bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of the Charge Attached to Micro-scale Devices Used in Fluidic Self-Assembly Processes
Authors: Tkaczyk Eric , Handa Vandna , Lee Sangwoo , McNally Helen , Gui Lichuan , Wereley Steve , Bashir Rashid
Published: April 2011

Self-assembly of micron sized and smaller particles has previously been demonstrated using biologically inspired events such as DNA hybridization and interactions of ligands and receptors. In order to implement these techniques to create practical electronic devices, a quantitative measure of the amount of substance attached to the device surface just prior to the final assembly is essential. In the present investigation, this crucial quantity was investigated from the electrophoretic mobility of particles, which was ascertained by examining their motion under applied electric fields ranging from 0 to 1 V/mm. Sequential CCD camera images processed with custom software enabled calculation of particle velocities during their viscous motion in an inexpensive electrophoresis chamber filled with a low-conductivity buffer solution. A linear fit through the velocity vs. electric field data points yielded the electrophoretic mobility, which was utilized in the Stokes equation to calculate the net amount of charge present on each device. For 5.44 micron carboxyl-coated polystyrene beads, this method indicated a charge of 2.69e-15 C per particle. The manufacturer of the beads, Spherotech corporation, quoted 6.37e-11 C as the expected charge. The more than three orders of magnitude discrepancy is at least partially attributable to the electrophoretic retardation and relaxation effects of small electrolyte ions in the buffer solution. The method was also applied to silicon islands in the shape of a cone frustum with similar dimensions to the beads. A mercapto-ethane-sulfonate monolayer, attached via thiol bonds to the gold-coated surface of the islands, provided the charge. The amount of charge on an island was calculated to average 2.48e-15 C, corresponding to a density of 3.82e10 mercapto-ethane-sulfonate groups per square centimeter of Au surface.
Nanowire and Nanotube Materials Prepared from Polymer Fiber Templates
Authors: Dong Hong , Nyame Verrad , Jones Wayne E.
Published: April 2011

The preparation of well-defined nanomaterials using template methods is well established in the materials literature including porous ceramics, open-framework layered structures and porous membranes. In an effort to prepare thermally and electrically conductive nanowire and nanotube materials, we have recently prepared carbon tubes using polymer fibers produced from an electrostatic, non-mechanical “electrospinning” process as templates. Poly(methyl methacrylate) (PMMA) fibers with average diameter of 150–200 nm were initially fabricated as core materials. The fibers were subsequently coated with a thin layer (20∼50 nm) of conductive polypyrrole (PPy) by in-situ polymerization. Upon high temperature (1000 °C) treatment under inert atmosphere, the PMMA core fibers decomposed completely, followed by carbonization of the PPy wall. The structure of the carbon tubes subsequently produced was demonstrated by SEM and TEM. The carbon tubes were analyzed by infrared, elemental analysis and electron diffraction. The results show that the tubes are largely carbon with a small amount of nitrogen and a relatively low crystallinity.
Characterization Of SnO2 Nanoparticles Deposited Via Layer-by-Layer Self Assembly And Investigation Of Their Sensing Properties
Authors: Ghan R. C. , Lvov Y. , Besser R. S.
Published: April 2011

A technique of Layer-by-Layer (LbL) self-assembly is used to deposit SnO2 nanoparticles on Quartz Crystal Microbalance (QCM) resonators, and on glass substrates which the authors believe has not been previously reported. Characterization of self-assembled SnO2 layers has been performed using QCM, Scanning Electron Microscopy (SEM), and Zeta Potential analysis.

We have successfully deposited SnO2 nanoparticles on QCM resonator using self-assembly technique. LbL self-assembly is a method of organization of ultra-thin films by interlayer electrostatic attraction. The thickness and mass of the self-assembled layers can be characterized by the frequency shift obtained using the QCM and empirical equations relating change in frequency with mass and thickness of deposited layers. The deposition of SnO2 nanolayers exhibited a linear reproducibility and the process of self-assembly was independent of the residence time of QCM resonator in the SnO2 nanoparticle colloidal solution. High resolution SEM analysis reveals that the SnO2 nanoparticle layers are uniformly deposited across the entire substrate. Electrical characterization was performed on SnO2 nanoparticle layers self-assembled on glass substrates which were patterned for two point (current-voltage) IV characteristic measurements. Two classes of samples were used. One sample was self-assembled glass substrate patterned with electrical contacts and calcined (baked at 350°C for one hour) to eliminate interlayered polyions and the other sample was not calcined. Results revealed that the calcined samples demonstrated linear ohmic behavior but the uncalcined showed some spurious points which we believe are due to the polyion layers.

Characterization of the self-assembled SnO2 nanoparticles is being carried out with the intention of fabricating a high-selectivity μ-gas sensor. A test chamber has been fabricated and results of resistance behavior of the sensor with variation in temperature have been presented.

The sensor can find applications in high selectivity sensing of chemical, industrial, domestic, and hazardous environments. After further research and development, this μ-gas sensors could be made generic to sense a variety of gases and employed for integrated on-chip product analysis in multiple chemical microsystem applications.
Fracture Mechanical Evaluation of GaAs Wafers
Authors: Schaper M. , Jurisch M. , Bergner F. , Hammer R.
Published: April 2011

Strength and fracture toughness of (100) oriented GaAs wafers are analyzed by fracture and indentation testing. Using finite element method (FEM) critical fracture stresses are calculated from the fracture loads of wafers tested under biaxial bending, whereas atomic force (AFM), scanning electron microscopy (SEM) and acoustic C-scan microscopy of deformation and cracking patterns around micro- and nano-indentations provided information on yielding, crack initiation and crack growth resistance. Through fracture mechanical evaluation of these results critical defect sizes are derived, which are tolerable without strength degradation. It is shown, that a fracture strength of at least 800MPa can be achieved by careful fabrication even of 6' wafers. This figure is much higher then the prescribed minimum strength level estimated to avoid premature failures during wafer handling and processing routes.
High-Resolution Study of Light and Heat Patterns in Infrared Emitting Devices
Authors: Malyutenko V.K.
Published: April 2011

We report on light and heat distributions in the active area of infrared lasers and light-emitting diodes operating at 300 K in the 0, 8–4,7 μm spectral range. To separate light and heat produced by these devices, we developed a high-resolution multi-spectral infrared (<1 m, 3–5 m and 8–12 m ranges) “vision” facility capable of providing <20 m spatial resolution and 10 s temporal resolution. We show how current crowding and Joule heating combined drastically decrease integral power emitted by light-emitting diodes and provoke remarkable non-uniformity in light and heat maps. As concerning stripe lasers, we comment on heat spreading and heat bottlenecks inside the laser dome and quality of heat sink.
A Study on Impact of Process Parameters to Metal Organic Chemical Vapor Deposition Grown (002) Zinc Oxide Thin Films, at 320°C
Authors: Chang Yuneng , Lu Hengchuan , Hung Yumeng , Lee Chunsung , Chen Jianming , Jian Yichang
Published: April 2011

This paper reports preparation of highly oriented (002) ZnO films by atmospheric pressure CVD at 320°C, which is far below previous reported values. In this study, a cold wall horizontal system was used to thermally decompose sublimed zinc acetylacetonate (Zn(acac)2, Zn(C5H702)2) vapor, and reacted with water vapor to produce ZnO films at temperatures above 320°C. Through experimental data, we discovered that low deposition temperature, using water vapor as co-reactant and substrates with ZnO buffer layer pre-coated by PVD are the key factors to prepare (002) ZnO films. By using Si(100) pre-coated with sputtered ZnO amorphous buffer layer as substrates, the ZnO growth rate is highest. While using copper oxide pre-coated Si substrates gave the lowest growth rate, and deposited ZnO film is amorphous. Considering influence of CVD co-reactant, using Zn(acac)2 and water vapor gives higher growth rate and better crystallinity than CVD using Zn(acac)2 and oxygen. Water vapor may supply hydrogen to react with released acetylacetonyl ligand (C5H7O2), and help the formation of stable acetylaceton (C5H8O2) molecule. DPA shows that film contain 46% O and 54% Zn. XPS of Zn Auger identified the valence of Zn being Zn2+. It seems that excessive Zn might present as discrete Zn2+ dispersed between ZnO lattices.
The Role of Hydrogen in Laser Crystallized Polycrystalline Silicon
Authors: Nickel N. H. , Brendel K.
Published: April 2011

Polycrystalline silicon produced by laser crystallization of hydrogenated amorphous silicon contains large amounts of residual hydrogen. This reservoir of hydrogen can be used to passivate additional grain boundary defects by annealing the specimens at low temperatures in vacuum. Information on hydrogen bonding is obtained from hydrogen diffusion measurements. Laser crystallization results in a pronounced increase of the hydrogen binding energy in the resulting poly-Si samples compared to the amorphous precursor material. Fully crystallized poly-Si contains H concentrations of up to 17 at.%.
500 °C Formation of Poly-Si1-xGex (x≥ 0.5) on SiO2 by Ion-beam Stimulated Solid Phase Crystallization
Authors: Tsunoda Isao , Kanno Hiroshi , Kenjo Atsushi , Sadoh Taizoh , Miyao Masanobu
Published: April 2011

Ion beam stimulated solid phase crystallization of a-Si1-xGex (0 ≤ x ≤ 1) on SiO2 has been investigated. The critical temperature to cause crystal nucleation can be successfully decreased by 150 °C for a-Si1-xGex with all Ge fractions (0 - 100 %) by using ion stimulation. As a result, crystal growth below the softening temperature (∼ 500 °C) of glass substrates was achieved for samples with Ge fractions exceeding 50 %. This method combined with Ge doping and ion stimulation will be a powerful tool to fabricate poly-SiGe TFTs on low cost glass substrates.
Exchange Bias and Training Effect in Polycrystalline Antiferromagnetic/Ferromagnetic Bilayers
Authors: Kirschner Markus , Suess Dieter , Schrefl Thomas , Fidler Josef
Published: April 2011

Exchange bias and training effect are simulated for IrMn/NiFe bilayers. As a function of the thickness of the antiferromagnet the bias field shows a maximum for a thickness of 22 nm. For decreasing antiferromagnetic thickness the domain wall energy approaches zero. For large thicknesses the high anisotropy energy hinders switching of the antiferromagnetic grains resulting in weak bias. Starting from the field cooled state as initial configuration a bias field of about 8 mT is obtained assuming a antiferromagnetic layer thickness of 20 nm, a ferromagnetic layer thickness of 10 nm, and a grain size of 10 nm. The next hysteresis cycle shows a reduction of the bias field by about 65%. Exchange bias and training effect in fully compensated antiferromagnet/ferromagnet bilayers are explained with a simple micromagnetic model. The model assumes no defects except for grain boundaries, and coupling is due to spin flop at a perfect interface. The simulations show that a weak exchange interaction between randomly oriented antiferromagnetic grains and spin flop coupling at a perfectly compensated interface are sufficient to support exchange bias.
Mössbauer Characterization of Iron Oxide Nanoclusters Grown within Aluminosilicate Matrices
Authors: Papaefthymiou Georgia C. , Bustamante A. , Scorzelli Rosa B.
Published: April 2011

Mössbauer spectroscopy uses the resonant absorption of nuclear radiation by 57Fe to probe the electronic and internal magnetic structure of iron based magnetic materials. The technique has a characteristic measuring time of 10 ns enabling investigation of spin relaxation phenomena in nanoscale particles; and determination of their magnetic properties in the absence of externally applied magnetic fields. We report on Mössbauer studies of γ-Fe2O3 nanoparticles synthesized within hexagonally packed mesoporous MCM-41 aluminosilicate matrices with cylindrical pores of 2.5 nm diameter. Data analysis allowed differentiation of particle-matrix interfacial versus particle-core interior iron sites. Interfacial iron atoms experience large electric field gradients resulting in quadrupole splitting values of ΔEq (surface) = (1.25 ± 0.05) mm/s, while core atoms exhibit smaller values of δEq (core) = (0.73± 0.05) mm/s at room temperature. Similarly, differences were observed in the values of the internal hyperfine fields at low temperatures indicating reduced strength in the exchange interactions at the particle surface, with interfacial atoms experiencing internal fields Hhf (surface) = (458 ± 1) kOe reduced relative to the core Hhf (core) = (488 ±1) kOe at 4.2 K. Particle/matrix interactions at the surface appear to perturb the electronic interactions deeper into the core than the magnetic exchange interactions.
Epitaxial Si films Grown on Lattice Matched (LaxY1-x)O3/Si (111) Structures by Molecular Beam Epitaxy
Authors: Narayanan V. , Guha S. , Bojarczuk N. A. , Copel M.
Published: April 2011

Growth of epitaxial Si epitaxial overlayers on lattice matched (LaxY1-x)2O3/Si (LaYO/Si) structures has been investigated by high resolution transmission electron microscopy and reflection high energy electron diffraction. Results indicate that smooth two-dimensional near lattice-matched LaYO (111) films can be grown on Si (111) substrates. However, subsequent Si epitaxial growth on the LaYO/Si structures nucleates as three-dimensional islands, a consequence of the high energy of the Si overlayer/LaYO interface. We have investigated the effect of growth temperature on the microstructure of the Si overlayers. Higher temperatures resulted in the nucleation of large faceted islands and rough overlayers while lower temperatures result in smaller islands that coalesce at an early stage and produce smoother films. In addition, formation of planar defects in these films is attributed to stacking errors on the {111} facets of initial Si islands with lower temperatures resulting in a higher density of stacking faults and twins.
Role of the First Atomic Layers in Epitaxial Relationship and Interface Characteristics of SrTiO3 Films on CeO2/YSZ/Si(001)
Authors: Yamada Tomoaki , Kiguchi Takanori , Wakiya Naoki , Shinozaki Kazuo , Mizutani Nobuyasu
Published: April 2011

The role of the first atomic layers in epitaxial relationship and interface characteristics of SrTiO3 films on CeO2/yttria-stabilized zirconia (YSZ)/Si(001) substrates was investigated. Although SrTiO3 film deposited on CeO2/YSZ/Si directly was preferentially (110)-oriented, epitaxial SrTiO3(001) films could be grown on CeO2/YSZ/Si by controlling first atomic layer of the films. In the case of SrTiO3 film starting from TiO2 layer, the neither ion drift nor charge injection occurred in the SrTiO3/CeO2 interface. On the other hand, for the film starting from SrO layer, an injection-type hysteresis was observed. This is probably due to the electron traps in the interface.
X-ray Photoelectron and UV Photoyield Spectroscopic Studies on Structural and Electronic Properties of SrxBiyTa 2O9 Films
Authors: Takahashi Mitsue , Noda Minoru , Okuyama Masanori
Published: April 2011

Photoelectron spectra by X-ray photoelectron spectroscopy (XPS) and UV-photoyield spectroscopy (UV-PYS) have been analyzed to study O2-annealing effects on band diagrams of ferroelectric SrxBiyTa2O9 (SBT) thin films deposited by pulsed laser deposition (PLD) and metalorganic dcecomposition (MOD) methods. XPS studies on the annealed PLD-SBT film has shown a rapid shift in its Bi 4f core peaks from the oxidized to the metallic ones, as the film suffer Ar+ bombardment. Surface of the annealed film has exhibited lower Fermi level than the as-deposited one in UV-PYS. The result suggests O2-annealing can suppress leakage current through PLD-SBT films. The UV-PYS studies on MOD-SBT have shown almost the intrinsic Fermi levels before and after the additional annealing. The XPS studies have shown that the additional annealing is not effective to improve stabilities of (Bi2O2)2+ layers, once the film is baked and crystallized.
An angular dependent X-ray photoemission study of Indium-tin-oxide surfaces
Authors: Fong H. H. , Song W. J. , So S. K.
Published: April 2011

The surface properties of indium-tin-oxide (ITO) thin films treated by UV ozone or plasma were analyzed by angular dependent X-ray photoelectron spectroscopy (ADXPS) and by ultraviolet photoemission (UPS). The chemical composition, chemical states and the work function of the ITO surfaces were deduced. Our analysis indicate that ITO surface is Sn-rich. Both UV ozone and O-plasma treatments are most effective in removing surface hydrocarbon. Among all treatments, O-plasma treated surface achieved the highest work function of 4.4eV, whereas argon ion sputtered surface had the lowest work function of 3.9eV. Both O-plasma and UV ozone treatments increase the surface oxygen concentration. It is proposed that O2-ions diffuse into ITO. The diffusion length is about 50Å as deduced from ADXPS. The stoichiometry of the surface is the major factor in controlling the surface work function of ITO. A surface band bending model is proposed to account for the change of work function due to “oxidized” ITO surface after UV-ozone or oxygen plasma treatments.
Atomistic simulation study of misfit strain relaxation mechanisms in heteroepitaxial islands
Authors: Dongare Avinash M. , Zhigilei Leonid V.
Published: April 2011

The mechanisms of the misfit strain relaxation in heteroepitaxial islands are investigated in two-dimensional molecular dynamics simulations. Stress distributions are analyzed for coherent and dislocated islands. Thermally-activated nucleation of misfit dislocations upon annealing at an elevated temperature and their motion from the edges of the islands towards the positions corresponding to the maximum strain relief is observed and related to the corresponding decrease of the total strain energy of the system. Differences between the predictions of the energy balance and force balance criteria for the appearance of misfit dislocations is discussed. Simulations of an island located at different distances form the edge of a mesa indicate that the energy of the system decreases sharply as the island position shifts toward the edge. These results suggest that there may be a region near the edge of a mesa where nucleation and growth of ordered arrays of islands is favored.
Experiments with in-situ thin film telephone cord buckling delamination propagation
Authors: Volinsky Alex A.
Published: April 2011

There are many different stress relief mechanisms observed in thin films. One of the mechanisms involves film debonding from the substrate. In the case of tensile residual stress a network of through-thickness cracks forms in the film. In the case of compressive residual stress thin film buckling and debonding from the substrate in the form of blisters is observed. The buckling delamination blisters can be either straight, or form periodic buckling patterns commonly known as telephone cord delamination morphology.

The mechanics of straight-sided blisters is well understood. Current study relies on the in-situ observation of phone cord delamination propagation in different thin film/substrate systems. Both straight and phone cord delaminations are shown to simultaneously propagate in the same film system. Straight-sided blisters propagate several times faster than the phone cords, and may be followed by thin film fracture along the line of maximum film buckling amplitude. Phone cord delaminations originally start as straight-sided blisters, but then deviate to the periodic phone cord geometry due to the fact that the compressive residual stress in the film is biaxial. Digital analysis of motion recordings shows that partial crack “healing” is present at the curved portions of the phone cords due to the “secondary” buckling pushing thin film back to the substrate. These experimental observations allow for the correct interpretation of the telephone cord delamination morphology.
Crack formation due to annealing of Al2O3 films grown on Si(100) by MOCVD
Authors: Singh M. P. , Shivashankar S.A.
Published: April 2011

We report crack formation in alumina films grown on Si(100), caused by annealing in a controlled oxidizing ambient. The films were grown in a low-pressure CVD reactor, using aluminium acetylacetonate as precursor. High purity argon and nitrous oxide were employed as carrier and oxidizing gas, respectively. The films were characterized by optical microscopy and SEM/EDAX. The proportion and chemical nature of the heteroatoms, namely C and H, incorporated into the films from the precursor, were characterized by XPS, and FTIR. As-deposited films do not exhibit any cracks, while post-deposition annealing results in cracks. Apart from the delamination of the films, annealing in nitrous oxide ambient leads to an unusual crack geometry, which we term the “railway-track”. These twin cracks are very straight and run parallel to each other for as much as several millimeters. Often, two such linear tracks meet at exactly 90°. Between some of these tracks lie bullet-like structures with very sharp tips, oriented in a specific direction. As cracks are generally activated by residual stress, both thermal and intrinsic, the origins of the stresses that generate these linear cracks are discussed. The redistribution of stress, arising from the removal of C and H during annealing, will also be discussed. An attempt has been made to correlate the formation of cracks with the crystal structure of the film.
Initial Stages of InAs Quantum Dots Evolution in GaAs/AlAs Matrixes
Authors: Yakimov Michael , Tokranov Vadim , Katnelson Alex , Oktyabrsky Serge
Published: April 2011

We have studied the first phases of post-growth evolution of InAs quantum dots (QDs) using in-situ Auger electron spectroscopy in conjunction with Reflection High Energy Electron Diffraction (RHEED). Direct evidence for InAs intermixing with about 6ML (monolayers) of the matrix material is found from Auger signal behavior during MBE overgrowth of InAs nanostructures. Re-establishment of 2D growth mode by overgrowth with GaAs or AlAs was monitored in single-layer and multi-layer QD structures using RHEED. Decay process of InAs QDs on the surface is found to have activation energy of about 1.1 eV that corresponds to In intermixing with the matrix rather than evaporation from the surface.
Morphological Evolution of Ag/Mica Films Grown by Pulsed Laser Deposition
Authors: Warrender Jeffrey M. , Aziz Michael J.
Published: April 2011

Many vapor-deposited metal-on-insulator films exhibit a morphological progression with increasing thickness consisting of several distinct stages: (1) nucleation of 3-dimensional na-nocrystalline islands; (2) elongation of the islands; (3) film percolation. Here we report a study of this progression during Pulsed Laser Deposition (PLD), a technique for film deposition that differs from thermal deposition in that the depositing species arrive in short energetic bursts, leading to instantaneous deposition fluxes orders of magnitude higher than can be achieved in thermal growth. Atomic Force Microscopy reveals that advancement through this same morphological progression occurs at lower thickness in PLD films relative to films grown under comparable conditions by thermal deposition, with PLD films having lower RMS roughness at a given thickness. We also observe that for a constant amount deposited per pulse, films deposited at higher laser pulse frequency are further advanced in morphological state. Kinetic Monte Carlo simulations reveal that PLD nucleation behavior differs from that of thermally deposited films, and this can account for the observed differences. Simulations also reveal a scaling of the percolation thickness with pulse frequency that is consistent with experiment.
Morphology Control of Pulsed-Laser Deposited Ag Quantum Dots
Authors: Machi Kinuyo , Nagare Sanshiro , Hamada Kenji , Senna Mamoru
Published: April 2011

Self-organized Ag nanodots were deposited on Si(100) by a pulsed laser deposition method. A compact apparatus was specially developed for this purpose with Nd:YAG-laser. Factors dominating size and morphology of the nanodots were examined by systematically varying species and pressure of the gas in the deposition chamber, deposition time, and the target –substrate distance (TSD). Pulse frequency (10Hz), pulse width (8ns) and laser wavelength (266nm) were kept constant. The dot size increased with pressure in the range between 0.005Pa to 1Pa, in Ar gas. At pressures as high as 100Pa, dot size decreased again with slightly different morphology. Increasing deposition time from 3, 5, to 10min brought about an increase in the average dot size from 5±2.1nm, 9±2.4nm, 10±3.0nm, respectively, under the constant Ar pressure, 100Pa. It is particularly to be noted that decreasing TSD from 100mm to 50mm brought about an increase in the dot size from 5±2.1nm to 9±3.3nm at Ar pressure, 100Pa, and deposition time, 3min. We discuss factors making self-organized Ag nanodots, and proposed key values to evaluate homogenize of dots assembly.
Bismuth-Induced Layer-by-Layer Growth in the Homoepitaxial Growth of Fe(100)
Authors: Kamiko Masao , Chihaya Hiroaki , Mizuno Hiroyuki , Xu Junhua , Kojima Isao , Yamamoto Ryoichi
Published: April 2011

We have investigated the effect of Bi on the homoepitaxial growth of Fe(100) by means of reflection high-energy electron diffraction (RHEED). It was clearly found that Bi induces layer-by-layer growth of Fe on Fe(100)-c(2×2)O reconstruction surface. The result of the dependence of the growth behavior as a function of Bi layer thickness suggests that there is optimum amount of Bi surfactant layer that induces the smoother layer-by-layer growth. A strong surface segregation of Bi was found at the top of surface and acts as a surfactant by promoting the interlayer transport.
Simulating Oxide Interfaces and Heterointerfaces
Authors: Harding John H. , Duffy Dorothy M. , Harris Duncan J.
Published: April 2011

Interfaces can be considered at a variety of length scales. All interfaces except grain boundaries are dielectric interfaces. In many cases, the geometric constraints of matching two lattices must be considered, together with the misfit strains that are often present. Continuum mechanics is useful for tackling such problems. In many cases, however, the local ordering of ions must also be considered. Atomistic simulation is therefore necessary, together with the problems associated with large length scales and long time scales. We discuss a number of examples to illustrate the issues involved and the compromises between different approaches that must be made.
The Effect of Y on the Strength of FeCrAl Alloy/Sapphire Interfaces
Authors: Basu Soumendra N. , Gupta Vijay K.
Published: April 2011

The effect of Y on the interfacial strength of the FeCrAl/sapphire system has been quantitatively measured by the laser-spallation technique in order to understand the ‘reactive element effect’. The presence of Y improved the interfacial strength of the FeCrAl/sapphire interface in the as-deposited state from 330±31 MPa to 686±36 MPa. However, after a high temperature anneal of 16 hours at 850°C, the interfacial strength of the Y-free samples increased to 545±68 MPa, while the interfacial strength of Y-containing sample decreased to 599±22 MPa. The increase in the interfacial strength of the Y-free films was attributed to an improvement in the crystalline quality of the interface. The decrease in interfacial strength of the annealed Y-containing film in spite of the improvement in the crystalline quality of the interface was attributed to the depletion of Y at the interface due to formation of Y2O3 precipitates, again consistent with the view that Y improves the strength of FeCrAl/sapphire interfaces significantly.
Stabilization of Indium Tin Oxide Films to Very High Temperatures
Authors: Gregory Otto J. , You Tao , Platek Michael , Crisman Everett
Published: April 2011

Thin film strain gages based on indium-tin-oxide (ITO) are being developed to measure to static and dynamic strain at temperatures approaching 1500°C. These ceramic strain gages exhibit excellent oxidation resistance and high temperature stability, surviving more than 25 hours of testing in air at 1470°C. Electron spectroscopy for chemical analysis (ESCA) studies indicated that interfacial reactions between ITO and alumina can increase the stability of ITO at elevated temperature. Solid state diffusion of aluminum into the ITO at these temperatures can produce a very stable ITO/Al2O3 solid solution [1, 2]. To determine the nature of the interfacial reaction product, ITO films were deposited onto both Al2O3 and AlN surfaces and thermally cycled to 1500°C. AlN films were used to reduce/eliminate oxygen transport to the interface, so that aluminum-indium interactions alone could be studied. ITO films were deposited onto Al2O3 and AlN films, which were rf sputtered on platinum-coated alumina substrates. The resulting ESCA depth files showed that an interfacial reaction had occurred between the ITO and the Al2O3 and AlN. The presence of two new indium-indium peaks at 448.85 and 456.40eV, corresponding to the indium 3d5 and 3d3 binding energies were observed in both cases; i.e. the AlN and the Al2O3. These binding energies are significantly higher than those associated with stoichiometric indium oxide. In addition, aluminum doped ITO films were formed by co-sputtering from multiple targets and electrical stability of these films was compared to undoped ITO films over the same temperature range (25–1500°C) [1–4].
Chemical Structure of N Atoms Incorporated Into 1 nm-thick SiO2/Si as Revealed with the Dissolution and Hydrogenation in Hydrofluoric Acid
Authors: Mizuta Naomi , Watanabe Satoru
Published: April 2011

By detecting vibrational frequencies for N–H structures, the chemical states of N atoms at silicon nitride on silicon, SiN/Si, and silicon oxide with nitrogen on silicon, SiO(N)/Si, systems were deduced after being chemically decollated with H atoms in dilute HF solution. Using the fact that the decollation was associated with the dissolution of these films, we obtained their depth profile. The frequency was increased to an extent of 10 cm-1 by the existence of a thin oxide layer between the SiN layer and the Si substrate. The N–H structure bound to the Si substrate was observed at 3390 cm-1 just before the completely removal of the surface layer. We also observed the NH structure of crystal SiN form, whose frequency was unchanged to be 3325 cm-1. The same technique was applied to detect the chemical structure of the N atoms in an ultra-thin SiO(N) with 5% of the N atoms. The frequency peak of the bulk N structure was observed with that of OH structures. The peak was shifted from 3375 cm-1 to 3405 cm-1 at the interface region, suggesting densification of the film in the interface region. Prior to complete removal, we observed the surface state of the N atoms and the H atoms. Then the frequency of the NH was unaffected by the film formed with the various methods. No SiH structure was observed on the resultant film surface during etching.
Direct Determination of the Stacking Order in Gd2O3 Epi-Layers on GaAs
Authors: Yacoby Yizhak , Sowwan Mukhles , Pindak Ron , Cross Julie , Walko Don , Stern Ed , Pitney John , MacHarrie Robert , Hong Minghwei , Clarke Roy
Published: April 2011

We have used Coherent Bragg Rod Analysis (COBRA) to investigate the atomic structure of a 5.6 nm thick Gd2O3 film epitaxially grown on a (100) GaAs substrate. COBRA is a method to directly obtain the structure of systems periodic in two-dimensions by determining the complex scattering factors along the substrate Bragg rods. The system electron density and atomic structure are obtained by Fourier transforming the complex scattering factors into real space. The results show that the stacking order of the first seven Gd2O3 film layers resembles the stacking order of Ga and As layers in GaAs then changes to the stacking order of cubic bulk Gd2O3. This behavior is distinctly different from the measured stacking order in a 2.7 nm thick Gd2O3 in which the GaAs stacking order persists throughout the entire film.
Melt Infiltration Processing of Foams Using Glass-Forming Alloys
Authors: San Marchi C. , Brothers A. , Dunand D. C.
Published: April 2011

Processing of foams from bulk metallic glass (BMG) alloys, using melt infiltration techniques, is reported for the first time. Foaming methods based on infiltration of two types of pattern materials are described: investment of a continuous refractory yielding very low relative density structures (5% dense relative to the BMG), and investment of a discontinuous refractory pellet bed yielding higher relative density (50–60% dense relative to the BMG). Both methods are capable of producing foam structures; however high surface area and diminished thermal conductivity, especially in lower density structures, make vitrification of the alloy difficult.
On Relaxation Kinetics in Liquid and Glassy Ag-Cu Metallic Alloy
Authors: Bakai Alexander S. , Lazarev Nikolai P. , Ngai Kia L.
Published: April 2011

Molecular dynamics simulations of structure, thermodynamic and kinetic properties of model metallic AgCu alloy are performed to elucidate its behavior at glass transition. In spite of small variations of inherent structure of the alloy the relaxation kinetics undergo dramatic changes at the glass transition. The time dependences of the mean square displacements and the non-Gaussianity parameter show the signatures of anomalous diffusion in an intermediate time region. Analysis of time evolution of van Hove correlation function indicates the existence both jump displacements and short-range cooperative atomic rearrangements. Below Tg these cooperative rearrangements do not contribute to long-range diffusion but they still dominate the relaxation at short time.
Assessment of Geochemical Containment Properties in the Near-field of a Deep Underground Repository
Authors: Pellegrini Delphine , De Windt Laurent
Published: April 2011

For safety evaluation of deep repositories, the evolution of chemical containment properties of clayey barriers in spent fuel disposal tunnels are assessed using reactive transport modelling. The disturbances related to cement components are more particularly studied for relevant time scales (100,000 years) and dimensions. Theoretical distribution coefficients (Kd) and maximum concentrations are derived for Cs, Tc and U and their sensitivity to the system evolution estimated. Mineralogical transformations and ion sorption are shown to be interdependent mechanisms controlling the intensity and spatial expansion of the alkaline plume. Simulations for a normal diffusive scenario and an altered one involving an advective flow lead to limited perturbations of the mineralogy and containment properties of the multi-barriers system, but emphasize the possibility of a migration pathway through the excavation damaged zone.
Polymer Pendant Crown Thioethers for Removal of Mercury from Acidic Waste Streams-Characterization and Extraction Performance
Authors: Baumann Theodore F. , Fox Glenn A. , Nelson Art J. , Andrews Joy C. , Bishop Darrell B. , Reynolds John G.
Published: April 2011

The removal and immobilization of mercury(II) ions from industrial waste streams is a difficult and expensive problem requiring a robust extractant that is resistant to corrosive conditions. We have now developed an acid-resistant thiacrown polymer that has potential utility as a selective and cost-effective Hg2+ extractant. A new crown thioether, 2-hydroxymethyl-1,4,8,11,14-pentathiacycloheptadecane ([17] aneS5-OH), was synthesized through reaction of 2,3-dimercapto-1-propanol with 4,7,10-trithiatridecane-1,13-di-p-toluenesulfonate; then treated with thionyl chloride to form 2-chloromethyl-1,4,8,11,14-pentathiacycloheptadecane ([17] aneS5-Cl); followed by conversion to 2-(N-methyl)aminomethyl-1,4,8,11,14-pentathiacycloheptadecane ([17] aneS5-NHMe), through reaction with methylamine. The synthesis of the 4-vinylbenzyl-substituted thiacrown was readily accomplished by treating with 4-vinylbenzyl chloride. Co-polymerization of the 4-vinylbenzyl-substituted thiacrown with DVB (80% divinylbenzene) using AIBN as the radical initiator generated the highly cross-linked crown thioether polymer. The polymer based material was tested for Hg(II) extraction activity from acidic solutions. The material was found to extract 95+% of the Hg in a pH range of around 1.5 to over 6.0, with contact times of less than 30 min and in the presence of high concentration of competing ions such as Pb, Cd, Al, and Fe. The spent polymer could also be stripped of the Hg2+ and reused without sufficient loss of loading capacity. Characterization of the binding sites by XPS and XAS show only some of the S atoms in the thiacrown participate in the binding of Hg. Our results indicate this polymer has the potential to treat highly acidic wastes efficiently. This thiacrown polymer is far more effective in extracting Hg2+ from aqueous solution than previously reported Hg2+ extrac-tants, not only being very fast and efficient and selective, but also independent of pH.
Investigation of reactor graphite processing with the carbon-14 retention.
Authors: Ojovan M. I. , Karlina O. K. , Klimov V. L. , Bergman G. A. , Pavlova G. Yu. , Yurchenko A. Yu. , Dmitriev S. A.
Published: April 2011

The system C – Al – TiO2 has been demonstrated to be a strong candidate for the processing of irradiated reactor graphite waste with the retention of biologic hazardous carbon-14 in chemically and thermal stable corundum-carbide ceramics. The corundum-carbide ceramics is obtained from the powdered precursors blend through self-sustaining thermochemical reactions. Investigations of the system C – Al – TiO2 were carried out both theoretically and experimentally. The refining thermodynamic calculations of the phase composition of resulting end product were performed for a wide variety of components content in the system being investigated. Aluminium oxycarbides production was taken into account in the calculations. Thermodynamic functions of aluminium oxycarbides Al4O4C and Al2OC have been calculated for this purpose using currently available literature evidences and own assessments of missing data. On the basis of thermodynamic simulation the proportions of the source substances were determined, which result in the aluminium oxycarbides production. These simulation results have been supported by XRD-analysis of produced specimens. The experimental processing of reactor graphite was conducted by the use of self-sustaining reactions in C – Al – TiO2 powder blends. Test specimens were produced by mass ranging from 0.1 to 3 kg in the argon atmosphere. Various techniques were used to characterize the produced specimens. The compressive strength of specimens of corundum-carbide matrices produced ranges from 7 to 13 MPa. The leaching rates of Cs-137 and Sr-90 from specimens ranged between 10-4 and 10-5 g/(cm2.day) respectively. The carry-over of the carbon combined in carbon monoxide from the reacting mixtures during exothermic process may run up to 1% wt. that appropriates roughly to less than 0.01% wt. of the carbon-14 in the irradiated reactor graphite.
Characterization of Uranium Speciation in a Metallic Matrix
Authors: Curran Gini , Allen Patrick G. , Caputo Daniel F. , Czerwinski Ken R.
Published: April 2011

Three metallic slag samples recovered from the site of their inadvertent creation several decades after the fact were sectioned and analyzed to determine uranium speciation to evaluate environmental behavior as well as assess proliferation resistance of the waste form. Uranium concentration in the highly inhomogeneous samples was up to 5% by weight as determined by gamma spectroscopy. Sample sections were milled in a hardened steel ball mill for x-ray absorption spectroscopy analysis (XAS). Powders were digested in a mixture of heated concentrated nitric acid and peroxide and analyzed for elemental content using ICP-AES and ICP-MS. Though elemental content of the samples varied widely, high concentrations of Al were consistently found. Other metals of significance were Ti, Fe, Ni, Cu, Zn, and Sn. High Pb concentrations were occasionally found. XAS analysis revealed the samples contained primarily uranyl and another phase identified as a uranium-aluminum melt.
A Study on the Chemical Forms and Migration Behavior of Carbon-14 Leached from the Simulated Hull Waste in the Underground condition
Authors: Kaneko Satoru , Tanabe Hiromi , Sasoh Michitaka , Takahashi Ryota , Shibano Takayuki , Tateyama Shinji
Published: April 2011

The chemical forms of carbon leaching from carbon-containing Zr and Fe-based metallic materials have been investigated to improve the estimation of the contribution of C-14 in the performance assessment of TRU waste disposal. Both organic and inorganic carbons were identified in the leached solution with carbon containing zirconium and steel, and the concentrations of total carbon (organic plus inorganic) in the leached solutions increased with time. The carbon concentrations in the leached solution for both metallic samples were higher at higher pH. With High Performance Liquid Chromatography (HPLC), organic carbons were identified to be low-molecular weight alcohols, carboxylic acids and aldehydes.

To explore the chemical state of carbon in the matrix materials, the leaching experiments were carried out also for ZrC, Fe3C, the powder mixtures of carbon and zirconium, and of carbon and iron. The low-molecular weight organic carbons were detected only in the case of carbides (ZrC and Fe3C). The chemical forms of carbon in the zirconium alloy were suggested to be carbide or carbon by H.D. Smith[1]. The present result suggests that the chemical forms of carbon in zirconium or iron are mainly in the form of carbide.

In the interest of performance assessment, the distribution coefficients of the organic carbon species identified in the leached solution for cement were obtained. As expected, some of them were shown to be larger than the values assumed in the performance assessment of Progress Report on Disposal Concept for TRU Waste in Japan[2].
Review of Corrosion Modes For Alloy 22 Regarding Lifetime Expectancy of Nuclear Waste Containers
Authors: Rebak Raúl B. , Estill John C.
Published: April 2011

Alloy 22 (UNS N06022) was selected to fabricate the corrosion resistant outer barrier of a two-layer nuclear waste package container. This paper reviews the main corrosion degradation modes that are predicted for the outer layer of the container. Current results show that the containers would perform well under general corrosion, localized corrosion and environmentally assisted cracking (EAC). For example, the general corrosion rate is expected to be below 100 nm/year and the container is predicted to be outside the range of potential for localized corrosion and environmentally assisted cracking.
Assessment of Crevice Corrosion and Hydrogen Induced Stress Corrosion Cracks of Ti-Pd Alloys for HLW Overpack In Deep Underground Water Environments
Authors: Nakayama Guen , Murakami Koichi , Akashi Masatsune
Published: April 2011

Crevice corrosion and hydrogen-induced stress corrosion cracking tendencies of titanium (Ti) alloys in deep underground water environments are investigated in the present paper. The crevice corrosion repassavation potential, ER,CREV of Ti-palladium (Pd) alloys was measured and compared with the free corrosion potential, ESP = +0.32 V vs. SHE. The minimum Pd content of the alloys for suppressing crevice corrosion in the envisaged most corrosive high-level radioactive waste (HLW) disposal environment, corresponding to the seawater originated underground water of 0.6 mol/L [NaCl] at 100 °C, is 0.05 %, Ti-Gr.17 alloy. The Pd content of 0.01 % is found to be sufficient for realizing satisfactory crevice corrosion resistance in transuranium (TRU) disposal environment of 0.6 mol/L [NaCl] at 80 °C. The hydrogen-induced stress corrosion cracking tendencies of the Ti alloys caused by the formation and cracking of hydride layers on alloy surfaces were assessed by galvanostatic and constant-load tests conducted in completely reducing environments. Test results indicate that Ti-Pd alloys are immune to stress-corrosion cracking in HLW underground disposal condition for 1000 years. Total electrical charge density in TRU waste overpacks for 60,000 years, estimated from analyses of thermal history in waste emplacement drifts, was found to be 7.5 MC/m2, suggesting the hydride layers formed were 30 μm thick and the crack depth was 15 μm on Ti-Gr.17. Thus, the depth of the stress-corrosion cracks is too small to be taken into engineering consideration. The above results suggest that Ti-Pd alloys with Pd content over 0.05 % for HLW and 0.01 % for TRU waste can be utilized as corrosion-resistant layers of waste-disposal containers of HLW and TRU waste.
Mechanism of Sulfate Segregation during Glass Melting
Authors: Hrma Pavel , Vienna John D. , Ricklefs Joel S.
Published: April 2011

Sulfate retention in glass during the vitrification process can be as low as 1/3 of the solubility limit, or can exceed the solubility limit if suspended in the glass in the form of droplets. This study is focused on the mechanism of incorporating and segregating sodium sulfate during the melting of an alkali-alumino-borosilicate glass batch. Batches were ramp heated at 4°C/min to temperatures ranging from 600°C to 1050°C and fractured for examination. Observation of the melts showed that as the batch temperature increases and the primary oxo-anionic, predominantly nitrate melt decomposes, the sulfate residue accumulates inside gas bubbles and is transported in them to the melt surface, where it remains segregated. The degree of sulfate incorporation into the final glass depends on the relative rates of sulfate dissolution in the borosilicate melt and sulfate lifting inside bubbles.
Experimental Determination of Dissolution Kinetics of Zr-Substituted Gd-Ti Pyrochlore Ceramics: Influence of Chemistry on Corrosion Resistance
Authors: J.P. Icenhower , W.J. Weber , N.J. Hess , S. Thevuthasen , B.D. Begg , B.P. McGrail , E.A. Rodriguez , J.L. Steele , K.N. Geiszler
Published: April 2011

The corrosion resistance of a series of zirconium-substituted gadolinium pyrochlore, Gd2(Ti1-x Zrx)2O7, where x = 0.0, 0.25, 0.50, 0.75, and 1.00, were evaluated using single-pass flow-through (SPFT) apparatus at 90°C and pH = 2. The zirconate end-member, Gd2Zr2O7, has a defect fluorite structure, which distinguishes it from the face-centered cubic structure of the true pyrochlore specimens. In addition to the chemical variation, the samples include annealed, un-annealed, and ion-bombarded monoliths. In the case of the titanate end-member, Gd2Ti2O7, the annealed specimen exhibited the least reactivity, followed by the un-annealed and ion-bombarded samples (2.39×10-3, 1.57×10-2, and 1.12×10-1 g m-2 d-1, respectively). With increasing zirconium content, the samples displayed less sensitivity to processing or surface modification with the zirconate end-member exhibiting no difference in reactivity between annealed, un-annealed, and ion-bombarded specimens (rate = 4.0×10-3 g m-2 d-1). In all cases, the dissolution rate decreased with increasing zirconium content to the Gd2(Ti0.25Zr0.75)2O7 composition (1.33x10-4 g m-2 d-1), but the zirconate end-member yielded rates nearly equal to that of the titanate end-member. These results demonstrate that to achieve the greatest radiation and corrosion resistance in this series, the Gd2(Ti0.25Zr0.75)2O7 composition should be considered.