bluuebunny/crossref_metadata_2025 huggingface dataset:
The Role of Rheological Characterization of Ceramic Dopes in Predicting Fiber Spinning Performance
Authors: Subramanian G. , Bike S. G. , Baskaran S. , Popovic D. , Halloran J. W.
Published: March 2011

We have previously shown that suspension dry spinning of green ceramic fibers can produce continuous fibers of alumina in an ethyl methacrylate binder. The spinning behavior of the dope and the particle packing in the dried fiber are highly dependent on the interparticle interactions in the dope prior to spinning. In particular, the interactions between the ceramic powder and both the dispersant and the binder are critical in determining the processability and spinnability of the dope. We have used rheological techniques to probe these interactions in alumina dispersions in methyl ethyl ketone employing ethyl methacrylate as the binder and a phosphate ester as the dispersant. Measurements of the viscosity of the dispersion as a function of dispersant concentration demonstrate that there is an optimum dispersant concentration to achieve a minimum viscosity at a given binder concentration. In addition, the relative viscosity (viscosity of the dispersion relative to that of the dispersing medium) is found to decrease significantly with increasing binder concentration. These results highlight the importance of characterizing the power-binder-dispersant interactions to fully understand the stability and ultimate spinnability of a ceramic dope. In addition, this work illustrates the general applicability of rheological characterization in ceramic fiber spinning.
On the Development of Rheological Properties of Cement Paste During the Induction Period
Authors: Yang Ming , Jennings H. M.
Published: March 2011

Although chemical reactions in cement slurries are very slow during the first few hours (induction period), the viscosity increases continuously. Relationships between various mixing methods, structure, and rhcology of cement paste throughout the induction period are being investigated, and some results are reported in this paper.
Surface-Enhanced Raman Spectroscopy from Colloids at High Pressures
Authors: Bradley Michael , Krech John , Efrima Shlomo
Published: March 2011

High pressure surface enhanced Raman (SERS) spectra are reported for a highly dense silver colloidal suspension, termed a MEtal Liquid-Like Film or MELLF. Comparison is made with the SERS spectrum of a dilute organosol. Raman signals due to adsorbed molecules and the solvent dichloromethane reveal appreciable frequency shifts as the colloidal environment is influenced by temperature, pressure, and packing. The C-Cl stretch of neat dichloromethane near 705 cm−1 shifts 1.7 cm −1 blue in a MELLF. Raman signals due to the adsorbed anisic acid in MELLFs blue shift about 2 cm −1 as 4 kilobars of pressure are applied; the solvent peaks shift blue only about 1 cm −1. Temperature influences the MELLF in two ways: desorption of anisic acid and formation of agglomerated particles.
Equilibrium-State Density Profiles of Centrifuged Cakes of Flocculated Suspensions
Authors: Shih Wei-Heng , Shih Wan Y. , Kim Seong-Il , Aksay Ilhan A.
Published: March 2011

Many advanced ceramics are formed by colloidal consolidation using techniques such as sedimentation, centrifugation, or pressure filtration. In all these, the minimization of density variations of various colloidally-consolidated cakes has not been examined systematically until recently. Schilling et al. used γ-ray densitometry to study the density variations in a sedimented cake and showed that the sediment of a flocculated alumina suspension exhibited significant density variations within the cake whereas the sediment of a dispersed alumina suspension showed a constant density profile. Auzerais et al. used a medical X-ray computer tomography (CT) to study the settling of dispersed and flocculated silica suspensions and obtained similar results: The sedimented cake of a dispersed silica suspension was fairly uniform whereas those of flocculated silica suspensions exhibited significant density variations. However, Shih et al. examined pressure-filtered cakes of flocculated alumina suspensions with γ-ray densitometry and showed that the density profiles of pressure-filtered cakes of flocculated alumina suspensions were uniform, in contrast to their sedimentation counterparts which showed significant density variations. These studies illustrate that how the local density varies within a consolidated cake depends not only on the suspension conditions but also on how the suspensions are consolidated, e.g., the consolidation pressure.
Coarsening of a Quiescent Electrorheological Fluid II: Theory
Authors: Halsey Thomas C.
Published: March 2011

The coarsening observed orthogonal to the field lines in light scattering studies of a quiescent electrorhcological fluid during the “liquid-solid” phase transition can be qualitatively understood using the thermal mechanism of chain interaction proposed by Halsey and Toor. By analyzing fluctuations in the interaction between chains, we predict a power-law increase of the column width with time, with a time constant that decreases as a power of the electric field. Lubrication forces between the particles may control the time scale of these fluctuations. These predictions are in good accord with light scattering measurements.
Limiting and Enhancement Effects in Laser Chemical Vapor Deposition
Authors: Allen S. D. , Jan R. Y. , Mazuk S. M. , Shin K. J. , Vernon S. D.
Published: March 2011

Laser chemical vapor deposition (LCVD) is a modification of conventional CVD using a laser heat source. The film growth characteristics differ considerably from conventional CVD in several ways, however. The use of an optical heat source means that the optical properties of the film/substrate system must be considered, e.g., for metals deposited on absorbing substrates, the film thickness and diameter may “self-limit” in some cases because the deposited film reflects most of the laser energy. On the other hand, the small area heated in LCVD results in a different diffusion geometry and access to higher surface temperatures than are achievable when large areas are heated. For favorable reactant systems, these enhancement effects can yield fast deposition rates and line deposition scan speeds greater than 10 cm/sec. This paper will review results of pulsed and cw LCVD of predominantly metal films using visible and infrared lasers.
Photochemical Vapor Deposition of Amorphous Silicon Using Mercury Photosensitization of Disilane
Authors: Tarui Yasuo , Aota Katsumi , Sugiura Takashi , Saitoh Tadashi
Published: March 2011

High-rate deposition of amorphous silicon films using the mercury-photosensitized reaction of disilane gas is described. The deposition rate depends upon reactant pressure, light intensity, and concentration of mercury atoms. A maximum rate of 100 nm/min is attained at a 250°C substrate temperature and a disilane pressure of 200 Pa. This rate is about 3 times higher than that for monosilane gas.

Generally, the optical gap of the deposited films range from 1.7 to 1.8 eV, although the value decreases slightly with increasing substrate temperature. Photoconductivity under AM1 irradiation is 2×10−4 mho·cm−1 at a 250°C substrate temperature and the ratio of photoconductivity to dark is around 104. From the infrared data, amorphous silicon films are found to include only an SiH bond at substrate temperatures of 200° to 300°C. Hydrogen content is 10 to 13%. These data suggest that silicon films can be used in thin-film electronic device fabrication.
Recent Advances in UV Laser Photodeposition
Authors: Tsao J. Y. , Ehrlich D. J.
Published: March 2011

Techniques for laser-photochemically depositing localized thin films are reviewed. A comparison is made between techniques relying on gas-phase and surface-phase photochemistry. New photoreactions, confined entirely to surface phases, are described, including multimolecular reactions based on methyl methacrylate, and multicomponent reactions based on mixtures of trimethylaluminum and titanium tetrachloride. Recent developments in the use of surface photochemistry to nucleate subsequent growth by pyrolytic chemical vapor deposition are also reported.
Laser-Excited Fluorescence Detection of Si2 During Silane CVD
Authors: Breiland William G. , Coltrin Michael E. , Ho Pauline
Published: March 2011

Using laser-excited fluorescence, Si2 has been observed in a CVD cell during the deposition of silicon from silane.The formation of Si2 was predicted by our numerical model for CVD which includes a detailed treatment of the chemical kinetics and fluid flow in the gas phase. Our observations of Si2 provide strong support for this model. We also find excellent agreement between the temperature dependence of silicon deposition rates predicted by the model and experimental deposition rates from the literature. These observations indicate that gas-phase chemical reaction kinetics are more important in silane CVD than has been recognized previously.
Uv Absorption Spectra and Photolysis of Some Group II and Group VI Alkyls
Authors: Irvine S. J. C. , Mullin J. B. , Robbins D. J. , Glasper J. L.
Published: March 2011

A preliminary study has been made of the UV photolysis of metal-organic compounds of Hg, Cd and Te which could be used for low-temperature, selective-area deposition of cadmium mercury telluride (CMT). High-resolution UV absorption spectra have been measured for dimethylcadmium (CdMe2), dimethylmercury (HgMe2) and diethyltelluride (TeEt2). Possible modes for photodissociation are discussed in the light of these results. The photodissociation of these alkyls was attempted in a hydrogen stream at atmospheric pressure using a mercury-xenon lamp, deposition being being onto a silica reaction tube. Yields of Cd, Hg and Te were measured under different deposition conditions to determine the dependence on UV intensity, alkyl concentration and flow velocity.
Time-Resolved Optical Reflectivity and Transmission During Laser-Induced Oxidation of Cadmium Films
Authors: Baufay L. , Wautelet M. , Pigeolet A. , Andrew R.
Published: March 2011

The laser-induced oxidation of 2000 Å thick cadmium films on glass substrates is studied by measuring the time-resolved reflectivity and transmission of a probe beam. Under CW laser irradiation, the thickness of the oxide layer is shown to increase linearly with time. Also, the velocity, v, of the CdO-Cd interface increases with increasing laser power, with a step when the melting point of Cd is attained. At the highest powers studied in this work, v varies as v = voexp(−a/P), with vo = 6100 Ås−1 and a=4.8 W.
Infrared Laser Photodesorption of Adsorbed Phases
Authors: Hussla Ingo , Chuang T. J.
Published: March 2011

An infrared laser generated from a Nd:YAG laser mixing with a dye laser has been used as a tunable coherent pulsed laser source to photodesorb ammonia from a Cu(100) surface after excitation of the ν3 mode. Timeresolved quadrupole mass spectrometry is sucessfully applied to determine the translational temperatures of the desorbing species from a monolayer coverage on the metal surface. Evidence for desorption induced by vibrational excitation has been obtained and the results are discussed in terms of rapid energy transfer mechanisms.
Excimer Laser-Induced Deposition of InP and Indium-Oxide Films
Authors: Donnelly V. M. , Geva M. , Long J. , Karlicek R. F.
Published: March 2011

InP and In-oxide films have been deposited on quartz, GaAs, and InP substrates by excimer laser-induced photodecomposition of (CH3)3InP(CH3)3 and P(CH3)3 vapors at 193 nm. The oxide film refractive index and stoichiometry are close to In2O3. Phosphorus incorporation in the films was greatly enhanced by focusing the laser beam to promote multiple-photon dissociation processes. These conditions also lead to enhanced carbon inclusion in the films, due to formation of species such as CH and CH2 in the gas phase. However, this carbon inclusion could be suppressed by focusing the beam onto the surface at normal incidence. In the irradiated zone InP could be deposited with P(CH3)3-to-(CH3)3InP(CH3)3 ratios of only ∼1:1. The technique offers several potential advantages over conventional metal-organic chemical vapor deposition (MOCVD), including lower temperature, enhanced rates, safer gases, and threedimensional film composition control.

Strong atomic In emission is observed in the gas-phase above the depositing film, due to a multiple photon dissociation process. Gasphase fluorescence from P, CH, and C was also observed. These emissions give insight into the photodecomposition mechanism and also serve as a monitor of metal-organic precursor concentrations.
Slipping Transition at a Polymer/Solid Interface
Authors: Migler K. , Hervet H. , Leger L.
Published: March 2011

Direct measurements of slippage of a polymer melt within 100 nm of a solid surface, under simple shear, are reported. In the case of a high molecular weight polydimethylsiloxane (PDMS) interacting weakly with the solid surface, a sharp transition between weak and strong slippage is observed as a function of shear stress. For strong polymer-surface interactions, slippage is highly reduced, and no transition is observed. The results are compared to a theoretical model recently proposed by Brochard and de Gennes.
A Dynamic Monte Carlo Simulation of Sorbate Mobility in Zeolites: The Effects of Molecular Crowding on Sorbate Mobility
Authors: Tassel Paul R. Van , Tantra Iwan , Davis H. Ted , Mccormick Alon V.
Published: March 2011

A finite lattice of adsorption sites, as shown by Monte Carlo simulation, is used to develop a simple hopping model of small molecules within the alpha cage of zeolite NaA. A two body attractive energetic interaction is employed for occupied pairs of nearest neighbor sites. A many body repulsive interaction term accounts for the crowding associated with site saturation. This term becomes important when the site-site spacing is less than the van der Waals diameter of the adsorbate. The dynamic Monte Carlo method is used to evaluate site to site hopping frequencies as a function of loading based on this potential energy function. As the sorbate-sorbate attractive interaction is increased (or, equivalently, as the temperature is reduced), mobility minima occur at certain lattice occupancies which may be explained by the formation of energetically favorable clusters on the cubocathedral lattice. In other words, molecular crowding can cause sorbate mobility to suffer minima as loading is increased. This prediction is in agreement with recent Xe NMR measurements.
Computer Simulation Study of Adsorption, Isosteric Heat and Phase Transitions of Methane on Graphite
Authors: Jiang Shaoyi , Gubbins Keith E.
Published: March 2011

We report Canonical (NVTMC), Grand Canonical (GOMC) and Gibbs Ensemble Monte Carlo (GEMC) simulations for adsorption of methane on graphite. Lennard-Jones (LJ) potentials are used for the intermolecular interactions, and both structured and structureless (10–4–3) solid-fluid potentials are considered. Several sets of methane-methane L.I parameters have been used in the literature, and we compare results obtained with these sets throughout our simulations. The adsorption isotherm and isosteric heat curve are obtained at 77.5 K and found in good agreement with experiments. The commensurateincommensurate transition (CIT) of methane on a graphite substrate with periodically varying adsorbate-adsorbent potential at 40.0 K is studied and is in qualitative agreement with experiment. The effect of varying the corrugation of the fluid-wall potential on the commensurate and incommensurate phases is explored. The GEMC simulations have been carried out to study the vapor-liquid equilibrium (VLE) of a two-dimensional (2D) LJ fluid with system sizes up to 3000 particles. The effect of system sizes on the critical behavior is investigated. The GEMC method has also been successfully applied to study the VLE in 2D adsorbed films for the first time.
Formation of Mn-As Centers in In1-xMnxAs Diluted Magnetic Semiconductors
Authors: Krol A. , Soo Y. L. , Ming Z. H. , Kao Y. H. , Munekata H. , Chang L. L.
Published: March 2011

XAFS spectra at the Mn K-edge were obtained for films of In1-xMnxAs (0.0014 ≤x ≤ 0.12) grown by MBE method at two different substrate temperatures Ts, = 200–210 °C and Ts, = 280–300 ° C. It has been found that Mn-As complexes which consist of a central Mn atom surrounded by six neighboring As most likely arranged in the form of a distorted trigonal antiprism with one or two additional Mn atoms placed on the long axis of the antiprism, can substitute for the In-As tetrahedron in the undistorted zincblende structure. For a composition of x = 0.12 we have found the formation of MnAs clusters with NiAs-like structure in the high-growth-temperature samples. We thus conclude that the magnetic properties of the In1-xMnx As semiconductors are mainly determined by the formation and local structure ol'the Mn-As complexes.
Elementary Rate Laws of Diffusion-Limited Species in the A+T→T Reaction in Low Dimension
Authors: Schoonover Rod , Kopelman Raoul
Published: March 2011

Through computer simulation we look at the elementary reaction rate laws of the trapping reaction A+T→T reaction on a one-dimensional lattice. In particular, we calculate the heterogeneity exponent h of the integrated reaction rate law. However, as the reaction probability p is varied, the heterogeneity exponent becomes a function of time. We find a bifurcation of asymptotic values of h: 1/2 for reactions where p ≤ 1.0 and 0 where p=0. In addition, the usual constraints of the trapping problem have been relaxed, and we look at systems where the A's move and the T remains immobile and the reverse case, where the T moves and the A's sit.
Exact Dynamics in a Model of the Bimolecular Reaction A+B→ 0
Authors: Clément Eric , Leroux-Hugon Patrick , Sander Leonard M.
Published: March 2011

We have previously given an exact solution [1] for the steady state of a model of the bimolecular reaction model A+B→ 0 due to Fichthorn et al. [2]. The dimensionality of the substrate plays a central role, and below d=2 segregation on macroscopic scales becomes important: above d=2 saturation sets in for finite size systems. Here we extend our treatment to give an exact account of the dynamics and show how various initial conditions develop into the segregated and saturated regimes. In certain conditions we find logarithmic relaxation which is related to the dimensionality.
Colloidal Aggregation in a Binary Mixture Near its Demixing Temperature
Authors: Broide Michael L. , Beysens Daniel
Published: March 2011

We have investigated temperature-induced aggregation of silica colloids in a binary mixture of 2,6-lutidine and water. Aggregation occurs in the one-phase region of the binary mixture and can be reversed by cooling the sample.

Using low-angle light scattering, we have determined the growth kinetics and aggregate structure for this system. We find that the time dependent scattered intensity is well described by I(q, t) = ¯(t)/[1 + (q¯R(t))2/10]2\, where the weight-average cluster mass ¯I(t) ⋧ t, and the average cluster radius ¯(t) -çt1/3.

Our results indicate that this experimental system generates compact clusters, ¯ ⋧ ¯ 3, and that the rate of aggregation is diffusion limited. The dense, non-fractal, structure we observe suggests that the bonds between the silica spheres are not rigid, and supports the hypothesis that aggregation is induced by the adsorption of lutidine on the silica surface.
Biotinylated Polythiophene Copolymer – a Novel Electroactive Biomaterial Utilizing the Biotin-Streptavidin Interaction
Authors: Lim Jeong-Ok , Kamath Manjunath , Marx Kenneth A. , Tripathy Sukant K. , Kaplan David L. , Samuelson Lynne A.
Published: March 2011

A novel hierarchical biomaterial capable of incorporating any biotinylated biomolecule has been created. Our strategy is to biotinylate one-dimensional electroactive polymers and use a bridging streptavidin protein on Langmuir-Blodgett (LB) organized films. The following copolymeric system which enables functionalization of other molecules and formation of good monolayers was employed. Biotinylated poly(3-methanolthiophene-co-3-undecylthiophene) (B-PMUT) demonstrated a significantly better isotherm implying superior molecular packing compared to poly(3-methanolthiophene-co-3-undecylthiophene) (PMUT) on the LB airwater surface. The isotherm showed significant area expansion when streptavidin was injected below the B-PMUT monolayer in 0.1mM NaH2PO4/0.1 M NaCl buffer (pH 6.8) subphase. We then incorporated biotinylated phycoerythrin (B-PE) into this novel biomaterial by binding the unoccupied biotin binding sites on the bound streptavidin (4 sites total). The pressure-area isotherm of the protein injected monolayer showed area expansion. A characteristic fluorescent emission peak at 576nm was detected from the monolayer transferred onto a solid substrate. These observations demonstrated the function of B-PMUT in hierarchical monolayer assembly of molecules incorporating the biotin / streptavidin interaction.
Specific Interaction of Influenza Virus with Organized Assemblies of Polydiacetylenes
Authors: Charych Deborah H. , Spevak Wayne , Nagy Jon O. , Bednarski Mark D.
Published: March 2011

Supramolecular organizates of liposomes and Langmuir-Blodgett (LB) films are described which are capable of specifically binding to pathogens such as influenza virus. The specific interaction is between the hemagglutinin protein of the virus and an α-C-glycoside of sialic acid expressed on the surface of the liposome or LB film. Sialic acidcontaining liposomes were found to inhibit influenza virus infectivity in cell culture, and may provide a basis for new materials which act as therapeutic agents. Sialic acid-containing LB films also specifically bind to the influenza virus. In this case, the conjugated polymer backbone acts as a built-in reporter of the binding event, measurable by a chromatic change in the visible absorption spectrum. These films may provide a basis for new materials which act as direct detectors of binding
Decalcification Studies on Avian Eggshell
Authors: Agarwal M. , Xiao S.Q. , Heuer A.H.
Published: March 2011

Avian eggshells are one of the most rapidly calcifying systems known. Although the entire shell contains ∼ 97 weight % CaCO3, etching in EDTA reveals great spatial variability in etching rate. A correlation between the etching rate of various regions and the relative positions of the different parts in the calcium reserve assembly (CRA) has been made; the CRA is the source of calcium during natural decalcification by chick embryos.
Spider Silk Proteins
Authors: Hinman Mike , dong Zhengyu , Xu Ming , Lewis Randolph V.
Published: March 2011

Dragline silk has been shown to consist of two proteins, Spidroins 1 and 2, which form this unique fiber. The cDNAs for these two proteins have been sequenced and a structure proposed which accounts for both the tensile strength and elasticity of dragline silk.
High Ionic Conductivity of Polymer Complexes Formed by Polypyridinium, Pyridinium, and Aluminium Chloride
Authors: Rikukawa Masahiro , Yamada Shinichiro , Sanui Kohei , Ogata Naoya , Watanabe Masayoshi
Published: March 2011

New ion conductive polymer complexes were formed by dissolving poly(1-butyl-4- vinylpyridinium) salts into room temperature molten salts consisting of 1-butylpyridinium salts and aluminium chloride. The viscoelastic films were fabricated from the molten salts added at least 10 mol % of the polypyridinium salts. The ionic conductivities of the polymer complexes were in the range of 10−3−10−4 Scm−1 at room temperature and were affected by their composition.
Oxidation States in Layered Nickel Oxide Based Electrode Materials
Authors: Delmas Claude
Published: March 2011

NiO2 slabs made of edge-sharing NiO6 octahedra are the main structural parts of the positive electrode materials involved in Ni-Cd, Ni-M- and Li-LiNiO2 secondary batteries. These electrochemical systems are among the best ones for applications. The behavior of all these electrode materials can be optimized by substituting several cations for nickel.

The effect of iron and cobalt substitution has been investigated in detail. The oxidation state modifications resulting from the electrochemical cycling have been characterized from magnetic, conductivity, thermoelectric-power and Mössbauer studies. The overall results show that nickel ions are oxidized to the tetravalent state before cobalt ions. More surprisingly, the oxidation of iron-nickel mixed phases shows the simultaneous presence of tetravalent iron and nickel ions in the low spin configuration. For the first time, in situ M6ssbauer measurements have been performed during the cycling of a nickel-cadmium cell.

This cationic distribution results from the competition between the intrinsic redox properties of the 3d cations and the accommodation of the oxidation levels to the ligand field imposed by the prevailing cation.
Polymer-Based Electrochemical Devices
Authors: Arbizzani C. , Mastragostino M. , Meneghello L. , Andrieu X. , Vicedo T.
Published: March 2011

Selected findings of ongoing investigations of variable light-transmission electrochromic devices using electronically conducting polymers as electrochromic materials are presented and discussed.

An obvious requisite for electrochromic windows is an all-solid configuration with polymer electrolyte; in this connection testing data of a new hybrid electrolyte based on a polymer network including a plasticizer are reported and discussed.
Structural and Physical Characterization of Li2O:P2O5:MO3 (M = Cr2, Mo, W) Ion Conducting Glasses
Authors: Chowdari B.V.R. , Tan K.L. , Chia W.T.
Published: March 2011

The conductivity of the Li2O:P2O5:MO3 (M = Cr2, Mo, W) glasses increases as P2O5 is progressively substituted by MO3 and as the Li2O content increases. Amongst the glass compositions studied, the 0.50Li2O:0.20P2O5:0.30WO3 glass has the highest conductivity at 25°C of 2. 1×10−6 ×−1 cm−1. The glass transition temperature of the glasses increases initially with network former substitution, reaches a maximum at around MO3/P2O5 = 1, and decreases with further substitution. X-ray photoelectron spectroscopy reveals the presence of M ions in more than one oxidation state and oxygen species such as P=O, P-O-P, P-O, M-O-M, M-O and P-O-M. Raman spectroscopy shows that the Li2O:P2O5:MoO3 and Li2O:P2O5:WO3 glasses consist of PO4, MoO4 (WO4) and MoO6 (WO6) polyhedra while the Li2O:P2O5:Cr2O3 glasses consist of the PO4 and CrO6 polyhedra only. The phosphate groups are preferentially modified by Li2O in comparison with the tungstate, molybdate and chromate groups. The increasing number of non-bridging oxygen atoms per phosphate group may be related to the increasing conductivity with the progressive substitution of MO3 for P2O5.
Protonic Conduction in Y-, Yb- and Sc-Doped SrZrO3 Ceramics
Authors: Liang K.C. , Lee I.Y. , Nowick A.S.
Published: March 2011

Protonic conduction of SrZrO3 doped with Y3+(5%), yb3+(5 and 10%) and Sc3+(5, 10, 15 and 20%) has been investigated in a frozen-in condition at 20-400°C following a high-temperature pre-treatment in water vapor. Water uptake was also determined gravimetrically. The pure sample shows no proton incorporation and relatively low conductivity. The oxygen partial pressure dependence of conductivity under dry atmosphere shows hole conduction only when P(O2) >10−5 atm. All of the doped samples show good protonic conduction and a non-classical H2O/D2O isotope effect. The conductivity and water uptake is always higher for samples slowly cooled from the pre-treatment than for quenched samples. The activation energy, as well as the pre-exponentials, of the slowly cooled samples consistently suggest Stage II behavior, with an activation energy for proton migration of 0.61±0.02eV and an effective proton concentration close to the actual concentration. It is concluded that SrZrO3 deserves serious consideration as a proton electrolyte.
Factors Affecting Ion Transport in Fast-Ion Conductivity Solids
Authors: Secco E. A.
Published: March 2011

Fast-ion conduction in solids is considered a paradigm for structure-property relation where ionic conductivity σ = nqµ, n the concentration of charge carrier q, and µ. the mobility of the carrier. The critical conductivity determining factor, ceteris paribus, is the carrier mobility which depends on the geometry of anion array and structure in the solid. Factors inherent in the structural framework include “free” volume, “bottleneck” size, lattice disorder, etc. Other non-structural factors that can play a vital role, even a dominant role, in enhancing ionic conductivity are charge carrier concentration, ion-ion interactions or bonding characteristics, vibrational amplitudes of neighboring ions, lattice compressibility or resiliency, rotational motion of anions, ion size, etc. Many aspects of these factors will be examined in the light of recent studies and the results on some isostructural and isomorphous sulfates and other related structures to evaluate their relative contributions.
Optical Spectroscopies of Lithium-Intercalated Compounds
Authors: Julien C.
Published: March 2011

Layered compounds are known to form lithium intercalation complexes as electron donor systems. A charge transfer which can strongly affect the electronic properties of the host lattice, and a change of preferential crystallographic parameters without destruction of the original structure are the main effects occuring during intercalation. Optical spectroscopies such as Raman scattering, far-infrared reflectivity, absorption measurements and photoluminescence have been carried out for the study of electronic and structural modifications. Upon lithium intercalation, lattice dynamics and electronic band structure change in numerous layered compounds. The optical properties of transition-metal dichalcogenides, non-transition metal chalcogenides and transition-metal oxides are presented and discussed with the aim of a better understanding of the intercalation process and establish some guide lines for improving the performances of these materials in their most important applications.
Femtosecond Electronic and Nuclear Dynamics in Nonlinear Optical Glasses
Authors: Banet Matthew J. , Nelson Keith A.
Published: March 2011

Nuclear and electronic responses in highly nonlinear optical glasses are investigated using femtosecond polarization discrimination four wave mixing experiments.
Synthesis and Characterization of Microcrystalline TiS2 for Use in Cathodes
Authors: Donahue Edward J. , Dominey Lawrence A. , Koch Victor R. , Blakley Thomas J. , Goldman Jay L.
Published: March 2011

Titanium disulfide is a particularly promising cathode material for very high cycle life applications in secondary lithium batteries due to the reversible nature of the intercalation of lithium into the host TiS2 lattice. It has long been known that the mechanical stress of the intercalation process is minimized if TiS2 crystal size is kept below 10μm. It has also been suspected that minimizing crystal thickness would improve the kinetics of at the onset of lithiation by minimizing the forces which would have to be overcome in expanding the host lattice. We have synthesized three different types of microcrystalline TiS2, two thin film and one powder, and have compared their performances to that of a large crystalline powder. Lithium ion diffusivity and pulse power performance of the four materials were compared. It was found that the two thin film materials exhibited extraordinary pulse power rate capabilities while the two powder materials were limited in their performance by the constraints of the composite cathode matrix.
A New Type of Cation-Conducting Rubbery Solid Electrolyte: The Ionic Rubber
Authors: Angell C. A. , Liu Changle , Sanchez E.
Published: March 2011

We show that the conductivity maximum, well known for salt-in-polymer electrolytes is not the maximum conductivity in the system when the salts used are chosen for their resistance to crystallization at high concentration. The polymer + salt system, with increasing salt content, goes through a transition zone characterized by a maximum in glass transition temperature. Beyond this point additional salt serves to plasticize the salt-crosslinked polymer system, establishing thereby a region of increasing conductivity in which the conductivity can reach very large values. We show that “polymer in-salt” solutions constitute a new type of rubbery solid electrolyte in which the conductivity is dominated by cation motion. Such systems are true hybrids of the previously distinct “superionic glass” and “polymer electrolyte” types of amorphous solid conductors.
Deuteron and Oxygen-17 NMR Studies of Molecular Motion in Methanol-Saturated Nafion Membranes
Authors: Chen R.S. , Jayakody J.R.P. , Greenbaum S.G.
Published: March 2011

Deuteron and oxygen-17 NMR linewidth and spin-lattice relaxation measurements in Nafion-117 films containing methanol at σ75% and σ100% saturation are reported. Molecular motion probed by room temperature measurements in stretched films and low T measurements in unstretched films is found to be quite rapid compared to previous results obtained for Nafion-117 containing water.
Comparisons Of Observed And Simulated Atomic Structures Of Pd/NiO Heterophase Interfaces
Authors: Buckett M. I. , Shaffer J. P. , Merkle Karl L.
Published: March 2011

High-resolution electron microscopy (HREM) and image simulations using the multislice algorithm have been used to study the atomic structure of a Pd/NiO (111) interface in an intemally oxidized sample. Samples prepared in this way result in cube-on-cube oriented or twin-related precipitates whose (111) interfaces exhibit a contrast modulation along the boundary plane in HREM images. Previous studies have reported that the observed structural period of this modulation corresponds qualitatively to the expected spacing if the boundary was composed of a network of misfit dislocations. In this study, rigid models of the (111) interface as viewed from the [110] direction were simulated using the EMS suite of programs. The questions we address are: (1) whether the terminating plane on the oxide side is made up of a Ni or an 0 layer, and (2) whether a rigid body translation normal to the interface exists. Finally, the results of the simulations are compared and contrasted to through-focal experimental images to investigate the origin of the contrast modulations and their possible relation to the extent of the misfit localization in these systems.
A Microstructural Study of Reaction-Bonded Silicon Carbide
Authors: Chowdhury K. Das , Carpenter R. W. , Braue W.
Published: March 2011

Interfaces in Reaction Bonded Silicon Carbide (RBSC) have been characterized by Analytical and High Resolution Electron Microscopy. Both Si/SiC and SiC/SiC interfaces were free of any oxygen impurity segregation, but contained metallic impurity precipitates. Oxygen was detected in the second phase particles in the SiC grains. A model is presented to explain the evolution of these second phase particles in the SiC grains.
Atomic Structures and Defects of As-Grown Nb1+αS2 Platelets on Nb Substrates
Authors: Zhou Chuxin , Hobbs L. W.
Published: March 2011

The interlocking of Nb1+αS2 platelets developed during sulfidation of Nb results in formation of a compact scale. The atomic structure and defects of these platelets were investigated using HREM. The resulting microstructure is very different from conventional microstructure consisting of polygonal grains and polyhedral grain boundaries because of the anisotropy of the crystal structure. The principal phase was identified as 3R-Nb2+αS2 intergrown with 2H-Nb1+αS2, or with some other arrangement of S-Nb-S slabs. The -S6- octahedral sites between two S-Nb-S slabs provide accommodation for extra Nb or foreign atoms and the large non-stoichiometry of Nb1+αS2. Stacking faults along the c axis account for the high density of planar defect structures observed within almost every platelet. Axial lattice fringe images and streaking in the diffraction pattern indicate that the planar defects are normal to the c direction.
Application of Z-Contrast Imaging to Obtain Column-by-Column Spectroscopic Analysis of Materials
Authors: Browning Nigel D. , Pennycook Stephen J.
Published: March 2011

Z-contrast imaging has been shown to be an effective method for obtaining a highresolution image from a scanning transmission electron microscope (STEM). The incoherent nature of the high-angle scattering makes image interpretation straightforward and intuitive with the resolution limited only by the 2.2 Å electron probe. The optimum experimental conditions for Z-contrast imaging also coincide with those used for analytical microscopy, enabling microanalysis to be performed with the same spatial resolution as the image. The detection limits afforded by a parallel detection system for electron energy loss spectroscopy (EELS) allows column-by-column core-loss spectroscopy to be performed using the Z-contrast image to position the electron probe. Preliminary results from the study of Yba2Cu3O7-δ illustrate the spatial resolution available with this technique and the potential applications for materials science.
Scanning Tunneling Microscopy for Hydrogen-Desorptioninduced Structural Change of Si(111) Surface
Authors: Morita Y. , Miki K. , Tokumoto H. , Sato T. , Sueyoshi T. , Iwatsuki M.
Published: March 2011

A scanning tunneling microscopy (STM) has revealed an atomic structure of Si(111)-√3× √3R30° which is induced by the hydrogen desorption at about 500 °C. There exist domains with the √3× √3R30° structures, indicating that each domain is formed by rearrangement of Si adatoms around each cluster present at room temperature. Near the domain boundary, the adatoms locate mostly at T4 sites and occasionally at H3 sites. The dynamic nature of the adatoms are predicted.
Metastable Structural Surface Excitations and Concerted Adatom Motions: a STM Study of Atomic Motions Within a Semiconductor Surface
Authors: Golovchenko Jene , Hwang Ing-Shouh , Ganz Eric , Theiss Silva K.
Published: March 2011

Knowledge about atomic scale motions is essential to the understanding of dynamical phenomena on surfaces, such as diffusion, phase transitions, and epitaxial growth. We demonstrate that the addition of a very small number of Pb atoms to a Ge(111) surface reduces the energy barrier for activated processes, thus allowing one to observe concerted atomic motions and metastable structures on this surface near room temperature using a tunneling microscope. The activation energy for surface diffusion of isolated substitutional Pb atoms in Ge(111)-c(2×8) was measured by observing individual atomic interchanges from 24°C to 79°C. We also observed the formaticn and annihilation of metastable structural surface excitations, which are associated with large numbers of germanium surface atoms in one row of the c(2×8) reconstruction shifting along that row like beads on an abacus. The effect provides a new mechanism for atomic transport on semiconductor surfaces and can explain a number of other observed phenomena associated with Ge(111) surfaces, including the surface diffusion of Pb atoms.
Atomic Arrangement of Al Near the Phase Boundaries Between-√3X-√3-Al and 7X7 Structures on Si(111) Surfaces
Authors: Takaoka Katsuya , Yoshimura Masamichi , Yao Takafumi , Sato Tomoshige , Sueyoshi Takashi , Iwatsuki Masashi
Published: March 2011

Scanning tunneling microscopy (STM) is used to study the structure of Al-√3×√3 domains on the Si(111)-7×7 surface and the atomic arrangement near the domain boundary. Al-√3×√3 domains grow from the lower side of the <112> step and extend over the Si-7×7 terrace. The phase transition is observed to occur in units of the 7×7 size. Detailed investigation at around the boundary reveals that faulted halves of the 7×7 unit are adjacent to the boundary on the Si-7×7 side, while on the Al-√3×√3 side, Al adatoms occupy the T4 sites except for the rows adjacent to the phase boundaries where Al atoms occupy the Si adatom sites. The latter Al atoms play an important role to retain the dimer structure at the boundary.
Steps on the (110) Surface of INP
Authors: Liang Yong , Packard William E. , Dow John D.
Published: March 2011

Three types of steps are observed on the cleaved InP(110) surface, using atomicresolution ultra-high vacuum (UHV) scanning tunneling microscopy (STM). The step edges are oriented along the (110), (111), and (112) directions. Atomic models of monatomic-height (111) and (112) steps indicate that the edges of each of these unrelaxed steps should have pairs of dangling bonds. We propose that the bonds dimerize, causing the edges to relax and form periodic structures along the edge.
Hrtem Observations Of A Σ=3 {112} Bicrystal Boundary In Aluminum
Authors: Medlin D. L. , Mills M. J. , Stobbs W. M. , Daw M. S. , Cosandey F.
Published: March 2011

We present here a study of the Σ=3 {112} incoherent twin boundary in aluminum. Atomistic studies of this boundary indicate that several high energy boundary structures may exist, with the lowest energy structure exhibiting a small rigid body shift parallel to the boundary. The observations presented here indicate that the rigid body shift does in fact occur and that its magnitude, as well as the local grain boundary structure, is well predicted by atomistic calculations using the Embedded Atom Method. The low energy boundary configuration is much narrower than the equivalent boundaries that have been observed in the lower stacking fault energy FCC metals.
Step-Like Current-Voltage Characteristics in Metal/a-Si:H/Metal Structures
Authors: Hajto J. , Snell A.J. , Rose M.J. , Owen A.E. , Osborne I.S. , Kosa T. , Holmes A. , Gibson R.A.G.
Published: March 2011

We present experimental results showing that Cr/p+/V amorphous silicon memory structures at room temperature exhibit step-like current-voltage characteristics associated with discrete, non-random resistance values. The resistance values observed are ∼26kΩ/i where i is an integer or half integer. The low bias current-voltage characteristics prior to the first step suggest that conduction in this regime is governed by tunneling across a region having very small dimensions, of the order of ∼5-7 Å, and having a diameter ∼30-50 Å.
Clusters in A Silane Glow Discharge: Mechanism of Their Formation and How to Avoid Them
Authors: Vepřek S. , Ambacher O. , Rieger W. , Schopper K. , Vepřek-Heijman M.G.J.
Published: March 2011

The formation of clusters in glow discharge plasma processing is of great concern with respect to the production yield. Their appearance, trapping and transport in silane plasmas have been the subject of several publications, but little is known about the mechanism of their formation and growth and how to avoid them in intense discharges used for high rate deposition of amorphous silicon. We present mass spectrometric and light scattering data and theoretical modelling which show that the formation of clusters in a clean silane discharge (total impurity ≈ 10 ppm) is due to a sequential growth of higher silanes SinH2n+2 with a strong, catastrophic-like onset starting from pentasilane. A selfconsistent mechanistic model will be presented together with a discussion of alternative ionic mechanisms. Several possibilities of how to avoid the cluster formation at high deposition rates of a-Si will be discussed and documented.
Piezoelectric Effect on Plasma Chemical Vapor Deposition of Hydrogenated Amorphous Silicon Films
Authors: Kawasaki Masashi , Sumiya Masatomo , Koinuma Hideomi
Published: March 2011

As a potential method for controlling the surface reaction of plasma CVD, mechanical vibration generated by a piezoelectric device was applied on the substrate during glow discharge decomposition of SiH4. The application of 2MHz vibration dramatically improved the photoconductivity of a-Si:H films prepared at a substrate temperature of 120°C. IR and CPM spectra for the films revealed that the piezoelectric vibration remarkably modulated the amorphous network structure and reduced the defect density to 4.3x1014cm −3 which is the best among the values ever reported.
Are there Charged Dangling Bonds in Device Quality Amorphous Silicon?
Authors: Brandt M.S. , Asano A. , Stutzmann M.
Published: March 2011

We discuss the possible existence of a considerable density of charged dangling bond defects in device-quality hydrogenated amorphous silicon, which for example has been postulated by recent thermal equilibrium models for the density-of-states distribution. Based on a quantitative analysis of spin resonance and light-induced spin resonance data at different temperatures as well as on subgap absorption measurements, we conclude that intrinsic a-Si:H only has a small density of charged defects caused by unintentional impurity doping. The same conclusion also holds for light-soaked a-Si:H and for samples which are dehydrogenated by annealing at high temperatures.
Electron Spin Resonance Study of the Dangling Bond in a-Si:H and Porous Silicon
Authors: Mc Mahon T.J. , Xiao Y.
Published: March 2011

We compare the electron spin resonance (ESR) signal of the dangling bond in porous silicon films, produced by electrochemical etching, to the ESR signal from hydrogenated amorphous Si (a-Si:H). The anisotropy of the ESR signal in porous Si showed g values varying as for the Pb Si/SiO2 interface dangling bond. The g value varies from g|| − 2.0020 to gL − 2.0080 with an inhomogeneously broadened line width increasing from 1.8 to 3.8 G. A porous Si ESR powder line, with superhyperfine and strain broadening intrinsic to porous Si, is compared to the a−Si:H dangling bond line. The result is more inhomogeneous broadening of line widths parallel and perpendicular to the dangling bond axis in a-Si:H, and less anisotropy in g|| − gL- No evidence was seen for light-induced metastability on a H-passivated porous Si film.
Investigation on Microvoids in Pecvd a-Si:H
Authors: Manfredotti C. , Fizzotti F. , Boero M. , Pastorino P. , Vittone E. , Rigato V.
Published: March 2011

The effect of microvoids on optical properties of a-Si:H deposited by PECVD of SiH4 has been investigated in the deposition temperature range between 143°C and 266°C. Microvoids seem not to affect the density up to H concentrations CH of 15%. The density is decreased only by H incorporation, which, at the same time, influences directly the optical energy gap Eg Above CH=15%, microvoids can easily accommodate H and no further variation either of Eg or the index of refraction n can be appreciated. Microvoids are proven to be affected not only by deposition temperature, but also by deposition time and by a further annealing step, even if at a relative extent.
Doping Dependence of Local Hydrogen Motion in Hydrogenated Amorphous Silicon
Authors: Hari P. , Taylor P.C. , Street R.A.
Published: March 2011

1H NMR dipolar echo measurements have been performed on a series of samples of phosphorus- and boron-doped a-Si:H. The dipolar echo sequence consists of three rf pulses followed by an echo in the form: (π/2)x - τ1 - (π /4)y - π2- (π /4)y - echo. The echo height is plotted against π2 and the slope yields the dipolar spin-lattice relaxation time (T1D). T1D is a measure of fluctuations in the local dipolar field surrounding each hydrogen atom in a-Si:H, and measurement of this quantity can be employed as a probe of hydrogen motion on a microscopic scale. The T1D measurements of 10-5 B-doped, 10-3 P-doped and undoped a-Si:H are compared to the previously measured T1D of 10-4 B-doped a-Si:H. The T1D values for 10-4B-doped, 10-4 B-doped and undoped a-Si:H are, respectively, 1.7 ms, 11 ms and 22 ms at 300 K. The T1D for 10-3 P-doped is found to be the same as for 10-5 B-doped within experimental error. These trends are similar to the variation of the macroscopic diffusion of hydrogen with respect to various doping levels, but the details of the local motion are very different from those of the macroscopic diffusion.