bluuebunny/crossref_metadata_2025 huggingface dataset:
Elastic Constants and Related Properties of the Group III-Nitrides
Authors: Kim Kwiseon , Lambrecht Walter R. L. , Segall B.
Published: April 2011

The elastic constants of the Group-III nitrides, c-BN, AlN and GaN were calculated from first-principles using the full-potential linear muffin-tin orbital method and local density approximation. The relation between the elatic constants in zincblende and wurtzite is studied by means of a tensor coordinate transformation approach. The latter combined with a correction for the internal displacement of the rotated tetrahedra is found to provide good results for the Ch11Ch12 and Ch44 but not for Ch13 and Ch33. These two require explicit calculations involving distortions along the c-axis. The calculations also provide information on the transverse optical phonons. By deriving Keating model parameters we show that BN is much stiffer against bond-angle distortions than the other nitrides.
The Phonon Densities of States of AlN and ZrN
Authors: Loong C.-K.
Published: April 2011

Phonons are thought to play a crucial role in the high thermal conductivity of AIN and ZrN. Using time-of-flight neutron spectroscopy, we have measured the phonon spectra of A1N and ZrN up to 300 meV (2400 cm−1). The one-phonon density of states (DOS) of AIN exhibits relatively sharp bands at about 33, 63, 83 and 91 meV. In addition, distinct multiple-phonon excitations were observed at ∼173 and 255 meV. The phonon DOS of ZrN displays similar features with the corresponding phonon energies shifted toward lower energies. The measured DOS of AIN is compared with results of molecular-dynamics simulations.
Structure and Quasiparticle Energies of Cubic, Wurtzite and Hexagonal BN
Authors: Cappellini Giancarlo , Fiorentini Vincenzo , Tenelsen Katrin , Bechstedt Friedhelm
Published: April 2011

We present local density functional theory (DFT-LDA) studies of the structural properties of boron nitride in the layered hexagonal (h-BN), zincblende (c-BN), and wurtzite (w-BN) structures, performed using a fast implementation of the norm-conserving pseud-opotential plane-wave method. Quasiparticle band structures are then calculated for all phases by means of an efficient GW self-energy scheme. To our knowledge, these are the first GW quasiparticle calculations for wurtzite BN including local-field and dynamical screening effects. DFT-LDA band gaps as functions of pressure and uniaxial distorsion for h-BN are also discussed.
Growth and Optical Properties of GaN Grown by MBE on Novel Lattice-Matched Oxide Substrates
Authors: Nicholls J.F.H. , Gallagher H. , Henderson B. , Trager-cowan C. , Middleton P.G. , O'Donnell K.P. , Cheng T.S. , Foxon C.T. , Chai B.H.T.
Published: April 2011

In this paper we demonstrate the feasibility of growing III-N semiconductors on novel lattice-matched oxide substrates. Although the growth parameters are not yet optimal, acceptable GaN layers have been grown.
Spatially-Resolved Photoluminescence and Raman Study on the GaN/Substrate Interface
Authors: Siegle H , Thurian P. , Eckey L. , Hoffmann A. , Thomsen C. , Meyer B K. , Detchprohm T. , Hiramatsu K. , Amano H. , Akasaki I.
Published: April 2011

We performed spatially-resolved photoluminescence and Raman experiments on the substrate interface region of wurtzite GaN layers. We found that the broad ”yellow” photoluminescence band is strong only near the interface. Our investigations reveal that both the substrate interface and a region of structural reorientation of the layer near the interface act as source of the photoluminescence. The Raman-scattering experiments show that at least a portion of the GaN layer near the substrate interface is oriented in such a way that the c-axis of the layer is parallel to the substrate interface. At a distance about 30 µm away from the interface the layer reorients by turning the c-axis by 90° into a direction perpendicular to the substrate interface.
Spin-Dependent Transport in GaN Light Emitting Diodes
Authors: Brandt M. S. , Reinacher N. M. , Ambacher O. , Stutzmann M.
Published: April 2011

Electrically detected magnetic resonance (EDMR) is used to study recombination processes in two types of gallium nitride light emitting diodes: in m/i/n/n+- and InGaN/AlGaN double-heterostructure devices. In the MIS-diodes, two resonances at g=1.96 and 2.00, corresponding to the effective mass donor and a deep defect are observed at room temperature. At low temperatures, an acceptor-related resonance at g=2.06 is visible as well. After current degradation, the spectra are dominated by the defect resonance, indicating that the creation of this defect is responsible for the decreased electroluminescence efficiency. In the double-heterostrucrure devices, EDMR can only be observed below 60 K showing the g=2.00 defect resonance. The same defect resonance is also observed in conventional electron spin resonance experiments under illumination (light-induced ESR).
Ex Situ and in Situ Methods for Oxide and Carbon Removal from AlN and GaN Surfaces
Authors: King Sean W. , Smith Laura L. , Barnak John P. , Ku Ja-Hum , Christman Jim A. , Benjamin Mark C. , Bremser Michael D. , Nemanich Robert J. , Davis Robert F.
Published: April 2011

Exposure to numerous acids and bases and UV/O3 oxidation were used to determine the best ex situ cleaning techniques for the (0001) surfaces of AIN and GaN. HF and HCI were the most effective in removing the oxide from AIN and GaN, respectively. However, AES and XPS revealed the surfaces to be terminated with F and CI which inhibited re-oxidation prior to loading into vacuum. TPD showed mat temperatures of 650 and 850°C are necessary to thermally desorb the CI and F, respectively. UV/O3 oxidation in air was not effective in removing hydrocarbons from either surface but was effective for oxide growth. In situ remote hydrogen plasma exposure at 450°C removed halogens and hydrocarbons remaining after ex situ cleaning of both AIN and GaN surfaces; however, oxide free surfaces could not be achieved. Thermal desorption of hydrocarbons from GaN in UHV was achieved at 650°C. Complete thermal desorption of the surface oxide in UHV was only achieved at temperatures > 800°C where some GaN decomposition occurred. Annealing GaN in NH3 at 700°C reduced the surface oxide without loss of surface stoichiometry.
Annealing Study of Ion Implanted MOCVD and MBE Grown GaN
Authors: Silkowski E. , Yeo Y. K. , Hengehold R. L. , Khan M. A. , Lei T. , Evans K. , Cerny C.
Published: April 2011

MOCVD and MBE grown GaN were implanted with Ar, Mg, Si, Be, C, and O, and annealed in a conventional oven under flowing NH3 or N2 gas. Absorption measurements confirmed that implantation damage was annealed out after 90 minutes at a temperature of 1000 °C. Surface damage caused by NH3 annealing was evident in absorption and photoluminescence measurements for annealing temperatures of over 1000 °C. Although most of the implants showed no unique luminescence peaks, systematic changes in the relative intensities of the exciton, donor-acceptor pair, and yellow peaks were noted. The Mg implanted samples showed evidence of the acceptor bound exciton line at 3.44 eV, and a unique peak at 3.3 eV possibly due to a Mg free-to-bound transition.
Schottky Barriers on p-GaN
Authors: Kuznetsov N.I. , Kalinina E.V. , Soloviev V.A. , Dmitriev V.A.
Published: April 2011

Schottky barriers were formed on p-GaN. p-GaN layers doped with Mg were grown by metalorganic chemical vapor deposition (MOCVD). 6H-SiC wafers were used as substrates. The barriers were made by vacuum thermal evaporation of Au. Capacitance-voltage (C-V) and current-voltage (I-V) characteristics of the barriers were investigated. The concentration of the ionized acceptors in the p-layers was measured to be about ∼1017 cm−3. The barrier height was determined to be 2.48 eV by C - V measurements at room temperature. The forward current flow mechanism through the barriers is discussed.
The Surface Chemistry of Triallylamine on Si(111) and its Coadsorption with Triethylgallium
Authors: Freundt Dirk , Landmesser Georg , Rizzi Angela , Lüth Hans
Published: April 2011

The surface chemistry of Triallylamine (TAA), (C3H5)3N on Si(111) has been studied by adsorption under UHV conditions and in-situ characterization. High Resolution Electron Energy Loss Spectroscopy (HREELS) yields the spectrum of vibration modes at the surface, and X-ray Photoelectron Spectroscopy (XPS) yields the chemical bonding and the partial concentration of the different adsorbates in the near surface region. The tertiary amine TAA physisorbs at RT without dissociation. Successive annealing steps of the physisorbed phase induce the dissociation of the amine at 400 °C. At higher temperatures the allyl groups are partially desorbed and the rest fully dissociated at 600 °C, where the hydrogen leaves the surface and the nitrogen and carbon start to diffuse into the Si substrate. A very similar behaviour is observed for the adsorption of TAA on a heated Si substrate. The coadsorption with Triethylgallium (TEG) in the temperature range 500–800 °C does not induce significant changes in the reaction at the Si surface. A negligible quantity of Ga is detected at the surface after codeposition in the whole investigated temperature range. The growth of a GaN phase has not been observed, neither on Si(111) nor on Al2O3(0001) substrates.
Correlation of surface morphology and optical properties of GaN by conventional and selective-area MOCVD
Authors: Li X. , Jones A. M. , Roh S. D. , Turnbull D. A. , Reuter E. E. , Gu S. Q. , Bishop S. G. , Coleman J. J.
Published: April 2011

We have studied GaN films grown by atmospheric pressure metalorganic chemical vapor deposition (MOCVD) on sapphire substrates using different buffer layer structures. Surface morphology was characterized by scanning electron microscopy (SEM). Optical properties were measured using photoluminescence (PL), cathodoluminescence (CL) spectroscopy and catho-luminescence wavelength imaging (CLWI) method. It is found that the hexagonal pit-like defects in morphology are associated with the D-A/e-A transition band in the PL and CL spectra. The same correlation of morphology with optical properties is observed for the GaN films grown by selective area epitaxy (SAE). In addition, the possibility of improving optical quality by SAE is investigated. The SAE depth profile is simulated for the first time, and satisfactory results are obtained.
Spectral Response of GaN P-N Junction Photovoltaic Structures
Authors: Walker D. , Zhang X. , Kung P. , Saxler A. , Xu J. , Razeghi M.
Published: April 2011

GaN ultraviolet photovoltaic and photoconductive detectors were grown on sapphire substrates by metalorganic chemical vapor deposition. The spectral response was analyzed considering the detector structure of a p-n junction connected back-to-back with a Schottkty barrier. Based on the one-dimensional model of abrupt p-n junctions, the diffusion length of minority carriers was derived to be about 0.1 μm in n-GaN. To further characterize the n-GaN material, photoconductivity experiments have also been realized. The majority carrier lifetime of about 0.1 ms was obtained by analyzing the voltage-dependent responsivity of GaN photoconductors The current-responsivity under a bias of 8 V was about 1 A/W.
Gas Phase Adduct Reactions in MOCVD Growth of GaN
Authors: Thon A. , Kuech T.F.
Published: April 2011

Gas phase reactions between trimethylgallium (TMG) and ammonia were studied at high temperatures, characteristic to MOCVD of GaN reactors, by means of insitu mass spectroscopy in a flow tube reactor. It is shown, that a very fast adduct formation followed by elimination of methane occurs. The decomposition of TMG and the adduct - derived compounds are both first order and have similar apparent activation energy. The pre-exponential factor of the adduct decomposition is smaller, and hence is responsible for the higher full decomposition temperature of the adduct relative to that of TMG.
Effect of Ambient Gas Pressure on Pulsed Laser Ablation Plume Dynamics and Znte Film Growth
Authors: Rouleau CM. , Lowndes D.H. , Strauss M.A. , Cao S. , Pedraza A.J. , Geohegan D.B. , Puretzky A.A. , Allard L.F.
Published: April 2011

Epitaxial thin films of nitrogen-doped p-ZnTe were grown on single-crystal, semi-insulating GaAs substrates via pulsed laser ablation of a stoichiometric ZnTe target. Both low pressure nitrogen ambients and high vacuum were used. Results of in situ reflection high energy electron diffraction (RHEED) and time-resolved ion probe measurements have been compared with ex situ Hall effect and transmission electron microscopy (TEM) measurements. A strong correlation was observed between the nature of the film's surface during growth (2-D vs. 3-D, assessed via RHEED) and the ambient gas pressures employed during deposition. The extended defect content (assessed via cross-sectional TEM) in the region >150 nm from the film/substrate interface was found to increase with the ambient gas pressure during deposition, which could not be explained by lattice mismatch alone. At sufficiently high pressures, misoriented, columnar grains developed which were not only consistent with the RHEED observations but also were correlated with a marked decrease in Hall mobility and a slight decrease in hole concentration. Ion probe measurements, which monitored the attenuation and slowing of the ion current arriving at the substrate surface, indicated that for increasing nitrogen pressure the fast (vacuum) velocity-distribution splits into a distinct fast and two collisionally-slowed components or modes. Gas-controlled variations in these components mirrored trends in electrical properties and microstructural measurements.
Fabrication of A Barium Titanate-Strontium Titanate Strained Layer Superlattice
Authors: Harkness S.D. , Singh R.K.
Published: April 2011

A thin film superlattice heterostructure composed of alternating BaTiO3 and SrTiO3 layers was grown on a thin YBa2Cu3O7 electrode templated on a (100) SrTiO3 wafer using the pulsed laser deposition method. Stranski-Krastanov nucleation of the layers was demonstrated using atomic force microscopy (AFM) when processing conditions were maintained at 6 millitorr oxygen partial pressure, and 550 °C substrate temperatures. High-resloution x-ray diffraction (HRXRD) measurements indicate that all the deformation was concentrated in the BaTiO3 layers with c/a extension to approximately 1.08. Rutherford backscattering spectroscopy (RBS) results indicate excellent crystallinity in the heterostructure. The microstructural data suggests that the theoretical critical thickness of the film has been surpassed by an order of magnitude.
Positive Ion Emission Accompanying UV Irradiation of Single Crystal Mgo and NanO3
Authors: Ermer D. R. , Shin J. J. , Langford S. C. , Dickinson J. T.
Published: April 2011

Although MgO is much more resistant to radiolysis by 248-nm photons than NaNO3, the ion emission processes at low fluence have much in common: both materials yield high energy ions (> 5 eV kinetic energy) with a strongly nonlinear fluence dependence. We report time-of-flight measurements of quadrupole mass-selected Mg+ from polished, single crystal MgO and Na+ from cleaved, single crystal NaNO3. At fluences between 10 and 1000 mJ/cm2, the Mg+ intensities show a strongly nonlinear fluence dependence which decreases to roughly second order behavior at fluences above 100 mJ/cm2. The Na+ intensities display third or fourth order emission kinetics throughout the experimental range of fluences. We attribute these emissions to cations adsorbed atop surface electron traps where the cation is ejected when the underlying trap is photo-ionized. The potential energy of this defect configuration accounts for the observed ion kinetic energies. However, the direct photo-ionization of surface vacancy/adsorbed ion defects with 5 eV photons should not be possible. Thus we propose that emission requires the photo-ionization of nearby electron traps, followed by photo-induced charge transfer to the empty traps. We show that a sequence of single-photon absorption events [involving photo-ionization, charge transfer, and electron retrapping] accounts for the strongly nonlinear fluence dependence.
A Non-Reactive Excimer-Based Surface Preparation and Cleaning Tool for Broad-Based Industrial Applications
Authors: Harvey E. C. , Fletcher J. , Engelsberg A. C.
Published: April 2011

A surface-cleaning and preparation method that uses high-energy photons and a laminar flowing inert gas has been demonstrated as a feasible technology for broad-based industrial applications such as semiconductors, electronics, optics, coated optical and magnetic media, automotive, aerospace and art restoration. This technology is flexible in tool embodiment and is environmentally friendly because no water and chemicals are not used.
CO2 Laser Cleaning of Hydrophilic Oxidized Silicon Surfaces
Authors: Boughaba S. , Sacher E. , Meunier M.
Published: April 2011

The removal of particles as small as 0.1 μm was achieved using a pulsed CO2 laser to induce the explosive vaporization of condensed water. The surfaces used were hydrophilic oxidized silicon. The contaminant particles were 0.1 μm alumina, 0.1-0.2 μm fumed silica, and 0.1 μm polystyrene latex; their zeta potentials in water vary from positive to negative. The effect of the laser beam energy flux on the cleaning efficiency was thoroughly investigated. It was varied between 0.5 and 3 J/cm2. Whatever the nature of the contaminants, the cleaning process was characterized by an upper limit, the surface damage threshold energy density, determined to be 1.5 J/cm2. If the removal efficiency drops for the lowest beam energy flux, i.e., 0.5 J/cm2, and 0.1 μmAl2O3 particles, no single, sharp removal threshold was observed. Another parameter of importance investigated was the thickness of the condensed water. It was varied by changing the time of exposure of the substrate surface to water vapor before laser irradiation, the vapor flow being fixed to 4700 ml/min. Exposure times ranging from 1.5 to 2.5 s were evaluated to be the most effective.
Structure-Property Relationship of Ceramic Coatings Produced by Laser Processing
Authors: De Hosson J.Th.M. , Zhou X.B.
Published: April 2011

This paper deals with a well known puzzling observation that wetting in some instances is improved by a chemical reaction between a liquid and a solid substrate in laser processing while in other systems just the opposite effect takes place. Here, contact angles of liquid Al on SiO2 and liquid Ti on Al2O3 are reported and some results of laser melt injection of SiO2 particles into molten Al.The surface and interface structures were explored by scanning electron microscopy and energy dispersive X-ray spectrometry. According to the experimental observations, it appears that the volume change of ceramic substrates during reaction plays a key role in the effect of chemical reaction on wetting.
Use of an Excimer Lamp for Photochemical Resistless Etching of Thermal Silicon Oxide Substrate
Authors: Kamata N. , Murahara M.
Published: April 2011

Photochemical resistless etching was carried out by using a Xe2* excimer lamp and a KrF excimer laser. The decomposition method with Xe2* excimer lamp increases the decomposition efficiency by 100 times than that of using ArF excimer laser and etchant gas, CHClF2. Xe2* excimer lamp irradiation allowed decomposition of CHClF2 gas to produce CF2 radical with a small quantity of gas. The CF2 radical was polymerized to form fluorocarbon layer on the SiO2 substrate. Simultaneously, circuit patterned KrF excimer laser was vertically irradiated the fluorocarbon layer on the substrate for resistless etching. The etching depth was about 1,000Â.
Species-resolved imaging and gated photon counting Spectroscopy of laser ablation plume dynamics During krf- and arf-laser pld of amorphous diamond films
Authors: Geohegan David B. , Puretzky Alexander A.
Published: April 2011

Gated photon counting spectroscopy and species-resolved ICCD photography have been applied to study the weak plasma luminescence which occurs following the propagation of the initial ablation plume in vacuum and during the ‘rebound’ of the plume with a substrate during pulsed laser deposition of amorphous diamond. These time- and spatially-resolved spectroscopic techniques were required in order to investigate notable differences between amorphous diamond-like carbon films formed by pulsed laser deposition from ArF (193 nm) and KrF (248 nm) irradiation of pyrolytic graphite in vacuum. Three principal regions of plume emission have been characterized: (1) a bright luminescent ball (v ∼3-5 cm/(μ.s) displaying nearly entirely C+ emission which appears to result from laser interaction with the initial ejecta, (2) a spherical ball of emission (v ∼1 cm/μs) displaying neutral carbon atomic emission lines and, at early times, jets of excited C2, and (3) a well-defined region of broadband emission (v ∼ 0.3 cm/μs) near the target surface first containing emission bands from C2, then weak, continuum emission thought to result from C3 and higher clusters and/or blackbody emission from hot clusters or nanoparticles. For both lasers, the measurements reveal an explosive interaction within the plume which results in a variety of new gas dynamic observations in vacuum:. These include (a) generation of instabilities or jets, (b) confinement of a residual part of the plume near the pellet surface, (c) cluster formation in the collisional, confined regions of the plume, and (d) reflection of the confined region backward to splash and redeposit on the pellet surface. Evidence for gas-phase formation of these clusters in vacuum is indicated from the dynamic evolution of the same cluster bands observed during the collision of the plume with the substrate surface during film growth. Addition of background gases strongly enhances the third (cluster) component, in accordance with plume-splitting phenomena. The combination of sensitive imaging and photon-counting diagnostic techniques permit an understanding of the importance of gas dynamic effects, such as clustering, on the time-of-flight distributions of species arriving during the deposition of thin films in both vacuum and background gases.
In Situ Diagnostics of Vuv Laser Cvd of Semiconductor Interfaces by Ftir Spectroscopy and Spectroscopic Ellipsometry
Authors: Barth M. , Knobloch J. , Hess P.
Published: April 2011

The growth of high quality amorphous hydrogenated semiconductor films was explored with different in situ spectroscopic methods. Nucleation of ArF laser-induced CVD of a-Ge:H on different substrates was investigated by real time ellipsometry, whereas the F2 laser (157nm) deposition of a-Si:H was monitored by FTIR transmission spectroscopy. The ellipsometric studies reveal a significant influence of the substrate surface on the nucleation stage, which in fact determines the electronic and mechanical properties of the bulk material. Coalescence of initial clusters occurs at a thickness of 16 Å for atomically smooth hydrogen-terminated c-Si substrates, whereas on native oxide covered c-Si substrates the bulk volume void fractions are not reached until 35 Å film thickness. For the first time we present a series of IR transmission spectra with monolayer resolution of the initial growth of a-Si:H. Hereby the film thickness was measured simultaneously using a quartz crystal microbalance with corresponding sensitivity. The results give evidence for cluster formation with a coalescence radius of about 20 Å. Difference spectra calculated for layers at different depths with definite thickness reveal that the hydrogen-rich interface layer stays at the substrate surface and does not move with the surface of the growing film. The decrease of the Urbach energy switching from native oxide to H-terminated substrates suggests a strong influence of the interface morphology on the bulk material quality.
Selective Area Epitaxy of GaAs Optical Waveguides by Laser Assisted Chemical Vapor Deposition
Authors: Roberts J.C. , Boutros K.S. , Bedair S.M.
Published: April 2011

Direct writing of GaAs optical waveguides has been achieved by laser assisted chemical vapor deposition (LCVD). The multimode waveguides have gaussian-like cross sections, smooth surfaces, and exhibit losses as low as 5.4 dB/cm. The LCVD technique offers the capability of maskless in situ selective epitaxial growth of diverse multilayer structures, and is therefore a novel alternative for the monolithic integration of optoelectronic integrated circuits.
Transient and Athermal Nucleation of Solids in Rapidly Quenched Liquid Si
Authors: Gupta Vikas V. , Im James S.
Published: April 2011

We have theoretically investigated the nature and kinetics of solid nucleation in supercooled liquid Si within the framework of the classical nucleation theory, and corresponding to the cases in which the liquids are quenched at extremely high quenching rates (from 109 to 1011 K/s). In doing so, we identify and draw a general conclusion that in addition to the well-treated phenomenon of transient nucleation, one must also consider the mechanism of athermal nucleation in order to properly elucidate the situations that are encountered at such high quenching rates. Moreover, contrary to the common notion that the transient effect is relevant at low temperatures where sluggish kinetics prevail, it is noted that the effect can also become prominent at near-equilibrium conditions due to the increase in the time needed by the embryos to reach the exceedingly large critical size.
Tem/Hrem Structural Characterization of Directionally Solidified Gaas-Cras Eutectic Crystals
Authors: Ruvimov Sergei , Liliental-Weber Zuzanna , Swider Wendy , Washburn Jack , Holmes Douglas E.
Published: April 2011

Conventional and high resolution electron microscopy have been applied to characterize the microstructure of the CrAs-GaAs eutectic. The CrAs-GaAs eutectic crystals were directionally solidified by the Czochralski method in order to produce an ordered array of CrAs rods embedded in a GaAs matrix. The CrAs rods of 2-3 μm in diameter align parallel to the growth axis of the ingot. Where the GaAs matrix is found to contain structural defects, the CrAs rods are effectively defect-free. The CrAs has an orthorombic structure with the parameters a=3.5±0.1 Å, b=6.2±0.1 Å,c=5.7±0.1 Å.The c-axis is close to the direction of solidification.
Interfacial Reactions in Metal-Matrix Composites
Authors: Heffelfinger J. R. , Kieschke R. R. , Carter C. B.
Published: April 2011

The interfacial reaction between Al2O3 (alumina) and a β-Ti alloy has been characterized by transmission electron microscopy, scanning electron microscopy, and X-ray energy-dispersive spectroscopy. Diffusion bonding single-crystal alumina and a β-Ti alloy was found to produce three interfacial regions: a region of intermetallics (Tl3Al and TiAl) located near the alumina interface, an α-Ti region, and a β-Ti region (rich in Mo, the β-phase stabilizer). Of the intermetallics to form, Ti3Al was found to form first and have an aligned, planar interface with the alumina. TiAl formed second and was found to separate grains of Ti3Al and the alumina. Reaction products observed in the diffusion-bonded alumina/β-Ti couples are compared with those observed in metal-matrix composites (MMCs), where a β-Ti alloy matrix is reinforced with alumina fibers. Different coatings used in MMCs are investigated for their ability to prevent the reaction between the matrix and fibers.
Interfacial Reactions Between Ain Substrate And 4-A Family Elements
Authors: Du Yong , He Xiangjun , Tao Kun
Published: April 2011

Interfacial reactions between A1N substrate and 4A-family elements including Ti, Zr and Hf were studied. The samples were prepared by Physical Vapour Deposition and annealed at different temperatures from 200°C to 800°C. X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) were employed to detect the compounds formed at the interfaces between them. For Ti/AIN system, when the samples were annealed from 600°C to 800°C for 1 hour, it was found from XRD patterns that TiAl3, TiN, and Ti4N3.x including Ti2N were formed at Ti/AIN interface. With the temperature increasing, the intensities of Ti, TiN(200), Ti2N and Ti4N3.x diffraction peaks decreased while that of TiAl3 and TiN(111) increased. For Zr/AlN system, it was found that the reactions between Zr and AlN resulted in the formation of Al3Zr at about 300°C and Al2Zr at about 500°C. According to RBS spectra, it can be assumed that Al3Zr was the direct product by the reaction between AlN and Zr and Al2Zr was formed by the reaction between Al3Zr and Zr. For Hf/AlN system, however, even the sample was annealed at 800°C, no compound resulted from interfacial reactions was detected.
Atomistic Image of the Kinetics of ‘Order-Order’ Reactions in Ni3Al+B
Authors: Kozubski R. , Pfeiler W.
Published: April 2011

Isothermal ‘order-order’ relaxations in Ll2-ordered N76Al24+0.19at.%B were studied by means of residual resistometry. This method made it possible to register very fine changes in the degree of LRO occurring about 1000K below the disordering temperature.
The experimental results of two simultaneous processes being involved in these order-order relaxations with a high activation energy of 4.6eV are explained with an atomistic model of atomic jumps to nn vacancies. The parallel processes are connected with selected jumps of atoms to nn vacancies on different sublattices with a high activation energy of vacancy formation being involved.
Analysis of TPD Spectra on Semiconductor Surfaces by Monte Carlo Simulations
Authors: Venkataramani Rajesh , Jensen Klavs F.
Published: April 2011

This work aims to provide a systematic approach for deriving desorption mechanisms on semiconductor surfaces from a coupling of temperature programmed desorption (TPD) experiments and Monte Carlo (MC) simulations. MC simulations are used to evaluate different desorption schemes to identify mechanisms consistent with experimental results. Effects of nearest neighbor interactions, island formation, and surface reconstructions are quantified through the simulations. Methyl desorption from Ga-rich GaAs is used as a case study to illustrate the MC procedure for interpretation of TPD spectra.
GaAs-on-Ge Heteroepitaxy by Atomic Hydrogen-Assisted Molecular Beam Epitaxy (H-MBE)
Authors: Okada Yoshitaka , Harris James S. , Sutoh Atsushi , Kawabe Mitsuo
Published: April 2011

The purpose of this work is to achieve a high-quality epitaxy of GaAs-on-Ge system at low growth temperatures of 300 ∼ 400°C, by atomic hydrogen-assisted molecular beam epitaxy (H-MBE), in attempt to reduce Ge segregation to a minimum and to realize a layer-by-layer two-dimensional (2D) growth mode from the initial stages of the growth. A high-quality heteroepitaxy is expected in H-MBE technique as atomic H is known to act as an effective surfactant modifying the kinetics and energetics of the growth, which are practically difficult to control on atomic-scale unless a third element like a surfactant is introduced into the growth system. It is shown with the support of reflection high-energy electron diffraction (RHEED), secondary ion mass spectroscopy (SIMS), and atomic force microscopy (AFM) characterization that an enhanced layer-by-layer 2D growth can actually be realized and (2×4) GaAs(001) surface can be achieved in low-temperature heteroepitaxy on vicinal Ge(001) substrates at 400 °C by H-MBE.
Interdiffusion During the Growth of Fe on Ag/Fe(110)
Authors: Persaud R. , Noro H. , Venables J. A.
Published: April 2011

We have previously shown the growth mode of Ag on Fe(110) to be Stranski-Krastanov with Ag islands growing on top of two intermediate Ag layers. In the present studies, Fe was deposited on thin annealed Ag layers on Fe(110). The growth and interdiffusion of these layers were monitored by reflection high energy electron diffraction (RHEED) and Auger electron spectroscopy (AES). For deposition at room temperature (RT), Fe islands grow in a (HO) orientation on the Ag/Fe(110) substrate. These islands form facets similar to those obtained at an equivalent coverage for the Fe/Fe(110) system. AES indicates that there is some intermixing between the deposited Fe atoms and underlying Ag layers at RT. During annealing, or for deposition at 250°C, Ag floats to the top while the Fe islands flatten to form layers at the Ag/Fe(110) interface.
Strain Relaxation at Low Misfits: Dislocation Injection vs. Surface Roughening
Authors: Perovic D.D. , Bahierathan B. , Houghton D.C. , Lafontaine H. , Baribeau J.-M.
Published: April 2011

Two competing strain relaxation mechanisms, namely misfit dislocation generation and surface roughening, have been extensively studied using the GexSi1-x/Si (x< 0.5) system as an example. A predictive model has been developed which accurately describes the nature of misfit dislocation nucleation and growth under non-equilibrium conditions. Using optical and electron microscopy, coupled with a refined theoretical description of dislocation nucleation, it is shown that strain relieving dislocations are readily generated at low misfits with a characteristic activation energy barrier regardless of the growth technique employed (i.e. MBE, RTCVD and UHVCVD). Secondly we have studied the alternative elastic strain relaxation mechanism involving surface undulation; x-ray diffraction, electron and atomic force microscopy have been used to characterize GexSi1-x/Si (x<0.5) structures grown by UHVCVD and MBE at relatively higher temperatures. A theoretical model has been used to model the critical thickness for surface wave generation. The conditions governing the interplay between dislocation formation and surface buckling are described in terms of a "morphological instability diagram".
Observations on the Mechanics of Strained Epitaxial Island Growth
Authors: Freund L. B. , Johnson H. T. , Kukta R. V.
Published: April 2011

An epitaxial material island which has a lattice parameter differing by a small amount for that of its substrate is considered within the framework of continuum mechanics. The strain distribution in the island is determined for a range of aspect ratio, taking into account the compliance of the substrate. It is demonstrated that the total free energy of a strained island is minimum for some value of aspect ratio, and that this value depends on the volume of the island. To consider strain relaxation, the nucleation of a dislocation at the edge of a strained island is examined and the equilibrium aspect ratio of a dislocated island is computed. In particular, it is shown that an island can reduce its free energy by reducing its aspect ratio and, simultaneously, forming an interface misfit dislocation. The simulations are based on the numerical finite element method.
Strain-Induced Diffusion in Heteroepitaxially Grown CuInSe2 on GaAs Substrates
Authors: Fons P. , Niki S. , Yamada A. , Okada A. , Tweet D.J.
Published: April 2011

A series of CuInSe2 thin films of varying thicknesses were grown on both GaAs(001) substrates and nominally lattice-matched In0.29Ga0.71As (001) linearly graded buffers by MBE at 450°C. Transmission electron microscopy and high resolution x-ray diffraction measurements revealed the presence of a second phase with chalcopyrite symmetry strained to the CuInSe2 thin film in-plane lattice constant for CuInSe2 films grown on GaAs substrates. Further examination confirmed that the second phase possessed chalcopyrite symmetry. No second phase was observed in films grown on nearly lattice-matched In0.29Ga0.71As (001) linearly graded buffers. Secondary ion mass spectrometry confirmed the presence of interdiffusion from of Ga from the substrate into the CuInSe2layer. It is speculated that this diffusion is related to the state of stress due to heteroepitaxial misfit.
Highly Refined Microstructures in Devitrified Alloys
Authors: Battezzati L.
Published: April 2011

The formation of nanosized microstructures from controlled devitrification of amorphous alloys is reviewed. The driving force for copious nucleation of crystals is discussed in terms of thermodynamic models for the free energy of crystallization and for the interfacial free energy. After fast nucleation and growth of crystals to nanometric size, there are evidences of a change in diffusion mechanism to slow growth. Examples are provided of primary processes in Fe-Zr-B and Al-Sm with data of XRD, TEM, DSC. Cases of eutectic and polymorphic transformations are also at hand (Ni-P, Cu-Ti-Al, Cu-Ti-Ni, Ti-Zr-Co-Cu-Al) showing that the thermodynamic and kinetic conditions leading to nanostructured materials are not unique.

Finally chemical effects are discussed such as those of impurities in crystallization (e. g. Zr-based alloys), in leaching of Ni-Zr-Al and in deposition reaction of electroless Ni-P.
Structural and Mechanical Properties of a Simulated Nickel Nanophase
Authors: D’Agostino G. , Van Swygenhoven H.
Published: April 2011

The present paper is aimed at studying the physics of a nickel nanophase at the atomic level. A dense polycrystal has been designed by ideally growing many nano-crystals from randomly distributed seeds and truncating them through a Voronoi construction. The sample has been brought to thermodynamic equilibrium and quenched to its local minimum energy thus leading to a mechanically stable system. The dynamic evolution has been simulated by means of classical molecular dynamics employing a Finnis-Sinclair interactive potential. Owing to the large number of atoms required, a parallel code has been developed. Elastic and plastic behaviour of the simulated sample has been compared with that of a perfect crystal. Evidence of an enhanced plastic behaviour has been observed when severe tensile stresses are applied.
Physical Properties of Partially Crystallized Fe80B20 Amorphous Alloys
Authors: Fiorani D. , Malizia F. , Ronconi F. , Vittori Antisari M.
Published: April 2011

The magnetic properties and hyperfine fields were investigated at low temperatures on amorphous Fe80B20 ribbons crystallized at the end of the nucleation-and-growth process without involving coarsening process. The results obtained by SQUID magnetometer and Mössbauer spectrometer show that saturation magnetization and mean magnetic hyperfine field values are greater than those in both the parent amorphous phase and in the fully crystallized structure where coarsening and grain growth processes are involved. Below 200 K irreversibility is observed in low field magnetization measurements. Transmission electron microscopy measurements reveal that spherulites of Fe3B include a radial structure made of small bcc-Fe acicular crystals about 200 nm long and 10 nm wide. In our opinion, magnetic properties and hyperfine fields are ruled by both high magnetic anisotropy of small monodomain acicular bcc-Fe crystallites and the structure of Fe atoms located at their surfaces.
Characterization of a Pulsed Arc Cluster Ion Source for the Production of Metal Clusters in Molecular Beams.
Authors: Piseri P. , Barborini E. , Milani P.
Published: April 2011

We have produced metal clusters with a molecular beam apparatus based on a Pulsed Arc Cluster Ion Source. The source has been optimized in order to generate intense and stable cluster beams of various elements, with a mass distribution ranging from the monomer up to several thousands of atoms. The source operation conditions can be varied in order to control the mass distribution, intensity and velocity of the aggregates. Preliminary results on the synthesis of granular thin films with this technique are also presented.
Characterization of Tib2/TISI2 Bilayer Structure Deposited by Sputtering
Authors: Sade G. , Pelleg J.
Published: April 2011

Bilayer of TiB2/TiSi2 was deposited by magnetron co-sputtering on silicon and alumina substrates, and this structure was investigated for structural and electrical properties. Substrate bias and annealing in vacuum have been applied to vary the film properties. X-ray diffraction (XRD) and cross-sectional transmission electron microscopy (XTEM) were used to characterize the structure, and chemical composition was characterized by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). Resistivity was measured by four probe method. Diffusion barrier properties were studied by AES. As deposited films are amorphous with resistivities of about 40 μΩcm. Post deposition annealing in vacuum shows that the amorphous titanium boride film is very stable. Crystallization starts above 1000°C as seen by XRD, and the crystallization temperature depends on the thickness of TiB2. TiSi2 C54 forms in the temperature range 586°C - 922°C, when TiB2 still remains in amorphous form. The TiSi2 sublayer serves as an additional effective diffusion barrier, preventing outdiffusion of boron from TiB2 into the Si substrate.
Titanium Silicidation and Secondary Defect Annihilation in ION Beam Processed Sige Layers
Authors: Larsen K. Kyllesbech , La Via F. , Lombardo S. , Raineri V. , Donaton R. A. , Campisano S. U.
Published: April 2011

The secondary defect annihilation by one- and two-step titanium silicidation in SiGe layers, formed by high dose Ge implantation, has been studied systematically as a function of the Ge fluence, implantation energy, silicide thickness, and silicide process conditions. In all cases the Ti thickness was kept below 20 nm, resulting in very thin Ti silicide layers typically less than 40 nm. The silicide phase was inspected by x-ray diffraction and transmission electron diffraction. Channelling Rutherford backscattering spectrometry and transmission electron microscopy were used to follow the end of range dislocation loop annihilation as a function of the silicide process conditions. The end of range loop annealing and the influence of silicidation is presented in this paper for Ge fluences above 3×1015 cm−2 and energies ranging from 70 keV to 140 keV. A model based on loop coarsening is presented which describes the observed loop annihilation behaviour.
Interpretation of the Infrared Spectra of β-FeSi2 by Molecular Dynamics Simulations
Authors: Miglio Leo , Meregalli Valeria
Published: April 2011

We report the vibrational spectra of β-FeSi2 calculated by molecular dynamics simulations with a tight binding potential and provide a quantitative confirmation of the anisotropic behaviour found by new Infrared (IR) measurements for small monocrystals This analysis allows for the interpretation of more complex IR results previously found for epitaxial samples.
Iridium Silicides Formation on High Doses Ge+ Implanted Si Layers
Authors: Curello G. , Gwilliam R. , Harry M. , Wilson R. J. , Sealy B. J. , Rodriguez T. , Jimenez-Leube J.
Published: April 2011

In this work iridium silicidation of high dose Ge+ implanted Si layers has been studied. Compositional graded SiGe layers with a Ge peak concentration between 6 at.% and 12 at.% have been fabricated using 200 keV Ge+ ion implantation into (100) Si. A 20 nm thick Ir film was then deposited by e-beam evaporation with thermal reaction being performed to both regrow the implantation damage and form the silicide. The crystal quality of the SiGe layer and its interaction with the Ir film have been studied by cross-sectional Transmission Electron Microscopy (XTEM) and Rutherford Backscattering Spectrometry (RBS).

Solid Phase Epitaxial Growth (SPEG) in the low dose case has produced a defect free SiGe layer with the formation of the IrSi phase. The annealing ambient was found to be critical for the silicidation. For the high dose case, as expected, strain relaxation related defects were observed to nucleate at a depth close to the projected range of the Ge+ implant and to extend up to the surface. A second rapid thermal annealing at higher temperatures, performed in forming gas, consumed most of the defective layer moving the silicide interface closer to the peak of the Ge distribution. A second low dose Ge+ implant following the metal deposition has been found to have a beneficial effect on the quality of the final interface. An amorphizing 500 keV Si+ implant followed by SPEG has finally been used to move the end of range defects far from the interface.
Fabrication of Epitaxial Silicides thin films by Combining Low-Energy Ion Beam Deposition and Silicon Molecular Beam Epitaxy
Authors: Shibatal H. , Makital Y. , Katsumata H. , Kimura S. , Kobayashil N. , Hasegawa M. , Hishita S. , Beye A. C. , Takahashi H. , Tanabe J. , Uekusa S.
Published: April 2011

We have developed successfully the combined ion beam and molecular beam epitaxy (CIBMBE) system with a newly designed Knudsen cell for Si effusion. The CIBMBE system was applied to the epitaxial growth of Sil., Cx alloy thin films on Si using low-energy ( 100 – 300 eV ) C+ ion beam. Preliminary results on the characterization of the deposited films suggest high potential and reliability of the new Knudsen cell for Si effusion, as well as high ability of the CIBMBE method to produce thermally non-equilibrium materials. In addition, they indicate that the value of x decreases with increasing IC, which suggests that the selective sputtering for deposited C atoms by incident C+ ion beams takes place during CIBMBE processing. Precipitates of β-SiC were also found to be formed in the deposited films, whose amount was observed to increase with increasing IC.
Structure and Electrical Properties of Cu/Ge Ohmic Contacts
Authors: Oktyabrsky S. , Aboelfotoh M. O. , Narayan J.
Published: April 2011

Chemistry, crystal structure, interfacial microstructure and electrical characteristics of novel Cu-Ge alloyed ohmic contacts to n-type GaAs with a very low specific contact resistivity ((4–6)×10−7 Ω·cm2 for n∼1×1017 cm−3) were investigated by various methods. The Cu-Ge alloys with a wide range of Ge concentration, from 15 to 40 at %, were prepared by depositing sequentially Cu and Ge layers (or vise versa) onto GaAs substrates at room temperature followed by annealing at 400°C. It is shown that Cu reacts only with Ge to form the ξ and ε1-Cu3Ge phases. The latter has an orthorhombic structure with average lattice parameters: a = 5.301 Å, bo = 4.204 Å, co = 4.555 Å, arising from the parent hexagonal ξ-phase by Cu-Ge ordering along ao. The interface with GaAs is atomically sharp and free from secondary phases. The ε1-Cu3Ge ordered phase which is chemically inert with respect to GaAs, is believed to be responsible for high thermal stability (up to 450°C), interface sharpness, high contact layer uniformity and low specific resistivity of 6 μΩ cm. Formation of the Cu-Ge phases creates a highly doped n+-GaAs surface layer which leads to the low contact resistivity.
First Stages of the Platinum Electroless Deposition on Silicon (100) from Hf Solutions.
Authors: Gorostiza P. , Servat J. , Morante J. R. , Sanz F.
Published: April 2011

Electroless metal deposition based upon the addition of fluoride anions to the metal salt aqueous solution have been developed recently on the assumption that the cleanness of the substrate will be guaranteed and the deposit will be of high purity. In this work, platinum is deposited on silicon (100) from fluorinated solution at two different pH's. The influence of pH is analyzed using Tapping Mode Atomic Force Microscopy (TMAFM) to characterize the main morphological properties of the deposit. Combined TMAFM and Transmission Electron Microscopy (TEM) images are presented and X-ray Photoelectron Spectroscopy (XPS) allows us to identify the chemical nature of the silicon surface.
Preparation of WSi2 by RTA Annealing of CVD-W thin Films
Authors: Gesheva K. A. , Stoyanov G. I. , Gogova D. S. , Beshkov G. D.
Published: April 2011

Wsi2 films were prepared by rapid thermal annealing (RTA) in the temperature range of 800 -1400 °C for time durations of 15 sec -3 minutes. In some of the treatment experiments different gases were involved and a conclusion is made about the role of hydrogen favoring Wsi crystal phase growing at 800 °C. W films with thichnesses in the range 200 Å - 1000 Å were deposited on monocrystalline Si by pyrolitical decomposition of W(CO)6 in CVD reactor at atmospheric pressure and argon atmosphere. Reflection High Energy Electron Diffraction (RHEED) and Scanning Electron Microscopy (SEM) technics were used for structural characterization and FPP-100 device for resistance measurements. Results show that by solid state reaction applied at different RTA processes WSi2 phase could be formed.Resistivities as low as 2-3 mΩ.cm are obtained for 800 -1000 °C.