bluuebunny/crossref_metadata_2025_split huggingface dataset:
Melting vs. Solidification of a Pure Metal Analysed by DSC
Authors: Clavaguera N. , Clavaguera-Mora M. T. , Fontán J. , Touron J. L. , Comas C. 
Published: April 2011

ABSTRACTThe aim of the present paper is to analyse the melting/solidification of pure metals resulting from non-equilibrium conditions. Attention is focused on the direct measurement of the calorimetric signal obtained under isothermal hold of the sample at a temperature close to the equilibrium melting temperature Tm, which results in both melting of an overheated solid and solidification of an undercooled melt. The non-equilibrium transformations are monitored by DSC under isothermal regime, with previous continuous heating/continuous cooling of the sample. The dependence of the calorimetric signal on thermodynamic factors, ΔH and ΔG, is explored. Here ΔH and ΔG are, respectively, the melting enthalpy and Gibbs free energy difference between the crystal and the liquid. In particular, the results of the investigation performed on the melting/solidification behaviour of pure In and Pb are presented.
Iron Precipitation and Dissolution in Float-Zone Silicon
Authors: Ramappa Deepak A. , Henley Worth B. 
Published: April 2011

ABSTRACTA quantitative analysis of the phase changes of iron in silicon from interstitial to precipitate phase and vice-versa is presented. Temperature dependent iron precipitation and dissolution in float-zone grown silicon wafers is experimentally investigated. A quantitative analysis of iron silicide precipitate stability and dissolution with respect to time and temperature is also presented. Precipitation of iron in silicon was analyzed by a quantitative assessment of change in interstitial iron using a surface photo voltage minority carrier lifetime analysis technique. Contamination levels of iron in the range 1011 to 1013 atoms/cm3 are investigated. It is concluded that maximum iron precipitation occurs in the temperature range of 500°C to 600°C. Iron precipitation is rapid in this region where more than 90% of the interstitial iron precipitates in a period of 30 minutes. Iron silicide precipitates were found to dissolve above a temperature of 760°C restoring iron back to an interstitial phase in the silicon matrix.
From Semiconductor to Metal in a Flash: Observing Ultrafast Laser-Induced Phase Transformations
Authors: Callan J. P. , Kim A. M.-T. , Huangt L. , Glezer E. N. , Mazur E. 
Published: April 2011

ABSTRACTWe use a new broadband spectroscopic technique to measure ultrafast changes in the dielectric function of a material over the spectral range 1.5–3.5 eV following intense 70-fs laser excitation. The results reveal the nature of the phase transformations which occur in the material following excitation. We studied the response of GaAs and Si. For GaAs, there are three distinct regimes of behavior as the pump fluence is increased — lattice heating, lattice disordering, and a semiconductor-to-metal transition.
Phase Transformation and Ion Beam Induced Crystallization in SiC Layers Formed by Mevva Implantation of Carbon into Silicon
Authors: Chen Dihu , Wong S. P. , Ho L. C. , Yan H. , Kwok R.W.M. 
Published: April 2011

ABSTRACTBuried SiC layers were synthesized by carbon implantation into silicon with a metal vapor vacuum arc ion source under various implantation and annealing conditions. The infrared absorption spectra of these samples were deconvoluted into two or three gaussian components depending on the preparation conditions. One component peaked at around 700 cm-1was assigned to amorphous SiC (a-SiC). The other two components, both peaked at 795 cm-1 but with different values of full width at half maximum (FWHM), were attributed to β-SiC. The one with a larger (smaller) FWHM corresponds to β-SiC of smaller (larger) grains. With this deconvolution scheme, the fraction of various SiC phases in these samples were determined. It was found that for the as-implanted samples there are critical energies and doses at which the crystalline SiC fraction increases abruptly. This was attributed to the ion beam induced crystallization (IBIC) effect. It was also shown that the IBIC effect leads to strong dependence of the β-SiC fraction on the order of implantation for samples synthesized by double-energy implantation. Analysis of the evolution of the β-SiC fraction with annealing time indicated that the crystallization process in these SiC layers could well be described by the classical random nucleation and growth theory.
Investigation Of Phase Formation During Cold Rolling Of Elemental Zr-Al-Ni-Cu Foils With Bulk Glass Forming Composition
Authors: Sagel A. , Sieber H. , Fecht H. J. , Perepezko J. H. 
Published: April 2011

ABSTRACTElemental Zr-Al-Ni-Cu foils of bulk glass forming composition were cold rolled at ambient temperature. The phase transformations during the cold deformation process were monitored with electron and X-ray diffraction and thermal analysis. After 120 deformation cycles a fully amorphous sample was obtained, as indicated by a distinct endothermic glass transition and a large exothermic crystallization reaction. The characteristics of the amorphous phase are compared with a liquid quenched metallic glass and mechanically alloyed elemental powder mixtures of similar composition. The amorphization reaction during cold rolling is similar to mechanical alloying and proceeds by the formation of a fine layered structure of the constituents, a rapid reduction of the layer thickness and of the average grain size to a nanometer scale and dissolution reactions in the hcp Zr lattice. While in the beginning of the cold rolling process the elemental foils were ductile, after several rolling passes the multilayered sample became brittle and, finally, displayed large elastic flexure in the amorphous state. Several thermal treatments of the multilayered and amorphous samples were performed in order to study thermally activated solid-state amorphization reaction as well as phase formation during crystallization.
Crystallization of Amorphous Ribbon in NiTi-Cu Shape Memory Alloy
Authors: Yang F. , Ma J. L. , Pu Z. J. , Wu K. H. 
Published: April 2011

ABSTRACTThe objective of this work is to study the crystallization process of the amorphous ribbon of NiTi-Cu based shape memory alloys. An amorphous material with a composition of Ti50Ni25Cu25 was used to conduct this study. First, a study was conducted to understand the crystallization kinetics of this amorphous material at the isothermal model and continuous heating mode, respectively. The characteristic parameters associated with the crystallization process, such as the start and finish time for isothermal crystallization, the peak temperature for continuous heating crystallization, and activation energy, are obtained. Based on the study of experimental data of crystallization kinetics, a series of isothermal annealing experiments was conducted to study the crystallization process and microstructure of fully crystallized materials. The TEM micrograph shows the crystal phase growths in the amorphous matrix as a perfect geometric sphere. A system analysis was conducted to explain the crystallization micro-mechanism.
Amorphous to Crystalline Phase Transformation in Metglas® Studied by Mössbauer Spectroscopy
Authors: Marquina V. , Gómez R. , Aburto S. , Jiménez M. , Ridaura R. , Marquina M. L. , Valenzuela R. 
Published: April 2011

ABSTRACTWe present differential scanning calorimetry (DSC) and in situ Mössbauer spectroscopy results for Metglas ribbons, to which different heat treatments were made. The Curie temperature of the amorphous phase is determined and the evolution of the magnetic field of this phase is studied as a function of temperature.
Phases Driven Far From Equilibrium by Applying Mechanical Energy: Phase Transformations to γ-PbSnF4 Upon Ball Milling
Authors: DÉnÉs Georges , Roux Delphine Le , Madamba M. Cecilia 
Published: April 2011

ABSTRACTThe technique of ball milling has been applied to various phases of superionic PbSnF4, namely on (i): highly stressed tetragonal α-PbSnF 4(aq1) obtained by precipitation from aqueous solutions, (ii): highly stressed tetragonal α-PbSnF4(aq2) obtained by reaction of a solid with an aqueous solution, (iii): stressed orthorhombic o-PbSnF4 obtained by precipitation from aqueous solutions, (iv): non-stressed tetragonal α-PbSnF4(ssr) obtained by direct reaction between SnF2 and
PbF2 at high temperature, and on (v): non-stressed tetragonal β-PbSnF4 obtained by direct reaction between SnF2 and PbF2 at high temperature. In all cases, transformation to microcrystalline cubic γ-PbSnF4 is observed very rapidly. This is a unique method for stabilizing high temperature γ-PbSnF4 at ambient temperature, which cannot be done by conventional methods, such as quenching. The phases obtained are totally disordered, microcrystalline, and have the memory of their origin.
Fabrication and Optical Pumping of Laser Cavities Made by Cleaving and Wet Chemical Etching
Authors: Stocker D. , Schubert E. F. , Grieshaber W. , Redwing J. M. , Boutros K. S. , Flynn J. S. , Vaudo R. P. 
Published: April 2011

AbstractWe report on fabrication and characterization of cleaved laser facets and photoelectrochemically wet etched laser facets in III-Nitrides grown by MOVPE on c-plane sapphire. The roughness of the cleaved facets in the InGaN/GaN double heterostructure (DH) laser cavities with a 1000-Å-thick active region is ≈25 rim, while that of the wet etched GaN facets is ≈100 nm. A theoretical model is developed for the maximum allowable laser facet roughness, which yields a value of 18 nrm for uncoated GaN and 22 rm for the uncoated DH. Optically pumped laser action at room temperature is demonstrated in the cleaved DH laser cavities. 2 Above the incident threshold pumping power of 1.3 MW/cm2, the differential quantum efficiency increases by a factor of 34, the emission linewidth decreases to 13.5 meV, and the output becomes highly TE polarized. Wet chemical etching a 1-mm-long laser cavity into the GaN homostructure is found to increase the differential quantum efficiency by a factor of 2.
Luminescence Properties of As, P, and Bi as Isoelectronic Traps in GaN
Authors: Jadwisienczak W. M. , Lozykowski H. J. 
Published: April 2011

AbstractPhotoluminescence spectra of high quality GaN epilayers, grown by MOCVD on sapphire substrates and implanted by isoelectronic ions: As, P, and Bi, were investigated. Post implant annealing was done at temperatures of up to 1150 °C, in a tube furnace under flowing NH3 or N2, and in a rapid thermal annealing system in ambient of N2. The PL of GaN: P annealed at 1150 °C in NH 3 exhibited strong pair-type modulated structures on the short wavelength shoulder of an emission band.The band at 2.914 eV is due to the recombination of bound exciton to P-hole isoelectronic traps (P-BE), and the modulated structure results from electron-hole recombination at pairs of neutral donors and a hole on P isoelectronic traps. The PL of GaN: As, GaN: Bi showed an emission with peaks at 2.597 eV and 3.241 eV, due to the recombination of an exciton bond to As and Bi isoelectronic-hole traps. We also studied thermal quenching excitation spectra, and PL kinetics. The experimental results are discussed using a simple spherical potential-well model for isoelectronic traps: As, P, and Bi replacing nitrogen in GaN.
High Temperature GaN and AlGaN Photovoltaic Detectors for UV Sensing Applications
Authors: Hove J. M. Van , Chow P. P. , Hickman R. , Klaassen J. J. , Wowchak A. M. , Polley C. J. 
Published: April 2011

AbstractAlGaN photodiode detectors are grown on (0001) sapphire by RF atomic nitrogen plasma molecular beam epitaxy. Both individual detectors and 1 × 10 element arrays are fabricated. The individual detectors have active areas of 0.5 mm2, 1.0 mm2, and 2.0 mm2. Individual elements in the l × 10 detector arrays range in size from 250×250 μm to 450×450 μm. The detectors are fabricated using a chlorine-based reactive ion etch (RIE) and refractory metal ohmic contacts. At room temperature, GaN p-i-n photovoltaic detectors show peak responsivity at 360 nm as high as 0.198 A/W, corresponding to an internal quantum efficiency of 85%. These detectors also exhibit five orders of magnitude of rejection for radiation longer than 500 nm. The electrical and spectral characteristics of these detectors are examined at elevated temperatures. The short wavelength UV responsivity remains fairly constant at elevated temperatures, while the peak responsivity actually increases with increasing temperature. The smooth surface morphology of heavily doped p-type material grown by MBE makes possible diode structures with a p-type bottom layer. The effect of the spectrally broader p-type material in the photodiode responsivity will be discussed.
Ohmic contact to GaN grown by MOCVD
Authors: Kim Dae-Woo , Baik Hong Koo , Kim Cha Yeon , Kim Sung Woo , Hong Chang Hee 
Published: April 2011

AbstractWe investigated the electrical properties and interfacial reactions of the Si/Ti based ohmic contacts to n-GaN grown by metal organic chemical vapor deposition and the electrical properties were related to the material reactions. The perfect ohmic characteristics were obtained after annealing at 700 °C for 3 min under N2 ambient, and Ti silicide was formed in Ti-Si based contact systems. The lowest value for the specific contact resistance of 3.86×10-6 Ωcm2 was obtained for Au(1000 Å)/Ni(400 Å)/Ti(400 Å)/Si(1460 Å)/Ti(150 Å) after annealing at 900 °C for 3min. It could be concluded from the material analyses that the ohmic characteristics of Ti-Si based contact systems were due to the low barrier height by the formation of Ti silicides with a low work function
InGaN/GaN/AiGaN-Based Laser Diodes with an Estimated Lifetime of Longer than 10,000 Hours
Authors: Nakamura Shuji 
Published: April 2011

AbstractInGaN multi-quantum-well (MQW) structure laser diodes with A10.14Ga0.86N/GaN modulation doped strained-layer superlattice cladding layers grown on an epitaxially laterally overgrown GaN substrate were demonstrated to have an estimated lifetime of more than 10,000 hours under continuous-wave operation at 20°C. Under operation at a high temperature of 50°C, the lifetime was longer than 1,000 hours. The activation energy of the lifetime was estimated to be 0.5 eV. With the operating current increasing above the threshold, a self-pulsation with a high frequency of 3.5 GHz was observed. The relative intensity noise (RIN) less than -145 dB/Hz was obtained even at the 6% optical feedback using the high-frequency modulation of 600 MHz. The threshold carrier density of the InGaN MQW-structure LDs was estimated to be 3 × 1019/cm3 using a carrier lifetime of 1.8 ns.
-Pulsed- Operation of -Cleaved-Facet- InGaN Laser -Diodes-
Authors: Sink R. K. , Abare A. C. , Kozodoy P. , Mack M. P. , Keller S. , Coldren L. A. , DenBaars S. P. , Bowers J. E. 
Published: April 2011

AbstractBlue-emitting nitride laser diodes have been fabricated on a-plane sapphire (1120). The active region is composed of 10 In.18Ga.82N quantum wells, which were grown by MOCVD at atmospheric and low pressure in a modified two-flow Thomas-Swan Ltd. horizontal reactor. The chemical precursors used were trimethylgallium (TMGa), trimethylindium (TMIn), trimethylaluminum (TMAI), ammonia, and disilane. The n- and p-contacts were formed by depositing Ti/Al/Ni/Au and Ni/Au/Ni/Au, respectively. Diode wafers were thinned to less than 50 μm before they were cleaved along the sapphire r-plane (1120).Lasers show TE polarization, spectral line narrowing, and far field interference patterns above the lasing threshold. The laser emission spectra peak at 410–420 nm. Under pulsed operation at room temperature, the lowest observed threshold current density was 15 kA/cm2 with threshold voltages ranging from 50–90 V. Differential efficiencies are as high as 7% with maximum output powers greater than 50 mW. Near and far field mode patterns are presented. Structures are gain-guided devices with each device occupying a mesa with a width of 125 μm. Device widths range from 3 to 20 μm, with lengths of 500 to 1200 μm.
Detection and Analysis of Phase Separation in Metalorganic Chemical Vapor Deposition InGaN
Authors: Piner E. L. , El-Masry N. A. , Liu S. X. , Bedair S. M. 
Published: April 2011

AbstractInGaN films in the 0–50% InN composition range have been analyzed for the occurrence of phase separation. The ñ0.5 jum thick InGaN films were grown by metalorganic chemical vapor deposition (MOCVD) in the 690 to 780°C temperature range and analyzed by θ−20 x-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area diffraction (SAD). As-grown films with up to 21% InN were single phase. However, for films with 28% InN and higher, the samples showed a spinodally decomposed microstructure as confirmed by TEM and extra spots in SAD patterns that corresponded to multiphase InGaN. An explanation of the data based on the GaN-InN pseudo-binary phase diagram is discussed.
Vacuum Pressure MOVCD Growth and Characterization of AlN Films On MgO(100), Sapphire, and Si
Authors: Serra A. D. , Magtoto N. P. , Ingram D. C. , Richardson H. H. 
Published: April 2011

abstractFilms of AlN were grown on MgO(100), Al2O3, and Si under vacuum pressure (10-3 to 10-4 Torr) at different substrate temperatures. They were examined ex situ with infrared reflectance spectroscopy, scanning electron microscopy, x-ray diffraction and rutherford backscattering spectroscopy. Highly oriented smooth films were grown at film thicknesses below 1 μm. Thicker films showed significantly more roughness but remained oriented with respect to the substrate. AIN growth was faster on Si than MgO(100) or Al2O3 and Si was the only substrate that growth was observed at 500°C.
Phase Separation and Atomic Ordering in AlGaInN Alloys
Authors: Moustakas T. D. , Singh R. , KOrakakis D. , Doppalapudi D. , Ng H.m. , Sampath A. , Iliopoulos E. , Misra M. 
Published: April 2011

AbstractThis paper reviews experimental results of phase separation and atomic long-range ordering in A1GaInN alloys, grown by plasma-assisted MBE. Phase separation has been observed in InxGal-x alloys and atomic ordering has been observed in AlxGa1-xN alloys, using XRD studies. Specifically, we find that alloys with In content in excess of 30% show an extra diffraction peak corresponding to an alloy with high In concentration (close to pure InN). The effect of phase separation on the optical properties of the films was also investigated by transmission and photoluminescence measurements. From these studies, we find that the degree of phase separation depends on the thickness of the alloy layer. Atomic long-range ordering has been observed in AlxGal-xN alloys over the entire alloy composition. The phenomenon was investigated by studying the superlattice peaks (0001), (0003) and (0005). The relative intensity of these peaks was found to be largest for the Al content in the 40–50 % range in qualitative agreement with expectations for an ordered structure of ideal Al0.5Ga0.5N stoichiometry. We found that the ratio of III/V fluxes has a significant effect on the degree of ordering.
Controlling 2d/3d Growth of Gan by Molecular Beam Epitaxy: From Superlattices to Quantum Dots
Authors: Daudin B. , Feuillet G. , Widmann F. , Samson Y. , Rouviere J. L. , Pelekanos N , Fishman G. 
Published: April 2011

AbstractBy controlling the Stranski-Krastanov growth mode of strained GaN deposited by molecular beam epitaxy on AlN, it is shown that islands with nanometric dimensions can be elaborated. The luminescence energy of the wetting layer is 4.6 eV, determined by cathodoluminescence experiments. The luminescence of dots with a mean size of 14 nm in diameter and 2nm in height is 3.8 eV and remains constant in intensity with increasing temperature, as an evidence of 0-dimension confinement effect. Theoretical analysis of the wetting layer luminescence energy is carried out, taking into account the non parabolicity in the conduction band.
Stress Controlled MBE-growth of GaN:Mg and GaN:Si
Authors: Kim Y. , Klockenbrink R. , Kisielowski C. , Krueger J. , Corlatan D. , Sudhir G. S , Peyrot Y. , Cho Y. , Rubin M. , Weber E. R. 
Published: April 2011

AbstractThe stress in GaN thin films grown on sapphire is shown to be determined by lattice mismatch, by differences in thermal-expansion-coefficients and by the incorporation of point defects. It can be controlled by the buffer layer thickness, the buffer layer growth temperature, the V/III flux ratio, and by doping. It is argued that a Fermi-level dependence of defect formation energies affects the material stoichiometry and thereby lattice constants and stresses. We observed that stress relaxation occurred if the stresses exceeded a critical compressive or tensile stress value. The stress changes materials properties. As an example, it is demonstrated that the electron Hall mobility in GaN:Si can be increased with constant electron carrier concentration if large compressive stress is present.
Selective Area Growth of GaN by MOVPE and HVPE
Authors: Hiramatsu K. , Matsushima H. , Shibata T. , Sawaki N. , Tadatomo K. , Okagawa H. , Ohuchi Y. , Honda Y. , Matsue T. 
Published: April 2011

AbstractRecent successful results on the selective area growth (SAG) of GaN that has been done by MOVPE and HVPE are shown. The SAG were carried out on MOVPE-grown GaN (0001) / sapphire substrates with lined or dotted SiO2 masks. Sub-micron GaN dot and line structures are fabricated by the SAG in MOVPE, so that smoothly overgrown GaN layers are successfully realized using the epitaxially lateral overgrowth (ELO) technique. The ELO structures are confirmed to be good quality GaN single crystal with a smooth surface, no grain boundaries, and low-dislocation densities. In addition, thick GaN bulk single crystals without any cracks are grown by the SAG in HVPE. Crystalline and optical properties of the GaN bulk are much improved. The reduction in the thermal strain due to the growth on the limited area as well as the ELO are found to be effective to reduce crystalline defects of the GaN bulk single crystals.
The Evolution of Nitride Semiconductors
Authors: Akasaki I. 
Published: April 2011

AbstractThe great scientific and commercial success of the group-III nitrides in recent years is the result of persistent fundamental research over a time span of three decades. In the late 60's and in the early 70's the very heart of gallium nitride research was located in J.I. Pankove's laboratory at RCA. There the first single crystalline GaN was grown by Maruska and Tietjen and the very first GaN light emitting diodes were produced by Pankove in September 1971, 26 years ago. Since then the community of nitride research has come a long and troublesome way, but it has succeeded. This 1997 Fall Meeting Symposium on Nitride Semiconductors of the Materials Research Society is dedicated to Professor J.I. Pankove for his outstanding and groundbreaking contributions in the early development of group-III nitride research. This paper reports a historical summary of the evolution of the field summarizing the landmark contributions that have led to the current status of success.
Scanning tunneling microscopy observation of surface reconstruction of GaN on sapphire and 6H-SiC
Authors: Smith A. R. , Ramachandran V. , Feenstra R. M. , Greve D. W. , Neugebauer J. , Northrup J. E. , Shin M. , Skowronski M. 
Published: April 2011

AbstractWe report studies of the surface structure of MBE-grown GaN layers on sapphire (0001) and 6H-(0001) SiC substrates. A different set of reconstructions is observed for nitrogen-face and gallium-face layers. The gallium-face has so far only been grown on MOCVD GaN/ sapphire substrates, while the nitrogen-face has been obtained on SiC and bare sapphire substrates.