bluuebunny/crossref_metadata_2025_split huggingface dataset:
Light-Emitting Devices Based on Gallium Nitride and Related Compound Semiconductors
Authors: Koike M. , Shibata N. , Yamasaki S. , Nagai S. , Asami S. , Kato H. , Koide N. , Amano H. , Akasaki I. 
Published: April 2011

ABSTRACTAsymmetric double heterostructures (ADH) of AlGaN/GaInN/GaN blue light emitting diodes (LEDs) and GaInN/GaN multiple quantum well (MQW) LEDs were fabricated by metalorganic vapor phase epitaxy (MOVPE). The ADH LEDs had spectral emissions peaking at 450 nm and the luminous intensify was 2.5 cd at 20 mA The output power was 3.6 mW at 20mA and the external quantum efficiency was as high as 5.1 % at 20 mA. The GaInN/GaN MQW structure was grown successfully by MOVPE. Fine multi-layer structures 7 – 9 nm thick were detected by secondary ion mass spectroscopy and transmission electron microscopy (TEM). The dislocation density in the MQW was as high as 0.5–2×109 cm−2 by TEM The optical efficiency of the MQW layer was higher than that of a bulk GalnN layer. The intensity of UV emission from MQW LEDs was greater than that of blue light from ADH blue LEDs. The UV emission increased as a super-linear function of injection current at -100°C.
AlGaN/GaN/AlGaN double-heterojunction blue LEDs on 6H-SiC substrates
Authors: Kong Hua-Shuang , Leonard Michelle , Bulman Gary , Negley Gerry , Edmond John 
Published: April 2011

ABSTRACTBlue LEDs with double-heterojunction (DH) have been produced in AIN-GaN system grown on n-type 6H-SiC substrates via metalorganic chemical vapor deposition (MOCVD). These devices employ a GaN active layer bordered by Mg doped p-type Al0.1Ga0.9N and Si doped n-type Al0.1Ga0.9N. A vertical device design was utilized with a p-type Au contact centered on the chip top side for wire bonding. The backside contact to the SiC is Ni. The peak emission from these devices is 430 nm with a FWHM of 65 nm, producing a deep blue color. The output power is 1.7 mW at 20 mA which corresponds to an external quantum efficiency of 3%.
Laser Ablation of Highly Oriented Cdse Thin Films and Cdte/Cdse Multilayers on Silicon Substrate
Authors: Ambrico M. , Martino R. , Smaldone D. , Capozzi V. , Lorusso G. , Perna G. , Giardini A. , Mele A. 
Published: April 2011

ABSTRACTLaser ablation technique has been successfully used for the deposition of CdSe and CdTe/CdSe multilayers on Si(100) and Si(l11) substrates. X-ray analysis showed that CdSe/Si films were highly oriented. Their orientation changed from (100) to (002) by varying the substrate temperature from 473 to 673K. High orientation was also obtained on multilayered polycrystalline structures of CdSe and CdTe on Si(lll). Photoluminescence experiments have also been carried out on the deposited films.
Laser Ablation Deposition of Ga2S3-La2S3 Glass Films
Authors: Asal R. , Rivers P.E. , Rutt H.N. 
Published: April 2011

ABSTRACTGallium - lanthanum sulphide glasses (GLS) show wide range transparency and low non radiative relaxation rates for dopant ions such as Ho3+, Er3+ etc. They also show permanent photomodification of the refractive index under visible illumination. We report laser ablation deposition of these glasses and preliminary results on film stoichiometry and deposition rate as a function of excimer laser fluence. The sulphur to metal and Ga/La ratios are found to have marked fluence dependencies. The films show considerably more Urbach tail absorption than bulk material. A novel method has been developed for mapping the permanent photomodified index.
Mechanical Properties of Laser Processed Diamond-Like Carbon Films
Authors: Kumar Ashok , Inturi R. B. , Vohra Y. , Ekanayake U. , Shu N. , Kjendal D. , Wattuhewa G. , Barnard J. A. 
Published: April 2011

ABSTRACTDiamond-like carbon (DLC) films have a unique combination of physical and chemical properties such as high hardness, optical transparency, low coefficient of friction and chemical inertness. A pulsed laser (248 nm) has been used to ablate a pyrolytic graphite target to deposit DLC films on Si (100) and 7059 Corning glass substrates. The deposition was carried out in high vacuum (≤ 10−6 Torr) at different temperatures ranging from room temperature to 400°C. The films were characterized by x-ray diffraction, scanning electron microscope, and Raman spectroscopie techniques. The mechanical properties (hardness and Young's modulus) of these films were characterized by nanoindentation. We have found that the films deposited at room temperature and 100°C show the characteristic features of DLC films and have the better hardness and modulus properties compared to the films fabricated at higher temperatures, which transform into amorphous carbon. Correlations of pulsed laser deposition process parameters with the properties of deposited DLC films will be discussed in this paper.
Pulsed Laser Deposition of Si Nanocluster Films
Authors: Marine W. , Movtchan I. , Simakine A. , Patrone L. , Dreyfus R. , Sentis M. , Autric M. , Merk N. 
Published: April 2011

ABSTRACTReactive laser ablation of Si targets by ArF* excimer laser (wavelength 193 nm, pulse width 15 ns (FWHM)) was performed in He, Ar or O2 0.05-1 Torr atmospheres and led to Si-SiOx nanocluster thin film formation within laser-induced plasma plume. Optical spectroscopy and optical Time-of-Flight (TOF) measurements were carried out during ablation-deposition experiments. A number of large weak emission bands in blue and green-yellow spectral branches were observed both in inert gases and in oxygen ambient atmospheres and attributed to the emission from excited nanoparticles in the plasma plume. TOF measurements proved a different spatio-temporal evolution of this emission compare to the emission of monoatomic particles. The films exhibit photoluminescence bands in the UV region (around 290 nm and between 310-370 nm), in the blue (between 420 and 500 nm), and in the green-yellow (at 520-560 nm). The relative intensities of the luminescence bands depend on the average cluster size, which is determined by preparation conditions (nature and pressure of the ambient gas, laser fluence).
Optimization and Transformation Analysis of Grain-Boundary-Location-Controlled Si Films
Authors: Kim H.J. , Im James S. 
Published: April 2011

ABSTRACTBy optimizing various experimental parameters, we were able to extend the width of the microstructually optimized regions in grain-boundary-location-controlled (GLC) Si films up to 10 μm. In situ transient reflectance (TR) measurements during the solidification process reveal that the underlying GLC transformation sequence is consistent with the artificially controlled super-lateral growth (ACSLG) scenario, from which the GLC process was developed and is being optimized. A definite change in the slope of the TR signal was found to appear at the transition between the vertical-and-lateral -growth and lateral-growth-only modes. Protrusions at the center of the GLC Si microstructure, which are observed in cross-sectional TEM micrographs and surface profile measurements, are formed as a result of the positive volume change associated with freezing of Si.
Adhesive Property Enhancement by Photochemical Modification on Polyimide Sheet Surface by Irradiation with Excimer Lamp
Authors: Okamoto T. , Hatao K. , Shimizu T. , Aoike M. , Murahara M. 
Published: April 2011

ABSTRACTPolyimide sheet surface was photochemically modified to be hydrophilic property with Xe2* excimer lamp ( λ =172nm) irradiation and pure water solution. The solution was sandwiched between the surface and fused silica glass. With the excimer lamp irradiation, the solution and the surface were excited; the surface was dehydrogenated by the hydrogen atoms which were photodissociated from pure water and replaced the photodissociated OH radicals. The hydrophilic property of the modified surface was evaluated by measuring the contact angle with water. The replacement of the OH radicals were confirmed by FTIR. The modified surface was bonded to stainless steel with an epoxy resin for evaluation of the adhesive strength by the shearing tensile test. As a result, the adhesion was increased to 1.4 times that of the non-irradiated sample.
Ablation of Si and Ge Using UV Femtosecond Laser Pulses
Authors: Herbst G. , Steiner M. , Marowsky G. , Matthias E. 
Published: April 2011

ABSTRACTLaser ablation of silicon and germanium was carried out in moderate vacuum with l00fs to 400fs pulses at 248nm and intensities up to 3x1013 W/cm2. Evidence for non-thermal material removal was found. Imaged multishot ablation patterns display the intensity dependent self-structuring effect, forming well-known columnar structures. It is shown that continued irradiation of these structures eventually results in comparatively clean ablation. An increase of ablation rate with depth was observed. The reason is an intensity enhancement inside the pits by reflective focussing to a level where bond-breaking takes place. Furthermore, it was noticed that ablation contours can be significantly improved by electrically grounding the target.
Numerical Simulation of Fz Single Crystal Growth Process with Radio-Frequency Induction Heating
Authors: Masuda Y. , Tsukada T. , Hozawa M. 
Published: April 2011

ABSTRACTAnalyses of a floating zone (FZ) crystal growth system with a radio frequency (RF) induction heating are carried out. The electromagnetic and temperature fields, and surface interfaces are solved for numerically. Finite element methods are used for the calculation of the temperature fields and interfaces and the hybrid finite element and boundary element methods are used for the calculation of the electromagnetic field. The calculation domain is divided into eleven regions, each of which, except for the RF coil region, require a coordinate transformation. In the present study, the silicon FZ growth system ,where the diameter of both feed-rod and single crystal were set to be 1cm was computed. The Lorentz force is found to play an important role in determining the melt free surface shape and the molten zone length. The effect of the current density, frequency of RF coil and crystal growth rate are investigated.
Formation of a Metastable Crystalline Phase During Ion Irradiation of Spinel
Authors: Devanathan R. , Yu N. , Sickafus K. E. , Nastasi M. 
Published: April 2011

ABSTRACTWe have examined the radiation resistance of magnesio-aluminate spinel by irradiating single crystals of MgAl2O4 with 400 keV Xe++ ions at 100 K. At low irradiation doses, the material transformed into a metastable crystalline phase with half the lattice spacing of the original crystal. Electron diffraction analysis revealed that this structural change can be explained in terms of the redistribution of cations among octahedral, tetrahedral, and three-fold coordinated interstitial sites of the close-packed anion lattice. Corresponding to this transformation, the hardness and elastic modulus increased with dose to values about 10% greater than those of unirradiated spinel. We believe that the formation of this metastable phase plays an important role in determining the radiation resistance of spinel.
Influence of Stacking Faults and Alloy Composition on Irradiation Induced Amorphization of Zrcr2, Zrfe2 And Zr3(Fei. X,Nix)
Authors: Faldowski Joseph A. , Motta Arthur T. , Howe Lawrence M. , Okamoto Paul R. 
Published: April 2011

ABSTRACTThe Zr-based intermetallic compounds ZrCr2, ZrFe2 and Zr3(Fei_x,Nix) were irradiated with high energy electrons at the HVEM/Tandem facility at Argonne National Laboratory to study their amorphization behavior. The results show that although ZrCr2 and ZrFe2 have the same Laves phase C15 fee crystal structure, their critical temperatures for amorphization under electron irradiation were 180 K and 80 K, showing that the substitution of Cr for Fe in the sublattice had a marked effect on the annealing characteristics of the material. The low temperature dose to amorphization was higher in ZrFe2 than in ZrCr2 by a factor of two. The presence of a high density of stacking faults had a strong effect on amorphization in both compounds causing the critical temperature to be increased by 10–15 K. By contrast, the addition of Ni to Zr3(Fei_x,Nix) had no effect on amorphization behavior for x=0. 1 and 0. 5. These results are discussed in terms of current models of amorphization based on defect accumulation and the attainment of a critical damage level, such as given by the Lindemann criterion.
Metastability at the nanometer scale
Authors: DESRÉ P.J. 
Published: April 2011

ABSTRACTUnder constraints and at the nanometer scale, transitory metastable states can be generated in multicomponents materials. Examples illustrating such specific states are presented. They concern i) The crystalline nucleation in a growing undercooled liquid droplet formed from a liquid parent phase, ii) The suppression of intermetallic nucleation in solid solutions or glasses subjected to sharp concentration gradients, iii) The nanocrystalline transitory state preceding amorphisation by ball milling. In connection with this latter example, a thermodynamic model for the nanocrytal to glass transition, based on an hypothesis of a topological disorder wetting at the nanograin boundaries, is proposed. Thermodynamics - Nucleation - Phase transitions - nanocrystals - metallic glasses
The Influence of Structural Similarity on Phase Transformations Between Bcc and the Laves Compounds
Authors: Sinkler W. 
Published: April 2011

ABSTRACTA fundamental aspect of martensitic or order-disorder phase transformations is the maintainence of correspondences between atoms or atomic sites in parent and precipitate phases. The present work concerns a structural relationship between initial and final phases in a transformation which is neither martensitic nor order-disorder. A structural relationship between the C14 Laves compound structure and body-centered cubic (bcc) is presented based on electron diffraction recorded in the course of the electron irradiation-induced transformation of the TiCr2 Laves compound to the bcc (β) phase. The diffraction evidence indicates a preferential orientation of β with respect to the initial Laves phase. Consistent with the diffraction data, it is shown how the structures can be formed from one another via small displacements of atom positions. It is suggested that structural relationships in first-order transformations may be significant as paths of minimal structural rearrangement by which such transformations may occur.
Calorimetric Study of the Energetics and Kinetics of Interdiffusion in Cu/Cu6sn5 Thin Film Diffusion Couples
Authors: Neils W. K. , Chromik R. R. , Dreyer K. F. , Grosman D. , Cotts E. J. 
Published: April 2011

ABSTRACTWe find differential scanning calorimetry to be suitable for the characterization of the energetics and kinetics of interdiflusion in solder/metal diffusion couples. Differential scanning calorimetry studies of interdiffusion in Cu/Cu6Sn5 diffusion couples have shown that the driving force for interdiffusion is similar for thin film composites and for bulk diffusion couples. The heat of formation of Cu3Sn from Cu6Sn5 and Cu thin films was found to be ΔHr = −4.3 + 0.3 kJ/mol. Portions of our differential scanning calorimetry scans are identified with diffusion limited growth of Cu3Sn. From these calorimetry data we have estimated D(cm2 / s) = Do exp(−E / kbT), where kb is Boltzmann's constant, D0 = 3.2 × 10–2 cm2/s, and E=0.87 eV/atom.
Ordering and Grain Growth Kinetics in CoPt Thin Films
Authors: Ristau R. A. , Barmak K. , Hess D. W. , Coffey K. R. , Parker M. A. , Howard J. K. 
Published: April 2011

ABSTRACTOrdering and grain growth have been studied in a 10 nm thick CoPt alloy film of equiatomic composition annealed in the temperature range 550–700°C by quantifying ordered domain size, volume fraction ordered, grain size, and grain size distribution. Ordering occurs by nucleation and growth of Ll0ordered domains, with a mean size of 3 nm at 550°C and 19 nm at 700°C. The volume percent ordered shows a dramatic increase from <y1% to approximately 28% between the two extremes of annealing temperature. The mean grain size of the as-deposited films is 5 nm and the entire film is face-centered cubic. Upon annealing in the temperature range 550–600°C, the mean grain size reaches a stagnation limit of 27 nm and the grain size distribution is log-normal. Grain growth resumes beyond 600°C and the mean grain size reaches as high as 55 nm at 700°C. The increase in the coercivity of the annealed films follows the increase in the ordered fraction more closely than the increase in grain size. The shape of the M-H loop shows evidence of coupling between the magnetically hard (ordered) and soft (disordered) regions.
Models of Crystallisation in Evaporating Droplets
Authors: Ford I.J. 
Published: April 2011

ABSTRACTThe spray drying of a droplet containing a substance in solution can produce solid particles with a variety of final shapes: hollow, punctured, squashed, as well as solid spheres. The geometry affects the properties of the product. Models are presented here which describe the processes of solvent evaporation and solute crystallisation as drying takes place. The formation of a crust on the surface of the droplet is addressed. It is proposed that such a crust with a thickness of two crystallite diameters can develop into dry hollow shell. Some example calculations of the spray drying of droplets of sodium chloride solution are described.
Effects of Diffusion of Co/Ni Cations on Sol-Gel Derived ZrO2 Polymorphic Transformations
Authors: Zeng H.C. , Qian M. 
Published: April 2011

ABSTRACTTransition metal incorporated ZrO2 gel matrices have been prepared by impregnation method and investigated with FTIR/DTA/XRD. The metastable tetragonal - monoclinic -tetragonal - cubic phase transformations are revealed in the DTA heating process up to 1400°C for the studied gels. High-temperature tetragonal to monoclinic transition is also observed in the cooling process. It is found that the diffusing metal cations stabilize the low-temperature tetragonal phase. However, for high-temperature (900°C) calcined gels, both as-prepared and metal-stabilized tetragonal phases are reduced substantially. Correlations between metal diffusion and gel polymorphic stabilities are also demonstrated.
Time-Dependent Nucleation and Growth of Crystalline Phase During a Rapid Quench into a Glassy State
Authors: Shneidman V.A. , Weinberg M.C. 
Published: April 2011

ABSTRACTCorrections to the standard expressions for the volume fraction of the crystalline phase which arise due to time-dependent nucleation effects are considered both for the isothermal (transient) and nonisothermal (quench) situations. Analytical results are tested against numerically exact solutions of the Turnbull-Fisher nucleation equations. Physical consequences of the obtained expressions are discussed.
Molecular Beam Epitaxial Growth of InAs/AIGaAsSb Deep Quantum Wells on GaAs Substrates
Authors: Kuze N. , Goto H. , Miya S. , Muramatsu S. , Matsui M. , Shibasaki I. 
Published: April 2011

ABSTRACTWe have investigated InAs deep quantum well structures (InAs DQWs) made from InAs/A1GaAsSb materials on GaAs substrates by molecular beam epitaxy (MBE). In the InAs DQWs, AlGaAsSb layers are lattice-matched to InAs. Using reflection high-energy electron diffraction (RHEED) linescan image analysis, we show that AlGaAsSb on GaAs surfaces quickly relaxes within 3 to 7 monolayers (MLs). The initial stages of AlxGa1-xAsSb (0≤x≤0.5) growth on GaAs (100) substrates and InAs growth on AlGaAsSb layers have been investigated by atomic force microscopy. The ridgeline shapes of AlGaAsSb are observed at the initial stage on GaAs surfaces. In the interface of the InAs/AIGaAsSb, two-dimensional (2D) growth of InAs has been observed. With a thin buffer layer of 600 nm AlGaAsSb, we have achieved very high electron mobilities of more than 32000 cm2/V-s at room temperature.
The Stability of Lattice Mismatched Thin Films
Authors: Guyer J.E. , Voorhees P.W. 
Published: April 2011

ABSTRACTWe examine the linear stability of a planar, alloy thin film, exposed to a deposition flux from the vapor. The film surface is subject to stresses generated by compositional inhomogeneity, as well as by film-substrate lattice mismatch. In addition to the misfit induced surface instability shown by numerous previous studies, we find that the deposition flux alone can produce instability and that complex interactions occur when both deposition and surface transport processes are present. Solute expansion stresses result in several novel behaviors. Under certain circumstances, the growing film can be completely stabilized by a tensile misfit and destabilized by the same magnitude of compressive misfit. The predictions of this theory are compared to the results of several experimental studies.
Solid-on-Solid Monte Carlo Investigation of Islanding Kinetics During Heteroepitaxy
Authors: Payne Ken , Drucker Jeff 
Published: April 2011

ABSTRACTWe have investigated the kinetics of islanding during heteroepitaxy using a solid-on-solid Monte Carlo (SOS-MC) simulation. We simulate deposition by randomly depositing atoms onto a square grid with periodic boundary conditions. Arrhenius surface diffusion kinetics are dependent on the sum of a surface energy barrier (Ed) and the number of nearest neighbors multiplied by an adatom interaction strength (Eb). We confine growth to the first layer above the simple cubic substrate and investigate coverages < 1/2 monolayer. We monitor the evolution of film microstructure by producing island size distributions and plots which compare a cluster's area to perimeter ratio with that of a circle. We find that our simulation qualitatively correlates with results of classical film nucleation theory. A simple model is used to demonstrate the existence of a 'probabilistic nucleation barrier'.
Spectral Sensitivities of X-Ray Diffraction to the Roughness of Si/SiO2 Interfaces
Authors: Evans-Lutterodt K.W. , Tang Mau-Tsu 
Published: April 2011

ABSTRACTResults from X-ray diffraction studies of the morphology of the growing Si(001 )/SiO2 interface are presented. We show the evolution of the root mean square roughness as a function of the growth variables, and we try to go beyond the root mean square parametrization of the interface by measuring the spectral distribution of interface fluctuations. Within our current experimental sensitivies we cannot resolve any fluctuations with a finite in-plane momentum transfer.
Effects of Crystalline Microstructure on Epitaxial Morphology
Authors: Family Fereydoon , Amar Jacques G. 
Published: April 2011

ABSTRACTIn the past simulations of epitaxial growth have used solid-on-solid (SOS) models to simulate the crystalline structure of both the substrate and the growing crystal. These models have produced results in the early stages of growth in good agreement with experiments for a number of different quantities, including the island density and the island size distribution. For multilayer growth, however, there exists a competition between microscopic effects such as the Ehrlich-Schwoebel step barrier and the crystalline microstructure. Therefore, the crystal structure and geometry are important in determining the dynamics and evolution of epitaxial structure and morphology. We present the results of large-scale realistic kinetic Monte-Carlo simulations of multilayer epitaxial growth on fcc(100) and bcc(100) surfaces. The influence of crystal structure on the formation and coarsening of mounds and facets is discussed. We also discuss and compare our results with recent experiments.