bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthetic Imogolite Paracrystals
Authors: Huling Jeffrey C. , Brinker C. Jeffrey , Ackerman William C. , Smith Douglas M. , Bailey Joseph K. , Farkas Janos
Published: March 2011

Imogolite is a structurally microporous tubular clay comprising one-dimensional pore channels that are ∼1 nm in diameter. In addition to its novel tubular morphology, a notable structural characteristic of imogolite is its occurrence in paracrystalline tube bundles in which the individual tubes are close-packed with their axes in parallel alignment. We have developed a technique that aligns and tightly packs the tube bundles over macroscopic dimensions, in a manner analogous to the alignment and packing of the individual imogolite tubes within the bundles. This extends the range of imogolite paracrystallinity, effectively eliminating mesoporosity and nontubular phases.
New Nanocomposite Structural Ceramics
Authors: Niihara K. , Nakahira A. , Sekino T.
Published: March 2011

The new materials design was established for the structural ceramics to break through the present monolithic and composite ceramics. In this concept, the ceramic-based composites were divided into two groups: micro and nanocomposite. The microcomposite is the so-called composite in which the micro-sized particles, whiskers, platelets and fibers are dispersed at the grain boundaries of matrix grains. The nanocomposites, on the other hand, have three types of structures: intra and intergranular nanocomposites and nano/nano composite. The intra and intergranular nanocomposites were found to show the tremendous improvement of mechanical properties even at elevated temperatures compared with those of monolithic and microcomposite ceramics. The nano/nano composites gave the new functions such as machinability and superplasticity like metals. Our final goal for developing supertough and strong ceramics was achieved by hybridizing the intra and intergranular nanocomposites with the micro-meter sized fibers. This new concept was found to be also applicable for ceramic-metal composite systems.
Characterizing The Microstructures Of TiN/TiB2 Nanocomposites With Energy Filtered Tem
Authors: Szabo V. , RÜhle M. , Su K. , Sneddon L.G. , Bonnell D.
Published: March 2011

Recent developments in boron chemistry have allowed the synthesis of TiN/TiB2 composites from polymeric precursors with grain sizes of the order of 10-500 nm. In order to optimize the properties through controlled processing, nucleation of the crystalline phases and subsequent microstructural evolution must be understood. However, the nitride and boride phases are difficult to distinguish in conventional TEM since the grains are too small for diffraction analysis and light elements are not detectable by energy dispersive X-ray spectroscopy.

For the characterization a prototype of an energy filtering TEM (EFTEM) which utilizes an imaging electron energy loss spectrometer incorporated into the column of a normal TEM has been used for elastic filtering and electron spectroscopic imaging (ESI). The ESI-technique allows us to obtain two-dimensional maps of the elemental distribution. These techniques are applied to advantage in the microstructural analysis of the TiN/TB2 nanocomposites.
Nanomaterials: Tin(IV) Sulfide Endo-and Exosemiconductors
Authors: Bowes Carol L. , Ozin Geoffrey A.
Published: March 2011

Endosemiconductors, materials produced when atom constituents of bulk semiconductors are reorganized into ordered arrays of single size and shape clusters encapsulated within a nanoporous host, are introduced with the report of a novel tin(IV) sulfide endosemiconductor synthesized by a two-step MOCVD-like self-assembly process. Template-mediated hydrothermal syntheses of phase-pure and large single crystal tin(IV) sulfide exosemiconductors, materials resulting from reorganization of those same atomic constituents into an open-framework crystalline nanoporous structure is also discussed. The properties of these nanomaterials are considered in terms of the degree of coupling between molecule-like constituent clusters, a concept which mediates the nanoworld of matter intermediate between molecular and bulk.
Development of High Performance Silicon Nitride Ceramics and their Applications
Authors: Tajima Yo
Published: March 2011

Progress in sintering process and improvement of mechanical properties of silicon nitride ceramics are reviewed. Emphases are placed on contributions of advanced sintering techniques and better understanding of sintering additives and microstructure-properties relations. Current applications as engine components and cutting tools are described, and future prospect is considered.
Infiltration/Pyrolysis Processing of Fiber-Reinforced Silicon Nitride
Authors: Schwab Stuart T. , Graef Renee C. , Blanchard Cheryl R. , Pan Yi-Ming , Davidson David L.
Published: March 2011

While its high-temperature strength, resistance to oxidation, and other properties make silicon nitride an attractive candidate for many advanced structural applications, its propensity for brittle failure has hindered its widespread adoption. One approach to avoiding brittle failure is through incorporation of continuous fiber-reinforcement; however, conventional (powderbased) methods of silicon nitride fabrication can degrade fibers and are not amenable to the production of complex shapes. The Southwest Research Institute has developed a number of polymeric precursors to silicon nitride which are available as thermosetting liquids, and we have shown that these materials can be used in combination with near net-shape manufacturing techniques to produce fiber-reinforced silicon nitride composites. Mechanical property tests conducted at room temperature suggest that these polymer-derived composites exhibit fracture behavior comparable to those produced through conventional techniques; micromechanical investigations conducted at 800°C indicate that non-brittle failure is maintained at elevated temperature.
Interface Structure of Si3N4 Matrix Composite with Nano-Meter Scale Sic Particles
Authors: Sasaki Gen , Suganuma Katsuaki , Fujita Teruaki , Hiraga Kenji , Niihara Koichi
Published: March 2011

²-Si3N4 matrix composites reinforced with nano-meter scale SiC particles were fabricated by hot-pressing the mixture of SiC and Si3N4 fine powders. Interface microstructure and crack propagation in the composite were observed by high resolution electron microscopy. The interface between SiC and Si3N4 had good coherence, but no preferred orientation was observed. At the interface between SiC and Si3N4, the (111) face of SiC particles was flat, and sometimes a disturbed lattice structure thinner than 1 nm was observed. Near the main cracks, the microcracking at fine SiC particles/Si3N4 matrix interface was frequently observed. The cracks propagated exactly along this interface. The interface microcracking seems to contribute to the improvement of fracture toughness.
Fabrication and Properties of Si3N4 with Rare Earth Apatite Grain Boundary Phases
Authors: Tiegs Terry N. , Nunn Stephen D. , Ploetz Kristin L. , Menchoffer Paul A. , Walls Claudia A.
Published: March 2011

The rare earth-oxide and nitride apatites were examined as grain boundary phases in silicon nitride to assess their potential for developing high toughness materials using gas-pressuresintering. Densification was dependent on the quantity of additives used with high densities achieved at equivalent oxygen contents of ∼8%. Fracture toughnesses (KIc) up to 8-10 MPa√m were obtained for some compositions. Ambient temperature flexural strengths were in the range of 400-720 MPa; however, the strengths atelevated temperatures (1200ºC) were reduced from these values.
Formation and Densification of R-α'-SiAIONS (R = Nd, Sm, Gd, Dy, Er and Yb)
Authors: Wang P.L. , Sun W.Y. , Yen T.S.
Published: March 2011

The densification behavior and formation characteristics of R-α'-Sialons (R = Nd, Sm, Gd, Dy, Er and Yb) hot-pressed in the temperature range of 1500ºC-1750ºC have been studied. The temperatures required for full densification decrease and the content of the α-Sialon phase increases with an increasing atomic number of R.
Parameters Affecting Pressureless Sintering of α'-Sialons with Lanthanide Modifying Cations
Authors: O'reilly K.P.J. , Redington M. , Hampshire S. , Leigh M.
Published: March 2011

μ-silicon nitride forms a range of solid solution Mx(Si,Al)12(0,N)16 where x = 2 and M is Li+, Ca2+, y3+ or certain lanthanide cations. This paper reports the formation of Ln-α'-sialons by the reaction of Si3N4 with AIN and Ln2O3 where Ln=Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y. Transformation reactions of Nd, Sm, Gd, Ho, Er and Y cations occurring during liquid phase pressureless sintering are reported. The effects of the volume and viscosity of the liquid phase and the amountof secondary N-melilite on sintering are discussed.
Non-Oxide Additives As Sintering Aids For Si3N4-Based Ceramics
Authors: Ge C. , Xia Y. , Chen L.
Published: March 2011

This article is a review of the selected activities since 1979 in using non-oxide additives as sintering aids for silicon nitride. Emphasis was placed on the work done in the authors' laboratory, and it is shown that ZrN and AIN in combined use can result in producing silicon nitride with good properties.
Oxidation Kinetics of Si2N2O Ceramics
Authors: Persson Jeanette , Käll Per-Olov , Nygren Mats
Published: March 2011

Ceramics based on silicon nitride have long been considered promising candidates for high temperature engineering applications due to their excellent refractory properties combined with high strength and good resistance to oxidation. It is well known, however, that the performance of ceramics varies considerably with chemical composition, for example with type and amount of intergranular phase. Especially the evaluation of the high temperature behaviour of the ceramics under varying conditions is therefore important in increasing the knowledge of these materials.
Corrosion of Silicon Nitride Ceramics by Nitric Acid
Authors: Kanbara Kunihiko , Uchida N. , Uematsu K. , Kurita T. , Yoshimoto K. , Suzuki Y.
Published: March 2011

Corrosion of silicon nitride was studied in boiling nitric acid to examine its feasibility as a drying pan material in the reprocessing of nuclear fuel. Unlike stainless steel (a conventional drying pan material), the weight loss and strength degradation were negligible in the concentration of nitric acid. The corrosion increased with decreasing concentration of nitric acid. At the concentration of 1-6N, the maximum losses of weight and strength were 0.8% and over 40%, respectively, in 200 h. Ionic species dissolved in nitric acid were determined by ICP analysis and were found to be accurately correlated to the weight loss and thickness of the corrosion layer determined by micrography. In the corrosion layer, grain boundary glassy phase was selectively dissolved. Strength loss was correlated to the weight loss and was ascribed to the reduced load bearing area due to corrosion.
The Effect of Polymers on Ceramic Suspension Rheology and Green Component Properties
Authors: Lewis Jennifer A. , Ogden Andrea L. , Schroeder David , Duchow Kirk J.
Published: March 2011

Ceramic suspensions were formulated based on an alumina/plasticized-polymer system. The total polymer volume in suspension was held constant, while the relative amount of high-to-low molecular weight polyvinyl butyral (PVB) in suspension was varied. Experiments were performed to elucidate the effects of polymer molecular weight and distribution on the rheological properties of these casting suspensions as well as on the green microstructure of tape-cast components. The polymer properties affected not only the suspension viscosity at a given shear rate as expected, but also the shear thinning behavior of each suspension. Tapes (thickness ≈ 250 μm) were cast from these suspensions and their properties were evaluated. Pore volume, a measure of the packing efficiency, was found to depend strongly on the polymer molecular weight and distribution. In addition, preliminary lamination studies revealed that dimensional stability and anisotropy were also affected by the relative amount of high-to-low molecular weight PVB. A direct correlation was shown to exist between the shear thinning behavior of these suspensions and the resulting dimensional anisotropy exhibited by the tapes cast from each of them. These results demonstrate that polymeric aids influence not only the suspension rheology, but the green component microstructure as well, and, hence, are an integral aspect of ceramic processing.
Extrusion Rheology and Structure of Alumina - Silicon Carbiide Composites
Authors: Blackburn S
Published: March 2011

Silicon carbide fibre reinforced alumina compacts were formed by extrusion. The powder and fibre were pre-mixed and milled before high shear kneading to produce a homogeneous dispersion of up to 30 vol% chopped SiC fibre with high green density. The rheology of the paste was characterised using a physically based model. It is demonstrated that the pressure drop and constituent paste parameters are all systematically reduced with increasing fibre loadings for a given moisture content. It is suggested that particle packing theory in combination with fibre interactions within the paste and die system offers an explanation for the observed results.
Structure and Rheology of Cement-Based Systems
Authors: Banfill P.F.G.
Published: March 2011

Fresh concrete and mortar conform closely to the Bingham model, but the rheology of cement pastes is more complex and structural breakdown occurs. This can be explained by the existence of forces between the surfaces of individual particles which are less significant in the coarser grained materials. The requirements of apparatus to determine the rheology of these materials are described and typical results reported. The behaviour of the materials in practical applications such as pumping, vibration and trowelling can be explained by the rheological parameters so obtained, and a consistent view of the performance of cement based materials may be developed.
Interparticle Forces and the Rheology of Colloidal Dispersions
Authors: Costello Bernard A. de L. , Luckham Paul F. , Tadros Tharwat F.
Published: March 2011

The forces between mica surfaces bearing adsorbed layers of graft copolymers of either polyethyleneoxide/ polymethylmethacrylate in water or polyhydroxystearic acid / polymethylmethacrylate in decalin have been measured. The forces are repulsive in nature and in both cases commence at a surface separation of ˜ 25 nm. They may be described by scaling theory. The results are compared to the rheology of particles stabilised by the same copolymers, in particular to the elastic modulus. It is found that these two parameters scale in the same way, but quantitative comparison reveals that the modulus predicted from the particle forces is some 1 – 2 orders of magnitude greater than that measured experimentally.
Rheology Control in High Solids Solvent Borne Coatings Containing Polymer Microgels
Authors: Boggs L. J. , Rivers M. , Bike S. G.
Published: March 2011

The focus of this work is to determine the type of interparticle forces that are primarily responsible for the rheology control of high solids solvent borne coatings containing polymer microgels. Rheological behavior is an important consideration when formulating high solids coatings due to the relatively low viscosities required for sufficient atomization during spray application and the difficulty of preventing the film from sagging during the bake cycle. Rheology control agents such as microgels are used to modify rheological properties where solvent evaporation is insufficient during the bake cycle to prevent sagging.

In this paper that describes the first phase of our work, we have characterized several microgel dispersions used as rheology control agents in high solids automotive topcoats using scanning electron microscopy (SEM) and steady shear viscosity measurements. The steady shear viscosity versus microgel volume fraction data was compared with the expected behavior of ideal hard sphere dispersions. One of the microgel dispersions showed very nearly ideal behavior while others deviated from the expected behavior at higher volume fractions. We have also investigated the steady shear behavior of increasing concentrations of microgel dispersions added to low molecular weight acrylic polymer, typical of resins used in high solids automotive coatings. These microgel dispersions induce a yield stress in the Newtonian resin that shows a strong dependence on microgel particle concentration.
Granular Fluids Rheometry
Authors: Meeten G H , Pafitis D
Published: March 2011

Many functional fluids, such as cement slurries or drilling muds, contain high-density solids, typically grains of 10–100 micron in diameter, suspended in a liquid of much lower density. Coaxial cylinder rheometers, conventionally used for oilwell fluids and dense suspensions generally, are shown to give large errors owing to gravitational or centrifugal migration of the high-density solids. Further errors can arise from slippage between the fluid and the smooth walls of the rheometer.

A modification is described to a coaxial cylinder rheometer, in which the fluid is circulated, using an external pump, through the sample cup and around the rotor/stator assembly. This circulation mixes and homogenises the fluid, prevents solids build-up in both the annular gap and the cup bottom, and provides an independently-controllable shear history. Thus stable and accurate data can be obtained for fluids which give measurement problems using standard rheometers.

Results are given for various power-law/yield stress granular fluids.
Structural Network Model of Dense Suspension
Authors: Jiang W. , Yang Nanru , Wang Z.
Published: March 2011

A structural network model for investigating dense suspension is introduced. The suspension may be considered as particle dispersion in liquid as a continuous phase and it is the combination of the three-dimensional arrangement of the fine particles and the forces acting between them that determines the physico-chemical behavior at all stages of the processing. The model assumes that microstructural features of dense suspension can be represented by simple linear network with a breakdown threshold. The conditions under which such a structural network model is valid for studying flow are discussed. The cement paste, asphalt, sand-water and clay-water system were investigated respectively using this model. An oscillating rheometer and a conventional rotational viscometer were used to carry out this study. The dynamical and viscoelastic properties of dense suspension were observed. All the qualitative features of the network results can be described theoretically by a statistical analysis of this problem. Soil mechanics principles which are focused on critical-state theory were applied to describe the stress-strain behavior of dense suspension.
The Resolution of Photoelectrochemically Etched Features
Authors: Cheng J. , Kohl P. A.
Published: March 2011

The profiles of features etched photoelectrochemically in n-InP are studied to determine the factors which govern their distortions and to determine the factor limiting spatial resolution for etch depths in the 100–200−μm range. The optimal conditions for etching straight grooves using laser light are determined. The application to front-to-back mask registration will be discussed.
Laser Photochemical Etching of GaP in KOH Aqueous Solutions
Authors: Johnson A. Wayne , Tisone Gary C.
Published: March 2011

Gallium phosphide is an important III-V semiconductor material for fabricating strained layer superlattices and high-speed and high-temperature microelectronics. Etching of this compound semiconductor with conventional techniques presents problems which may be solved by photon-induced electro-chemistry. We have shown that rapid localized etching of n-GaP in KOH can be driven with the UV lines of an argon-ion laser. The level and type of doping and the laser intensity determine the etch rates, which are nearly 60 nm/sec at 3500 Wcm−2 for n-doped material.
Deep-UV, Light-Assisted, Wet Etching of Compound Semiconductors
Authors: Podlesnik D. V. , Gilgen H. H. , Osgood R. M.
Published: March 2011

Deep-UV, laser-light-assisted, wet etching of compound semiconductors is reported. As ccmpared to results with visible light, the etching rates per unit power density in the ultraviolet are considerably faster; a factor of >30 is seen under typical conditions. A correlation between the UV absorption in different etching solutions and the light-enhanced etching rates is examined. Gratings with 100-nm resolution have been produced and high-aspect-ratio via-holes have been etched.
Single-Crystal Silicon Etching Characteristics Using Excimer Laser Cℓ2 GAS
Authors: Arikado T. , Sekine M. , Okano H. , Horiike Y.
Published: March 2011

Single-crystal Si etching characteristics using an excimer laser (308 nm, XeCℓ) in the Cℓ2 gas have been studied. In lightly doped n-type and p-type Si, the etch rate of (100) is higher than that of (111), thus the (111) sidewall appears clearly for the irradiation to (100), while both orientations show almost the same etch rates in n+-doped Si. The n-type Si is etched spontaneously even by photo-dissociated Cℓ radicals generated in the gas phase, but no p-type Si etching occurs without direct irradiation. In addition, both types of etch rate-dependence on sheet resistance demonstrate that the number of electrons in the conduction band plays an essential role in the Si etching. This fact supports the field-assisted mechanism in the plasma etching proposed by Winters.
Spatial-Resolution Limits of Laser Patterning: Submicrometer Projection Microchemistry
Authors: Ehrlich D. J. , Tsao J. Y.
Published: March 2011

The predictions of a simple two-dimensional model for the sensitivity to process contrast of direct-write and projection laser microchemistry are reviewed. Microchemical reactions excited by UV image projection are demonstrated using a 30X reduction reflecting system and excimer laser illumination. Well-resolved images with submicrometer features are obtained by: (1) reaction of an Al/O cermet, (2) projection doping of Si in BCl3,(3) projection etching of Pyrex glass in H2, and (4) reactive patterning of an organic bilayer. Linewidths of 0.5 – 0.2 μm have been demonstrated for projection imaging in these systems.
Mechanism of Laser-Enhanced Etching of Silicon
Authors: Houle F. A.
Published: March 2011

Recent studies of the laser-enhanced etching of silicon by XeF2 have demonstrated that rapid reaction rates are attributable to intrinsic effects of above band gap radiation, that is, that photo-generated charge carriers influence the etching reaction. The mechanism proposed to account for this is described.
Laser-Assisted Local Etching of Gallium Arsenide
Authors: Takai M. , Tokuda J. , Nakai H. , Gamo K. , Namba S.
Published: March 2011

Pyrolytic local etching of GaAs using focused Ar laser beams in C12 or CCl4 gas atmospheres has been performed to investigate the possibility of maskless etching processes by laser beams. Etching rates from 0.3 to 40 μ/scan with an etched linewidth down to 5 μ were obtained. In the case of CC1 4 , a carbon line buried in GaAs was obtained for a single scan of a laser beam at a pressure above 80 Torr with low scanning speeds or at a pressure above 120 Torr.
Sensitive, Non-Intrusive, In Situ Measurements of Plasma Electric Fields
Authors: Gottscho Richard A , Moore Cameron A. , Davis Glenn P.
Published: March 2011

We report a new technique for the in situ, non-intrusive, and sensitive measurement of plasma electric fields with high spatial resolution. Fields as small as 40 V/cm can be characterized by spectrally resolving laser-induced fluorescence from Stark-mixed parity levels. The technique is demonstrated by exciting the A1 11−X 1Σ+ band system of BC1, produced in an rf discharge through BCI3. The characterization and absolute measurement of sheath fields, which have been elusive, are now possible. These fields are preeminent in governing charged particle transport to and between electrode surfaces and in maintaining the glow discharge.
Laser-Induced Oxidation and Crystallization of Thin Amorphous Sputtered Cr Films
Authors: Birjega M. I. , Constantin C. A. , Dinescu M. , Florescu I. Th. , Mihailescu I. N. , Nanu L. , Popescu-Pogrion N. , Sarbu C.
Published: March 2011

The crystallization and oxidation processes of thin, free-standing (FS), sputtered Cr films under the action of cw CO2 laser irradiation were studied by transmission electron microscopy (TEM) and transmission electron diffraction (TED). The crystallization is induced at power densities above 28.65 W cm−2, dwell time of 1 s, and the oxidation at power densities of 48.1 W cm−2 and longer dwell times.
Wafer-Scale Laser Pantography: IV. Physics of Direct Laser-Writing Micron-Dimension Transistors
Authors: Herman Irving P. , Mcwilliams Bruce M. , Mitlitsky Fred , Wah Chin Hon , Hyde Roderick A. , Wood Lowell L.
Published: March 2011

The processes involved in the fabrication of micron-dimension transistors and small-scale integrated circuits using only the technique of direct laser-writing by localized pyrolytic surface reactions are discussed. New experimental findings in the deposition of tungsten by silicon. surface reduction of tungsten hexafluoride and doped polysilicon are presented. The techniques used to fabricate laser beam-written n-MOSFET's are being extended to make unipolar JFET's and bipolar lateral pnp transistors.
Infrared Laser-Induced Heterogeneous Reactions: Fluence-dependent Branching Ratios in 2-Propanol with CuO
Authors: Farneth William E. , Zimmerman Patrick G. , Hogenkamp Derk J.
Published: March 2011

The heterogeneous decomposition of 2-propanol vapor in the presence of CuO solid can be induced by irradiation with a pulsed CO2 laser. The reaction produces both propene and acetone. In contrast, the homogeneous multiphoton-induced decomposition of 2-propanol vapor yields only propene. The branching ratio ([hydrocarbon]/[acetone]) in the heterogeneous experiments has been examined as a function of laser pulse energy. While the yield of acetone increases monotonically with increasing fluence, yields of hydrocarbon show two distinctly different regimes of fluence dependence. Reactions have been run with both d8 and h8 2-propanol and on 1:1 mixtures. Neither reaction channel shows significant isotopic selectivity over a range of experimental conditions. This data will be discussed in light of a model that involves energy deposition in the solid, followed by either heterogeneous reaction of adsorbed material or energy transfer and subsequent multiphoton excitation of the alcohol vapor.
Local Doping of GaAs by Laser-Stimulated Diffusion From the Gas Phase
Authors: KrÄutle H. , Roth W. , Krings A. , Beneking H.
Published: March 2011

Semi-insulating GaAs as well as MOCVD GaAs layers have been doped in situ with Se in a MOCVD system. H2Se diluted in an H2 + AsH3 atmosphere, which avoids surface decomposition, is used as the doping source. The surface is heated locally for less than 1 μs with a 3-ns Nd-YAG-laser pulse (frequency doubled: λ = 532 nm, pulse ratio 5 s−1). During this short time adsorbed Se atoms are incorporated into the heated surface region.

This process allows us to achieve heavily doped thin layers with Se concentrations in the order of 1021 cm−3. Outside the irradiated area the crystal remains undoped.

Se concentrations measured with secondary ion mass spectroscopy (SIMS) and carrier concentrations measured with the van der Pauw method indicate the diffusion of adsorbed Se atoms into GaAs. The distribution and activation of Se depends on laser power and substrate temperature.
Doping of GaAs From Silane Decomposition Under Pulsed Laser Irradiation
Authors: Pribat D. , Dieumegard D. , Dessertenne B. , Chaplart J.
Published: March 2011

We have studied silicon incorporation in GaAs subsequent to Nd-YAG laser irradiation through high pressure silane atmospheres. The process involves SiH4 pyrolysis at contact with a laser-melted GaAs surface, and incorporation of the released Si atoms in the melt. SIMS analyses have allowed us to study silicon incorporation as a function of SiH4 pressure, laser energy density and number of laser shots. The high sheet resistance of the doped layers indicates that the silicon atoms are poorly electrically activated. A compensation mechanism is discussed based on oxygen penetration from native GaAs oxide layers.
Properties of Dielectric Thin Films Formed by Laser Evaporation
Authors: Sankur H.
Published: March 2011

The technique of laser evaporation for the deposition of thin films has been applied to a large class of materials including oxides, fluorides and II-VI semiconductors. The evaporations were performed in high vacuum or under O2 pressures of 10−3 Torr, on several types of substrates, by using CO2 lasers in CW and pulse modes. The thin films thus obtained have been characterized for their structural, optical and electrical properties.

Entire ranges of mixtures in several binary systems (e.g., SnO2-SiO2), have been obtained by coevaporation, using mirrors to steer the laser beam among sources.

Conditions that affect the stoichiometry and structural properties (laser parameters, background pressure, evaporation rate, substrate temperature) have been established for each material system. Differences in the evaporation behavior of materials under CW and pulsed conditions have been investigated for the case of ZnO. Present and future applications of this technique in the optical devices field are also discussed.
Column IIIA Metal film Deposition by Laser Photoionization of Metal-Halide Molecules in the Vapor Phase
Authors: Geohegan D. B. , Mccown A. W. , Eden J. G.
Published: March 2011

Films of Column IIIA metals (In, Tℓ and Aℓ) have been deposited on several different substrates (stainless steel, nickel and copper) by photoionizing the corresponding metal-iodide or bromide (such as TℓI, InI or AℓI3) in the vapor phase and in the presence of a uniform electric field. These experiments were prompted by the measurement of large photoionization cross-sections for ion production (i.e., MX + 2ħ ω → M+ + X + e- or MX + ħω → M+ + X-) in these molecules at 193 nm. The effective cross-sections for the photoionization of TℓI and InI at 193 nm have been measured to be 2.2·10−17 cm2 and < 7·10−18 cm2, respectively. Depletions of the metal-halide ground state greater than 60% have been observed for ArF peak laser intensities of only 5 MW − cm−2.
Theory of Nuclear Relaxation in Confining Systems. Application to Non Wetting Liquids in Porous Silica Glasses
Authors: Korb J.-P. , Delville A. , Xu Shu , Jonas J.
Published: March 2011

This work shows how the geometrical confinements enhances the nuclear relaxation of a non wetting liquid in a model porous systems. Application of the proposed theory is made to interpret the size and frequency dependences of the 1H relaxation of methylcyclohexane liquid in sol-gel porous silica glasses with narrow pore-size distribution.
NMR Relaxation of quadrupolar Nuclei as a Probe of the Motion of Guest Species in Sodalite Cavities
Authors: Jelinek R. , Ozin G. A.
Published: March 2011

Useful information on interactions and motion of guest molecules in sodalite cavities is obtained by estimating the spin-lattice and spin-echo decay rates of encapsulated Br− ions. An extremely fast spin-lattice relaxation rate is observed for 81Br nuclei, adjacent to Br−-empty cages which contain rapidly tumbling water molecules. We detect a further significant different T1 of the 81Br in Na8Br2- sodalite and AgsBr2-sodalite, respectively, which probably indicates a less restricted motion within the cavities of the Ag+-exchanged material. Spin-echo decay experiments additionally indicate a difference between the dynamic properties of the Br− anion in the encapsulated Na4Br and Ag4Br clusters, respectively.
Computer Simulations of Diffusion in Monolayers Physisorbed in Model Pores
Authors: Bojan Mary J. , Steele William
Published: March 2011

Two types of model pore have been considered as sorbents of methane at 300 K: the first is a straight cylinder with atomically rough walls characteristic of an amorphous solid. Three cylinder radii plus the reference flat surface were taken for study. The second is a parallel-walled slit pore made up of graphite basal planes that had been modified by the insertion of sulfide atoms. Here, two values of sulfur loading were taken together with the reference pure graphite pore. Two values of the wall spacing were assumed for each sulfur loading. Thermodynamic and structural properties are presented elsewhere; here, the dependence of diffusion constants as a function of the monolayer density is presented for methane in the various model pores. It is shown that these diffusivities depend primarily on the methane-methane collisions in the monolayer films. There is a slight dependence upon the nature of the solid surface which is interpreted in terms of the hindrances produced by soft obstacles to molecular motion parallel to the surfaces.
Visualisation of Fractal Fingering Using NMR Imaging
Authors: Davies Eleanor S. , Carpenter T. Adrian , Hall Laurance D. , Hall Christopher
Published: March 2011

Fractal fingering is a well known phenomenon, ususally visualised using photography. Previous experiments have shown that the patterns can be visualised using NMR imaging, and in this paper we show that the fractal dimension of such a pattern can be easily calculated.
Interface Effect on Dipole-Dipole Interaction
Authors: Urbakh Michael , Klafter Joseph
Published: March 2011

The nature of the pair interaction between dipoles embedded in a liquid in the vicinity of a non-metallic interface is investigated in the continuum limit. It is shown that the dipole-dipole interaction can be significantly modified in the presence of a boundary in liquids characterized by a nonlocal dielectric function or in liquids whose dielectric properties change due to geometrical restrictions. Different limits are studied and relationships to experimental observables are discussed.
The Critical Thickness of the Dislocation-Free Stranski Krastanow Pattern of Growth.
Authors: Grinfeld Michael A.
Published: March 2011

It was demonstrated earlier [1,2] in the framework of equilibrium thermodynamics that the morphological stability of the free boundaries and interfaces in crystals is extremely sensitive to the presence of shear stresses. Relying on that idea we have established the formula H = μσ/τ2 of a critical thickness of solidifying He4 films and of the dislocation-free Stranski-Krastanow growth of epitaxial films (where σ – the coefficient of surface tension, μ - the shear module of the crystal, τ - the external or misfit stress). In this report we present certain facts pertaining to possible patterns of the growing corrugations and introduce the second critical thickness at which a symmetry change in the patterns has to occur.
Preparation of High-Conductive High-Temperature PTC Resistor Ba1-x SrxPb1+yO3+z
Authors: Nagamoto H. , Kagotani H. , Koya T.
Published: March 2011

The positive temperature coefficient of resistivity (PTCR) effect in Ba1-xSrxPb1+yO3+z has been systematically studied. The effect of the PTC resistivity was strongly influenced by the preparation condition. The PTCR effect in metallic-conducting BaPb1+yO3+z. is confirmed around 700 °C, and the temperature where the PTCR effect starts can be successfully shifted to higher temperature range by substituting strontium for the A-site barium. The magnitude of the PTCR effect was increased and the resistibility was reduced by the enhancement of the sintering. In addition to Pb(IV) in the perovskite structure, Pb(II) is detected at the grain boundary in the sintered body.
The Escape of Particles from a Confining Potential well
Authors: Lavine James P. , Banghart Edmund K. , Pimbley Joseph M.
Published: March 2011

Many electron devices and chemical reactions depend on the escape rate of particles confined by potential wells. When the diffusion coefficient of the particle is small, the carrier continuity or the Smoluchowski equation is used to study the escape rate. This equation includes diffusion and field-aided drift. In this work solutions to the Smoluchowski equation are probed to show how the escape rate depends on the potential well shape and well depth. It is found that the escape rate varies by up to two orders of magnitude when the potential shape differs for a fixed well depth.
One-Diohliensilonall A + B = 0 Reactmion with One Immobile Species
Authors: Argyrakisa Panos , Kopelman Raoul
Published: March 2011

The elementary batch reaction A + B = 0 is re-examined via Monte-Carlo simulations on a one-dimensional lattice. The relative mobility of the A and B species is varied in this model, but the initial densities of the A and B are always the same. We calculate the rates, the density profiles, and the particle distribution functions. The rate power law is conserved, i.e., the well-known 1/4 behavior is established for all mobilities. The rate coefficient is the only mobility-dependent quantity. The interparticle distribution functions show that the aggregation depends on the relative mobility but the segregation does not. This subtle difference has no effect on the asymptotic reaction order, which is close to 5.
Non-Classfcal Kinetiics in Hydrogen-Deuterium Exchange Reaction on Metal Catalyst
Authors: Choi Inchan , Kopelman Raoul
Published: March 2011

Monte Carlo simulations of the A2 + B2→ P (with P = AA, AB, and BB) reaction on various monodisperse island systems provided various models for the reaction H2 + D2→ HD on alumina supported platinum catalysts. Anomalous reaction kinetics and reaction orders due to the effects of diffusion, reactant correlation, and ensemble character of the catalyst in low dimensional systems are observed not only at early time but also at steady state. Concentration effects and spillover studies indicate that surface diffusion and hydrogen spillover may be responsible for the anomalous behaviors.
Local Reaction Probability Effects in Non-Classical Kinetics: Batch and Steady State
Authors: Shi Zhong-You , Kopelman Raoul
Published: March 2011

The reaction A+A→0 is simulated in 1-D and 2-D square lattices with various local reaction probabilities, P. The effective reaction order, X, and the nearest neighbor distance distribution (NNDD), are evaluated in all these reactions. For batch reactions, sharp increases in X with increasing P occur at early times. Classical reaction limited kinetics is obtained at early times only when P→0. At long times, all reactions are in the non-classical, diffusion limited regime, regardless of P. For steady state reactions, our results demonstrate a similar behavior of X with P. The NNDD at steady state in 1-D media at P=1.0, i.e. diffusion limited reaction, follows the previously reported skewed exponential shape. This is no longer true for P<I. Finally, at P→0, as expected, an exponential (Poissonian) distribution is obtained for both reaction conditions.
Interfacial Dynamics of Water-in-Oil Dropliets: a Temperature-Jump Investigation
Authors: Alexandridis Paschalis , Holzwarth Josef F. , Hatton T. Alan
Published: March 2011

The dynamic response of water-in-oil AOT microemulsion droplets to perturbations caused by rapid energy transfer has been interpreted in terms of the surfactant interface bending rigidity. The Iodine Laser Temperature Jump technique was used to rapidly (1 μs) increase the microemulsion temperature and thus disturb the system equilibrium. The dynamic relaxation to the new equilibrium position was monitored by measuring the turbidity of the microemulsion over a I ms time interval immediately after the temperature jump. The rate and direction of the turbidity change depended on the initial temperature, size and salt content of the water droplets. We observed characteristic times of 2 to 10 μs and attributed them to the relaxation of the surfactant interface. A bending modulus of 0.4 kT was derived for the AOT interface, using a model for the shape perturbation of a spherical interface.
Numerircal Determination of Nucleatilon Parameters in Polymoriphic Crystalliization from Solutiions
Authors: Merlo M. , Santos A. , Duport L. Gago
Published: March 2011

A numerical model based in nucleation and growth algorithms has been designed to compute the temporal sequences of precipitation and phase transformation kinetics in metastable solutions of polymorphic or hydrated substances. A outline of the model is made for the particular case of crystallization of several hydrated phases from nickel nitrate solutions
Picosecond Studies of Nonequilibrium Flux Dynamics in Superconductors
Authors: Freeman M. R.
Published: March 2011

A fast time-domain magneto-optical technique is used to explore magnetic flux dynamics in the optically driven nonequilibrium state of Type I superconducting Pb films. It is found that the effective penetration of flux through the nonequilibrium intermediate state can be dramatically faster than through the normal metal. The system is probed through the application of rapid transient magnetic field pulses. Above the superconducting transition temperature, a direct measure of the diffusion coefficient of the magnetic field in the normal metal is obtained, on a time scale where the inhomogeneous spatial distribution of scattering sites is relevant. In the nonequilibrium superconductor the observations are dominated by coupling of the field transients to local motion of magnetic flux threading the normal domains. Studies as a function of how far the system is driven from equilibrium, and of the effect of a static applied magnetic field, indicate that the observations reflect the dynamics of normal/superconducting interfaces, and are strongly dependent on the microscopic arrangement of the intermediate state. By contrasting the response of pure Pb films to that of Pb1−xInx alloys, a comparison to Type II superconductivity is made.
Interfacial Properties of Isotropic Semi-Flexible Polymer Blends
Authors: Liu Andrea J. , Fredrickson Glenn H.
Published: March 2011

We analyze interfacial behavior in binary blends of polymers with different flexibilities. Our starting point is a free energy functional calculated from a microscopic model of wormlike chains. We show how this functional can be used to calculate interfacial properties within the Cahn-Hilliard approach. Here we present preliminary results applicable to chains that are globally coil-like. At the interface between two isotropic phases, each rich in a different polymer, we find that the polymers tend to be extended parallel to the interface. Thus their shape is oblate rather than spherical at the interface.
Angular-Resolved ESCA Studies of Cadmium Arachidate Monolayers on Si (100): Inelastic Mean-Free Path and Depth Profile Analysis
Authors: Letellier Shelli R. , Vogel Viola , Ratner Buddy D. , Leach-Scampavia Deborah
Published: March 2011

Angular-resolved ESCA was used to study single cadmium arachidate monolayers transferred to Si (100) wafers by the Langmuir-Blodgett technique. We find the monolayers to be of high integrity with respect to those defects which enhance the escape probability of substrate photoelectrons through the overlayer. The inelastic mean-free pathlengths of Si (2p) and C (1s) electrons were calculated to be 49±6 Å and 45±6 Å for the kinetic energies of 1388 eV and 1202 eV, respectively. The overall ordering of the hydrocarbon chains is less than for alkane thiols assembled on noble metals. We find that the precision of the Tyler algorithm to deconvolute angular-resolved ESCA data into depth profiles is accurate within 10% for predicting the thickness of the hydrocarbon overlayer but less precise for intermediate layers.
Biopolymer-Thin Film Interactions
Authors: Maloney K. M. , Grainger D. W.
Published: March 2011

Biopolymer self assembly in heterogeneous lipid monolayers at the air-water interface was investigated. Fluorescence microscopy allowed the visualization of protein recognition and binding to these microstructured membranes. Mimicking proteininduced membrane microstructuring and protein docking was achieved in ternary mixed lipid monolayer systems.
Photovoltaic Effects and Charge Transport Studies in Phycobiliproteins
Authors: Beladakere N. N. , Ravindran T. , Bihari B. , Sengupta S. , Marx K. A. , Kumar J. , Tripathy S. K. , Wiley B. , Kaplan D. L.
Published: March 2011

Phycobiliproteins form highly efficient light absorbing systems in certain algae. We have investigated the charge-transport phenomena in these proteins by analyzing the dark current-voltage and photocurrent characteristics obtained across Au-phycobiliprotein-Au samples. A photovoltaic effect was observed for Au-phycoerythrin-Au sample. At low intensity levels, the photocurrent closely follows Onsager's law of geminate recombination in three dimensions.
Sub-Micrometer Hydroxyapatite Bioceramics
Authors: Shaoxian Zeng , Jingkun Guo , Zhixiong Yang , Jie Cai , Wanpeng Cao
Published: March 2011

We studied the microstructures of hydroxyapatite (HA) ceramics which were sintered under three different conditions. It was found that all the ceramics were of sub-micrometer structure. The synthetic HA ceramics were also compared with human enamel. It is concluded that human enamel has higher strength because of its unique microstructure.
Assembly of α-Hemolysin: a Proteinaceous Pore with Potential Applications in Materials Synthesis
Authors: Bayley Hagan , Krishnasastry Musti , Walker Barbara , Kasianowicz John
Published: March 2011

α-Hemolysin (αHL) is secreted by the bacteriumStaphylococcus aureusas a watersoluble polypeptide of 293 amino acid residues. When presented with lipid bilayers or the detergent deoxycholate (DOC), aHL assembles into hexameric cylindrical pores that each contain one channel ∼ 1 to 2 nm in Internal diameter. A long-term goal of this laboratory is to use wild-type or re-engineered αHL pores as components of nanoscale materials: for example, to confer novel permeability properties upon thin films. The implementation of this concept would be facilitated by a better understanding of the mechanism by which the pore assembles. Reviewed here are findings that have given us insight Into the assembly mechanism, including the results of recent mutagenesis experiments. A critical summary is given of knowledge about the conformation of the monomer In solution, the hexamerIc pore and two proposed intermediates in assembly (a membrane-bound monomer and an oligomeric pore precursor). Future directions are outlined Including the prospects of obtaining three-dimensional structural data on the αHL pore or its precursors, methods for obtaining better monolayer sheets and new experiments on the topography of the pore and its precursors. The role of membrane receptors in facilitating the assembly of αHL is also discussed. Finally, it is demonstrated that despite our rather rudimentary knowledge of the assembly process, the Information gained so far still allows the design of mutant (αHL polypeptides with useful properties. For example, αHL mutants whose pore-forming ability is activated by proteases have been made.