bluuebunny/crossref_metadata_2025_split huggingface dataset:
Growth and Characterization of Lithium Niobate Thin Films on Diamond/Si(100) Substrates
Authors: Wang Shunxi , Su Qingxin , Robert Marc A. , Rabson Thomas A. 
Published: April 2011

AbstractA low temperature metal-organic decomposition process for depositing LiNbO3 thin films on diamond/Si(100) substrates is reported. X-ray diffraction studies show that the films are highly textured polycrystalline LiNbO3 with a (012) orientation. Scanning electron microscopy analyses reveal that the LiNbO3 thin films have dense, smooth surface without cracks and pores, and adhere very well to the diamond substrates. The grain size in the LiNbO3 thin films is in the range of ∼0.2-0.5 μm. The effect of the processing procedures on the surface morphology of the LiNbO3 films is investigated. Possible reasons for the elimination of microcracks in the LiNbO3 films are discussed.
Light-Induced Structural Phase Transition in Confining Gallium and Associated Gigantic Optical Nonlinearity
Authors: Albanis V. , Dhanjal S. , Emelyanov V. , Petropoulos P. , Richardson D. J. , Zheludev N. I. 
Published: April 2011

AbstractWe report a light-induced, surface-assisted structural phase transition from a common orthorhombic phase of crystalline gallium (α-gallium) to a highly reflective, metastable phase of more ‘metallic’ nature. The transition has been observed at the interface of gallium with fused silica at temperatures just below the metal's bulk melting point and affects only several tens of gallium atomic layers. The transition is fully reversible and occurs on a nanosecond/microsecond time scale. The transition appears to show some characteristic features of a second order structural phase transition, including an increase of the transition relaxation times at the critical temperature (of approximately 30°C). The transition has no apparent optical intensity threshold, and is induced by radiation of very low intensity of only 10−4 − 10−5 W/μm2. The two gallium phases involved in the phase transition have significantly different dielectric properties which gives rise to a gigantic cubic optical nonlinearity, χ(3) ∼ 1 esu. The transition can be stimulated by light at any wavelength in the visible and the infrared ranges out to at least 1.55μm. The effect is therefore of great interest for applications requiring light by light control at milliwatt power levels.
Recent Advances in Simulation of Dendritic Polymers
Authors: Çağin Tahir , Miklis Paul J. , Wang Guofeng , Zamanakos Georgios , Martin Ryan , Li Hao , Mainz Daniel T. , Nagarajan Vaidehi , Goddard William A. 
Published: April 2011

AbstractDendrimers and hyperbranched polymers represent a revolution in methodology for directed synthesis of monodisperse polymers with enormous possibility of novel architectures. They demonstrate ability to attain micelle-like structures with distinct internal and external character. Furthermore polyfunctional character of dendrimers allows varied response to environment and promise as selective sensors, carrier for drugs, encapsulation of toxic chemicals and metals. One of the key problems are the characterization of the structures. Theory and simulation can be essential to provide and predict structure and properties. Here, we present some recent advances in theory, modeling and simulation of dendritic polymers.
Simulation of Thermal Stability and Friction: A Lubricant Confined Between Monolayers of Wear Inhibitors on Iron Oxide
Authors: Çağin T. , Zhou Y. , Yamaguchi E. S. , Frazier R. , Ho A. , Tang Y. , Goddard W. A. 
Published: April 2011

AbstractTo understand antiwear phenomena in motor engines at the atomic level and provide evidence inselecting future ashless wear inhibitors, we studied the thermal stability of the self-assembled monolayer(SAM) model for dithiophosphate (DTP) and dithiocarbamate (DTC) molecules on the iron oxidesurface using molecular dynamics. The interactions for DTP, DTC and Fe2O3 are evaluated based on aforce field derived from fitting to ab initio quantum chemical calculations of dimethyl DTP (and DTC)and Fe(OH)2(H2O)2-DTP (DTC) clusters. MD simulations at constant-NPT are conducted to assesrelative thermal stabilities of the DTP and DTC with different pendant groups (n-propyl, i-propyl, npentyl.and i-pentyl). To investigate frictional process, we employ a steady state MD method, in whichone of the Fe2O3 slabs maintained at a constant linear velocity. We obtain the time averaged normaland frictional forces from the interatomic forces. Then, we calculated the friction coefficient at theinterface between SAMs of DTP and the confined lubricant, hexadecane, to assess the shear stability ofDTPs with different pendant groups.
Impurity Induced Slowing oF Nucleation in Emulsified Liquids
Authors: Herhold Amy , Ertaş Deniz , Levine Alex J. , King H. E. 
Published: April 2011

AbstractWe report detailed nucleation studies on the liquid -to -solid transition of hexadecane using nearly monodisperse hexadecane -in -water emulsions. A careful consideration of the kinetics of isothermal and nonisothermal freezing show deviations from predictions of classical nucleation theory, if one assumes that the emulsion droplet population is homogeneous. Similar deviations have been observed previously [3]. As an explanation, we propose a novel argument based on the dynamic generation of droplet heterogeneity mediated by mobile impurities. This proposal is in excellent agreement with existing data.
Plasma Deposition of Diamond-Like Carbon and Carbon-Nitride Films in an Electron Cyclotron Resonance-Radio Frequency Discharge
Authors: Turban Guy , Zarrabian Marjan , Hong Junegie 
Published: April 2011

AbstractHydrogenated and nitrogenated amorphous carbon films, a-C:H and a-C:H:N, were elaborated by Plasma Enhanced Chemical Vapor Deposition (PECVD) in a dual Electron Cyclotron Resonance - Radio Frequency (ECR-RF) discharge of methane and/or nitrogen. The use of a low pressure plasma (2.6 mTorr) and a capacitive coupling of the substrate, separately from the electrical power of the ECR source, leads to reach new conditions of preparation. The ions and radicals fluxes, Φi and ΦR, determined respectively from the Langmuir probe measurements and the Mass Spectrometry (MS) give a ratio ΦR/Φi of order of 20. The CH3 radicals were identified and their concentration was measured from the technique of threshold ionization. It is shown that, even at low pressure, numerous ion-molecule reactions take place in the gas phase which explain the formation of major ions CH5+. and C2H5+.
The plasma-surface interaction is studied by in-situ kinetic ellipsometry and by ex-situ X-ray Photoelectron Spectroscopy (XPS) measurements of deposited films. The role of the impact energy of ions, during the growth of films, is studied by Ultra-Violet-Visible spectroscopic ellipsometry.
A new technique of deposition by alternating sequences of «C H4 deposition - treatment by N2, plasma » is described in this paper. The resulted a-C:H:N films are compared to those elaborated from CH4-N2 plasmas. The aim of the discussion on the presented results is to better understand the mechanism of the growth of amorphous carbon films by PECVD.
Surface Immobilization of Synthetic Proteins Via Plasma Polymer Interlayers
Authors: Griesser Hans J , McLean Keith M , Beumer Gerrit J , Gong Xiaoyi , Kingshot Peter , Johnson Graham , Steele John G 
Published: April 2011

AbstractCoatings of biologically active molecules on synthetic ”bulk“materials are of much interest for biomedical applications since they can in principle elicit specific, predictable. controlled responses of the host environment to an implanted device. However, issues such as shelf life. storage conditions, biological safety, and enzymatic attack in the biological environment must be considered; synthetic proteins may offer advantages. In this study we investigated the covalent immobilization onto polymeric materials of synthetic proteins which possess some properties that mimic those of the natural protein collagen, particularly the ability to form triple helical structures, and thus may provide similar bio-responses while avoiding enzymatic degradation. In order to perform immobilization of these collagen-like molecules (CLMs) under mild reaction conditions, the bulk materials are first equipped with suitable surface groups using rf plasma methods. Plasma polymer interlayers offer advantages as versatile reactive platforms for the immobilization of proteins and other biologically active molecules. Application of a thin plasma polymer coating from an aldehyde monomer is particularly suitable as it enables direct immobilization of CLMs by reaction with their terminal amine groups, using reductive amination chemistry. An alternative route is via plasma polymer layers that contain carboxylic acid groups and using carbodiimnide chemistry. A third route makes use of alkylamme plasma polymer interlayers, which are less process sensitive than aldehyde and acid plasma coatings. A layer of poly-carboxylic acid compounds such as carboxylic acid terminated PAMAM-starburst dendrimers or carboxymethylated dextran is then attached by carbodiimide chemistry onto the amine plasma layer. Amine-terminated CLMs can then be immobilized onto the poly-carboxylic acid layer. Surface analytical methods have been used to characterize the immobilization steps and to assess the surface coverage. Initial cell attachment and growth assays indicate that the biological performance of the CLMs depends on their amino acid sequence.
Highly Transparent Arcproof Films for Space Applications
Authors: Adorjan A. J. , Alexander C. , Blanchard T. L. , Bruckner E. , Ferrante R. , Gajdos S. M. , Mayer K. , Pal A. M. , Walters P. A. , Hambourger P. D. , Dever J. A. , Rutledge S. , Fu Henry 
Published: April 2011

AbstractHighly transparent films with tailorable sheet resistivity were prepared by ion-beam sputtering of indium tin oxide (ITO) with MgF2or SiO2in the presence of high-purity air. Sheet resistivities of 103−101ohms/square (ω/–) and visible transmittances as high as 92% (not corrected for substrate absorption) were obtained in films ∼30 nm thick. Resistivity increased by as much as two orders of magnitude in the first year after preparation; however, thicker films (e.g. 80 nm) were much more stable but somewhat less transparent. Preliminary data from exposure of film samples to atomic oxygen in a plasma asher indicate minimal degradation in optical properties. Heat-treating pure ITO in air produced transparent, slightly conductive films but with poorer stability of sheet resistivity in air than co-deposited ITO with either SiO2, or MgF2. Electrical transport measurements yielded new information on the electronic properties of ITO and related materials. These films show promise as low-absorption static bleedoff coatings for space photovoltaic arrays as well as CRT faceplates and other commercial applications.
Rare Earth Doped Yttrium Aluminium Garnet (YAG) Selective Emitters
Authors: Chubb Donald L. , Pal AnnaMaria T. , Patton Martin O. , Jenkins Phillip P. 
Published: April 2011

AbstractAs a result of their electron structure, rare earth ions in crystals at high temperature emit radiation in several narrow bands rather than in a continuous blackbody manner. This study presents a spectral emittance model for films and cylinders of rare earth doped yttrium aluminum garnets. Good agreement between experimental and theoretical film spectral emittances was found for erbium and holmium aluminum garnets. Spectral emittances of films are sensitive to temperature differences across the film. For operating conditions of interest, the film emitter experiences a linear temperature variation whereas the cylinder emitter has a more advantageous uniform temperature. Emitter efficiency is also a sensitive function of temperature. For holminum aluminum garnet film the efficiency is 0.35 at 1446K but only 0.27 at 1270 K.
Artificial Effects on Cryogenic Fracture Toughness of the Main Structural Alloy for the Super Light Weight Tank
Authors: Chen P.S. , Stanton W.P. 
Published: April 2011

AbstractAt Marshall Space Flight Center (MSFC), a new aging technique has been developed that can significantly enhance the cryogenic fracture toughness (CFT) of Alloy 2195, as well as reducing the statistical spread of fracture toughness values. This technique improves cryogenic properties by promoting T1 nucleation and growth in the matrix, so that T1 nucleation and growth can be suppressed in the subgrain boundaries. It also minimizes mechanical property scatter due to unavoidable variations in thermomechanical processing parameters and alloy chemistry.
Fatigue-Crack Propagation in Gamma-Based Titanium Aluminide Alloys at Large and Small Crack Sizes
Authors: Kruzic J. J , Campbell J. P , Ritchie R. O. 
Published: April 2011

ABSTRACTMost evaluations of the fracture and fatigue-crack propagation properties of γ + α2titanium aluminide alloys to date have been performed using standard "large-crack" samples, e.g., compact-tension specimens containing crack sizes which are on the order of tens of millimeters, i.e., large compared to microstructural dimensions. However, these alloys have been targeted for applications, such as blades in gas-turbine engines, where relevant crack sizes are much smaller (<500 µm) and where the small-crack fatigue threshold may be the most relevant design parameter. In this study, we compare and contrast the cyclic crack-growth behavior of both large (a > 5 mm) and small (c ∼ 25–300 µm) cracks in a γ-TiAl based alloy, of composition Ti-47A1–2Nb-2Cr-0.2B (at%), specifically for duplex (average grain size ∼17 µm) and refined lamellar (average colony size ∼150 µm) microstructures. It is found that, whereas the lamellar microstructure displays far superior fracture toughness and fatigue-crack growth resistance in the presence of large cracks, in small-crack testing the duplex microstructure exhibits a better combination of properties. The reasons for such contrasting behavior are examined in terms of the intrinsic and extrinsic (i.e., crack bridging) contributions to cyclic crack advance.
Solute Partitioning and Interfacial Segregation in TiAl-Based Alloys
Authors: Larson D. J. , Miller M. K. 
Published: April 2011

ABSTRACTAtom probe microscopy has been used to investigate elemental partitioning and segregation behavior in a TiAl-based alloy with a variety of alloying additions including Cr, Nb, W and B. These results indicate that in a stress-relieved state (2 h at 900°C) and a reheated state (2 h at 900°C, 2184 h at 800°C and 2 h at 1210°C) chromium, and to a lesser extent tungsten, is partitioned to the α2phase. However, in an annealed state (2 h at 900°C and 720 h at 800°C), these elements are partitioned to the, γ phase. Segregation of chromium and tungsten to lamellar interfaces is observed in the stress-relieved material, but significant segregation was not observed in material subjected to the other heat treatments. A W- and B-enriched precipitate was observed in the reheated material and provides a possible explanation for the low tungsten concentrations measured in the matrix phases.
Deformation of Polysynthetically Twinned TiAl Single Crystals with Near-Hard Orientations
Authors: Kim Min-Chul , Nomura M. , Vitek V. , Pope D. P. 
Published: April 2011

ABSTRACTCompression tests were performed on specially-oriented PST TiAl crystals to which strain gages were attached in order to precisely measure the three axial strains in the samples during deformation. It was found that all samples deform by plane strain except when the compression axis is nearly perpendicular to the lamellar planes. This measurement technique was used to determine the orientations in which the various slip systems are operative in PST samples, and this, in turn was employed to explain the shape of the flow stress vs. orientation curve. An important component of this explanation is the fact that slip of ordinary dislocations and twinning are closely coupled in this material, implying that the twinning must occur relatively slowly-at about the same rate that ordinary dislocations move. Atomistic calculations have shown that a slow twinning process is to be expected in this material at low temperatures, perhaps even by a thermally activated process.
Processing and Properties of FeAl Sheets Obtained by Roll Compaction and Sintering of Water Atomized Powder
Authors: Deevi S. C. , Hajaligol M. R. , Sikka V. K. , McKernon J. , Scorey C. R. 
Published: April 2011

ABSTRACTThe low ductilities of FeAl alloys led us to explore powder metallurgical processing technology to obtain sheets of 0.2mm thickness as opposed to manufacturing processes based on hot rolling of cast FeAl alloys. In our approach, water atomized FeAl powders were roll compacted to 0.66mm with a polymeric binder using two counter rotating rolls to a green density of 3.1 g/cc. Roll compacted green sheets were then de-bindered in nitrogen in the temperature range of 300 to 600°C for several hours prior to sintering the sheets in vacuum. Sintered sheets were rolled down from 0.66 to 0.20 mm in three different stages resulting in a total reduction of 69% Vacuum annealing of the sheets was carried out between each stage of the reduction process to eliminate edge cracking associated with the work hardening of the FeAl. The properties of the FeAl sheets depend on the Al content, annealing temperature and time in a vacuum furnace. The fine microstructure of FeAl sheets led to tensile elongations of 4 to 6%. The sheets are formable at room temperature, and possess excellent mechanical properties both at room and high temperatures.
Directional Solidification of Mo5Si3-MoSi2 Eutectic
Authors: Borowicz S. M. , Heatherly L. , Zee R. H. , George E. P. 
Published: April 2011

ABSTRACTThe Mo-Si phase diagram exhibits a Mo5Si3-MoSi2 eutectic at the 54% Si composition. Since the terminal phases have comparable melting points and are equidistant from the eutectic composition, there is the possibility of obtaining lamellar microstructures in this system. In addition, if the alloys are directionally solidified, there is the further possibility of obtaining aligned lamellae. In this study, a high temperature (xenon-arc-lamp) optical floating zone furnace is utilized to directionally solidify Mo-Si alloys of the eutectic composition. Growth conditions are systematically varied to investigate their effects on the solidification microstructure. Growth rates and rotation speeds are identified that result in lamellar microstructures.
Point Defect Behavior in B2-Type Intermetallic Compound FeAl
Authors: Haraguchi T. , Kogachi M. 
Published: April 2011

ABSTRACTPoint defect behavior in B2-type FeAI alloys is investigated from a thermodynamic point of view, based on the Bragg-Williams method. The model is developed by taking new defect formation mechanisms, random vacancy distribution (RVD), and antisite atom recovering (ASAR), into consideration, which were proposed based on the current findings in in situ neutron and X-ray diffraction studies for the B2 FeAl. The condition for appearance of the RVD and ASAR states is given. Application of this model to B2 FeAl alloys shows that the RVD-like behavior is reproduced in the Ferich composition region and also a rapid increase in vacancy concentration observed in the Al-rich region can be interpreted by the ASAR process by antisite Al atoms.
Processing and Properties of Mo5Si3 Single Crystals and Alloys
Authors: Chu F. , Thoma D. J. , McClellan K. J. , Peralta P. , Li F. X. , Fodran E. 
Published: April 2011

ABSTRACTAmong the high-temperature intermetallic systems, transition-metal silicides are attractive because of their high melting temperatures (many greater than 2273 K) and potential oxidation resistance. In particular, Mo5Si3 exhibits a very high melting point (2453 K) and also has a solubility range of 2 – 3 atomic percent, which can aid in processing and alloy design strategies. The focus of this study is to evaluate the processing and properties of Mo5Si3 and Mo5Si3-base ntermetallics. For the optimal baseline comparison, high-purity single crystals have been fabricated, and thermal and elastic properties have been experimentally measured. Although Mo5Si3 has a strong thermal expansion anisotropy, ts elastic anisotropy factors and the Poisson's ratios indicate that Mo5Si3 is less anisotropic in elasticity. The combination of the thermal and elastic properties has been employed to calculate the thermal residual stress and to explain the potential for grain boundary cracking during processing. Room temperature Vickers indentation tests of Mo5Si3 have been performed. The orientation dependence of hardness and fracture toughness of Mo5Si3 single crystals have been obtained. The corresponding deformation and fracture modes have been revealed by microscopy studies. Finally, micro- and macroalloyed Mo5Si3 with aluminum and boron will be briefly explored with property assessments.
Deformation of Two-Phase Alloys Based on C15 Laves Phase HfV2 + Nb
Authors: Kimura Yoshisato , Luzzi D. E. , Pope D. P. 
Published: April 2011

ABSTRACTTo investigate the deformation behavior of the C15 HfV2+Nb Laves phase, compression tests were conducted on the C15/bcc two-phase alloys at very low temperatures down to 4.2 K. Transmission electron microscopy revealed that substantial mechanical twinning takes place in the C15 Laves phase at room temperature and 77 K. A deep minimum in the flow stress, with a drop of nearly 500 MPa, appears at around 77 K for the C15/bcc two-phase alloy. Since no such anomaly is seen in the bcc phase, we believe that the cause of this can be attributed to mechanical twinning in the C15 Laves phase. A high density of ultra-fine twin bands is the characteristic feature of twinning in the C15 matrix. We also investigated the phase relations between the C15 HfV2 Nb and bcc (V, Nb) solid solution in the Hf-V-Nb ternary system in an attempt to understand why we were unsuccessful in our attempts to grow single crystals of the Laves phase.
Nature of Slip in γ-Titanium Aluminide Above the Yield Stress Anomaly Temperature
Authors: Jiao S. , Bird N. , Hirsch P. B. , Taylor G. 
Published: April 2011

ABSTRACTCrystals of γ-TiAl, containing ∼54.5 at% Al, with various orientations were deformed at different temperatures and examined by transmission electron microscopy (TEM). It was found that while in many cases slip and climb of ordinary dislocations tend to predominate, slip by [001] dislocations can be important also. The occurrence of [001] slip has not been reported before. The values of critical resolved shear stress were determined and strong locks on [001] dislocations have been identified as local segments of ½ ⟨112] dislocations arising from interactions between [001] and ½⟨110] dislocations.
High-Resolution Electron Microscopy of Dislocation Cores in NiAl
Authors: Stöckle D. , Sigle W. , Seeger A. 
Published: April 2011

ABSTRACTThe atomic structure of dislocation cores in NiAl is studied by high-resolution transmission electron microscopy (HRTEM) and molecular dynamics (MD) calculations. Results are presented on dislocations with Burgers vectors b=a<100> and a<111>. A comparison with HRTEM image simulations indicates that the core of a 45° a <100> dislocation consists of Al atoms. The Burgers vector distribution shows a width of 2.2b. This corresponds very closely to MD results and is consistent with the relatively low Peierls stress of this dislocation. By detailed image analysis the angular dependence of the shear stress components of the dislocation are made visible. MD results obtained from 45° dislocations with opposite screw components suggest, that the helicity of the screw component might be discernible from high-resolution electron micrographs. A a<111> dislocation with <110> line direction is shown which exhibits a rather wide dissociation, probably into two a/2<111> partials.