do not contain a μc-SiC phase because hydrogen is not eliminated from the carbon containing film precursors, thus inhibiting the development of crystalline Si-C network.
The Functional Dependence of Leaching on The Surface Area-To-Solution Volume Ratio
Authors: Machiels Albert J. , Pescatore Claudio 
Published: March 2011

ABSTRACTThe effects of the surface area-to-solution volume ratio on waste glass leach rates are investigated from a theoretical point of view. Simple leach models are discussed first. Correlation variables to interpret the results of similar leaching experiments performed at different values of the surface area-to-solution volume ratio are obtained for static leach testing. For dynamic leaching conditions, the source term required for risk assessment is derived and its dependence on the leachant flow rate and leach specimen surface area is discussed. The findings are upheld by a more complex leach model, the mathematical formulation of which has been implemented in a computer code named LIX. When tested against actual PNL 76–68 glass leaching data, LIX shows excellent capabilities in reproducing the experimental evidence, in particular the effects of the surface area-to-solution volume ratio.
Trench Water Chemistry at Commercially Operated Low-Level Radioactive Waste Disposal Sites
Authors: Pietrzak R. F. , Dayal R. , Kinsley M. T. , Clinton J. , Czyscinski K. S. , Weiss A. J. 
Published: March 2011

ABSTRACTWater samples from the disposal trenches of two low-level radioactive waste burial sites were analyzed for their inorganic, organic, and radionuclide contents. Since oxidation of the trench waters can occur during their movement along the groundwater flow path,experiments were performed to measure the chemical and physical changes that occur in these waters upon oxidation. In addition to the highly acidic conditions of the oxidized Maxey Flats trench water, low concentrations of chelating agents, shown to exist in trench waters, may be responsible for keeping radionuclides in solution following oxidation of anoxic trench leachates from Maxey Flats and West Valley burial sites.
Strontium Leachability of Hydrofracture Grouts for Sludge-Slurries
Authors: Morgan M. T. , Mcdaniel E. W. , Moore J. G. , Devaney H. E. , Dole L. R. 
Published: March 2011

ABSTRACTThis paper summarizes a series of experiments to determine the strontium leachability of cement-based sludge-slurry hydrofracture grouts.The hydrofracture process has been used at ORNL since 1966 for the routine disposal of intermediate-level waste (ILW) solutions. In this process, cement and other additives are mixed with a waste stream to form grout, which is then injected into a shale bed at a pressure sufficient to cause fracturing along the horizontal bedding planes. This injected grout soon hardens, fixing the radionuclides between layers of the massive Conasauga shale formation.Modified IAEA dynamic leach tests on hydrofracture grout specimens showed improved leach resistance (by a factor of 3 to 5) as the curing time increased from 28 d to 91 d. A weak trend toward lower leachability with increased amounts of dry solids was observed.The moving boundary-plus-diffusion leach model fits the dynamic leach data successfully in most cases. An apparent diffusion coefficient of 5 × 10−12 cm2/s and a moving boundary coefficent of 1 × 10−7 s−1 were obtained when one of the best grout compositions was leached in distilled water.
Electrical Conductivity Measurements of Leachates For The Rapid Assessment of Waste Form Corrosion Resistance
Authors: Sales B. C. , Petek M. , Boatner L. A. 
Published: March 2011

ABSTRACTMeasurements of the electrical conductivity of leachate solutions as a function of time can be used as an efficient, informative means of evaluation and comparison in the development of nuclear waste forms and in the preliminary analysis of their corrosion resistance in distilled water. Three separate applications of this technique are described in this work. These are: (1) its use in the optimization of the corrosion resistance of a crystalline wasteform (monazite); (2) a study of the protective ability of the surface layer (“gel layer”) which forms on the nuclear waste glass Frit 21 + 20 wt. % SRW in distilled water, and (3) making comparisons of the overall corrosion resistance of three different nuclear wasteforms (i.e., monazite, SYNROC, and borosilicate glass). A complete solution analysis of the borosilicate glass leachate and a straightforward analysis of the conductivity results agree to within ±20%. In the absence of a complete, time consuming solution analysis, conductivity measurements can be used to estimate reliably the total ionic concentration in the leachate to within a factor of 2.
Suitability of Natural Geomedia for Radwaste Storage
Authors: Fyfe W. S. 
Published: March 2011

ABSTRACTSelection of the best rock types for radwaste disposal will depend on their having minimal permeability, maximal
flow dispersion, minimal chance of forming new wide aperture fractures, maximal ion retention, and minimal thermal and mining disturbance. While no rock is perfect, thinly bedded complex sedimentary sequences may have good properties, either as repository rocks, or as cover to a repository.Long time prediction of such favorable properties of a rock at a given site may be best modelled from studies of in situ rock properties. Fracture flow, dispersion history, and geological stability can be derived from direct observations of rocks themselves, and can provide the parameters needed for convincing demonstration of repository security for appropriate times.
Technetium Behavior in Sulfide and Ferrous Iron Solutions
Authors: Lee Suk Y. , Bondietti Ernest A. 
Published: March 2011

ABSTRACTPertechnetate oxyanion (99TcO4−), a potentially mobile species in leachate from a breached radioactive waste repository, was removed from a brine solution by precipitation with sulfide, iron, and ferrous sulfide at environmental pH's. Maghemite (γ-Fe23 ) and goethite (α-FeOOH) were the dominant minerals in the precipitate obtained from the TcO4−)-ferrous iron reaction. The observation of small particle size and poor crystallinity of the minerals formed in the presence of Tc suggested that the Tc was incorporated into the mineral structure after reduction to a lower valence state. Amorphous ferrous sulfide, an initial phase precipitating in the TcOÝ-ferrous iron-sulfide reaction, was transformed to goethite and hematite (α-Fe2O3 ) on aging. The black precipitate obtained from the TcOÝ-sulfide reaction was poorly crystallized technetium sulfide (Tc2S7 ) which was insoluble in both acid and alkaline solution in the absence of strong oxidants. The results suggested that ferrous- and/or sulfide-bearing groundwaters and minerals in host rocks or backfill barriers could reduce the mobility of Tc through the formation of less-soluble Tc-bearing iron and/or sulfide minerals.
Ion Implantation Damage in Silicate Glasses
Authors: Arnold George W. 
Published: March 2011

ABSTRACTIon implantation is a rapid technique for simulating damage induced by α-recoil nuclei in nuclear waste forms. The simulation has been found to be quite good in TEM comparisons with natural α-decay damage in minerals, but leach rate differences have been observed in glass studies and were attributed to dose-rate differences. The similarities between ion implantation and recoil nuclei as a means of producing damage suggest that insights into the long-term behavior of glass waste forms can be obtained by examination of what is known about ion-implantation damage in silicate glasses. This paper briefly reviews these effects and shows that leaching results in certain nuclear waste glasses can be understood as resulting from plastic flow and track overlap. Phase separation is also seen to be a possible consequence of damage-induced compositional changes.