bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Effects During Microwave Plasma Sintering of Ceramics
Authors: Hsu Matthew , Sweeney Mwry P. , Johnson D. Lynn
Published: March 2011

A variety of ceramic materials have been heated in various microwave excited plasmas at reduced pressures. Temperatures were measured by optical fiber thermometry. Specimen heating was accomplished by direct contact with the plasma, as well as direct coupling withthe microwave energy, although the latter was screened heavily by the plasma. Higher specimen temperatures were achieved in polyatomic gases which have greater reactional enthalpy. In general, insulating materials achieved higher temperatures than semiconducting or covalently bonded materials.
Model-Informed Microwave Processing of Materials
Authors: Voss W.A. Geoffrey , Kua H.K.
Published: March 2011

This paper reviews the expanding application of microwaves for processing solid materials, both natural and synthetic. The Canadian interest ranges from food processing to forest products, ceramic drying and curing to the preprocessing of rare minerals and ores, with the zeolite family of particular industrial interest.

In all cases, across the world, the number of process variables is large and the known physical data are limited. Yet the engineer requires to know only a few specific properties which, in general, involve rate and limit functions. The problem posed here, which has to be considered as a part of the unification of the subject of electromagnetic heating, concerns the careful use of atomistic modelling to achieve a model-informed empiricism for process development. As an example, it is shown in this paper that the majority of solids have the same piecewise linear approximate temperature model for absorbing and reflecting power: more than twenty variables affecting the dielectric properties can then be reduced to five or six which need to be measured. Correctly interpreted, this approach (due, in its broad philosophic format, to M.F. Ashby, 1987) may help solve many electromagnetic engineering problems, including those associated with breakdown and thermal-runaway.
A Novel Microwave Device Designed to Preserve Cell Structure in Milliseconds
Authors: Login Gary R. , Kissell Susan , Dwyer Barbara K. , Dvorak Ann M.
Published: March 2011

We describe an innovative microwave instrument, designed in collaboration with and owned by Raytheon Company. The instrument permits the manipulation of biological specimens in their fluid milieu during the actual period of rapid tissue fixation. The specimen chamber is designed for sample containers up to 1.7 cm in diameter and 4.5 cm in height. Reflected power is reproducibly low, limiting the need for pretuning the microwave output to the sample. Microwave exposure can be controlled in 1 msecond increments with a range of 10 mseconds to 10 seconds. Mammalian cells and tissues fixed by this microwave device were evaluated by light and electron microscopy. Preliminary findings show large regions of excellent preservation in tissues and in cell suspensions in -100 mseconds.
Present and Future Uses of Microwave Power
Authors: Richard DR. , Smith D.
Published: March 2011

The purpose of this paper is to broadly assess the industrial applications of microwave power and to perhaps formulate some of the ingredients for a successful application. Traditional applications are reviewed and the ingredients for their success are noted. Also discussed will be a few applications that were not successful. Future uses of microwave power are hypothesized based upon research and development efforts in progress throughout industry.
The Development of New Microwave Heating Applications at Ontario Hydro'S Research Division
Authors: Oda Steven J. , Balbaa Ibrahim S. , Barber Bruce T.
Published: March 2011

This paper reviews the results from two relatively new microwave heating studies under development at Ontario Hydro's Research Division. The first study involves the development of a hybrid kiln to process advanced ceramics at high temperatures. Using a combination of resistive heating elements and microwave heating, this new device has been operated to show significant process advantages in terms of time and energy savings. A description of the hybrid kiln is presented together with the test results for calcining and sintering a variety of ceramic materials.

The second investigation involves the use of microwave heating for the treatment of hazardous wastes. The selective heating ability of microwaves has been applied to reduce the environmental impact of wastes generated from industrial processes. An example is provided to illustrate the advantages and difficulties of applying this technology.
Microwave Processing of Polymers and Polymeric Composites
Authors: Charles DR. , Lee Y-C
Published: March 2011

Microwave energy is commonly considered as a fast and efficient source of energy for heating materials. This perception can be easily verified by the proliferation of microwave ovens in household kitchens and the emerging usage of the technology in the food industry. From the standpoint of material science, coupling of microwave energy into materials during processing can be more than just shortening the heat-up time in conventional thermal treatment; this energy source can provide an additional degree of control over the properties developed during processing.
Enhanced Chemical Bonding at the Fiber-Matrix Interphase in Microwave Processed Composites
Authors: Drzal L. T. , Hook K. J. , Agrawal R. K.
Published: March 2011

The effect of microwave processing on the chemical interactions occurring between the carbon fiber surface and the epoxy matrix constituents was investigated using X-ray Photoelectron Spectroscopy (XPS). Monofunctional model compounds of the matrix constituents were exposed to the carbon fibers at temperatures similar to those encountered during composite processing. The microwave treatment resulted in a substantial increase in the amount of chemical interaction between the fiber surface and the epoxy resin but little difference for the amine component of the matrix when compared to thermal processing. An epoxy resin/amine hardener adduct compound used to determine the hydroxyl group interaction with the carbon fiber surface indicated a low level of chemical interaction of the hydroxyl with the carbon fiber surface under the conditions used in this study.
The Consolidation and Processing of Graphite Fiber/Polymer Composites by Controlled Mode Microwaves
Authors: Treacy D.J. , Evans D.A. , Boyce J.S. , Mccoy J.F. , Treadway B.W.
Published: March 2011

Composite laminates have been cured under pressure in a tunable microwave cavity. A 7-in. diam cavity with a sliding short was tuned to produce single mode or controlled hybrid mode standing waves at 2.45 GHz. Graphite/epoxy laminates were processed with power inputs as low as 2 W/g.

A low loss press was designed and built to operate inside the cavity. The press can apply 100 psi pressure on a 9-in. square laminate. An empirical approach has been used to develop processing conditions for high quality laminates. Graphite/epoxy composites were cured in 90 min or less. A simple on-off temperature control loop modulated power input to the cavity with a coaxial switch.

Mechanical testing and differential scanning calorimetry have been used to evaluate the composites. The material properties have been related to processing conditions.
Microwave Heating for Manufacturing Carbon-Fiber Thermoplastics
Authors: Lind A.C. , Medgyesi-Mitschang L.N. , Kurz J.E. , Mckinney H.F. , Wear F.C.
Published: March 2011

Traditionally, polymeric composite parts are heated and consolidated in an autoclave. For large parts, such as transport aircraft fuselages or submarine hulls, size becomes a limiting factor. To overcome this limitation and to reduce labor costs we are developing an automated tape placement process. In this process we build composite parts one layer at a time with tape containing carbon fibers impregnated with a thermoplastic. As the tape comes into contact with the part, we apply heat to melt the thermoplastic and apply pressure to consolidate the tape to the part. To support this effort we have developed a proprietary microwave applicator that is suitable for rapidly heating carbon-fiber composites in an automated tape placement process. Small carbon-fiber/poly(aryl-ether-ether-ketone) parts made using the microwave applicator have interlaminar shear strengths of 100 MPa (14.5 ksi), which is almost equal to the 103 MPa (15.0 ksi) obtained using an autoclave.
Hydrolysis of Adenosine Triphosphate by Conventional or Microwave Heating
Authors: Jahngen Edwin G. E. , Lentz Ronald R. , Pesheck Peter S. , Sackett Patricia Holt
Published: March 2011

The hydrolysis rate of adenosine-5'-triphosphate (ATP) has been reported to be 25 times greater during microwave heating than during conventional heating at comparable temperatures (100 to 105 °C). This remarkable rate increase was both attributed to and cited as evidence for a nonthermal microwave effect. Attempts to replicate those findings under carefully controlled microwave exposure conditions and with special attention being paid to accurate temperature measurements lead to the conclusion that the hydrolysis rate is related solely to temperature.
On-Line Transverse Control of Materials by Means of Microwave Imaging Techniques
Authors: Bolomey J.Ch. , Cottard G. , Cown B.J.
Published: March 2011

This paper analyzes of the impact of a new generation of microwave sensors on the transverse control of conveyed products and materials. Such sensors, resulting from recent developments in microwave imaging technology, offer significant improvements in comparison to other more classical microwave sensors. The main features of the new sensors are presented and discussed.
Measurements of the Dielectric Properties of Irradiated Low-Loss by Microwave Reflectometry and Micro-Calorimetry
Authors: Buckley S.N. , Agnew P.
Published: March 2011

An rf reflectometer has been used to measure dielectric losses in alumina ceramics during irradiation by 3 MeV protons. The equipment was able to detect tan ȯ changes of 5×10−5, but calibration by micro-calorimetry revealed large systematic losses, up to 2.5×10−3 Irradiation at 300 K resulted in a progressive increase in dielectric loss but no prompt increments.
Thermal Conduction Measurements of Materials using Microwave Energy
Authors: Giedd R. E. , Giedd G. R.
Published: March 2011

We have developed a new technique to measure the thermal conductivity of materials using microwave energy. A thermal wave is induced in a material of unknown thermal conductivity using a pulse of microwave energy. This energy is incident on one side of the material. The corresponding temperature rise of the opposite side of the material is measured. The thermal diffusivity of the material can then be determined in the same way as ‘laser flash’[1]. Some of the advantages of the microwave system are the relatively low cost of the magnetron compared to the high energy laser, easily variable pulse length, and accurate measurement of the reflected energy.

The microwave system consists of a 2.45 GHz magnetron that is pulse modulated to energies as high as 10 J. A typical pulse lasts for 1 ms with rise and fall times of 10µs. This is achieved by a high voltage source (5 – 8 kV at 1 – 2 A), switched by a high power, rf transmitting tube connected in the filament circuit of the magnetron.
Applications of Microwave Treatment of Hazardous Wastes: a) Non-Volatile Organics; b) Heavy Metals
Authors: Dauerman Leonard , Windgasse Gabriele , Gu Huiping , Ibrahim Nagui , Sedhom El-Hamy
Published: March 2011

This laboratory is characterizing the mechanisms underlying the potential applications of microwave treatment to the remediation of hazardous waste streams under an Environmental Protection Agency Basic Research grant. Applications that have been investigated encompass the following processes(1-14): volatilization of organics from substrates; ‘chemical fixation’ of non-volatile organics in substrates; ‘chemical fixation’ of heavy metals in substrates; kinetics of decomposition of organics in the gas phase using fixed and ‘lossy’ beds. To-date the work has been carried out on a bench-scale level. Pilot plant studies are now beginning. This paper will focus on studies carried out on non-volatile organics and heavy metals, specifically, chromium.
A Unique Application of a Microwave Induced Plasma for Material Synthesis
Authors: Salsman Johanina B. , Holderfield S. P.
Published: March 2011

Research conducted at the Bureau of Mines, Tuscaloosa Research Center has resulted in a process of forming tungsten carbide (WC) in a microwave induced plasma (MIP). This process allows for the formation of 99.96 pet WC with a 0.04 pet free carbon content and grain sizes on the order of 0.05 µm in approximately 10 minutes. Commercial methods of producing WC require that a mixture of metallic tungsten and elemental carbon be heated to temperatures of 1,500°C for up to 7 hours. Therefore, the new Bureau developed method is significantly less energy intensive, requiring only 13 pct of the energy used in conventional WC processing methods, and is less expensive although initial capital outlay may be high.

The Bureau process involves using a 915 MHz, 30 kW variable power microwave generator to sustain a carbon monoxide plasma. The reaction chamber is constructed of a WR 975 rectangular waveguide that is short circuited at the end. The reaction takes place inside the waveguide at an electric field maximum. After the reaction chamber is readied, the microwave generator is turned on which ignites the plasma within seconds. In approximately 10 minutes, the reaction is complete resulting in a commercially acceptable product.
On the Development of Biomimetic Sensors: Immobilizaton of Lipid Bilayers in Layered Ceramics
Authors: Russell Michael W. , Mehrotra Vivek , Giannelis Emmanuel P.
Published: March 2011

Artificial membranes possessing physicochemical properties similar to biological membranes have been synthesized by immobilization of synthetic amphiphiles in layered ceramics. The intercalated bilayer-forming amphiphiles exhibit a gallery height of about 39 Å. Retention of bilayer-forming characteristics is further confirmed by the presence of a crystal to liquid-crystal phase transition. A dramatic increase in the membrane capacitance at the tansition temperature is attributed to an increase in membrane fluidity.
Streptavidin-Phycoerythrin Conjugated Proteins Bound to Biotin on Langmuir-Blodgett Films of Biotinylated Lipid Monolayers
Authors: Samuelson Lynne A. , Kaplan D. L. , Marx K. A. , Miller P. , Galotti D. M. , Kumar J. , Tripathy S. K.
Published: March 2011

Studies involving the specific and non-specific surface recognition of biotin on biotinylated LB lipid monolayers by streptavidin and avidin conjugated phycoerythrin are presented. Both streptavidin and avidin conjugates were injected under the monolayer and found to preferentially adsorb to the biotinylated monolayers at the air-water interface. Pressure-area isotherms displayed a biotin-streptavidin/avidin complex dependent increase in surface pressure at expanded areas indicating protein adsorption. The binding of protein was confirmed by transferring the monolayer films to solid supports and measuring the characteristic intense phycoerythrin fluorescence at 576 nm. The effect of protein charge, monolayer packing density and structure, and activation of the tetramer proteins towards specific and non-specific binding are discussed. These results suggest a novel and general methodology for the two-dimensional ordering of protein monolayers with potential bioelectronic, optical and protein structure research applications.
Mineral Induction by Matrix from Mineralized Biological Tissues
Authors: Crenshaw Miles A.
Published: March 2011

The polymeric matrix of mineralized tissues controls the form and structure of the mineral that is deposited. This matrix has an insoluble fraction which provides a structural framework for the mineralized tissue, and a soluble fraction which is rich in polyanionic
macromolecules. One hypothesis envisages mineral being nucleated by an atomic dimensional matching between crystal lattice and anionic spacing in the polyanionic macromolecules. An alternate hypothesis considers that fixed polyanions provide a surface for an adsorbed layer, enriched in lattice ions by ionotropy, to induce mineral formation from the metastable body fluids.

We found that soluble matrix polyanions, immobilized by attachment to insoluble substrates, would induce mineral from metastable solutions. The insoluble substrates included natural and synthetic hydrogels not derived from mineralized tissues. Whether the polyanions were prepared from apatitic or CaCO3 tissues, the mineral induced was independent of the source and was determined by the composition of the solution. Other immobilized, calcium-binding, polyanionic macromolecules, obtained from non-mineralizing tissues, also induced mineral.

These and other data indicate that mineral induction by biological matrices is less specific than implied in the atomic dimensional matching extension of the epitaxial hypothesis.
Processability of Composite Materials Containing Chitosan
Authors: Allan G. Graham , Muvundamina Mutombo
Published: March 2011

The processability of polypropylene fibers into composite materials was characterized by dynamic wettability measurements. Single fibers were immersed in a series of aqueous acidic solutions of chitosan. Variations in the wetting force, observed for progressive and successive immersions of the fibers in the liquid, indicated adsorption of species out of the solution or the presence of foreign materials on the surface of the solid. The value of the advancing wetting force was used to assess the coating of the fibers by the liquid. Data on the surface composition of the fibers were obtained by electron spectroscopy for chemical analysis. The conditions of preparation of the composite materials containing chitosan were determined from the correlation of the observations on wettability, surface composition and scanning electron microscopy.
Assembly Characteristics and Structural Motifs in an Aquatic Insect's Biopolymer
Authors: Case Steven T. , Wellman Susan E. , Hamodrakas Stavros
Published: March 2011

Secretory proteins of Chironomus tentans larvae form insoluble fibers that are spun into threads used to construct underwater feeding and pupation tubes. The physical properties of spun fibers should reflect their protein constituents.

The disassembly and reassembly of secretory protein complexes in vitro were studied by solution turbidity, electron microscopy and circular dichroism spectroscopy. Secretory proteins were able to reform complexes with a similar morphology and dichroic spectrum to that of native complexes. These complexes are stabilized by electrostatic and disulfide bonds.

cDNA and genomic cloning indicate that spIs, the 1000-kDa secretory proteins, primarily consist of alternating “constant” and “subrepeat” regions. We synthesized and purified synthetic peptides for each region and used circular dichroism and infrared spectroscopy to measure their secondary structure. Constant peptide consists of α-helix and β-turn. Subrepeat peptide consists of poly(Gly) II-type helix and β-turn.

We conclude that spIs form the fibrous backbone of a novel biopolymer with alternating α-helices and poly(Gly)II helices punctuated by β-turns. Such fibers may have unique physical properties.
Liquid Crystalline Characteristics of Natural Silk Secretions
Authors: Kerkam Keven , Kaplan David , Lombardi Stephen , Viney Christopher
Published: March 2011

We have used transmitted polarized light microscopy to examine the fluid contents of silk glands taken from Bombyx mori silkworms and Nephila clavipes orb-weaving spiders. In the absence of shear, the secretions are optically isotropic. As the concentration is allowed to increase by evaporation, microstructures typical of the nematic liquid crystalline state are observed. Thus it appears that naturally spun silk becomes liquid crystalline en route to solidifying into fiber - which is advantageous to introducing and retaining global molecular alignment. This will facilitate the formation of strong, stiff fibers without the need for a significant post-spinning draw. We have also found that natural silk does not exhibit the defects in molecular alignment that are typical of synthetic polymer fibers spun from liquid crystalline solutions or melts.
Conformational Energy Studies of Model Silk Fibroin Peptides
Authors: Fossey Stephen A. , Nemethy G. , Gibson K. D. , Scheraga H. A.
Published: March 2011

Silk-like proteins are a topic of long-standing scientific interest and recently are being considered for such uses as high performance fibers [1] and enzyme-immobilizing substrates [2]. The structure of silk (in particular, the metastable silk I form) is critical in understanding the formation and processing of these materials.

Computations provide a useful tool for the detailed modeling of the structures of fibrous proteins. Conformational energy calculations on representative model polypeptides have been used successfully to elucidate the structure of collagen [3]. We have applied this method to the study of the crystalline region of Bombvx mori silk fibroin [4].
Oriented Collagen Matrices: the Control of Biomineralizaton in Bone
Authors: Nakamura Osamu , Fink David J. , Caplan Arnold I.
Published: March 2011

Bone-forming cells fabricate a highly ordered collagen matrix (osteoid) which subsequently mineralizes. A variety of cell culture systems exist for osteogenic cells, yet none of these is optimal for the organized formation of a mineralized matrix. We have generated collagen substrates which have different degrees of fibrillar orientation, and have cultured osteogenic cells on these matrices. In this format, von Kossa-stained sections show that highly oriented collagen matrix starts to calcify in 6–7 days, while a random fibrillar matrix does not mineralize even after 21 days. Mineral has been detected only within the collagen matrix with a narrow, unmineralized region between the cells and the mineral.
Monolayer Studies of Synthetic Poly (α-Amino Acids)
Authors: Fasman Gerald D.
Published: March 2011

Synthetic poly-α-amino acids spread at the air-water interface can form monomolecular films. These polymers may assume several conformations, namely the α-helix, β-pleated sheets or random coils. The stabilizing forces can be inter- or intramolecular and are mainly hydrogen bonding and hydrophobic interactions. The area/residue values for helical polymers differ significantly from those of β-sheets.

Poly-α-amino acids can form both cholesteric and nematic structures. Synthetic polypeptides of amphiphilic character, of both α and β conformers, can by synthesized and are very surface active. These polymers associate with cell membranes or lipoproteins. Many biologically active polypeptides, such as hormones, form amphiphilic α-helices and these ligands bind to receptor sites on cell surfaces.

These polypeptides offer a source of materials whose properties can be varied as desired, providing opportunities for rationale drug design.
Monolayers from Genetically Engineered Protein Pores
Authors: Bayley Hagan
Published: March 2011

A selection of microscopic pores is being made by genetic manipulation of a bacterial channel protein, α-hemolysin (α-HL). It will include: pores with different internal diameters, with differential selectivity for the passage of classes of molecules, and with different gating properties. The pores will be made into monolayers and incorporated into materials such as thin films to confer novel permeability properties upon them. Such products will have several technological applications, for example as molecular filters in sensors or as components of optically gated devices in electronics.
Inorganic Particles Produced by Microorganisms
Authors: Frankel Richard B.
Published: March 2011

The processes by which microorganisms, particularly bacteria, produce inorganic mineral particles are reviewed.
Bacterial Production of Iron Sulfides
Authors: Bazylinski Dennis A.
Published: March 2011

Iron sulfide production by bacteria can be classified as extracellular or intracellular. Extracellular iron sulfide production is mediated by anaerobic, dissimilatory sulfate-reducing bacteria which produce sulfide as a product of their respiration. Released sulfide reacts with iron (and other metals) in the extracellular environment producing a variety of iron sulfide minerals including “amorphous iron sulfide”, mackinawite, greigite, pyrrhotite, marcasite, and pyrite. The type of minerals formed is dependent upon pH, Eh, and other physical and chemical factors. Extracellular production of these minerals are examples of biologically-induced mineralization in which mineral formation occurs from chemical and/or physical changes in the surrounding environment by the organism.
Recent Progress in Atomic Layer Epitaxy of III–V Compounds
Authors: Bedair S. M.
Published: March 2011

The potential applications of Atomic Layer Epitaxy of III–V compounds will be outlined. These include the growth of special structures and devices such as ordered alloys, ultra-thin quantum wells, non-alloyed contacts, planar doped FET's and HBT's. Also, the main challenges facing ALE will be outlined along with possible solutions. These include reactor design, control of carbon doping and the growth of ternary alloys. A general assessment of the ALE technology will be provided.
Laser Assisted Atomic Layer Epitaxy-A Vehicle to Optoelectronic Integration
Authors: Chen Q. , Osinski J. S. , Beyler C. A. , Cao M. , Dapkus P. D. , Alwan J. J. , Coleman J. J.
Published: March 2011

Two implementations of laser assisted atomic layer epitaxy(LALE) for selective area growth of GaAs using trimethylgallium and AsH3 as precursors are described. A wide range of growth parameters lead to self-limiting monolayer/cycle growth which is suited for precise layer thickness control. By combining LALE with conventional metalorganic chemical vapor deposition, A10.3Ga0.7As/GaAs double heterostructures including LALE GaAs have been grown, permitting electrical and optical characterization to be performed on the thin and small areas of the LALE deposits. The information is used in a growth parameter optimization process resulting in device quality GaAs. Quantum well lasers with active region grown by LALE are demonstrated for the first time. The application of LALE to optoelectronic integration is demonstrated by depositing small area quantum wells as the gain medium in an otherwise transparent waveguide.
Multi-Wafer Atomic Layer Epitaxy Reactor for Device Quality GaAs
Authors: Colter P. C. , Hussien S. A. , Dip A. , Erdogan M. U. , Bedair S. M.
Published: March 2011

Reactor design considerations are discussed relevant to the two main problems, carbon contamination and low growth rate, facing Atomic Layer Epitaxy (ALE) of GaAs. A new reactor design addressing these problems is described. It utilizes the concept of rotating the substrate between streams of reactant gases. The growth chamber provides baffles and gas jets to shear off and sweep away the thermal boundary layer after exposure to the reactive gas streams. Construction is based on modification of a commercially available low pressure MOCVD reactor equipped with a. load lock. The reactor is capable of processing three, two-inch wafers. A background carbon concentration of about 1015cm−3 and a 77°K mobility of 30,000 cm2/V-sec were achieved. Self limited growth was observed for a growth temperature as high as 600 °C. Controlled p- and n-type doping was accomplished by changing growth conditions and adding silane.
A Possibility of ALE Growth of InN by using InCl3
Authors: Higuchi Kazuhito , Unno Akio , Shiraishi Tadashi
Published: March 2011

A possibility of the Atomic Layer Epitaxy, ALE, for InN was demonstrated by using InC13/N2 and NH3/N2. The InCl3 is a solid at room temperature and can be supplied in the reactor by heating with N2 carrier gas. When the solid InCl3 is heated in an inert gas, InCl, InCl3 and In2Cl3 gases are formed. It was clear that the In2Cl5 which is the largest molecule of the three results in solid structural defects. The ALE growth temperature was from 440°C to 505°C. The fact that the ALE was performed at the temperature range from 440°C to 505°C indicates that In was supplied as InC13, suggesting the possibility of InN ALE by using InCl3 and NH3.
Growth Mechanisms During Si/Ge Deposition
Authors: Crowell John E. , Lu Guangquan , Ning Bob M. J.
Published: March 2011

The adsorption and decomposition behavior of disilane and digermane are quite similar on the Ge(111) surface. Both precursors are weakly bound at low temperatures, but dissociatively adsorb at temperatures above 150K. Trihydride species are produced and stable at low temperatures, but decompose to di- and monohydride species at slightly higher temperatures. The desorption of hydrogen from the resulting layer is strongly dependent on the Si and Ge composition of the layer.
Layer-by-Layer Oxidation of Silicon
Authors: Yasaka T. , Takakura M. , Miyazaki S. , Hirose M.
Published: March 2011

Growth kinetics of native oxide on HF-treated Si surfaces terminated with Si-H bonds has been studied by angle-resolved x-ray photoelectron spectroscopy. The oxide growth rate in pure water for an n+ Si(100) surface is significantly high compared to that of p+, and the n or p type Si oxidation rate is in between. This is explained by the formation of ions through electron transfer from Si to adsorbed O2 molecules and the resulting enhancement of the oxidation rate. The oxide growth on Si(100) is faster than (110) and (111) as interpreted in terms of the steric hindrance for molecular oxygen adsorption on the hydrogen terminated silicon 1×1 surface structures.
The Mechanisms and Kinetics of Surface Reactions of Trimethylgallium on GaAs (001) Surfaces and Its Relevance to Atomic Layer Epitaxy
Authors: Maa B. Y. , Dapkus P. D.
Published: March 2011

X-ray photoelectron spectroscopy (XPS) and reflection high energy electron diffraction (RHEED) have been applied to study the stable adsorbed Ga species and surface structures after GaAs (001) 2 × 4 As-rich surfaces are exposed to TMGa. These studies show that Ga atoms are the final adsorbed species, that Ga deposition is saturated at one atomic layer at temperatures between 360 and 530 °C and that the surface converts from a 2 × 4 to a 4 × 6 reconstruction after TMGa adsorption. To understand the surface reaction kinetics involved, reflectance-difference spectroscopy (RDS), an in situ rea-ltime optical technique developed by Aspnes et al., is applied to investigate TMGa adsorption on (001) GaAs surfaces. The kinetics of the surface reactions and reconstructions have been characterized over the temperature range from 400 to 500 °C using RDS. The transient RDS behaviors are interpreted by the application of a model that involves selective adsorption and reaction of TMGa at surface As sites and at Ga vacancies on Ga-rich reconstructed surfaces. Based upon these interpretations, rates of reaction and by product desorption are determined that suggest optimal strategies for ALE growth of GaAs.
Cadmium Sulphide Thin Films Grown By Atomic Layer Epitaxy
Authors: Rautiainen Aimo , Koskinen Yrjö , Skarp Jarmo , Lindfors Sven
Published: March 2011

Polycrystalline cadmium sulphide (CdS) thin films were grown by Atomic Layer Epitaxy (ALE) using indium tin oxide and tin oxide coated glass substrates. Some of the experiments were made using elemental reactants, and others with inorganic compounds as reactants. Films were characterized using various techniques such as XRD, SEM and optical transmission spectroscopy. Growth rate of CdS films was observed to be 1/4 - 1/3 monolayer per cycle with elemental reactants. A full monolayer/cycle coverage was obtained when using CdCl2 and H2S as reactants. The crystalline structure of the CdS films wis β-cubic (111) when using elemental reactants. The mixed structure was observed when inorganic compounds were used as reactants. Only the hexagonal phase was observed, when substrate surface was pretreated before CdS deposition.
Low Temperature Epitaxial Growth of High Temperature Superconductors:Bi-Sr-Ca-Cu-O.
Authors: Kawai Maki , Mori Masami , Watabe Shunji , Liu Ziyuan , Tabira Yasunori , Ishizawa Nobuo
Published: March 2011

Molecular beam epitaxy of ultra thin films of Bi2Sr2CuO8-(2201 phase) is realized on the surface of SrTiO3 (100) and LaAlO3 (100) at the substrate temperature of 573 K, using 10-5Pa of NO2 as an oxidant. The film epitaxially grown from the surface of the substrate has identical in-plane lattice constant to the substrate itself. Such a growth can only be obtained on the substrate with similar lattice constant to those of the material to be formed. The crystallinity of the film strongly depended on the sequence of the metal depositions and the oxidation process. In the case of the Bi system, the elementary unit of the epitaxial growth has proved to be the subunit of the perovskite structure (Sr-Cu-Sr). The structure of the film grown on a substrate with large mismatch (MgO) is also discussed.
Study Of The Growth Mechanisms of NbS2 Scales Using Marker Experiments
Authors: Zhou Chuxin , Hobbs L. W.
Published: March 2011

ABSTRACT Au thin films were deposited using electron beam evaporation onto the surface of Nb metal to serve as thin film markers to study the growth mechanisms of NbS2 scales. Scanning Auger microscopy (SAM) was used to measure the depth profiles for the compositions of Au, Nb, S, Si and O across the sulfide scale. Three other marker experiments were also studied. All four marker experiments indicated that the inward diffusion of sulfur is the dominant process responsible for the growth of NbS2 scales.
Low-Temperature Growth of Thin Films of A12O3 with Trimethylaluminum and Hydrogen Peroxide
Authors: Fan J. F. , Sugioka K. , Toyoda K.
Published: March 2011

Thin films of A12O3 were prepared by sequential surface chemical reaction of trimethylaluminum and hydrogen peroxide at low temperatures. It has been found that hydrogen peroxide reacts very easily with trimethylaluminum, resulting in growth of A12O3 at the temperature as low as the room temperature. Another favorable feature of the technique is that the growth of excellent A12O3 occurs identically wherever the reactants reach, making it possible to completely coat the surface of the sample with arbitrary shape.
Real-Time Optical Diagnostics For Measuring And Controlling Epitaxial Growth
Authors: Aspnes D. E. , Bhat R. , Colas E. , Florez L. T. , Gregory S. , Harbison J. P. , Kamiya I. , Quinn W. E. , Schwarz S. A. , Tanaka H. , Wassermeier M.
Published: March 2011

A variety of optical methods are now available for studying surface processes and for monitoring layer thicknesses and compositions during semiconductor crystal growth by molecular beam epitaxy (MBE), organometallic chemical vapor deposition (OMCVD), and related techniques. New capabilities for surface analysis are being provided by developing techniques such as reflectance-difference spectroscopy (RDS), which use intrinsic symmetries to suppress ordinarily dominant bulk contributions. Bulk and microstructural properties such as compositions and layer thicknesses can be determined by techniques such as spectroellipsometry (SE), which return information integrated over the penetration depth of light. Recent advances include the application of reflectance to monitor dynamic surface processes, RDS to characterize (001) GaAs surfaces in OMCVD environments, and SE to control growth of AlxGa1-x, As materials and structures.
Ftir Studies Of Organometallic Surface Chemistry Relevant To Atomic Layer Epitaxy.
Authors: Annapragada Ananth V. , Salim Sateria , Jensen Klavs F.
Published: March 2011

The adsorption and surface reactions of trimethylgallium and tertiarybutylarsine on GaAs(100) surfaces have been investigated by Fourier transform infrared spectroscopy. Adsorbed methyl groups resulting from the dissociative chemisorption of trimethylgallium on GaAs(100) are shown to form As-H and CH2 species on the surface. The CH2 groups are stable on the surface at temperatures as high as 550 °C. The surface coverage is low (∼0.2% of a monolayer) and is reduced by the presence of hydrogen on the surface. This dehydrogenation of surface methyl groups could be a possible route to carbon incorporation in GaAs grown by atomic layer epitaxy. Tertiarybutylarsine is shown to decompose primarily by homolysis to form a tertiary butylgroup and AsH2. At temperatures below 400°C on trimethylgallium dosed surfaces, the decomposition products appear to cause the hydrogenation of methylene groups remaining from prior surface dosing with trimethylaallium. At high temperatures, the tertiarybutyl radical appears to undergo dehydrogenation reactions to an unsaturated species which is stable on the surface. In contrast, the dehydrogenation does not appear to occur on surfaces treated with tertiarybutylarsine. The data for trimethylgallium and tertiarybutylarsine support the general assertion that surface As-H species play a critical role in the removal of hydrocarbon species from the growth surface.
Thermoelectric Properties of Hot-Pressed Ultra-Fine Particulate Sige Powder Alloys with Inert Additions
Authors: Beaty John S. , Rolfe Jonathan L , Vandersande Jan W.
Published: March 2011

The objective of the work reported here is to reduce the thermal conductivity of thermoelectric materials in order to improve their figureof- merit and conversion efficiency. Theory predicts that the addition of ultra-fine, inert, phonon-scattering centers to thermoelectric materials will reduce their thermal conductivity [1]. To investigate this prediction, ultra-fine particulates (20Å to 120Å) of silicon nitride have been added to boron doped, p-type, 80/20 SiGe. All of the SiGe samples produced from ultra-fine powder have lower thermal conductivities, than that for standard SiGe, but high temperature heat treatment increases the thermal conductivity back to the value for standard SiGe. However, the SiGe samples with silicon nitride, inert, phonon-scattering centers, retained the lower thermal conductivity after several heat treatments. A reduction of approximately 25% in thermal conductivity has been achieved in these samples.
Oxygen Effects in Mechanically Alloyed Si80 Ge20 Doped with GaP and P
Authors: Cook B. A. , Harringa J. L. , Beaudry B. J.
Published: March 2011

A neutron activation study was performed to follow the total oxygen content during the preparation sequence of mechanically alloyed Si-20 at.% Ge n-type alloys using both elemental powders and chunk starting materials. The Si-20 at. % Ge alloys were doped with 1.6 at. % GaP and 3.4.at. % P and the total oxygen concentration was measured in the starting materials, after six hours of mechanical alloying in a helium environment, after hot pressing, and after a short 1100°C soak in fused silica ampoules. The alloys containing high oxygen levels showed low carrier mobility and low thermal conductivity whereas those containing low oxygen showed high mobility and thermal conductivity. The microstructure, as observed by optical metallography and SEM, was found to differ greatly with oxygen content as the low oxygen alloys showed relatively large, well defined grains and the high oxygen alloys showed evidence of poor sintering and limited grain growth.
High Temperature Thermoelectric Properties of Boron Carbide
Authors: Aselage T. L.
Published: March 2011

Boron carbides are refractory solids with potential for application as very high temperature p-type thermoelectrics in power conversion applications. The thermoelectric properties of boron carbides are unconventional. In particular, the electrical conductivity is consistent with the thermally activated hopping of a high density (≈ 1021/cm3) of bipolarons; the Seebeck coefficient is anomalously large and increases with increasing temperature; and the thermal conductivity is surprisingly low. In this paper, these unusual properties and their relationship to the unusual structure and bonding present in boron carbides are reviewed. Finally, the potential for utilization of boron carbides at very high temperatures (up to 2200°C) and for preparing n-type materials is discussed.
Review of Lead-Telluride Bonding Concepts
Authors: Elsner Norbert B.
Published: March 2011

Over the past few years, there has been a trend to use thermoelectrics for generating power from waste heat or coupling the thermoelectrics with fossil fuel driven appliances or Diesel engines to make them more efficient and/or independent of outside power. PbTe based alloys are being considered for some of these applications. Presented below are some of the techniques that have been pursued in making electrical contacts. Because PbTe can be used up to ∼ 600°C, these alloys offer more efficiency than the (Bi,Sb)2 (SeTe)3 based alloys which are only useful to <300° C. Unfortunately, at these h~gher temperatures, the PbTe based alloys need to be encapsulated to prevent oxidation. This latter step is not addressed in this paper, but can significantly add to the price of a PbTe generator.
Thermoelectric Properties of Single Crystal Alloys Bi8Sb32Te60, Bi9Sb31Te60and Bi10Sb30Te60Grown by the T.H.M. Method
Authors: Caillat T. , Carle M. , Fleurial J. P. , Scherrer H. , Scherrer S.
Published: March 2011

It has been reported that high figures of merit could be achieved on bismuth telluride grown by T.H.M. (Travelling Heater Method). Further improvements could be obtained for the p-type materials by studying solid solutions formed by bismuth telluride and antimony telluride.

A good knowledge of the ternary phase diagram is necessary to obtain homogeneous ingots by T.H.M..

We present the results of the determination of ternary phase diagram (Bi-Sb-Te). The equilibrium data between liquid and solid alloys Bi8Sb32Te60, Bi9Sb31Te60and Bi10Sb30Te60are also reported and it allows their elaboration by T.H.M..

Thermoelectric characterization of ternary samples is carried out as a function of stoichiometric deviations. Measurements of electrical and thermal conductivities as well as Seebeck coefficient were done at room temperature for the Bi8Sb32Te60, Bi9Sb31Te60and Bi10Sb30Te60alloys.

The values of the figure of merit remain interesting for the alloys studied and a maximum value of 3.2 10−3K−1is reached for the Bi9Sb31Te60alloy.
Properties of Bi-Te-Sb Single Crzystals Grown by the Czochralski Method for Thermoelectric Cooling
Authors: Anatychuk Lukyan I. , Klim Vladimip A. , Kshevetsky Stanislav A.
Published: March 2011

Materials based on Bi.Te, Se, Sb and produced by pressing, extrusion or zone recrystalization are used usually for the thermoelectric cooling. But by Czochralski method materiales have been far less grown. Researches on growing of monocrystalline ingots on the base of combinations Bi-Se-Te and Bi-Sb-Te have been done by [1,2]. The same researches have been made at our Institute.
Thermoelectric Power Studies on La2-xSrxNiO4-δ
Authors: Liu C.-J. , Sánchez M. G. , Cowan D. O.
Published: March 2011

Thermoelectric power (S) has been measured on La2-xSrxNiO4-δ. Both nonmetallic (0.5 < × < 1.0) and metallic materials (1.1 ≤ × ≤ 1. 5) have been investigated between 80 and 310 K. The sign of S changes from negative to positive between 150 and 220 K for both metallic and nonmetallic samples. The position at which the curve crosses from negative to positive depends upon the composition (x). For example, when × = 1.15 (metallic conductivity) S changes from negative to positive at about 220 K. However, if this sample is heated to 1000° C under argon, the material becomes nonmetallic and the sign of S remains positive between 80 and 310 K. These results may indicate that more than one type of carrier is involved. The absolute magnitude of S at 300 K decreases with × for 0.5 ≤ × ≤ 1.15 and then increases with × for 1.15 ≤ × ≤ 1.5. In the heavily doped material where S becomes more negative with increasing doping, the thermoelectric power strongly indicates that electrons and not holes are the majority carriers.
Radiation Defect Study in the P-Type Copper Seleind
Authors: Marchuk N. D. , Dolgolenko A. P.
Published: March 2011

P-Cu2-δ Se(δ=0.025) samples, self-doped through a departure from the stoichiometry(po= 4.8·1020) and cadmium-doped up to a concentration po= 5.6·1020cm−3 were studied in the course of their irradiation in a reactor up to a fluance of -6·1020 n·cm−2 of fast neutrons at a temperature of -500-550° C. The dependence of the resistivity and thermo-emf on the fast neutron fluence is described in terms of the theory of effective medium and representation of defect clusters as dielectric inclusions in a conducting matrix of p-Cu2Se(Cd) and p-Cu2_δSe samples.

Defect clusters of a mean radius of -27 Å are shown to appear not only because of scattering of the fast pile neutrons on copper and selenium atoms, but also due to a nuclear reaction 112Cd(n,γ)114Cd on thermal neutrons with an efficiency of 3.43 cm−1. Increase of the conductivity in the process of the reactor irradiation of p-Cu2-δSe at small fluences of fast neutrons and appearance of a whitish deposit of selenium on the surface of samples after high fluences of fast neutrons were observed.
Is there a Lower Limit to the Thermal Conductivity of Solids?
Authors: Cahill David G. , Pohl R. O.
Published: March 2011

The thermal conductivity of various systematically disordered crystals has been measured. It has been found that the lowest thermal conductivity above ∼100 K that can be achieved is equal to that of the amorphous phase. This experimentally observed lower limit of the thermal conductivity can be described with a model proposed by Einstein in which the elastic energy propagates in a random walk among the atoms which are vibrating with random phases, and which is called the minimum thermal conductivity. This heat transport mechanism resembles somewhat that commonly accepted in liquids.
A New Method for Thermal Diffusivity Measurements in Metals Utilizing the Thermo-Electric Effect
Authors: Shai Isaac , Laor Uri , Gilad Ilan
Published: March 2011

A new method for the measurement of the thermal diffusivity in metals, using transient conditions, is demonstrated. This method is using the principle of superposition of thermal loads. Only time measurements are required, and no accurate temperature and heat flow rate measurements are needed. The method utilizes the Seebeck effect for the measurement of the time dependence of the temperature. A solution of the heat transfer equation for the model pertinent to the described method is derived, and results obtained for several materials are presented.
On the Changing of Thermoelectric Material Properties at Large Heat Fluxes
Authors: Anatychuk Lukyan I. , Bulat Lev P.
Published: March 2011

One of the main trends of the thermoelectric instrument-making development is the microminiaturization of instruments and devices. Thermoelectric converter compactness is achieved by this. As thermoelement geometric dimentions reduce, temperature gradients in materials increase. From this it follows the research problem directed at the investigation of transport phenomena in thermoelectric materials at sufficiently large heat fluxes. Enthusiasm on investigation statement is warmed by the consideration about possible improvement of the efficiency at thermoelectric convertion when in thermoelectric materials temperature gradients of 106 - 109 K/cm/1/ have been realized.
On anisotropic thermoelectric materials figure of merit increase
Authors: Rnotyjchuk Lukygen I. , Lusts Oleg J.
Published: March 2011

The thermoelemernts based on the Seebeck coefficlent anisotropy in homogeneous media are known as well as classical thormoelements and thermopiles using Seebeck effact in the circuit of haterogeneous materials [1] Some our variants of such thormoelement have been patented particularly in the USA [2,3]. The simplest of this kind thermoelements called anisotropic is represented in figtl. The voltage produced by the thermoelement.