bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tensile Strength and Creep Resistance in Nanocrystalline Cu, Pd and Ag
Authors: Nieman G. W. , Weertman J. R. , Siegel R. W. 
Published: March 2011

ABSTRACTMeasurements of tensile strength and creep resistance have been made on bulk samples of nanocrystalline Cu, Pd and Ag consolidated from powders by cold compaction. Samples of Cu-Cu2O have also been tested. Yield strength for samples with mean grain sizes of 5–80 nm and bulk densities on the order of 95% of theoretical density are increased 2–5 times over that measured in pure, annealed samples of the same composition with micrometer grain sizes. Ductility in the nanocrystalline Cu has exceeded 6% true strain, however, nanocrystalline Pd samples were much less ductile. Constant load creep tests performed at room temperature at stresses of >100 MPa indicate logarithmic creep. The mechanical properties results are interpreted to be due to grain size-related strengthening and processing flaw-related weakening.
Thermodynamics of Nano-Grain Boundaries
Authors: Fecht Hans J. 
Published: March 2011

ABSTRACTA universal, accurate and simple method is developed to describe the thermodynamic properties of disordered grain boundaries in nanocrystalline metals. Based on a free volume approach at negative pressure of the universal equation of state, the maximum free volume, bulk modulus, specific heat at constant pressure, thermal expansion coefficient, excess enthalpy, excess entropy and free energy of grain boundaries are derived from well-known thermodynamic relationships. Describing nanocrystalline metals as a bimodal material with a grain boundary component and a crystalline component, their thermodynamic properties can then be estimated by appropriate scaling of the boundary-to-volume ratio.
Carbon ARC Generation of C60
Authors: Haufler R. E. , Chai Y. , Chibante L. P. F. , Conceicao J. , Jin Changming , Wang Lai-Sheng , Maruyama Shigeo , Smalley R. E. 
Published: March 2011

ABSTRACTGeneration of C60 at a rate of more than 10 grams per day has been accomplished by operation of a carbon arc in an atmosphere of helium. Optimum yield of 15% was found to occur near 100–200 torr, but yields greater than 3% were found throughout the range between 50 and 760 torr. A model is proposed to explain the observed behavior based on competition between annealing of graphitic sheets to curve so that they minimize dangling bonds, and further rapid growth of these sheets in the gas phase to form giant fullerenes. In agreement with predictions of this model, laser vaporization of graphite targets was found to produce macroscopic quantities of C60 only when performed in an oven above 1000 C.
Laser Annealing of Semiconductor Clusters: Trimethylamine Reactions with Positive and Negative Clusters
Authors: Maruyama S. , Anderson L. R. , Smalley R. E. 
Published: March 2011

ABSTRACTReaction studies with trimethylamine on positively charged laser-annealed silicon clusters of 39, 43, and 48 atoms magnetically levitated in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer reveal the same relative reaction pattern as previously observed for identical studies with ammonia and ethylene. The 39th cluster was found to be considerably less reactive than the other positive cluster sizes, and significantly, its negative ion is also relatively less reactive than the 43rd and 48th. The continued observation of this reactivity trend provides additional experimental evidence that the annealed clusters adopt well-organized structures, and that these crystal forms are similar for both charge states.
Spectrometric Characterization of Purified C60 and C70
Authors: Lykke Keith R. , Pellin Michael J. , Wurz Peter , Gruen Dieter M. , Hunt Jerry E. , Wasielewski Michael R. 
Published: March 2011

ABSTRACTC60 and C70 were synthesized and purified according to published procedures. Both nanosecond and picosecond laser desorption from coated substrates gave copious positive and negative ions. Mass spectra (TOF and FTMS) with excellent signal to noise, showing only the C60 and C70 mass peaks, have been observed. Well-resolved isotopic structure was seen in the FTMS spectra in agreement with the natural abundance of carbon. Laser desorption and multiphoton ionization/photodissociation of the neutral species, as well as electronic absorption, FTIR, and fluorescence spectra, have been obtained.
Diffraction Symmetry in Crystalline, Close-Packed C60
Authors: Fleming R. M. , Siegrist T. , Marsh P. M. , Hessen B. , Kortan A. R. , Murphy D. W. , Haddon R. C. , Tycko R. , Dabbagh G. , Mujsce A. M. , Kaplan M. L. , Zahurak S. M. 
Published: March 2011

ABSTRACTWe have grown crystals of the carbon structure C60 by sublimation. In contrast to solution-grown crystals, the sublimed crystals have long range order with no evidence of solvent inclusions. Sublimed C60 forms three dimensional, faceted crystals with a close-packed, face-centered cubic unit cell. We have refined a crystal structure using the “soccer ball” model of the C60 molecule. The results indicate that the C60 molecule has the expected spherical shape, however the data are not sufficiently accurate to unambiguously determine atomic positions.
High Resolution Plan View Imaging of Clean and Au Deposited Si(111) surfaces
Authors: Ozawa S. , Tanaka Y. , Kobayashi K. , Yamamoto N. , Yagi K. 
Published: March 2011

ABSTRACTHigh resolution plan view images of clean and Au deposited Si(111) surfaces are presented. Corner holes and small holes between dimers of the DAS model of the 7×7 structure were clearly resolved. In the case of the Si(111)5×1-Au structure the 5 times period fringes did not show fine details.
Photoelectron Diffraction of Magnetic Ultrathin Films: Fe/Cu(001)
Authors: Tobin J. G. , Wagner M. K. , Guo X.-O. , Tong. S. Y. 
Published: March 2011

ABSTRACTThe preliminary results of an ongoing investigation of Fe/Cu(001) are presented here. Energy dependent photoelectron diffraction, including the spin-dependent variant using the multiplet split Fe 3s state, is being used to investigate the nanoscale structures formed by near-monolayer deposits of Fe onto Cu(001). Core-level photoemission from the Fe3p and Fe3s states has been generated using synchrotron radiation as the tunable excitation source. Tentatively, a comparison of the experimental Fe3p cross section measurements with multiple scattering calculations indicates that the Fe is in a fourfold hollow site with a spacing of 3.6Å between it and the atom directly beneath it, in the third layer. This is consistent with an FCC structure. The possibility of utilizing spin-dleendent photoelectron diffraction to investigate magnetic ultrathin films will be demonstrated, using our preliminary spectra of the multiplet-split Fe3s of near-monolayer Fe/Cu(001).
X-Ray Reflectometry of Single- and Multi-Layer Thin Films
Authors: Parrish W. , Erickson C. , Huang T. C. , Hart M. , Gilles B. , Toraya H. 
Published: March 2011

ABSTRACTThis paper describes the instrumentation and technique for the routine characterization of thin Films, multi-layers and substrates by grazing incidence X-ray reflectometry with a rotating anode and CuKα1, line source. Ge 220 channel monochromators with two reflections per channel were used with one CM placed before and the other after the specimen. In many applications the second CM could be replaced with a narrow receiving slit. The specimen holder was designed to make fine translations of the specimen for alignment, a base was designed to permit precise positioning of the diffractometer, and a high-speed Rigaku scintillation counter was used. The alignment and calibration are described and some typical data given to illustrate the capability of the method.
Substrate Dependent Texture and Heteroepitaxy for Group IIIA Nitride Films by the X-Ray Precession Method
Authors: Kistenmacher T. J. , Bryden W. A. , Wickenden D. K. , Ecelberger S. A. 
Published: March 2011

ABSTRACTThe X-ray precession method has been utilized to study texture and heteroepitaxy for thin films of the Group IIIA nitrides deposited on a variety of amorphous and single-crystal substrates. Films of InN were synthesized by reactive rfmagnetron sputtering [employing an elemental target and N2 as the sputtering gas], while the GaN films were deposited by metalorganic chemical vapor deposition [utilizing (CH 3 ) 3Ga and NH3 as sources]. The quality of (00.1) textured films of InN on fused quartz and slightly off-axis (111) Si are taken as initial examples of the versatility of the X-ray precession method. The powder rings evolving from a lack of azimuthal coherence for InN films grown on quartz are contrasted with the scattering from weakly correlated (pseudo heteroepitaxial) domains for films grown on (111) Si. These latter scattering features are then compared with those from the true heteroepitaxial deposition of InN onto the (111) face of cubic ZrO2. And, finally, the scattering from the heteroepitaxial growth of InN and GaN on the (00.1) face of sapphire and some initial studies on the effect of nucleation layers on twinning in the GaN films are presented.
UHV Microscopy of the Reconstructed Au (001) Surface
Authors: Dunn D. N. , Marks L. D. , Zhang J. P. 
Published: March 2011

ABSTRACTWe investigate the evolution of the microstructure of a reconstructed Au (001) single crystal surface using ultra high vacuum transmission electron microscopy (UHV-TEM). Bulk single crystal Au (001) surfaces were prepared via standard metallographic techniques and sputter anneal cycles. After a clean surface was obtained, the (001) surface was found to reconstruct into two nearly orthogonal domains of dimensions (5 × ∼ 20 ) along the <110> directions of the unreconstructed F.C.C. (001) surface. Transmission electron diffraction patterns (TED) and dark field microscopy are the two primary techniques used to determine the symmetry and dimensions of the reconstructed surface.
Rheed Oscillation During the Epitaxial Growth of Layered Materials
Authors: Shimada Toshihiro , Ohuchi Fumio S. , Koma Atsushi 
Published: March 2011

ABSTRACTRHEED intensity oscillations have been observed during the epitaxial growth of layered NbSe2, MoSe2 on GaAs(111) substrates. Monolayer- and bilayer- mode oscillations have been observed at different diffraction points. The existence of bilayer-mode oscillation is interpreted as showing the polytype of the grown films. The present report demonstrate the utility of RHEED oscillation for analyzing the structure of ultrathin films of layered materials. The epitaxial growth of TaSe2 on layered substrates is also reported.
High Energy Transmission Electron Diffraction From Surface Monolayers During Silicon Oxidation
Authors: Ross Frances M. , Gibson J. Murray 
Published: March 2011

ABSTRACTWe have examined the behaviour of the clean Si (111) 7x7 reconstructed surface during exposure to oxygen over a range of temperature and pressure in a UHV transmission electron microscope (TEM). We present preliminary results of our study, discussing both the etching of the silicon surface by oxygen at elevated temperatures and lower oxygen pressures, and its roughening and oxidation at higher oxygen pressures. We achieve great sensitivity to the structure of the surface monolayers by analysing the diffraction of high energy electrons by these surface layers and can resolve the movement of individual monatomic surface steps. Our most dramatic result to date is a demonstation that surface steps do not move during the growth of native oxide.
Peculiar Doping Behavior of Si:Be.
Authors: Tarnow Eugen , Zhang S.B. , Chang K.J. , Chadi D.J. 
Published: March 2011

ABSTRACTThe total energies and structures of a number of Be-induced defects in Si are investigated using ab-initio local density calculations. Our primary results are: 1) The geometry of the isoelectronic center is found to correspond to a [111] substitutionalinterstitial pair (SIP); 2) The low energy defect spectrum includes large Be complexes containing at least one substitutional atom; and 3) Simple bonding rules exist for the stability of the different types of bonds in the material. Thus the Si-Be bond is found to be stable for all defect configurations while the Be-Be bond is metastable.
A Cluster Calculation of B and P Impurities in Amorphous Silicon
Authors: Enrique Sansores L. , Valladares R.M. , Cogordan J.A. , Valladares A.A. 
Published: March 2011

ABSTRACTThe local density of states and charge density contours of clusters of the type ISi20H28, where I can be Si, B or P, was calculated using the well-known pseudopotential SCF Hartree-Fock Method (and the HONDO Program). It is found that the covalent nature of the bonding in pure silicon gets altered and gives rise to an ionic component when B and P are substituted in the center of the cluster. Also, the local density of states in the neighborhood of a Si atom, nearest neighbor to the center of the cluster, show a splitting of the p-states at the top of the valence band in pure silicon when B is substituted, and a new p-state appears in the band gap when P is sustituted. These results are analyzed in the light of the local changes and its relevance to the solid state properties.
First-Principles Study of Photoexcited Defects in Polysilane Chains
Authors: Mintmire J. W. , Mowrey R. C. , Brenner D. W. , Dunlap B. I. , White C. T. 
Published: March 2011

ABSTRACTOrganopolysilane materials have recently demonstrated potential technological importance as positive photoresists, photoconductors, and nonlinear optical materials. Many of the technological applications of these materials depend intimately on the photoexcitation process in these materials, possibly resulting in either bond scission or the creation of mobile charge carriers. Herein we present some preliminary results of a model simulation of the photoexcitation process in oligomeric polysilane chains using a recently developed first-principles local-density functional method for the calculation of electronic structures,total energies, and gradients of the total energy with respect to nuclear coordinates.
X-Ray Characterization of Defects in Irradiated Iron
Authors: Peisl J. , Franz H. , Schmalzbauer A. , Wallner G. 
Published: March 2011

ABSTRACTWe report on a thorough X-ray study of irradiation induced defects in iron. Single crystals were irradiated at 4.6 K with reactor neutrons and at 90 K with 2 MeV electrons. After irradiation and subsequent thermal annealing, we measured the defect induced diffuse scattering of X-rays (Huang scattering) and the small angle scattering of synchrotron radiation. Simultaneously, lattice parameter and electrical resistivity changes were measured. The single defect properties are determined from low dose electron irradiated samples and yield the lattice distortions, i.e., the volume change and defect symmetry as described by the force dipole tensor. Excellent agreement of the experimental results with calculated values from literature is observed. After neutron irradiation, defects are correlated within displacement cascades. The correlations for vacanciesand interstitials are described by a spatial correlation volume. These results are compared with computer simulations usingthe Marlowe code. During thermal annealing the irradiation induced defects agglomerate at characteristic temperatures and we observe changes in the spatial correlations of the defects. There is a clear difference between electron and neutron irradiated samples concerning defect recovery in stage 1.
In-Situ NMR Investigation of Dynamical Behavior of Point and Line Defects During Deformation of NaCl
Authors: Detemple K. , Kanert O. , Linga Murty K. , Dehosson J.Th.M. 
Published: March 2011

ABSTRACTSpin lattice relaxation time in the rotating frame [T1ρ] is investigated in pure NaCl single crystals as a function of temperature in-situ during deformation. Transition from 2- phonon Raman process to atomic diffusion was noted at around 500K in the undeformed material and the activation energy was determined to be that for the diffusion of extrinsic vacancies. Enhanced spin relaxation rates were noted during constant strain-rate deformation at temperatures from ambient to about 750K. These enhancements were identified to arise from dislocation motion at lower temperatures while enhanced diffusion due to excess vacancies at higher temperatures. This excess concentration increased with increased strain-rate and in-situ annealing of deforma-tion induced excess vacancies is noted at high temperatures.
Heterocyclization of Acetylene to Thiophene at Defects on the Pd(111) Surface
Authors: Gellman Andrew J. 
Published: March 2011

ABSTRACTWe have studied a novel surface reaction in which acetylene (C2H2) cyclizes with sulfur atoms on the Pd(111) surface to form thiophene (C4H4 S). The reaction occurs at defects in the (√7 ×√7)R19° sulfur overlayer that is formed on this surface. The surfaces were prepared by decomposing H2S on the clean Pd(111) surface and annealing to temperatures in the range 600K to 1100K to produce defects i the sulfur overlayer. The reaction occurs to greatest extent on surfaces annealed to high temperatures and only on surfaces with coverages approaching saturation. The defects have been characterized by adsorption of CO using both vibrational spectroscopyand measurementsof desorption kinetics. On the sulfided surface CO is bound in a linear configuration to a single Pd atom. At defects in the sulfur overlayer CO is bound in a bridging site between two atoms, as on the clean surface.
Weak Localization Effects in Fluorineintercalated Graphite Fibers
Authors: Di Vittorio S.L. , Dresselhaus M.S. , Bayot V. , Piraux L. , Issi J-P. , Endo M. , Nakajima T. 
Published: March 2011

ABSTRACTThe intercalation of fluorine into graphite introduces defects into the highly crystalline pristine fibers. These defectsare studied using temperature-dependent resistivity and magnetoresistance measurements. A logarithmic increase in resistivity at low temperature is observed, whereas the high temperature behavior is metallic. At weak magnetic fields and low temperatures, a negative magnetoresistance is observed, which becomes positive at high fields. These effects are explainedusing the two theories of weak localization and hole-hole interaction. In the light of TEM pictures of the microstructure of the fluorinated fibers, the origin of the defects in the intercalated fibers is discussed.
Characterization of Activated Carbon Fibers
Authors: Fung A. W. P. , Rao A. M. , Kuriyama K. , Dresselhaus M. S. , Dresseliiaus G. , Endot M. 
Published: March 2011

AbstractLow-temperature electrical conductivity and Raman scattering are studied as characterization tools for activated carbon fibers, which have a high density of defects and a huge specific surface area. The transport mechanism at low temperature is governed by variablerange hopping, as in other strongly disordered systems. From the Raman spectra obtained, we deduce that the long phenolic fibers are more disordered than the acrylic fibers and that increased specific surface area corresponds to increased disorder. The average in-plane microcrystallite size is about 20–30 Å.
Properties of Cu in GaAs
Authors: Leon Rosa , Kaminska Maria , Man Yu Kin , Weber Eicke 
Published: March 2011

ABSTRACT:The electrical properties and preferred lattice sites of Cu in GaAs were studied combining electrical and optical measurements with Particle Induced X-ray Emission (PIXE) and Channeling. For electronic characterization, Deep Level Transient Spectroscopy (DLTS), Hall Effect measurements, and Photoluminescence (PL) were used. From this comprehensive study it was determined that Cu introduces two levels in the bandgap, that the concentration of electrically active copper is considerably smaller than the total copper concentration, and that most of the Cu in GaAs is not of purely substitutional character.
Evidence of Defect Levels in P and N-Type Electron Irradiated Si
Authors: Kouimtzi S.D. 
Published: March 2011

ABSTRACTCapacitance bridge measurements at low temperature on irradiated specimens of p and n-type Si are reported. Electronic defect levels are seen at Ev+0.10 eV , Ev+0.14 eV and Ec−0.11 eV. The change of the band structure caused by irradiation is also described.
Raman Studies of Znse Lattice Damage and Recovery Due to N Implantation and Annealing
Authors: Deneuville A. , Ayyub P. , Park C. H. , Anderson T. , Lowen P. , Jones K.S. , Holloway P. H. 
Published: March 2011

ABSTRACTThe “bulk” and near-surface regions of N implanted heteroepitaxial ZnSe films were studied using the full width at half maximum (FWHM) of the LO phonon Raman line. The “bulk” FWHM has a minimum below an annealing temperature Ta = 400°C, and increases for higher Ta. This is attributed to the relaxation of residual stress, and to an increased stress from the formation of Zn vacancies. The surface FWHM has a deep minimum near Ta = 500°C which is attributed to the relaxation of the implantation damage at lower Ta, and stress induced by Zn vacancy formation at higher Ta. Another wider peak is found just after implantation and for Ta = 600°C, and results from a sum of two peaks attributed to the heavily damaged region around Rp and to the region with Zn vacancies.
Influence of Current Injection into a-Sin:H Films on Charge Trapping Defects
Authors: Oku Tomoki , Kawabata Kiyoshi , Higaki Yukio , Matsui Teruhito , Takano Hirozo , Otsubo Mutsuyuki 
Published: March 2011

ABSTRACTThe degradation mechanism of a-SiN:H films under current injection is investigated. It is shown that the degradation of a-SiN:H films is closely related to the hole trapping into Si-Si, Si-H, and Si0 defects. It is presumably concluded that the hole trapping centers are the Si-Si defects in the valence band tail. We estimate that the hole trapping cross-section is nearly equal to 10−20cm2.
Contactless Deep Level Transient Spectroscopy Using Microwave Reflection
Authors: Wang M. S. , Borrego J. M. 
Published: March 2011

ABSTRACTContactless deep level transient spectroscopy using microwave reflection at 35 GHz is presented and it is proved to be a powerful technique for characterizing trapping levels in semiconductors without the necessity of special sample preparation. The technique consists of measuring the transient decay in photoconductivity after a monochromatic light pulse has been applied to the semiconductor. The photoconductivity after the light pulse is caused by emission of carriers from trapping levels filled during the light pulse and by scanning the sample temperature it is possible to determine their activation energy. On Si-implanted layers on LEC grown SI-GaAs substrate we have detected three trapping levels, located at 0.15, 0.18 and 0.27 eV below the conduction band, by using a 1060 nm YAG laser, and one level, 0.13 eV below the conduction band, by using a 633 nm HeNe laser. The technique has been applied to LEC SI-GaAs and no trapping levels have been observed above the EL2 level.