bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication and Luminescence of Etched Quantum Rings and Vertically Coupled Dots
Authors: Philippa G. E. , Galeana J. A. Mejia , Cassou C. , Wang P. D. , Guasch C. , Vögele B. , Holland M. C. , Torres C. M. Sotomayor
Published: April 2011

The fabrication of GaAs-GaAIAs coupled quantum dots and of quantum rings using electron beam lithography and dry etching is described. Coupled dots of physical diameter of 500 and 250 nm were fabricated and processed with top electrical contacts to apply an electric field. We show that the emission spectrum of coupled dots is modified by the electric field. Quantum rings of 400 nm outer diameter and wall thickness of 25 nm were fabricated. The emission spectrum from rings showed the quantum well emission shifted to higher energies and although its intensity decreased by about one order of magnitude there was little linewidth broadening.
In-Situ and Ex-Situ Studies of Silicon Interfaces and Nanostructures by Ellipsometry and Rds
Authors: Rossowl U. , Mantese L. , Frotscher U. , Aspnes D. E. , Richter W.
Published: April 2011

We report surface-induced optical anisotropy (SIOA) spectra and dielectric function data of vicinal Si(001) surfaces using reflectance-difference spectroscopy (RDS) and spectroscopic ellipsometry (SE). To find the main contributions of the optical response we took data for clean and by hydrogen, oxygen, and arsenic modified surfaces. The SIOA lineshapes, as measured by reflectance-difference (RD) spectroscopy, can be either derivative-like or similar to the dielectric function as measured by SE. The derivative-like spectra appear to be associated with step contributions while the dielectric-function-like behavior appears to arise from terrace dimers and/or changes in chemical species bonded to the steps. In addition, we present SE data of silicon nanostructures formed by electrochemical etching and find that their behavior is dominated by interface properties.
Scanning Electron Microscopy (Sem), Transmission Electron Microscopy (Tem) and Secondary Ion Mass Spectroscopy (Sims) Characterization of the Morphology of Aluminum Bond Pads for Surface Reflectivity Applications.
Authors: Schade M. , Ai R. , Stein Y. , Anderson T.
Published: April 2011

Extreme variations in surface reflectivity/topography have been observed on silicon wafers with evaporated aluminum metallization following thermal annealing processes. Such topographic variations negatively impacted the performance of wire bonder pattern recognition systems. It was proposed that this variation was attributed to differences in deposition rates during evaporation of the aluminum front metallization. SEM analysis revealed that the topographically rough sites, deemed as normal for this processing sequence, had large numbers of hillocks, while the smooth sites exhibited limited numbers of hillocks after heat treatment. SIMS depth profiling analyses did not indicate that any elemental difference existed between the smooth and the rough sites, although interfacial differences were detected. Specifically, the Al-Si interface for the rough surface was more graded in nature while the Al-Si interface for the smooth surface was more abrupt. TEM analysis of the rough sites revealed that a three-dimensional island growth mechanism prevailed during film growth, resulting in uneven surface development, whereas analysis of the smooth sites showed a columnar grain structure.
Obic Modelling, Numerical Computation and Measurement of Silicon Parameters in The Presence of Defects
Authors: Barbero F. , Maggio G. M. , Moore R. A.
Published: April 2011

In recent years the use of non-destructive techniques involving the generation of minority carriers by means of an electron beam (EBIC) or a LASER beam (OBIC) have proven to be useful in the study of the electrical properties of process-induced defects in bulk silicon. The development of a model and algorithm to obtain the diffusion length L, the surface recombination ratio S and the defect-increased recombination, by collecting the LASER-Beam-Induced-Current scanning the sample using a Schottky diode is presented. First a model to obtain the probability of collection of an electron-hole-pair generated by a point source is derived. The finite size of the collecting junction, L and S make the solution of the diffusion equation available only in integral form; it is therefore necessary to perform a numerical integration. Then a least-squares algorithm for identifying L and S in the case of bulk silicon without defects is obtained. Lastly the effect of a finite size generation volume and the increased recombination due to a line defect is taken into account. The effect of S and the distance of the defect from the surface on the signal contrast is analysed. This determines the information depth of the collected signal. It is shown how a high value of surface recombination ratio reduces the contrast and therefore impairs the possibility of detecting low-strength defects.

An analysis of the experimental results is performed and they are found to be in good agreement with the model.
Structural Characterization of Reactive Ion Etched Semiconductor Nanostructures Using X-Ray Reciprocal Space Mapping
Authors: Bauer G. , Darhuber A. A. , Holy V.
Published: April 2011

We have studied GaAs/AlAs periodic quantum dot arrays using high resolution x-ray diffraction (reciprocal space mapping) around the (004) and (113) reciprocal lattice points. From the distribution of the diffracted intensities we deduced the average strain status of the dots. From the numerical simulations it is evident that random elastic strain fields are present, which extend through almost the entire volume of the quantum dot. The simulations of the x-ray measurements revealed that the crystalline part of the dots is considerably smaller as scanning electron micrographs would indicate.
Dopant Quantification By X-Ray Absorption Spectroscopy: Zn IN InP
Authors: Niu L. , Karlicek R. F. , Geva M. , Citrin P. H.
Published: April 2011

X-ray absorption spectroscopy has been applied to layered Zn-doped InP structures containing systematically varying amounts of Zn spanning a factor of -40. The structures, similar to those used in optoelectronic laser devices, were characterized with x-ray absorption spectroscopy and SIMS to determine quantitatively the Zn concentrations. In addition to being non-destructive, the former technique was shown to be substantially more precise. A well-defined concentration regime is established in which substitutionally occupied Zn is directly proportional to Zn exposure during growth.
The Uniformity Of Surface Passivation After (NH 4)2S Treatment Studied By Near-Field Scanning Optical Microscopy
Authors: Liu Jutong , Kuech T. F.
Published: April 2011

We have achieved spatially resolved room temperature photoluminescence (PL) from MOVPE GaAs (001) surfaces by Near-Field Scanning Optical Microscopy (NSOM). The PL intensity variation was related to the change of surface state density. Using this technique, the uniformity of surface passivation after (NH 4)2S treatment has been studied. We have performed the topography, reflection and PL measurements by NSOM as well as the topography measurements by Atomic Force Microscopy (AFM) on the as grown, etched and sulfur passivated GaAs samples. The uniformity of GaAs with a thin Al0.65Ga0.35As cap layer has also been studied and compared with the (NH 4)2S treatment. We found the sub-micron scale variations in PL intensity which were not correlated to the topographic features. Theoretical modeling has been used to obtain semi-quantitative analysis of the experimental results.
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 Å. 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 (CV) characteristics with low hysteresis.
Cathodoluminescence Spectroscopy For Evaluation Of Defect Passivation In GaSb
Authors: Pal U. , Piqueras J. , Dutta P. S. , Bhat H. L. , Dubey G. C. , Kumar Vikram , Dieguez E.
Published: April 2011

Cathodoluminescence (CL) technique has been employed to study the optical properties of GaSb after deposition of hydrogenated amorphous silicon (a-Si:H). CL images recorded at various depths in the samples clearly show passivation of extended defects on the surface as well as in the bulk region. The passivation of various recombination centres in the bulk is attributed to formation of hydrogen-impurity complexes by diffusion of hydrogen ions from the plasma. Enhancement in luminescence intensity is seen due to passivation of non-radiative recombination centres. The passivation efficiency is found to improve with increase in a-Si:H deposition temperature.
Cathodoluminescence Study Of Diffusion Length And Surface Recombination Velocity In III-V Multiple Quantum Well Structures
Authors: Chao L.- L. , Freiler M. B. , Levy M. , Lin J.-L. , Cargill G. S. , Osgood R. M. , McLANE G. F.
Published: April 2011

We describe studies of luminescence and lateral transport properties of excited carriers in GaAs- A1GaAs multiple quantum well (MQW) structures by cathodoluminescence measurements in a scanning electron microscope. We examine the effect of in-plane, etch-defined feature size on MQW luminescence efficiency and variability, and determine the diffusion length and its temperature dependence from ˜ 8K to 250K. Our measurements also provide information about nonradiative surface recombination velocity at the side walls of etch-defined MQW structures.
Raman Spectroscopic Study Of Ion-Implanted And Annealed Silicon.
Authors: Tuschel David. D. , Lavine James P. , Russell Jeffrey B.
Published: April 2011

Raman spectroscopy is used to characterize silicon implanted with arsenic and then annealed. The implant dose ranged from 2 × 1012 to 2 × 1013/cm2. The as-implanted samples show a decreased Raman intensity of the 520 cm−1 optical mode, and increased Raman intensity between 400 and 500 cm−1 with respect to an unimplanted silicon wafer. The higher arsenic doses show an increase in the second-order transverse acoustic-mode (TA) intensity around 300 cm−1 relative to the secondorder transverse optical-mode (TO) intensity near 970 cm−1. Annealing restores the 2TA/2TO relative intensities and sharpens the weak peaks between 600 and 900 cm−1. The Raman spectrum is altered by the lowest dose implant and the annealing steps do not lead to a complete recovery of the pre-implant Raman spectrum. This permits the monitoring of lowdose ion-implant damage recovery with Raman spectroscopy.
In-Situ Fiberoptic Thermometry Measurements Of Wafer Temperature During Plasma Etching Using An Electron Cyclotron Resonance Source
Authors: Thomas S. , Berg E. W. , Pang S. W.
Published: April 2011

The increase in wafer temperature due to plasma heating during etching has been studied. Si and InP were etched using a high ion density discharge generated by an electron cyclotron resonance source. The wafer temperature was measured in-situ using fiberoptic thermometry as microwave power, rf power, chamber pressure, and gas flow were varied. Wafer temperatures increased with both microwave and rf power, and decreased with chamber pressure. For rf power of 50 W, chamber pressure of 1 mTorr, a source distance of 13 cm, and 10 sccm Ar flow, an increase in microwave power from 50 to 500 W caused the temperature to increase from 62 to 186 °C. Additionally, the use of He flowing at the backside of the wafer for temperature control was analyzed. By setting the backside He pressure at 3 Torr, the temperature increased from 20 °C at the beginning of the etch to only 29 °C after 12 min. Time dependent etch characteristics of InP were studied and related to the wafer temperature measurements. At 100 W microwave power, the InP etch rate increased from 100 to 400 nm/min as the wafer temperature rose from 20 to 150 °C. As the temperature increased above 150 °C, the profile became more undercut and the surface morphology improved. By setting the stage temperature to -100 °C and using 3 Torr He pressure at the backside of the wafer, the InP etch rate remained constant during etching and undercutting was suppressed. For 500 W microwave power, a fast InP etch rate of 2 μm/min was obtained when the wafer temperature was <110 °C, and it increased to over 4 μm/min when the temperature was >150 °C.
Structural Relaxation of Densified Silica Glass by Thermal Annealing
Authors: Kitamura Naoyuki , Fukumi Kohei , Makihara Masaki , Yamashita Hiroshi
Published: April 2011

Thermal relaxation of glass structure has been studied on silica glasses densified by hot isostatic pressing. Density of the glasses relaxed toward the value of an undensified glass by thermal annealing. Relaxation rates of density of the glasses were measured after the annealing at several temperatures. Fast and slow relaxation processes were found from the analysis by using a stretched exponential relaxation function Φ(t)=exp{−(t/τeffβ}). The slow process becomes dominant after the fast process. Raman scattering spectrum also has been measured through the thermal relaxation. The width of the main band at 450cm−1 increased by the annealing and recovered the value for the undensified glass after the fast process. The bands at 1060 and 1200 cm−1 shifted back to the positions for the undensified glass. The high density state(Δρ/ρ∼0.5%), however, was maintained even after the fast process. From these results, it is deduced that the fast process is due to the recovery of the O3Si-O-SiO3 tilt angle and Si-O-Si bond angle to the mean values for the undensified glass.
Structural Developments in Fragile Glass Forming Oxides
Authors: Masnik J. E. , Nickolayev O. , Kieffer J. , Bass J. D.
Published: April 2011

Brillouin light has been used to measure the complex mechanical modulus of the molecular scale structure in oxide melts. The storage modulus reflects the degree of networking and structural integrity, while the loss modulus, which can be attributed to aperiodic motions of structural components, provides a measure of the mobility of these entities. rom the loss modulus it is possible to derive the zero-shear rate viscosity, which is characteristic of a structure in thermodynamic equilibrium, and thereby provide a less encumbered insight into the molecular scale mechanisms that are underlying to the viscous momentum transport.

In this paper we compare the visco-elastic behavior of alkali borates and alkali tellurites, particularly in the temperature range between Tg and the equilibrium melting point. While in borates several mechanisms can be identified as contributing to structural relaxation, in tellurites a single mechanism dominates. The assumption of thermo-rheological simplicity, however, is invalid, and a new visco-elastic model has been developed for the description of our results.
Diffusional Dynamics Near the Glass Transition in Amorphous Polymer Thin Films
Authors: Deppe Denise D. , Torkelson John M.
Published: April 2011

A novel experimental approach involving the fluorescence nonradiative energy transfer technique is employed to study transport processes in thin polymer films near the glass transition through the measurement of energy transfer efficiency, E. Using a layered thin film sample geometry, values of the small molecule diffusion coefficient, , as low as 8 × 10−16 cm2/sec are measured within diffusion times of 3.5 hours. These studies reveal a significant dependence of both the magnitude and temperature dependence of on diffusant size.
Fractional Debye-Stokes-Einstein Law in Polymeric Liquid Crystals
Authors: Andreozzi L. , Donati C. , Giordano M. , Leporini D.
Published: April 2011

The viscosities of amorphous and semicrystalline polymeric liquid crystals η have been measured by dynamic mechanical analysis. They have been compared with the rotational correlation times of molecular probes, as drawn by Electron Spin Resonance spectroscopy on two different time scales. In all the cases the correlation times of the spinning motion of a cigar-like probes τ| and η are related by a fractional Debye-Stokes-Einstein law, i.e.η| α ηξ, ξ ≤ 1.
Kinetic Roughening of Quenched Xenon Films
Authors: Heilmann Ralf K. , Suter Robert M.
Published: April 2011

We investigate the growth of quenched Xe films formed by deposition onto a cold (15-35K) substrate via in situ measurements of x-ray reflectivity and diffraction. Surface roughness, film density, and crystallinity are determined as a function of Xe film thickness, substrate temperature and Xe flux in order to test for dynamic scaling behavior. Deposition of polycrystalline films with random crystallite orientations is achieved through heating of a grafoil sheet that is enclosed in the sample cell and has previously been covered with bulk Xe. At 16K the films are sufficiently quenched to be stable over several days, while at 25K annealing takes place. Differing atomic mobilities at different temperatures lead to contrasting scaling behavior. The substrate remains unchanged under repeated film deposition and desorption and therefore allows a systematic comparison of different films.
Fractal Growth of Clusters and Pores During Annealing of Aluminum Thin Films Deposited on Silica.
Authors: Fleury Vincent , Balazs Lazlo , Duclos Franck
Published: April 2011

Annealing of anAlthin-film on SiO2 at temperatures in the range 400-660°C leads to a chemical reaction (oxidation ofAland reduction of Si) whih proceeds via irreversible growth of 2-D aggregates which belong to a class of clusters first described in MBE.
Image Analysis and Saxs Characterisation of Mixed Aerogels
Authors: Blacher S. , Tihon Ph. , Pirard R. , Pirard J. P. , Brouers F. , Sahouli B. , Diez B. , Sobry R. , Van den Bosshe G.
Published: April 2011

The fractal structure of SiO2 - ZrO2 mixed aerogel prepared for catalytic purpose is investigated using morphological statistical methods, small angle X-ray scattering and N2 adsorption-desorption measurements. These three methods provide a description of the aerogel structure over several decades.
Verification and Application of a New Adsorption Model for Fractal Surfaces
Authors: Segars Ronald , Piscitelle Louis
Published: April 2011

A recently proposed isotherm model for adsorption on fractal surfaces is fitted to a wide range of isotherm data obtained from the literature. All curve fitting attempts produced good fits and the model parameters obtained are shown to be physically reasonable. Also, all significant model parametrs can be obtained from a single isotherm. As expected, when surface roughness is taken into account, the specific surface area determined from monolayer volume may be significantly higher than that obtained using the standard smooth surface isotherm models.
Investigation of Aggregate Structures on Length Scales from About 5 to 10,000 Å
Authors: Schmidt Paul W. , Ehrburger-Dolle Francoise , Pfeifer Peter , Rieker Thomas , Kapoor Yogendra M. , Voss Daniel J.
Published: April 2011

Small-angle x-ray scattering has been used to investigate the structure of some carbon blacks, some silicas, and an alumina-silica catalyst carrier on length scales from about 5 to 10,000 Å. Equations developed for structural studies of fractal and non-fractal aggregates of primary particles have been employed to analyze the scattering data. From the intensity data, the average diameters of the primary particles could be calculated or estimated. Despite the very different origins of the samples and the fact that the average diameters of the particles varied from about 30 to over 1000 Å, the scattered intensities from the samples had many common features. The data showed that the primary particles had a uniform density and were bounded by smooth or fractal surfaces. On length scales greater than the diameters of the primary particles but not more than a few times larger than the average diameters of the aggregates, some of the aggregates were mass fractals, and others were surface fractals.
Modelling of the Structural and Dynamical Properties of Porous Silicon
Authors: Gavartin J. L. , Matthai C. C.
Published: April 2011

The changes in the radial distribution function (RDF) and vibrational density of states (DOS) of porous silicon (p-Si) with change of porosity are studied within a modified diffusion limited aggregation model and molecular dynamics simulations. By decomposing the first peak of the radial distribution function of p-Si on to partial RDFs, for atoms having different coordinations, and partial RDFs, for bonds connecting atoms with different coordinations, we show that appearance of the structure in the first peak of the RDF in p-Si is stipulated by bonds between undercoordinated surface atoms. The vibrational DOS projected on surface atoms are also shown to be different from that corresponding to crystalline phonons. It is characterised by the relative increase of the intensity of vibrations in the acoustic region and by appearance of surface-like vibrations split from the optical band.
Phenomena Rlated to Concurrent Multiple Complex Plane Representations of the Immittance Data
Authors: Alim Mohammad A.
Published: April 2011

The concurrent multiple complex plane representation of the single/multiple semicircular relaxation(s) for the same immittance data provides a choice of selecting simultaneously operative phenomena within a heterogeneous system. The origin of this representation and the selection criteria of the phenomena are highlighted via structure-property-processing relationships. These include the development of a single equivalent circuit model by acquiring knowledge on the type of aterials, history, chemistry, composition, processing variables, microstructures, etc. The correspondence within the complex planes is attributed to the relative magnitudes of the contributing elements in the equivalent circuit model and dominance of the operative phenomena. The limitations concerning the transformation of the data from one complex plane to the other are reviewed, considering Debye/non-Debye conduction processes within the series-parallel microstructural network of electrical paths.
Electrical Properties and Defect Structure in The Sr-Fe-Co-O System
Authors: Ma B. , Chao C.-C. , Park J.-H. , Segret C. U. , Balachandran U.
Published: April 2011

The ceramic Sr-Fe-Co-O has potential use as a membrane in gas separation. This material exhibits high conductivity of both electrons and oxygen ions. It allows oxygen to penetrate at high flux rates without other gas components. Electrical properties are essential to understanding the oxygen transport mechanism and defect structure of this material. By using a gas-tight electrochemical cell with flowing air as the reference environment, we were able to achieve an oxygen partial pressure (P02) as low as 10−16 atm. Total and ionic conductivities of Sr-Fe-Co-O have been studied as a function of P02 at elevated temperature. In air, both total and ionic conductivities increase with temperature, while the ionic transference number is almost independent of temperature, with a value of ≈0.4. Experimental results show that ionic conductivity decreases with decreasing P02 at high P02 (≥10−6 atm). This suggests that interstitial oxygen ions and electron holes are the dominant charge carriers. At 800°C in air, total conductivity and ionic conductivity are 17 and 7 S/cm, respectively. Defect dynamics in this system can be understood by means of the trivalence-to-divalence transition of Fe ions when P02 is reduced. By using the conductivity results, we estimated oxygen penneation through a ceramic membrane made of this material. The calculated oxygen permeability agrees with the experimental value obtained directly from an operating methane conversion reactor.
Dielectric Constant of Sodium Silicate Glasses in Relation to Their Chemical Structure
Authors: Hsieh C. H. , Jain H.
Published: April 2011

The chemical structure of a series of aluminum substituted sodium trisilicate glasses is determined by x-ray photoelectron spectroscopy. It reveals a significant change of the chemical structure around the sodium cations and oxygen anions with the addition of aluminum. A microscopic model is developed to understand the composition dependence of the dielectric constant of these glasses in terms of the changes of chemical structure.
Grain Boundary Dopant and Heat Treatment Effects on the Electrical Properties of Polycrystalline ZnO
Authors: Chen T. D. , Lee J.-R. , Tuller H. L. , Chiang Y.-M.
Published: April 2011

Simplified varistor systems of bismuth- and cobalt-doped zinc oxide are studied. A prior study has shown that the distributions of bismuth segregation at the grain boundaries in such samples can be controlled by varying microstructure and heat treatment. Current-voltage and deep level transient spectroscopy measurements were done to evaluate the corresponding electrical properties. Low leakage and α values of ˜30 were attained, despite the nominal, twocomponent doping of these simplified varistors. Moreover, these samples show the signature defects that are found in many multi-dopant, commercial devices: two shallow bulk traps at ˜0.14 eV and ˜0.24 eV and one prominent interfacial trap at ˜1 eV.
Modelling of Electrical Conductivity of n-p Ceramic Composite Using Equivalent Circuits
Authors: Choi Gyeong Man , Jun Seok Taek
Published: April 2011

Composition dependence of electrical conductivity of ceramic composite was analyzed using a ZnO(n-type semiconductor)-CuO(p-type semiconductor) composite as a model. The contributions from grain and grain boundaries to the total conductivity of the composite were determined. New equivalent circuits were proposed which represented the distribution and connection of n and p grains and the total electrical conductivity was analyzed using the proposed circuits. Dominant equivalent circuit changed with composition and the total conductivity was determined by the exponential fractional change of two equivalent circuits. Effect of grain size on the grain boundary and total conductivity were also examined.
The Detection And Mapping Of Defects In Organic Coatings Using Local Electrochemical Impedance Methods
Authors: Taylor S. R. , Wittmann M. W.
Published: April 2011

Coating failure initiates as a local event at defects which can result from chemical heterogeneities in the resin or physical defects such as bubbles, underfilm deposits, or pinholes. The ability to detect, map the location, as well as make quantitativein-situmeasurements of coating heterogeneities will help identify the source of failure (i.e. coating chemistry, method of application, cure schedule, etc.) and provide insight into the mechanisms of coating degradation. This study used a 5 electrode arrangement to perform local electrochemical impedance spectroscopy (LEIS) on coated steel substrates. Using single frequency measurements, LEIS could successfully detect and map both intentional chemical heterogeneities and physical defects such as subsurface bubbles, underfilm deposits, and pinholes. Efforts to optimize probe design and instrumentation are ongoing.
Y2BaCuO5Addition and Its Effects on Critical Currents in Large grains of YBa2Cu3O7-σ: A Quantitative Microstructural Study
Authors: Chopra Manoj , Meng R. L. , Chu C. W. , Chan Siu-Wai
Published: April 2011

The addition of Y2BaCuO5(211) particles to large grain Yba2Cu3O7−δ(Y123) has significantly improved the critical current (Jc) in this material. Here a systematic quantitative analysis on the effect of the measured 211 present in large grains of Y123 has been performed, after the process of melt texturing, both on a microscopic and a nanoscopic scale with a systematic variation of the initial volume percent of 211 addition. From the correlation between critical current measurements and quantitative microscopy of both (001) and (110) sections, a maximum value of weighted Jcis observed corresponding to a measured Y123 volume percent of 20%. Although an increasing addition of 211 is effective in producing efficient flux pinning sites in the Y123 matrix, percolation paths in the Y123 matrix become limited for supercurrent. Accounting for the loss of liquid phase, we estimate an optimum initial volume of 211 for highest Jc to be 40%. Further correlation between the Jcand the true flux pinning force (Fp) shows a maximum pinning force for an initial 211 addition of 40%. However the pinning efficiency of the superconducting Y123 matrix is found to improve with an increasing 211 addition. Hence an optimum amount of 211 addition is essential for obtaining the best possible electrical characteristics in the superconducting composite.
AC Properties of Carbon Black Filled Polymer Blends
Authors: Brouers F. , Royen I. , Blacher S. , Pirard R. , Gubbels F. , Jerome R. , Sarychev A.
Published: April 2011

The macroscopic electrical properties of carbon black filled polyethylene (PE)/polystyrene (PS) blends depend strongly on the selective localization of carbon black particles in one of the phases of the polyblend. The electrical and dielectric properties of these materials can be understood in the framework of the double percolation theory. It appears that in the vicinity of the carbon black percolation threshold, the electrical conduction is dominated by tunneling. The recent theory of Brouers and Sarychev which includes quantum tunneling in the percolation scaling laws provides the basis for a discussion of the observed frequency dependence of the conductivity and the dielectric constant in the range 10−3 – 106 Hz and its relation to the blend morphology.
Numerical Study of D.C. Conductivity & A.C. Impedance for the Close-Packed Mixture of Hard Spheres
Authors: Han D. G. , Choi G. M.
Published: April 2011

Using a computational methodology, we studied average electrical properties, or, more specifically, d.c. conductivity and a.c. impedance spectra, of macroscopic mixtures of hard spheres numerically. Numerical results were compared with the calculated results of analytic equations which were generally used to describe the d.c. and a.c. electrical properties of composites. It is the purpose of this paper to provide information regarding to the geometrical arrangement effects. It was found that geometrical arrangement effects become more important as the sample size becomes smaller and the filling fraction closer to an effective percolation threshold.
Process-Monitoring Via Impedance Spectroscopy
Authors: Seitz Martin A. , Hirthe Richard W. , Koehler Charles J.
Published: April 2011

The improvement of process yields and efficiency are often dependent upon the availability of sensors that allow real-time in-process control. The sensitivity of impedance techniques to physical, chemical, and microstructural features of a material system offers significant potential in developing real-time sensors. Two examples of how impedance techniques can be used to follow changes in materials throughout out a process are discussed. The first of these involves monitoring the processibility and viability of solder pastes used in surface mount technology. The second example deals with monitoring the state of an ion exchange resin bed as used in water softeners.
AC Conductivity of Crystalline Materials and Glasses Ascribed to ADWPs
Authors: Nowick A. S. , Vaysleyb A. V. , Jain H. , Lu X.
Published: April 2011

The behavior of the frequency dependence of the conductivity, σ(ω), of numerous crystalline materials and glasses is close to an ω1.0 dependence in the limit of low temperatures and/or high frequencies (referred to as the “nearly constant loss”, or NCL, regime). Detailed analysis of this behavior, including the frequency dependence of both ε′ and ε″, shows that it can be described phenomenologically as produced by a broad distribution of asymmetric double-well potentials (ADWPs) with low activation energies. In order to obtain an understanding of the atomic origins of such potentials, we investigate the composition dependence of this behavior in such materials as crystalline CeO2:1%Y3+ ceramics with variable [Y3+] and alkali germanate glasses with variable alkali concentration. The appearance of a discrete loss peak in CeO2: 1%Y3+ helps us understand the ADWPs as due to “off-symmetry” configurations that undergo wiggling motion between adjacent minimum-energy positions.
Control of R7T7 Nuclear Glass Alteration Kinetics Under Saturation Conditions
Authors: Gin S.
Published: April 2011

The hypothesis of French nuclear waste glass disposal in a geological repository implies a comprehensive assessment of all the glass elements liable to participate in controlling the material alteration kinetics. The hypothetical existence of kinetically limiting elements other than silica could account for the observed R7T7 glass behavior in the presence of certain clays, and notably the continued high alteration rates observed even after silica saturation occurs. Flowing experiments with solutions near silica saturation but highly subsaturated with respect to aluminum hydroxide were defined to investigate the possible limiting role of aluminum. Experiments were conducted at different flow rates with the same constant steady-state H4 SiO4 activity for all the tests. The glass dissolution rate was observed to depend on the solution flow rate, indicating that under these conditions the kinetics are not controlled by dissolved silica alone. An additional experiment, in which only the Al(OH)4− activity in solution was allowed to vary, demonstrated the critical role of this element. Several interpretations are discussed.
Surface Characterization of Simulated Low-Level Radioactive Waste Glasses Corroded in Water and LiOH Buffer Solution
Authors: Li H. , Schweiger M. J. , Hrma P. , Feng X
Published: April 2011

Chemical durability of simulated radioactive low-level waste (LLW) baseline glass, 6- 5412, was found to decrease with the addition of either phosphate or sulfate, or chromium oxide. Scanning electron microscopic study of corroded samples suggests that the effect of these components on glass chemical durability may be attributed to cluster formation of: Na-O-P-O or Na-O-S-O, or (O0)3-Cr3+(O−)3 groups. Preferential corrosion attack was severe on certain corroded sample surface areas that are possibly enriched in these clusters. Durability tests in a solution with LiOH as a buffer suggest that chlorine in the glass slightly improved glass corrosion resistance, while fluorine significantly deteriorated glass corrosion resistance.
7-Years Leaching Tests of NPP Vitrified Radioactive Waste
Authors: Barinov A. S. , Ojovan M. I. , Ojovan N. V.
Published: April 2011

Long term tests of vitrified intermediate level waste from nuclear power plants were performed in a shallow ground repository as well as on an open testing area. Borosilicate glasses were tested. Radionuclide leaching differs significantly in natural conditions in contrast to laboratory behaviour. Average leaching factors were obtained for open area tests as well as for repository tests. These factors should be used for long term predictions since they take into account the real character of leaching.
Modelling Glass Dissolution with a Monte Carlo Technique
Authors: Aertsens Marc , Iseghem Pierre Van
Published: April 2011

We present a Monte Carlo simulation method for modelling glass dissolution in aqueous solutions. This simulation method is consistent with transition state theory, and therefore also with the glass dissolution rate law, used for instance in the Grambow model. The simulation method allows to add dynamics (kinetics) to the existing thermodynamic models for glass dissolution. Using this method, it is possible to model non stoichiometric dissolution of the glass.

Besides, we introduce a simple, first version of a model in which we use the simulation method. In this model, we approximate the glass by a lattice. We assume that the glass contains two components: a network former and a network modifier. Bonds between two network formers are assumed to be much stronger than any other bond in the system. We observe that above a threshold value for the concentration of network modifiers, the glass dissolves fast. No surface layer develops and the dissolution rate is constant (linear stoichiometric dissolution). Below this threshold, the glass is more durable and surface layers are formed. As time goes on, the thickness of the surface layers grows. The dissolution of the glass is not stoichiometric. This behaviour agrees with experimental results.
A Melting Route to Synroc for Hanford HLW Immobilization
Authors: Vance E. R. , Day R. A. , Carter M. L. , Jostsons A.
Published: April 2011

For the HLW fractions of certain Hanford tank wastes, wasteforms consisting mainly of crystalline Synroc phases in an aluminosilicate matrix can be formed by melting at 1350–1450°C in a neutral atmosphere, with waste loadings of up to 70 wt%, depending on the waste composition. The leachability of all measured elements in 7-day PCT tests was <0.1 g/m2/d at 90°C in the best materials.
Options and Choices in the Disposition of Excess Weapon Plutonium
Authors: Garwin R. L.
Published: April 2011

More than 50 tons of weapon-related plutonium (WPu) is expected to become excess andavailable for disposition by the year 2003 in Russia and a similar amount in the United States.Per two reports from the Committee on International Security and Arms Control of the NationalAcademy of Sciences (1994 1 and 1995 2), the hazard of theft and incorporation into nuclearweapons impels us to guard this Pu carefully and as soon as possible to transform it into a formless accessible for use in nuclear weapons. To this end, CISAC adopted the “Spent FuelStandard” for the disposed WPu, which, if met, renders the WPu no greater hazard per kg thanthe much larger amount of reactor Pu in the form of spent fuel, since CISAC finds that separatedRPu can be used for nuclear weapons with little additional difficulty beyond that posed byseparated WPu. Many disposition routes can be eliminated on the basis of cost or other metric.The two principal survivors (of about equal cost and difficulty for the United States) are thepartial burning of WPu as MOX and the direct vitrification of WPu (as oxide) with high-level‘defense wastes’. Both these approaches should be pursued urgently, with experiments toqualify the processes, until one is selected on the basis of hard evidence. Either approach wouldcost about $1 B, within a factor two, to dispose of 50 tons of excess WPu. The CISAC analysiswill be presented, with comments on utility of RPu in weapons, on the DOE PlutoniumDisposition Study, and on ‘explosive criticality’ in the repository.
Ceramic Waste Form for Residues from Molten Salt Oxidation of Mixed Wastes
Authors: Konynenburg Richard A. Van , Hopper Robert W. , Rard Joseph A. , Ryerson Frederick J. , Phinney Douglas L. , Hutcheon Ian D. , Curtis Paul G.
Published: April 2011

A ceramic waste form based on Synroc-D is under development for the incorporation of the mineral residues from molten salt oxidation treatment of mixed low-level wastes. Samples containing as many as 32 chemical elements have been fabricated, characterized, and leach-tested. Universal Treatment Standards have been satisfied for all regulated elements except two (lead and vanadium). Efforts are underway to further improve chemical durability.
Synthesis of Zircon for Immobilization of Actinides
Authors: Burakov B. E. , Anderson E. B. , Rovsha V. S. , Ushakov S. V. , Ewing R. C. , Lutze W. , Weber W. J.
Published: April 2011

A new method of synthesis for actinide-doped zircon is presented based on studies of zircons formed by crystallization from the reactor core melt generated in the course of the accident at the Chernobyl Nuclear Power Plant. These zircons have compositions in the range (Zr0.94, U0.06)SiO4to (Zr0.9, U0.1)SiO4. Hot-pressing of oxides was studied to make Zr-based waste forms. The results demonstrate the efficacy of using metallic zirconium in synthesizing high-actinide zircons. In the event of deviations from zircon's ideal stoichiometry, ZrO2forms, which is also an effective host phase for actinide elements. Waste streams high in zirconium and actinides could be converted into Zr-based waste forms. The adaptation and modification of the mixed-oxide reactor fuel (MOX) production process is proposed as a process for the production of (Zr,Pu)SiO4, a durable waste form for excess weapons plutonium.
Effect of Conjoint Additions of Rare Earth Element Oxides on the Phase Stability of Zirconia
Authors: Maddrell Ewan R.
Published: April 2011

The ability of the cubic phase of zirconia to accommodate in solid solution the oxides of rare earth elements with differing cationic radii has been investigated. Mixed oxide phase assemblages were prepared by hydrolysing zirconium butoxide with solutions of rare earth element nitrates followed by drying, calcining and sintering. The resulting products were characterised by X-ray diffraction and energy dispersive spectroscopy. The cubic zirconia phase can accept into solid solution the larger, non-cubic stabilising, rare earth element ions such as lanthanum in the presence of the cubic stabilising oxides of yttrium and samarium. As the proportion of the larger rare earth element ions is increased the formation of pyrochlore type compounds is favoured.
Aeschynite and Euxenite Structure-Types as Host Phases for Rare-Earths and Actinides from HLW
Authors: Gong W. L. , Ewing R. C. , Wang L. M. , Xie H. S.
Published: April 2011

Aeschynite and euxenite structure-types are proposed as host phases for rare earth elements and actinides. Aeschynite and euxenite structure types are represented by the general formula: (REE,Y,Th,U,Ca)(Ti,Nb,Ta)2O6. In both structure-types, a variety of large cations such as rareearths and actinides can be accommodated in the tunnels of connected holes in aeschynite or the interlayer space in euxenite. The waste loadings (rare-earths and actinides) in aeschynite and euxenite are at least 40 wt. % based on chemical compositions of naturally occurring aeschynite and euxenite.

The sol-gel method has been successfully used to prepare aeschynite and euxenite as preferred crystalline ceramics. The aged gels and finally calcined products have been characterized by infrared and Raman spectroscopy, differential thermal analysis, and X-ray diffraction analysis. The fabrication technology of aeschynite and euxenite type ceramics is feasible by using hot-pressing as a final processing stage. The mechanistic processes of aeschynite and euxenite formation by the sol-gel method as described as REE(OH)3 · Nb(OH)5·Ti(OH)4 coprecipitation; the polymerization of Nb and Ti hydroxides to form isolated (Nb,Ti)2O10 di-octahedra through oxygen and hydroxyl bridges accompanied by a dehydration reaction; welding together of isolated “pieces” of (Nb,Ti) 2010 to form longer (Nb,Ti)2O10 di-octahedral chains; REE being connected to the dioctahedral chains through oxygen and hydroxyl bridges; and to gradually form small threedimensional nucleates of aeschynite and euxenite. Critical data from the literature on radiation effects and secondary alteration are reviewed as a part of the evaluation of the long-term performance of these phases.
Excess Pu Disposition in Zirconolite-Rich synroc
Authors: Vance E. R. , Jostsons A. , Day R. A. , Ball C. J. , Begg B. D. , Angel P. J.
Published: April 2011

The design philosophy of a zirconolite-rich Synroc variant, hot-pressed at 1200°C/20 MPa, for immobilizing excess weapons Pu is summarized. Phase analysis of Synroc variants containing different (nominated) proportions of zirconolite, Pu and Gd is presented. The presence of hollandite allows the incorporation of radioactive Cs to reduce diversion risks. The influence of chloride impurities on Synroc properties was studied to bear on the usage of encapsulated 137CSCI for this purpose. The maximum incorporation of the neutron poisons Gd and Hf in solid solution in zirconolite from XRD/SEM is 0.5–0.7 and 1.0 formula units respectively, with the value for Gd depending on the charge compensation scheme employed. The use of deep boreholes for disposal would promote the self-annealing of radiation damage from α-decays. The production of zirconolite-rich Synroc ceramics via fired PuO2 or a liquid Pu/microsphere precursor is also discussed. The choice of processing atmosphere for a zirconolite-rich ceramic containing Pu is oxidizing to neutral for Pu-only and Pu + Cs immobilization options, and reducing for a Pu + fission product option
Leachability of Nd, U, Th, and Sr from Cements in a CO2 Free Atmosphere
Authors: Serne R. J. , Rai D. , Martin P. F. , Felmy A. R. , Rao L. , Ueta S.
Published: April 2011

To determine the leachability and concentration-controlling solids for nuclides contained in solidified low-level nuclear wastes, cement doped with neodymium, uranium, thorium and strontium was prepared and cured in a CO2-free atmosphere. Leaching tests were conducted by equilibrating aliquots of the crushed doped cement with CO2-free deionized water at pcH+ values ranging from 7.5 to 12.5 in an effort to determine if solubility constraints could be used to predict leachable concentrations of Nd (an analog of trivalent actinides), U, Th, and Sr. Steady state concentrations of Nd, U, Th and Sr were attained within a few days. The observed Nd concentrations continually decreased with the increase in pcH+ from about 7.5 to 9.0, and were at detection limit at pcH+ values > 9.0. The comparison of these results with thermodynamic data suggests that Nd(OH)3(am) is the controlling solid phase. The observed U concentrations decreased by two orders of magnitude with a unit increase in pcH+ in the range of 7.5 to 9.0 and were at the detection limit at pcH+ > 9.0. From the multitude of U(VI) solids that can form under the test conditions, the data suggest that CaUO4 is the likely controlling solid. The concentration of Th was at the detection limit over the entire pcH+ range covered. Based on previous work, ThO2(am) is likely to be the controlling solid. In the absence of CO2, no solubility-controlling solid was found for Sr.
The Effect of Water Vapor on the Corrosion of Carbon Steel at 65°c
Authors: Gdowski Gregory E. , Estill John C.
Published: April 2011

AISI 1020 carbon steel was exposed to air at various relative humidities at 65°C. A “critical relative humidity” (CRH) of 75–85% was determined. The CRH is the transitional relative humidity where oxidation/corrosion changes from dry oxidation to aqueous film electrochemical corrosion. Short term testing suggests that aqueous film electrochemical corrosion results in the formation of an inner oxide of Fe3O4, and an outer oxide of a powdery Fe2O3 and/or Fe2O3·xH2O.
Long-Term Thermal Stability of Alloy 825 as a High-Level Nuclear Waste Container Material
Authors: Dunn D. S. , Pan Y.-M. , Cragnolino G. A. , Sridhar N.
Published: April 2011

The thermal exposure of Fe-Cr-Ni-Mo materials to certain temperature regimes often results in the formation of grain boundary carbides and the associated depletion of alloying elements. This phenomenon, termed sensitization, is frequently the result of welding processes or in service exposure to elevated temperatures. In this investigation, alloy 825, a candidate high-level nuclear waste (HLW) container material, was thermally exposed to temperatures in the range of 550 to 800 °C for periods of up to 1,000 hr. Sensitization of the material was evaluated by corrosion tests and grain boundary analyses using an analytical electron microscope. The sensitized microstructure was found to contain M23C6-type carbides as well as a Cr-depleted region in the vicinity of the grain boundaries. The degree of sensitization was correlated to the extent of Cr depletion in the grain boundary region.