bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Method for the Electronic and Chemical Passivation of GaAs Surfaces Using Cs2
Authors: Lee Ju-Hyung , Xu Yanzhen , Burrows Veronica A. , McMillan Paul F.
Published: April 2011

A new GaAs surface passivation method, CS2 treatment at moderate temperature was developed for effective passivation of GaAs surfaces. The CS2 treatment of GaAs surfaces at 350 °C and 10 atm leads to deposition of a homogeneous film, with a thickness of several hundred A. The passivation layer thus produced causes a significant enhancement in room temperature photoluminescence intensity and the passivation effect of the sulfide film was confirmed by Raman spectroscopy. The passivation layer remained electrically and chemically stable over a period of nine months under ambient atmospheric conditions. In-depth Auger electron spectroscopy (AES) revealed that the carbon and oxygen content in the film was negligible, whereas sulfur was uniformly distributed throughout the film. A metal-insulator-semiconductor diode whose insulating layer is produced by the CS2 treatment shows well-defined accumulation and depletion regions in its capacitance-voltage (C-V) characteristics with low hysteresis.
Characterization of the Interface Between Metal Contacts and Epilayers of Doped Silicon Carbide
Authors: George M. A. , Larkin D. J. , Petit J. , Burger A. , Morgan S. H. , Collins W. E.
Published: April 2011

Aluminum contacts on chemical vapor deposited (CVD) SiC films were studied to examine variations in the chemical, morphological and electrical properties of the samples. Nitrogen and aluminum doped substrates were prepared to give n-type and p-type SiC epilayers respectively. These preparations were examined by surface sensitive spectroscopies and by atomic force microscopy (AFM). Samples were studied both before and after the deposition of aluminum films to compare differences between SiC(p++)/metal and SiC(n++)/metal contact interfacial properties. Aluminum has generally been found to have good adherence to the n+ epilayer but do not form good ohmic contacts, while metal films deposited on p+ epilayers have had poor adherence but have been found to provide better ohmic character. AFM images revealed nanometer sized clusters, attributed to excess Si on the n+ epilayers, while no clusters were observed on the p+ epilayers. XPS studies of the as-prepared samples indicated that the n+ epilayers had higher concentrations of oxides which may enhance adhesion. The chemical composition and morphology is discussed and correlated to the electrical properties obtained for the various samples.
Gold Nanocomposites Prepared by Reactive Sputtering
Authors: Maya L. , Paranthaman M. , Thundat T. , Allen W. R. , Glover A. L. , Mabon J. C.
Published: April 2011

Reactive sputtering of gold and selected gold alloys in oxygen and nitrogen plasmas generated in a DC glow discharge was studied. Gold alloys examined were various compositions with gallium, aluminum and silicon. Gold is transported unreacted from a gold target to the substrate in a nitrogen plasma to form polycrystalline films, but gold alloys produce fine dispersions of gold in the corresponding ceramic nitride matrix which was crystalline for gallium and amorphous for silicon and aluminum. This contrasts with the behavior in an oxygen plasma which produces pure gold oxide, Au2O3, from a gold target and gold oxide-silicon oxide nanocomposites from Au/Si alloys. Gold oxide is thermally labile and reverts to the elements at 350 °C. Stress in gold oxide films was detected in the decomposition profile, volatile evolution versus temperature, as an event occurring at a lower temperature. The thermal lability of gold oxide was utilized to generate gold nanocomposites in silica with different metal loading through pyrolysis of the corresponding precursor gold oxide-silica films. The properties of gold oxide and gold nanocomposites are described.
Thermal and Mechanical Characteristics of Polyimide Based Ceramers
Authors: McDaniel P. R. , StClair T. L.
Published: April 2011

Polymer dominated polyimide/preceramic ceramers have been prepared by two different techniques. Both methods currently offer high potential of generating a novel nanostructure with well consolidated moldings of the multiphased systems. The first method involves microencapsulation of sub-micron polymer particles of LARC• IA (Langley Research Center Improved Adhesive) in a TiO2 coating and the other method utilizes LARCTM IA amic acid and TEOS in a sol-gel process. Each has allowed for the formation of ceramers possessing properties of both inorganic glasses and organic polymers. Processing, thermal characterization, and mechanical properties of the resultant materials will be discussed.
AB-Initio Calculations of CzSil-z-yGey, Compounds for Silicon-Based Heterojunction Devices
Authors: Berding M. A. , Sher A. , Schilfgaarde M. Van
Published: April 2011

We present recent results on the properties of ordered group IV compounds containing carbon, silicon and germanium. Our calculations are done using a full-potential -linearized muffin-tin orbital (FP-LMTO) method within the local density approximation (LDA). Twenty-seven fully relaxed compounds represented by six different compound structures have been examined. With the exception of SiC, all compounds are found to be metastable. Two trends emerge: compounds that have carbon on a common sublattice are less unbound because of their relatively low strain, and carbon-germanium bonds are disfavored. Simple two-body (bond-length) and three-body (bond-angle) empirical fits to our first-principles results are not adequate to predict excess energies with sufficient accuracy to be reliably predictive for other structures. Some compounds have direct gaps. When carbon shares a sublattice with silicon or germanium, the large strain results in a narrowing of the band gap, and in some cases the compound is metallic. The most promising structures with the lowest excess energy contain carbon on one sublattice and do not lattice match to silicon, but match rather well to silicon carbide.
Optical-based Flux Monitoring of Atomic Antimony Sources for Molecular Beam Epitaxy
Authors: Brewer P. D. , Killeen K. P.
Published: April 2011

In this paper we discuss the use of optical-based flux monitoring (OFM) for real-time control of atomic antimony fluxes for applications in molecular beam epitaxy. Atomic antimony beams were generated using a two-zone cracking effusion cell. The product distribution of the source was characterized using a time-of-flight mass spectrometer employing resonance-enhanced laser ionization. A double-pass OFM system has been developed to monitor the atomic antimony beam that is capable of precise flux measurement during MBE growth.
Real-Time Composition And Thickness Control Techniques In A Metalorganic Chemical Vapor Deposition Process
Authors: Gaffneyt M. S. , Reavesl C. M. , Holmes A. L , Smith R. S. , DenBaars S. P.
Published: April 2011

Metalorganic chemical vapor deposition (MOCVD) is a process used to manufacture electronic and optoelectronic devices that has traditionally lacked real-time growth monitoring and control. We have developed control strategies that incorporate monitors as real-time control sensors to improve MOCVD growth. An analog control system with an ultrasonic concentration monitor was used to reject bubbler concentration disturbances which exist under normal operation, during the growth of a four-period GaInAs/InP superlattice. Using X-ray diffraction, it was determined that the normally occurring concentration variations led to a wider GaInAs peak in the uncompensated growths as compared to the compensated growths, indicating that closed loop control improved GaInAs composition regulation. In further analysis of the X-ray diffraction curves, superlattice peaks were used as a measure of high crystalline quality. The compensated curve clearly displayed eight orders of satellite peaks, whereas the uncompensated curve shows little evidence of satellite peaks.
Near Field Scanning Optical Microscopy and Spectroscopy of Electronic Materials and Structures
Authors: Duncan W. M.
Published: April 2011

A Near Field Scanning Optical Microscope (NSOM) with spectroscopic capability is applied to imaging semiconductor and microelectronic structures. NSOM combined with spectroscopic analysis provides physical and chemical information of thin films and defects with ultra high spatial resolution. We have studied epitaxial and bulk samples and partially fabricated SiO2/Si CMOS structures to investigate the spatial resolution and imaging modes of NSOM. Reflected intensity contrast in NSOM yields images of defect networks in InGaAs/InAlAs/GaAs epitaxial layers and shows thickness variations in SiO2 films on Si. Surface topological changes observed in NSOM demonstrate a spatial resolution of significantly better than 0.25 μm. Fluorescence imaging is examined for chemically identifying materials and defects.
Imaging of Silicon Carrier Dynamics with Near-Field Scanning Optical Microscopy
Authors: Rosa A. H. La , Yakobson B. I. , Hallen H. D.
Published: April 2011

A contactless high spatial resolution technique has been developed to characterize semiconductor materials using the Near-Field Scanning Optical Microscope. The technique can be used to non-invasively measure: surface topography, defect content, and carrier lifetime variations in silicon. The success of the technique relies on the sensitive detection of changes in infrared transmission induced by local generation of free carriers using pulsed visible radiation. Here we extend the application of this technique to characterize silicon on insulator materials. We also include computer simulation results to address the role played by diffusion in the ultimate lateral resolution that can be achieved using this technique.
Quantitative Photoreflectance Experiments on Indium Phosphide Surfaces and Structures
Authors: Hildebrandt S. , Schreiber J. , Kuzmenko R. , Gansha A. , Kircher W. , Höring L.
Published: April 2011

Photoreflectance (PR) modulation spectroscopy is a widely used optical technique on GaAs but it has been applied much more rarely on InP being an equally important optoelectronic compound semiconductor. Typical PR spectral lineshapes in the fundamental gap region of various InP materials are investigated. Spectral components such as Franz-Keldysh oscillations, lowfield features, and epilayer interference phenomena are analyzed. Current applications concern the determination of the surface electric field, investigations of ion etching and hydrogenation processing, and the characterization of homo- and strained heteroepitaxial layers by means of synchronous phase and complex fitting analysis.
Origin of the 1.3 eV Transition in InP/InAlAs/InP Heterostructure
Authors: Benyattou T. , Garcia-Perez M. A. , Moneger S. , Guillot G; , Caneau C.
Published: April 2011

We report in this paper results from photoluminescence studies on InP/AlInAs/InP double heterostructure. We particuliary focus on the 1.26 eV recombination (also refered as the 1.3 eV transition) that originates from the inverse interface. We will show that its optical properties is related to the non commutativity of the AlInAs/InP band offset.
Three-Dimensional Active Gratings for Light Emission Control
Authors: Romanov S. G. , Fokin A. , Butko V. , Johnson N. P. , Torres C. M. Sotomayor
Published: April 2011

Three dimensional lattices of semiconductor nanostructures were prepared using porous artificial opals as templates. Opals are natural gratings for visible light, and the template forces the semiconductor to follow the size (typically 100 nm) and symmetry (fcc) of their void-like lattice. The purpose of using this material is to match the wavelength of the emitted light from the semiconductor component with one of the lattice's own modes to enhance the luminescence efficiency. TiO2 was grown using in-cavity, multiple step synthesis by CVD. The band gap of the composite is near 3 eV. Raman scattering, absorption and photoluminescence (PL) spectra were examined for various amounts of TiO2 in opal. Transmission of the PL through the composite shows an intensity decrease at 2.15 eV which is not in the region of interband absorption of composite components. This corresponds to the structure possessing an overall refractive index between that of opal (1.45) and rutile (2.3) of 1.8.
Real Time Measurement of Epilayer Strain Using a Simplified Wafer Curvature Technique
Authors: Floro J. A. , Chason E. , Lee S. R.
Published: April 2011

We describe a technique for measuring thin film stress using wafer curvature that is robust, compact, easy to setup, and sufficiently sensitive to serve as a routine diagnostic of semiconductor epilayer strain in real time during MBE or CVD growth. We demonstrate, using growth of SiGe alloys on Si, that the critical thickness for misfit dislocation can clearly be resolved, and that the subsequent strain relaxation kinetics during growth or post-growth annealing are readily obtained.
Combined Room Temperature Photoluminescence And High Resolution X-Ray Diffraction Mapping Of Semiconductor Wafers
Authors: Cockerton S , Cooke M L , Bowen D K , Tanner B K
Published: April 2011

We describe the characteristics and performance of a combined desk-side high resolution X-ray diffractometer and room temperature photoluminescence spectrometer designed for rapid mapping of compound semiconductors in a production line context. The combined data for AIGaAs on GaAs suggest that recent measurements of the lattice constant and the Poisson ratio of AlAs may be more reliable than earlier published values. We illustrate the instrument performance in showing that for lattice matched ternary GaInP on GaAs systems, the X-ray rocking curve maps are much more sensitive to composition variation than the photoluminescence spectra.
Characterization Of Micropipes And Other Defect Structures In 6H-SiC Through Fluorescence Microscopy
Authors: Vetter W. D. , Dudley M. , Wong T.- F. , Frderich J. T.
Published: April 2011

Crystals of silicon carbide, and other polytypic materials often have micropipes associated with screw dislocations of large Burgers vectors running along their axial dimensions. These defects are considered the most deleterious to the performance of SiC semiconductor devices.

Optical micrographs of micropipes in silicon carbide crystals are ordinarily faint. To obtain micrographs showing higher contrast and detail, laser scanning confocal microscopy (LSCM) and simple fluorescence microscopy were used on 6H-SiC single crystals after infiltrating them with a low-viscosity epoxy containing a fluorescent dye. “Staining” the micropipes rendered them much more visible both in fluorescence and conventional optical microscopies. Details of their structures and shapes were revealed, and their dimensions were measured accurately, using LSCM and other, less sophisticated, fluorescence microscopies. Other voids present, such as microcracks, were also visualized. Observations by this optical technique were related to information obtained by synchrotron white beam x-ray topography.
Brillouin Light Scattering Determination of the Glass Transition in Thin, Freely-Standing Poly(styrene) Films
Authors: Forrest J. A. , Dalnoki-Veress K. , Dutcher J. R. , Rowat A. C. , Stevens J. R.
Published: April 2011

We have used Brillouin light scattering (BLS) to measure the glass transition temperature of thin, freely-standing poly(styrene) (PS) films. The freely-standing films were prepared by spincoating solutions of PS in toluene onto glass substrates, annealing the supported films in vacuum, and then using a water surface transfer technique to place the films across a 3 mm diameter orifice. Ellipsometry measurements of similar floated films transferred to Si(001) wafers allow the determination of the film thicknesses. Atomic force microscopy measurements revealed that the films have an rms roughness of less than 10 A˚. With the freely-standing films placed in an optical furnace, we performed BLS measurements of the films using a high-contrast, multipassed, tandem Fabry-Perot interferometer. We obtained a reliable, reproducible measure of the glass transition temperature, Tg, from the large changes in the frequencies of the thermally-excited, viscoelastic, film-guided waves within the PS films as the films were heated above Tg. BLS results for bulk PS and a 1800 A˚ thick, freely-standing PS film are presented. We find the same glass transition temperature for the 1800 A˚ thick film as the bulk PS sample. This Tg value is the same as that obtained using differential scanning calorimetry (DSC).
Relaxation Behavior in Polystyrene Near and Above the Glass Transiton Studied by Ultrasonic Technique
Authors: Sahnoune A. , Piché L.
Published: April 2011

We report measurements of the temperature and pressure dependence of ultrasonic modulus in polystyrene between 340 and 550 K and applied pressures up to 775 bar. The real and imaginary parts of the modulus are analyzed within the Havriliak-Negami model and very good agreement is found over the entire temperature and pressure ranges. Using the Vogel-Tammann-Fulcher equation for the relaxation time, the Kauzmann temperature TK and the fragility parameter D of polystyrene were determined. The value of D indicates that polystyrene is a fragile-glass former.
The Role of Stochastic Noise on the Glass Transition
Authors: Perez-Cardenas Fernando C. , Gan Hao
Published: April 2011

Glasses are amorphous solids that exhibit an intricate structural relaxation. A broad relaxation time spectrum always emerges when these systems are perturbed. By using a Langevin-type differential equation to describe the structure dynamicsof these materials, it is depicted how the broad relaxation time spectrum arises due to the stochastic noise and how this affects the system's structure evolution as it is cooled down into the glass transition region. This stochastic model provides a macroscopic as well a microscopic view of the glass relaxation process.
An Experimental Study of the Dynamics of Contact Lines
Authors: Kumar S. , Robbins M. O. , Reich D. H.
Published: April 2011

We have studied the dynamics of contact lines formed by water-alkane interfaces in capillaries with random surface disorder. We find that the contact-line velocity V scales with the applied capillary pressure P as V∼ (P – Pt)ζ over two decades in V. This is consistent with a critical depinning transition. We obtain this result by using a sensitive ac differential-pressure measurement technique to measure dP/dV. We find that dP/dV αV−0 8 (5) implying that 1/ζ = 0. 20 (5).
Simulation of Dynamics of Solid-Liquid Transition
Authors: Kogure Y. , Masuyama H. , Doyama M.
Published: April 2011

Molecular dynamics simulations on the solid-liquid transition of copper crystals have been performed. The configulation and the motion of atoms are monitored by RDF. It is seen that the height of the first peak in the RDF, which located at the nearest neighbour distance, decreased drastically as the temperature is increased.
Pinning of Water Imbibition Front In Porous Media
Authors: Wong Po-Zen , Delker Thomas , Hott Morgan , Pengra David B.
Published: April 2011

We report a study of the dynamics of capillary rise of water in a column of glass beads. The water column height h is measured as a function of time t. Analyzing the late-time data in terms of critical pinning, dh/dt α (P − Pa)β, we find an anomalously large exponent β. A similar measurement for contact line pinning in capillary tubes indicates β < 1. We discuss these findings in light of recent theories for domain wall pinning in the random-field Ising model and suggest a new equation of motion which corresponds to the Wolf-Villain model with quenched noise.
Growth Equation with a Conservation Law
Authors: Lauritsen Kent Bækgaard
Published: April 2011

We investigate an interface growth equation with a conservation law. The interaction is characterized by an integral kernel. The equation contains the Kardar-Parisi-Zhang, Sun-Guo-Grant, and Molecular-Beam Epitaxy growth equations as special cases and allows for a unified investigation of growth equations. We perform a dynamic renormalization-group analysis and determine the scaling behavior and universality classes for such growth models with a conservation law.
Morphology of the Fungus Aspergillus Oryzae and Nidulans
Authors: Miyazima Sasuke , Matsuura Shu
Published: April 2011

A variety of growth manner of the fungus Aspergillus oryzae and nidulans under varying environmental conditions such as the nutrient concentration, and medium stiffness are investigated, ranging from a homogeneous Eden-like to a ramified DLA-like pattern. The roughness σ(i, h) of the growth front of the band-shaped colony, where h is the mean front height within l of the l horizontal range, satisfies the self-affine fractal relation under favorable environmental conditions.
Stereological Estimation of Fractal Number of Fracture Planes in Concrete
Authors: Stroeven P.
Published: April 2011

Concrete is a man-made material containing a particulate filler designed on the basis of a sieve curve. In case of river aggregate, the particles are approximately spherical and smoothtextured. The particle-matrix interface is mostly the weakest chain link in the mechanical system. This implies damage evolution to start at particle-matrix interfaces. In case of direct tension, these interface cracks will be on average perpendicular to the loading direction. In case of direct compression, they will be parallel to the loading direction. A single fracture surface is formed in tension and a series of fracture surfaces in compression. They are the result of crack concentration within a process zone, in which the engineering crack closely meanders around a dividing plane. This allows to model these fracture surfaces on different resolution levels. It is shown, using stereological notions, that the very phenomenon is of a non-ideal fractal nature. Estimates for fractal dimension of fracture surfaces in concretes based on sieve curves at the border of the practical range are found to closely match experimental data reported in the literature.
Fractal and Dendritic Growth of Surface Aggregates
Authors: Brune H. , Bromann K. , Kern K. , Jacobsen J. , Stoltze P. , Jacobsen K. , Nørskov J.
Published: April 2011

The similarity of patterns formed in non-equilibrium growth processes in physics, chemistry and biology is conspicuous and many attempts have been made to discover common mechanisms underlying their growth. The central question in this context is what causes some patterns to be dendritic, as e.g. snowflakes, while others grow fractal (randomly ramified). Here we report a crossover from fractal to dendritic patterns for growth in two dimensions: the diffusion limited aggregation of Ag atoms on a Pt(111) surface as observed by means of variable temperature STM. The microscopic mechanism of dendritic growth can be analyzed for the present system. It originates from the anisotropy of the diffusion of adatoms at corner sites which is linked to the trigonal symmetry of the substrate. This corner diffusion is observed to be active as soon as islands form, therefore, the classical DLA clusters with the hit and stick mechanism do not form. The ideas on the mechanism for dendritic growth have been verified by kinetic Monte-Carlo simulations which are in excellent agreement with experiment.
Why are computer simulations of growth useful?
Authors: Jensen Pablo , Bardotti Laurent , Barabási Albert-László , Larralde Hernán , Havlin Shlomo , Stanley H. Eugene
Published: April 2011

We show how computer simulations can give unique information on the growth of nanostructures and thin films. Specifically, they can predict the morphologies and the island size distributions corresponding to different growth mechanisms. This information cannot be obtained from other approaches such as mean-field mathematical theories or scaling analysis. Special attention is given to the effects of small cluster mobility on experimental results.
Fractal Analysis of the Microstructure of Aisi 304 Steel.
Authors: Hinojosa M. , Trejo V. , Ortiz U.
Published: April 2011

The present work reports the results of fractal analysis of the grain boundaries of AISI 304 stainless steel. Microstructure in the non deformed condition is compared against microstructure with 50% tensile strain. Observations were made by optical microscopy, magnifications used were 50, 100, 200, 400, and 1000x. Measurements were made over digitized images using image analysis. Fractal dimension of the grain boundaries were obtained using Richardson plots of perimeter against yardstick length. Our results agree well with reported values for different natural fractal curves. We found that, in general, grains exhibit two different fractal dimensions: one structure dimension that gives information about the morfology of the grain and one texture dimension which accounts for the fine details of the grain boundary.
Evaluation of Inaccessible Pore Structures in Random Porous Solids
Authors: Yoshizawa N. , Yamada Y. , Shiraishi M. , Kaneko K. , Setoyama N.
Published: April 2011

A fine pore characterization method is investigated for a disordered solid including inaccessible pores. Here inaccessible pores denote ones into which N2 molecule cannot access at 77 K. Activated carbons prepared differently are examined. The basic idea of the method is as follows: (1) Pores are classified into effective micropores (further devided into smaller and larger micropores distinguished from DR (Dubinin-Radushkevich) analysis and inaccessible pores. (2) Volume fraction is determined for each type of pore considering densities. (3) Debye-Bueche plot derived from SAXS analysis is used to estimate the average transversal length of solid part and pore, respectively, convinedwith their volume fractions obtained from (1) and (2). (4) In case of a porous systemwith a symmetrical shape of pores, relative number and size of inaccessible pore to effective micropore are calculated.
Solid Electrolytes: Microstructural Characterization by Conductivity Spectroscopy
Authors: Funke K.
Published: April 2011

In conductivity spectroscopy, ionic conductivities of solid electrolytes are measured continuously from a few Hertz up to the mid-infrared, i.e., in a frequency range covering more than twelve decades. In this paper we present experimental conductivity spectra of various cryst alline and glassy ionic conductors. Tracing the characteristic patterns of the spectra back to their generic processes provides a powerful means for probing the motion of the ions on atomic scales of space and time. The technique is particularly useful for exploring the single-particle potentials felt by the ions and, hence, for elucidating details of the surrounding structure. In our examples we discuss widths, anisotropies, and geometrical arrangements of sites in crystals as well as the existence of non-equivalent sites in glass.
Electrical Characterization of Impurities in and Contacts on Mercuric Iodide
Authors: Van Scyoc J. M. , Gilbert T. S. , James R. B.
Published: April 2011

Mercuric iodide (HgI2) is a semiconductor that has shown great promise for use in roomtemperature high-resolution x-ray and gamma-ray spectrometers. Its widespread usage has been limited, however, by low yield and long-term reliability problems. The processing of this material is still in its infancy compared to silicon, so research efforts continue to pursue the root causes of device failures. Two likely sources of performance limitations are impurities and poor contacts. Significant efforts have been expended in developing and using various purification schemes. However, quantitative chemical analyses have shown that several metallic impurities still exist at the high ppb level. In addition, it has not yet been definitively determined which impurities are most problematic and at what level they have a detrimental effect. Leakage currents and currentvoltage measurements have been used to study the movement of mobile impurity-related defect centers in the bulk mercuric iodide. In particular, this method has been used to quantify the drift of metallic impurities, such as Ag and Cu, which are known to or believed to degrade HgI2 detectors. Four-point-probe sheet resistance measurements have been used to study the stability of contacts and the formation of reaction layers. In particular, such measurements have revealed that the Pd contacts currently used for the highest quality detectors are not as stable as previously thought, as the films of Pd react with the HgI2 to form the amalgam PdHg.
Impedance Spectroscopy of Upper Mantle Earth Materials
Authors: Tyburczy J. A. , Roberts J. J.
Published: April 2011

Earth scientists study electrical properties of Earth materials to understand mechanisms of transport and deformation under conditions existing in the Earth's interior, and for comparison with direct determinations of the conductivity – depth structure of the Earth. We have performed impedance spectroscopic studies of natural and artificial (hot-pressed and sintered) rocks composed of (Mg9Fe1)2SiO4 olivine, a major constituent of the Earth's upper mantle between 40 and 400 km depth. The studies were performed over the frequency range 105 to 10−4 Hz at 1 bar total pressure and temperatures of 800 – 1400 °C under controlled oxygen atmospheres. Complex impedance plane analysis of the results shows depressed impedance arcs corresponding to grain interior and grain boundary transport in series, analogous to the behavior of zirconia and other materials. Distinct grain boundary phases that might cause the resistive grain boundary behavior are not observed. The exponent of the oxygen pressure dependence of the grain boundary conductivity ranges from 0.02 to −0.08, which is very different than the 1/5.5 to 1/7 dependence of the polaronic grain interior mechanism. However, lack of constraints on the composition of the intergranular material limit interpretation of these exponents in terms of mechanism. Key issues for application to the Earth's interior are determination of the mechanism and pressure dependence of the grain boundary transport.
Effect of Sol-gel Coating on Microstructure and Electrical Properties of Microwave Garnets
Authors: Cho Yong. S. , Brissette Leo , Amarakoon Vasantha. R. W.
Published: April 2011

Microwave magnetic properties of Gd substituted yttrium iron garnets are known to depend on their microstructural characteristics such as porosity and grain size. Surface coating of the garnet powders through a gelation of Si and Mn organic solution was conducted to inhibit the grain boundary movement during sintering with considerable densification. High density and uniform microstructure were obtained after sintering at 1400°C in O2 atmosphere. Grain growth kinetics were studied with variation in sintering time as a function of grain size. An activation energy of 102.9 kcal/mol was obtained for grain growth of the sol-gel coated sample. Grain boundary region was investigated by using TEM and EDS. A very thin grain boundary layer was observed with Si segregation in the region. Electrical resistivity at 100 Hz was 1.46×109 Ωcm for the sol-gel coated sample sintered at 1400°C for 3hrs in O2. Above results were discussed and compared with those obtained by the conventional batch mixing of additives.
Scaling of Complex Conductivity for A Percolating Metal-Insulator Composite with Inter granular Tunneling Above and Below the Superconducting Transition
Authors: Mclachlan D. S. , Pakhomov A. B. , Oblachova I. I. , Brouers F. , Sarychev A.
Published: April 2011

The complex conductivity was measured on 3d granular NbC-KCI composite samples at varying metal volume fraction p, frequency ω and temperature above and below the superconductivity critical Tc. The observed frequency dispersion is anomalous in that it is not in accord with the scaling theory of percolation transition. The results are compared with a recently developed scaling theory, which takes both intercluster tunneling and intercluster capacitance into account. The experimental estimates for the new critical exponents are in reasonable agreement with the theory. The very low value of the crossover frequency can also be understood. We also present the data showing the dispersion of the complex conductivity well below the superconducting transition Tc of NbC.
Impedance Spectroscopy of Ferromagnetic Materials
Authors: Valenzuela R. , Irvine J. T. S.
Published: April 2011

Impedance spectroscopy has been widely used to analyze polarization phenomena in dielectric, ferroelectric and solid electrolyte materials. In this paper, we review its extension to ferromagnetic materials, and discuss its application to the case of irreversible domain wall displacements which lead to ferromagnetic hysteresis phenomena.
Electrical Resistivity and Dielectric Properties of Hardened Cement Paste and Mortar
Authors: Buerchler D. , Elsener B. , Boehni H.
Published: April 2011

Water content, porosity, pore solution composition, resistivity and dielectric properties of hardened cement paste and mortar samples have been studied as a function of time and relative humidities. A model for the resistivity of cement based materials is presented and an interpretation of the dielectric properties is proposed.
Humidity Effects on Porous Silica Thin Films
Authors: Kokan J. R. , Gerhardt R. A.
Published: April 2011

Impedance Spectroscopy is being used to study the humidity sensitivity of porous silica thin films. The films are processed via a colloidal sol-gel method which leaves some remnant potassium and sodium. Previous work on bulk porous silica samples processed by the same method showed that the dielectric properties and ac conductivity were very sensitive to changes in humidity. The aim of this work was to determine if the same dependencies could be found in the thin films. The capacitance, dielectric loss, and ac conductivity of the films were measured in a controlled environment chamber from 20–80% RH for frequencies ranging from 10Hz–10MHz. In addition to characterizing films with varying amounts of residual alkali ions obtained through leaching, we have also measured films that were surface doped with controlled amounts of KCl, LiCl, or NaCl. Relative humidity dependencies in the films are not as dramatic as in the bulk samples. The reasons for this behavior are not yet clear, but may be associated with the porosity, thickness, and surface area of the films.
Redox Behavior of Palladium Ion in Oxide Glasses
Authors: Yamashita Masaru , Nishii Junji , Akai Tomoko , Yamanaka Hiroshi
Published: April 2011

Reduction and separation of Pd were investigated in soda-lime-alumino-borosilicate glass. The dependence on raw materials, melting atmosphere, concentration of Pd and melting temperature was examined by electrochemical oxygen activity measurement, optical absorbance, X-ray diffraction and microscopic observation. Pd ions were slowly reduced during melting and metal particles were formed. The separation was enhanced in a reducing atmosphere, at high temperature, for long melting periods and with high concentration of Pd. Pd metal particles of about 10 to 30 μm in diameter were observed by SEM and X-ray diffraction.
Vitrification of Simulated Intermediate-Level French and Russian Wastes in “Cold Crucible” Based Plant
Authors: Lifanov F. A. , Stefanovsky S. V. , Kobelev A. P. , Kornev V. I. , Savkin A. E. , Knyazev O. A. , Lashchenova T. N. , Merlin S. , Roux P.
Published: April 2011

Comparative tests on SGN and Radon simulated ILW vitrification with a cold crucible based experimental plant were performed. The batch was fed as paste with 20 wt.% moisture. An operation conditions, the ability of the cold crucible to maintain the differential pressure during the operation, process variables, product properties, off-gas and condensate compositions, the effect of melt agitation on melter capacity and cesium loss have been determined. Melt viscosity and resistivity have been measured. Material structures were studied using infra-red spectroscopy and electron microscopy. Leach rates of sodium and potassium cations as well as Cs-137 have been measured. The behavior of sulfate and chloride ions in the vitrification process as well as their solubility in SGN and “Radon” glasses have been investigated.
Secondary Phase Formation and the Microstructural Evolution of Surface Layers During Vapor Phase Alteration of the French Son68 Nuclear Waste Glass at 200 °C
Authors: Gong W. L. , Ewing R. C. , Wang L. M. , Vernaz E. , Bates J. K. , Ebert W. L.
Published: April 2011

The SON68 inactive “R7T7” composition is the French reference glass for the LWR nuclear waste glass. Vapor phase alteration was used to accelerate the reaction progress of glass corrosion and to develop the characteristic suite of secondary, alteration phases. Extensive solid-state characterization (AEM/SEM/HRTEM) was completed on six inactive R7T7 waste glasses which were altered in the presence of saturated water vapor (200 °C) for 91, 241, 908, 1000, 1013, and 1021 days. The AEM samples were examined in cross-section (lattice-fringe imaging, microdiffraction, and quantitative thin-film EDS analysis). The glass monoliths were invariably covered with a thin altered rind. The layer became thicker with time: 0.5μm for 22 days; 4 μm for 91 days; 6 μm for 241 days; 10 μm for 908 days; 26 μm for 1013 days; and <35μm for 1021 days. The composite alteration layer of the SON68 samples is at least four time less thick than that of the SRL 131 glass composition.

Six distinctive zones, based on phase chemistry and microstructure, were distinguished within the well-developed surface layers. Numerous crystalline phases such as analcime, tobermorite, apatite, and weeksite were identified on the surfaces of the reacted glasses as precipitates. Two crystalline phases, Ag2TeO3 and (Ca,Sr)Mo3O9(OH)2, were found within the inner zones of surface layers, and they must have nucleated in situ, indicating that Ag, Te, Sr, and Mo can be retained within the surface layer. The majority of the surface layer volume is composed of two morphologically and chemically different structures: one consists of well-crystallized fibrous smectite aggregates occurring along with cavities, the A-domain; and the other consists of poorlycrystallized regions containing needle-like smectite (montmorillonite) crystallites, a silica-rich amorphous matrix, and possibly ZrO2 particles, the B-domain. The retention of rare-earths and Zr mostly occurred within B-domains and that of transition elements, such as Zn, Cr, Ni, and Mn, in A-domains. The recrystallization of poorly-crystallized B-domains into well-crystallized Adomains may influence the long-term behavior of rare-earths, Zr, and transition elements. The mechanism of surface layer formation during vapor phase alteration is discussed based on the cross-sectional AEM studies of surface layers of the SON68 waste glasses.
Long-Term Results from Unsaturated Durability Testing of Actinide-Doped DWPF and WVDP Waste Glasses
Authors: Fortner Jeffrey A. , Bates John K.
Published: April 2011

Results from durability drip tests designed to simulate the unsaturated conditions in the proposed Yucca Mountain Repository are reported for two actinide-doped glasses used as model waste forms. These tests are being conducted with reference glass compositions doped with neptunium, plutonium, and americium from the Defense Waste Processing Facility (DWPF) and the West Valley Demonstration Project (WVDP), and have been ongoing for over 8 years. Solution compositions, including transuranics, have been periodically determined, and selected analyses of colloid formation and composition, glass corrosion layers, and solid alteration phases have been obtained by scanning and analytical transmission electron microscopies. The importance of integrated testing has been demonstrated, as complex interactions among the glass, the groundwater, and the sensitized stainless steel have been observed. The cumulative releases of both glassforming and dopant elements are presented along with identification of reaction phases and their partitioning between solution and solid phases. Alteration phases, including smectite clay, iron silicates, uranium silicates, and calcium thorium phosphate, have been observed forming on the glass and stainless steel and have occasionally been found suspended in solution as colloids. Actinides, except neptunium, concentrate into alteration phases or sorb onto the stainless steel. The subsequent transport of the actinides is then controlled by these phases.
Corrosion of Waste Glasses in Boom Clay: Studies of Element Concentrations by Sims
Authors: Lodding A. , Van Iseghem P.
Published: April 2011

In-situ corrosion tests on nuclear waste glasses in Boom clay provided direct contact glass-clay at 90°C, for periods of 2, 3.5 and 7.5 years. The corroded reference glasses (two R7T7 type glasses, four Pamela type glasses), were studied in terms of SIMS (secondary ion mass spectroscopy) and mass losses.

The Al2O3 rich Pamela glasses appear to corrode in a selective-substitutional way, the other glasses dissolve almost congruently. Differences in the corrosion extent between the glasses are associated with compositional differences and secondary phase formation. SIMS analysis provides the reaction layer thickness and the relative element behaviour in this layer. Although relatively few, the data have provided a coherent picture of glass corrosion, in terms of corrosion mechanisms, time and glass composition dependence.
Investigation of Urtite as an Analog of Waste Slag from a Plasma Shaff Furnace
Authors: Dmitriev S. A. , Stefanovsky S. V.
Published: April 2011

abstract

Mineralogical-geochemical investigation of a sample of nepheline syenite (urtite) as a natural analog of final radioactive waste form has been performed. The specimen of urtite consists of nepheline, alkali feldspar, pyroxene, sphene, apatite and minor magnetite and amphibole. As a first approximation, urtite simulates the mineral composition of waste slag produced in a plasma shaft furnace at SIA “Radon”. Determination of chemical compositions of the minerals by electron-probe microanalysis has shown that the main phases that hosted radionuclides and their geochemical analogs are as follows: nepheline (Rb and probably Cs), feldspar (Ba), sphene (Zr, Nb, REE, and actinides) and apatite (Sr, REE, and actinides).
Anomalous Diffusion in Radwaste Glasses
Authors: Ojovan M. I. , Karlina O. K , Kachalov M. B.
Published: April 2011

Fractal structure domains for inhomogeneities in radwaste glasses were determined. SEM and TEM photos were analyzed for this aim as well as the Cs-137 leaching process for glass specimens. Unusual character of leaching was observed provided by anomalous diffusion of radionuclides through fractal cluster made of inhomogeneous particles.
Performance Assessment of Zircon as a Waste Form for Excess Weapons Plutonium Under Deep Borehole Burial Conditions
Authors: Weber W. J. , Ewing R. C. , Lutze W.
Published: April 2011

Zircon (ZrSiO4) is proposed as a waste form for excess weapons-grade plutonium. Zircon is an extremely durable ceramic that is often found as an accessory mineral in Precambrian terranes with ages up to 4 billion years. The chemical durability of zircon in groundwater far exceeds that of other waste forms, as modeled leach rates may be as low as 10-11g/m2d. At least 10 wt% Pu can substitute for Zr in zircon. Self-radiation damage from alpha decay leads to a crystalline-to-amorphous transformation that is modeled as a function of time and temperature for deep borehole conditions. Based on the results of this assessment, zircon could meet all necessary durability and criticality criteria required for a Pu waste form. The types of data used in this analysis are generally not available for other crystalline ceramics or glasses.
The Interaction Between Synroc-C and Pure Water or Boom Clay
Authors: Iseghem Pierre Van , Jiang Wei , Blanchaert Marc , Hart Kaye , Lodding Alexander
Published: April 2011

We investigated the interaction between Synroc-C and deionized water or Boom clay disposal media. We used powdered Synroc-C to achieve high SA/V (surface area to volume) conditions (100, 1000, 10000 m-1). The temperature was 90°C. Reaction progress up to 10+6 days/mi was reached. We conclude that dissolution in DW is mainly controlled by initial ion exchange, followed by matrix dissolution. In both Boom clay media (a 500 g/l and a 2000 g/l clay/claywater mixture) matrix dissolution is dominating. The depletion depth of the main Synroc constituent Ti is below 250 nm in the clay media, and below 2 nm in DW after 110 days corrosion at 100 m-1. The corrosion rates are very small, though we cannot present meaningful values. The effect of Boom clay is mainly to increase the solubility of Ti, Zr and the rare earths in solution.
Neptunium-Doped Synroc: Partitioning, Leach Data and Secondary Phase Development
Authors: Smith Katherine L. , Blackford Mark G. , Lumpkin Gregory R. , Hart Kaye P. , Robinson Brett J.
Published: April 2011

Np-doped Synroc was subjected to modified MCC-1 leach tests in demineralised water at 70°C. Normalised total differential Np leach rates were about 10−4 g m−2 d−1 initially, decreased to about 10−5 g m−2 d−1 after 60 days and stayed approximately constant for periods totalling up to 2283 d. Scanning electron microscope (SEM) and analytical transmission electron microscope (AEM) examination of discs leached for periods totalling 56 d or longer showed that they were covered with crystalline anatase, brookite and ilmenite. The crystalline secondary phases initially nucleated in polishing scratches and on perovskite grains. However, after leaching for a total of 422 d most of the surface was covered. None of the secondary phases contained observable amounts of Np (< 0.2 wt%). These data are discussed in relation to previous work.
The CaO-TiO2-ZrO2 System at 1200 °C and the Solubilities of Hf and Gd in Zirconolite
Authors: Swenson D. , Nieh T. G. , Fournelle J. H.
Published: April 2011

Phase equilibria are established in the CaO-TiO2-ZrO2 system at 1200 °C, using X-ray diffraction and electron probe microanalysis. The existence of two previously reported ternary phases, zirconolite (CaZrTi2O7) and calzirtite (Ca2Zr5Ti2O16), is confirmed. Each of these phases exhibits a significant range of homogeneity between TiO2 and ZrO2 while maintaining a nearly constant concentration of CaO. The ternary solubilities of the constituent binary phases are found to be negligible, with the exceptions of the perovskites, which display mutual solubility of at least 22 mol.% and may in fact form a series of continuous solid solutions. The solubilities of Hf and Gd in zirconolite are also investigated. While Hf-bearing samples did not reach thermodynamic equilibrium under the experimental conditions employed, the existence of a Hf analog to zirconolite, CaHfTi2O7, is conclusively demonstrated. The phase is stable at the stoichiometric composition, and its lattice parameters are very close to those reported in the literature for stoichiometric zirconolite. A Gd-bearing sample of the composition Ca0.88Zr0.88Gd0.24Ti2O7 is found to be essentially single phase zirconolite, in agreement with previous investigations at higher temperatures.