bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nanocrystalline Gallium Nitride from Gallium Azide Precursors
Authors: Manz A. H. , Frank A. C. , Sussek H. , Stowasser F. , Fischer R. A. 
Published: April 2011

ABSTRACTHigh quality nanoscale, phase-pure hexagonal gallium nitride (GaN) crystallites have been synthesized using the thermally induced explosion of the molecular precursor (Et3N)Ga(N3)3. The method allows the control of the particle size from 2 to 24 nm. X-ray diffraction and Rietveld simulations revealed a platelet-like shape of the larger particles in contrast to the rather spherical smaller crystallites. An increasing blue-shift of the high energy luminescence with decreasing crystal size was found (up to 4.4 eV at 5 K). A preliminary analysis of the surface chemistry of has been carried out based on silylation and deuteration experiments and IR spectroscopy, indicating hydrophilic, O-H and N-H terminated particles.
Microstructural Evaluation of Sintered Nanoscale Sic Powders Prepared by various Processing Routes
Authors: Schmidt W. R. , McCarthy G. , Palosz B. , Stel'makh S. , Aloshina M. , Gierlotka S. , Zinn P. , Keil D. G. , Calcote H. F. 
Published: April 2011

ABSTRACTMicrostructural analysis was performed on several crystalline SiC samples previously prepared by three separate processing methods and subsequently sintered under high pressure and high temperature conditions using the cubic anvil cell MAX80 at Hasylab. Microcrystalline SiC was prepared using SHS conditions, while nanocrystalline SiC was prepared using both combustion synthesis methods and polymer precursors. High purity, highly disordered nanocrystalline SiC powders, with average particle diameters below 100 nm, were synthesized via combustion methods from precise mixtures of silane and acetylene. The properties of the silicon carbide powders prepared in this manner were dependent on the initial stoichiometry and pressure of the combustion mixture. Pyrolysis of polymer precursors to SiC was also used to fabricate ceramic powders containing uniformly-sized, highly disordered nanocrystalline SiC grains. The grain sizes ranged from approximately 3 nm to greater than 50 nm, and depended on the initial composition of the polymer, the pyrolysis conditions, as well as the annealing atmosphere, temperature and time. This paper describes the preparation methods for each of the SiC powders, the densification procedure, and preliminary results obtained primarily from transmission electron microscopy and X-ray diffraction analysis.
Detailed study on the characterization of silver nanocluster in poly(methyl methacrylate)
Authors: Yanagihara Naohisa , Uchida Kazutaka , Wakabayashi Muyuki , Hara Toru 
Published: April 2011

ABSTRACTSolid sol of silver in poly(methyl methacrylate), Ag/PMMA, was prepared by bulk polymerization of methyl methacrylate solution of silver (I) triflluoroacetate (AgTfa) and followed by postheating. The formation of the metallic Ag nanocluster was characterized by visible spectroscopy, and effects of the concentrations of AIBN and AgTfa and the heat-treatment duration on the formation of Ag cluster were investigated. Furthermore, based on the kinetic study of MMA in the presence of AgTfa, possible mechanism for the reduction and agglomeration of silver is proposed.
Particle adhesion: interaction forces and mechanical effects: extrapolation to the nanometer-size range
Authors: Rimai D. S. , Demejo L. P. , Gady B. , Quesnel D. J. , Bowen R. C. , Reifenberger R. , Busnaina A. A. 
Published: April 2011

ABSTRACTThe physics of particle adhesion is a complex subject and depends on the interaction mechanisms and the mechanical properties of the contacting materials. These interactions, which tend to be caused by van der Waals and electrostatic interactions, generate stresses that, in turn, result in deformations of the contacting materials. Most of today's understanding of particle adhesion is based on theories that assume that the adhesion-induced strains are small. However, for small particles, the strains can be quite large, resulting in yielding and plastic deformations. In some instances, the entire particle can become engulfed by the substrate. This paper discusses the nature of the deformations, as are presently known, and extrapolates today's understanding of particle adhesion, which is based on the micrometer-size scale, to nanometer-size particles.
Synthesis and microstructure of conformal coatings on particulates
Authors: Rajan K. , Sajgalik P. , Singh R. K. , Kumar D. , Fitz-Gerald J. 
Published: April 2011

ABSTRACTIn this paper we present an overview of two very different approaches to the synthesis of composite particulates which result in a “core-shell” type structure. It is shown that both these synthesis approaches result in very characteristic interface structures between the outer coating and the host particles. One synthesis strategy is to use laser ablation deposition on individual particles and the other is to “coat” particles ‘in-situ’ by taking advantage of solid state diffusional transformations. Examination of the interface between the outer shell and the core of the particle shows that textured or toptactical growth occurs and it is suggested that this unique crystallographic characteristic may be responsible for the properties offered by these engineered particulates. The applications of such engineered particulates is also discussed.
Optical properties of gold clusters precipitated on zirconia particles
Authors: Valmalette J.-C. , Dutta J. , Scholz S. M. , Hofmann H. 
Published: April 2011

ABSTRACTWe have studied precipitation of noble metals with a view to extending these synthetic processes to other metals. In this paper we discuss the synthesis of gold clusters on the surface of oxide fine particles (in the range 60–100nm). The influence of pH of the solution, the concentration of metal and the reducing agent are discussed. The size distribution of the precipitated gold clusters, determined by transmission electron microscopy, are around 2–10 nm. The interface between the gold clusters and oxide has been investigated by HRTEM. Optical measurements of the zirconia supported gold clusters shows a significant shift in the plasmon resonance. A model based on effective medium theory is proposed taking into account the high refractive index of zirconia.
Swelling of SiO2 Quartz Induced by Energetic Heavy Ions
Authors: Trautmann C. , Costantini J. M. , Meftah A. , Schwartz K. , Stoquert J. P. , Toulemonde M. 
Published: April 2011

ABSTRACTA pronounced swelling effect occurs when irradiating SiO2 quartz with heavy ions (F, S, Cu, Kr, Xe, Ta, and Pb) in the electronic energy loss regime. Using a profilometer, the out-of-plane swelling was measured by scanning over the border line between an irradiated and a virgin area of the sample surface. The step height varied between 20 and 300 nm depending on the fluence, the electronic energy loss and the total range of the ions. From complementary Rutherford backscattering experiments under channelling condition (RBS-C), the damage fraction and corresponding track radii were extracted. Normalising the step height per incoming ion and by the projected range, a critical energy loss of 1.8 ± 0.5 keV/nm was found which is in good agreement with the threshold observed by RBS-C. Swelling can be explained by the amorphisation induced along the ion trajectories. The experimental results in quartz are compared to swelling data obtained under similar irradiation conditions in LiNbO3
Correlation of Intermediate Ion Energy Induced Extended Defect Continuity to Enhanced Pinning Potential in Tl-2212 Films
Authors: Provencio P. Newcomer , Venturini E. L. , Doyle B. L. , Brice D. K. , Schöne H. 
Published: April 2011

ABSTRACTLattice defects are introduced into the structure to suppress the motion of magnetic vortices and enhance the critical current density in high temperature superconductors. Point defects are not very effective pinning sites for the cuprate superconductors; however, extended defects, such as linear tracks, have been shown to be strong pinning sites. We study the superconducting cuprate TI-2212 (the numbers designate Tl-Ba-Ca-Cu stoichiometry). Large enhancements of vortex pinning potential were observed in TI-2212 after high-intermediate energy heavy-ion irradiations where non-continuous extended defects were induced at dE/dx of 9 to 15.2 keV/nm (60 MeV Au, 60 MeV Cu, and 30 MeV Au) and continuous linear defects were induced at 19.5keV/nm (88MeV Au). Our research addresses the question of pinning in highly anisotropic materials like Tl-2212 where the vortices are “pancakes” rather than “rods” and suitable defect structures may be discontinuous extended damage domains. The defect microstructure and the effectiveness of the pinning potential in TI-2212 after irradiation by intermediate energy Au at lower dE/dx of 5–15 keV/nm, where recoils are more significant, is studied using high resolution transmission electron microscopy digital imaging and a SQUID magnetometer. The nature of the ion irradiation damage at these intermediate dE/dx will be correlated to the average vortex pinning potential and the TRIMRC calculations for recoils.
Transmission Electron Microscopy Study of Cascade Collapse in Copper During in- Situ Ion- Irradiation at Elevated Temperatures
Authors: Daulton T. L. , Kirk M. A. , Rehn L. E. 
Published: April 2011

ABSTRACTThe basic mechanisms driving the collapse of point defects produced in collision cascades are investigated by transmission electron microscope (TEM) characterization of defect microstructures produced in fcc-Cu irradiated with low-fluences of heavy (100 keV Kr) ions at elevated temperature (23–600°C). Areal defect yields are determined from direct TEM observation of the total defect production integrated over the duration of the in-situ ion-irradiation. They are unequivocally demonstrated to decrease with increasing lattice temperature. This decrease in defect yield indicates a proportional decrease in the probability of collapse of cascade regions into defects of size where visible contrast is produced in a TEM.
Energetic Particle Synthesis of Metastable Layers for Superior Mechancial Properties
Authors: Follstaedt D. M. , Knapp J. A. , Myers S. M. , Dugger M. T. , Friedmann T. A. , Sullivan J. P. , Monteiro O. R. , Ager J. W. , Brown I. G. , Christenson T. 
Published: April 2011

ABSTRACTEnergetic particle methods have been used to synthesize two metastable layers with superior mechanical properties: amorphous Ni implanted with overlapping Ti and C, and amorphous diamond-like carbon (DLC) formed by vacuum-arc deposition or pulsed laser deposition. Elastic modulus, yield stress and hardness were reliably determined for both materials by fitting finiteelement simulations to the observed layer/substrate responses during nanoindentation. Both materials show exceptional properties, i.e., the yield stress of amorphous Ni(Ti,C) exceeds that of hardened steels and other metallic glasses, and the hardness of DLC (up to 88 GPa) approaches that of crystalline diamond (∼100 GPa). Tribological performance of the layers during unlubricated sliding contact appears favorable for treating Ni-based micro-electromechanical systems: stick-slip adhesion to Ni is eliminated, giving a low coefficient of friction (∼0.3–0.2) and greatly reduced wear. We discuss how energetic particle synthesis is critical to forming these phases and manipulating their properties for optimum performance.
Tribological Properties of Si-DLC Coatings Synthesized with Nitrogen, Argon Plus Nitrogen, and Argon Ion Beams
Authors: Fountzoulas C. G. , Demaree J. D. , Sengupta L. C. , Hirvonen J. K. , Dimitrov D. 
Published: April 2011

ABSTRACTHard, adherent, and low-friction silicon-containing diamond-like carbon coatings (Si-DLC) have been synthesized at room temperature by 40 keV (N+ plus N2+), 50%Ar+/50% (N+ plus N2+), and Ar+ ion beam assisted deposition (IBAD) of a tetraphenyl-tetramethyl-trisiloxane oil on silicon and sapphire substrates. X-ray diffraction analysis indicated that all coatings were amorphous. The average coating wear rate and the average unlubricated steel ball-on-disk friction coefficient, μ, decreased with increasing fraction of nitrogen in the ion beam, along with an increase in the average coating growth rate. The Knoop microhardness and nanohardness values of the coatings synthesized by the mixed argon and nitrogen ion beam were higher than the values for the coatings synthesized with 100% nitrogen or 100%argon ion beams. These friction/wear improvements are tentatively attributed to both increased hardening due to greater penetration and ionization induced hardening by the lighter (N) ions and to the presence of Si02 on the surface of N-bombarded samples.
Mesoscale Engineering of Nanocomposite Nonlinear Optical Materials
Authors: Haglund R. F. , Afonso C. N. , Feldman L. C. , Gonella F. , Luepke G. , Magruder R. H. , Mazzoldi P. , Osborne D. H. , Solis J. , Zuhr R. A. 
Published: April 2011

ABSTRACTComplex nonlinear optical materials comprising elemental, compound or alloy quantum dots embedded in appropriate dielectric or semiconducting hosts may be suitable for deployment in photonic devices. Ion implantation, ion exchange followed by ion implantation, and pulsed laser deposition have all been used to synthesize these materials. However, the correlation between the parameters of energetic-beam synthesis and the nonlinear optical properties is still very rudimentary when one starts to ask what is happening at nanoscale dimensions. Systems integration of corplex nonlinear optical materials requires that the mesoscale materials science be well understood within the context of device structures. We discuss the effects of beam energy and energy density on quantum-dot size and spatial distribution, thermal conductivity, quantum-dot composition, crystallinity and defects — and, in turn, on the third-order optical susceptibility of the composite material. Examples from recent work in our laboratories are used to illustrate these effects.
Ion Assisted Reaction In Polymer And Ceramics
Authors: Koh S. K. , Choi S. C. , Han. S. , Jung H-J 
Published: April 2011

AbstracrIon assisted reaction (IAR), which was firstly presented in 1995 MRS Fall meeting, has been reviewed for the surface modifications of polymer and ceramics. The reaction is assisted by energetic ions from 0.5 to 1.5 keV, doses 1014 to 1017 ions/cm2, and blowing rate of oxygen 0 ∼ 8 ml/min. Hydrophilic surfaces of polymers (wetting angle < 20° and surface energy 60 ∼ 70 erg/cm2) have been accomplished by the reaction, and an improvement of wettability and an increment of the surface energy are mainly due to the polar force and hydrophilic functional groups such as C=O, (C=O)-O, C-O, etc., without surface damage. The IAR was also applied on aluminum nitride in an O2 environment and AMON on AIN is formed by the Ar+ irradiation. The improvement of bond strength of Cu films on the AIN surface resulted from the interface bonds between Cu and the surface layers. Comparisons between the conventional surface treatments and the IAR are described in terms of physical bombardment, surface damage, functional group, and chain mobility in polymer.
Atomistic simulation of defect production in β-SiC
Authors: Devanathan R. , Weber W. J. , de la Rubia T. Diaz 
Published: April 2011

ABSTRACTThe process of defect formation and the threshold energies for Si and C displacements along various crystallographic directions in cubic silicon carbide (β-SiC) have been examined using molecular dynamics simulations. A combination of Tersoff and first-principles potentials was used to model the inter-atomic interactions. The lowest threshold energies for C and Si displacements were found to be 28 and 36 eV, respectively. These displacement threshold energies show excellent agreement with the results of recent first-principles calculations in SiC and with experimental observations. Simulation of a 10 keV Si cascade yielded values of about 0.1 ps for the cascade lifetime and about 3.5 for the ratio of the number of surviving C defects to Si defects. Anti-site defects were found on both Si and C sublattices. These defects may play an important role in the amorphization of SiC by energetic particle irradiation.
Suppression of Antiphase Disorder in GaAs Grown on Relaxed GeSi Buffers by Metal-Organic Chemical Vapor Deposition
Authors: Ting S. M. , Samavedam Srikanth B. , Currie Matthew T. , Langdo Thomas A. , Fitzgerald E. A. 
Published: April 2011

AbstractDue to the prohibitively high 4.1% lattice mismatch, direct growth of GaAs on Si invariably leads to very high dislocation densities (> 108/cm2) which have precluded its use in device applications despite numerous attempts. However, the growth of low threading dislocation density (∼2 × 106/cm2) relaxed graded Ge/GexSi1−x/Si heterostructures can bridge the gap between lattice constants by replacing the high mismatch GaAs/Si interface with a low mismatch (< 0.1%) GaAs/Ge interface. Although the lattice mismatch problem is thus eliminated, the heterovalent GaAs/Ge interface remains highly susceptible to antiphase disorder. Since antiphase boundaries (APBs) nucleated at the GaAs/Ge interface act as scattering and nonradiative recombination centers, growth of device quality GaAs on Ge/GexSi1−x/Si demands effective suppression of antiphase disorder. The current work investigates the sublattice location of GaAs on 6° offcut (001) Ge/GexSi1−x/Si substrates as a function of atmospheric pressure metal-organic chemical vapor deposition (MOCVD) growth initiation parameters. Two distinct GaAs phases are observed, one dominant at temperatures > 600°C and another at temperatures <500°C. Incomplete phase transitions during pre-growth thermal cycling account for the appearance of localized bands of anti-phase disorder where the polarity of the GaAs film switches. We suspect that background arsenic levels in the MOCVD system are largely responsible for inducing the observed phase transitions. The complete suppression of antiphase disorder under optimized growth conditions is demonstrated by transmission electron microscopy (TEM)
Control of The Sb Redistribution in Strained SiGe Layers Using Point Defect Injection
Authors: Kuznetsovl A.Yu. , Cardenast J. , Grahnt J.V. , Svensson B.G. , Nylandsted Larsenl A. , Lundsgaard Hansen J. 
Published: April 2011

AbstractSb diffusion in strained Si1−xGex (x = 0.1 and 0.2) layers during nitridation (in NH3, 810 °C) and oxidation (in dry O2, 825 and 900 °C) of Si/Si1−xGex/Si heterostructures is measured and, subsequently, compared with that obtained for treatments in vacuum. An enhancement (ν) or retardation (η) of Sb diffusion in strained Si1−xGex after nitridation/oxidation anneals is detected. For example, 810 (NH3) and 900 °C (O2) anneals results in ν ∼ 2 and η ∼ 0.15 in strained Si0.9Ge0.1, respectively. The retardation of Sb diffusion is attributed to the injection of excess self-interstitials (I) and strongly indicating low interstitialcy fraction of Sb diffusion in strained Si1−xGex. The enhancement of Sb diffusion may be due to direct injection of vacancies (V), but only if the V diffusivities are significantly different in Si and Si1−xGex, or depletion of I in the strained Si1−xGex layers caused by the excess V concentration at the top surface of silicon layer
Electronically Enhanced Reaction of Process-Induced Defects in GaAs
Authors: Wada K. , Nakanishi H. , Yamada K. , Kimerling L.C. 
Published: April 2011

AbstractThe present paper reviews current understanding on enhanced reactions of process-induced defects in GaAs under electronic excitation. Device processing to be employed for point defect generation is Be ion implantation and Ar plasma etching. It is shown that reduction of electronic active centers is clearly enhanced by annealing under forward bias application and by annealing under reverse bias application at temperature as low as 200°C. The enhancement mechanisms are discussed in terms of recombination-enhanced defect reaction and structural instability induced by charge state effect.
Gettering of Iron and Surface Oxygen by High-Energy Boron ion Implantation in Silicon
Authors: Jain Amitabh , Mercer Douglas E. , Yu Ning , Lowell John K. 
Published: April 2011

AbstractThe gettering of transition metals in silicon presents new challenges since older schemes such as internal gettering cease to be effective with newer technologies. The oxygen concentration in active regions is also a matter of concern when denuding cycles are not employed. Implantation of a deep layer of boron is a promising technique. The effects of boron implants at 1.7 MeV in the dose range 1014 – 1015 at./cm2 were studied with regard to the redistribution of both Fe and 0 after a thermal cycle. Fe was introduced onto the front surface of wafers by deposition after boron implantation. The redistribution of these species was monitored through SIMS depth profiles. In addition, diffusion length measurements from the back surface of the wafers were employed as a new means of assessing Fe gettering. In general there is a lowering of the surface oxygen concentration that increases with dose, or with temperature in the range 850-1000°C. The oxygen concentration can be lowered to a level comparable to denuded wafers at the upper end of this range. The amount of Fe gettering is higher after 850°C than after 1000°C at a given dose. Diffusion length measurements correlate well with SIMS data and provide a convenient method of investigating Fe gettering. This study has demonstrated the feasibility of optimizing a combination of dose and temperature for the gettering of Fe and the lowering of surface oxygen concentration to an acceptable level for device fabrication.
Charge Redistribution and Defect Relaxation in Heavily Damaged Silicon Studied Using Time Analyzed Transient Spectroscopy
Authors: Mohapatra Y.N. , Giri P.K. 
Published: April 2011

AbstractWe have carried out electrical characterization of defects in heavily damaged silicon, where damage is created by MeV heavy ions at doses near but below amorphization threshold. Trapping kinetics over several orders of magnitude in time have been monitored using isothermal spectroscopy called Time Analyzed Transient Spectroscopy (TATS). Two distinct effects regarding the nature of changes in density of states in the gap have been demonstrated. Firstly, we show that charge redistribution among multiple traps occur such that only the occupancy of the deeper states increase at the cost of shallower ones for long time filling. Secondly, a novel defect relaxation mechanism is observed for samples with relatively lower damage. A trap is seen to exhibit progressive deepening in energy with increase in filling time, finally stabilizing for large filling times. From the athermal nature of associated TATS peaks, it is argued that the relaxation involves large entropic contribution to free energy. The necessity of using a time domain relaxation spectroscopy such as TATS in the study of different mechanisms of relaxation is demonstrated.
Hydrogen Enhanced Defect Reactions in Silicon: Interstitial Atom - Vacancy
Authors: Nazarov A.N. , Pinchuk V.M. , Yanchuk T.V. , Lysenko V.S. 
Published: April 2011

AbstractIn the paper the model of interaction of the hydrogenated vacancy with silicon interstitial and different dopants (B, P and As) in crystalline silicon is considered. Quantum chemical calculations using the SCF MO LCAO technique in the NDDO valence approach show that the hydrogenation of the vacancy leads to the considerable decrease of the energy barrier height for the interstitial atom incorporation into the vacancy site of the crystalline lattice. The potential barriers for incorporation of the interstitial into the site and for leaving the atoms from the site have been calculated as a function of hydrogen localization in the vicinity of the vacancy (inside and outside of the vacancy), the charge state of hydrogen localized outside the vacancy (HO, H+ and H-) and the transport direction (<111>, <110> and <100>) of the atoms both to the vacancy and out from it. The theory is compared with the reported experimental results.