bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solid molecular phases of Hydrogen via constant-pressure first-principles Molecular Dynamics
Authors: Kohanoff Jorge , Scandolo Sandro 
Published: April 2011

ABSTRACTBy performing constant pressure ab initio molecular dynamics simulations we analyse the high pressure phases of molecular solid hydrogen. We use a gradient corrected LDA, and a freshly implemented efficient technique for Brillouin zone sampling. An extremely good k-point sampling turns out to be crucial for obtaining the correct ground state. Our constant pressure approach allows us to optimize simultaneously the ori-entational degrees of freedom, the lattice constants, and the space group. This can be done either by a local optimization tehcnique, or by running molecular dynamics (MD) trajectories. The MD allows for the system to undergo structural transformations spontaneously. In the lower pressure, namely for the broken symmetry phase (BSP or phase II), we find a quadrupolar orthorhombic structure, of Pca21 symmetry. By means of an MD investigation, we find, at higher pressures, a slightly distorted orthorhombic structure of Cmc21 symmetry. This structure cannot be straightforwardly identified with the H-A phase (or phase III) because: 1) it is metallic, and 2) the Raman vibron discontinuity would be far too large compared to experiment. In fact, we argue that this phase is the first metallic molecular phase of hydrogen. Metallization would happen then, not via a band-overlap mechanism, but due to a structural transformation. By comparing total enthalpies, we also give suggestions for the structure of phase III.
Magnetism, Electronic Properties and Structure at High Density State of Magnetic Solids
Authors: Gavrejuk A. G. , Stepanov G. N. , Trojan L. A. , Sidorov V. A. , Lyubutin I. S. , Palosz B. , Steumakh S. , Winzenick M. 
Published: April 2011

ABSTRACTWe develop and apply high pressure techniques to study the modification of electronic structure, magnetic properties, and local crystal structure, in magnetic materials under high pressure. The variation in inter-atomic distances and atomic volumes in the high pressure regime provides new information for elucidating electronic processes in solids, and for understanding the connection between electronic structure and magnetic properties of matter.For our samples we used rare-earth orthoferrites, which are of the perovskite-type structure, and Heusler alloys, with the cubic structure. Those materials are known to be magnetic insulators and magnetic metals, respectively.We studied the following properties induced by high pressure: electronic structure, spin crossover effects, magnetic to non-magnetic transitions, and insulator-to-metal transitions. The problems of delocalization, distribution of spin, and charge density distribution in dielectric materials, semiconductors, and metals, as well as chemical bonding can be investigated in this way.
Ab-Initio Simulation of Solid State Polymerization of Acetylene Under Pressure
Authors: Bernasconi M. , Parrinello M. , Chiarotti G. L. , Focher P. , Tosatti E. 
Published: April 2011

ABSTRACTWe have recently devised a new method for the ab initio simulation of solid-solid phase transformations under pressure. The method is here applied to the study of the solid-state polymerization of acetylene under pressure and the generation of hydrogenated amorphous carbon from compression of polyacetylene.
Experimental Issues in In-Situ Synchrotron X-Ray Diffraction at High Pressure and Temperature by Using a Laser-Heated Diamond-Anvil Cell
Authors: Yoo C. S. , Cynn H. , Campbell A. , Hu J.-Z. 
Published: April 2011

ABSTRACTAn integrated technique of diamond-anvil cell, laser-heating and synchrotron x-ray diffraction technologies is capable of structural investigation of condensed matter in an extended region of high pressures and temperatures above 100 GPa and 3000 K. The feasibility of this technique to obtain reliable data, however, strongly depends on several experimental issues, including optical and x-ray setups, thermal gradients, pressure homogeneity, preferred orientation, and chemical reaction. In this paper, we discuss about these experimental issues together with future perspectives of this technique for obtaining accurate data.
Growth of Icosahedral Boron-Rich Clusters at High Pressure
Authors: McMillan Paul F. , Hubert Herve , Chizmeshya Andrew 
Published: April 2011

ABSTRACTThe stoichiometry of boron suboxide (B6O1-x) synthesized at high pressure lies closer to the nominal composition (x = 0) than materials obtained at atmospheric pressure. The crystallinity of materials obtained in the presence of molten B2O3 is also higher than for sintered powders. Further, for syntheses at 1700–1800 °C between 4 and approximately 5–6 GPa, the well-crystallized particles are dominated by large (up to ∼40 μm in diameter) icosahedral multiply-twinned particles. This unusual morphology is obtained by Mackay packing; i.e., by assembly of successive shells of icosahedral B12 units around a central icosahedral nucleus. The result is a multiply-twinned particle in which each of the 20 elements has the R 3 m space group of the α-B structure.
Synthesis and Characterization of Nanosized Silicon Carbide
Authors: Klein S. , Winterer M. , Hahn H. 
Published: April 2011

ABSTRACTNanosized silicon carbide powders are synthesized by the Chemical Vapor Synthesis (CVS). Grain and particle sizes are measured by XRD and BET. Agglomeration, crystallinity and the chemical composition of the SiC samples are investigated as a function of storage conditions and the CVS process parameters: precursor material, synthesis temperature and reactor length. Grain and particle sizes below 10 nm are observed in all samples.
Novel method for synthesis of engineered particulates with thin coatings
Authors: Fitz-Gerald J. , Singh R. K. 
Published: April 2011

ABSTRACTParticulate coatings have wide ranging applications in several new technologies such as flatpanel displays, sintering of advanced ceramics, rechargeable batteries, etc. In this paper, we show the feasibility of the pulsed laser ablation technique to make very thin, uniformly distributed and discrete coatings in particulate systems so that the properties of the core particles can be suitably modified. Presently, laser ablation techniques have been primarily applied to deposit thin films on flat substrate materials. To deposit discontinuous particulate coatings, the laser induced plume from the target comes in contact with an agitated bed of core particles (size 1–800μm). The pressure and nature of the background gas (inert or active) controls the cluster size of the particles in the laser plume. Experiments were conducted for laser deposition of silver particles on alumina core particles by excimer laser (wavelength = 248 nm and pulse duration = 25 nanosecond) irradiation of silver targets. The surface coverage and the coating of the film wasf found to depend on the laser parameters (energy density and number of laser pulses) as well as the residence time of the core particles in the plume regime. The films were characterized by wavelength and energy dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy techniques.
Characterization of Diamond like Carbon film Fabricated by ECR Plasma CVD at room Temperature
Authors: Kuramoto K. , Domoto Y. , Hirano H. , Tarui H. , Kiyama S. 
Published: April 2011

ABSTRACTLow temperature (about 50°C) fabrication of diamond like carbon (DLC) films with a high hardness (>3000Hv) and a high electrical resistivity (>1011 Ωm) has been achieved.In order to obtain such a result, the effect of ion impingement on the growth and structural change of DLC films in an electron cyclotron resonance (ECR) plasma enhanced chemical vapor deposition (CVD) method was investigated. It was confirmed that ion impingement was fundamentally required in the growth of DLC films. Furthermore, impingement with ions energized by bias voltages between 50V and 150V had a major influence on the sp 2/sp 3 configuration in DLC films. This configuration is found to be rather sensitive to optoelectronic properties but not so sensitive to film hardness.Additionally, this method could fabricate ultrathin DLC films that exhibited excellent wear resistance for protective applications.
Synthesis of Hard Nitride Coatings by ion Beam Assisted Deposition
Authors: Demaree J. D. , Fountzoulas C. G. , Hirvonen J. K. , Monserrat M. E. , Halada G. P. , Clayton C. R. 
Published: April 2011

ABSTRACTIon beam assisted deposition (IBAD) has been used to deposit chromium nitride coatings using 1200 eV nitrogen ions from an RF-type ion source and thermally evaporated chromium. The ion/atom arrival ratio R was varied from 0 to 8 to modify the coating composition, microstructure, growth rate and stress state in order to optimize the properties of the material for use as a possible substitute for electroplated chromium in a number of anti-corrosion and tribological applications. The coatings were examined using Rutherford backscattering spectrometry and x-ray photoelectron spectroscopy, and contained up to 44 at % nitrogen in a mixture of bcc Cr-N, Cr2N, and CrN. The microstructure of the coatings was examined by scanning electron microscopy, and the tribological behavior of the coatings was examined using an automated scratch testing and nanoindentation. XPS examination of the coatings indicates that nitrogen near the surface was bound to the metal as CrN and Cr2N in most of the coatings studied by XPS, which is expected to significantly affect their corrosion behavior. The high R values needed to form large amounts of the CrN phase in the bulk of the coating causes significant sputtering during deposition. This study indicates that it is not possible to form a coating consisting solely of cubic CrN by IBAD under these experimental conditions (room temperature substrate and partial pressure of nitrogen of 1.8 × 10−2 Pa). Nevertheless, the IBAD coatings produced were hard, in a compressive stress state, and highly adherent, all properties that make them candidates for use in selected Army applications.
Properties of C and CN Films Prepared by Mass-Separated Hyper-Thermal Carbon and Nitrogen Ions
Authors: Tsubouchi N. , Horino Y. , Enders B. , Chayahara A. , Kinomura A. , Fujii K. 
Published: April 2011

ABSTRACTAmorphous carbon films and CN films were prepared by ion beam deposition using isotopically mass-separated, hyper-thermal (50–400eV) ion species such as 12C2−, 12C14N− or simultaneous 12C2− and 14N+ under high vacuum condition. Film properties such as structures, bonding states, compositions, etc. were investigated. The optical band gaps of amorphous carbon films deposited by using 12C2−ions or CN films deposited by using 12C14N− ions were estimated from optical constants. The gaps were about 2.3eV for the amorphous carbon films and about 0.8 eV for the CN films. Energy dependence of optical constants of CN films formed by simultaneous deposition of C2− and N+ was investigated. The refractive index (n) and extinction coefficient (k) at λ = 675nm increased 1.5 to 2.4 and 0.3 to 1.3, respectively, with increasing N+ kinetic energy. The relations between bonding states and kinetic energy of hyper-thermal ions are discussed.
Vanadium Oxide Precipitates in Sapphire Formed by Ion Implantation
Authors: Abe Hiroaki , Naramoto Hiroshi , Yamamoto Shunya 
Published: April 2011

ABSTRACTSome vanadium oxides undergo phase transformations which give rise to attributable for large variations in optical and electronic properties. Since one can expect dynamic rearrangement of implanted species and a distorted lattice due to implantation, we investigated the precipitation process under ion implantation at high temperature. Sapphire samples were implanted with 300-keV V+ ions at temperatures from 470 to 1070 K in a transmission electron microscope interfaced with ion accelerators. Evolution of vanadium oxide precipitates was observed simultaneously. Damage evolution such as dislocation loops and voids were observed at fluences of the order of 1018-1019 and 1020 ions/m2, respectively. At implantation fluence of the order of 1021 ions/m2, dot and plate contrast was observed in addition to radiation damage. Electron diffraction analysis reveals that hexagonal and monoclinic V2O3, tetragonal and monoclinic VO2, and V7O13 precipitates were formed in the substrate depending on the surface normal of the substrate. Some of precipitates were thermally unstable phases. Crystallographic relationship between matrix and the precipitates was investigated as well as the swelling effect both in the substrate and in the precipitates. Temperature dependence reveals precipitation starts at temperature higher than 670 K.
Simulation of Interstitial Cluster Mobility and Cluster Mediated Surface Topologies
Authors: Wirth B. D. , Odette G. R. , Maroudas D. , Lucas G. E. 
Published: April 2011

ABSTRACTMolecular statics and molecular dynamics (MD) simulations based on the embedded atom method (EAM) are used to model the energetics and mobility of tightly bound clusters of selfinterstitial atoms (SIA) in bcc iron. Single and clusters of SIA are directly produced in displacement cascades generated in neutron and high energy charged particle beam irradiations. The clusters are composed of <111> split dumbbells and crowdions with binding energies in excess of 1 eV. Clusters containing specified ‘magic’ numbers of SIA can be described as perfect prismatic dislocation loops with Burgers vector b=a/2<111>; however, the core region is extended compared to an isolated edge dislocation and the loops are intrinsically kinked. As the loops grow, SIA occupy successive edge rows, with minimum energy cusps found at the magic numbers corresponding to filled hexagonal shells. The SIA clusters are highly mobile, undergoing rapid one-dimensional diffusion on their glide prism. The activation energy for glide diffusion is less than 0.3 eV and the corresponding mechanism is related to easy motion of the intrinsic kinks. The kinks, which are preferentially observed on the hexagonal corners, propagate around the loop periphery, resulting in stochastic increments of glide. Image drift forces bias cluster motion near free surfaces and the consequential annihilation of clusters at the surface produces islands bounded by hexagonal ledges. The potential effect of islands modifying surface topology is also discussed. While these simulations are specific to iron, similar behavior is expected for other cubic alloys.
Arc Suppression and Defect Reduction in Semiconductor Metallization
Authors: Li Xiangbing , Loo David , Stimson Brad , Seamons Scott , Narasimhan Murali 
Published: April 2011

AbstractSuppression of arcing between the target and plasma during PVD is a key issue for defect reduction, yield improvement and high quality metallization in microelectronics manufacturing. An integrated mini sparcle product has been designed for Endura HP PVD™ sputtering sources. Characteristics of arcing and mechanisms for suppression are discussed here. Process characterization with Ti, TiN and Al sputtering proves that the arc suppression unit has little adverse impact on film properties. The uniformity of reactive sputtered TiN is improved with arc suppression. Marathon evaluation indicates significant reduction in TiN defect and Interconnect metal stack defect. The study of the application for a wide variety of materials (Al, Ti, TiN, SiW, Si) establishes a correlation between deposition rate loss and sputtering power and this relation is found to be almost independent of the materials sputtered. The impact on throughput for typical metal stack is also presented in this paper.
Growth and Luminescence Properties of III-N:Er Materials Doped During Chemical Beam Epitaxy
Authors: Mackenzie J. D. , Abernathy C. R. , Pearton S. J. , Hömmerich U. , Seo J. T. , Ren F. , Wilson R. G. , Chen Paul , Zavada J. M. 
Published: April 2011

AbstractThe incorporation and optical activation of Er in III-N optically-pumped and electroluminescent structures has been studied. For the first time, strong Er3+-related photoluminescence (PL) was measured at 300K for GaN:Er doped during growth on c-plane Al2O3 and Si. Also, room temperature electroluminescence was observed for simple GaN:Er structures on Si. Experiments to evaluate the effects C and 0 on the optical activity of Er indicated that these impurities enhance Er PL and EL in GaN. GaN films doped with Er to a concentration of 3 ×1018 cm−3 with [0] ∼ 1020 cm−3 and [C] ∼1021 cm−3 luminesce at 1.54 pim with an intensity ∼2 orders of magnitude greater than films with oxygen and carbon backgrounds of less than 1019 cm−3. Implantation and activation annealing was also shown to increase Er3+ signal in p(Mg)-i(Er)-n(Si) structures where C and 0 implant profiles were made to coincide with the Er-doped layers. The thermal PL quenching behavior was also markedly different for samples of varying 0 and C content. Er3+ photoluminescence from Gan:Er/Al2O3 samples with high O and C concentrations quenched by only 10% between 15 K and 300 K while the integrated PL signal from samples with lower [O] and [C] quenched ∼85% over the same temperature range.
Comparison of Oxygen and Hydrogen Gettering at High-Temperature Post-Implantation Annealing of Hydrogen and Helium Implanted Czochralski Silicon
Authors: Job R. , Fahrner W. R. , Ivanov A. I. , Palmetshofer L. , Ulyashin A. G 
Published: April 2011

AbstractP-type Czochralski (Cz) Si was implanted with H (180 keV, 2.7.1016 cm−2) or He (300 keV, 1.1016 cm−2) ions. The gettering of O and H atoms by the buried implantation damage layers during annealing up to 4 hours (1000°C in H2 or N2 ambient) was studied by secondary ion mass spectroscopy (SIMS) and spreading resistance probe (SRP) measurements. Buried defect layers act as good getter centers for O and H atoms at appropriate heat treatments. The enhanced gettering of O atoms in H implanted Cz Si (as compared to the gettering of O in He implanted samples) as well as the enhanced gettering of O during annealing in H2 flow (as compared to N2 ambient) can be explained by a hydrogen enhanced O diffusion towards the defect layers. According to a strong accumulation of O at the buried damage layers and near the surface some anomalies of the SRP profiles can be observed after post-implantation annealing.
Interface Defects and Rectification Properties of Heterojunctions Between Solid C60 and GaAs
Authors: Chen K.M. , Zhang Y.X. , Jin S.X. , Wu K. , Liu H.F. 
Published: April 2011

AbstractSolid C60/GaAs contacts were fabricated by growing solid C60 films on both n-type and p-type GaAs(100) substrates through vacuum deposition. The electronic states at C60/GaAs interfaces were studied. Both C60/n-GaAs and C60/p-GaAs contacts were found to be strong rectification junctions with a rectifying ratio higher than 106 at a bias of ± 1.OV. Two distinct traps were also observed at the C60/GaAs interfaces with deep level transient spectroscopy (DLTS); one is the electron trap at 0.35 eV below the GaAs conduction band and the other is a hole trap at 0.45 eV above the GaAs valence band.
Donor Neutralization by Fluorine Containing Plasmas in Si -Doped N -Type GaAs Crystals
Authors: Wada J. , Matsukura Y. , Ogihara T. , Furukawa Y. , Tanaka H. 
Published: April 2011

AbstractCF4, SF6 and CF 4/O2 plasma-induced damage in silicon-doped n-type GaAs crystals have been investigated by using Hall measurements, and SIMS analysis. We observed that the carrier density degraded with post annealing after plasma exposure. The degree of deactivation of carrier density with post annealing was strongly dependent on the plasma chemistries and the self-bias Vdc of the plasmas. From SIMS analysis, fluorine contamination was observed in the surface region of GaAs crystals after CF4 plasma exposure. The internal diffusion of fluorine atoms and the localization of fluorine atoms in n-type GaAs layers were observed after post annealing at 400°C. From these results, we proposed a mechanism of plasma induced damage in which internally diffused fluorine atoms neutralize the donor silicon by forminq a Si-F bond. We determined the effective diffusion coefficient of fluorine in GaAs as 1.5 × 10−11 cm2/s (at 400°C).
Injection-Level Spectroscopy of Metal Impurities in Silicon
Authors: Ahrenkiel R.K. , Johnston S. 
Published: April 2011

AbstractUsing a modified photoconductive eddy-current technique, excess carrier decay can be measured and used to identify the specific defect dominating recombination. As the dynamic range of the measurement system is linear over about three orders of magnitude, the injection-level spectroscopy technique can be performed in a single measurement for rapid defect identification.
Picosecond time-resolved studies of defect-related recombination in high resistivity CdTe, CdZnTe
Authors: Ghislotti G. , Ielmini D. , Riedo E. , Martinelli M. 
Published: April 2011

AbstractHigh resistivity CdTe:In and CdZnTe samples were studied by means of continuos and picosecond time-resolved photoluminescence (PL). Detected PL signal is affected by non-radiative trapping into defects, while radiative recombination has an excitonic character. Time-resolved PL can be described by two lifetimes: the first (30-60 ps) takes into account fast non radiative recombination, the second in the range 200-300 ps can be related to exciton decay.
A Molecular Dynamics Study of Step Motions on Vicinal Silicon Surfaces
Authors: Mazzone A.M. 
Published: April 2011

AbstractA Molecular Dynamics simulation method has been applied to the motion of steps on a surface vicinal to {100}in Si. Undulation of the steps and ‘kissing sites’ are observed to arise from thermal fluctuations at 300°K. The dependence of the characteristic energy of these configurations on the terrace width complies with a free fermion picture which also includes dipolar and nearest neighbours interactions.
On the Shear Strength and Mixed-mode Fracture Toughness of a Lead-Tin and a Tin-Silver Solder
Authors: Manoharan M. , SIOW K. S. , WEISER M. W. 
Published: April 2011

ABSTRACTThe increasing demands on solder joints have made it imperative that they perform not only their traditional role of electrical connection but also possess good mechanical integrity. One such key mechanical property is the shear strength of the solder. A number of specimen geometries can be used to evaluate the shear strength of solders, each with its advantages and limitations. This study uses a modified double lap shear geometry to measure the shear strength of the solders as a function of strain rate. It is ahown that the shear strength measured this way is truly reflective of the complex composite formed by the copper, solder and intermetallics and may be more representative of actual conditions of use rather than measurements of the shear strengths of the bulk solder. The study also uses a modified compact tension specimen to measure the fracture of the solder under combined tensile-shear loading conditions. It is shown that the solder fracture under these conditions follows the general principles of a mixed-mode fracture mechanism map.