bluuebunny/crossref_metadata_2025 huggingface dataset:
Microwave Resonator Techniques for Sorting Dielectric Objects
Authors: Kraszewski Andrzej W. , Nelson Stuart O.
Published: March 2011

Microwave resonators have been found to be sensitive devices for sorting dielectric objects of irregular shapes according to their volumes, for detecting voids inside objects of similar shape or for determining moisture content in objects of varying volumes. Fundamental principles of operation as well as experimental results are discussed in the paper.
Microwave Photoconductivity Measurements to Characterize Semiconductors
Authors: Kunst M.
Published: March 2011

After a general survey of characterization techniques the use of transient photoconductivity measurements in the microwave frequency range for the characterization of semiconductors and semiconductor devices for (opto)electronic applications is treated. Experimental details and applications of these measurements are given.
Patterning of Microwave Plasma Deposited Diamond Films
Authors: Leksono Moeljanto W. , Shanks Howard R.
Published: March 2011

Patterning has been successfully performed on diamond films deposited on polished silicon wafers from CH4 and H2 gases using microwave plasma chemical vapor deposition. The selectivity was achieved using a lift off process on silicon wafers which had been polished with diamond paste. The lift off process involves deposition and patterning of a thin ZnO film followed by deposition of amorphous silicon using a glow discharge technique. This is followed by microwave plasma CVD of the diamond film. The film is deposited selectively on the crystalline silicon areas of the substrate. Quality and patterning resolution of the resulting diamond films have been determined.
First Results of In-Can Microwave Processing Experiments for Radioactive Liquid Wastes at the Oak Ridge National Laboratory
Authors: White T. L. , Youngblood E. L. , Berry J. B. , Mattus A. J.
Published: March 2011

The Oak Ridge National Laboratory (ORNL) Waste Handling and Packaging Plant is developing a microwave process to reduce and solidify remote-handled transuranic (RH-TRU) liquids and sludges presently stored in large tanks at ORNL. Testing has recently begun on an in-drum microwave process using nonradioactive RH-TRU surrogates. The microwave process development effort has focused on an in-drum process to dry the RH-TRU liquids and sludges in the final storage container and then melt the salt residues to form a solid monolith. A 1/3-scale proprietary microwave applicator was designed, fabricated, and tested to demonstrate the essential features of the microwave design and to provide input into the design of the fullscale applicator. Conductivity cell measurements suggest that the microwave energy heats near the surface of the surrogate over a wide range of temperatures. The final wasteform meets the waste acceptance criteria for the Waste Isolation Pilot Plant, a federal repository for defense transuranic wastes near Carlsbad, New Mexico.
Application of Gyrotron Radiation for Coating and Welding
Authors: Paton B. E. , Sklyarevich V. E.
Published: March 2011

The availability of high power high frequency microwave sources of up to tens of kW has opened up important technological and industrial applications of microwave radiation. The particular use of gyrotrons for generating the high power microwaves is considered.

The application of high power microwaves for fusing wear resistant coatings onto refractory materials is discussed, together with the brazing of ceramics, welding together of thick metal parts and the rapid heating and curing of polymers for high reliability long life environmental coatings.

It is shown that the use of high power gyrotron radiation enables considerable improvements to be made on conventional technologies for high temperature processing of materials and enables the development of new and efficient processes.
Synthesis of Ultrafine, Multicomponent Particles Using Phospholipid Vesicles
Authors: Liu H. , Graff G. L. , Hyde M. , Sarikaya M. , Aksay I. A.
Published: March 2011

Because of their unique properties of self-assembly and selective ion permeability across the lipid bilayers, phospholipid vesicles were used as reaction vessels for the synthesis of ultrafine, multicomponent ceramic particles containing Y, Ba, Cu, and Ag. Chemical inhomogeneities in the system were limited to the individual particle size (< 50 nun), which was a considerable improvement over particles prepared using bulk precipitation routes. The consistent barium deficiency was a serious problem that arose when attempting to control the stoichiometry of the multicomponent system. Our experimental evidence suggests that chemical interactions between the barium cations and the vesicleforming phospholipid may inhibit the precipitation of barium salts. In a parallel study, we performed consolidation studies on vesicle-precipitated Ag2O particles before and after the removal of the phospholipid molecules. Particle packing was greatly improved in the surfactant coated particles. This demonstrates the multifunctionality of this biomimetic system in which the vesicle membrane simultaneously acts as: (i) a reaction cell for particle precipitation, (ii) an ion selective membrane that affects precipitation kinetics, (iii) a barrier to prevent spontaneous agglomeration of the ultrafine particles, and (iv) a lubricant/dispersantth atfacilitatesp article rearrangementd uring consolidation.
Wavelength Dependence of the Photorefractive and Photodiffractive Properties of Holographic Thin Films Based on Bacteriorhodopsin
Authors: Birge Robert R. , Izgi K. Can , Stuart Jeffrey A. , Tallent Jack R.
Published: March 2011

The photorefractive and photodiffractive properties of a 2 × 10−3 M, 30μim thin film of bacteriorhodopsin at - 40°C are analyzed by using optical absorption spectroscopy, the Kramers- Kronig transformation and coupled wave theory. Conversion of M to bR generates a dispersion in the refractive index that has a broad negative band from 450 to 540 nm [Δn500nm - -0.0016] and a broad positive band from 590 to 700 nm [Δn605nm - 0.0016]. The large change in refractive index for moderate solute concentration is due to the formation of the protonated Schiff base chromophore in bR which generates a large red shift in the absorption spectrum as well as a large increase in oscillator strength. The integrated diffraction efficiency from 300 - 800nm is dominated by refractive index contributions (ηphase) which are maximum in regions of minimal bR and M absorption. The maximum in the refractive (phase) component occurs at 451 nm (ηphase - 9.7%) whereas the maximum in the absorption component occurs at 575 nm (ηabs - 2.2%). The maximum efficiency of diffraction is observed at ∼440 nm (ηtotal - 10.7%). Adequate diffractive performance for most applications is predicted for write wavelengths in the regions 380 - 420 & 500 - 650 nm and for read wavelengths from 380 to 740 nm.
Controlling Surface Properties with Peptides: New Methods in Molecular Self-Assembly
Authors: Wilson Troy , Bednarski Mark D.
Published: March 2011

As part of our investigation into the design and applications of proteolytic enzymes, we required a convenient method to attach peptides to the surface of a variety of materials. In this paper we report the synthesis and characterization of a class of peptide derivatized lipids (PDL's) that can be self-assembled into monomolecular films. These films can be used to control interfacial properties such as wetting and adhesion and provide a simple method to coat surfaces with amino acids.
Novel Polymer Synthesis using Enzymatic Catalysis in Nonaqueous Media
Authors: Dordick Jonathan S. , Patil Damodar. R. , Ryu Keungarp , Rethwisch David G.
Published: March 2011

The use of enzymes in organic solvents has enabled two distinct polymer syntheses to be performed. The first is the enzyme-catalyzed polycondensation of sucrose with an adipic acid derivative in pyridine. Taking advantage of the extremely high regioselectivity of proleather, an alkaline protease, sucrose has been polymerized with 6 and 1' ester linkages. The result is a highly water-soluble product with sucrose an integral part of the polymer backbone. The polyester is degraded by the proleather in aqueous solution, thereby suggesting that the polymer is biodegradable. The second polymer synthesis is the free-radical polymerization of phenols using horseradish peroxidase in dioxane-water mixtures. Molecular weights in excess of 25,000 have been produced. The scope of polymerization can be predicted based on enzyme kinetics in organic media and using a Monte Carlo simulation. Astonishingly accurate simulations have been run that suggest that the high degree of control afforded by enzymatic catalysis over conventional chemical catalysts can be usedpredictively in polymer synthesis. This is of great importance in process control of polymer syntheses.
Transient Potentials Transmitted by an Artificial Electrochemical Synapse
Authors: Triffet T. , Calvert P. , Huntoon T. W.
Published: March 2011

Experiments have been made with a simple device consisting of two asymmetrically insulated electrodes separated by a thin electrolytic layer. This device has been found to exhibit a wide variety of transient potentials similar to those transmitted by biological synapses, thus suggesting the possibility of constructing a network of similar devices which simulates the behaviour of a biological neural network.
The Avian Eggshell as a Model of Biomineralization
Authors: Arias Jose L. , Fernandez Maria S. , Laraia Vincent J. , Janicki Jaroslaw , Heuer Arthur H. , Caplan Arnold I.
Published: March 2011

The avian eggshell is one of the most rapidly mineralizing biological systems known. By understandi'ng the key components and steps in this process, we hope to provide relevant information for fabrication of ceramic composites. The calcification of the eggshell occurs in three main steps: 1) fabrication of an organic matrix, 2) nucleation of an inorganic phase on the organic matrix, and 3) space-filling growth of the calcite phase. The different layers of an eggshell can be separately isolated and studied. Three approaches have been used in our study of the eggshell: 1) characterization of the organization and chemical composition of the shell, 2) selective removal or blocking of particular components to improve the remineralization of demineralized shells, and 3) addition of new components to produce composite ceramics of different kinds. In this preliminary communication, the organization of the shell matrix and membranes and their association with the crystal phase, the immunohistochemical occurrence and distribution of types I and X collagen, and of different proteoglycans are reviewed. Also the preliminary findings of the remineralization of the intact or modified eggshell are presented. These experiments allow us to identify the essential steps in forming a natural composite ceramic.
Growth of TiO2 Particles within a Polymeric Matrix
Authors: Burdon J. W. , Calvert Paul
Published: March 2011

As a simple model for biomineralization we are investigating the deposition of oxide particles into polymers by the in situ hydrolysis of oxides. By light scattering and electron microscopy we have observed the development of titania in polyvinylchloride. Hydrolysis is due to exposure to atmospheric moisture after film formation under very dry conditions. We believe of alkoxide initially phase separate and then are hydrolysed. Using a strongly Aolymer as a matrix for silica formation we present evidence for catalysis of particle -tby the matrix.
Mechanics of Natural Composites
Authors: Saliba Joseph E. , Schiavone Rebecca C. , Gunderson Stephen L. , Taylor Denise G.
Published: March 2011

This study was initiated to investigate the structural response of the bessbeetle to determine potential advantageous ramifications and effects on the optimization of synthetic composite materials. The result of the micromechanics sensitivity study of various parameters are presented. Variables such as fiber size and shape, fiber volume fraction, ratio of modulus of elasticity of fiber over matrix, are changed one variable at a time, and the response quantities such as stress and tranverse modulus are presented.
The Use of Carbohydrate Protein Conjugates of Proteases [CPC(Proteases)] for the Catalytic Formation of Peptide Bonds
Authors: Wang Peng , Hill Tara G. , Bednarski Mark D. , Callstrom Matthew R.
Published: March 2011

The discovery of catalysts that can selectively couple unprotected peptide fragments would revolutionize protein chemistry by allowing convergent polypeptide synthesis. Proteolytic enzymes have the capability to perform this chemistry because the protein can specifically recognize and bind to C-terminal and N-terminal peptide sequences, activate the C-terminal peptide sequence by forming an acyl-enzyme intermediate, and couple the two peptide fragments together. However, barriers that limit the use of proteases as catalysts for convergent peptide synthesis include (i) the stability of proteolytic enzymes in organic solvent systems; (ii) a simple and effective C-erminal and N-terminal protecting group strategy; and (iii) the isolation of the polypeptide product from the reaction mixture. In the previous paper we reported the stabilization of enzymes by the covalent attachment of proteins through their ο-lysine residues to a series of carbohydrate-based macromolecules. In this paper we report the use of carbohydrate protein conjugates of proteases [CPC(proteases)] as catalysts for peptide bond synthesis and a general strategy for convergent oligopeptide synthesis.
Decolorization of Chitosan
Authors: Allan G. Graham , Muvundamina Mutombo
Published: March 2011

The industrial process for extracting chitosan from low cost shellfish waste is well known. It comprises three basic steps: deproteinization, demineralization of the shells to yield chitin, followed by deacetylation of chitin to produce chitosan. However, the product obtained from the process often still contains many impurities. In general, these encompass minerals and carotenoids bonded to chitosan. The treatment of chitosan flakes with aqueous solutions of inorganic polybasic acids permits the removal of the impurities mentioned above. This paper describes an engineering-type procedure which develops a pure, colorless material having a controlled molecular weight.
Enzymatic Synthesis of Materials — An Overview
Authors: Alper Mark
Published: March 2011

One of the more impressive features of the living organism is the degree of control it is able to exercise over its chemistry.

A set of molecules in a given environment will react predictably according to the laws of chemistry. Quite often, as the synthetic organic chemist is ruefully aware, these laws allow more than one reaction to take place, and a multitude of products to be synthesized. The set of molecules that makes up the living organism is also governed by the laws of chemistry. The organism is able to, however, limit reactivity to a single product. In many cases this is a necessity; multiple reactions can often lead to unacceptable inefficiency or death.

Those involved in the synthesis of new, nonbiological materials with enhanced properties could benefit from this level of control. In the simple case, production of only the single desired product in high yields would be a great economic boon. On another level, this control could lead to the production of materials that are otherwise inaccessible. An obvious example is the modification of a polymer. Only with precise reaction control can all the monomers be modified in the same way.

Organisms achieve their required degree of control of chemical reactions through a mechanism of positive regulation. Under the conditions found in an organism, virtually no reaction will take place at a rate that is sufficient to sustain the life processes. Those that do occur take place only in the presence of a catalyst. To allow a reaction to occur, the organism simply synthesizes the catalyst that is specific for that reaction and does so only at the appropriate time and place and to the required extent. Should that reaction no longer be needed, the catalyst is destroyed or inactivated.
Recent Studies on the Application of Enzymes in the Synthesis of Polyesters
Authors: Morrow Cary J. , Brazwell Eugenia M. , Filos Dianela , Mercure Juanita , Romero Rosemary , Wallace J. Shield
Published: March 2011

Enzyme-catalyzed preparation of polymers offers several potentially valuable advantages over the usual polymerization procedures. This paper summarizes our successful use of lipase-catalyzed polycondensations to prepare both a series of achiral [AA-BB]xpolyesters from bis(2,2,2- trichloroethyl) alkanedioates and diols and of an optically active, epoxy-substituted polyester having a stereochemical purity estimated to be greater than 96%, from racemic bis(2,2,2-trichloroethyl)trans-3,4-epoxyhexanedioate and 1,4-butanediol. All of the reactions were carried out at ambient temperature in anhydrous, low to intermediate polarity, organic solvents such as ether, THF, 2-ethoxyethyl ether, dibenzyl ether,o-dichlorobenzene, or methylene choride, using porcine pancreatic lipase (PPL) as the catalyst. The molecular weight achieved by the polycondensation is limited by accumulation of the trihaloethanol that forms as the reaction progresses, probably because it frees enzyme-bound water permitting hydrolysis of the polymer to occur. This problem has been alleviated by using a high boiling solvent and removing the alcohol by placing the re'action mixture under vacuum.
Engineering Enzymes for Enhanced Thermostability
Authors: Shih Phoebe , Malcolm Bruce A. , Kirsch Jack F.
Published: March 2011

Chicken egg-white lysozyme (CEWL) is used as a model to attempt to engineer proteins for enhanced thermostability. Site-directed mutagenesis is employed for selective amino acid substitution to probe the contribution of an individual amino acid in a given sequence to thermostability. A linear correlation is found between the side-chain volume of a triplet of amino acid residues located at the interior core of the protein and its thermostability. Additional mutant constructs at the core position reveal that hyperpacking can disrupt other intramolecular contacts and offset the hydrophobic stabilization due to denser packing. Multiple substitutions at different loci of the protein are combined to analyze the additivity of thermostability mutations.
Comments on the Role of Molecular Genetics in Polymer Materials Science
Authors: Fournier Maurille J. , Mason Thomas L. , Tirrell David A.
Published: March 2011

The most fundamental goal of the synthetic chemist is control of molecular architecture. With respect to small molecules (i.e., those of molecular weight less than a few thousand), this means absolute control of chemical connectivity and stereochemistry – complete specification of molecular structure. But in macromolecular chemistry, controlled architecture has meant something quite different. Because polymerizations are in general statistical processes, conventional polymeric materials are characterized by substantial heterogeneity in chain length, sequence and stereochemistry [1]. Control is exercised in a statistical sense only, and considerable skill is required to control even the average properties of the chain population and the dispersity in those properties.
Poly(L-Lysine) Adsorption to Fluoropolymer Films
Authors: Shoichet Molly S. , McCarthy Thomas J.
Published: March 2011

The adsorption of poly(l-lysine) (PLL) from aqueous solution to poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) is investigated. Adsorption is controlled by choice of solvent (and PLL solution conformation) or by FEP surface chemistry. PLL adsorbs from pH 11 buffer solution to FEP: PLL adsorption is concomitant with the liberation of water molecules from the FEP-water interface resulting in a decreased interfacial free energy between organic and aqueous phases. PLL does not adsorb from an aqueous pH 7 solution to FEP unless the FEP surface is carboxylic acid-functionalized (FEPCO2H):an ionic interaction between FEP-carboxylate and PLL-ammonium enhances adsorption.

The surface modifications are charaterized by attenuated total reflectance infrared spectroscopy (ATR IR), ultraviolet-visible spectrophotometry (UV-vis), contact angle, and quantitatively by x-ray photoelectron spectroscopy (XPS). The adsorbed amount of PLL to FEP (from pH 11) is proportional to molecular weight whereas the adsorbed amount of PLL to FEP-CO2H (pH 7) is independent of molecular weight and likely proportional to surface charge density. The modified film samples (relative to the unmodified film samples) show improved characteristics in terms of wettability, chemical reactivity, adhesion, cell growth.
The Role of Gas Phase Decomposition in the ALE Growth of III–V Compounds
Authors: Reid K. G. , Urdianyk H. M. , El-Masry N. A. , Bedair S. M.
Published: March 2011

The effects of the growth temperature and exposure time to TMGa for ALE of gallium arsenide was studied using TMGa and AsH3 in a modified, vertical, atmospheric, MOCVD reactor with a rotating susceptor. It was found that the temperature range for ALE growth could -be extended from 450°C to 700°C by adjustment of the exposure time to TMGa. The maximum exposure time to TMGa was found to decrease as growth temperature increased with high temperature growth limited to exposures of only fractions of a second. Beyond a critical exposure time to TMGa, gallium droplets form on the surface. It is known that premature decomposition of TMGa in the heated gaseous boundary layer causes the formation of the gallium droplets and the consequent loss of ALE growth.
Study of As and P Incorporation Behavior in GaAsP by Gas-Source Molecular-Beam Epitaxy
Authors: Liang B. W. , Hou H. Q. , Tu C. W.
Published: March 2011

A simple kinetic model has been developed to explain the agreement between in situ and ex situ determination of phosphorus composition in GaAs1−xPx (x < 0.4) epilayers grown on GaAs (001) by gas-source molecular-beam epitaxy (GSMBE). The in situ determination is by monitoring the intensity oscillations of reflection high-energy-electron diffraction during group-V-limited growth, and the ex situ determination is by x-ray rocking curve measurement of GaAs1−xPx/GaAs strained-layer superlattices grown under group-III-limited growth condition.
The Surface Chemistry of GaAs Atomic Layer Epitaxy
Authors: Creighton J. Randall , Banse Barbara A.
Published: March 2011

In this paper we review three proposed mechanisms for GaAs ALE and review or present data in support or contradiction of these mechanisms. Surface chemistry results clearly demonstrate that TMGa irreversibly chemisorbs on the Ga-rich GaAs(100) surface. The reactive sticking coefficient (RSC) of TMGa on the adsorbate-free Ga-rich GaAs(100) surface was measured to be ∼0.5, conclusively demonstrating that the “selective adsorption” mechanism of ALE is not valid. We describe kinetic evidence for methyl radical desorption in support of the “adsorbate inhibition” mechanism. The methyl radical desorption rates determined by temperature programmed desorption (TPD) demonstrate that desorption is at least a factor of ∼10 faster from the As-rich c(2 × 8)/(2 × 4) surface than from the Garich surface. It is this disparity in CHs desorption rates between the As-rich and Ga-rich surfaces that is largely responsible for GaAs ALE behavior. A gallium alkyl radical (e.g. MMGa) is also observed during TPD and molecular beam experiments, in partial support of the “flux balance” mechanism. Stoichiometry issues of ALE are also discussed. We have discovered that arsine exposures typical of atmospheric pressure and reduced pressure ALE lead to As coverages ≥ 1 ML, which provides the likely solution to the stoichiometry question regarding the arsine cycle.
Growth of (GaAs)1−x (Si2)x Metastable Alloys using Migration-Enhanced Epitaxy
Authors: Rao T. Sudersena , Horikoshi Y.
Published: March 2011

Epitaxial (GaAs)1−x (Si2)x metastable alloys have been grown on GaAs (100) substrates using Migration-Enhanced Epitaxy in the composition range of 0<x<0.25. The lattice constant a0 of the alloys was found to decrease with increasing Si content from 0.56543nm at x=0 to 0.5601nm at x=0.25. Double-crystal x-ray diffraction rocking curve measurements and cross-sectional transmission electron microscopy studies made on a 10 period (GaAs)1−x(Si2)x/GaAs strained layer superlattice indicated sharp and abrupt interfaces. High crystalline quality GaAs has been grown on Si substrates using (GaAs)0.80(Si2)0.20/GaAs strained layer superlattices as buffer layers.
High-Conductance GaAs Tunnel Diodes by OMVPE
Authors: Venkatasubramanian R. , Timmons M. L. , Colpitts T. S.
Published: March 2011

GaAs p+-n+ tunnel diodes have been grown by atmospheric-pressure organometallic vapor phase epitaxy (OMVPE) using zinc as the dopant for the p+ regions and either Se or Si as the dopant for the n+ regions. At a growth temperature of 700° C, using a “cycled” growth for just the Zn-doped p++-GaAs layer both the conductance and the peak current of the tunnel diode has been increased by a factor of ˜65. The conductance of the tunnel diode, maximized at a growth temperature of 650 °C with the cycled growth, is comparable to the best reported values by MBE. Cycled growths for n+ Se-doped regions reduce the tunnel-diode conductance by more than two orders of magnitude. However, the cycled growth for n+-GaAs regions formed with Si doping shows no conductance degradation. A model for these observations is presented.
UV Photostimulated Si Atomic-Layer Epitaxy
Authors: Lubben D. , Tsu R. , Bramblett T. R. , Greene J. E.
Published: March 2011

Single-crystal Si films have been grown on Si(001)2×1 substrates by UVphotostimulated atomic-layer epitaxy (ALE) from Si2H6. The ALE deposition rate R per growth cycle remains constant at 0.4 monolayers (ML) over a wide range of deposition parameters: growth temperature (Ts= 180–400 °C), Si2H6 exposure (peak pressure during gas pulse = 0.1−5 mTorr), laser energy density ( = 250–450 mJ cm−2 where is determined by Ts), and number of UV laser pulses per cycle. A film growth mocrel, based upon the results of the present deposition experiments and Monte Carlo simulations, together with our previous adsorption/desorption measurements, Is used to describe the reaction pathway for the process. The Hterminated silylene-saturated surface formed by adsorption and desorption of disilene is thermally stable and passive to further Si2H6 exposure. ArF or KrF laser pulses (≅20 ns) are used to desorb H, following a Si2H6 exposure, and the growth cycle is repeated until the desired film thickness is obtained. At Ts < 180 °C, the growth process becomes rate limited by the surface dissociation step and R decreases exponentially as a function of 1/Ts with an activation energy of ≅0.5 eV. At Ts > 400 °C, H is thermally desorbed and pyrolytic growth competes with ALE. Transmission electron micrographs together with selected-area electron diffraction patterns show that the ALE films are epitaxial layers with no observed extended defects or strain.
Digital Process for advanced VLSI's and Surface Reaction Study
Authors: Sakaue H. , Asami K. , Ichihara T. , Ishizuka S. , Kawamura K. , Horiike Y.
Published: March 2011

Digital etching was carried out by repeating the fundamental reaction cycles of adsorption, reaction and desorption for fluorine(F) or chlorine(Cl)/Si systems. In the F/Si case, atomic layer etching of Si(100) was achieved by adsorption of F atoms produced by a remote discharge of F2/99.8%He on the cooled Si surface and subsequent Ar* ion (≅20eV) irradiation. The digital method revealed that the cryogenic etching occurred by ion bombardment on physiosorbed F atoms on the cooled Si surface. Adsorption of Cl atoms on Si at room temperature allowed self-limiting reaction with etch rate of 0.4 Å/cycle. The etching increased rapidly over 40 V of substrate voltage. Secondly, reaction of TES (triethylsilane) with hydrogen(H) atoms was also found to lead to conformal CVD (Chemical Vapor Deposition) of Si film involving organic species. Then Si oxide and nitride films were formed by digital CVD which repeated a cycle of first deposition of this film and subsequent its oxidation and nitridation. The electrically excellent multilayer stacked oxide and nitride film was filled in to deep trench. Insitu FTIR-ATR spectroscopy demonstrated that the surface reaction was predominant for the TES/H process.
Decomposition of Alkylsilanes on Silicon Surfaces Using Transmission Ftir Spectroscopy
Authors: Dillon A. C. , Robinson M. B. , Han M. Y. , George S. M.
Published: March 2011

Fourier transform infrared (FTIR) transmission spectroscopy was used to monitor the decomposition of alkylsilanes such as diethylsilane (DES) [(CH3 CH2)2SiH2], di-t-butylsilane (DTBS) [((CH3)3C)2SiH2] and ethylsilane (ES) [CH3CH2SiH3 on high-surface-area porous silicon samples. The FTIR spectra revealed that tKe akylsilanes dissociatively adsorb on porous silicon at 300 K to form SiH and Si-alkyl species. As the silicon surface was progressively annealed, the Si-alkyl species decomposed and produced gas phase ethylene (DES,ES) or isobutylene (DTBS). The decomposition of the alkyl group was accompanied by the growth of additional SiH surface species. These reaction products were consistent with a [β-hydride elimination reaction. Above 700 K, the SiH surface species decreased concurrently with the desorption of H2 from the porous silicon surface. The uptake of surface species was also monitored at various adsorption temperatures to determine the optimal exposure temperatures for carbon-free silicon deposition. Carbon contamination was not detected at adsorption temperatures below 640 K prior to H2 desorption. Because the alkylsilane adsorption process is self-limiting at temperatures below 640 K, alkylsilanes may be useful molecular precursors for the atomic layer epitaxy (ALE) of silicon.
The Etching of Silicon by Oxygen Observed by in situ Tem
Authors: Ross Frances M. , Gibson J. Murray
Published: March 2011

We describe observations made in situ in a modified UHV transmission electron microscope of the process of etching of the Si (111) surface by oxygen. Etching occurs by the motion of individual bilayer steps across the surface and by analysing the step motion we discuss the etching mechanism in the context of macroscopic parameters.
P-Type Conversion of Nitrogen Doped ZnSe Films Grown By Mocvd
Authors: Khan Babar A. , Taskar Nikhil , Dorman Donald , Shahzad Khalid
Published: March 2011

We have obtained p-type zinc selenide films by nitrogen doping combined with a post growth anneal. These films were grown on <100> gallium arsenide substrates using a low-pressure MOCVD process. Ammonia gas was used as the source for nitrogen. The as-grown films were annealed and then studied by photoluminescence (PL) and capacitance-voltage (CV) techniques. The PL data is dominated by the acceptor-bound exciton peak and donor-acceptor pair spectrum associated with the nitrogen acceptor. The C-V data shows that the films are p-type, with the highest measured net acceptor concentration of 3×1016/cm3.
Analysis and Calibration of the Flow Characteristics of A Pressure Controlled Vapor Source For Gas Source Doping: CdTe:l
Authors: Rajavel D. , Wagner B. K. , Maruyama K. , Benz R. G. , Conte A. , Summers C. J.
Published: March 2011

A pressure controlled vapor source was developed for the gas source doping of (Hg,Cd)Te alloys. The dopant source has been subjected to extensive tests, and the flow characteristics determined. The dopant source was used to control the flow rates of ethyliodide for the n-type doping of CdTe. Highly conductive CdTe:l films were grown by molecular beam epitaxy.
Formation of CdTe and GaAs by Electrochemical Atomic Layer Epitaxy (ECALE)
Authors: Suggs D. Wayne , Villegas Ignacio , Gregory Brian W. , Stickney John L.
Published: March 2011

The principles of Atomic Layer Epitaxy (ALE) have been applied to the formation of compound semiconductors by an electrochemical technique, referred to as Electrochemical Atomic Layer Epitaxy (ECALE). Atomic layers of the component elements are alternately electrodeposited at underpotential (UPD) from separate solutions and at separate potentials. Results are presented concerning the structures of both CdTe and GaAs deposits formed by ECALE. Studies were performed using singlecrystalline Au electrodes in a UHV surface analysis instrument coupled directly with an electrochemical cell. This instrument was used in order to prevent corruption by contact with air during transfer to the surface analysis environment.
Plasma Enhanced OMCVD Atomic Layered Growth of Y-BA-CU Oxide Films
Authors: Duray S. J. , Buchholz D. B. , Song S. N. , Richeson D. S. , Ketterson J. B. , Marks T. J. , Chang R. P. H.
Published: March 2011

We report the results of a pulsed organo-metallic beam epitaxy (POMBE) process for growing complex oxide films at low background gas pressure (10-4 -10-2 torr) and low substrate temperature (600 to 700 C) using organo-metallic precursors in an oxygen plasma environment. Our results show that POMBE can extend the capability of organo-metallic chemical vapor deposition to growing complex oxide films with high precision both in composition and structure without the need for post-deposition oxidation and heat treatments. The growth of phase-pure, highly oriented Y-Ba-Cu-O superconducting oxide films ([Tc (R=0)=90.5K] and Jc (77K, 50K gauss)=l.l×105 A/cm2) is given as an example. Similar to the pulsed laser deposition process, the POMBE method has the potential for in-situ processing of multilayer structures (e.g. junctions).
Growth of SrS Thin Films by Atomic Layer Epitaxy
Authors: Leskela M. , Niinistö L. , Nykänen E. , Soininen P. , Tiitta M.
Published: March 2011

The growth of strontium sulfide thin films in a flow-type Atomic Layer Epitaxy reactor from Sr(thd)2 (thd = 2,2,6,6-tetramethyl-3,5-heptanedione) and H2S has been studied. The growth is independent on flow rate and duration of the purge gas (N2) pulse and it does not depend on the Sr(thd)2 and H2S pulses either provided their amounts are sufficient to saturate the surface. The variables significantly affecting the growth rate are the substrate temperature and source temperature for Sr(thd)2. The observed lower than one monolayer growth rate is mainly due to the large size of the Sr(thd)2 molecule.
Rheed Intensity Oscillation During the Epitaxial Growth of Silver and Gold Films
Authors: Mae Kazuki , Kyuno Kentaro , Kaneko Takeo , Yamamoto Ryoichi
Published: March 2011

The intensity oscillation of reflection high-energy electron diffraction (RHEED) during the autoepitaxy of Au on Au(001) and Ag on Ag(001) and during the heteroepitaxy of Au on Ag(001) and Ag on Au(001) were measured at 310 and 330 K. The morphologies of the growing surfaces are discussed in terms of the surface energies and the surface reconstruction. RHEED intensity oscillation during Au deposition on Ag(001) at 330 K rapidly decayed at the 6th period when reconstruction of the Au(001) surface appeared. Such a rapid decay was not observed at 310 K. On the other hand, the reconstruction entirely disappeared at the first minimum of the RHEED intensity oscillation in the case of Ag deposition on Au.
In Situ Rheed and Hrem Study of Initial Stages of Interfacial Reactions of Uhv Deposited Titanium Thin Films on Silicon
Authors: Wang M. H. , Chen L. J.
Published: March 2011

The initial stages of interfacial reactions of ultrahigh vacuum (UHV) deposited Ti thin films on silicon have been studied by in-situ reflected high energy electron diffraction (RHEED) and transmission electron microscopy (TEM).

An amorphous interlayer was found to form during the deposition of the first 1.7-nm-thick Ti layer. In samples annealed at 450 °C for 30–120 min, Ti5Si3, located at the Ti/a-interlayer interface, was identified to be the first nucleated phase. Ti5Si3, Ti5Si4, TiSi and C49-TiSi2 were observed in samples annealed at 475 °C for 30 and 60 min as well as at 500 °C for 10 and 20 min. Fundamental issues in silicide formation are discussed in light of the discovery of the formation of the amorphous interlayer and as many as four
different silicide phases in the initial stages of interfacial reactions of UHV deposited Ti thin films on silicon.
Morphology of Vapor Evaporated Mo Thin Films
Authors: Cheng Y. , Stearns M. B.
Published: March 2011

Studies were made of the dependence of the morphology of Mo films, prepared by ebeam evaporation in an UHV system, on the substrate temperature and deposition angle. The main characterization techniques used were large angle x-ray scattering and cross-sectional high resolution electron microscopy.
Hreels Study of the Adsorption of Organometallics on GaAs(001) Surfaces
Authors: Närmann A. , Purtell R. J. , Yu M. L.
Published: March 2011

Trimethylgallium (TMGa), Triethylgallium (TEGa) and Diethylgalliumchloride (DEGaCl) are used in combination with arsine (AsH3) in atomic layer epitaxy of GaAs. We simulated this process in a UHV system by dosing a c(2×8) or (1×6) reconstructed GaAs(001) surface with arsine and organometallics at different temperatures. After the surface reconstruction was verfied by LEED, the sample was transferred in situ to the HREELS (high resolution electron energy loss spectroscopy) chamber. We present new studies on the adsorption and pyrolysis of organometallics on GaAs(001) surfaces.

As a result we find that TMGa adsorbs molecularly on an As-rich cooled surface but decomposes upon adsorption on a Ga-stabilized (1×6) surface. These two adsorption states are identified by the geometrical position of the Gamethyl compound on the surface (Ga-C bond parallel or normal to the surface). The removal of the adsorbed species occurs on an As-rich surface at temperatures higher than 450°C and on the Ga-stabilized surface at 350°C.

For TEGa and DEGaCl we found similar results.
A Study of Hydrogen Atom Adsorption on Gallium Arsenide (100) by Multiple Internal Reflection Infrared Spectroscopy
Authors: Gee Paul E. , Hicks Robert F.
Published: March 2011

We have studied the adsorption of hydrogen atoms on GaAs (100) by multiple internal reflection infrared spectroscopy. The crystal was etched in 1:1:10 H3PO4/H2O2-/H2O solution and in 1:1 HCI/H2O solution, then annealed to 580°C in the vacuum chamber. Hydrogen adsorption was carried out at -90 and 45°C. At both temperatures, a monolayer forms giving rise to infrared bands for arsenic hydride and gallium hydride at 2105 and 1860 cm−1, respectively. The arsenic hydride vibration is polarized parallel to the surface, whereas the gallium hydride vibration is polarized normal to the surface. By monitoring the changes in the intensity of the infrared absorption bands with time during exposure to H atoms and during heating, the kinetics of hydrogen adsorption and desorption can be measured. At -90°C, the H atom sticking probability follows the Langmuir model, S/So = (1-θH). Upon heating the crystal, the arsenic hydride rapidly decomposes near 120°C, while the gallium hydride slowly decomposes between 150 and 400°C.
Ideal Crystal Growth from Kink Sites and Fractional-Layer Growth on GaAs Vicinal Substrate by MOCVD
Authors: Fukui Takashi , Saito Hisao
Published: March 2011

(AIAs)1/2(GaAs)1/2 fractional-layer superlattices (FLSs) are grown on (001) vicinal substrates by metalorganic chemical vapor deposition. Various kinds of GaAs substrates are used. When the substrate is misoriented to [110] direction by 1.92° and [110] by 0.10°, uniform superlattice periods in a large surface area are observed with a bright field transmission electron microscope (TEM). The results suggest ideal crystal growth from kink sites during MOCVD growth, and the distances between the kink sites are equal.

On a substrate misoriented to [110] by 1.90°, the superlattice periods exhibit an undulation. This shows that kink flow mode growth is not dominant in the [110] direction. On a substrate misoriented to [010[ by 2.0°, no superlattice periods were observed. From the above results, we discuss the growth mechanisms.

Polarization dependent photolumlnescence and optical absorption spectra of FLS were also observed. Electron wave interference devices with lateral periodic potential were fabricated.
In-situ Measurement of GaAs Optical Constants and Surface Quality, as Functions of Temperature
Authors: Yao Huade , Snyder Paul G.
Published: March 2011

In-situ spectroscopic ellipsometry (SE) was applied to monitor GaAs (100) surface changes induced at elevated temperatures inside an ultrahigh vacuum (UHV) chamber (<1×10−9 torr base pressure, without As overpressure). The real time data showed clearly the evolution of the native-oxide desorption at ∼577°C, on a molecular-beam-epitaxy (MBE)-grown GaAs (100) surface. In addition, surface degradation was found before and after the oxide desorption. A clean and smooth surface was obtained from an arsenic-capped, MBE-grown GaAs sample, after the arsenic coating was evaporated at ∼350 °C inside the UHV. Pseudodielectric functions <ε>GaAs, from 1.6 eV to 4.5 eV, were obtained through the SE measurements, from this oxide-free surface, at temperatures ranging from room temperature (RT) to ∼610 °C. These <ε> data were used as reference data to develop an algorithm for determining surface temperatures from in-situ SE measurements, thus turning the SE instrument into a sensitive optical thermometer.
Studies of Oxide Desorption From GaAs by Diffuse Electron Scatfering and Optical Reflectivity
Authors: Buuren T. Van , Tiedje T. , Weilmeier M. K. , Colbow K. M. , Mackenzie J. A.
Published: March 2011

We have determined that the temperature for desorption of gallium oude from GaAs increases linearly with oxide thickness, for oxide layers between about 6Å and 26Å thick. Different thicknesses of oxide layers were created by varying the exposure time of the GaAs wafers to a low pressure oxygen plasma. In addition, we show by diffuse light scattering that highly polished GaAs substrates roughen during the oxide desorption. These results are interpreted in terms of a model in which the oxide evaporates inhomogeneously. The oxide desorption was also studied by monitoring the secondary electrons produced by the high energy electrons from the RHEED gun. After the gallium oxide desorption there is a reversible, order of magnitude, increase in the number of secondary electrons produced. We interpret this result as evidence for the formation of microscopic gallium droplets on the GaAs surface.
LPE Growth of Doped Sige Layers Using Multicomponent Phase Diagrams Calculations
Authors: Fleurial J.-P. , Borshchevsky A. , Irvine D.
Published: March 2011

Heavy doping of n-type Si-Ge alloys is necessary for improving their high temperature thermoelectric properties. Because of the limited solid solubility of the best dopant available, phosphorus, simultaneous additions of gallium were started several years ago. The substantially higher carrier concentration values obtained in such super-saturated, hot-pressed SiGe/GaP materials point to significant changes in dopant solid solubilities. To better understand the behavior of these alloys, investigation of homogeneous single crystalline materials were needed. As a near-thermodynamic equilibrium technique with processing temperatures well below the melting point of these materials, liquid-phase epitaxy (LPE) was particularly suited to the study of the mechanisms of multidoping. Based on successful crystal growth of Si1-xGex thin films using metals such as Ga, In, Sn and Bi for solvents, several experiments were designed to grow multi-doped SiGe layers with III-V dopant combinations. Knowledge of ternary and quaternary phase diagrams is essential to develop the LPE process. Ternary Si-Ge-M systems computations in good agreement with experimental determinations were used to calculate some of the necessary multicomponent phase diagrams and assess the strength of the various III–V interactions.
Electrical Characterization of Sige Thin Films
Authors: Mccormack J. A. , Fleurial J.-P.
Published: March 2011

An apparatus for measuring electrical resistivity and Hall coefficient on both thin films and bulk material over a temperature range of 300K to 1300K has been built. A unique alumina fixture, with four molybdenum probes, allows arbitrarily shaped samples, up to 2.5 cm diameter, to be measured using van der Pauw's method. The system is fully automated and is constructed with commercially available components. Measurements of the electrical properties of doped and undoped Si-Ge thin films, grown by liquid phase epitaxy reported here, are to illustrate the capabilities of the apparatus.
Electronic Structure of Ru2 Si3
Authors: Pecheur P. , Toussaint G.
Published: March 2011

The electronic structure of Ru2Si3 has been calculated with the empirical tight binding method and the recursion procedure. The calculation strongly indicates that there exists a gap in the structure, which makes Ru2Si3 semiconducting, as found experimentally and explains the stability of the chimney-ladder phases for a valence electron concentration per transition metal atom smaller than 14.
From Garbage to Perfection: A Structural - Chemical view of Thermoelectric Materials
Authors: Tuomi Donald
Published: March 2011

The development of growing markets for thermoelectric devices strongly depends upon improving the performance of the Peltier effect alloys. Breaking out of the specialty niches requires doubling present figures of merit, Z, of commercial alloys though each incremental gain potentially opens additional specialty niches.

The alloys are polycomponent, heavily doped, N and P type semiconductors. Optimization to the highest Z's requires controlling bulk phase interactions of phase diagram, compositional, crystal growth, and processing variables influencing the imperfection structures impacting on alloy quality. From the first, the system complexity reeds recognition so the performance optimizing variables become clearly identified. This is crucial to commercial production.

The (BiSb)2 (TeSe)3 provide both N and P type alloy model systems useful in understanding 1he general challenge of performance optimization. Illustrations of the imperfection structural chemical limitations on attainable performance by varied technologies are given.

In seeking other superior performance alloys the experimental designs for exploratory research need immediately to address the identification of the dominating imperfection variables in order to recognize quickly the potentials present.
Film Materials on the Base of Bi2Te3 and Microbattaries of Them
Authors: Anatychuk Lukyan I. , Pazinkov Valeri V.
Published: March 2011

As, both numerous investigations and practical applications testify, thermobatteries based on film material possess such principal advanteges as high technology and possibility of thermobattery with a great number of legs manufacture-They have also two main drawbacks: relatively small time stability and low efficiency due to shunting of substrate on which thermobattery is formed.
Thin Film Ruthenium Oxide - Iridium Oxide Thermocouples
Authors: Kreider Kenneth G.
Published: March 2011

Ruthenium oxide and iridium oxide have outstanding resistance to corrosion. These oxides are also excellent electrical conductors and have been used as biochemical charge injection electrodes. Their unique electrical and electrochemical properties have also led to their consideration as high temperature pH electrodes. Thin films are the most useful form for these applications as they permit the miniaturization of fast response sensors and electrodes.

This study was used to characterize the thermoelectric and electrical conductance parameters of ruthenium and iridium oxide sputtered thin films. The electric and thermoelectric properties of the thin films were found to be sensitive to the annealing temperature of the sputtered oxides. The properties of the film are related to the microstructure, stoichiometry and crystal structure as determined by x-ray diffraction. Heat treatments were used to stabilize the thermoelectric response and the thermal coefficient of resistivity.