bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mineral Induction by Matrix from Mineralized Biological Tissues
Authors: Crenshaw Miles A. 
Published: March 2011

AbstractThe 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

AbstractThe 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

AbstractSecretory 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

AbstractWe 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

AbstractBone-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

AbstractSynthetic 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

AbstractA 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.
Bacterial Production of Iron Sulfides
Authors: Bazylinski Dennis A. 
Published: March 2011

AbstractIron 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

ABSTRACTThe 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

ABSTRACTTwo 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

ABSTRACTReactor 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

ABSTRACTA 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

ABSTRACTThe 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

ABSTRACTGrowth 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

ABSTRACTX-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

ABSTRACTPolycrystalline 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

ABSTRACTMolecular 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

ABSTRACTABSTRACT 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

ABSTRACTThin 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

ABSTRACTA 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTA 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.