bluuebunny/crossref_metadata_2025_split huggingface dataset:
Visible Electro- and Photoluminescence from Porous Silicon and its Related Optoelectronic Properties
Authors: Koshida Nobuyoshi , Koyama Hideki 
Published: March 2011

ABSTRACTThe optoelectronic properties of porous Si (PS) are presented in terms of electroluminescence (EL), photoluminescence (PL), photoconduction (PC), and optical absorption. Observations of injection-type EL, efficient PL, band-gap widening, and photosensitivities In the visible region are consistent with the quantum size effect model in PS.
Infrared and Visible Emission from Si Layers
Authors: Kux A. , Lugli P. , Ostermeir R. , Koch F. , Deboy G. 
Published: March 2011

ABSTRACTWe present an experimental study of light emission in silicon devices, mainly MOSFETs, p-i-n diodes, and MIS structures. The special analysis shows important features below as well as above the gap, indicating the type of mechanism responsible for the light emission. Striking differences we found between planar and vertical-type structures.
Structure and Composition of Luminescent Laterally Anodized Porous Si
Authors: Jung K. H. , Shih S. , Hsieh T. Y. , Campbell J. C. , Kwong D. L. , George T. , Lin T. L. , Liu H. Y. , Zavada J. , Novak S. 
Published: March 2011

ABSTRACTWe have made structural and compositional studies of luminescent laterally anodized porous Si. Scanning electron microscopy reveals a surface with a network of cracks, while transmission electron microscopy shows a dual porous Si structure in which the upper layer is amorphous and the lower layer is either amorphous or crystalline, depending on anodization conditions. X-ray diffraction verified the presence of the amorphous layer. Secondary ion mass spectroscopy reveals very high concentrations of H, B, C, N, O, and F in the amorphous layer. Our results indirectly suggest that the amorphous layer is primarily responsible for luminescence.
Excitation Spectra of the Visible Photoluminescence of Anodized Porous Silicon
Authors: Motohiro Tomoyoshi , Kachi Tetsu , Miura Fusayoshi , Takeda Yasuhiko , Hyodo Shi-Aki , Noda Shoji 
Published: March 2011

ABSTRACTPorous silicon samples photoluminous in orange, pink or greenish-yellow were formed by anodization. The shapes and wave length positions of their photoluminescence peaks were not influenced by the excitation wavelength. The photoluminescence intensity at any wavelength between 520nm and 800nm varied as a function of the excitation wavelength In accordance with the imaginary part of the spectral refractive index of bulk silicon. Thus the excitation process responsible for the visible photoluminescence of porous silicon seems to be bulk-silicon-like.
Electro- and Photoluminescence from Ultrathin SImGEn Superlattices
Authors: Presting H. , Menczigar U. , Abstreiter G. , Kibbel H. , Kasper E. 
Published: March 2011

ABSTRACTP-i-n doped short-period SimGen strained layer superlattices (SLS) are grown on (100) silicon substrates by low temperature molecular beam epitaxy (300C°<∼Tg<∼400C°). The SLS's are grown with period lengths around 10 monolayers (ML) to a thickness of 250nm on a rather thin (50nm) homogeneous Si1−ybGeyb alloy buffer layer serving as strain symmetrizing substrate. Photoluminescence at T=5K is observed for various SimGen SLS samples, the strongest signal was found for a Si5 Ge5 SLS. Samples with identical SLS's but different buffer layer composition and thicknesses are grown to study the influence of strain on the PL. Electroluminescence (EL) at the same energy range is observed from mounted SimGen SLS mesa and waveguide diodes up to T=130K – for the first time reported in strain symmetrized short-period SimGen SLS. The intensity and peak positon of the EL signal was found to be dependent on the injected electrical power.
NP Heterojunction Porous Silicon Light-Emitting Diode
Authors: Kalkhoran Nader M. , Namavar F. , Maruska H. P. 
Published: March 2011

ABSTRACTWe report the first demonstration of visible light emission from an all solid-state n-p heterojunction diode based on porous silicon. The p-type silicon was electrochemically etched in a hydrofluoric acid solution to form a porous silicon region; the n-p heterojunction diode was fabricated by depositing a wide bandgap n-type semiconductor, indium-tin-oxide (ITO), onto the surface of the porous silicon. With positive bias applied, electroluminescence was observed with a relatively narrow peak at about 580 nm. The device showed strong rectifying properties and no light emission was observed under reverse bias condition. Photoluminescence in the red, orange, yellow, and green was also observed in separate sample preparations.
Comparison of in Situ and Laboratory Corrosion Experiments with Borosilicate Nuclear Waste Glass
Authors: Lutze Werner , Ewing Rodney C. 
Published: March 2011

ABSTRACTThe comparison of laboratory data from the corrosion of borosilicate nuclear waste glass (German SM513LW11 and French R7T7) with data from the Materials Interface Interactions Test (MIIT) and Repository Systems Simulation Test (RSST) illustrates the inherent limitations of in situ tests. Although in situ tests may confirm the short term behavior of waste forms and identify phenomena associated with the repository system, they do not provide the fundamental basis for the extrapolation of long-term behavior.
Empirical Dissolution Rate Law for the Glass R7T7 Contacting Halite- and Silica-Saturated Brines
Authors: Grambow B. , Lutze W. , Müller R. 
Published: March 2011

ABSTRACTWe report on the time dependence of release of glass constituents during static dissolution experiments with the COGEMA glass R7T7 in saline MgCl2 and NaCl dominated solutions at temperatures between 110 and 190°C. The experiments were performed at high S/V values to ensure silica saturation almost from the start of the tests. The results show a square root of time dependence indicating diffusion as rate-controlling with apparent diffusion coefficients similar to that of water diffusion in alkali silicate, borosilicate glasses or long-term weathered obsidians.
Effect of Platinoids on French LWR Reference Glass Properties
Authors: Pacaud F. , Fillet C. , Jacquet-Francillon N. 
Published: March 2011

ABSTRACTNine samples of the “R7T7” glass composition selected to vitrify fission product solutions in France were prepared with added platinoid elements (ruthenium, rhoditun and palladium) in soluble form and as insoluble metal particles in solution, and their major properties were measured. Regardless of the initial form when added to the glass the platinoids always formed the same heterogeneous inclusions in the final glass: RuO2 precipitates which were often found as aggregates, and polymetallic (Pd, Rh & Te) inclusions.The particles tended to settle in the molten glass. The viscosity increased by about 20% at 1100°C. The mechanical properties and short-term leach rates were not significantly affected. Crystallization increased by a factor of 2 or 3 in heat-treated glass specimens but did not exceed a few volume percent. However, as the short-term leach rate did not significantly increase, the glass properties were very satisfactory.
Radiological Protection Criteria for Solid Waste Disposal: Historical Developments and New Ideas
Authors: Cooper J R , Mobbs S F , Barraclough I 
Published: March 2011

ABSTRACTThe historical development of international advice on radiological protection criteria for solid waste disposal is described, and problems associated with the interpretation of existing criteria are discussed. These problems arise largely because of the long timescales over which radionuclides may be released from solid waste repositories. In an attempt to aid in the interpretation of existing international advice, the UK National Radiological Protection Board is issuing new guidance on radiological protection criteria for solid waste disposal and its application. Aspects of this new guidance are described.
Mechanisms for the Retardation of Uranium (VI) Migration
Authors: Silva Robert J. 
Published: March 2011

ABSTRACTThis report covers the investigation of mechanisms for the retardation of U(VI) migration. It describes (1) the measurement of the solubility of UO22+as afunction of pH and equilibration time, (2) the calculation of solubility using solution thermochemical data, (3) the measurement of the sorption of UO22+by silica as a function of pH and supporting electrolyte concentration, and (4) attempts to simulate the uranium sorption isotherms in terms of the U solution thermochemical data, measured properties of the silica and proposed sorption reaction mechanisms.
Dissolution Kinetics of UO2. I. Flow-Through tests on UO2.00 Pellets and Polycrystalline Schoepite Samples in Oxygenated, Carbonate/Bicarbonate Buffer Solutions at 25°C
Authors: Nguyen Son N. , Weed Homer C. , Leider Herman R. , Stout Ray B. 
Published: March 2011

ABSTRACTThe modelling of radionuclide release from waste forms is an important part of the performance assessment of a potential, high-level radioactive waste repository. Since spent fuel consists of UO2 containing actinide elements and other fission products, it is necessary to determine the principal parameters affecting UO2 dissolution and quantify their effects on the dissolution rate before any prediction of long term release rates of radionuclides from the spent fuel can be made.
Leaching of Actinides from Nuclear Waste Glass: French Experience
Authors: Vernaz E.Y. , Godon N. 
Published: March 2011

ABSTRACTResults are presented for a large number of aqueous leach tests on glass specimens doped with 237Np, 238Pu, 239pu, 241Am or 244Cm. The effects of the leaching mode (static or dynamic), temperature and environmental materials are discussed. The amount of actinides contained in the alteration film is characterized by the retention factor RF = NL(B)/NL(act). The neptunium retention factor ranged from 1 to 10 depending on the test conditions; for plutonium and americium, the retention factor varied from 6 to 1300.In general, the retention factor increased with the temperature. The very important influence of the environmental materials shows that there is competition for actinide retention between the alteration film and the surrounding materials, but in every case the amount of ca activity released into solution is very low.
X-RAY Photoelectron Spectroscopic Study of Cigar Lake Uranium Ore: A Natural Analog for Used Fuel
Authors: Sunder S. , Cramer J.J. , Miller N.H. 
Published: March 2011

ABSTRACTX-ray photoelectron spectroscopy (XPS) was used to study samples from the Cigar Lake uranium deposit in northern Saskatchewan. Two uranium-rich sections, CS-615 and CS-620 were studied. Peaks due to U, 0, C, Pb, Si, Ca, Al, S, Cu and Th were seen in the XPS spectra. Concentrations of Pb of up to 14 wt% were measured by XPS and correspond to the Pb ingrowth by radioactive decay during the 1.3 billion years since the ore was formed. High-resolution spectra were recorded for the U, Pb, 0, and C bands. Lead was in the +2 oxidation state in all samples. The carbon signal indicated the presence of organic carbon, while the oxygen bands indicated the presence of significant amounts of water in the samples. The samples from the CS-615 section had U6+/U4+ratios between 0.16 and 0.29. However, the U6+/U4+ratios for section CS-620 were about 0.7 but this is attributed to oxidation of the ore by water during the drilling and cutting processes. The significance of the results for disposal concepts in nuclear fuel waste management programs is discussed.
Immobilization of Actinides by Hydroxylapatite
Authors: Gauglitz R. , Holterdorf M. , Franke W. , Marx G. 
Published: March 2011

ABSTRACTIn cooperation with the Ministry of Research and Technology we investigated the influence of hydroxylapatite (HAP) added to the backfill material of a radioactive waste disposal located in a salt dome. The time dependence of the sorption and precipitation of radionuclides has been studied in three different praxisrelevant salt brines under variation of temperature and pH-value.Performing batch experiments uranium and thorium phosphates were precipitated fromUO2(NO3)2andTh(NO3)4solutions at 75°C, the amounts of the relevant actinide compounds also exceeding that of HAP. The isolated precipitates were investigated by use of X-ray-powder-diffractometry and SEM. For the various uranium systems two mineral phases were obtained. From solution II and also from Q-brine the mineral saléeiteMg(UO2)2(PO4)2·9H2Owas formed. From solution III meta-autuniteCa(UO2)2(PO4)2·6H2O, a dehydration product of autunite, was precipitated.
Diffusivity of Uranium(VI) in Water-Saturated Inada Granite.
Authors: Idemitsu Kazuya , Furuya Hirotaka , Murayama Kenji , Inagaki Yaohiro 
Published: March 2011

ABSTRACTIn the safety assessment of high level radioactive waste disposal, a significant retardation of nuclides can be expected. When radionuclides released from an underground repository are transported with the moving groundwater along cracks in the rock, the radionuclides will be retarded by not only adsorption on the surface of the cracks but also diffusion into the micropores of rock matrix.Diffusivities of U(VI) were measured in water-saturated granite that was mined in the middle of Japan. The measured penetration profile of U(VI) was composed of two parts. Those were a steep slope near the surface and a gradual slope in the deeper part. This profile was successfully explained by considering two diffusion paths in granite. One diffusion path was possibly a fissure with a width of a few microns and another was a network of submicron pores. The volume of submicron pores was approximately 80% of the total pore volume in the granite. The orders of magnitude of apparent diffusivities for U(VI) were 10−13-10−12 m2/s through the fissure and 10−15 m2/s through the network of pores. The ratio of geometrical factors in the two paths was also calculated from each apparent diffusivity and was almost unity. This ratio calculated suggests that the pore network in the granite matrix has a similar shape to the fissure, thus the microstructure of the granite seems to be fractal.
Radioelement Behaviour in a Cementitious Environment
Authors: Bayliss S. , Haworth A. , McCrohon R. , Moreton A.D. , Oliver P. , Pilkington N.J. , Smith A.J. , Smith-Briggs J.L. 
Published: March 2011

ABSTRACTThe Nirex Safety Assessment Research Programme (NSARP) comprises scientific research to support the safety assessment of a deep geological repository for low- and intermediate-level radioactive wastes. The NSARP addresses several areas of research, one of which is a continuing investigation of the behaviour of radioelements in a cementitious environment. This paper draws together recent experimental measurements of solubility and sorption under such conditions, along with the results of interpretive thermochemical and sorption modelling. Under conditions similar to those expected in the repository, the predicted solubility of selenium is about 3xl0−8M. Experimental measurements confirm that at low redox potential the solubility of selenium is substantially less than that previously observed under an air atmosphere, and is closer to the predictions of the thermochemical modelling. The solubility of sodium stannate has been studied after heating solutions at 50, 80 and 200°C. Crystalline tin solids were formed at all temperatures. For solutions heated at 200°C the solids were identified as cassiterite. The solubilities of all of the crystalline solids were 1x10−6M to 1x10−9M which are at least five orders of magnitude lower than that of the original sodium stannate. Distribution ratios (Rd) between 1x103 and 5x103 ml g-1 have been measured for the sorption of tetravalent technetium on to a cementitious material. Preliminary results from an in-diffusion experiment involving americium and an intact cement sample are in good agreement (at 1sx104 ml g-1) with Rd values determined from previously reported batch sorption experiments.
Diffusivity and Porosity in Rock Matrix Related to the Ionic Strength in the Solution
Authors: Valkiainen M. , Uusheimo K. , Olin M. , Muurinen A. 
Published: March 2011

ABSTRACTThe nature of diffusivity and porosity in rock was studied as a function of various parameters. The phenomena of main interest were dead-end porosity, ion-exclusion and sorption. The rock types studied were rapakivi granite, granite and gneiss, and tracer techniques with 36Cl, 22Na+ and 3H (HTO) were used as a research method. A mathematical solution for outdiffusion from a porous cylinder was developed by applying a corrected form of Fick's second law for a case where part of the pores are so-called dead-end pores. With this model the theoretical curve could be closely fitted to the measured values. It was found that the rock-capacity factor is an increasing function of the ionic concentration of the solution in the case of Cl indicating ion-exclusion, while the opposite is true in the case of Na+ indicating ion-exchange type sorption. The effective diffusion coefficient was also found to vary as a function of the salinity in the case of 36Cl. In the case of 22Na, the effect was opposite and weaker. The diffusion of tritium through the rock samples was clearly higher than the diffusion of 36Cl. Part of the difference is explained by the smaller effective porosity for 36Cl. The rest can probably be explained by the steric effects on the chloride ion caused by the negatively charged pore surfaces in the narrow pores.
Cationic Corrosion Inhibitors for Alkaliborosilicate Glass
Authors: Zwicky H.U. , Graber TH. , Grauer R. , Restani R. 
Published: March 2011

ABSTRACTThe dissolution behaviour of two alkali borosilicate glasses has been investigated at 90°C in the presence of potential corrosion inhibitors. The added materials were selected on the basis of surface chemistry considerations: Since the dissolution rate of silicate solid phases in alkaline solutions increases with growing negative surface charge, it should be expected that sorbing cations reduce the reaction rates. Due to the formation of insoluble hydroxides and silicates and to the dominance of neutral or negatively charged hydroxo complexes in the pH range of interest, the selection of potential inhibitors is very restricted.The precipitated hydroxides of Al, Zn, Cd and Pb were chosen as the solid phases. Compared with the experiments in pure water, glass dissolution is enhanced in presence of Al(OH)3 and Zn(OH)2. The concentration of the aqua ions is too low for an inhibiting effect. Sorption of silicic acid on the hydroxide accelerates the glass dissolution. Addition of PbO had a strong inhibiting effect in a 28 days experiment. At longer times an insoluble lead silicate is formed and thereby the glass dissolution rate is increased. Cd on the other hand is still effective as an inhibitor after 365 days.Based on the present results, the possibility of using glass corrosion inhibitors in a repository is considered not to be worthwhile.
Hydrogenated Amorphous Silicon/Aluminum Interaction at Low Temperatures
Authors: Shahidul Haque M. , Naseem H. A. , Brown W. D. , Ang S. S. 
Published: March 2011

ABSTRACTAnnealing effects on the Al/a-Si:H structure in the temperature range 100°C to 300°C have been studied. Aluminum was evaporated on device quality phosphorous doped n+ a-Si:H films deposited in a UHV-PECVD system. The transmission line model (TLM) technique was used to measure the sheet resistance and contact resistivity of the films. For samples where Al covered the entire a-Si:H surface during annealing, sheet resistance and contact resistivity were found to decrease monotonically with annealing temperature. On the other hand, samples annealed after patterning Al pads showed a minimum in sheet resistance and contact resistivity at temperatures between 170°C and 200°C with a steep increase beyond 250°C. Optical and scanning electron microscopy, as well as surface profilometry, were used to study the surface morphology. A simple model involving Al interaction with the a-Si:H at the surface is proposed to explain the electrical behavior.
X-Ray Detectors Based on “Thick” a-Si:H Layers Deposited by the VHF-GD Process
Authors: Chabloz P. , Keppner H. , Baertschi V. , Shah A. , Chatellard D. , Egger J.-P. , Denoréaz M. , Jeannet E. , Germond J.-F. , Vuilleumier R. 
Published: March 2011

ABSTRACTIn spite of its low absorption coefficient for X-rays, amorphous Silicon can be an interesting alternative approach for X-ray detection because of its low cost, its potential for large-area deposition and the possibility to deposit on a curved surface. For this application, basically two approaches have been proposed up to now: either a thick solar cell type n-i-p structure (the i-layer as to be sufficiently thick i.e typically 50 μm or more), or a normal solar cell type n-i-p structure (with a relatively thin i-layer, i.e (typically 1 to 2 μm) together with a fluorescent layer emitting visible light composed e.g. of CsJ. In this paper, we present first results of a X-ray detectors with thick i-layers (15 to 100 μm) prepared by the high deposition rate VHF-GD technique introduced at our laboratory. Detectors with low leakage currents (<4nA/cm2) under high reverse bias voltages (about 100 V) could be fabricated at rates as high as 22 Å/s. As substrates, aluminium as well as TCO-coated glass substrates were used. The detectors have a n-i-p structure, where highly conductive (100 S/cm) n-doped μc-Si:H was first deposited. For the substrate preparation, a high energy Ar plasma was applied before the first deposition step; in this way excellent sticking conditions could be achieved, although in the thicker detectors considerable curvature due to the internal mechanical stress could be observed. A medical X-ray radiation source was used, where the detector was exposed to a continuous X-ray spectrum at acceleration voltages between 80 kV and 240 kV. The paper presents measurements on the linearity of the detector, as well as on the value of the reverse current in the dark, which must be as small as possible to have the best signal to noise ratio.
1Improvement of Thick a-Si Radiation Detectors by Field Profile Tailoring
Authors: Drewery J.S. , Cho G. , Jing T. , Kaplan S.N. , Mireshghi A. , Perez-Mendez V. , Wildermuth D. 
Published: March 2011

ABSTRACTApplication of thick (∼50 μm) a-Si p-i-n diodes as a direct radiation detector for minimum ionizing particles is hampered by the need to apply large bias voltages in order fully to deplete the detecting intrinsic layer, which typically contains 5–10×1014 ionizable dangling bonds per cm3. By insertion of thin p-type layers at intervals within the intrinsic layer, the required depletion voltage can be reduced by a factor of at least 1/(n+1) where n is the number of layers inserted. This principle is demonstrated for devices approximately 12μm in thickness. It is shown that electron losses within the p type layer can be kept to minimum by choice of a low doping concentration for the introduced p layers.
Dynamic Thresholding with the Three-Terminal Optically Addressed Spatial Light Modulator
Authors: Rice Robert A. , Close Peter J. , Moddel Garret 
Published: March 2011

ABSTRACTStandard, non-patterned optically addressed spatial light modulators (OASLMs), comprising an a-Si:H photodiode and a ferroelectric liquid crystal (FLC), have a fixed write-light intensity threshold when driven at a particular frequency. We present a patterned OASLM in which the threshold may be varied. The structure and operation of this device is significantly different from the standard OASL.M. While the square-wave drive for the non-patterned OASLM provides a time-varying voltage for the device, the thresholding OASLM uses a dc drive, with spatially separated bias voltages. By varying the voltage applied to a patterned metal layer between the a-Si:H and FLC, we achieved dynamic thresholding over one decade of write-light intensity. Fabricated devices have response times as low as 200 μsec, and contrast ratios as high as 50:1.