bluuebunny/crossref_metadata_2025_split huggingface dataset:
Confinement Effects on The Local Motion in Nanocomposites
Authors: Anastasiadis S. H. , Karatasos K. , Vlachos G. , Manias E. , Giannelis E. P. 
Published: April 2011

AbstractThe local segmental dynamics of polymers confined within the 15–20 Å interlayer spacing of nanocomposites consisting of poly(methyl phenyl siloxane) intercalated within organically modified silicates, has been investigated utilizing Dielectric Relaxation Spectroscopy. The effect of confinement on the local reorientational dynamics is evident by the observation of a relaxation mode, which is much faster than the segmental α-relaxation of the bulk polymer and exhibits much weaker temperature dependence. This is attributed to the restrictions placed by the interlayer spacing on the cooperative volume required for the ax-relaxation.
Molecular Dynamics of Alkanes in Faujasite Zeolites
Authors: Clark L. A. , Ye G. T. , Gupta A. , Hall L. L. , Snurr R. Q. 
Published: April 2011

AbstractMolecular dynamics simulations of C1 through C14 n-alkanes have been used to elucidate diffusion mechanisms in siliceous faujasite zeolites. Additional simulations of the bulk liquids were conducted to compare the liquid and adsorbed phases. Macroscopic quantities, such as heats of adsorption, diffusivities, and activation energies, were calculated and compare well with experimental values. In addition, the simulations provide detailed information about the mechanisms of alkane diffusion in the confined pores of faujasite.
Thin Conducting Polymer Films: Effect of Thickness on Wetting Behavior of Polyaniline Ultra Thin Films
Authors: Li J. , Hill T. H. , Gregory R. V. , Perahial D. 
Published: April 2011

AbstractWetting properties and surface structure of polyaniline (PANI) thin films were studied as a function of the polymer thickness, using AFM and neutron reflectivity. Increasing the oxidation state as well as polymer thickness was found to increase the tendency of the polymer to form polycrystalline films. Three main regions with characteristic behavior were observed: ultra thin films of the order of several molecular layers, an intermediate thickness film of several molecular layers to ∼150nm, and films thicker than 150nm. In the ultra thin region the polymer formed nano-scale spherical domains. In the intermediate one, the films tend to be continuous and amorphous. In the thick films, crystallinity was observed.
Experimental Chemical Kinetics of an A+B→0 System Showing Non-Classical Effects of Initial Reactant Distribution
Authors: Monson Eric , Kopelman Raoul 
Published: April 2011

AbstractWe demonstrate here the implementation of an experimental system suitable for the study of the diffusion-limited A+B→0, non-classical reaction behavior. Using a combination of a fluorescent calcium indicator and a calcium ion which is initially “caged”, a pulse of near-UV light initiates the reaction which is followed as product formation vs. time. Sensitive dependence on the initial reactant distribution is observed through patterns in the uncaging UV light profile. The reaction progress passes through two non-classical time regimes, one due to roughness originating from laser speckles, followed by one exhibiting the three-dimensional Zeldovich rate of (1/ρA − 1/ρA0) ˜ t3/4, with features matching Monte Carlo simulations on this initial distribution.
Effect of Dimensionality and Anisotropy on the Holstein Polaron
Authors: Lindenberg Katja , Romero A. H. , Brown D. W. 
Published: April 2011

AbstractWe apply weak-coupling perturbation theory and strong-coupling perturbation theory to the Holstein molecular crystal model in order to elucidate the effects of anisotropy on polaron properties in D dimensions. The ground state energy is considered as a primary criterion through which to study the effects of anisotropy on the self-trapping transition, with particular attention given to shifting of the self-trapping line and the adiabatic critical point. The effects of dimensionality and anisotropy on electron-phonon correlations and polaronic mass enhancement are studied, with particular attention given to the polaron radius and the characteristics of quasi-l-D and quasi-2-D structures. Perturbative results are confirmed by selected comparisons with variational calculations and quantum Monte Carlo data.
Sliding Friction by Atomic Force Microscopy
Authors: Pasquier V. , Drake J. M. 
Published: April 2011

AbstractLateral Force Microscopy offers the possibility of exploring tribological properties of interfaces atthe nanoscale. Our research focused on some crucial conditions that must be fuffilled to obtainquantitative and reliable LFM friction measurements. We have characterized the mechanical andvibrational properties of the cantilever. Precise force calibration were made based on ourknowledge of the intrinsic coupling modes of the cantilever. We report measurements of the slidingfriction between two silica surfaces. The load dependence of the friction force was analyzedassuming different models for the contact, from Hertzian to Amontons law.
In SITU Spectroscopic Diagnostics of the Influence of Chamber Wall Polymer on Oxide Etch Rate
Authors: Lee Szetsen , Tien Yu-Chung , Hsu Chin-Fa 
Published: April 2011

AbstractThe drift of PECVD TEOS etch rate has been observed during MERIE oxide etch for damascene process. Etch rate typically fluctuates between 5300 Å/min. and 6000 Å/min. depending on chamber condition. Studies using fluorocarbon based chemistry show high TEOS etch rate when chamber wall is heavily coated with polymer deposition. Low etch rate appears when chamber has less deposition. Hysteresis behavior has been observed in TEOS etch rate and emission intensity trends ofF and CFx (x = 1 ∼ 3). From the correlation between etch rate and emission intensity, a model is proposed to explain the impact of chamber wall polymer deposition on TEOS etch rate. It clearly shows that F is directly responsible for the etch of TEOS. Comparing to F, CFx plasma chemistry has a closer link in chamber wall polymer formation, but less contribution in the etch of TEOS.
Plasma-Induced Stabilization of Pmma Surfaces for Enhanced Adhesion of Plasma-Deposited Coatings
Authors: Klemberg-Sapieha J. E. , Martinu L. , Yamasaki N. L. S. , Lantman C. W. 
Published: April 2011

AbstractAdhesion of plasma-deposited optical and protective coatings, such as amorphous hydrogenated silicon nitride, SiN1.3, on polymethyl-methacrylate (PMMA) substrates has been found to be limited by a cohesive failure inside the PMMA bulk. Using direct exposure to a low pressure plasma in helium or to vacuum ultraviolet radiation generated from H2 plasma for an extended period of time, we succeeded to obtain excellent adhesion even under a humidity test at elevated temperature. We found, using a multitechnique approach, that such improved adhesion is achieved by forming a crosslinked, mechanically stabilized layer in the interfacial region, which possesses a physical thickness of 50 to 100 nm.
Analysis of Vibrational Properties of Thin Films Using in-Situ Infrared Ellipsometry: Applications to Polymerlike Amorphous Carbon Films
Authors: Heitz T. , Drevillon B. , Godet C. , Bouree J. E. , Clerc C. 
Published: April 2011

AbstractAn original method is developed to investigate vibrational properties of thin films using infrared (IR) ellipsometry. The procedure is based on in-situ measurements as a function of deposition time. Out of absorption bands, the IR refractive index can be determined and related both to film density and oscillator strengths of electronic transitions. Thanks to band decomposition performed for a given film at different thicknesses, line frequency, band width and intensity of each vibration can be precisely determined, even in case of band overlapping or low IR oscillator strengths. As an illustration, C-H bonding of 1000 Å-thick plasmadeposited polymerlike hydrogenated carbon (PLC) films has been studied. Analysis of the interface between highly saturated PLC films and crystalline silicon reveals the formation of a 20 Å interlayer. Bulk analysis evidences weak vibrations located at 1405 and 1440 cm−1 which had not been observed so far and which are related to π bonds. By combining elastic recoil detection measurements and IR analysis, effective charges of sp3 CHn groups have been calculated. For methyl and methylene groups, these charges are similar to those of hydrocarbon compounds. As far as the sp3 CHn group is concerned, a strong decrease of the effective charge versus film density is evidenced and attributed to the formation of distorted weakly hydrogenated regions induced by ion bombardment.
Infrared-Sensitive Photovoltaic Devices for Thermophotovoltaic Applications
Authors: Fatemi Navid S. , Wilt David M. , Hoffman Richard W. , Weizer Victor G. 
Published: April 2011

AbstractOne of the critical components in a thermophotovoltaic (TPV) system is the infrared-sensitive photovoltaic (PV) semiconductor device that converts the emitted radiation to electricity. Currently, several semiconductor material systems are under development by various workers in the field. The most common are InGaAs/InP, GaSb, and InGaSbAs/GaSb. These devices normally have electronic energy bandgap values in the range of 0.50-0.74 eV. In addition, the design and structure of these devices fall into two distinct formats: conventional planar and monolithic interconnected module (MIM). The conventional planar devices normally have one semiconductor junction and are high-current/low-voltage devices. In a MIM, small area PV cells are connected in series monolithically, on a semi-insulating substrate. This results in the formation of a single high-voltage/low-current module. Electrical and optical performance results for MIMs with electronic energy bandgaps of 0.60 and 0.74 eV will be presented.
Synthesis of Thin Film Battery Components by the Spray Decomposition Technique
Authors: Weil K.S. , Kumta P.N. , Harris J. D. , Hepp A. F. 
Published: April 2011

AbstractThin film LiCoO2 anodes and SnO2 cathodes on the order of 1-10 µtm thick have been synthesized using a spray decomposition technique, employing a lithium-nickel nitrate/methanol solution and tin ethylhexanoate/methanol solution, respectively. Preliminary electrochemical test results on the films indicate that the LiCoO2 anodes in general display a relatively high open circuit voltage (OCV) of ∼4.10-4.25V, good specific capacity on the order of 120 mAh/g, and acceptable cycle-ability, with a 16-25% decay in operating voltage after 50 cycles. The SnO2 films display excellent performance characteristics, upon an expected initial drop in capacity, with an OCV of 1.00-1.10V, specific capacity of ∼600 mAh/g, and virtually no decay in operating voltage after 50 cycles. The solid-state electrolyte, lithium phosphate, was prepared in thin film form by a similar spray processing technique. Additionally, it has been demonstrated that spray decomposition can be used to sequentially deposit the anode, electrolyte, and cathode film layers to form a layered thin film battery (TFB), although electrochemical testing of this thin film device has not yet been conducted.
Microstructural Effects on the Creep and Crack Propagation Behaviours of ³-Ti Aluminide Alloy
Authors: Lupinc V. , Onofrio G. , Nazmy M. , Staubli M. 
Published: April 2011

ABSTRACTGamma titanium aluminides class of materials possess several unique physical and mechanical properties. These characteristics can be attractive for specific industrial applications. By applying different heat treatment schedules one can change the microstructural features of this class of materials. In the present investigation, two heat treatment schedules were used to produce two different microstructures, duplex (D) and nearly lamellar (NL) in the cast and HIP'ed Ti-47Al-2W- 0.5Si alloy.The tensile strength and creep behaviour, in the 700–850°C temperature range, of this alloy have been determined and correlated to the corresponding microstructures. In addition, the fatigue crack propagation behaviour in this alloy has been studied at different temperatures. The results on the creep behaviour showed that the alloy with nearly lamellar microstructure has a strongly improved creep strength as compared with that of the duplex microstructure.
Characterizing Deformation Mechanisms in Ni3Ge-Fe3Ge Intermetallic Alloys
Authors: Balk T. J. , Kumar Mukul , Mryasov O. N. , Freeman A. J. , Hemker K. J. 
Published: April 2011

ABSTRACTThe Ni3Ge-Fe3Ge model system provides us with a unique opportunity to characterize the mechanisms of deformation in both anomalous and normal L12 intermetallic alloys. The elastic moduli of alloys in this system have been measured and used as benchmarks for first principles calculations. At 77K, increasing the Fe content has been found to result in a dramatic increase in flow stress. The Ni-rich alloys exhibit a yield strength anomaly, but as Ni is replaced by Fe, the anomalous temperature dependence gradually disappears, and no yield strength anomaly is observed for alloys with more than 25 at% Fe. At low temperatures and Fe contents, the deformation microstructure has been found to be dominated by Kear-Wilsdorf locking; but a transition from octahedral glide and Kear-Wilsdorf locking to cube glide is observed as either Fe content or temperature is increased. This transition is related to changes that occur in the core structures of dissociated superdislocations and planar fault energies measured through computer simulations of weak-beam TEM images.
Dislocation Dynamics During the Deformation of Intermetallic Alloys and the Flow Stress Anomaly
Authors: Messerschmidt U. , Bartsch M. , Guder S. , Häussler D. 
Published: April 2011

ABSTRACTIn situ straining experiments on NiAl, NiAl-0.2at% Ta, γ-TiAl, and MoSi2 in a high-voltage electron microscope showed a transition from the obstacle controlled dislocation motion or the Peierls mechanism at low temperatures to either an unstable or viscous motion at high temperatures. It is suggested that the viscous motion is due to the formation of point defect atmospheres around the dislocations, which cause additional drag and may be responsible for the flow stress anomaly in some of these materials. The atmospheres may be of an extrinsic or an intrinsic nature. A new model is proposed for the origin of intrinsic atmospheres assuming that the energy of a dislocation in an intermetallic alloy may be lowest if the dislocations contain a number of point defects in their core. The dragging of atmospheres may lead to an “inverse” dependence of the strain rate sensitivity on the strain rate, as observed experimentally. The macroscopic deformation data of the studied materials are discussed in terms of the model.
The Influence of Solid Solutions on Flow Behavior in -γ-TiAl
Authors: Woodward C. , Kajihara S. A. , Rao S. I. , Dimiduk D. M. 
Published: April 2011

ABSTRACTModifications of alloy chemistry are often used to tailor the intrinsic flow behavior of structural materials. Models of solution strengthening, high temperature yield stress and creep must relate the effects of chemistry to the mechanisms that influence these material properties. In ordered alloys, additional information regarding the crystallographic site occupancy of ternary elements is required. In this study relaxed structures and energies for intrinsic and substitutional point defects are calculated using a first principles plane-wave-pseudopotential method. Calculated defect energies are used to predict the density and site preferences of solid-solutions (Si, Cr, Nb, Mo, Ta and W) in ³TiAl. Size and modulus misfit parameters are calculated and the interaction of these defects with a dissociated ordinary screw dislocation evaluated within anisotropic elasticity theory. The derived interaction strength is then related to solid-solution strengthening for these defect centers. Predicted solid-solution effects are in good agreement with experimental observations for the binary alloy.
Effect of Hot Rolling on the Microstructure and Mechanical Properties of Ti3Al Based Dual Phase Alloys
Authors: Wu Jiansheng , Zhang Lanting , Hua Wei , Qiu Guohua 
Published: April 2011

ABSTRACTDevelopment of α2-Ti3A1 based dual phase alloys have shown some promising potentials in property improvement by introducing Ti5Si3sulicide phase into the matrix via Si alloying. However, the presence of coarse network of Ti5Si3phase formed by eutectic reaction in the as-cast state also embrittles the alloy. Both hot rolling and powder metallurgy are considered to be the possible ways to refine the Ti5Si3phase in the matrix. Two Ti-Al-Si-Nb alloys whose Si contents are 2 and 5 at. % respectively were arc melted into ingots and then hot rolled to sheets in this investigation. Optical metallographic examination correlates the microstructures of the as-cast and as-rolled alloys with the different rolling amounts, showing that the coarse silicide network is broken into small particles after hot rolling. Mechanical property testing from room temperature to 8000°C indicates that the strength and plastic elongation of the hot-rolled alloys are much higher than those of the as-cast ones. The data obtained in this investigation are comparable with those obtained in the P/M processed specimens. Fracture surfaces of the alloys are also examined.
Characterization of Laser-Deposited TiAl Alloys
Authors: Zhang X. D. , Brice C. , Grylls R. J. , Evans D. J. , Fraser H. L. 
Published: April 2011

ABSTRACTMicrostructure of TiAl produced by Laser Engineered Net Shaping (LENS) has been characterized using optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It has been shown that the substrate has a significant effect on the microstructure deposited. Depending on operational parameters, either equiaxed γ-TiAl/α2 -Ti3AI or single phase α 2 microstructure can be obtained. In-situ heating experiments reveal that nucleation of lamellae often starts at grain boundaries in this retained α 2grains. By careful control of post heat treatment, an ultra fine lamellar microstructure may be obtained, which may significantly improve tensile property in these alloys [3].
On the Formation of Silicide Precipitates in Niobium-Silicide Based Composites
Authors: Bewlay B. P. , Grylls R. J. , Fraser H. L. 
Published: April 2011

ABSTRACTComposites based on Nb-Si are attractive candidates for use as structural materials at the very high temperatures required for future aircraft engines. The composites described were produced by directional solidification, which gives a microstructure consisting of Nb dendrites with an Nb3Si-Nb eutectic. The aim of this paper is to provide a detailed characterization of precipitates observed in the Nb dendrites in both binary and higher-order alloys. The precipitates possess the Nb3Si stoichiometry, but not the stable Nb3Si structure. The precipitates form a metastable orthorhombic crystal structure which is related to the Nb matrix via a simple orientation relationship.
An Investigation on Dynamic Tensile Properties of TiAl Intermetallic Alloy
Authors: Wang Yu , Lin Dongliang , Zhou Yuanxing , Xia Yuanming , Law Chi C. 
Published: April 2011

ABSTRACTRoom-temperature tensile properties of polycrystalline Ti–;47A1–2Mn–;2Nb alloy with nearly lamellar (NL) microstructures were investigated at the strain rates between 10-;5 and 1000 s-1 using a self-designed Split-Hopkinson tensile bar setup with a rotating disk and conventional testing machine. It was found that tensile ductility varies within a narrow range with the strain rate while dynamic strengths (σd) of the alloy are obviously higher than static strengths (σs). There exists a linear relationship between σs and the logarithm of the strain rate , and between σ d and the strain rate itself (). Fractography analysis indicated that the alloy fractured in a mixed mode of predominant transgranular cleavage and minor intergranular cracking under static and dynamic strain rates. Environmental effect was excluded from the main cause for the room-temperature brittleness of the investigated alloy.
The Influence of Second-Phase Dispersion on Environmental Embrittlement of Ni3(Si, Ti) Alloys
Authors: Takasugi T. , Hanada S. 
Published: April 2011

ABSTRACTSome quaternary Ni3(Si, Ti) alloyed with transition elements V, Nb, Zr and Hf was prepared beyond their maximum solubility limits to investigate the effect of second-phase dispersion on moisture-induced embrittlement. V-added Ni3(Si, Ti) alloy contained ductile fcc-type Ni solid solution as the second-phase, while Nb-, Zr- and Hf-added Ni3(Si, Ti) alloys contained hard dispersion compounds as the second-phase. V- and Nb-added Ni3(Si, Ti) alloys did not display reduced tensile elongation in air, indicating that their second phases have the effect of suppressing the moisture-induced embrittlement. Possible mechanisms for the beneficial effect by the second phase on the moisture-induced embrittlement of V- and Nb-added Ni 3(Si, Ti) alloys are discussed in association with hydrogen behavior and deformation property in the constituent phases or at matrix/second-phase interface.
Self-Diffusion of Both Components in the Intermetallic Laves Phase NbCo2
Authors: Denkinger M. , Mehrer H. 
Published: April 2011

ABSTRACTSelf-diffusion of57Co and95Nb in the cubic Laves phase NbCo2 has been studied using the radiotracer method. The temperature dependences of the self-diffusivities are described for Nb31Co69 by,and for Nb29Co71 by,The diffusivity of 95Nb in Nb31Co69 is considerably lower than that of 57Co. The latter increases significantly with increasing Co content.The results are discussed in terms of vacancy mediated diffusion in connection with structural aspects of the Laves phase together with the scarce information available for defects in NbCo2. The results are compared with interdiffusion data from our laboratory and with self-diffusion in the also close-packed L12 intermetallics.
Mechanical Properties of L12 Type Zn3Ti-Base Alloy
Authors: Hosoda Hideki , Hanada Shuji 
Published: April 2011

ABSTRACTAn alloy composed of L12-type Zn3Ti was investigated in terms of phase stability and mechanical properties. Zn and Ti powders were mixed at a composition of Zn-25mol%Ti using a ball mill in Ar, and an ingot was made by melting the powders. Optical microscopy, X-ray diffraction analysis and thermogravimetry - differential thermal analysis were carried out. Mechanical properties were investigated by Vickers hardness tests at room temperature (RT) and compression tests from RT to 703K in Ar. It is found that (1) the alloy is mainly composed of L12 Zn3Ti, (2) the alloy has weak positive temperature dependence of strength, and (3) normalized strength by melting point is comparable to that of L12 Al3Ti-Cr alloys. L12 Zn3Ti has HV178 and is brittle at RT. Reaction temperatures of Zn-rich portion of the Zn-Ti phase diagram were also reinvestigated and a peritectic-reaction temperature between Zn3Ti and liquid + Zn2Ti is determined to be at 880K.
An Assessment of the Method Used to Determine Activation Parameters in L12 Alloys
Authors: Matterstock B. , Saada G. , Bonneville J. , Martin J. L 
Published: April 2011

ABSTRACTThe characterisation of dislocation mechanisms in connection with macroscopic mechanical properties are usually performed through transient tests, such as strain-rate jumps, load relaxations or creep experiments. The present paper includes a careful and complete theoretical analysis of the relaxation and the creep kinetics. We experimentally show that the plastic strain-rate is continuous at the transition between constant strain-rate conditions and both load relaxation and creep test. The product of the plastic strain-rate at the onset of the transient test () with the characteristic time (tk) of the transient is found to be independent of , as theoretically expected. This is a clear indication that the assumptions underlying the theoretical analysis are relevant.