bluuebunny/crossref_metadata_2025_split huggingface dataset:
Assembling Small Fullerenes: A Molecular Dynamics Study
Authors: Gallic Giulia , Canning Andrew , Kim Jeongnim 
Published: April 2011

ABSTRACTUsing tight-binding molecular dynamics, we have performed two series of computer experiments assembling small fullerenes: first, we have simulated the deposition of C28 clusters on a semiconducting surface, and then we have performed calculations mimicking the gas phase growth of a small fullerene solid. The results of the two computations are discussed and compared to those obtained for ordered forms of C28 solids.
Electron Emission Through Tetrahedral Amorphous Carbon Coatings on Mo and Si Emitters
Authors: Choi W. B. , Myers A. F. , Ding M. Q. , Sharma A. K. , Narayan J. , Hren J. J. , Cuomo J. J. 
Published: April 2011

ABSTRACTThe field emission properties of molybdenum and silicon emitter coated with tetrahedral amorphous carbon (or amorphous diamond) were studied. The tetrahedral amorphous carbon was deposited by laser ablation and showed a uniformly coated columnar structure over the entire emitter. In general, current conditioning improved stability and increased the current density. Coatings of ta-C on Mo emitters with and without nitrogen incorporated both yielded significantly higher emissivity than uncoated emitters. Nitrogen incorporation reduced the effective workfunction and the sp3/sp2 ratio. However similar depositions on Si emitters reduced the emissivity, and may be attributable to the residual oxide at the ta-C/Si interface. Annealing in a hydrogen atmosphere enhanced emissivity from both ta-C/Mo and ta-C/Si emitters. In general, thick coatings lowered the emissivity and the slope of the I-V curves. A temperature dependence of emission was observed only in the low field regions.
On the Effects of the Thermal Treatment on the Structural, Mechanical and Tribological Properties of Amorphous Carbon-Nitrogen Films Deposited by Magnetron Sputtering
Authors: Lacerda M. M. , Freire F. L. 
Published: April 2011

ABSTRACTAmorphous carbon-nitrogen films, a-CNx, deposited by rf-magnetron sputtering in N2 atmosphere were annealed in vacuum at temperatures between 300 and 700 °C. The annealing time was 30 minutes. The modifications on the film microstructure were monitored by infrared spectroscopy (IR), while the composition and the atomic density were determined by Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERDA) and nuclear reaction analysis (NRA). The internal stress was determined by measuring the film-induced bending of the substrate and the hardness was measured by nanoindentation. Atomic force microscopy (AFM) provided the friction coefficient and the surface roughness. The ratio between nitrogen and carbon atomic concentration decreases for temperatures higher than 500 °C, whereas the film density increases with the annealing temperature: 40 % in the temperature range here studied. The behavior of the D and G Raman bands, IR active due to the nitrogen incorporation in the carbon network, suggests a progressive increase of the size of the graphite-like domains. The hardness of the as-deposited a-CNx film is around 2 GPa. However, both hardness and internal stress increase by a factor of three in samples annealed at 700 °C, while the surface roughness and the friction coefficient decrease by a factor of about two.
Studies of the Growth and Local Atomic Bonding of a-CxNyHz Films
Authors: Efstathiadis H. , Akkerman Z. , Smith F. W. 
Published: April 2011

ABSTRACTA systematic study of the growth and local atomic bonding (LAB) of a series of a-CxNyHz alloy films prepared via plasma enhanced chemical vapor deposition (PECVD) from mixtures of NH3/C2H2 and N2/C2H2 is presented. The effects of the reactants and their ratio on the film composition and bonding of hydrogen, the optical constants, and the optical energy gap have been determined. It is found that the presence of nitrogen and hydrogen in the plasma decreases the net film deposition rate due to enhanced etching and that incorporation of nitrogen into the film is limited to N/C ≈0.1. For the films deposited from N2/C2H2 as the concentration of N in the film increases, the concentration of C also increases while that of H decreases. No evidence for the type of bonding expected in the theoretically-predicted C3N4 compound has been found. It is observed that hydrogen is preferentially bonded to nitrogen and there is evidence for N-H…N hydrogen bonding in the films. The predictions of the free energy model (FEM) previously developed for the bonding in a-CxNyHz alloys are compared with these experimental results. The importance of entropy in determining the most stable state of these alloys is demonstrated. The FEM successfully predicts and explains some of the experimentally-observed properties of the alloys.
Structure, Optical and Electrical Properties of Pulsed Laser Deposited and Ion Beam Deposited CNx Films
Authors: Chan K. F. , Zhao X.-A. , Ong C. W. 
Published: April 2011

ABSTRACTCNx films were deposited using pulsed laser deposition (PLD) and ion beam deposition (IBD). The PLD films deposited at substrate temperature Ts = 25°C and high N2 partial pressure have the highest N content (fN) and polymerlike structure, accompanied by large band gap (Eg) and low electrical conductivity (σroom). The rise in Ts lowers fN and induces graphitization of the film structure, so Eg reduces and σroom increases. IBD (with and without N2+ assist) films are graphitic. Higher Ts further enhances the graphitization of the film structure, such that the conduction and valence bands overlap, and σroom approaches to that of graphite. No evidence was found to show successful formation of the hypothetical β-C3N4 phase in the films.
X-Ray Structural Study of Li3N at High Pressure
Authors: Ho Allen C. , Granger Maurice K. , Ruoff Arthur L. 
Published: April 2011

ABSTRACTThe equation of state (EOS) of Li3N has been determined by energy-dispersive x-ray diffraction (EDXD) using synchrotron radiation up to 35 GPa at ambient temperature. Both the hexagonal D6h4(P63/mmc) and the hexagonal D6h1(P6/mmm) phases were present at ambient pressure. The D6h1 -structure completely transforms into the D6h4 -structure at modest pressure. The change in Gibb's free energy as a function of pressure for Li3N was calculated using the experimental EOS.
High-Pressure Properties of Na3ClO Anti-perovskite from First Principles: an exploratory study
Authors: Chizmeshya A. V. G. , Sankey O. F. , McMillan P. F. 
Published: April 2011

ABSTRACTWe present the results of an exploratory theoretical study of Na3ClO in the anti-perovskite structure. The FLAPW method is used to calculate the static lattice properties, pressure equation of state, and the ferroic Flu phonon frequencies in the cubic PmSm phase. We also compute the compression behavior of NaCl and Na2O and find that the lattice energy of Na3ClO at ambient pressure (static lattice) is only marginally larger than of products, in agreement with experiment. However, detailed calculations reveal M- and R-point phonon instabilities in the ideal cubic phase and suggest the existence of lower symmetry structure involving slight rotations of ONa6 octahedra.
Magnetic Collapse and the Behavior of Transition Metal Oxides: FeO at High Pressures
Authors: Cohen R. E. , Fei Y. , Downs R. , Mazin I. I. , Isaak D. G. 
Published: April 2011

ABSTRACTLinearized augmented plane wave (LAPW) results are presented for FeO at high pressures using the Generalized Gradient Approximation (GGA) to study the high-spin low-spin transition previously predicted by LAPW with the Local Density Approximation (LDA) and Linear Muffin Tin Orbital (LMTO-ASA) methods within the GGA. We find a first-order transition at a pressure of about 105 GPa for the cubic lattice, consistent with earlier LAPW results, but much lower than obtained with the LMTO. The results are generally consistent with recent Mössbauer experiments that show a transition at about 100 GPa. We also discuss the origin of the transition, and show that it is not due to electrostatic crystal-field effects, but is rather due to hybridization and band widening with pressure. Examination of experimental data and computations suggest that the high pressure hexagonal phase of FeO is likely a polytype between the B8 NiAs and anti-B8 AsNi structures. The former is predicted to be an antiferromagnetic metal, and the latter an antiferromagnetic insulator. Implications for geophysics are discussed.
Ruby's Optical Transitions: Effects of Pressure-Induced Phase Transformation
Authors: Duan Wenhui , Paiva G. , Wentzcovitch Renata M. , Fazzio A. 
Published: April 2011

ABSTRACTHere we summarize our investigation of the effect of a recently observed phase transformation on ruby's optical transitions. This study involved a first principles calculation of the electronic and structural properties of a chromium impurity in alumina host lattices and a subsequent calculation of the multiple structure using eigenvalues and eigenvectors derived from the first principles calculation. This investigation is relevant to clarify the behavior of the fluorescent optical transitions which are used as pressure sensor in diamond anvil experiments across the structural transformation.
Diffusivity and Nuclear Spin Relaxation Measurements at High Pressure in Methanol
Authors: Marzke R. F. , Raffaelle D. P. , Wolf G. H. , Yarger J. L. 
Published: April 2011

ABSTRACTDiffusivity D and nuclear spin relaxation times T1 and T2 have been measured by NMR to 4.0 GPa in methanol, using a diamond anvil cell probe. In pure MeOH, D−1 and T2 show essentially identical activation volumes. However, these are ∼18% larger than the activation volume of viscosity. By relating these observations to an average molecular correlation time a pressure-dependent infinite-frequency shear modulus G∞ can be inferred, using two independent approaches. The relation between diffusivity and viscosity shows increasing departure from Stokes-Einstein behavior with increasing pressure, if a constant hydrodynamic radius is assumed. This departure is attributed to the pressure dependence of G∞, and can be described empirically by a simple modification of the Stokes-Einstein relation.
Laser Peening of Metals - Enabling Laser Technology
Authors: Brent Dane C. , Hackel Lloyd A. 
Published: April 2011

ABSTRACTLaser shot peening, a surface treatment for metals, is shown to induce compressive residual stresses of over 0.040 inch to provide improved resistance to vairous forms of failure. A solid state laser technology employing Nd:glass slabs and phase conjugation enables this process to move into high throughput production processing. Details of the technology are discussed.
High Pressure Carbon Behavior Induced from Carbide Hugoniots
Authors: Sekine T. , Takazawa E. , Kobayashi T. 
Published: April 2011

ABSTRACTInvestigations of Hugoniots the diamond-type carbides(various SiC) and NaCl-type carbides such as TiC give some insights into the high-pressure carbon behaviors. The experimental results of phase transitions of a-SiC and β-SiC, together with those of diamond-structure Si, imply that the candidate as post-diamond phase has sixfold coordination and that a possible transition pressure is about 1–2 TPa. The NaCl-type carbide Hugoniots indicate that sixfold coordinated C is very stable at high pressures. The partial molar volume of carbon in the NaCl-type carbides ranges between 1.4 to 2.6 cnvVg-atom C at 1 atm and reaches about 2.8 cm3/g-atom C at 100 GPa. Taking into account structural variations of the corresponding metals, the volume of the sixfold coordinated C is estimated to be 1.7 cm3/g-atom C, about half of that of diamond, and the post-diamond phase appears to be extremely hard.
Influence of surface silanol structure and hydration forces on alkoxide-derived silica gel structure
Authors: Kamiya H. , Yoshida M. , Mitsui M. 
Published: April 2011

ABSTRACTThe effects of the surface silanol structure and interaction force between solid surfaces in water on the gel structure using acid catalyzed hydrolysis alkoxide-derived silica gels with various preparation conditions. The present study focused on the amount of catalysts and H2O/TEOS mole ratios. Surface silanol structure, interaction between solid surfaces and the structure in dried-gels were determined by a FT-nIR, FT-IR, Atomic Force Microscope (AFM) and a mercury porosimetry, respectively. As results, when a relatively low H2O/TEOS mole ratio ( from 4 to 40) was used, surface silanol was almost hydrogen bonded silanol, and isolated silanol disappeared. Since this hydrogen-bonded silanol formed a hydrogen bonded water layer on silica surface, short-range additional hydration force (less than 2 nm) appeared between solid surface and the tip of AFM. When H2O/TEOS mole ratio increase in the range from 20 to 40, the surface density of isolated silanol increased and that of residual Si-OC2H5 decreased. Relatively long-range additional repulsive force on these silica gels reached 20 nm from solid surface. The pore diameter in each dried gel almost corresponded to the surface distance, which acted the additional repulsive force.
Nanocrystalline Materials as Potential Gas Sensing Elements
Authors: Coles G. S. V. , Williams G. 
Published: April 2011

ABSTRACTSensors and Transducers, and in the specific context of this paper gas sensors, are currently amongst the largest growth areas in the modem electronics industry and this seems likely to continue for the foreseeable future. Nanocrystalline materials posses many properties that could make them ideal as potential gas sensing elements with many advantages over their microcrystalline counterparts. Most importantly these include increased surface area coupled with reduced sintering temperatures and times. However, it should also be noted that there are several disadvantages including the comparatively high cost of materials and increased electrical resistance.This paper reviews the operating mechanisms of semiconductor gas sensors and the possible advantages of using nano sized powders to produce gas sensitive devices. Results are presented which have been obtained from several materials produced by laser evaporation including alumina (Al2O3), zirconia (ZrO2), and tin dioxide (SnO2) in contaminated atmospheres incorporating carbon monoxide, hydrogen and methane.
Orientation and Electrical Resistivity of Aluminum Oxide Films Prepared by Ion Beam Assisted Plasma Cvd
Authors: Nakai H. , Harasaki O. , Shinohara J. 
Published: April 2011

ABSTRACTAluminum oxide (A12O3) films were prepared on a nickel based superalloy (Inconel 718) by ion beam assisted plasma CVD at the multiple incident angles of the ion beams to a substrate. Crystal structure of these films was analyzed by X-ray diffraction (XRD). Electrical resistance of the films was measured at temperatures ranging from room temperature to 850°C. The incident angle of the ion beams influenced the orientation of A12O3 crystals. The net integrated intensity was calculated in order to compare the intensity among the different thickness samples whose thickness is thinner than X-ray penetration depth. The electrical resistivity depends on the relative X-ray intensity of (110) and (300) of α-A12O3.
Defect production during ion-assisted deposition of molybdenum films studied by molecular dynamics
Authors: Klaver Peter , Thijsse Barend 
Published: April 2011

ABSTRACTLow energy argon-ion assisted growth of thin molybdenum films (∼ 60 Å) has been studied by molecular dynamics simulations. The effects of a single ion impact are discussed, but more particularly we consider film growth from a manufacturing viewpoint and examine the properties of the completed films. Results for ion-beam assisted deposition are compared with those for unassisted growth (i.e. physical vapor deposition). Surface morphology, defect generation, argon incorporation, and the various responsible atomic mechanisms are discussed.
Charge State of Copper-Silicide Precipitates in Silicon and its Application to the Understanding of Copper Precipitation Kinetics
Authors: Istratov A.A. , Vyvenko O.F. , Flink C. , Heiser T. , Hieslmair H. , Weber E.R. 
Published: April 2011

AbstractDeep level spectra obtained on n-type silicon samples after copper diffusion and rapid quench give evidence of a positive charge state of the precipitates in p-type silicon. Non-exponential precipitation behavior of interstitial Cu is demonstrated and explained. The possibility of Coulomb interaction between copper ions and copper precipitates is suggested and its influence on Cu precipitation kinetics is disCussed.
Behavior of Deep Defects After Hydrogen Passivation in Znte Studied by Photoluminescence and Photoconductivity
Authors: Bhunia S. , Bose D.N. 
Published: April 2011

AbstractThe effects of hydrogen passivation in undoped p-ZnTe single crystals were studied by photoluminescence (PL) and photoconductivity (PC) measurements. Samples were exposed to r.f hydrogen plasma at 250 °C for different durations. Before passivation PL peaks were observed at 2.06 eV, 1.47 eV, 1.33 eV and 1.06 eV. After 60 minutes exposure, samples showed strong band edge green luminescence at 2.37 eV due to an exciton bound to a Cu acceptor. Further exposure to plasma resulted in disappearance of 2.37eV and 2.34 eV peaks due to damage. In PC studies the dark current was found to decrease by a factor of 70 on 60 minutes passivation. From the temperature dependence of PC gain, the minority carrier lifetime τn, was found to go through a maximum of 4.5 × 10−7 sec at 220 K before passivation. After 60 minutes exposure, τn, remained constant at 4.5 × 10−7 sec for T > 220 K and decreased for T < 220 K. The activation energies of τn, were determined and show marked changes on passivation for T > 220 K. Comparison between PL and PC studies showed that the deep acceptor level OTe responsible for emission at 2.06 eV is passivated giving rise to strong band edge emission at 2.37 eV while emission due to the midgap impurity levels at 1.47, 1.33 and 1.05 eV remained unaffected. The thermal activation energies of the PL peaks have also been determined and allow the construction of a defect energy level diagram for ZnTe.
Defect Engineering In Ion-Implanted Diamond
Authors: Gippius A.A. , Khmelnitski R.A. , Dravin V.A. , Tkachenko S.D. 
Published: April 2011

AbstractOptical interference studies of graphitized layers formed in diamond by ion implantation and annealing provided the data on the depth and the thickness of the layers as well as their optical parzmeters. The latter were found to be close to those of dispersed graphite. Cathodoluminescince analysis of implanted diamond samples gave evidence of vacancy migration over macroscopic distances (∼1001μ).
Advanced Knowledge for Impurity Motion of Oxygen in Silicon and its Application to Defect-State Analysis
Authors: Yamada-Kaneta H. 
Published: April 2011

AbstractWe review our two models for the impurity excitation of the oxygen in silicon. The first model aims to explain the energies and intensities of the infrared absorption lines. The coupled excitation is formulated for the first time under the D3d symmetry. Taking into account the lowenergy excitation of the oxygen, the A2u local mode, and the anharmonic coupling between them, we quantitatively describe the absorption lines in the 30-, 1100-, and 1200-cm−1 bands, including those of the 18O isotope. We next take into account the A1g local mode, the Eu resonant mode, and the couplings between the excitation elements. This enables us to qualitatively explain the origin and characteristic aspects of other absorptions, e.g., the 500- and 1700-cm−1 bands. The second model is a simplification of the first one with the coupling to the band (extended) phonons included. The model describes the strong temperature dependence of the line widths observed for both of the phonon-resonant 30-cm−1 band and the phonon-off-resonant 1100-cm−1 band. The life-time limiting process causing the finite line-widths is shown to be the one-phonon transitions in the energy-level ladders of the low-energy excitation each belonging to the ground and the first excited states of the A2u local mode. The vibrational excitations of the similar impurity systems in Si, Ge, Ge xSi1−x crystals are analyzed.
Characterization of Deep Impurities in Semiconductors by Terahertz Tunnel Ionization
Authors: Ziemann E. , Ganichev S.D. , Yassievich I.N. , Schmalzv K. , Prettl W. 
Published: April 2011

AbstractThe ionization of deep impurity centers by high intensity far-infrared radiation, with photon energies tens of times lower than the impurity binding energy, has been investigated. It is shown that the ionization is caused by phonon-assisted tunneling in the electric field of radiation, in which carrier emission is accompanied by electron tunneling and defect tunneling in the configuration space. The field and temperature dependencies of the ionization probability allow to obtain defect parameters like tunneling times and the Huang-Rhys factor as well as the basic structure of the defect adiabatic potentials. In very strong fields, the ionization changes to direct tunneling without assistance of phonons. It is shown that for the case of charged impurities and in a relatively low electric field strength the Poole-Frenkel effect plays a dominant role in ionization, which allows to identify the charge state of the center. Within a broad range of intensities, wavelengths and temperature, the terahertz electric field of the radiation acts as a static field. An enhancement of tunneling with increase of frequency has been observed for very high frequencies or low temperatures.
Thermo-Mechanical Stresses in Laminated Polymer Films on Silicon Substrates
Authors: Kim Jin S. , Paik Kyung W. , Oh Seung H. , Seo Hyun S. 
Published: April 2011

ABSTRACTThermo-mechanical stresses in MCM-D substrate are important reliability and fabrication issues. The differences in coefficient of thermal expansion (CTE) between substrate, polymer, and metal leads to complicated stress fields in multilevel interconnect structures. While the majority of reports in the literature have focused on spin-coated polyimides, this paper mainly focuses on laminated polymer dielectrics. This study uses material sets representing typical MCM-D structures to monitor the stress level in the polymer films. The substrate deflection caused by composite stresses during fabrication and thermal cycling test is determined by a curvature measurement technique. A simple analytical model which predicts a stress contribution from each individual layer during MCM-D substrate fabrication is proposed and developed by computer simulation as well. The composite stress or bowing in multilayer structures is due to the summation of each individual layer contribution. From a thermo-mechanical stress viewpoint, Ultem® thermoplastic and the epoxy thermoset adhesive exhibit quite different behaviors. In case of the epoxy thermoset adhesive, the amount of bowing increases as number of layers increases and its behavior can be predicted by an elastic model. However, in the case of the Ultem® thermoplastic adhesive, bow values become stabilized as number of layers increases because of the stress relaxation effect of the thermoplastic adhesive during lamination process above Tg of the Ultem® thermoplastic.
Intergranular Coupling and Grain Isolation of Thin Co Films
Authors: Gong Heng , Yang Wei , Lambeth David N. , Laughlin David E. 
Published: April 2011

AbstractThe effects of rapid oxidation and overcoat diffusion processes on the intergranular coupling and grain isolation in thin Co films were studied. The oxidation process was found to be strongly temperature dependent. The optimal coercivities can only be achieved within a narrow range of temperatures, while further increasing the temperature incurs significant thermal instability. CrMn underlayers were confirmed to be more effective in enhancing the grain isolation by the grain boundary diffusion during the oxidation process. The oxidation process does not change the Co anisotropy, and hence the coercivity increase is appears to be a result of better grain isolation. The in-situ diffusion of Ag and Cr overcoats were also found to have siginificant effects on the grain isolation in Co and CoCr films.