bluuebunny/crossref_metadata_2025_split huggingface dataset:
Athermal Fracture of Covalent Bonds
Authors: Gilman J. J. 
Published: April 2011

AbstractMost fracture is athermal. Either because it occurs at low temperatures; or because it occurs too fast for thermal activation to be effective. Thus it must be directly activated by applied stresses. This can occur via quantum tunneling when the chemical bonding of a solid resides in localized (covalent) bonds. Then applied stresses can cause the bonding electrons to become delocalized (anti-bonded) through quantum tunneling. That is, the bonds become broken. The process is related to the Zener tunneling process that is thought to be responsible for dielectric breakdown in semiconductors. Under a driving force, bonding electrons tunnel at constant energy from their bonding states into anti-bonding states through the forbidden gap in the bonding energy spectrum.
Experiments and Simulations of Directionally dependent Fracture along Copper/Sapphire Interfaces
Authors: Kysar Jeffrey W. 
Published: April 2011

AbstractTo test the hypothesis that the brittleness and ductility of crystalline materials are controlled by a competition between dislocation nucleation and cleavage failure at a crack tip, Riceet al.[1] designed a four-point bend copper/sapphire bicrystal which has two cracks that propagate along the interface in opposing directions. They predicted, on the basis of the Rice-Thomson model [2], that the specimen would exhibit a directionally dependent fracture behavior; that is, one crack would propagate more readily than the other. Beltz and Wang [3] carried out the experiments and reported that the specimen exhibits a directionally dependent fracture behavior in accordance with the predictions. In the present work, these experiments are repeated independently and it is shown thatthe orientation of the experimentally observed directionally dependent behavior is opposite that of the predicted orientation.Furthermore, we show that Beltz and Wang incorrectly measured the orientation of the directional dependence in their experimental results. A correct interpretation of their results is consistent with the present work.Taking advantage of the transparent sapphire, the normal crack opening displacement (NCOD) profile of both cracks is measured with optical interferometry. The measurements show that, away from the very tip of the crack, the NCOD takes the form of a constant angle, irrespective of load level. The opening angle of the apparently brittle crack is smaller than that of the apparently ductile crack. Complementary measurements of the very tip of the crack with Atomic Force Microscopy show that the near-tip crack opening profiles of the brittle and ductile cracks differ significantly.The specimen is analyzed with the Finite Element Method, taking into account the elastic and plastic properties of the single crystal constituents. Since the very essence of the observed phenomenon is one of crack growth, the two cracks are simulated as they grow quasistatically along the interface. The asymptotic deformation fields, characteristic of single crystals, of the growing interfacial cracks are identified. The stress and strain fields, as well as the NCOD, are calculated. We present a plausible explanation of the directional dependence of fracture on the basis of the continuum plastic fields surrounding the quasistatically growing cracks.
Atomistic Modeling of Grain Boundary Fracture in Diamond
Authors: Shenderova O.A. , Brenner D.W. , Omeltchenko A. , Su X. , Yang L. 
Published: April 2011

AbstractMolecular dynamics simulations using a bond-order potential were carried out to investigate the behavior under load of several <001> and <011> symmetrical tilt grain boundaries in diamond. Cohesive energies, work for fracture, maximum stresses and strains as functions of the type of grain boundary were evaluated. It was found that special short-periodic GBs possess higher strength and resistance to a crack propagation than GBs in the nearby misorientation range. Crack behavior in polycrystalline diamond samples under an applied load was also simulated, and found to be predominantly transgranular.
Metallorganic Chemical Vapor Deposition of Ir Films With Iridium Acetylacetonate and Carbonyl Precursors
Authors: Sun Y.-M. , Endle J. , Smith K. , Ekerdt J. G. , Hance R. L. , Alluri P. , White J. M. 
Published: April 2011

AbstractIridium acetylacetonate, dicarbonylacetylacetonato iridium, and tetrakisiridium dodecacarbonyl (iridium carbonyl) have been evaluated for metallorganic chemical vapor deposition (CVD) of pure iridium films. Temperature programmed mass spectroscopy reveals that iridium tris-acetylacetonate and dicarbonylacetylactonato iridium have high thermal stability and sublime at 200 and 100 °C in vacuum, respectively. Iridium carbonyl decomposes upon sublimation at temperatures above 120 °C. Pure CVD Ir films were obtained using iridium carbonyl; however, carbon is incorporated into the iridium films with the iridium trisacetylacetonate and dicarbonylacetylactonato iridium precursors unless a reactive gas, such as oxygen is co-dosed. Co-dosed oxygen also increases the film deposition rate and significantly decreases the film growth temperatures. Particles were found on the films grown with iridium carbonyl between 280 to 400 °C, indicating that gas phase nucleation occurred during deposition.
Origin of Imprint in Ferroelectric CSD SrBi2Ta2O9 Thin Films
Authors: Grossmann M. , Lohse O. , Bolten D. , Waser R. , Hartner W. , Schindler G. , Nagel N. , Dehm C. 
Published: April 2011

AbstractThe imprint behavior of CSD processed SrBi2Ta2O9 (SBT) thin films has been investigated as a function of time, applied bias, illumination with band gap light and post anneal under different oxygen partial pressures. Applying a bias in the direction of the polarization enhances the tendency of the capacitor to exhibit a voltage shift as well as illuminating the poled capacitor with band gap light. Post anneal after top electrode deposition and patterning under slightly reducing atmospheres does not affect the imprint rate. From these experimental results, a model is presented which explains the imprint behavior of SBT films by transport of electronic charges from the electrodes into the film and subsequent trapping of these charges near the interface.
Optical Properties of Sol-Gel Derived PbTiO3 and PbZr1−xTiO3 Ferroelectric Thin Films
Authors: Meng Xiangjian , Huang Zhiming , Ye Hongjian , Cheng Jiangong , Yang Pingxiong , Chu Junhao 
Published: April 2011

AbstractWith sol-gel processing and rapid thermal annealing (RTA), crack-free PbTiO3 and PbZr1−xTixO3(x=0.2-0.8) ferroelectric thin films were prepared on Si(100) and Pt/Ti/SiO2/Si(100) substrates respectively. Results from x-ray diffraction (XRD) show that the films are single perovskite phase structure. Scanning electron microscopy (SEM) was used to determine the grain sizes of the thin films. Energy dispersive spectroscopy (EDS) of x rays was used to analyze the composition of the films. From infrared reflection spectroscopy in the wavelength region of 40-700 cm−1 at 300K, the vibrational mode frequencies in PbTiO3 thin films on silicon substrates were obtained at the wavenumbers of 79, 155, 206, 298, 344, 461, 520 and 621 cm−1. Among these phonon modes, the modes at 298 and 461 cm−1 have not been reported before. The infrared optical constants and the thickness of PZT thin films on Pt/Ti/SiO2/Si(100) substrates were directly measured in the wavelength region of 2-12μm by an automatic wavelength swept infrared spectroscopic ellipsometer. These constants include: refractive index (n), extinction coefficient (k), thickness of the films and absorption coefficient (α). Possible correlation among the processing, microstructure and optical properties of the thin films were discussed.
Dielectric Relaxation in a Deeply Supercooled Liquid Crystals Confined in Random Porous Media
Authors: Sinha G. P. , Aliev F. M. 
Published: April 2011

AbstractLiquid crystals (LCs)—pentylcyanobiphenyl (5CB) and octylcyanobiphenyl (8CB)—were confined in random porous media with narrow pores of mean size equal to 100 Å and investigated by means of broad band dielectric spectroscopy in deeply supercooled state. In liquid crystalline phases, bulk 5CB and 8CB have two dielectrically active modes. The main mode with the relaxation time τ ∼ 10”8s is due to the rotation of molecules about their short axis, and the secondary mode is due to the tumbling motion of molecules with the relaxation time ツ ∼ 10”10s. Bulk 5CB and 8CB are nonglass formers and they crystallize at cooling. The confinement strongly influences the dynamical behavior of LCs and is resulted in qualitative changes in their properties. Deep supercooling of LCs in pores up to ∼ 150 degrees below the bulk crystallization temperature was observed. The relaxation rate of the process due to the molecular rotation in deeply supercooled state is slower than at the temperatures corresponding to nematic phase by many orders of magnitude. This slowing down is accompanied by anomalous broadening of the dielectric spectra.Other new properties observed in confined LCs are two low frequency relaxation processes absent in bulk LCs. One of these processes is due to the molecular relaxation in the surface layers at liquid crystal-solid pore wall interface. The second process is probably a collective mode due to the relaxation of the surface induced polarization. The collective process due to surface polarization and the surface molecular mode show features typical for glass formers.
Plasma Grafit Polymerized Styrene as an Electron-beam Resist
Authors: Morita Shinzo , Ogawa Shinji , Suzuki Mikinori , Kashem Md. Abul 
Published: April 2011

AbstractPlasma graft polymerized styrene was formed by a reactor with a parallel plate electrode system on a pulsed plasma polymerized styrene film in a monomer vapor, where the pulsed plasma polymerization was performed by a low frequency 100%pulse modulation of 13.56 MHz power source in styrene vapor. The pulse duration was varied in the range of 0.01∼1 sec and ON time/duty cycle ratio was 1/10 and 1/20. The processes were monitored by a quartz crystal microbalance. The initial stage of plasma polymerization and grafting are discussed in this paper. Also sub 100 nm lines and spaces pattern on the resist delineated by an electron-beam pattering machine was developed by hexane.
Plasma Sterilization: Spore Destruction by Microwave Plasmas
Authors: Lerouge S. , Fozza A. C. , Wertheimer M. R. , Marchand R. , Tabrizian M. , Yahia L'H 
Published: April 2011

AbstractLow-pressure plasmas are now being used for sterilization at ambient temperature. In this work, we have studied the possible mechanism of spore destruction by plasma, and compare it with etching of synthetic polymers. Bacillus subtilis spores were inoculated at the bottom of special glass vials and subjected to different plasma gas compositions, all known to etch polymers. The mortality rate of spores was found to vary with gas composition, between less than a 2 log decrease in 8 minutes for a pure oxygen plasma, to a 6 log decrease with 02CF4 mixture. Examination by scanning electron microscopy (SEM) showed that spores were significantly etched after 30 minutes of plasma exposure, but not completely. We speculate about their etch resistance, compared with that of synthetic polymers, on the basis of their morphology and their complex coating structure.
Electrodeposited CIS-Based Solar Cell Materials
Authors: Raffaelle R.P. , Potdevin T. , Mantovani J.G. , Friedfeld R. , Gorse J. , Breen M. , Bailey S.G. , Fhepp A.F. 
Published: April 2011

AbstractWe have been investigating the synthesis of novel materials and device structures based on CuInSe2 or CIS system We are interested in developing CIS for use in thin film photoltaic solar cells used in space power systems. Non-stoichiometric native defects allow CIS to be selectively doped n or p type by controlling the Cu to In ratio. The Cu to In ratio of an electrodeposited CIS thin film is shown to be directly proportional to the deposition voltage. This behavior has allowed us to deposit different semiconductor-type films, pn junctions, and multilayer structures from the same aqueous solution. The affect of annealing in an Argon atmosphere and the addition of a wetting agent to our deposition solutions on the structural and electrical behavior of our films was measured. A dramatic improvement in the crystallinity, which was proportional to the annealing temperature was observed. The addition of a wetting agent to the solution was shown to improve the surface morphology and provide uniformity in the grain size. The electrical characterization of Schottky barriers on the CIS showed a decrease in several orders of magnitude of the carrier density with annealing. The ability to incorporate our CIS-based films in pn junction devices using CdS window layers was demonstrated by the rectifying current versus voltage behavior of these junctions.
Genetically Engineered Nanostructure Devices
Authors: Klimeck Gerhard , Salazar-Lazaro Carlos H. , Stoica Adrian , Cwik Thomas 
Published: April 2011

AbstractMaterial variations on an atomic scale enable the quantum mechanical functionality of devices such as resonant tunneling diodes (RTDs), quantum well infrared photodetectors (QWIPs), quantum well lasers, and heterostructure field effect transistors (HFETs). The design and optimization of such heterostructure devices requires a detailed understanding of quantum mechanical electron transport. The Nanoelectronic Modeling Tool (NEMO) is a general-purpose quantum device design and analysis tool that addresses this problem. NEMO was combined with a parallelized genetic algorithm package (PGAPACK) to optimize structural and material parameters. The electron transport simulations presented here are based on a full band simulation, including effects of non-parabolic bands in the longitudinal and transverse directions relative to the electron transport and Hartree charge self-consistency. The first result of the genetic algorithm driven quantum transport calculation with convergence of a random structure population to experimental data is presented.
Materials for Thermal Control for Mars Surface Operations
Authors: Hickey Gregory S. 
Published: April 2011

AbstractThe thermal environment for Mars surface exploration provides unique challenges for materials for use in structure and thermal control. The Sojourner Mars Rover has a lightweight integrated structure/insulation that has been environmentally tested and qualified for the Pathfinder mission to Mars. The basic structure with insulation, called the Warm Electronics Box (WEB), accounts for only 10% of the total Rover mass. The WEB is a thermal isolating composite structure with co-cured thermal control surfaces and an ultra-lightweight hydrophobic solid silica aerogel which minimizes conduction and radiation. This design provides excellent thermal insulation at low gas pressures and meets the structural requirements for spacecraft launch loads and for a 60 g impact landing at Mars without damage to the insulation or structure. Since the Pathfinder mission, this basic design concept has been developed and improved for future Mars surface robotic missions.
Work Hardening Characteristics and Recovery of Gamma Base Titanium Aluminides
Authors: Appel F , Sparka U. , Müllauer J. 
Published: April 2011

ABSTRACTThe work hardening behaviour of gamma base titanium aluminides was investigated by mechanical testing, electron microscope observations and recovery experiments. The main objectives of the paper are: (i) to ascertain the nature of work hardening at room temperature, (ii) to identify deformation induced glide obstacles which can be overcome with the aid of thermal activation, (iii) to assess the thermal stability of deformation induced defect structures.
Orientation Effect on the Stress Response by Strain-Rate Change at 400K in Ni3Al Single Crystals
Authors: Demura M. , Hirano T. 
Published: April 2011

ABSTRACTCyclic strain-rate change tests were performed by using binary, stoichiometric Ni3Al single crystalline specimens with different tensile orientations at 400 K. In all the specimens, the flow stress was independent of strain rate in steady state and exhibited a temporary change by the strain-rate change. The characteristics of the temporary stress change, the initial stress change and transient time, were independent of orientation. Based on the multiplication-immobilization model, we concluded that the immobilization mechanism, the Kear-Wilsdorf locking mechanism, is independent of orientation in binary, stoichiometric Ni3Al.
On the Role of Lamellar Interfaces on the Strength and Ductility of Two-Phase Titanium-Aluminum
Authors: Wiezorek Jürg M. K , Dong Xiao Dong , Mills Michael J. , Fraser Hamish L 
Published: April 2011

ABSTRACTThe deformation mechanisms active in hard orientation compressed pst-TiAl have been studied by transmission electron microscopy (TEM). The observed deformation modes involved soft superdislocation and hard ordinary dislocation slip, and hard twin systems. The transfer of these twin shears occurred across all types of (γ/γ)-interfaces. Transfer mechanisms have been determined on the basis of crystallographic analyses of the TEM data. The active modes of deformation were consistent with macroscopic shape changes observed for the pst-TiAl when the twin shear transfer mechanisms were considered. Based on these observations it has been proposed that the strength and ductility of polycrystalline fully-lamellar TiAl may be improved by reducing the width of both γ- and α2-lamellae.
Ductility and Fracture of FeAl: Effects of Composition and Environment
Authors: Cohront J. W. , Lin Y. , Zee R. H. , George E. P. 
Published: April 2011

ABSTRACTIn ultrahigh vacuum (UHV), the ductility of FeAl decreases with increasing Al content and fracture becomes increasingly intergranular. Boron improves ductility by segregating to the grain boundaries and suppressing grain-boundary fracture. However, with increasing Al concentration, even the B-doped alloys become brittle and fracture intergranularly. Hydrogen gas at low pressures embritties FeAl, although not as severely as atmospheric moisture. Ductility is highest in UHV followed by that in O2, vacuum, and air.
Effect of A12Ti Phase on Plastic Behavior in Ti-62.5at%Al Single Crystals
Authors: Nakano Takayoshi , Hayashi Koutarou , Ashida Keishi , Umakoshi Yukichi 
Published: April 2011

ABSTRACTThe microstructure and plastic deformation behavior in Ti-62.5at.%Al single crystals were investigated focusing on effect of the formation of h- and r-AI2Ti precipitates. Crystal structure, morphology and volume fraction of the precipitates depended strongly on the annealing temperature. The r-A12Ti phase precipitated as a plate in the Li0 matrix containing A15Ti3 superstructure below 1200°C, while the h-Al2Ti phase appeared at the higher temperature. The r-A12Ti had six-fold periodicity along the c-axis of the L10 structure and formed a semi-coherent boundary with the matrix maintaining an orientation relationship with {101)r-A12Ti//{101)L10 In contrast, small particles of h-A12Ti with three-fold periodicity along the b-axis were homogeneously distributed in the matrix forming an obscure coherent phase boundary.Yield stress for specimens with a [201] loading axis anomaly increased showing a maximum peak around 800°C and then rapidly decreased. [111] <110] slip was dominant in the Li0 matrix and research-article-Al2Ti precipitates at temperatures below the peak, while slip occurred on (001) above the peak temperature. The anomalous strengthening and the change in operative slip system were discussed focusing on the effect of anisotoropy of APB energy and formation of Al2Ti precipitates.
Determination of the Effect of Hf Additions on Phase Stability in Nb-Silicide Based In-Situ Composites
Authors: Bewlay B. P. , Zhao J.-C. , Jackson M. R. , Bishop R. R. 
Published: April 2011

ABSTRACTIn-situ composites based on Nb-Si alloys are potential candidates for application as structural materials in future aircraft engines. In order to achieve the balance of properties that is required, additional alloying species, such as Ti, Hf, Mo, Cr, Al, are employed. The present paper describes the effect of Hf additions on phase stability of Nb-Si alloys. Liquid-solid and solid-state phase equilibria have been investigated. The Nb-Hf-Si liquidus surface and the isothermal section at 1500°C will be described. A broad range of Nb and Hf compositions were investigated for Si concentrations up to 35.0%.
Fine Structures of the Pyramidal Slip Dislocations in Ti3Al Single Crystals at Temperatures of the Yield Stress Anomaly
Authors: Minonishi Yasuhide 
Published: April 2011

ABSTRACTThe <1126>(1121) pyramidal slip in Ti3Al shows the so-called yield stress anomaly. A marked change in dislocation configuration is observed in the temperature range concerned; dislocations observed at the lowest temperature of the range, −70°C, are ordinary pairs of edge c+a/2 superpartial dislocations coupled by antiphase boundaries (APBs) while at the other extreme temperature 700°C, pairs of unlike superpartials coupled by APBs are observed. The change in dislocation configurations is interpreted as resulting from immobilization of edge c+a/2 superpartial segments by climb dissociation onto the basal plane.
Internal Friction in Plastically Deformed High-Purity NiAl Single Crystals
Authors: Hirscher M. , Schaible D. 
Published: April 2011

ABSTRACTHigh-purity stoichiometric NiAl single crystals have been prepared by crucible-free inductive zone melting and afterwards well annealed at temperatures below 1200 K. Internal friction measurements of torsionally deformed single crystals show two relaxation maxima at 500 and 800 K which anneal during the measurement. The first maximum can be assigned to the dislocation motion by kinkpair formation and the annealing to pinning of these dislocations by interstitial impurity atoms. The second maximum is attributed to the Snoek-Köster relaxation of dislocations in the presence of mobile interstitial impurity atoms and the annealing to the pinning of dislocations by vacancies. The kink-pair formation enthalpy in NiAl was estimated.
First-Principles Total Energy Study of NbCr2 + V Laves Phase Ternary System
Authors: Ormeci Alim , Chen S. P. , Wills John M. , Albers R. C. 
Published: April 2011

ABSTRACTThe C15 NbCr2 + V Laves phase ternary system is studied by using a first-principles, self-consistent, full-potential total energy method. Equilibrium lattice parameters, cohesive energies, density of states and formation energies of substitutional defects are calculated. Results of all these calculations show that in the C15 NbCr2 + V compounds, V atoms substitute Cr atoms only.