bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanical and Tribological Properties of a-GeCx Films Deposited by DC-Magnetron Sputtering
Authors: Jacobsohn L. G. , Reigada D. C. , Freire F. L. , Prioli R. , Zanette S. I. , Caride A. O. , Nascimento F. C. , Lepienski C. M. 
Published: April 2011

ABSTRACTAmorphous carbon-germanium films were grown by dc-magnetron sputtering at different argon plasma pressures ranging from 0.17 and 1.4 Pa. The water-cooled sample holder was grounded. The film thickness were typically 0.5 μm. The ratio between germanium and carbon atomic concentration ranges up to 2.8, as measured by Rutherford backscattering spectrometry (RBS). Elastic recoil detection technique was used to measure hydrogen contamination. The film hardness was measured by nanoindentation techniques and the internal stress was determined by the bending of the substrate. The incorporation of Ge reduces both the film hardness and the internal stress. Hardness and internal stress increases when the films are deposited in lower pressures. Atomic Force Microscopy (AFM) was used to measure the surface roughness, which was found to be insensitive to the pressure and to the Ge content. A possible influence of the thickness on the morphology of pure carbon films is discussed. The friction coefficient measured by AFM is independent on the film composition within experimental errors.
Curling and Annealing Study of Sputtered Thin Spinel Films Delaminated from Lift-Off Polyimide
Authors: Dannenberg Rand , King Alexander H. , Gambino Richard J. , Doctor Alan J. 
Published: April 2011

ABSTRACTFilms of Mnl.56Co0.96Ni0.48O4, 6–10 ¼m thick, were RF-magnetron sputtered onto the high temperature lift-off polyimide PiRL®; (made by Brewer Science, Inc.), and patterned into long, narrow beams using photolithography. The beams would self-delaminate, curling towards the substrate upon cooling from 300°C to room temperature after sputtering, as a result of the stress gradient in the film, caused by the deposition process. The typical radius of curvature is 8000 ¼m. Upon annealing at temperatures as low as 250°C for 10 minutes, the delaminated films continue to curl. The films curl to equilibrium radii that are functions of the annealing atmosphere and temperature. Films annealed in H2/N2 or vacuum curl more slowly than in air. TEM reveals that the first 100 nm of film is relatively porous, nanocrystalline spinel which densify instantaneously when exposed to high electron beam currents. Analysis of TEM photographs before and after annealing at 250°C indicate that the level of porosity decreases in the films by 1% which can account for the change in the curl radius. The first layers of film at the PiRL-film interface are prevented from fully densifying while on the substrate. When the film delaminates and the constraint is removed, the initial layer can densify, sintering at low temperature because the large specific surface area of the nano-crystalline microstructure provides high driving forces. The nature of the substrate-induced constraint is not fully understood. Water vapor and other light elements may be released from the polyimide if it were to continue to imidize during the deposition, and a SIMS study has been undertaken to investigate this possibility. Alternatively, the constraint may be purely mechanical, where the sintering rate is reduced as in constrained sintering of films from slurry. This effect may be important to understand when ceramic films are patterned with lift-off techniques. Empirical expressions describing the curl are developed.
Molecular-Dynamics Simulations of Ballistic Damages Caused by an Energetic Recoil Nucleus on a Nuclear Glassy Network
Authors: Delaye J-M , Ghaleb D. 
Published: April 2011

ABSTRACTWe have studied the damage caused by an energetic recoil nucleus on the glassy network, from a ballistic viewpoint, using molecular dynamics method. The energies of the displacement cascades performed have been limited to 6keV up to now. This energy represents approximately one tenth of the energy of a recoil nucleus emitted during ca disintegrations in a real nuclear glass. The composition studied comprises the major elements of the real glass: SiO2, B203, Na20, A1203, ZrO2, and the atomic interactions are represented by Born-Mayer-Huggins potentials with formal atomic charges completed by three-body terms. The study described here must be considered in the light of earlier studies in which the authors investigated the complete sequence of a displacement cascade, revealing atom movements occurring when the Coulomb force field is modified in the glass matrix.As in the ballistic collision sequence, network formers and modifiers exhibit different behaviour. Network modifiers react more quickly and more violently to a modification of the Coulomb field, and relaxation of the alkali metal atoms occurs together with the relaxation of the three-dimensional network of formers. Relaxation of the alkali metals is a key factor ensuring more thorough relaxation of the network formers; the authors have previously shown that preventing relaxation of the alkali metals limits network relaxation.A more comprehensive description of a displacement cascade can thus be proposed. It is important to distinguish between the ballistic collision sequence per se, which begins first and displaces mainly network formers and oxygen atoms by individual movements, and the network relaxation sequence due to modification of the Coulomb fields, which begins with a slight delay following the collision sequence.
From Laboratory Experiments to a Geological Disposal Vault: Calculation of Used Nuclear Fuel Dissolution Rates
Authors: Sunder S. , Shoesmith D.W. , Kolar M. , Leneveu D.M. 
Published: April 2011

ABSTRACTCalculation of used nuclear fuel dissolution rates in a geological disposal vault requires a knowledge of the redox conditions in the vault. For redox conditions less oxidizing than those causing UO2 oxidation to the U3O7 stage, a thermodynamically-based model is appropriate. For more oxidizing redox conditions a kinetic or an electrochemical model is needed to calculate these rates. The redox conditions in a disposal vault will be affected by the radiolysis of groundwater by the ionizing radiation associated with the fuel. Therefore, we have calculated the alpha-, beta- and gamma-dose rates in water in contact with the reference used fuel in the Canadian Nuclear Fuel Waste Management Program (CNFWMP) as a function of cooling time. Also, we have determined dissolution rates of UO2 fuel as a function of alpha and gamma dose rates from our electrochemical measurements. These room-temperature rates are used to calculate the dissolution rates of used fuel at 100°C, the highest temperature expected in a container in the CNFWMP, as a function of time since emplacement. It is shown that beta radiolysis of water will be the main cause of oxidation of used CANDU fuel in a failed container. The use of a kinetic or an electrochemical corrosion model, to calculate fuel dissolution rates, is required for a period of ∼ 1000 a following emplacement of copper containers in the geologic disposal vault envisaged in the CNFWMP. Beyond this time period a thermodynamically-based model adequately predicts the fuel dissolution rates. The results presented in this paper can be adopted to calculate used fuel dissolution rates for other used UO2 fuels in other waste management programs.
Influence of Temperature on Hydraulic Conductivity in Compacted Bentonite
Authors: Cho W. J. , Lee J. O. , Chun K. S. 
Published: April 2011

ABSTRACTThe hydraulic conductivities in water saturated bentonites at different densities were measured within temperature range of 20 to 80 °C. The results show that the hydraulic conductivities increase with increasing temperature. The hydraulic conductivities of bentonites at the temperature of 80 °C increase up to about 3 times as high as those at 20 °C. The measured values are in good agreement with those predicted. The change in viscosity of water with temperature contributes greatly to increase of hydraulic conductivity.
Simulation of Transport of Uranium (VI) Species Through the Bed of Bentonite
Authors: Ştamberg K. , Vopálka D. , Škrkal J. , Beneš P. , Chalupská K. 
Published: April 2011

ABSTRACTThe transport of six U(VI) species, HCO31−and CO32−, through the bentonite bed was modelled as diffusion in pore water combined with sorption/desorption on the surface of bentonite particles. The studied system consisted of the Czech commercial sodium bentonite SABENYL and synthetic granitic water spiked with233U(VI), where equilibrium distribution of233U was experimentally determined at first. The transport was simulated by means of eight dynamic, 1 D- partial differential equations while the equilibrium sorption/desorption was assumed. Three types of surface complexation models, namely the Constant Capacitance Model (CCM), Diffuse Double Layer Model (DLM) and the so-called Chemical Equilibrium Model (CEM), were used for the description of sorption/desorption interaction processes. The characteristic parameters of the individual models were obtained from evaluation of experimental data. The results of the simulation were expressed as path-length dependent concentrations of total U(VI), total carbonates and of individual migration species, as path-length dependent pH and uraniumKd, values at a given time and as time dependent concentrations of the total U(VI) at a given migration distance. It has been found that the transport of U(VI) through the bentonite bed is significantly influenced first of all by the value of pH and by total carbonates concentration. The important length dependent changes of the pH andKdvalues were determined.
Coprecipitation of Ni With Calcite: An Experimental Study
Authors: Carlsson T. , Aalto H. 
Published: April 2011

ABSTRACTAt the Finnish candidate sites for a nuclear waste repository calcite (CaCO3) is a common fracture mineral, that may participate in coprecipitation processes. The objective of this work was to study the coprecipitation of the trace element Ni with CaCO3 under controlled conditions. The experiments were carried out at 30 °C in vessels closed to the atmosphere. Calcite-saturated 0.05 M NaCI solutions containing trace amounts of Ni2+ were contacted with calcite for periods of up to 42 days. The experimental data indicate that Ni coprecipitates with calcite as a result of recrystallization. The amounts of coprecipitated Ni and recrystallized calcite were determined using liquid scintillation counting and the isotopes 63Ni and 45Ca. The results are supported by a complementary SEM/EDS analysis of the solid phase.
Gas Flow Through Water-Saturated Shear Zones: Field and Laboratory Experiments and Their Interpretation
Authors: Marschall P. , Croisé J. , Fischer U. , Senger R. , Wyss E. 
Published: April 2011

ABSTRACTGas threshold pressure tests and gas tracer tests have been performed at the Grimsel Test Site to study two-phase flow processes in a shear zone. In addition, capillary pressure and gas permeability measurements were carried out in the laboratory on drillcore samples. The laboratory investigations were complemented by assessing the pore structure of the shear zone material. The interpretation of the field tests with numerical models indicated that the structural and two-phase flow parameters to be determined are highly correlated with one another and, consequently, the parameter estimates can be rather uncertain. The joint interpretation of field and laboratory results, however, led to a more stringent description of the two-phase flow processes, expressed by a better overall fit of the test data and smaller uncertainty ranges of the estimated parameters. The results showed that the gas mobility in the shear zone was very high even at high water saturation and gas flow was limited to the narrow zones of brittle deformation along the shear zone.
PHOTO- AND DARK CURRENT NOISE IN a-Si:H PIN DIODES AT FORWARD AND REVERSE BIAS
Authors: Blecher F. , Seibel K. , Bohm M. 
Published: April 2011

ABSTRACTThe noise spectra of hydrogenated amorphous silicon pin diodes are measured in the dark and under illumination at reverse and forward bias. The noise coefficients of 1/f noise at different operating points are determined. The superposition of the different noise mechanisms is investigated. A new empirical model and a method to calculate the noise in pin diodes is suggested. Transport and noise mechanisms are discussed.
Refinement of Plas Samples by Using Afm Image and First Observation of Plas Signals on Amorphous Carbon Nitridea-CNx Films
Authors: Furukawa H. , Nitta S. , Hioki M. , Iwasaki T. , Itoh T. , Nonomura S. 
Published: April 2011

ABSTRACTThe shape of several waveguide end of samples for photoluminescence absorption spectroscopy (PLAS) was studied by atomic force microscope (AFM), because there was an experimental problem where some samples for PLAS did not work. Using the result of AFM, the waveguide end was reshaped by plasma dry etching. The shortening of the etching time was an effective method to improve the structure of the waveguide end. Secondly, the PLAS method was extended to the other materials from a-Si:H. The PLAS signal of amorphous carbon nitride a-CNx was detected for the first time. Amorphous carbon nitride a-CNx film itself and the interface between a-CNx and a-Si02 are found as good as a-Si:H and the interface between a-Si:H and a-Si 3N4+x:H, respectively.
Longitudinal Vibrational Absorption Modes of Hydrogenated Amorphous Silicon Nitride Thin Films
Authors: Li Tong , Kanicki Jerzy 
Published: April 2011

ABSTRACTWe have identified longitudinal and transverse optical modes of Si-N bond in vibrational absorption spectrum of hydrogenated amorphous silicon nitride thin films. The locations of longitudinal optical resonances coincide with transverse mode of Si-O and closely neighbor bending modes of N-H, Si-H2 bond. Furthermore, the conventionally assigned asymmetric and symmetric stretching modes of Si-N bond are merely transverse modes of Si-N bond. Features of pure longitudinal vibrational modes can be revealed by subtracting appropriately scaled transverse mode components from the vibrational absorption spectrum. Analysis of the longitudinal spectrum indicates that, in addition to their association with Si-N bond, the density of the peak located at about 1215 cm−1 is also well correlated to hydrogen and nitride content in the film, while the density of the peak located at about 880 cm−1 is closed related to silicon density in the film. Peak located at about 1040 cm−1 is the longitudinal mode associated with Si-N bond.
Light-Induced Degradation Effects in a-Si:H Observed by Raman Scattering Measurements
Authors: Stradins P. , Kondo M. , Hata N. , Matsuda A. 
Published: April 2011

ABSTRACTWe have attempted to observe changes in the Raman scattering spectrum of a-Si:H due to light exposure. We do not find any detectable shift of the position or change in the width of the TO phonon peak. We find, however, other unexpected degradation phenomena in the Raman spectrum of a-Si:H samples which are attributed to light induced changes in the high energy tail of room temperature luminescence. Raman scattering has a relatively large (10-20% of TO peak height) broad background which extends to 2000cm−1 in the Stokes region and tails into the anti-Stokes region. Multiple phonon processes, geminate radiative recombination and surface oxide contributions are considered. Degradation phenomena and the broad background signal are observed in a-Si:H deposited on different substrates as well as in free-standing films. Degradation processes in bare fused quartz substrates are also investigated. Small structural changes surrounding the light-induced defects are proposed and discussed.
Reduction of Neutral Dangling Bond Density by Light Soaking in Nanocrystalline Silicon
Authors: Matsumoto Takahiro , Masumoto Yasuaki , Kondo Michio 
Published: April 2011

ABSTRACTThe effects of light exposure on neutral defect density at the surface of nanocrystalline Si are investigated by electron-spin resonance (ESR) experiments. A decrease of the neutral dangling bond density by light soaking was observed in this nanostructure. The reduction rate of ESR signal intensity becomes large with increasing light exposure intensity, and the reduction occurs from the excitation energy higher than 2 eV in vacuum. The reduction of the defect density can be explained in terms of the conversion of neutral states to charged states by carrier trapping.
Chimney-Shaped and Plateau-Shaped Gate Electrode Field Emission Arrays
Authors: Tarntair F. G. , Wang C. C. , Hong W.K. , Huang H. K. , Cheng H. C. 
Published: April 2011

AbstractA triode structure of chimney-shaped field emitter arrays is proposed in this article. This triode structure includes the chimney-shaped emitter, thermal oxidation dioxide, and the plateau-shaped singlecrystalline silicon gate electrode. For the application of the matrix-addressable and large area flat panel display, the uniform structure of the emitters and the yield become critical manufacturing issues when attempting to control nano-meter size features. The uniformity and yield of the chimney-shaped emitters are very well controlled. The nano-sized gate-to-emitter separations can be created by the changing thickness of the insulator. The uniformity of the insulator and emitter material can be controlled within 3% which can be obtained by most large area thin film deposition tools, not by photolithography.
Characterization of Tetrahedrally Bonded Amorphous Carbon Via Capacitance Techniques
Authors: Palinginis Kimon C. , Ilie A. , Kleinsorge B. , Milne W.I. , Cohen J. D. 
Published: April 2011

AbstractWe report the results of junction capacitance measurements on thin tetrahedral amorphous carbon (ta-C) films to deduce their defect densities. We find defect densities in the range 3 - 7 × 1017 cm−3 in the undoped ta-C films, and roughly an order of magnitude larger in the nitrogen doped (n-type) films. In some cases fairly uniform defect profiles were obtained covering a thickness of a couple of hundreds angstroems. We also observed a thermal activation process of carriers from defect states at the ta-C/c-Si interface with an activation energy in the range of 0.4eV to 0.5eV.
Optical Birefringence to Determine Morphological Changes in Low-K Thin Film CVD Polymers
Authors: Senkevich Jay J. , Simkovic Viktor , Desu Seshu B. 
Published: April 2011

ABSTRACTA great interest exists to reduce power consumption, cross-talk, and RC-delay in ULSI devices by replacing SiO2(k=3.9−4.3) with a polymeric material (k<3.0). Unlike SiO2, polymeric thin films exhibit a complex morphology which varies with the polymer's thermal history, deposition temperature, and film thickness. Since the morphology of the polymer thin film ultimately affects its properties such as its dielectric constant, methods need to be developed to understand the morphological changes in polymer thin films. Further, the polymer thin films must exhibit a high thermal stability due to the relatively high back-end-of-line (BEOL) processing temperature. The polymers which exhibit high thermal stability often contain a mainchain benzene ring. Since benzene has a high anisotropic molecular polarizability, optical birefringence can be used to monitor the polymer chain conformation as a function of the polymer's thermal history, thickness or deposition conditions. Poly(p-xylylene) and poly(tetraflouro-p-xylylene) are shown to have a large negative birefringence, increasing until polymer decomposition. Poly(p-xylylene) becomes increasingly more negatively birefringent after a crystallographic phase change at 220°C. A high negative birefringence results in a large in-plane capacitance, negatively impacting the polymers potential benefit. owever, poly(chlorop-xylylene) and poly(dichloro-p-xylylene) exhibit positive birefringence, which increases until their crystalline melting points at ∼290°C and ∼380°C and thereafter decreases due to film disruption. Conclusions will be drawn based on this positive birefringence for the future molecular design of CVD polymers to decrease their in-plane dielectric constant. Urther poly(chloro-p-xylylene) and poly(p-xylylene) are investigated as a function of deposition temperature and film thickness.
Comparative Study Of Gan Movpe Growth Processes Using Two Different “Surface Preparation-Carrier Gas” Combinations
Authors: Vennegues P. , Haffouz S. , Bouille A. , Leroux M. , Beaumont B. 
Published: April 2011

ABSTRACTThe growth modes and resulting microstructures of GaN films grown by Metalorganic Vapor Phase Epitaxy (MOVPE) on (0001) sapphire with either a simple nitridation of the surface and N2 as carrier gas or with a treatment of the nitridated surface under silane and ammonia with a mixture of H2 and N2 as carrier gas have been investigated. The second process results in a three dimensional first stage of the growth before a coalescence of the islands and the smoothing of the surface. Using this growth process, the defects density can be decreased down to 3.108 cm−2. This reduction in defect density has a drastic effect on photoluminescence properties of the material, and the luminescence efficiency can be increased by a factor of 20. It is also observed that the strain of this material is much higher as compared with material grown with the first process.
Influence of C, N and O Ion-Implantation on Yellow Luminescence
Authors: Zhang R. , Zhang L. , Perkins N. , Kuech T. F. 
Published: April 2011

ABSTRACTInfluence of C, N and O ion-implantation on the yellow luminescence (YL) of halide vapor phase epitaxy (HVPE) and metal-organic vapor phase epitaxy (MOVPE) grown GaN has been studied by photoluminescence (PL) spectroscopy. For the HVPE-grown samples, only C implantation produces a significant enhancement of YL while its corresponding overall PL integrated intensity is only ˜72% of its original value. Implantation of O or N do not appreciably change the YL but decrease the BE integrated intensities by a factor of ten. The full-width-halfmaximum (FWHM) of the BE band expanded to about 1.4 × of the original value in all three cases. These results indicate that one source of the YL is strongly correlated to incorporation of C into the GaN film. The C-induced defect complexes in GaN are optically active while O or N does not lead to any new luminescence features. The variable-temperature PL measurements on the C-implanted HVPE-grown GaN reveal that the FWHM of the YL band increases linearly and the peak energy of the YL changes very little with the increasing measurement temperature, while the integrated intensity of the YL band decreases monotonically. This trend of the YL FWHM and peak energy with the measurement temperature can be explained by a two-channel transition model. For MOVPE-grown GaN films., all ion-implanted samples exhibit a significant loss of both the YL and overall integrated PL intensity. Residual C contamination in the MOVPE samples could be large compared to the additional ion-implanted carbon leading to a reduced impact of the ion-implanted carbon.
Polar Optical Phonon Instability and Intervalley Transfer in Gallium Nitride
Authors: Foutz B. E. , O'leary S. K. , Shur M. S. , Eastman L. F. , Gelmont B. L. , Stroscio M. 
Published: April 2011

ABSTRACTWe develop a simple, one-dimensional, analytical model, which describes electron transport in gallium nitride. We focus on the polar optical phonon scattering mechanism, as this is the dominant energy loss mechanism at room temperature. Equating the power gained from the field with that lost through scattering, we demonstrate that beyond a critical electric field, 114 kV/cm at T = 300 K, the power gained from the field exceeds that lost due to polar optical phonon scattering. This polar optical phonon instability leads to a dramatic increase in the electron energy, this being responsible for the onset of intervalley transitions. The predictions of our analytical model are compared with those of Monte Carlo simulations, and are found to be in satisfactory agreement.