bluuebunny/crossref_metadata_2025 huggingface dataset:
MoirÉ Pattern Studies of Thin Layers Deposited on (001)Si Substrates: Cases of Tisi2 and GaAs.
Authors: Rocher A. , Wallart X. , Charasse M.N.
Published: March 2011

Moiré pattern images have been used to investigate the crystalline quality of thin films deposited on (100)Si substrates. Observations performed on TiSi2 show a three-dimensional growth process and two different epitaxial modes. In the case of GaAs epilayers, it is shown that the residual strains are not uniformly distributed in the layer. Residual strain and threading dislocations are related to imperfections of the misfit dislocation network.
Spin Relaxation Spectroscopy of the D-Center in Hydrogenated Amorphous Silicon
Authors: Zafar Sufi , Schiff E. A.
Published: March 2011

Measurements of the dependence of the D-center electron paramagnetic resonance absorption signal upon the incident microwave power are reported in undoped hydrogenated amorphous silicon (a-Si:H) for specimens prepared at differing deposition temperatures and also as the state of a given specimen was varied by illumination and subsequent annealing. These measurements are sensitive to electron spin relaxation processes of the D-center. Substantial variation in spin-relaxation behavior was found, corresponding to approximately one order of magnitude in the spin relaxation rate; no significant variations in absorption lineshape were observed. A model for these spin relaxation observations invoking two differing local microstructures near the D-center is proposed. The model indicates that illumination increases the density of defects in one microstructure but can irreversibly diminish the density in a second.
Thermal Equilibrium Defects in Hydrogenated Amorphous Silicon Based Alloy Films
Authors: Xu Xixiang , Morimoto Akiharu , Kumeda Minoru , Shimizu Tatsuo
Published: March 2011

Both the temperature dependence at elevated temperature and the increase after fast cooling from elevated temperature of the density of dangling bonds are measured by ESR for undoped hydrogenated amorphous silicon–based alloy films, a–Si:H, a–Si1−xCx:H, a–Si1−xNx:H and a–Si1−xOx:H. Both a–Si:H and a–Si1−xCx:H clearly show the increase in the density of dangling bonds at elevated temperature, while the increase is less prominent for a–Si1−xNx:H and a–Si1−xOx:H. The observed results for both a–Si:H and a–Si1−xCx:H are fairly well reproduced by the model recently proposed by Smith et al. The results of CPM measurements combined with those of ESR measurements suggest that the density of charged dangling bonds present in undoped a–Si:H also increases after fast cooling from elevated temperature.
Distribution of Gap States in Highly Photosensitive a-SiC:H
Authors: Akita S. , Nakayama Y. , Yamano M. , Kawamura T.
Published: March 2011

The effect of carbon incorporation into a-Si:H has been investigated in terms of gap states. The shallow and deep states are measured by a combination of two methods of the time-of-flight and the depletion discharge transient spectroscopy. The results show that the carbon incorporation of 10Z into a-Si:H leads to a slight increase in the conduction-band tail states and an extention of the deep states distribution. However, the increase in the shallow states affects little change in the electron transport properties. The origin of the deep states is also discussed.
Low Temperature Characteristics of Hydrogenated Amorphous Silicon Field Effect Transistors
Authors: Bae Byung-Seong , Cho Deok-Ho , Lee Jae-Hee , Lee Choochon , Jang Jin
Published: March 2011

We investigated the temperature dependent characteristics of hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFT's) at temperatures down to 20 K. With decreasing temperature, the threshold voltage increased, the field effect mobility and the on-current decreased. The measured on-currents versus inverse temperature above 80 K are represented as the sum of two exponentially varied currents. It is concluded that on-current is nearest-neighbour hopping between 120 K and 80 K. Below this temperature, the temperature dependence of on-current is explained by variable range hopping and below about 30 K on-current becomes nearly independent of temperature. At very low temperature hopping probability may be governed not by temperature but by temperature independent tunneling, depending on the overlap of the wave function. The explanation of threshold voltage increase at low temperature is given.
From the Understanding of the Reaction Mechanism Towards Optimizing the Deposition Rate and Optoelectronic Properties of a-Si:H
Authors: Veprek S. , Heintze M. , Bayer R. , Jurčik-Rajman N.
Published: March 2011

We present new results of kinetic studies of the deposition of high quality a-Si:H which strongly support the reaction mechanism suggested in our earlier papers: 1. SiH4 → SiH2; 2. SiH2 + SiS4 → Si2H6 (SiH2 + Si2H6 → Si3H6); 3. Si2H6 → 2a-Si:H (Si3H8 → 3a-Si:H). The “SiH3 mechanism”, as promoted by several workers, is in contradiction with these experimental facts.

The di- and trisilane, which have a much higher reactive sticking coefficient than monosilane, play the role of reactive intermediates which facilitate the heterogeneous decomposition of silicon carrying species at the surface of the growing film. The values of the reactive sticking coefficient of Si2H6 and Si3H8 depend on the surface coverage by chemisorbed hydrogen; they increase with decreasing surface coverage. Under the conditions of the growth of high quality a-Si:H films the reactive sticking coefficient of disilane amounts to 10−4 to 10−2 which is in a good agreement with recent data of other authors.

The rate determining step of the growth of high quality a-Si:H films is the desorption of hydrogen from the surface of the growing film. This can be strongly enhanced by ion bombardment at impact energy of <100 eV. In this way, homogeneous, good quality films were deposited at rates up to 1800 Angströms/min, and there is a well justified hope that this rate can be further increased.
Comments on Electron and Hole Transport in the Band Tail States of Amorphous Silicon at Low Temperatures
Authors: Silver M. , Spear W. E.
Published: March 2011

Recent experimental results on the low temperature drift mobility in amorphous silicon are examined on the basis of the approach to hopping transport developed by Silver and Bässler. It is shown on general grounds that the main features of the experimental results cannot be explained by a purely exponential tail state distribution, but are consistent with the distribution used by Spear and Cloude (1988) in model calculations.
Optical Bias Enhanced Transient Photoconductivity in a-Si:H
Authors: Chen Xing , Tai Chen-Yu
Published: March 2011

Optical bias enhancement in transient photocurrent, by a factor of more than 10, is observed in a-Si:H films. The transient photocurrent is found to decay exponentially shortly after the light pulse is turned off. The exponential decay constant of the transient current is found to be proportional to (optical bias level)−0.38 at room temperature. A theory based on the multiple trapping model is developed to explain the experimental result. This effect is applied to study the density of state of the sample as well as the process of charge recombination.
Current-Voltage Characteristics-What Do Experiments Really Tell Us?
Authors: Shapiro Finley R. , Silver Marvin
Published: March 2011

Experimentally measured current-voltage measurements in amorphous silicon hydride pin diodes have been fit to computer simulations by Hack and den Boer [1] using relatively small values for the neutral and charged trap capture rates. Silver and Cannella [2] have proposed larger values for the capture rates, accompanied by larger electron and hole band mobilities. We discuss here the possible reasons for expecting the larger values for the capture rates, and their influence on current voltage measurements both with and without the higher mobilities. It is found that the simulated I-V results using only the larger capture rates are much smaller than those for Hack and den Boer's parameters. However, when the large values are used for both the capture rates and the mobilities, the I-V relationship is quite similar to that for the smaller capture rates and mobilities. We also show the differences in the simulated transient currents for the different sets of parameters, and we discuss the causes of these differences.
High-Quality A-Si Films Prepared by the Direct Photo-Cvd Method
Authors: Nakano S. , Wakisaka K. , Kameda M. , Isomura M. , Matsuyama T. , Nakamura N. , Tsuda S. , Ohnishi M. , Kuwano Y.
Published: March 2011

A high-efficiency integrated-type a-Si solar cell submodule with a size of 10cm × 10cm has been fabricated and a total area efficiency of 9.6% is obtained by using a high-quality p-layer doped with B(CH3)3 We have developed an advanced direct photo-CVD method. High-quallt” a-SI films with low tail characteristic energy and low light-induced degradation is prepared by this method. We have also studied the role of Si-H2 bonds on the light-induced effect. The result implies that Si-H bonds stabilize the defect states, resulting in a large light-induced degradation.
Preparation and Evaluation of p-Type Materials for a-Si Solar Cells Using DC Plasma Discharge Deposition of Trimethylboron (B(CH3)3)
Authors: Fieselmann Benjamin F. , Goldstein B.
Published: March 2011

Amorphous SiC p-layers doped with trimethylboron (B(CH3) 3) were prepared with optical and electrical properties superior to those prepared with B2H6. Devices were prepared with efficiencies as high as 11.4% using trimethyl boron. The improved properties of B(CH3)3-doped a-SiC result from the fact that trimethylboron is a more effective doping agent than B2H6 and produces p-layers with a higher bandgap.
Cpm Measurenents on a-Si:H Based Pin Solar Cells: Thickness and Bias Voltage Effects
Authors: Rübel H. , Gorn M. , Scheppat B. , Geyer R. , Lechner P. , Kniffler N.
Published: March 2011

We use measurements of subbandgap photocurrent spectra on films, barrier structures and pin cells of different thicknesses to estimate the valence band tailing and to characterize the dangling bond defect region. Large differences in signal sizes in the structures are observed and particularly for thick and thin pin-diodes, the dependence of the signal on voltage bias is discussed. In pin-diodes, these effects can be explained by a change of defect occupation in the i-layer.
Raman Spectroscopy of a.SiGe:H Alloys
Authors: Yang L. , Newton J. , Fieselmann B.
Published: March 2011

Raman spectroscopy is used to characterize the microscopic bonding structure of a-SiGe:H alloys. Excess Ge-Ge bonding over what is predicted for random alloys is observed. Correlation between the degree of Ge-Ge clustering and the transport properties of the alloys is demonstrated. Implications of the experimental findings regarding improvement in the quality of the alloy material are discussed.
Photoluminescence of Amorphous Hydrogenated Carbon Films, a-C:H
Authors: Vassilyev V. A. , Volkov A. S. , Musabekov E. , Terukov E. I. , Chelnokov V. E. , Chernyshov S. V.
Published: March 2011

Results are presented on the photoluminescence of plasma deposited amorphous carbon (a-C:H) films. Emission and exci tation spectra anti-Stokes emission, PL decay and fatigue, T-dependence of PL and photobleaching were mesuared. The data are discussed in terms of radiative recombination of the strongly localized electron-hole pairs.

As recently shown, in amorphous hydrogenated carbon films (a-C:H) powerful talls of localized states occur in the mobility gap that are due to a high degree of structural disorder [1] while a radiative recombination in this material is highly efficient [2, 3]. These properties, in our view, make a-C:H suitable for verification of models of recombination kinetics of photoexcited charge carriers in highly disordered systems with the use of photoluminescence (PL).
Proton and Neutron Damage in Thick Amorphous Silicon Diodes
Authors: Hollingsworth R. E. , Xi J. , Madan A. , Cecil F. E.
Published: March 2011

Thin film amorphous silicon diodes are being examined as a possible high energy particle detector for use in the superconducting super collider. One of the key requirements for any such detector is the ability to withstand relatively high doses of high energy particles without degradation of performance. We report here results of degradation studies of amorphous silicon p-i-n diodes to protons and neutrons with energies in excess of 100 keV.
Raman Studies of a-Si:H/a-SiNx and a-Si/a-SiNx Superlattices
Authors: Honma I. , Tanaka T. , Komiyama H. , Tanaka K.
Published: March 2011

First observation is reported of the deposition rate dependence of Raman-detected structural disorder in a-Si:H/a-SiNx semiconductor superlattices as well as a-Si/a-SiNx ones. FWHM of TO-like Raman peak of a-Si:H in the multilayer structure rapidly decreases as deposition rate decreases, while that of a- Si decreases more slowly. The results demonstrate that the structural disorder of a-Si:H/a-SiNx decreases as time to grow a monolayer (TGM) increases in a time range of a second, and also suggest that hydrogen covering the growing surface enhances the structural-relaxation velocity of disordered amorphous network.
Dissolution and Reaction studies of Cszr2(PO4)3 and Zr Phosphates in Aqueous Media
Authors: Vance E.R. , Ahmad J.
Published: March 2011

Cs dissolution kinetics for Cszr2(PO4)3 in a variety of aqueous media at 70°C approximately obeyed a first-order law. However in 0.1 M NaHCO3,at1/2 law was appropriate. The Cs extraction was a minimum under neutral conditions. In the pH range of 1–4, the Cs extraction varied approximately as [H+]0.3 and was a stronger function of pH in alkaline media.
The survival of α-Zr phosphate gel in water at 300°C was essentially confirmed. ZrP2O7, reacted sluggishly with water at 200–300°C to produce an apparently fully-protonated analogue of NaZr2(PO4)3
Theory of Corrosion of Alkali-Borosilicate Glass
Authors: Clark David E. , Hench Larry L.
Published: March 2011

The alkali-borosilicate (ABS) system provides the basis for a wide variety of commercially important products among which are the nuclear waste glasses. Although a large number of investigations have been undertaken in the last five years, the corrosion mechanisms of the ABS glasses have not been characterized nearly as well as for the soda-lime-silicate (NCS) glasses commonly used for containers. It is well known that the corrosion of the latter glasses involves ion exchange, network dissolution, and precipitation mechanisms resulting in the development of one of five types of surface films. In the present paper we compare the corrosion behavior to the ABS and NCS glasses and discuss our current understanding of ABS glass corrosion in terms of mechanisms, kinetics, surface film formation and thermodynamics.
Effects of Solution Chemistry and Atmosphere on Leaching of Alkali Borosilicate Glass
Authors: Hermansson Hans-Peter , Christensen Hilbert , Clark David E. , Werme Lars
Published: March 2011

The leaching behavior of two alkali-borosilicate glasses containing 9 wt% simulated fission products and 1.6 wt% uranium oxide has been studied. Samples were exposed to one of eight types of leachants including doubly distilled water, simulated ground silicate water, a brine solution, and solutions containing various concentrations of iron, aluminium or sodium maintained at either 25°C, 40°C or 90°C for up to 182 days. The most aggressive leachants were the solutions containing sodium (excluding brine) and simulated ground silicate water. These solutions increased the extent of leaching by a factor of 2–3 over that for distilled water for one of the glasses. A partially protective surface film rich in magnesium potassium and chlorine was formed on the glasses exposed to the brine solution.

In order to evaluate the effects of atmosphere on leaching, samples were also immersed in doubly distilled water over which the relative concentrations of oxygen, nitrogen and carbon dioxide were varied. Increasing the carbon dioxide concentration from 0 to 50% resulted in a factor of 3 increase in the leaching rate.
The Buffering Mechanisms in Leaching of Composites of Cement with Radioactive Waste
Authors: Barnes Mary W. , Roy Della M.
Published: March 2011

Composites of cement and radioactive waste are being used for disposal of low level waste and may be used for high level waste. It is important to be able to predict their behavior in case of intrusion of leaching waters. The purpose of this paper is to determine the mechanisms of leaching of the cement and how the presence of radioactive waste components affects these mechanisms in composites.
Extended Leach Studies of Actinide-Doped SRL 131 Glass
Authors: Bates John K. , Lam Daniel J. , Steindler Martin J.
Published: March 2011

The effects on the leachability of SRL 131 glass as a result of slight changes in the glass composition were monitored by leachate and surface analyses. The compositional changes had marked effects on solution and layer composition and on the precipitated alteration products that formed after 546 days of static leaching. The leaching behavior of long-lived actinide elements were measured, with Pu and Am showing little tendency to become solubilized and Np and U continuously accumulating in solution.
Long-Term Radioactivity Release from Solidified High-Level Waste - Part II Parametric Study of Waste form Properties, Temperature and Time
Authors: Altenhein Friedrich K. , Lutze Werner , Ewing Rodney C.
Published: March 2011

The computer code QTERM has been used to calculate the total released activity from a single glass block when in contact with brine in a salt dome repository as a function of: (1) waste form properties, (2) leaching mechanisms, (3) retention or precipitation of specific radionuclides in surface layers, (4) thermal history of the repository and (5) decreasing activity as a function of time.
Natural Analogues—A Way to Increase Confidence in Predictions of Long-Term Performance of Radioactive Waste Disposal
Authors: Birchard G. F. , Alexander D. H.
Published: March 2011

No exact analogue to a radioactive waste disposal system exists but by studying natural analogues of the most important components or subsystems of a waste repository, confidence in long-term predictions can be increased. The U.S. Nuclear Regulatory Commission (NRC) is supporting research on igneous intrusions into proposed repository-type host rock (basalt, tuff, crystalline hard-rock, and salt), on uranium ore body analogues, on actinide solubility as a function of natural complexing agents in closed basin lakes and on field migration of radionuclide species at low-level waste and uranium mill tailings disposal sites. The NRC is studying analogues to ensure that important parameters which might be overlooked in laboratory tests and in modeling because of problems with scaling time, space and geologic complexity can be identified and their importance bounded.
Nuclear Waste Management in France
Authors: Lefevre J. , Sugier A.
Published: March 2011

On October 6, and 7 1982, after a two-day Parliamentary Debate, the continuation of the French nuclear power program was approved. Installed nuclear capacities, should reach 56000 elMN by 1990, i.e. 28% of energy supplies.

The nuclear waste volumes entailed by such a nuclear electricity program, with the accompanying fuel cycle operations and the other nuclear waste producing activities, are the following: Low and Medium Level waste volumes should reach 800,000 cubic meters by the year 2000 - slightly less than was planned for two years ago, because of reduced power consumption, and therefore capacities forecasts. Alpha-bearing and vitrified Wastes should reach respectively 45,000 cubic meters and 3,000 cubic meters by the year 2000.

These waste quantities now make it urgent to set up a wholly comprehensive industrial scale program for their treatment, conditioning and final disposal, together with the relevant research and development activities.
United Kingdom Regulatory Procedures for Radioactive Wastes
Authors: Feates F S , Richards H J
Published: March 2011

In the United Kingdom the responsibility for radioactive waste management policy lies with the environmental Ministers. The Department of the Environment is also responsible in England for authorisation of all radioactive waste disposal activities and has its own Radiochemical Inspectorate to ensure that government policy is implemented. An independent Radioactive Waste Management Advisory Committee reports directly to the Secretary of State for the Environment.

Low-level wastes are currently disposed of by shallow burial or to the deep ocean. Sites for the disposal of intermediate-level wastes are being sought as a matter of urgency and heat-emitting, reprocessing wastes will be stored on the surface for at least fifty years. The rationale of this policy is explained.
A Review of the Current Status of Radiation Effects in Solid Nuclear Waste Forms
Authors: Weber William J.
Published: March 2011

The current status of radiation effects in solid nuclear waste forms is reviewed. The general nature of radiation effects and the simulation techniques used are briefly discussed. Recently reported data on radiation effects are presented and discussed, and those areas requiring further theoretical or experimental study are identified.
Radiolysis of Groundwater from HLW Stored in Copper Canisters
Authors: Christensen Hilbert , Bjergbakke Erling
Published: March 2011

A large number of computer calculations of the radiolysis of ground water outside copper canisters have been carried out within the Swedish Nuclear Fuel safety Project.

At dose rates higher than 5 × 10−2rad/s the hydrggen concentration is constant, approximately 10−3mol/dm3, and independent of time and dose rate. Therefore the rate of difiusion out of the system is constant, approximately 7 × 10−4mol/year. At dose rates lower than 5 × 10−4rad/s the logarithm of the hydrogen production is proportional to the logarithm of the dose rate. The hydrogen production depends on fuel type, burn-up and canister thickness only to the extent that the dose rate varies with these parameters. The hydrogen production is independent of the volume of water in which the energy is assumed to be absorbed (5 or 15 cm layers outside the surface of the canister).

The hydrogen production depends on the concentration of Fe2+ions in the water. In the basic calculations the concentration was assumed to be 5 ppm. An increase to 50 ppm increases the total hydrogen production after one million years outside a 1 cm thick canister from 360 to 1000 mol. A decrease to 0.5 ppm decreases the same yield to 80 mol.
Irradiation Effects in the Storage and Disposal of Radioactive Ion-Exchange Resins
Authors: Swyler Karl J. , Dodge Cleveland E. , Dayal Ramesh , Weiss Allen J.
Published: March 2011

Research is under way to characterize the effects of self-irradiation on radwastes which may be generated when organic ion-exchange media are used in water demineralization or decontamination operations at nuclear facilities. External factors affecting the relation between laboratory evaluations and field performance are emphasized. Initial experiments do not yet indicate substantial radiation dose-rate effects on radiolytic gas yields or acid product formation, when (fully swollen) sulfonic acid resins are irradiated in a sealed air environment. At the same time, oxygen gas is removed from the environment of irradiated resins. Interaction between mild steel coupons and acidic species produced in the irradiation induced decomposition of sulfonic acid resin results in irradiation enhanced corrosion. Corrosion rates depend on radiation dose rate, moisture content and resin chemical loading. In some cases, corrosion rates decrease with time, suggesting depletion of acidic species within the resin bed, or a synergistic interaction between resin and corrosion coupon. Implications of these and other results on evaluating field behavior of radwaste containing ion-exchange media are discussed.
Toward a Comprehensive Model of Chemical Transport in Porous Media
Authors: Miller Constance W.
Published: March 2011

A chemical transport model, CHEMTRN, that includes advection, dispersion/diffusion, complexation, sorption, precipitation or dissolution of solids, and the dissociation of water has been written. The transport, mass action and site constraint equations are written in a differential/algebraic form and solved simultaneously. The sorption process is modelled by either ion-exchange or surface complexation. The model has been used to investigate the applicability of a kD model for simulating the transport of chemical species in groundwater systems, to simulate precipitation/dissolution of minerals, and to consider the effect of surface complexation on sorption.
Compliance Assessments of Hypothetical Geological Nuclear Waste Isolation Systems with the Draft Epa Standard
Authors: Siegel M. D. , Chu M. S. , Pepping R. E.
Published: March 2011

Estimates of potential radionuclide releases from HLW storage facilities in geologic formations are an integral part of the technical basis for the regulation of nuclear waste disposal. We have attempted to assess the importance of the variation of several variables and model assumptions to the calculation of radionuclide discharge from hypothetical repositories. The conceptual models of the repository sites are consistent with our current understanding of the characteristics of the geologic environments being studied by the Department of Energy. It must be stressed that we have not attempted to accurately model any real sites; at the present time, the available data are not sufficient for this purpose. Large uncertainties exist in the characterization of the solubilities and sorption of radionuclides, in the description of the regional and local hydrogeology and in the mathematical treatment of contaminant transport in the presence of fracture flow and matrix diffusion. The fraction of waste that could be accessed by breaching the repository, the effects of mixing processes within the facility and the probability of human intrusion are not known. We have completed preliminary calculations of potential radionuclide discharges from hypothetical repositories in tuff and bedded salt [1,2]. Our theoretical approach and computational methods are illustrated in this paper with examples for a repository in volcanic tuff. We also briefly discuss the importance of radionuclide source term assumptions to the calculations for a bedded salt repository.
Long-Term Thermomechanical and Thermohydrological Factors Controlling the Optimal Design of a Nuclear Waste Repository
Authors: Wang J. S. Y. , Mangold D. C. , Tsang C. F.
Published: March 2011

Surface uplift and buoyancy flow are two of the major long-term, far-field perturbations to the geologic formations around a nuclear waste repository. The allowable surface uplift has been accepted in the literature as a criterion limiting the repository waste loading density. It has also been recognized in generic modeling studies that the buoyancy distortion of the ambient groundwater flow around a repository is a major mechanism for radionuclide transport. However, the buoyancy considerations have yet to be quantified for the purpose of optimal design of a radioactive waste repository. We suggest the possibility of using the buoyancy gradient when compared with the ambient regional (horizontal) gradient as a measurable thermohydrologic factor that controls the design of waste loading. This study indicates that the buoyancy gradient could in some cases become the main controlling factor. To decrease the buoyancy effects, much lower values of waste loading density should be considered in the design of the waste repository.
Ceramization of Inorganic Ion Exchangers Loaded with Nuclear-Waste into Red Clay Tiles
Authors: Lehto Jukka , Heinonen Olli J. , Miettinen Jorma K.
Published: March 2011

A new method to ceramize inorganic ion exchangers loaded with nuclear waste has been developed. It is simpler and cheaper than methods used previously, e.g. hot pressing. The inorganic ion exchangers, sodium titanate and ZrO2, were turned into final ceramic waste form by mixing them with a Finnish red clay in weight ratio 1:4 at maximum. The tiles moulded frKm the wet, bakeable mixture were ceramized at 1020–1060°C. The leach rates of Sr, Cs and Co from the tiles determind by a 7 dynam c ISO-test were after six months of leaching 10−6−10−7 g/cm2/d, in decreasing order. Mechanically the tiles are very durable: flexural strengths were in the range of 20–45 meganewtons per square meter.
Geophysical Modeling of a Low-Level Nuclear Waste Disposal Site
Authors: Horton Keith A. , Isaacson Louis , Morey Rexford M.
Published: March 2011

Geophysical measurements can, depending on the techniques employed, be used at low-level nuclear waste disposal sites to map the subsurface stratigraphy, identify interfaces, locate objects and targets, and aid in selecting locations for obtaining sample cores and placing monitoring wells. The geophysical techniques of ground penetrating radar and electrical resistivity have been applied in a complementary manner at nuclear waste disposal sites. The data obtained from the field surveys have been integrated in developing geophysical models of these sites.

A two-layer electromagnetic geologic model has been developed that allows the prediction of radar attenuation and depth of penetration. Field tests conducted at a lowlevel nuclear waste disposal site show values consistent with the model.
Formulation and Durability of Tailored Cenentitious Hosts Applied to TRU Waste Generated at the Rocky Flats Plant
Authors: Kessler J. H. , Rogers G. C. , Dole L. R. , Morgan M. T.
Published: March 2011

At Oak Ridge National Laboratory, we have developed cementitious grout formulations which can incorporate up to 50 wt % of a transuranic (TRU) waste generated during startup operations at the Rocky Flats Plant Building 374, Golden, Colorado. Trial grout mixes were tested in order to minimize the water content and maximize the waste loading. The effects of water reducers and set regulators on these mixes were also examined.

Durability and physical property measurements were performed on formulations containing 40 wt % waste, which are compatible with standard processing equipment. The densities, porosities, and compressive strengths of these solids are reported. Compressive strengths of the samples were found to increase by as much as 69% after the sample had been exposed to leachants for 28 d at 900 C.
Alteration of Nuclear Waste Glass by Hydration
Authors: Bates John K. , Steindler Martin J.
Published: March 2011

Aging of simulated nuclear waste glass by contact with a humid atmosphere results in the formation of a double hydration layer penetrating into the glass and in the formation of alteration products on the glass surface. This hydration process has been studied as a function of time, temperature, glass composition and water vapor pressure. A dual stage hydration rate was observed and rate constants were determined at each temperature. An Arrhenius plot for the initial stage alteration rate indicates the reaction mechanism does not change between the temperature limits of the experiment (120-240°C). This conclusion is supported by the sequence of mineral formation on the surface. This hydration process provides a means of accelerating aging reactions while simulating conditions that may exist in a nuclear waste repository.
Determination of Crystal Site Occupancy in an Improved Synroc-D Ceramic using Analytical Electron Microscopy
Authors: Tafto J. , Clarke D. R. , Spence J. C. H.
Published: March 2011

The rate of radiation damage from radioactive species in nuclear waste ceramics and the long term stability of the crystalline phases may depend on the crystallographic site of the emitting species. It is therefore of importance to determine the site occupancy of the radioactive elements. Hitherto, no established crystallographic technique has been suitable for such studies due to the small grain size and the many different phases in nuclear waste ceramics, such as Synroc. By taking advantage of the fact that an electron beam can be focussed, and the electron intensity localized, to a particular crystal site by electron diffraction, a new technique capable of locating small concentrations of atoms in small crystal volumes >(10 nm)3 has recently been developed. The application of the technique to determining the site occupancy of solutes, including U, Sr, Th, in the perovskite and ulvo-spinel phases of a Synroc ceramic is described. In the perovskite phase, U, Th, Sr, Zr and Mn, are shown to substitute on the Ca site with Fe partitioning between the Ca and Ti sites.
Diamond-Like Films Obtained by Sputtering from a Glassy Carbon Target
Authors: Niemann E. , Herkert R. , Leidich D.
Published: March 2011

Diamond-like a-C:H films were obtained by reactive dc-magnetron sputtering from a glassy carbon target in an argon-hydrogen atmosphere. To our knowledge, this is the first time that glassy carbon is used as target material. The a-C:H films are transparent and hard. The a-C:H films can be used as protection and antireflection coatings on a-Si:H photoreceptors. The electrical, optical and structural properties of the a-C:H films are examined.
Determination of the Energy Gap in Photoconducting Insulators Through Current Noise Measuremen
Authors: Carbone A. , Demichelis F. , Mazzetti P.
Published: March 2011

Measurements of the current noise power spectrum of the photoconducting insulators CdS and CdSe irradiated with monochromatic light of different wavelength A are reported.

It is shown that there is an abrupt change of about one order of magnitude in the low frequency power density of the noise when A crosses the photoconductor gap value Ag and the photocurrent and the device conductance are kept constant by varying the light intensity.

The effect is explained in terms of an abrupt increase of the carrier recombination rate when the photon energy becomes larger than the energy gap of the photoconductor. Possible applications of these results are briefly discussed.
Measurement of the Electro-Optic Coefficient for Gallium Arsenide and Cadmium Telluride Modulator Rods
Authors: Herrit Gary L , Reedy Herman E.
Published: March 2011

Cadmium telluride and gallium arsenide remain the only viable materials for electro-optic modulator applications in the 10 μm wavelength range. Primarily the modulators are used as Q switches, cavity dumpers, amplitude modulators, and frequency modulators for infrared applications, such as laser radar and guidance systems. Designers of optical and electrical systems incorporating these modulators require accurate values for the electro-optic coefficient, r41.

A test arrangement, based on a modified version of the cross polarizer technique, was used to measure the electro-optic coefficients for cadmium telluride and gallium arsenide single crystals. The first part of this paper describes our test arrangement for measuring the r41 coefficient. The second part of the paper will discuss the test results. The r41 coefficient for CdTe was found to be 5.5 × 10−12 m/V in the unclamped region and 4.1 × 10−12 m/V in the clamped reion. Values for the r41 coefficient in GaAs were found to be 1.3 × 10−12 m/V and 1.9 × 10−12 m/V in the unclamped and clamped regions, respectively. All measurements were at 10.6 μm. Also investigated are the piezoelectric resonance values for both materials and the effect the resonances have on the measured r41 coefficient in the clamped and unclamped regions.
Diamondlike Carbon as a Moisture Barrier and Antireflecting Coating on Optical Materialst
Authors: Woollam John A. , De Bhola N , Chen L. Y. , Pouch John J. , Alterovitz Samuel A.
Published: March 2011

Introduction

Diamondlike carbon (DLC) is amorphous, hard, semitransparent, and is under consideration for use as a coating material for infrared optics DLC is also designated as a-C:H to indicate its amorphous nature as well as to indicate the presence of large (20 to 55 percent) amounts of hydrogen in the film.
Characterization of Ti:LiNbo3 Optical Channel Waveguides Fabricated using Rapid Thermal Annealing
Authors: Ramabadran Uma , Brabander Gregory N. De , Boyd Joseph T. , Jackson Howard E. , Sriram S.
Published: March 2011

Rapid thermal annealing has been used to initiate diffusion of Ti in LiNbO3 for the fabrication of optical waveguides. The sample with the most rapid initial ramp of temperature to 875 C was found to have the lowest propagation loss of 1 dB/cm. In order to more fully understand these channel waveguides, we have utilized Raman microprobe spectroscopy. Preliminary results suggest that the presence of the Ti in the LiNbO3 lattice dramatically alters the Raman response.
A few Problem in the Vapor Deposition of Diamond
Authors: Setaka Nobuo
Published: March 2011

Recently, there is considerable interest in semiconductor diamond films prepared by vapor deposition. The fact originates from their unique properties and potential for the devices operating at high temperature and high power. What diamond films were feasible by vapor deposition, provide the driving force for developing diamond for advanced electronic devices. However, there exist many large barriers. Their presence tends to de-press futher progress in the investigation and industrialization.

The purpose of this paper is to point out the problems actually encountered in developing it and to describe its future direction on the basis of my present understanding.
Moisture and Plastic Package Stability
Authors: Kinsman K.R. , Jahsman W.E. , Sundahl R.C.
Published: March 2011

Polymers used to encapsulate microelectronic devices absorb moisture – it's their nature. But only recently, with the growing use of surface mount technologies, has this phenomenon fostered concern much beyond the traditional chemical (corrosion) issues. The mechanical stability of plastic encapsulated components in use is now affected by moisture and its complex relation to interfacial adhesion and stress distributions within the package under different environmental (test) conditions. Strategies to defend against moisture-associated problems involve control of the application environment (removing moisture), improving package structural designs (increasing robustness), and managing materials choice to reduce moisture sensitivity. Each strategy has limitations, both physical and practical (economic), and all currently are being pursued. This paper will review the technical challenges, with particular emphasis on the state of affairs with regard to material development and application.
Low Dielectric, Hydrophobic Polyimide Homopolymers and Poly(Siloxane Imide) Segmented Copolymers for Electronic Applications
Authors: Arnold C. A. , Chen Y. P. , Chen D. H. , Rogers M. E. , McGrath J. E.
Published: March 2011

Polyimides generally possess excellent thermal and mechanical properties, making them attractive candidates for high performance applications. To be useful for microelectronic applications, however, these materials must also be good insulators, as well as be readily processable.

The incorporation of flexible polysiloxane segments into the polyimide backbone structure has been shown to yield soluble, processable copolyimides with good thermal and mechanical properties. In addition, the siloxane component imparts a number of other significant benefits for electronic applications. These include reduced water sorption, surface modification, good thermal and ultraviolet stability, and resistance to degradation in oxygen plasma environments. For polar polyimide systems, siloxane incorporation will also reduce the dielectric constant. The use of other less polar, more hydrophobic monomers will consistently yield soluble systems with lower dielectric constants as well.

In this work, a series of high molecular weight, soluble polyimide homopolymers and segmented polysiloxane-polyimide copolymers were synthesized by a solution technique. The solution procedure, conducted at lower temperatures (˜170°C) than the classical bulk thermal imidization (300°C), has been shown to yield polyimides of enhanced solubility. In order to further enhance processability, molecular weight was controlled through the incorporation of monofunctional reagents such as phthalic anhydride and maleic anhydride, yielding nonreactive or potentially reactive endgroups, respectively. A series of maleic anhydride terminated imide oligomers with varying molecular weights were synthesized based upon the hexafluoropropane linked dianhydride and bisaniline diamine. In their oligomeric state, they exhibited enhanced solubility compared with their linear high molecular weight analogue. As these monomers were relatively nonpolar and hydrophobic, they afforded polyimides of low dielectric constant and a low level of water sorption. After thermally crosslinking the endgroups, the advantages of insoluble network systems could be realized. Particular advantages for electronic applications include thermal and dimensional stability over a wide temperature range, good mechanical properties, and chemical resistance. Structure-property characterization, including water sorption, dielectric constants, solubility behavior and thermal/mechanical properties will be reported.
Acetylene-Terminated Polyimide Composites for Advanced Electronic Packaging Applications
Authors: Ibrahim A. Mahammad
Published: March 2011

Surface mount technology (SMT) is an electronic packaging technology wherein the leads of electronic components are soldered directly to metallized pads on the surface of a printed circuit board (PCB). The SMT with leadless ceramic chip carriers (LCCCs) is used to design, fabricate, and assemble affordable, high-speed, high-density electronic modules with reduced size and weight and improved electrical performance. In surface mount devices, the LCCCs are soldered directly onto the fabric composite PCB substrate. New high-performance composite substrate materials must be developed to take full advantage of SMT. Fabricating a PCB that will perform reliably throughout its intended life is also an increasingly important requirement, especially if the goal is to satisfy the high reliability required in military applications. Consequently, SMT is driving the development of PCB substrate materials with improved thermal and electrical properties. In our continuing effort to meet these military demands, we evaluated high-temperature resistant/high-performance acetylene-terminated polyimide composites for use in SMT PCBs. This paper focusses on the processing and on the thermal, thermomechanical, and dynamic mechanical properties data developed for these acetylene-terminated polyimide composites for their potential evaluation as PCBs. The characterization includes such properties as in-plane coefficient of thermal expansion (CTE), out-of-plane CTE, and glass transition temperature (Tg), which determine the solder joint reliability, plated-through-hole (PTH) reliability, and dimensional stability.
FTIR and XPS Studies of Polyimide/Metal Interface Formation
Authors: Stewart William C. , Leu Jihperng , Jensen Klavs F.
Published: March 2011

We describe infrared and x-ray photoelectron spectroscopy studies of the interfaces formed when the PMDA/ODA polyamic acid is imidized on gold, chromium, and copper. Polyimide films ranging from 34 Å to 1328 Å are analyzed as part of these studies. The IR and XPS results indicate that the gold interacts very little with the polyimide, while copper produces significant changes in the IR and XPS spectra. At elevated cure temperatures passivated chromium also reacts with the polyimide. In structures with chromium and copper, the thermal stability of the polyimide at the interface is reduced from that of bulk polyimide. The data demonstrate that the metals interact with the polymer structure at the point where ring closure occurs to form the polyimide from polyarnic acid.
Control of Thin Film Materials Properties Used in High Density Multichip Interconnect
Authors: Rechell J.J.H.
Published: March 2011

Most literature on High Density Multichip Interconnect (HDMI) focuses almost exclusively on processing of the organic dielectric. Nevertheless, it is only one of the components in High Density Multichip Modules.

Substrate properties, metal dielectric adhesion, internal stresses in the various films, and many other physico-chemical properties of the materials, can all be affected by neighbouring layers or process parameters improperly identified. Thus, in the course of process development, the real causes of difficulties and observed phenomenas can easily be misconstrued.

This paper reviews some of the relationships between the properties of the thin film metallization and their effects on the dielectric layers. It also points out to some of the difficulties that can occur when treating the dielectric and the metallic layers as separate issues.
Investigations into the use of Adhesives For Level-1 Microelectronic Interconnections
Authors: Hogerton Peter B. , Hall J. B. , Pujol J. M. , Reylek R. S.
Published: March 2011

In relation to other surface mounting methods for bare integrated circuits, Flipped Direct Chip Attachment (FDCA) provides the most compact level-1 interconnection. High performance adhesives represent an interesting alternative to solders and conductive pastes, which are now being used for FDCA interconnections. These materials may provide the ability to achieve higher interconnection density on a larger chip and at the same time provide encapsulation of the active face of the chip. They may also provide simpler and cleaner manufacturing processes, resulting in lower installed costs.

The purpose of this paper is to describe recent findings that are relevant to the question of whether FDCA with adhesives is a viable concept. Experimental results are reported that provide a description of the characteristics of pressure engaged interconnections that were obtained using a proprietary structural adhesive system. In addition, results of a thermomechanical modeling study are reported that provide estimates of the thermal stress distribution in an FDCA adhesive bond.
Protective Coating of Integrated Circuits for Operation in Corrosive Environments
Authors: Charlson E.J. , Sabeti R. , Charlson E. M. , Yasuda H. K.
Published: March 2011

This paper describes the development of a technique for protecting non-hermetically packaged integrated circuits for use inside the human body. A two layer combination consisting of a thin adhesion-promoting primer of plasma polymerized methane covered with a thicker layer of Parylene®-C has been found to provide excellent protection during long term exposure to simulated body fluids under continuous DC bias. The process for synthesizing the two layer combination in continuous vacuum is described. Results from adhesion and electrical testing of passive test structures are given. A new technique for the formation of small openings in thick polymer coatings for neural stimulation and sensing sites of implantable sensors is described. The technique uses biased thin film resistors formed on the passivation layer to provide localized heated areas which prevent polymer deposition during synthesis.
Gravimetric Measurements of Moisture Uptake in Polyimide Films Used in Integrated Circuit Packaging
Authors: Denton Denice D. , Pranjoto Hartono
Published: March 2011

Polyimide is used extensively in a variety of integrated circuit packaging applications. It is a good dielectric material with excellent planarizing capabilities, but like most polymers, it absorbs moisture. This hygroscopic behavior can lead to reliability problems in integrated circuit packages. The effects of variations in process history on moisture uptake are examined using gravimetric measurement techniques. In particular, the effects of cure schedule and exposure to high temperature/high humidity environments on steady state moisture uptake are reported. Steady state moisture uptake is shown to be a decreasing function of cure temperature. Moreover, the steady state moisture uptake in polyimide is greater after the samples have been “aged” in a high temperature and humidity ambient. Electrical measurements are used to examine the effects of cure temperature on diffusion kinetics of moisture in polyimide. The diffusion coefficient decreases with increasing cure temperature.