bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stress in Sputtered Co90Fe10/Ag GMR Multilayers
Authors: Jarratt J. D. , Inturi V. R. , Weston J. L. , Barnard J. A. 
Published: April 2011

AbstractStress, giant magnetoresistance (GMR), structure, and magnetic properties of sputtered (Co90Fe10X Å/Ag Y Å)×20 multilayer films have been investigated at room temperature where X ranges from 7.5 to 25 Å and Y from 10 to 60 Å. These films exhibit distinct GMR behaviors dependent on individual layer thicknesses, including layered granular-type GMR in CoFe 7.5 Å samples and ‘discontinuous’ GMR (DGMR) in CoFe 15 and 25 Å samples with Ag thicknesses over 30 Å. No antiferromagnetic coupling was observed. CoFe 10 Å samples act as a transition between GMR behaviors. Compressive stress decreases with increasing Ag thickness in the CoFe 7.5 Å samples. In the CoFe 15 and 25 Å samples the stress fluctuates similarly depending on Ag thickness. The difference in stress and MR behavior between the CoFe 7.5 Å and the 15 and 25 Å samples is thought to be due to incomplete CoFe layering in the CoFe 7.5 Å samples. In the CoFe 15 Å DGMR samples, high temperature annealing resulted in tensile stresses large enough to cause film detachment. X-ray diffraction reveals a strong (111) growth texture as well as satellite peaks from coherent layering. This (111) texture is also evidenced by patterns with hexagonal symmetry formed by the detached films.
Calculation of Equilibrium Island Morphologies for Strained Epitaxial Systems
Authors: Kukta R. V. , Freund L. B. 
Published: April 2011

AbstractStrained islands grown coherently on a relatively thick substrate with similar elastic properties are considered within the framework of continuum mechanics. The condition of uniform surface chemical potential is imposed to calculate two-dimensional equilibrium island shapes. The stress distribution in the equilibrium islands is shown to be highly nonhomogeneous. The effects of introducing a single misfit dislocation at the island-substrate interface are considered. It is found that there is critical island volume above which a dislocation decreases the total free energy of the system. The dislocation alters the stress distribution in the island, causing the island to relax via mass transport to an equilibrium shape with a lower height-to-width aspect ratio and a smaller surface chemical potential than the island prior to the introduction of the dislocation.
XPS-Study of Excimer Laser-Reconstructed Alumina Surface
Authors: Georgiev D. G. , Kolev K. , Laude L. D. , Brouxhon O. 
Published: April 2011

AbstractSintered alumina ceramics are recognized as important industrial materials. For many of their applications however, a suitable pretreatment is required aiming at improving the ceramic surface properties. Since excimer lasers have recently proved to be efficient in ceramic processing, a detailed investigation of sintered alumina surface modifications upon excimer irradiation has been performed. In a previous work the results of low-angle X-ray diffraction analysis reveal emergence of the alumina gamma-phase within the upper 10nm of the material. This presence is further demonstrated by the XPS-study reported here. The photoelectron data are compared with information obtained by optical methods.
Microstructure Control for Thin Film Metallization
Authors: Was G. S. , Srolovitz D. J. , Ma Z. , Liang D. 
Published: April 2011

AbstractA strategy was developed for controlling hillock formation in thin metal films by controlling the fiber texture to be of a relatively “weak” orientation. Two-dimensional molecular dynamics (MD) simulations were performed to determine the parameter dependencies of texturing under ion beam assisted deposition. Simulations showed that even for film orientations that have a lower number of nearest neighbor surface bonds, the reduction in sputtering rate by ion channeling will favor the growth of the grains aligned with their channeling direction in the direction of the ion beam. Higher energies should result in greater sputtering and a higher surface roughness. Confirmatory experiments were performed by growing Al films using ion beam assisted deposition in which the Ne ion beam was normal to the substrate surface. For all energies above 0 eV/atom, the fiber texture contained a (220) component and, at high normalized energies, the fiber texture was heavily (220) dominated. Subsequent annealing at 450°C for 30 min. resulted in hillock formation in the PVD (physical vapor deposition) condition, a reduction in the hillock density by two orders of magnitude in the 120 eV/atom condition and complete elimination of hillocking above 800 eV/atom. Although the surface roughness increased with ion beam energy as modeled by MD, the surface became smoother during annealing. These results show that the fiber texture can be controlled in a thin metal film in such a way as to eliminate hillock formation, that molecular dynamics simulation is a valuable predictive tool for guiding experiments in the development of thin film microstructures and that ion beam assisted deposition is an effective, practical tool for controlling microstructures of thin metal films.
Structural Transition in Cu/Fe Multilayered Thin Films
Authors: Nguyen Tai D. , Chaiken Alison , Barbee Troy W. 
Published: April 2011

AbstractMicrostructural development of Fe and Cu in Cu/Fe multilayers of layer thickness 1.5–10 nm prepared on Si, Ge, and MgO substrates by ion beam sputtering has been studied using x-ray diffraction and cross-sectional transmission electron microscopy (TEM). High-angle x-ray results show an fcc Cu structure and a distorted bcc structure in the Fe layers at 5 nm-layer-thickness and smaller, and bcc Fe (110) and fcc Cu (111) peaks in the 10 nm-layer-thickness samples. Lowangle x-ray diffraction indicates that the layers in the samples grown on MgO substrates have a more uniform and smooth layered structure than the multilayers grown on Si and Ge substrates, which results from larger grains in the MgO substrate samples for the same layer thickness. Relationships among growth, microstructure, and interfaces with layer thickness are discussed.
Compliant Substrates for Reduction of Strain Relief in Mismatched Overlayers
Authors: Carter-Coman Carrie , Bicknell-Tassius Robert , Brown April S. , Jokerst Nan Marie 
Published: April 2011

AbstractThin film compliant substrates can be used to extend the critical thickness in mismatched overlayers. A metastability model has been coupled with recent experimental strain relief data to determine the critical thickness of InGaAs epilayers grown on GaAs compliant substrates of variable thickness. The results of this model are also compared to other compliant substrate critical thickness models.
Effect of Stress on Coherently Grown Au-Ni (001) Solid Solutions
Authors: Abadias G. , Gehanno V. , Marty A. , Gilles B. , Dynna M. 
Published: April 2011

AbstractThe effect of epitaxial stress on the stability of Au-Ni solid solutions grown by MBE on Au(001) is investigated. Experimental studies (TEM, GIXD) have shown that the elastic energy of the AuNi alloys is relaxed via two competing ways: twinning and an ordering process in which pseudo-periodic antiphase structures based on the L10 unit cell are found. The stabilisation of a metastable ordered L10 phase in the stressed Au-Ni system is explained using thermodynamic calculations based on the minimisation of free energy including elastic contributions.
Low Temperature Epitaxial Growth of CeO2(110) Layers on Si(100) Using Bias Evaporation
Authors: Inoue Tomoyasu , Yamamoto Yasuhiro , Satoh Masataka 
Published: April 2011

AbstractEpitaxial growth of CeO2 layers on silicon (100) substrates is studied using electron-beam evaporation under substrate bias application in an ultrahigh vacuum. Both negative and positive biases are proved to be effective for lowering the epitaxial temperature. Sample current characteristics are measured as a function of the bias voltage. Under negative bias conditions, as the bias voltage increases, the sample current varies from negative to positive with a transition point at -42 V and then reaches a saturation value of ∼ +4 μA above -60 V. Use of a negative bias of -60 V leads to epitaxial growth temperature lowering of ∼, 40°C. Under a positive bias, the sample current is negative and its absolute value increases with the bias voltage, where the sample current components are to be anions and electrons (46°) as determined by mass separation with a magnetic field application. It is experimentally clarified that the degree of enhancement of epitaxial growth is greater than that in the negative bias experiment (750°C at +60 V bias, i. e., epitaxial growth temperature lowering of 70°C) and the enhancement is attributed to the electron component. It is found that a negative current of ∼ -0.15 mA flows at zero bias, indicating that even in conventional evaporation, electrons somewhat promote epitaxial growth.
Van Der Waals Epitaxy of II-Vi Semiconductors on Layered Chalcogenide (0001) Substrates: Towards Buffer Layers for Lattice Mismatched Systems?
Authors: Löher T. , Klein A. , Schaar-Gabriel E. , Rudolph R. , Tomm Y. , Giersig M. , Pettenkofer C. , Jaegermann W. 
Published: April 2011

AbstractThe II-VI semiconductor CdS was grown by molecular beam epitaxy on the van der Waals faces of the layered semiconductor InSe. Chemical, electronic and morphological properties of the deposited films were investigated by means of low energy electron diffraction (LEED), soft x-ray photoelectron spectroscopy (SXPS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). In contrast to observations made on other layered crystals, nucleation of CdS on InSe is possible also at elevated temperatures which is attributed to the small lattice mismatch. The growth front of CdS corresponds to the sulfur terminated polar (111)-B surface which has a strong tendency to form facets.
Diamond Growth on (a) Large Mo Cylinders at 30 Torr and (b) Flat Mo at One Atmospheric Pressure of H2 and CH4
Authors: Ramesham R. , Rose M. F. 
Published: April 2011

Abstract(a) Polycrystalline diamond films have been grown on cylindrical Mo substrates by hot filament and microwave plasma CVD techniques using a gas mixture of hydrogen and methane. A single hot tungsten filament has been used to demonstrate the growth of adherent diamond films on large cylinders. To our knowledge this is the first report on such large cylindrical substrate (area: 41 cm2 ) using a single filament of active length of 3.75 cm. (b) Polycrystalline diamond films have been deposited by hot-filament technique for the first time using methane and hydrogen at an atmospheric pressure of hydrogen on flat substrates. The diamond growth has been performed at various pressures ranging from 34.5 to 750 Torr. The as-deposited films were analyzed by SEM and Raman to determine morphology and chemical nature, respectively.A. Growth of Diamond Film on Molybdenum Cylinders
Ultraviolet Excimer Lamp Photoassisted Selective Palladium Activation of Coarse Grain 96% Alumina Ceramic for Selective Electroless Copper Plating
Authors: Macauley D.J. , Kelly P.V. , Crean G.M. 
Published: April 2011

AbstractSelective electroless metallisation for electronic interconnect applications requires the selective activation of insulating substrate surfaces prior to plating. Photoselective activation has emerged as a solution with significant potential to minimise the number of activation process steps. This paper reports a photoselective activation process using ultraviolet excimer lamps to decompose a proprietary palladium‐based ultraviolet‐sensitive photochemical coating. The morphology of the photochemical coating, irradiation process conditions for decomposition to produce palladium metal activation sites, the morphology of the coating and activation, and the adhesion of electroless copper on coarse grain 96% alumina ceramic are reported. Copper feature resolution of better than 50 μm is demonstrated. The process is demonstrated to require photochemical solution concentrations an order of magnitude lower than reported palladium acetate activation processes.
Monitoring of indium x-ray peak to optimize InxGa1-xN layer grown by metalorganic chemical vapor deposition
Authors: Lu Hongqiang , Thothathiri Malathi , Wu Ziming , Bhat Ishwara 
Published: April 2011

ABSTRACTIndium droplet formation during the epitaxial growth of InxGa1-xN films is a serious problem for achieving high quality films with high indium mole fraction. In this paper, we studied the formation of indium droplets on the InxGa1-xN films grown by metalorganic chemical vapor deposition (MOCVD) using single crystal x-ray diffraction. It is found that the indium (101) peak in the x-ray diffraction spectra can be utilized as a quantitative measure to determine the amounts of indium droplets on the film. It is shown by monitoring the indium diffraction peak that the density of indium droplets increases at lower growth temperature. To suppress these indium droplets, a modulation growth technique is used. Indium droplet formation in the modulation growth is investigated and it is revealed in our study that the indium droplets problem has been partially relieved by the modulation growth technique.
Characteristics of InGaN Multiquantum-Well-Structure Laser Diodes
Authors: Nakamura Shuji 
Published: April 2011

ABSTRACTThe continuous-wave (CW) operation of InGaN multi-quantum-well-structure laser diodes (LDs) was demonstrated at room temperature (RT) with a lifetime of 35 hours. The threshold current and the voltage of the LDs were 80 mA and 5.5 V, respectively. The threshold current density was 3.6 kA/cm2. Longitudinal modes with a mode separation of 0.042 nm were observed under CW operation at RT. When the temperature of the LDs was varied, large mode hopping of the emission wavelength was observed. The carrier lifetime and the threshold carrier density were estimated to be 10 ns and 2 × 1020/cm3, respectively. The beam full width at half-power values for the parallel and the perpendicular near-field patterns were 1.6 µm and 0.8 µm, respectively. Those of the far-field patterns were 6.8° and 33.6°, respectively.
Stimulated Emission and Gain Measurements from InGaN/GaN Heterostructures
Authors: Shmagin I. K. , Muth J. F. , Krishnankutty S. , Kolbas R. M. , Keller S. , Mishra U. K. , DenBaars S. P. 
Published: April 2011

ABSTRACTInGaN/GaN Heterostructures were deposited on c-plane sapphire substrates by atmospheric pressure Metalorganic Chemical Vapor Deposition (MOCVD). A frequency tripled modelocked Ti-sapphire laser with a 250 fs pulse operating at 280 nm was used for photoexcitation. Photopumped stimulated emission was observed from InGaN/GaN single heterostructures (SH’s) in both edge and surface emitting configurations. A sharp threshold at the onset of stimulated emission and a strong nonlinear dependence of output emission on input power density was observed. Distinct Fabry-Perot modes corresponding to both cavity configurations were also observed. Gain coefficients were measured from an In0. 14Ga0.86N film using the method developed by Shaklee and Leheny for the edge emitting configuration.
MBE Growth and Optical Characterization of InGaN/AlGaN Multiquantum Wells
Authors: Singh R. , Herzog W.D. , Doppalapudi D. , ÜnlÜ M.S. , Goldberg B.B. , Moustakas T.D. 
Published: April 2011

ABSTRACTWe report the growth of InGaN/AIGaN MQWs on c-plane sapphire by electron cyclotron resonance assisted molecular beam epitaxy (ECR-MBE). Two types of structures were investigated; one employing a GaN and the other a A1GaN barrier layer. The first structure consists of five periods of 80 Å thick In0.09Ga0.91N wells separated by 90 Å thick GaN barriers. The second structure consists of|seven periods of 120 Å thick In0.35Ga0.65N wells and Al0.1Ga0.9N barriers. The substrate temperature was kept constant during the growth of both the wells and the barriers, thus avoiding the need for any temperature cycling during the growth, which may lead to interfacial contamination. The films were characterized by cross sectional transmission electron microscopy (TEM), room temperature photoluminescence (PL) and sub-micron resolution luminescence microscopy. TEM images show sharp and abrupt interfaces, thus confirming the high interfacial quality of the MQW structures. Both structures exhibit strong RT luminescence emission peaking at 387 nm (FWHM = 16nm) for the In0.09Ga0.91N/GaN structure and at 463 nm (FWHM = 28nm) for the In0.35Ga0.65N/A10.1Ga0 9N structure. The high resolution luminescence microscopy studies reveal that the radiative recombination for the InGaN quantum wells is 60–70 times more efficient than for the underlying GaN film.
Growth and Characterization of AlN on 6H-SiC Substrates
Authors: Lekova M. , Auner G. W. , Jin F. , Naik R. , Naik V. 
Published: April 2011

ABSTRACTAIN/SiC structures are of current importance for the development of high temperature electronic devices. A systematic study of the growth and structure of AIN on Lely grown 6H-SiC was performed. The SiC substrates were chemically etched followed by thermal desorption at 875 °C under UHV conditions. AFM and RHEED images show the relative improvement in surface morphology following the cleaning procedure. AIN films were grown on 6H-SiC substrates using plasma source molecular beam epitaxy (PSMBE). Substrate temperatures were varied from 400 °C to 800 °C and deposition energies from 1 eV to 25 eV during AIN growth. The AIN crystal structure and topology were analyzed by RHEED and AFM. The AIN/SiC film microstructure are correlated with the quality of the SiC surface and the parameters of the AIN deposition process. Epitaxial growth of AIN(0002) was strongly dependent on the SiC surface quality and deposition energy. The highest quality AIN was achieved at growth temperatures of approximately 600 °C and 15 eV ion energy. Higher ion energy resulted in amorphous film growth.
Low Pressure CVD of GaN from GaCl3 and NH3
Authors: Topf M. , Koynov S. , Fischer S. , Dirnstorfer I. , Kriegseis W. , Burkhardt W. , Meyer B.K. 
Published: April 2011

ABSTRACTWe report on the heteroepitaxial growth of GaN from GaCl3 and NH3 on (0001) A12O3 and (0001) 6H-SiC substrates. In order to enable homogeneous growth within the entire deposition zone one has to use low process pressures in the 10-1 mbar range, where still a growth rate of ∼ 2 μm/h can be achieved. We present a simple model to describe our process and explain our observations. A comparison of GaN deposited on different substrates and with GaN buffer layers is given by low temperature Photoluminescence (PL). Furthermore, impurities are traced by secondary ion mass spectroscopy (SIMS).
Structural Characteristics of MOCVD Grown AlN Films with Different Carbon Concentration
Authors: Li Yun-Xin , Salamanca-Riba Lourdes , Spencer M. G. , Wongchigul K. , Zhou P. , Tang X. , Talyansky V. , Venkatesan T. 
Published: April 2011

ABSTRACTThe structural characteristics of MOCVD AlN films with different carbon doping concentrations grown on sapphire were investigated by XRD (θ–2θ scans, ϕ scans and rocking curves ), HRTEM and Auger spectroscopy. The AlN:C films have very high crystalline quality and low resistivity. The epitaxial relationship between AlN and Sapphire is: (0001)AlN //(0001)Sap, [ 12 10]AlN//[0 110] Sap and [10 10]AlN //[ 2110]Sap. With increasing carbon concentration, the AlN films have higher carrier concentrations, and lower resistivities even though they have higher defect density. The resistivity decreases by 8 orders of magnitude with C doping. When the carbon concentration reaches 11%, an interfacial layer of ∼5nm was observed in HRTEM images. This layer suggests that some C in the film is diffusing into the sapphire substrate. However, optical diffractograms obtained from the negatives of the HRTEM showed no appreciable change in the structure of the interfacial layer compared to the pure substrate.
Spin Resonance Investigations of GaN and AlGaN
Authors: Reinacher N. M. , Angerer H. , Ambacher O. , Brandt M. S. , Stutzmann M. 
Published: April 2011

ABSTRACTElectron Spin Resonance (ESR) and related methods have been used to study defects in GaN and in AlxGa1-xN ternary alloys. In particular, Light-induced ESR of a thick MOCVD grown layer of GaN shows that the ESR signature of the deep defect appears for excitation energies > 2.6 eV and saturates above 2.7 eV. This information provides a direct measure of the energetic level position of the diamagnetic to paramagnetic transition of this center. Furthermore, standard ESR investigations of MBE-grown layers of AlxGa1-xN alloys were performed with emphasis on the effective-mass donor resonance. Composition and temperature-dependent measurements of the resonance position are presented.
Multiphoton Excitation Studies on GaN with PS Pulses
Authors: Libon I. H. , Voelkmann C. , Kim D. , Petrova-Koch V. , Shen Y. R. 
Published: April 2011

ABSTRACTWe report the observation of UV photoluminescence (PL) from wurtzite GaN by multiphoton excitation. The dependence of the PL intensity on excitation intensity as well as PL excitation measurements with sub-bandgap photon energies indicate the existence of deep defect states centered at about 1.0 eV above the top of the valence band. This result was confirmed by a sum-frequency excitation spectrum. We correlate these measurements with the omnipresent yellow luminescence in GaN. Our two-photon PL excitation spectrum yields a two-photon absorption coefficient that agrees very well with theoretical predictions.
Depth Profile of the Excitonic Luminescence in Gallium-Nitride Layers
Authors: Siegle H. , Hoffmann A. , Eckey L. , Thomsen C. , Detchprohm T. , Hiramatsu K. , Davis T. , Steeds J. W. 
Published: April 2011

ABSTRACTWe present results of spatially-resolved photoluminescence and Raman measurements on a 200 μm thick GaN layer grown on sapphire by hydride vapor phase epitaxy. Our microphotoluminescence measurements reveal that the peak position of the excitonic and donoracceptor-pair transitions strongly depends on the distance to the substrate interface. We observed a strong blue shift near the interface and discuss the influence of strain, which we quantified by micro-Raman experiments.
Subpicosecond Time-Resolved Raman Studies of Nonequilibrium Excitations in Wurtzite GaN
Authors: Tsen K. T. , Joshi R. P. , Ferry D. K. , Botchkarev A. , Sverdlov B. , Salvador A. , Morkoc H. 
Published: April 2011

ABSTRACTNon-equilibrium electron distributions as well as phonon dynamics in wurtzite GaN have been measured by subpicosecond time-resolved Raman spectroscopy. Our experimental results have demonstrated that for electron densities n ≥ 5 × l017cm−3, the non-equilibrium electron distributions in wurtzite GaN can be very well described by Fermi-Dirac distribution functions with the temperature of electrons substantially higher than that of the lattice. The population relaxation time of longitudinal optical phonons was directly measured to be τ ≅ 5 ± 1 ps at T = 25 K. The experimental results on the temperature dependence of the lifetime of longitudinal optical phonons suggest that the primary decay channels for these phonons are the decay into (1) one transverse optical phonon and one high energy, longitudinal or transverse acoustical phonons; and (2) one transverse optical phonon and one E2 phonon.