bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Techniques for Microwave Characterization of Percolating Dielectric -Metallic Media and Resolution of Discrepancies in Measured Data
Authors: Moore Rick , Lust Lisa , Hopkins Edward , Friederich Paul
Published: April 2011

The measured microwave effective dielectric properties of metal-dielectric composites show discrepancies when data from free space, resonant cavity or transmission line measurements are compared. Discrepancies are especially evident for materials where the metallic concentration is near the percolation threshold. This paper presents theory and measured data which highlight and resolve these discrepancies. Electrical correlation length is the relevant parameter which must be considered in choice of measurement technique. Agreement between effective medium models and measurement are best when focussed beam measurement techniques are utilized so as to produce planar wave-fronts whose extent is 3–4 freespace wavelengths when incident on the sample.
Computer Simulation of Impedance for 2-D Conductor-Insulator Composite
Authors: Han Dae Gon , Choi Gyeong Man
Published: April 2011

Using a computer simulation, impedance spectra of mixtures of conducting and insulating hard spheres which have random or regular arrangements of the components are studied. These simulations can be used to calculate the a.c. electrical properties of a multi-component composite using a personal computer. It is shown in this study that a.c. impedance spectra are sensitive functions of the filling fraction and the geometrical arrangement of the components, and especially, the impedance spectra of the composite show the abnormal arc originated from the isolated clusters in the composite.
Investigation of the Dopant Distribution in thin Epitaxial Silicon Layers by Means of Spreading Resistance Probe and Secondary Ion Mass Spectrometry
Authors: Karpov Ilya , Hartford Catherine , Moran Greg , Krishnakumar Subramania , Choma Ron , Linn Jack
Published: April 2011

In this paper, we examine the dopant distributions in 1.8 to 4 micron-thick boron- and phosphorus-doped epitaxial silicon layers. These layers were grown by chemical vapor deposition (CVD) on arsenic-, antimony-, or boron-doped (100)- and (111)-oriented substrates. We performed doping profile studies by means of local resistivity measurements using a spreading resistance probe (SRP). Chemical profiles of the dopants were also obtained using secondary ion mass spectrometry (SIMS).
Conductance Transients Study of Slow Traps in Al/SiNx:H/Si and Al/SiNx:H/InP Metal-Insulator-Semiconductor Structures
Authors: Dueñas S. , Peláez R. , Castán E. , Barbolla J. , Mártil I. , Gonzalez-Diaz G.
Published: April 2011

We have obtained Al/SiNx:H/Si and Al/SiNx:H/InP Metal-Insulator-Semiconductor devices by directly depositing silicon nitride thin films on silicon and indium phosphide wafers by the Electron Cyclotron Resonance Plasma method at 200°C. The electrical properties of the structures were first analyzed by Capacitance-Voltage measurements and Deep-Level Transient Spectroscopy (DLTS). Some discrepancies in the absolute value of the interface trap densities were found. Later on, Admittance measurements were carried out and room and low temperature conductance transients in the silicon nitride/semiconductor interfaces were found. The shape of the conductance transients varied with the frequency and temperature at which they were obtained. This behavior, as well as the previously mentioned discrepancies, are explained in terms of a disorder-induced gap-state continuum model for the interfacial defects. A perfect agreement between experiment and theory is obtained proving the validity of the model.
X-Ray Absorption Spectroscopy as an in-situ Tool in Materials Science
Authors: Ressler T. , Wong Joe , Metz W.
Published: April 2011

In addition to being an established technique for ex-situ structural studies, x-ray absorption spectroscopy (XAS) has recently been realized to be a powerful tool for in-situ time-resolved investigations in materials science. This paper describes two complementary techniques: quick-scanning EXAFS (QEXAFS) and energy-dispersive XAS (DXAS) which offer time resolution in the seconds and milliseconds range, respectively. Formation of a heterogeneous catalyst from a solid-state reaction of a precursor is presented as an example of a time-resolved XAS application.
Effect of Current Distribution on Quartz Crystal Microbalance Measurements
Authors: Kelly James J. , Durning Christopher J. , West Alan C.
Published: April 2011

Spatially nonuniform electrodeposition can cause discrepancies between predicted and experimentally measured mass loadings on an electrochemical quartz crystal microbalance (EQCM) since the sensitivity of the quartz crystal varies significantly from point to point. These discrepancies can be significant even if the current distribution is nearly uniform. These effects were examined experimentally by varying the conductivity of the electrolyte and the current density during the electrodeposition of copper on an EQCM, effecting changes in the spatial, deposited-mass distribution in a controlled manner. The resulting frequency shifts are in agreement with results predicted by current distribution simulations, validated a posteriori with profilometry measurements. Our results permit determination of the spatial variation of the quartz crystal sensitivity factor or of the current distribution on the EQCM.
In-Situ Monitoring during PLD of Complex Oxides using Rheed at High Oxygen Pressure
Authors: Rijnders Guus J. H. M. , Koster Gertian , Blank Dave H. A. , Rogalla Horst
Published: April 2011

Several groups have monitored the growth of complex oxides in-situ using Reflection High Energy Electron Diffraction (RHEED). In order to utilize RHEED during growth, films are deposited at low background oxygen pressures. Because of the low oxidation power at low pressures, low substrate temperatures have to be used. This hampers, in general, the film crystallinity. Furthermore, the background pressure in Pulsed Laser Deposition (PLD) is an important parameter, because it influences the shape and size of the plasma and, therefore, the deposition rate and homogeneity of the film.

We have developed a high-pressure RHEED system, which can be used for growth monitoring during the deposition of complex oxides at standard PLD conditions. Clear diffraction patterns are observable up to 50 Pa, due to the minimized scattering losses.

SrTi03 substrate treatments as well as growth studies of Yba2Cu3O7−δ, using atomic layers of SrO or BaO as a buffer-layer, will be discussed in this contribution. It will be shown that monitoring and control of thin film growth by PLD on an atomic level is feasible, even in quite high background pressures.
In Situ Fhir Spectroscopic Detection of Adsorbed Species on Sapphire Substrates in a Diamond ECR-Pacvd System
Authors: Shahedipour F. , Zhu S. , White H. W.
Published: April 2011

In situ Fourier Transform Infrared Reflection Absorption Spectroscopy (FTIRRAS) has been used to study the adsorbed plasma species on sapphire substrate throughout the nucleation and deposition stages under diamond deposition conditions. The focus of this work has been on one of the most fundamental questions in the area of diamond film synthesis that concerns the gas species (precursors) responsible for diamond nucleation and growth especially on foreign substrates. It is experimentally shown here that the most probable precursor for diamond nucleation in methane-hydrogen plasma are methyl radicals.

Diamond deposition on randomly oriented sapphire substrates has been successfully achieved under low pressure- low temperature deposition conditions using an electron cyclotron resonance microwave plasma assisted chemical vapor deposition (ECR-PACVD) system. The deposited thin films were characterized by Raman spectroscopy, and scanning electron microscopy.
Spectroscopic Determination of C2 Densities in AR/H 2/CH 4 and AR/H2/C60 Microwave Plasmas For Nanocrystalline Diamond Synthesis
Authors: Goyette A. N. , Lawler J. E. , Anderson L. W. , Gruen D. M. , Mccauley T. G. , Zhou D. , Krauss A. R.
Published: April 2011

We have measured the steady state concentration of gas phase C2 in Ar/H2/CH4 and Ar/H2/C60 microwave plasmas used for the deposition of nanocrystalline diamond films. High sensitivity white light absorption spectroscopy is used to monitor the C2 density using the d 3 Π ← a3Π (0,0) vibrational band of C2 as chamber pressure, microwave power, substrate temperature and feed gas mixtures are varied in both chemistries. Understanding how these parameters influence the C2 density in the plasma volume provides insight into discharge mechanisms relevant to the deposition of nanocrystalline diamond.
CVD Growth and Excimer Laser Processing of SiGe Alloys Monitored by Single Wavelength Ellipsometry and Atomic Force Microscopy
Authors: Larciprete R. , Padeletti G. , Cozzi S. , Pieretti S.
Published: April 2011

Single wavelength ellipsometry was used to monitor the CVD growth of Si(1-x)Gex alloys onSi and to evaluate the effect of sample irradiation by KrF laser pulses, performed during or afterthe CVD growth. The information obtained was correlated with AFM analysis results in order tooptimize the growth parameters for an improved morphological quality of the alloy layers.
Closed-Loop Control of MBE Using an Integrated Multi-Sensor System
Authors: Roth John A.
Published: April 2011

The use of in situ sensors to achieve real-time control of molecular beam epitaxy (MBE) is a rapidly evolving technology that promises to revolutionize MBE in terms of process repeatability and first-pass success, and consequently to improve the overall yield and reduce the cost of the process. To achieve robust real-time control of MBE, we have constructed a multiple-sensor control system comprising in situ sensors for substrate temperature, for effusion cell fluxes, and for the epitaxial layer composition and thickness, along with advanced software to manage the sensor information and execute sensor-feedback control algorithms. This system has been used to grow a number of different III-V semiconductor materials and device structures, including heterojunction bipolar transistors, resonant tunneling devices, and mid-IR lasers. In the present paper, we present results demonstrating control and regulation of substrate temperature and epitaxial layer composition during the growth of lattice-matched InGaAs and InA1As on InP. The control algorithms and software used in the system are described, and we discuss how the synergistic application of multiple sensors allows the regime of composition control to be expanded beyond what would be possible with only a single composition sensor.
Nanoindentation of Soft Films On Hard Substrates: Experiments And Finite Element Simulations
Authors: Pharr G. M. , Bolshakov A. , Tsui T. Y. , Hay Jack C.
Published: April 2011

Experiments and finite element simulations have been performed to examine errors in the measurement of hardness and elastic modulus caused by pile-up when soft films deposited on hard substrates are tested by nanoindentation methods. Pile-up is exacerbated in soft-film/hardsubstrate systems by the constraint imposed on plastic deformation in the film by the relatively non-deformable substrate. To experimentally examine pile-up effects, soft aluminum films with thicknesses of240, 650, and 1700 nm were deposited on hard soda-lime glass substrates and tested by nanoindentation techniques. This system is attractive because the elastic modulus of the film and the substrate are approximately the same, but the substrate is harder than the film by a factor of about ten. Consequently, substrate influences on the indentation load-displacement behavior are manifested primarily by differences in the plastic flow characteristics alone. The elastic modulus of the film/substrate system, as measured by nanoindentation techniques, exhibits an increase with indenter penetration depth which peaks at a value approximately 30% greater than the true film modulus at a penetration depth close to the film thickness. Finite element simulation shows that this unusual behavior is caused by substrate-induced enhancement of pile-up. Finite element simulation also shows that the amount of pile-up increases with increasing penetration depth, and that the pile-up geometry depends on the work-hardening characteristics of the film. Because of these effects, nanoindentation techniques overestimate the true film hardness and elastic modulus by as much as 68% and 35%, respectively, depending on the work-hardening behavior of the film and the indenter penetration depth. The largest errors occur in non-work-hardening materials at penetration depths close to the film thickness, for which substrate-induced enhancement of pile-up is greatest.
Full Field Measurements of Curvature using Coherent Gradient Sensing: Application to Thin Film Characterization
Authors: Rosakis A. J. , Singh R. P. , Tsuji Y. , Kolawa E. , Moore N. R.
Published: April 2011

This paper introduces coherent gradient sensing (CGS) as an optical, full-field, real-time, non-intrusive and non-contact technique for measurement of curvature and curvature changes in thin film and micro-mechanical structures. The technique is applied to determine components of the curvature tensor field in multilayered thin films deposited on silicon wafers. Curvature field measurements using CGS are compared with average curvatures obtained using high-resolution x-ray diffraction. Finally, examples are presented to demonstrate the capability of CGS in measuring curvature in a variety of thin film and micro-mechanical structures.
Strain Relaxation in Iv-vi Semiconductor Layers Grown on Silicon (100) Substrates
Authors: Sachar H. K. , McCann P. J. , Fang X. M.
Published: April 2011

The large thermal expansion coefficient mismatch between IV–VI semiconductors and silicon results in significant tensile strain when structures are cooled down following growth at high temperatures. Molecular beam epitaxy (MBE) growth of PbSe on Si (100) at 280°C on BaF2/CaF2 buffer layers results in high crack-density because of this strain. Interestingly, crack- free layers of PbSe can be grown by LPE on Si (100) by using MBE-grown PbSe/BaF2/CaF2 buffer layer structures. Unlike LPE-grown PbSe layers, however, a high crack-density was observed in Pbl-xSnxSe1-yTey layers grown by LPE on Si (100) using similar buffer layer structures. It is hypothesized that the addition of tellurium, which is known to increase IV-VI material hardness, inhibits plastic deformation and thus crack formation becomes the thermal strain relief mechanism. Ternary Pbl-xSnxSe layers grown by LPE exhibited much lower crack densities as compared to the quaternary layers and supported the conclusion that tellurium induced solid solution hardening occurs in the IV-VI materials system.
Interfacial Stability and Misfit Dislocation Formation in InAs/Gaas(110) Heteroepitaxy
Authors: Zepeda-Ruiz Luis A. , Maroudas Dimitrios , Weinberg W. Henry
Published: April 2011

A comprehensive atomic-scale study is presented of the mechanical behavior of the InAs epitaxial film, the interfacial stability with respect to misfit dislocation formation, and the film surface morphology in InAs/GaAs(110) heteroepitaxy. If a GaAs buffer layer of ten-monolayer thickness is used in the epitaxial growth, a transition is predicted from a coherent to a semi- coherent interface consisting of a regular array of edge interfacial misfit dislocations at a critical film thickness of six monolayers. A second transition to a semicoherent interface consisting of a completely developed network of perpendicularly intersecting misfit dislocations is predicted at thicknesses greater than 150 monolayers. Our simulation results are in excellent agreement with recent experimental data.
Dynamic Hardness of Thin Films and its Thickness Dependence
Authors: Iwasa Mikio , Tanaka Koji , Barnard John A. , Bradt Richard C.
Published: April 2011

Thin films of indium tin oxide, silica and chromium were deposited on the soda-lime-silica glass substrates with the thickness ranging from 50 to 2000 nano-meter. Their dynamic hardness were measured by the nano-indentation method with the indentation depth from 50 to 200 nano-meter. The hardness of indium tin oxide film increased and that of silica decreased with increasing film thickness. The hardness of chromium was almost constant regardless of film thickness. When the hardness of thin film was higher than that of substrate, the influence of substrate was greater compared with the reverse case. The dynamic hardness of engineering ceramics were about fifty percent higher than the ordinary Vickers hardness, but the ranking order was in good agreement. The Young's modulus from nano-indentation were a little higher than those by resonance method.
Mechanical and Tribological Properties of Zrc/Vc Alloy Films Deposited by Sputtering and Pulsed Laser Deposition
Authors: Brock W. F. , Krzanowski J. E. , Leuchtner R. E. , Legore L. J. , Frankel D. J.
Published: April 2011

A study has been conducted on ZrC/VC alloy thin films prepared by both pulsed laser deposition (PLD) and RF magnetron sputtering. The phase formation, wear properties, and hardness of these thin films were examined. An alloy target comprised of 36% VC and 64% ZrC (atomic %) was used to deposit films at 200°, 2000°, and 400° C. The nominal film thickness was 0.6 μm. X-ray diffraction (XRD) analysis revealed these films were solid-solution alloys and showed a preference for (100) orientation for sputter-deposited films and a (110) orientation for laser deposition. More highly oriented films were obtained at elevated temperatures as evidenced by rocking curve measurements on the PLD films. The FWHM of the peaks ranged from 2.2° to 8.3° for films deposited at 400° C and 20° C, respectively.

Using time-of-flight quadmpole mass spectrometry (TOFQMS), we performed plume diagnostics to measure particle energies and the thermalization effects of the background gas. In vacuum, typical ion energies ranged from ˜5–100 eV while the neutral atoms had kinetic energies from ˜1–5 eV. Our measurements show that the background gas can be used to selectively thermalize low mass components in the plume. From measured kinetic energies and collision effects of the gas, the changes in crystallographic structure of the alloy with pressure appear to result from collision-induced effects from condensation of the Zr atoms. This ‘heavy’ atom effect may be an important new processing parameter with which to adjust film morphology and crystal texture.
Diamond Coatings on Surface-Modified Carbide Tools Using KrF Pulsed Laser
Authors: Lee Dong-Gu , Singh Rajiv K.
Published: April 2011

The surface of a cemented carbide was modified using a KrF pulsed laser process to achieve a microrough structure, leading to stronger adherence of diamond films to cemented carbide substrates. The surface morphology and roughness were investigated with laser conditions. After the surface modification with the laser and the etching of the modified surface, heat treatment was performed prior to deposition of diamond film in order to observe changes in surface morphology and adhesion. Diamond films were grown by chemical vapor deposition process. The results indicated that the heat treatment of the modified cemented carbide improved the adhesion of diamond films by the recrystallization of tungsten carbides into the fine and long grains. As laser energy for the modification of a cemented carbide increased, the surface roughness increased and tungsten carbide (WC) was transformed to WC1−x(X =0–0.3) and then to W2C.
Correlation of Stress With Photo-Degradation in Hydrogenated Amorphous Silicon Prepared by Hot-Wire CVD
Authors: Han Daxing , Gotoh Tamihiro , Nishio Motoi , Sakamoto Tomonari , Nonomura Shuichi , Nitta Shoji , Wang Qi , Iwaniczko Eugene
Published: April 2011

An innovative bending-beam method is used to study the stress of thin film a-Si:H deposited on thin quartz by hot-wire chemical vapor deposition (CVD) techniques. When the deposition temperature increases from 280 to 440 °C the hydrogen content decreases from 8 to <1 at.%, and the initial compressive stress also decreases from 420 to 74 MPa. We found that there is a 10−4 photo-induced increase of the initial compressive stress under 300 mW/cm2 light-soaking, which can be recovered to the initial value by thermal annealing at 160 °C for 1 h. The results imply that the Si-H bonds contribute to the compressive stress in the a-Si:H film. There is no simple correlation between the stress and the photodegradation of the electronic properties.
Micro-Raman Study of Mechanical Stress in Polycrystalline Silicon Bridges
Authors: Talaat H. , Negm S. , Schaffer H. , Kaltsas G. , Nassiopoulou A. G.
Published: April 2011

Micro-Raman spectroscopy is used to study mechanical stress distribution in polycrystalline silicon bridges on cavities micromachined in crystalline Si wafers. The influence of the processing parameters such as the thickness of polycrystalline membrane, the annealing conditions (before or after removal of the sacrificial porous-Si layer ), are studied. The results indicate that the annealing reduces the residual stress by an order of magnitude and that the membrane thickness of 2.5 μm has the least residual stress.
Measurement of Nonuniform Stresses in Semiconductors by the Micro-Raman Method
Authors: Pinardi K. , Jain S. C. , Maes H. E. , Overstraeten R. Van , Willander M. , Atkinson A.
Published: April 2011

Micro-Raman measurements axe performed with a focused laser beam. Because of its finite diameter (∼ 1 μm) and penetration depth, the laser beam samples a “large volume” of the sample. In a nonuniformly strained sample, spectra originating from different points are different. Therefore the observed spectrum depends on both the strain distribution in the sample and the absorption coefficient of the laser light. We describe a method to calculate the Raman spectra taking these factors into account. The calculated spectra show excellent agreement with the experimental results.
Fracture Tests Of Polysilicon Film
Authors: Sharpe W. N. , Yuan B. , Edwards R. L.
Published: April 2011

A new test approach is presented to measure the fracture toughness of thin films. The polysilicon specimen is a center-cracked panel that is 3.5 μm thick and 3 mm wide with a 100 μm long slot in the center. It is subjected to tensile loading, and the crack-opening displacement is measured by interferometry. The average toughness is 1.4 ± 0.65 MPa-m1/2.
Curvature Of Rectangular Coated Foils With Different Width-To-Length Ratios
Authors: Tran M. D. , Vellinga W. P. , Dautzenberg J. H.
Published: April 2011

This paper concerns the bending of rectangular foils with different width-to-length ratios, coated with a layer with high internal stress. Framework for the interpretation of experimental results is a description of the bending based on geometrically nonlinear elasticity. Calculations indicate that the (mean) biaxial modulus of coatings on foils may be determined by this method. Fully isotropic and isotropic-orthotropic bilayers are considered. Preliminary experimental results, of unbalanced magnetron sputtered PVD TiN coatings on stainless steel foil, are shown to be in qualitative agreement with the geometrically non-linear description of the bending of coated foils, provided anisotropy of the substrate and clamping conditions are taken into account.
Nanoindentation Hardness of Compositionally Modulated Ti/TiN Multilayered Films
Authors: Kusano Eiji , Kitagawa Masaru , Nanto Hidehito , Kinbara Akira
Published: April 2011

A detailed study of microhardness of multilayered films has been strongly needed to reveal effects of film layer structures and deposition conditions on the film hardness. A nanoindentation method is a useful method to investigate mechanical properties of thin films prepared on substrate materials. In this respect we have deposited a several types of Ti/TiN multilayered films and estimated their hardness by a nanoindentation method. The desired compositional modulation was obtained by changing the flow rate of N2gas periodically using a computer system. The modulation period has been varied from 10 to 40nm by changing a flow rate control pattern. The total thickness of the film was about 500nm including the underlayer of the TiO2(50nm)/Ti(50nm) multilayer for all samples with different modulation period. Substrates used in the experiment were borosilicate glass and not heated during film deposition. The compositional distribution toward to the film depth orientation was estimated by Auger electron spectroscopy. The dynamic hardness of the films has been estimated by a nanoindenter as a function of the modulation period. It was found that there existed an optimum modulation period of 20nm to enhance the film hardness by multilayer structure.. The maximum value of microhardness obtained for the optimum modulation period was 29GPa, which was much larger than that of the monolithic TiN coating of 15GPa. The hardness measurement results show that the behavior for dynamic hardness was different from that for plastic deformation hardness obtained.
Structure And Stress Evaluation Of Diamond Films Deposited On Ti-6A1-4V Alloy At Low Temperature Using Ch4/O2/H2 And CO/H2 Gas Mixtures
Authors: Catledge Shane A. , Vohra Yogesh K.
Published: April 2011

Low temperature diamond deposition on metal substrates is motivated by the need to reduce thermal stress so that the film adhesion is satisfactory. Although the use of oxygen-con- taining gas mixtures have been shown to extend the temperature range for which diamond can grow as well as to improve film quality, most studies have focused on the use of silicon as sub- strates and have neglected technologically important metallic systems. To this end, microwave plasma chemical vapor deposition (MPCVD) was used to grow diamond films on Ti-6A1-4V alloy at low temperature (615 to 780 C) using CH4/O2/H2 and CO/H2 gas mixtures. In-situ pyrometric interferometry (ISPI) shows that as the oxygen concentration increases, the onset time for dia- mond nucleation and subsequent film surface roughness increases while the average growth rate decreases. Micro-Raman spectroscopy shows improved film quality and suggests a trend toward increasing in-plane compressive stress with increasing oxygen concentration. Glancing-angle x- ray diffraction (XRD) was complimentary to the Raman data and indicates the presence of a TiC interfacial layer thickness which decreases with increasing oxygen concentration. We found that the CO/H2 mixture resulted in poorly adhered “white soot” films with low diamond content whereas the CH4/O2/H2 mixture yielded well adhered high quality diamond films.
Critical Issues In Measuring The Mechanical Properties Of Hard Films On Soft Substrates By Nanoindentation Techniques
Authors: Hay Jack C. , Pharr G. M.
Published: April 2011

This study explores the difficulties encountered when using conventional nanoindentation techniques to measure the Young's modulus and hardness of hard films on soft substrates. In general, the indentation measurement of film/substrate systems is affected by four material properties: the Young's modulus and hardness of the film, and the Young's modulus and hardness of the substrate. For the particular case of a hard film on a soft substrate, there is a tendency for the material around the hardness impression to sink-in which results from the large difference in yielding of the two materials. In this study, a ‘model’ system consisting of NiP on annealed Cu was used to explore the behavior. This system is interesting because the film and substrate have similar Young's moduli, minimizing the elastic behavior as a variable. In contrast, the hardness of NiP is approximately 7–18 GPa, and that of the annealed copper is less than 1 GPa, providing a factor of 10 difference in the plastic flow characteristics. Experimental results indicate that standard analytical methods for determining the contact depth, hardness and Young's modulus do not work well for the case of a hard film on a soft substrate. At shallow contact depths, the measured indentation modulus is close to that of the film, but at larger depths sink-in phenomena result in an overestimation of the contact area, and an indentation modulus which is less than the Young's modulus of both the film and substrate. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) provide critical details of the physical processes involved, and illustrate how the standard data analyses overestimate the true contact area.
Disposal of Spent Sealed Radiation Sources in Borehole Repositories
Authors: Sobolev I.A. , Timofeev E.M. , Ojovan M.I. , Shiryaev V.V. , Arustamov A.E. , Kachalov M.B.
Published: April 2011

In Russia the spent sealed radiation sources are disposed of into shallow ground borehole repositories. Design and status of the repositories as well as the basis for the safe disposal of the sources with metal matrices are presented.
Alkaline Degradation of Cellulose: Estimation of the Concentration of Isosaccharinic Acid in Cement Porewater
Authors: Van Loon L.R. , Glaus M.A. , Stallone S. , Laube A.
Published: April 2011

The sorption of radionuclides on repository components (e.g. cement) is an important process since it controls the release of radionuclides from the repository [1]. A strong sorption of radionuclides is desirable since it will allow only a small release of radionuclides to the geo-and biosphere. The strong sorption behaviour of radionuclides, however, could possibly be decreased by several orders of magnitude by the presence of organic ligands. Ligands such as EDTA, NTA, citric acid etc. are inherent components of radioactive waste since these complexing agents are used in nuclear power stations for decontaminating purposes. Other ligands might be formed by degrading organic polymers present in low and intermediate level radioactive waste [2, 3]. Cellulose materials such as cotton, paper and wood form a substantial part (ca. 50 %) of the organic waste [1]. The use of large amounts of cement for constructing a repository causes alkaline environments in which the pH of the pore solution will remain above 12.5 for periods of the order of 105years [4]. It is well known from the literature that cellulose is unstable under alkaline conditions and will degrade to water soluble, low molecular weight compounds by the peeling-off reaction [5]. The main degradation product of cellulose is isosaccharinic acid (ISA), which is stable under alkaline conditions [5-10]. ISA enhances the solubility of Pu(IV) [7, 8] and has an adverse effect on the sorption of Eu(III), Th(IV) and Ni(II) [6]. For instance, in a solution of 10-3M ISA, the solubility of Pu(IV) at pH 12 increases by a factor of 20000 [11]. The sorption of Pu(IV) [8], Eu(III), Th(IV) and Ni(II) [6], however, was affected to only a minor extent. The observed effects were - by analogy with gluconic acid [12] - interpreted to be due to a strong complexation of these metals. The concentration of ISA in the pore water is the key parameter for evaluating its effect on radionuclide sorption [13].

A full assessment of the effect of cellulose degradation on the sorption requires a detailed understanding of the mechanisms involved. The present study gives an overview of the different processes involved and describes how to quantify the concentration of isosaccharinic acid in the pore water of a repository.
A Method of Characteristics Solution of Nuclide Transport With Decay Chain
Authors: Lee Youn-Myoung , Kang Chul-Hyung
Published: April 2011

A method of solvng advecton-dsperson equaton wth decay chan of arbtrary length by usng the method of characterstcs s ntroduced. n specfc cases where the advecton s domnant rather than dsperson, the method s known to be useful mnmzng the numercal dsperson. The suggested models consdered to be effectve through several llustratons for the case that decay chan of arbtrary lengths nvolved durng transport, whch s dffcult to solve by standard numercal solutons when the medum becomes more complcated.
The War Over Kds at the Waste Isolation Pilot Plant
Authors: Lee William W.-L.
Published: April 2011

This paper traces the history of distribution coefficients used to calculate radionuclide transport in performance assessments for the Waste Isolation Pilot Plant (WIPP), to obtain technical lessons for performance assessment in general. The WIPP is a geologic repository for transuranic waste. The U. S. Department of Energy (DOE) has filed a compliance certification application1with the Environmental Protection Agency. If the application is approved, the USDOE plans to operate the WIPP starting in November 1997, making the WIPP the first operational repository in the United States.
Application of Petrological and Petrophysical Data for the Assessment of Radionuclide Retardation in Metavolcanites
Authors: Petrov V.A. , Poluektov V.V. , Kupriyanova E.Yu.
Published: April 2011

An attempt was made to analyze the mechanism of the distribution of Sr and Cs isotopes depending upon petrochemical and petrophysical characteristics of metavolcanites of the basement forming the territory of the Production Association (PA) Mayak, Chelyabinsk District, Russia. It was found that radionuclide reterdation depends on the structure, density and mineralogy of intact rock.
Weathering Conditions and Behavior of Fission Products in Oklo Reactors
Authors: Pourcelot L. , Gauthier-Lafaye F.
Published: April 2011

Two billion years ago, natural fission reactions occured in the uranium ore deposit of Oklo (Gabon), mainly due to the high concentrations of fissile 235U. At that time, high uranium contents (40-60 % U) allowed reaching criticality when oxidised uranium bearing fluids met reduced fluids accompanying the migration of hydrocarbons. Natural fission reactors consist of a core made of uraninite crystals embedded in a clay matrix (mainly chlorites). The thickness of the clay layer range between few centimetres to 2 meters. Fission products are mostly located in the uraninite grains but newly crystallised minerals such as phosphate minerals, clays and metallic aggregates retain some proportions of migrated fissiogenic elements [1].
SrI2 Diffusion Experiment in Granite From Underground Research Laboratory in Manitoba, Canada
Authors: Yamaguchi T. , Nakayama S. , Vandergraaf T.T.
Published: April 2011

It is important to quantify the diffusion of radionuclides into pores in rock and to understand the diffusion mechanism to evaluate the migration of radionuclides in deep geological formations. The diffusivity of ions into the rock matrix is usually estimated using a theory for the diffusion in porous material, in which a proportional relationship exists between the effective diffusivity in rock and the diffusivity in the bulk of the solution. In this study, diffision of nonsorbing Γ and sorbing Sr2+ was observed simultaneously and the results were compared.
Report on Workshop on Solute Transport in Compacted Bentonite
Authors: Hugi Markus , Apted Mick , Gilby David
Published: April 2011

This workshop produced a lively discussion covering a number of issues relating to the transport of radionuclides through compacted bentonite. The predominant themes were:

– the structural and chemical inhomogeneity of the compacted bentonite barrier

– the process of radionuclide sorption in bentonite

– the postulated process of surface diffusion

The main points of interest in this discussion are summarised here and some general conclusions are drawn.
Fundamental Science of f-Elements in Selected Immobilization Glasses: Significance for TRU Disposal Schemes
Authors: Haire R. G. , Assefa Z. , Stump N.
Published: April 2011

We have investigated certain aspects of the fundamental chemistry and materials science of the 4fand several 5f-elements in three glass matrices. Two of these matrices were high-temperature (850° and 1450°C melting points) silicate-based glasses and the third was a sol-gel glass. Optical spectroscopy was the principal investigating tool. One aspect of the work here was to ascertain the oxidation state exhibited by these elements in the different glasses, as well as the factors that control and/or may alter this state. An important finding was noting a general correlation between the oxidation states obtained in the two high-temperature glasses and those observed in the oxides of these elements. Of the twenty three f-elements considered here, only three exceptions (Ce, Am and Bk) or examples of variable behavior (Pr, Tb, U and Cf) to this correlation were noted. One explanation offered for the exceptions is based on the stability afforded by the oxides' fluorite lattice. The correlation also applied to the sol-gel glasses after they had been heated. Other oxidation states for some elements could be obtained in the sol-gel glasses prepared at 25°C. Presented here is a summary of the oxidation states observed for these elements in three glass matrices and how these states correlate with those observed in the oxides of these elements and with the relative oxidation potentials for the elements.
X-Ray Absorption Fine Structure of Aged, Pu-Doped Glass and Ceramic Waste Forms
Authors: Hess N.J. , Weber W.J. , Conradson S.D.
Published: April 2011

X-Ray Absorption Fine Structure (XAFS) spectroscopic studies were performed on a suite of compositionally identical Pu-doped simulated waste glasses prepared 15 years ago at different aactivities by varying the239Pu/f238Pu isotopic ratio. The resulting α-activities range from 1.9 × 107to 4.2 × 109 Bq/g. These samples have a current, accumulated dose that ranges from 8.8 × 1018to 1.9 × 1018αdecays/g. A second suite of polycrystalline zircon samples that were synthesized 16 years ago with 10.0 wt.% Pu was also investigated. The239Pu238Pu isotopic ratio in these samples resulted in α-activities of 2.5 × 108and 5.6 × 1010Bq/g and an accumulated dose of 1.2 × 1017and 2.8 × 1019α-decays/g. The multicomponent composition of the simulated waste glass permitted XAFS investigation at six elemental absorption edges. For both the glass and ceramic waste forms, initial analysis of Extended X-Ray Absorption Fine Structure (EXAFS) and X-Ray Absorption Near Edge Structure (XANES) indicate that the local environment around the cations exhibit different degrees of disorder as a result of the accumulated a-decay dose. In general cations with short cationoxygen bonds show little effect from self-radiation where as cations with long cation-oxygen bonds show a greater degree of disorder with accumulated a-decay dose.
Effects of Water Redox Conditions and Presence of Magnetite on Leaching of Pu and Np From HLW Glass
Authors: Inagaki Y. , Sakata H. , Furuya H. , Idemitsu K. , Arima T. , Banba T. , Maeda T. , Matsumoto S. , Tamura Y. , Kikkawa S.
Published: April 2011

The objective of this study is to evaluate the effects of water redox conditions and of the presence of iron corrosion products (magnetite) on the release of actinides from HLW glasses. Static corrosion tests were performed on a simulated HLW glass doped with Pu and Np in deionized water in the presence of magnetite under oxidizing and reducing conditions. The tests under oxidizing conditions were performed in air, while the tests under reducing conditions were performed in mixed gas (Ar+5%H2) atmosphere.

The following results were obtained: (1) The presence of magnetite enhances formation of colloids containing Pu and Np in the leachates under both redox conditions. (2) Redox conditions have no remarkable influence on the release of Pu. (3) The reducing conditions combined with the presence of magnetite cause a decrease in the concentrations of Np dissolved species, which is probably the result of the reduction of Np(V) to Np(IV) at the magnetite surface.
Research Priorities in Nuclear Waste Management: A View From the Far Field
Authors: Richardson Philip J.
Published: April 2011

First of all I would like to express my appreciation to the MRS for the opportunity to address this symposium. I am especially pleased to be speaking alongside Charles McCombie and Soren Norrby, who have both made me feel welcome whenever we have met in the past. I have been more active in Sweden over the last few years, as Soren will know. Perhaps it is now time I turned my attentions to Switzerland as well.
Sintered (Sr,U)-Containing Zirconolite Ceramics Study
Authors: Stefanovsky S.V. , Ioudintsev S.V. , Ochkin A.V. , Ptashkin A.G. , Chizhevskaya S.V.
Published: April 2011

Zirconolite-rich ceramics, containing strontium (∼1 wt.%) or uranium (5-20 wt.%) were prepared by cold pressing of mechanically activated oxide powders and sintering in air at 1200 TC for 2 hours. They were examined with XRD, optical and electron microscopy (SEM/TEM/EDS) methods. Zirconolite content in the samples was found to be as much as 85-90 vol.%, Baddeleyite, rutile, and perovskite (in the Sr-containing sample only) were present as minor phases. In the U-containing samples, two zirconolite varieties with different Zr/U ratio were found: zirconolite-1 and zirconolite-2 with average compositions Ca0.90Zr0.95U0.10Ti2.00O7.00, and Ca1.15Zr0.40U0.50Ti2.02O7.00 respectively. The amount of zirconolite-2 increases from ∼1 vol.% in the sample with the lowest uranium content to >50 vol.% in the sample containing ∼20 % U02. In the latter sample about 5 vol.% of cubic pyrochlore-type phase was also present.
Commentary on Studies of 36Cl in the Exploratory Studies Facility at Yucca Mountain, Nevada
Authors: Murphy William M.
Published: April 2011

36Cl data from the Exploratory Studies Facility (ESF) at Yucca Mountain, Nevada, reported by LANL researchers [1,2,3,4] provide important empirical constraints on the velocity and pathways for water flow under natural conditions in the unsaturated zone at Yucca Mountain. It has been concluded that some data exhibiting exceptionally high 36Cl/Cl ratios (i.e., greater than 1250×10−15 [3]) indicate unambiguous bomb pulse contamination and fast groundwater travel times to depths of the proposed waste emplacement horizon. Several lines of evidence indicate that some ESF samples with 36Cl/Cl ratios greater than 900×10−15 to 1000×10−15 are also affected by bomb pulse contamination. The distribution of 36Cl/Cl data can be well represented by a mixture of two normally distributed populations, which are hypothesized to represent uncontaminated and bomb pulse contaminated sets. The transition between these groups occurs at 36Cl/Cl between 600×10−15and 1000× 10−15, and the hypothesized contaminated samvles comprise 20 to 25 percent of the total. Shapiro-Wilk statistics confirm that when samples with 36Cl/Cl ratios greater than about 1000×10−15 are included, the distribution deviates from normality. Variation in the Earth's magnetic field, which is a primary mechanism for variation in natural 36Cl production, also appears to be normally distributed, supporting the hypothesis that natural, relatively undecayed 36Cl/Cl ratios are normally distributed. Further evidence that samples with 36Cl/Cl greater than 950×10−15 to 1000×10−15 are likely to have a bomb pulse component is provided by the spatial correlation of these samples with those containing unambiguous contamination at values greater than 1250×10−15. Zones in which elevated 36Cl/Cl ratios are localized constitute about 23 percent of the length of the ESF at the level of the proposed waste emplacement horizon.
The Role of Engineered Barriers in the Performance Assessment of a Repository for L/ILW
Authors: Askarieh M.M. , Chambers A.N. , Hickford G.E. , Sharland S.M.
Published: April 2011

Designs for repositories for the underground disposal of radioactive waste throughout the world are generally based on the ‘multiple barrier’ concept. This comprises engineered barriers that are the introduced features of the disposal facility, and natural barriers provided by the host geology. In the near field of the repository, the engineered barriers can provide both physical and chemical containment. This paper is mainly concerned with the deep disposal of intermediatelevel and low-level waste. In particular, it reviews current understanding concerning the evolution of the chemical and physical barriers for the disposal concept developed by United Kingdom Nirex Limited. Examples of work from underlying research programmes that support this understanding are discussed. The paper also discusses the representation of the engineered barriers in performance assessment calculations.
Dissolution of a Complex Borosilicate Glass at 60°C: The Influence of pH and Proton Adsorption on the Congruence of Short-Term Leaching
Authors: Abraitis P. K. , Vaughan D. J. , Livens F. R. , Monteith J. , Trivedi D. P. , Small J. S.
Published: April 2011

The short-term dissolution behaviour of a complex borosilicate glass has been investigated by controlled pH leaching, surface titration and leach rate temperature dependence experiments. The results indicate that the rates, congruence and mechanisms of dissolution vary significantly with pH. At low pH, dissolution occurs via a proton-promoted mechanism which results in enhanced release of B and many network modifying elements (relative to Si). At 60°C in high pH media, dissolution is essentially congruent. Here, dissolution is surface reaction controlled and occurs via a hydroxyl-promoted network dissolution process. Selective leaching is favoured at low and near-neutral pH. Congruent dissolution occurs in solutions of pH greater than that at the point of zero net proton charge.
Influence of Iron(II) and Iron(III) Ions on the Corrosion of MTR Fuel Element Claddings in Repository-Relevant Brines
Authors: Zschunke S. , Fachinger J.
Published: April 2011

After the USA decided in 1988 to no longer accept spent fuel elements from German material test reactors (MTR), a national back-end fuel cycle alternative was sought in the Federal Republic of Germany [1]. The aim is their direct final disposal in deep, stable geologic formations. The corrosion of material test reactor (MTR)-fuel element claddings (aluminium) in repository-relevant brines was examined. Before the aluminium cladding material can corrode, the POLLUX cask, containing the fuel elements, must be corroded. In this case, iron(II) and iron(III) ions are present in the brine. These ions decisively influence the corrosion of the MTR fuel element cladding material, therefore the mechanism responsible for this phenomenon should be identified. Tests were performed in which Fe(II) and Fe(III) salts were added to the brines. In these experiments, the percentage mass decrease of the aluminium cladding, the iron content of the brine, as well as the pH value were determined. As expected the results provided the information about the corrosion mechanism. The higher the concentration of iron ions in the brines, the higher the aluminium corrosion rate was for all three brines. Identical redox equilibria between Fe(II) and Fe(III) were formed in the brine, irrespective of whether Fe(II) or Fe(III) salt had been added. It is assumed that the acceleration of the corrosion rate is based on the fact that Fe(II) is reduced to metallic iron by absorbing the electrons produced during the oxidation of aluminium to Al(III). The aluminium cladding material does not function as a barrier for the release of radionuclides from the fuel elements. The results of this study show that the 0.38 mm thick aluminium cladding will corrode through after approximately four weeks.
Waste Management in a National Research Laboratory
Authors: Beer H.-F. , Jermann M.
Published: April 2011

Because of its experience in handling radioactive materials including waste generated on-site PSI was charged with managing the treatment and interim storage of the radioactive waste from medicine, industry and research in Switzerland. Combustible operational waste from the Swiss nuclear power plants is conditioned on a contract base and stored temporarily at the sites of the power plants. Because of the decommissioning of old facilities provoked by the change in the research priorities at PSI, temporarily an additional amount of waste is released on-site to be treated. PSI possesses the facilities and the organisational structure to fulfil the tasks it is charged with. In the near future the major part of the conditioning procedures, except the conditioning of some of the waste containing α-emitters, will be performed by ZWILAG. PSI will stay responsible for the management, organisation and interim storage of all radioactive waste, except for nuclear power plant waste, as before.