bluuebunny/crossref_metadata_2025 huggingface dataset:
Results from Simulated Remote-Handled Transuranic Waste Experiments at the Waste Isolation Pilot Plant (WIPP)
Authors: Molecke Martin A.
Published: March 2011

Multi-year, simulated remote-handled transuranic waste (RH TRU, nonradioactive) experiments are being conducted underground in the Waste Isolation Pilot Plant (WIPP) facility. These experiments involve the near-reference (thermal and geometrical) testing of eight full-size RH TRU test containers emplaced into horizontal, unlined rock salt boreholes. Half of the test emplacements are partially filled with bentonite/silica-sand backfill material. All test containers were electrically heated at about 115 W/each for three years, then raised to about 300 W/each for the remaining time. Each test borehole was instrumented with a selection of remote-reading thermocouples, pressure gages, borehole vertical-closure gages, and vertical and horizontal borehole-diameter closure gages. Each test emplacements was also periodically opened for visual inspections of brine intrusions and any interactions with waste package materials, materials sampling, manual closure measurements, and observations of borehole changes. Effects of heat on borehole closure rates and near-field materials (metals, backfill, rock salt, and intruding brine) interactions were closely monitored as a function of time. This paper summarizes results for the first five years of in situ test operation with supporting instrumentation and laboratory data and interpretations. Some details of RH TRU waste package materials, designs, and assorted underground test observations are also discussed. Based on the results, the tested RH TRU waste packages, materials, and emplacement geometry in unlined salt boreholes appear to be quite adequate for initial WIPP repository-phase operations.
Modelling in-situ Matrix Diffusion at Palmottu Natural Analogue Study Site in SW Finland.
Authors: Rasilainen Karl , Suksi Juhani
Published: March 2011

Radioactive disequilibria, between U-238, U-234, and Th-230, in crystalline rock adjacent to a fracture, indicates mass transfer of U and Th between water in the fracture and the rock. The matrix diffusion theory was used to interpret the observed profiles of mobilized nuclides around the natural fracture. The interpretation of the profiles was based on the use of uranium series disequilibrium code, URSE, and migration code FTRANS. The model system was characterized using all available site-specific data, and the system evolution was outlined using the geology of the Palmottu site. The simulated concentration profiles, as a function of depth from the fracture surface, indicate that measured profiles can be modelled by matrix diffusion, assuming realistic initial and boundary conditions and diffusion times of 300,000 years.
Surface-Discharging Hydrothermal Systems at Yucca Mountain – Examining the Evidence
Authors: Levy SchÖn S.
Published: March 2011

Exposures of altered rock that have been thought to form by recent discharge of water from depth were examined to address a concern that hydrothermal processes could compromise the isolation capability of a potential high-level nuclear waste repository at Yucca Mountain. The suspected hot-spring and hydrothermal-vent deposits are more likely the products of infiltration of meteoric water into newly deposited and still-hot pyroclastic flows >12 Myr ago.
Corrosion Model Validation in High Level Nuclear Waste Package Research
Authors: Mcneil M. B. , Moody J.B.
Published: March 2011

The strategies for waste package (WP) performance validation will be based on site specific geologic and hydrogeochemical information plus models which can be used to predict potential WP lifetimes. The development and application of such models will include the evaluation of natural analogues (NA). These analogues are needed to resolve issues related to the validation of models. Natural analogues have not had extensive use or widespread acceptance in the area of waste package failure prediction. This lack of acceptance is due to the anticipated choice of alloys for waste package containers. Few of these alloys are similar to naturally occurring metals, and the proposed HLW repositories are in general in geologic settings not very similar to those in which naturally occurring metals are generally found.

Natural and archaeological analogues can be used, however, in analysis of possible waste package failures as a means of testing proposed models for failure. In fact, the analogues are the only available mechanisms for testing models of long-term waste package behavior. A strategy is outlined for incorporating natural and archaeological analogue studies into waste package research, and examples are discussed. The natural/archaeological analogues approach which appears most promising is to use archaeological and mineral samples to develop an understanding of the identities and rates of the mineral alteration reactions at or near the surface of the package, improving present capability for estmating the lifetimes of metallic waste package containers.
Increases in Leach Rate due to Possible Cracking in Silicate Glasses
Authors: Sang J.C. , Barkatt A. , Talmy I.G. , Norr M.K.
Published: March 2011

Comparative studies of two multi-component silicate glasses have confirmed the observation that glasses with a relatively low SiO2 + AlO3/2 content may exhibit temporary increases in leach rate during the initial stages of their exposure to water. SEM studies of the leached glass surfaces strongly support the assumption that this phenomenon is due to cracking of the leached glass and a consequent increase of the exposed surface area.
A Justification for the Use of Data from Accelerated Leach Tests of Glass
Authors: Ahn Tae M. , Interrante Charles G. , Weller Richard A.
Published: March 2011

A case is made for the use of short-term laboratory data in making predictions on the likelihood of significant colloid formation in supersaturated leachates of glass, under long-term repository conditions, using “accelerated tests” with a large ratio of the surface area of the glass to the leachate volume. In the repository conditions in which colloids can form, long-term leaching may be a kinetically-controlled process that involves the continuous formation of colloids. If this kinetic process dominates, it could lead to a significant increase in the predicted rates of radionuclide release. The question is whether or not colloids may form after prolonged times; the delayed formation would make it difficult to use short-term laboratory test results to represent (or predict) the long-term and cumulative effects of radionuclides. In this work, the pertinent long-term kinetic processes are identified in part. Classical nucleation theory for particle formation, as a potential condensation mechanism for colloid formation, is applied to explain pertinent experimental data on colloid formation. The classical theory, which is justified for this discussion, indicates that as supersaturation of a leachate is decreased, the nucleation rate decreases most significantly, while the incubation time increases at a small rate. As a result of this decreased nucleation rate, the significance of colloids tends to vanish, and usefulness of data from “accelerated“ laboratory tests may be applicable to long-term behavior.
Long-Term Predictions Relating to Environment Sensitive Cracking.
Authors: Parkins R. N.
Published: March 2011

Consideration is given to the environmental requirements of environment sensitive cracking (ESC) of ferritic steels, involving hydrogen-induced or dissolution-related mechanisms of cracking. Pitting, with associated local pH changes, may result in hydrogeninduced cracking of simple ferritic steels, as has been observed with high pressure gas pipelines in contact with ground waters, and may constitute a greater potential failure mechanism for waste containers than dissolution-related cracking with its requirement of relatively concentrated solutions. However, the stochastic nature of pit initiation, together with the distributions of crack nucleation and growth rates, suggest that a probabilistic, as opposed to a purely deterministic, approach will need to be applied to life prediction estimates for waste containers.
Experiments and Modelling Studies Concerning Localised Corrosion of Carbon Steel and Stainless Steel Containers for Intermediate- and Low-Level Radioactive Waste
Authors: Hoch A.R. , Naish C.C. , Sharland S.M. , Smith A.C. , Taylor K.J.
Published: March 2011

Current plans for disposal of low- and intermediate-level radioactive wastes (LLW and ILW) in the UK include enclosing much of the waste in carbon steel or stainless steel containers. Modelling and experimental studies that aim to characterise the period and extent of the localised corrosion in these containers are described. The period, during which localised corrosion can be initiated and sustained in the post-closure phase of the repository is estimated. The likely modes of localised corrosion are identified, based on further consideration of the environmental conditions to which the metals are exposed. Detailed research in progress includes investigation of the rate of pitting corrosion for carbon steel, and the possible occurrence of crevice corrosion of stainless steel.
Thermodynamic Modelling of the Effect of Hydroxycarboxylic Acids on the Solubility of Plutonium at High pH
Authors: Moreton Anthony D
Published: March 2011

A number of the hydroxycarboxylic acids generated by the alkaline degradation of cellulosic wastes under reducing conditions in a cementitious repository can significantly increase the solubility of the actinides at high pH, especially plutonium. The solubility of plutonium at pH 12, in the presence of a range of hydroxycarboxylic acids containing a number of hydroxyl groups and between one and three carboxylate groups, has been modelled using the HARPHRQ code. All the plutonium-organic complexes assumed in the model are based on a stable unit in which a central plutonium ion is bound by four oxygen atoms. The oxygen atoms can be provided either by a deprotonated hydroxyl group on one of the ligands, or by hydroxide ions.
A Comparative Study of Europium, Thorium and Uranium Binding to an Aquatic Fulvic Acid
Authors: NordÉn M. , Albinsson Y. , Ephraim J.H. , Allard B.
Published: March 2011

Advances in safe management and disposal of radioactive waste have shown that a comprehensive program requires the incorporation of dissolved organics into radwaste and transport effluent models, with respect to their binding of radionuclides. The binding of Eu3+, Th4+and UO22+to a well-characterized aquatic fulvic acid has been studied using an ultrafiltration method at a bulk electrolyte concentration of 0.10 M NaClO4, trace amounts of radionuclides and fulvic acid concentrations of 60 and 120 mg/l. The results expressed as the overall complex formation function, βov, versus pH show the following order: Th4+> Eu3+> UO22+. The estimated βov, values have been discussed by considering the aqueous chemistry of Eu3+, Th4+and UO22+vis-à-vis the solution chemistry of the fulvic acid sample.
The Role of Siderophores in the Transport of Radionuclides
Authors: Hersman Larry E. , Palmer Philip D. , Hobart David E.
Published: March 2011

Iron exists in aerobic soil and water environments most commonly as insoluble Fe(III). Siderophores are powerful, microbially produced chelating agents that are used to mobilize the insoluble Fe(III) cation. Over 80 siderophores have been isolated and characterized, with some reportedly having iron-binding constants as high as 1052. Fe(III) and Pu(IV) are similar in their charge/ionic radius ratio (4.6 and 4.2, respectively); therefore, Pu(IV) may serve as analog to Fe(III). It is possible that some radioactive wastes could be chelated by naturally occurring siderophores, thereby altering the transport rates of those elements through the subsurface environment. This investigation wn 9 initiated to investigate that possibility. The binding of239Pu(IV) by four chelating agents is reported in this paper: a siderophore isolated and purified from aPseudomonassp.; desferal, a ferrioxamine siderophore commonly used for deferration therapy; EDTA, ethylenediaminetetraacetic acid; and, citrate, trisodium salt.
Transport of Neptunium Through Yucca Mountain Tuffs
Authors: Triay I. R. , Robinson B. A. , Mitchell A. J. , Overly C. M. , Lopez R. M.
Published: March 2011

Neptunium has a high solubility in groundwaters from Yucca Mountain [1]. Uranium in nuclear reactors produces 237Np which has a half-life of 2.14 × 106 years. Consequently, the transport of 237Np through tuffs is of major importance in assessing the performance of a high-level nuclear waste repository at Yucca Mountain. The objective of this work is to determine the amount of Np retardation that is provided by the minerals in Yucca Mountain tuffs as a function of groundwater chemistry.
Colloid Properties in Granitic Groundwater Systems, with Emphasis on the Impact on Safety Assessment of a Radioactive Waste Repository
Authors: Degueldre C.
Published: March 2011

Since colloids are present in all groundwaters, they are studied because of their potential role in the migration of relevant radionuclides in the geosphere. Colloid sampling and characterization campaigns have been carried out in the Grimsel area, Switzerland (Transitgas tunnel, Grimsel Test Site) and in the North Switzerland/Black Forest area (Menzenschwand, Bad Sickingen, Zurzach, Leuggem). On the basis of results obtained for 25 groundwaters a consistent picture is emerging. Colloids in granitic systems are basically composed of components of the aquifer materials (clay, silica). Under the hydrogeochemical conditions existing at depth in crystalline rock systems, colloid concentrations are not expected to exceed 100 ppb. However, under transient conditions when physical and/or chemical changes are occuring (e.g., hydrothermal activity), colloid generation may be enhanced. Colloid concentration of 10 ppm may be observed when the calcium concentration is low enough (<5 ppm).

Whereas reversible sorption on the host rock leads to conservative predictions for radionuclide migration rates, the reverse is true for sorption onto colloids. The most conservative assumptions are therefore reversible nuclide sorption and colloid attachment on the rock and irreversible sorption on colloids.

For calcium concentrations larger than 5 ppm, and sorption capacities at the nM level, their presence in granitic aquifer can be neglected in safety analyses when reversible sorption onto colloids is considered. This situation could change when sorption is followed by aggregation or incrustation processes. This study shows that for the colloid conservative size distributions found and for the granitic water conducting fissures considered, sorption-agglomeration reactions are unlikely to take place. Therefore, irreversible sorption by this mecanism is improbable.
Is it Possible to Demonstrate Compliance with the Regulations for High-Level-Waste Repositories?
Authors: Bingham Felton W.
Published: March 2011

The regulations that currently govern repositories for spent fuel and high-level waste require demonstrations that are sometimes described as impossible to make. To make them will require an understanding of the current and the future phenomena at repository sites; it will also require credible estimates of the probabilities that the phenomena will occur in the distant future. Experts in many fields—earth sciences, statistics, numerical modeling, and the law—have questioned whether any amount of data collection can allow modelers to meet these requirements with enough confidence to satisfy the regulators. In recent years some performance assessments have begun to shed light on this question because they use results of actual site investigations. Although these studies do not settle the question definitively, a review of a recent totalsystem assessment suggests that compliance may be possible to demonstrate. The review also suggests, however, that the demonstration can be only at the “reasonable” levels of assurance mentioned, but not defined, in the regulations.
Iterative Performance Assessment for the Greater Confinement Disposal Facilities: Preliminary Results of Round Two
Authors: Olague Natalie E. , Baer T.A. , Conrad S.H.
Published: March 2011

The Department of Energy's Nevada Operations Office has disposed of a small quantity of transuranic waste at the Greater Confinement Disposal (GCD) facility in Area 5 of the Nevada Test Site. The Environmental Protection Agency standards for disposal of transuranic waste (40 CFR 191) require that a performance assessment be conducted and an iterative approach has been adopted. This approach consists of using performance assessment results to guide the collection of site characterization data, and in turn, new site characterization data is incorporated into each successive iteration of the performance assessment. The results of the first iteration indicated that the GCD site should be able to comply with 40 CFR 191. This paper presents results of the second iteration based on results from site-specific environmental tracer studies. These studies indicate significantly lower recharge values then those used in the first performance assessment iteration. For performance assessment these results imply that the downward ground-water advection pathway may be negligible, and therefore, the upward liquid diffusion pathway becomes more significant. The models and the model parameters that were used to simulate this upward pathway have been refined. The preliminary results from these models still indicate that the GCD facility should be able to comply with the Containment Requirements in 40 CFR 191.
The Use of Formal and Informal Expert Judgments When Interpreting Data for Performance Assessments
Authors: Rechard Rob P. , Trauth Kathleen M. , Rath Jonathan S. , Guzowski Robert V. , Hora Stephen C. , Tierney Martin S.
Published: March 2011

This paper discusses the general process by which data and information are compiled and used for defining modeling parameters. These modeling parameters are input for the mathematical models that are used in performance assessments of the Waste Isolation Pilot Plant (WIPP), near Carlsbad, NM, which is designed to safely manage, store, and dispose of transuranic radioactive wastes. The physical and temporal scales, and the difficulty of obtaining measurements in geologic media make interpretation of measured data, including the difference between laboratory experiment scale and repository scale, important tasks. In most instances, standard scientific practices can ensure consistency of data use. To illustrate this point, an example is provided of the interpretation of field measurements of intrinsic permeability for use in computational models using the bootstrap technique. In some cases, sufficient information can never be collected, interpretation of the information is controversial, or information from diverse disciplines must be used. A procedure that formalizes the standard scientific practices under these conditions has been developed. An example is provided of how this procedure has been applied in eliciting expert judgments on markers to deter inadvertant human intrusion into the WIPP.
Molecular Dynamics Simulations of Shock-Defect Interactions in Two-Dimensional Nonreactive Crystals
Authors: Sinkovits Robert S. , Phillips Lee , Oran Elaine S. , Boris Jay P.
Published: March 2011

The interactions of shocks with defects in two-dimensional square and hexagonal lattices of particles interacting through Lennard-Jones potentials are studied using molecular dynamics. In perfect lattices at zero temperature, shocks directed along one of the principal axes propagate through the crystal causing no permanent disruption. Vacancies, interstitials, and to a lesser degree, massive defects are all effective at converting directed shock motion into thermalized two-dimensional motion. Measures of lattice disruption quantitatively describe the effects of the different defects. The square lattice is unstable at nonzero temperatures, as shown by its tendency upon impact to reorganize into the lower-energy hexagonal state. This transition also occurs in the disordered region associated with the shock-defect interaction. The hexagonal lattice can be made arbitrarily stable even for shock-vacancy interactions through appropriate choice of potential parameters. In reactive crystals, these defect sites may be responsible for the onset of detonation. All calculations are performed using a program optimized for the massively parallel Connection Machine.
Delayed Initiation in a Model Energetic Material
Authors: Robertson D. H. , Brenner D. W. , White C. T.
Published: March 2011

We present a simulation studying the initiation of a model energetic molecular solid. For low-velocity, massive flyer-plate impact, the model detonation initiates behind a compaction shock. This detonation front subsequently overtakes the compaction shock exhibiting a behavior qualitatively similar to that observed in experminental studies of homogeneous initiation and delayed detonation from low velocity impact.
Growth and Defects of Explosives Crystals
Authors: Cady Howard H.
Published: March 2011

Large single crystals of PETN, RDX, and TNT can be grown easily from evaporating ethyl acetate solutions. The crystals all share a similar type of defect that may not be commonly recognized. The defect generates conical faces, ideally mosaic crystals, and may account for the “polymorphs” of TNT and detonator grades of PETN.

TATB crystals manufactured by the amination of trichlorotrinitrobenzene in dry toluene entrain two forms of ammonium chloride. One of these forms causes “worm holes” in the TATB crystals that may be the reason for its unusually low failure diameter.

Strained HMX crystals form mechanical twins that can spontaneously revert back to theuntwinned form when the straining force is removed. Large strains or temperatures above 100°C lock in the mechanical twins.
Experimental Study and Model Calculations of Metal Combustion in Al/Ap Underwater Explosives
Authors: Miller Philip J. , Guirguis Raafat H.
Published: March 2011

A small-scale laboratory experiment in which the detonation products are confined was designed such as to yield for small charges (as little as 1/2 gram) gas expansion rates comparable to those due to the underwater detonation of large-scale charges. The resulting slow expansion allows the aluminum and the other non-ideal components typically used in underwater explosives to react to completion within the time frame of the experiment. Both ideal and non-ideal aluminized explosives were tested. The traditional Jones-Wilkins-Lee (JWL) equation of state reproduced the measurements in the case of the ideal explosives. An extended JWL equation of state in which the time-dependent late energy release is introduced was adjusted until it reproduced the measurements of the non-ideal explosive tested. This derived time-dependent equation of state also reproduced the data of large-scale cylinder tests and underwater detonations using the same non-ideal explosive.
Detonation Studies in Dispersed Solid Particulate Explosives Using High Speed Time-Resolved Holography
Authors: Ehrlich Michael J. , Wagner James W. , Friedman Jacob , Egghart Heinrich
Published: March 2011

Introduction

Clouds of dispersed explosive or combustible solid particles are detonable and such systems may exhibit self-sustained detonation [1–8]. However, the method by which individual particles in the explosive cloud interact to sustain detonation is not well understood. The similar case of liquid fuel/air explosives was investigated in detail during the 1960's and 1970's. For these systems, it was established that incident shock waves serve to shatter large liquid droplets into a mist of micro-droplets. These microdroplets are almost instantaneously accelerated to the convective flow velocity behind the shock wave. The energy released upon ignition of the micromist supports the shock wave and selfsustained detonation results [9–11].
Combustion Synthesis of Composite Materials
Authors: Moore J. J.
Published: March 2011

This paper discusses the of application of combustion synthesis of ceramic and ceramic-metal composites. Several model exothermic combustion synthesis reactions are being used to investigate the effect of reaction parameters, eg. stoichiometry, green density, combustion environment and mode, particle size, physical properties of reactants and products, on the stability and control of the synthesis reaction, product morphology and properties and performance.
Energy Transfer Dynamics and Impact Sensitivity
Authors: Fried Laurence E. , Ruggiero Anthony J.
Published: March 2011

In this paper we focus on the relation between impact sensitivity and energy transfer rates. When a crystal receives an impact, low frequency lattice vibrations (called phonons) are excited. Typical phonon frequencies are 0-200 cm-1. This energy must then be converted to vibron frequencies (1000–2000 cm-1) before bond breaking can occur. We derive a simple formula for the energy transfer rate in terms of the density of vibrational states and the vibron-phonon coupling. We are able to estimate the phonon upconversion rate in widely varying energetic materials such as TATB, HMX, and Pb styphnate by examining existing inelastic neutron scattering data. We find that the estimated energy transfer rates in pure unreacted material are strongly correlated with impact sensitivity.
Time Lag Diffusion Method for a Solid Propellant Emitting Gases
Authors: Baird James K. , Chen Jenn-Shing
Published: March 2011

In the ordinary application of the time-lag method to the measurement of the diffusion coefficient of a gas passing through a plane sheet of an inert solid, the gas is pressurized on one side of the sheet and evacuated on the other. After decay of transients, the cumulative amount, Q(t), of gas diffused through the sheet in time, t, assumes the “time-lag” form, Q(t) = A(t - L). Measurements of the slope, A, and the intercept, L, can be used to determine the diffusion coefficient and the solubility of the gas in the solid. We have rederived this law for the case of a solid which is actively evolving this same gas at an arbitrary rate and have used it to predict the rate of outgasing of the solid upon standing. Practical applications of the theory include radioactive decay of minerals, rejection of plasticizers by plastics, and the decomposition of solid rocket propellants.
Shocked Energetic Molecular Materials: Chemical Reaction Initiation and Hot Spot Formation
Authors: Fayer M. D. , Tokmakoff Andrei , Dlott Dana D.
Published: March 2011

A theoretical model is developed to describe multiphonon up-pumping of internal vibrations. The dominant mechanism for up-pumping is anharmonic coupling of excited phonon modes with low frequency molecular vibrations, termed doorway modes. Quantitative calculations were performed which show the extent and rate of multiphonon up-pumping caused by shock excitation. The time dependence of chemical reactivity behind the front is calculated using reaction rate laws for the decomposition of nitramine explosives. A mechanism for hot spot formation, based on defect induced local increases in anharmonic coupling, is discussed.
Relationship Between Radiation Stability and Molecular Structure of Nitramine Explosives
Authors: Pinto James J.
Published: March 2011

The radiation stabilities of the nitramine explosives 1,4-dinitroglycolurile (DINGU), 1,4-dimethyl-2,5-dinitroglycolurile (DMD) and hexanitrohexaazaisowurtzitane (HNIW) have been determined using XPS. Samples were exposed to x-rays for times up to eight hours while photoelectron spectra were recorded in the carbon, oxygen, and nitrogen Is energy regions and mass spectra were recorded of gases evolved during the decomposition process. These data are compared to the previously determined stabilities for cyclotrimethylene trinitramine (RDX) and cyclotetramethylene tetranitramine (HlMX). The N1s spectra of the irradiated materials show the NO2 peak decreases relative to the total nitrogen signal while low binding energy peaks grow. The rate of loss of the NO2 peak was fit to first order kinetics and the rate constants obtained show some correlation with the N-N bond strength as measured by the average N-N bond distance and the average NO2 asymetric stretch frequency. Despite the differences in structure of these molecules (DINGU and DMD are bicyclic rings, RDX and HMX are rings and HNIW is a cage) the radiation stability appears to be controlled by the strength of the N-N bond.
Thin Film Infrared Laser Pyrolysis Studies of Thermal Decomposition Mechanisms in Nitramine Propellants
Authors: Botcher Tod R. , Wight Charles A.
Published: March 2011

Thin films of RDX (1,3,5-trinitro-1,3,5-triazine) have been prepared by vapor deposition onto a 77 K substrate window and pyrolyzed with a pulsed CO2 laser. Each sample is rapidly quenched after the laser pulse by heat conduction into the cold substrate, and the initial reaction products are trapped on the window for examination by transmission FTIR spectroscopy. We have detected N2O4, the dimer of nitrogen dioxide, as an initial condensed phase pyrolysis product, confirming that scission of one of the N-N bonds is the first step in the reaction mechanism. No evidence was found for formation of methylene nitramine via a proposed concerted depolymerization pathway.
Energy Localization and the Initiation of Explosive Crystals by Shock or Impact
Authors: Coffey C. S.
Published: March 2011

The initiation of chemical reaction in explosive crystals during shock or impact is shown to be a solid state, quantum mechanical, process not accessible by a classical continuum approach. The process by which dislocations move in a solid is analyzed in terms of quantum mechanical tunneling. The motion of these dislocations significantly perturbs the lattice and creates phonons which, for low dislocation velocities can cause local ignition sites and for high dislocation velocities, can have energies sufficient to directly pump the internal vibrational modes of the explosive molecules and cause rapid molecular dissociation.
Molecular Modeling of Slip Supposed to Occur in the Shock Initiation of Crystalline PETN
Authors: Ritchie James P.
Published: March 2011

Some molecular modeling of slip using both rigid and flexible molecules of PETN in perfect, but finite, lattices has been performed. Studies of rigid displacement show slip on (001)<010> to be relatively unhindered. The shock orientation with a maximum resolved shear stress in this direction would, therefore, be expected to be insensitive. Molecular mechanics calculations have also been performed. The results show that it is likely that molecular deformations occur and have an important effect in determining the shear strength of crystalline PETN.
Si and Ge Nanocrystallites Embedded in CaF2 by Molecular Beam Epitaxy (MBE)
Authors: Taylor A. P. , Kim B. M. , Persans P. D. , Schowalter L. J.
Published: March 2011

Thin films of CaF2 containing layers of Si and Ge nanocrystallites were grown epitaxially on Si( 111) substrates by MBE while varying the substrate temperature. The sticking coefficient of both Si and Ge to CaF2 are less than unity at the temperatures studied. Evidence that chemical reactions are minimal between Si and CaF2 leading to the formation of volatile species such as SiFx is presented and it is surmised that the dominant mechanism for re-evaporation is thermal desorption. Both Si and Ge sticking coefficients vary exponentially with 1/T and activation energies are determined. A cluster growth model describing the evolution of the amount of Si in clusters over time is given. Solving in the limit of low cluster coverage, a solution that varies linearly with time and exponentially with 1/T is obtained. Weak room temperature photoluminescence from Si nanocrystallites in CaF2 is seen, however, it is unclear whether the luminescence is coming from the Si nanocrystallites or the CaF2. Second harmonic generation is observed from samples containing single layers of Ge in CaF2.
Pholuminuksence Studies on Porous Silioon Quantum Confinement Mechanism
Authors: Zhang Shulin , He Kuoksan , Hou Yangtian , Wang Xin , Li Jingjian , Diao Peng , Qian Bidong , Cai Shengmin , Fujishijma Akira
Published: March 2011

A novel step—like and pinning behavior of photoluminescence peak energy connected with changes in the concentration of HIF and current density were for the first time observed for p— type porous silicon. Based on a theoretical calculation of the electron structure of the silicon quantum wire it is argued that these behaviors can be explained in terms of a novel formation mechanism model of porous silicon.
Characterization of Ge and C Implanted Sil-xGex and Sil-y-zGeyCz Layers
Authors: Gupta Ashawant , Cheng Yao-Wu , Qiao Jianmin , Rahman M. Mahmudur , Yang Cary Y. , Im Seongil , Cheung Nathan W. , Yu Paul K.L.
Published: March 2011

In an attempt to substantiate our previous findings of boron deactivation and/or donor complex formation due to high-dose Ge and C implantation, SiGe and SiGeC layers were fabricated and characterized. Cross-sectional transmission electron microscopy indicated that the SiGe layer with peak Ge concentration of 5 at% was strained; whereas, for higher concentrations, stacking faults were observed from the surface to the projected range of Ge as a result of strain relaxation. Results of spreading resistance profiling were found to be consistent with the model of dopant deactivation due to Ge implantation and subsequent solid phase epitaxial growth of the amorphous layer. Furthermore, for unstrained SiGe layers (Ge peak concentration ≥7 at%), formation of donor complexes is indicated. Preliminary photoluminescence results correlate with the spreading resistance profiling results and indicate shallow donor complex formation.
Multi-Wavelength Ellipsometry for Effective Characterization of Thin Epitaxial Si1−xGex Layers on Silicon Substrate
Authors: Eichler Michael , Weidner Marita , Morgenstern Thomas
Published: March 2011

The range of composition (x) is one of the parameters we often have to measure if Si1-xGex layers are generated by chemical vapour deposition (CVD). It is important in this case, in which way the optical properties of Si1-xGex layers depend on the range of composition. We are interested in using multi-wavelength ellipsometry as a technique for rapid, nondestructive characterization of these samples, without large preparations, especially for series of measurements (2D profiles or wafer-lots). The number of unknown parameters and the multiple solutions are reduced by using several wavelengths during the measurement. The calculation is prepared by the help of parameter-correlation based on results of spectroscopical ellipsometry. To examine the results, thickness and composition were controlled for selected samples by cross-sectional transmission electron microscopy (XTEM) and X-ray double crystal diffractometry (DCD).
Selective Removal of Silicon-Germanium: Chemical and Reactive Ion Etching
Authors: Johnson F. Scott , Misra Veena , Wortman J. J. , Martin Leanne R. , Harris Gari A. , Maher Dennis M.
Published: March 2011

The use of both chemical and reactive ion etching for the selective removal of SixGe1-x alloys with respect to both silicon and silicon dioxide has been investigated. We have found that a solution of NH4OH:H2O2:H2O is effective in selectively etching the SixGe1-x films with respect to both of these materials. The chemical composition of the substrate surface after removal of insitu doped SixGe1-x films was evaluated using EDS and SIMS. Diffusion from insitu doped Si0.7Ge0.3, followed by selective removal, was used to demonstrate self-aligned npn dopant profiles with narrow base widths. Reactive ion etching of SixGe1-x alloys was investigated using SF6, CF4, and Cl2 based chemistries. Pressure, power, and gas flow ratios were optimized to provide the least isotropic etch possible for SixGe1-x films containing approximately 40% Ge. Selectivity and degree of anisotropic etching were determined as a function of Ge content for samples with 0% to 100% Ge. Samples were analyzed using SEM and ellipsometry. Highest selectivities were achieved using SF6 and O2.
Nanocrystalline SiC Formation From Sputter-Deposited Non-Equilibrium a-SixC1−x Alloys
Authors: Wang Hong , Ma Z. , Allen L. H. , Rigsbee J. M.
Published: March 2011

There exists considerable interest in the synthesis of nanocrystalline SiC particles embedded in an a-SixC1−x:H matrix. This study investigated the formation of nanocrystalline SiC by annealing a non-equilibrium a-Si0.35C0.65 alloy sputter deposited onto oxidized (100) Si. Evolution of the microstructure was characterized by thin film sheet resistance measurements, glancing angle X-ray diffraction (GAXRD) and transmission electron microscopy (TEM). It was found that films annealed at temperatures below 850°C remained amorphous. Annealing at temperatures above 850°C resulted in the formation of SiC nanocrystallites, as revealed by GAXRD and TEM. The electrical conductivity also showed an abrupt increase around 950°C. Prolonged annealing resulted in a further increase in conductivity, implying that the transformation continued. Annealing at 1100°C for 3 hours increased the film conductivity by two orders of magnitude relative to the as-deposited film.
No Correlation Between Porous Silicon Photoluminescence and Surface Hydrogen Species
Authors: Geoqrg S.M. , Robinson M.B. , Dillon A.C.
Published: March 2011

The photoluminescence (PL) of porous silicon has been attributed to quantum confinement, amorphous silicon, or surface species such as hydrogen, polysilanes or siloxene. Our research has tested the early claims that surface hydrogen is responsible for PL. Our initial studies examined the effect of thermal annealing on surface hydrogen and PL in situ in an ultrahigh vacuum chamber. The results showed that the PL decreased between 450–550 whereas H2 was desorbed from surface SiH2 species between 500–575 K. There was no direct correlation between the PL and the loss of SiH2 surface species. Our most recent investigations have monitored PL and surface hydrogen species as a function of HF etching time for electrochemically anodized porous silicon samples that were not initially photoluminescent. While the surface hydrogen species continually decreased versus HF etching time, the photoluminescence did not appear until after HF etching times of 20–80 minutes depending on initial sample porosity. These results again illustrated that there is no direct correlation between the PL and surface hydrogen species.
SiGe/Si Quantum Wells by MBE : A Photoluminesence Study
Authors: Houghton D.C. , Rowell N.L. , Noel J.-P. , Aers G. , Davies M. , Wang A. , Perovic D.D.
Published: March 2011

Strained Sil-xGex quantum wells and multi-quantum wells, synthesized by solid source ebeam evaporated MBE on Si(100) substrates have been studied by low temperature photoluminescence (PL) spectroscopy. Phonon resolved transitions originating from excitons bound to shallow impurities in Sil-xGex layers were observed over the temperature range 2K to 100K and used to characterize Sil-xGex/Si heterostructures. Thin Sil-xGex quantum wells exhibited phonon-resolved PL spectra, similar to bulk material, but shifted in energy due to strain, quantum well width and Ge fraction. In single quantum wells confinement shifts up to ∼200 meV were observed (1.2 nm wells with x = 0.38) and NP linewidths down to 1.37 meV were obtained. The confinement shifts were modeled by hole confinement in Sil-xGex wells. An annealing study was performed to investigate the role of Si-Ge interdiffusion on luminescence. Both the geometrical shape and optical emission of the quantum well were found to significantly change through intermixing. In addition to near edge luminescence a broad band of intense luminescence was obtained from several Sil-xGex/Si heterostructures. Some layers exhibited both types of PL spectra. However, the broad PL band (peak energy ∼120meV below the strained bandgap) was predominant when the alloy layer thickness was greater than 2 - 10nm, depending on x, growth temperature, and substrate surface preparation. The strength of the broad PL band was correlated with the areal density of strain perturbations (∼109cm−2 per quantum well corresponding to a spacing of 300nm in the plane of the well; local lattice dilation ∼ 1.5 nm in diameter) observed in plan-view TEM. The first few wells of MQW exhibited only band edge luminescence as was revealed by etching off the upper MQW periods. In addition, post growth anneals at temperatures in the range 700°C to 1100°C were found to enhance band edge luminescence, while the broad luminescence band decayed to zero intensity. Interdiffusion at these these temperatures has been shown to dramatically change the QW shape and consequently interfacial asperities would be expected to disappear, consequently only shallow phonon resolved luminescence is observed in PL after annealing. The influence of PL measurement parameters such as excitation power density and PL sample temperature on the relative strengths of band edge versus broad band luminescence were also consistent with the presence of exciton traps at sites of reduced bandgap.
Models and Mechanisms for the Luminescence of Porous Si
Authors: Koch F.
Published: March 2011

Explanations for the efficient, visible luminescence of porous Si fall broadly into three categories. At the extremes are the pure quantum-well point of view and the molecular agents hypothesis. We make here the case for a model in which the dominant absorption characteristics are those of a quantum well, but luminescence occurs via boundary states on the nanocrystalline particles. This so-called “smart quantum-well” mechanism accounts for the multiple emission bands of porous Si in a natural way. In particular, the infrared band is assigned as an electronic transition to a deep level. From this we determine the conduction band shift with particle size.
Photoluminescence Study of Radiative Recombination in Porous Silicon
Authors: Wang Chun , Gaspari Franco , Zukotynski Stefan
Published: March 2011

Photoluminescence has been studied in porous silicon. Two types of radiative recombination centers have been identified. One gives rise to luminescence at about 820 nm and is believed to be related to Si-H bonds. The second gives rise to luminescence at about 770 nm and is likely associated with S-O bonds. Above about 20K radiative recombination is assisted by excited states of the recombination centre located about 10 meV above the ground state. The Si-H recombination centre is a single electron center whereas the Si-O center appears to be a multi-electron center.
A phenomenological investigation on porous silicon electroluminescence
Authors: Steiner P. , Lang W. , Kozlowski F. , Sandmaier H.
Published: March 2011

The processing of light emitting diodes in porous silicon with green/blue electroluminescence spectrum is described. The spectral behavicur and the degradation are investigated. A phenomenological theory for the luminescence is given.
Correlation of Electrical, Structural, and Optical Properties of Erbium in Silicon
Authors: Benton J. L. , Eaglesham D. J. , Almonte M. , Citrin P. H. , Marcus M. A. , Adler D. L. , Jacobson D. C. , Poate J. M.
Published: March 2011

An understanding of the electrical, structural, and optical properites of Er in Si is necessary to evaluate this system as an opto-electronic material. Extended x-ray absorption fine structure, EXAFS, measurements of Er-implanted Si show that the optically active impurity complex is Er surrounded by an O cage of 6 atoms. The Er photoluminescence intensity is a square root function of excitation power, while the free exciton intensity increases linearly. The square root dependence of the 1.54μm-intensity is independent of measurement temperature and independent of co-implanted species. Ion-implantation of Er in Si introduces donor activity, but spreading resistance carrier concentration profiles indicate that these donors do not effect the optical activity of the Er.
X-Ray Diffraction and Reflectance, Raman Scattering and Photoluminescence Characterization of Thermally Annealed Epitaxial SI1-XGEX Layers
Authors: LíbeznÝ M. , De Wolf I. , Poortmans J. , Van Ammel A. , Caymax M. , HolÝ V. , Vižď F. , KubĚna J. , Werner K. , Ishida M.
Published: March 2011

Sil-xGex, undoped strained layers with a pure Si-capping layer were grown epitaxially by UHV CVD on Si (100) substrates. The samples were subjected to thermal treatments corresponding to typical deviceprocessing. Effects connected with thermally induced relaxations were studied by Raman scattering, XRD, photoluminescence (PL) and defect etching. The thickness of the layers was determined from X-ray reflectance measurement. Strain values for the as-grown and relaxed samples were extracted from Raman scattering, XRD measurements and defect etching and correlated. Sil-xGex-layer related peaks were observed in PL spectra of several samples. An explanation why those peaks are not observed in all the samples is suggested.
Intrinsic Optical and Electrical Properties of Strain-Adjusted Short-Period SimGen Superlattices
Authors: Olajos Janos , Engvall Jesper , Grimmeiss Hermann G. , Kasper Erich , Kibbel Horst , Presting Hartmut
Published: March 2011

Interband optical transitions are observed in a series of strain-adjusted, short-period Si/Ge superlattices by means of photocurrent spectroscopy, infrared absorption, photo (PL)- and electroluminescence (EL). The onsets of the interband absorption in the energy range of 0.7 - 0.9 eV are in good agreement with the observed PL and EL. Bandgap-related EL is observed in mesa diodes at room temperature, whereas the PL disappears at about 40K. In samples, annealed at growth temperatures (550°C) and higher, a systematic shift of the bandgap is observed which is discussed in terms of a process involving interdiffusion of the Si and Ge atoms. Photocurrent measurements at low temperatures support the model from PL studies suggesting that the photogenerated electrons are immobile in the SLS at low temperatures and have to be thermally ionized from shallow levels.
Load- and Depth-Sensing Indentation Tester for Properties Measurement at Non-Ambient Temperatures
Authors: Yoder Karl B. , Stone Donald S.
Published: March 2011

The ability to measure the temperature-dependence of the hardness of thin films is useful from both an applications and a scientific standpoint. For this reason, we have designed and constructed a load- and depth-sensing indentation tester combining sub-nanometer resolution with the ability to operate over a range of temperatures, currently 150K to 400K. This paper describes the new experimental apparatus and reports preliminary data on 440C stainless steel substrates with and without a 0.75 μm ZrN coating.
Mechanics of Contacts at Less than 100Å Scale: Indentation and AFM
Authors: Jarvis S.P. , Weihs T.P. , Oral A. , Pethica J.B.
Published: March 2011

Understanding of both low load Nanoindentation and Atomic Force Microscopy relies on a knowledge of the mechanical response of contacts at the few nanometre scale. To investigate this area we have developed a new type of AFM/Indenter which applies forces (<1nN up to 1mN) to a tip mounted on a cantilever. The displacement of the cantilever is detected using laser heterodyne interferometry. The combination gives a direct measurement of contact compliance at very low loads. Contacts of diameter below 100Å can be repeatably made.

We show that a water film is generally present in the contact during operation in air, and show how its size can be estimated from our data. One implication is that ambient operation of AFM in both repulsive and attractive modes may necessitate the presence of a liquid lubricating film, explaining the relative lack of damage in many AFM measurements. The estimation of contact area from stiffness is complicated by this layer. We show that the contact stresses are likely to be very high.