bluuebunny/crossref_metadata_2025_split huggingface dataset:
Light Emission Properties of GaN-Based Double Heterostructures and Quantum Wells
Authors: Loeber D.A.S. , Redwing J.M. , Anderson N.G. , Tischler M.A. 
Published: April 2011

ABSTRACTEdge emission characteristics of optically pumped GaN-AlGaN double heterostructures and quantum wells are examined. The samples, which were grown by metalorganic vapor phase epitaxy, are photoexcited with light from a pulsed nitrogen laser. The pump light is focused to a narrow stripe on the sample surface, oriented perpendicular to a cleaved edge, and the edge luminescence is collected and analyzed. We first compare emission characteristics of highly excited GaN-AlGaN double heterostructures grown simultaneously on SiC and sapphire substrates. Polarization resolved spectral properties of edge luminescence from both structures is studied as a function of pump intensity and excitation stripe length. Characteristics indicative of stimulated emission are observed, particularly in the sample grown on SiC. We then present results demonstrating laser emission from a GaN-AlGaN separate-confinement quantum-well heterostructure. At high pump intensities, band edge emission from the quantum well exhibits five narrow (∼1 Å) modes which are evenly spaced by 10Å to within the resolution of the spectrometer. This represents the first demonstration of laser action in a GaN-based quantum-well structure.
Laser MBE for Atomically Defined Ceramic Film Growth
Authors: Koinuma H. , Kawasaki M. , Yoshimoto M. 
Published: April 2011

ABSTRACTLaser MBE is a process especially useful for epitaxial layer-by-layer growth of ceramic thin films directly from sintered ceramic targets. By employing high vacuum MBE conditions, the process has a restriction in the controllability of chemical composition, e.g. nonstoi chiometry in oxides and nitrides, as compared with conventional pulsed laser deposition, but instead gains the possibility of in situ monitoring of surface reaction on an atomic scale by RHEED. Ever since our first success in observing RHEED intensity oscillation for CeO2 film growth on Si(l11), we have verified the molecular layer epitaxy by laser MBE for perovskite oxides (SrTiO3, BaTiO3, SrVO3 ,etc) and infinite-layer cuprates MCuO2 (M= Sr, Ba, Ca) on SrTiO3 substrates as well as for oxide and nitride films on Si substrates. Key factors to design the laser MBE system, operation parameters, and recent experimental results are presented and discussed.
Fs Spectroscopy of Phonon Emission and Absorption for A Cold Plasma in Gallium Arsenide
Authors: Agnesi A. , Cavalleri A. , Malvezzi A.M. , Reali G.C. 
Published: April 2011

ABSTRACTDegenerate pump and probe measurements on bulk GaAs <100> surfaces with sub-100 fs near infrared laser pulses have been performed in the 0.8 − 3 × 1017 carriers cm-3 excitation range at room temperature. Transient reflectivity data reveal the progressive extinction of the LO-phonon emission channel when the excess excitation energy is decreased. At these wavelengths and for low excitation levels, acoustic phonon absorption from conduction band minimum is observed. Surface recombination rates are deduced from the picosecond evolution of the reflectivity.
Epitaxial Tin Films on Sapphire and Silicon-on-Sapphire by Pulsed Laser Deposition
Authors: Vispute R.D. , Dovidenko K. , Jagannadham K. , Narayan J. 
Published: April 2011

ABSTRACTWe have investigated epitaxial growth of TiN on sapphire and electronic grade silicon-on-sapphire (SOS) by PLD. A pulsed KrF excimer laser was used to ablate the stoichiometric TiN target in the deposition chamber maintained at a base pressure of 3xl0-7 Torr. Epitaxial growth was achieved at deposition temperatures of 500-700°C. The films were characterized by x-ray diffraction technique, Raman spectroscopy, high resolution electron transmission microscopy and four-point-probe electrical resistivity. The x-ray diffraction and TEM results showed that the TiN films deposited on sapphire (0001) and SOS above 500oC were single crystal in nature. The epitaxial relationship for TiN on sapphire was found to be TiN[1 1 1]||Al2O3[0001] and in-plane alignment of TiN[110]||Al2O3[1010]. In case of growth on SOS, epitaxy of TiN on Si was cube-on-cube and is similar to that of TiN grown on bulk Si substrates. Four-point-probe electrical resistivity measurements showed characteristic metallic behavior of these films as a function of temperature with the lowest value of resistivity of about 20-22μΩ-cm at room temperature. This paper describes the fundamental issues related to epitaxy, defect formation and nitride-oxide interfaces. It is also shown that the TiN films on sapphire and SOS have unique characteristics and are promising for metallization in advanced microelectronics.
Femtosecond Laser Deposition of Diamond-Like Carbon Films
Authors: Qian F. , Singh R. K. , Dutta S. , Pronko P.P. , Weber W.H. 
Published: April 2011

ABSTRACTWe have deposited unhydrogenated diamond-like carbon (DLC) films with 100 femtosecond laser pulses, at intensities in the 3x1014 - 6.5x1015 W/cm2 range. Film surface topography, optical property, and bonding structure were examined, respectively, with atomic force microscopy (AFM), spectroscopie ellipsometry (SE) and Raman spectrometry. The femtosecond pulse generated plasma was studied through time-of-flight (TOF) experiment. The most probable kinetic energy of carbon ions was estimated to be in the 300 – 2000 eV range, increasing with laser intensity. In addition, a unique ‘suprathermal’ component with kinetic energy ranging from 4 to 40 keV was observed in the TOF spectrum. This high energy peak is believed to originate from fast ions in a solid density plasma created during the absorption of each femtosecond laser pulse.
Laser Melting and Recrystallization of Bulk Si by Nanosecond UV Laser Pulses
Authors: Garcia C. , Prieto A.C. , Jimenez J. , Sanz L.F. 
Published: April 2011

ABSTRACTLaser ablation of semiconductors presents an increasing interest for both thin film growth and surface modification. We present herein a study of the damage produced in bulk silicon by nanoseconds UV laser pulses with energy above the melting threshold. This study is carried out with a Raman microprobe. Polarized microRaman was used to reveal the main changes in the melted and recrystallized volume. These changes were observed in the liquid/solid boundaries, where tensile stress due to the induced thermal wave is more important. The morphology of the melted region evidences matter accumulation at such a boundary.
Laser Encapsulation of Metallic Films in SiO2
Authors: Pedraza A. J. , Cao S. , Lowndes D. H. , Allard L. F. 
Published: April 2011

ABSTRACTThin films of gold, copper and iron deposited on silica were driven into the substrate by a laser pulse. This transport takes place only when the irradiation is performed at a laser energy density of 0.7 J/cm2 or lower. Cross sectional transmission electron microscopy (TEM) of the irradiated specimens reveals two distinctive stages in the encapsulation process. In the first, the film melts and clusters into small particles and in the second one the particles are driven into the substrate by the laser pulse. The particle size of encapsulated metal varies from 5 to 50 nm. Selected area diffraction of the large particles and lattice fringe images of the smaller particles reveal pure metals, e.g., gold, copper or iron. Titanium films laser irradiated are not encapsulated in silica; instead, these films react with silica forming an amorphous compound. Apparently, one of the conditions required for encapsulation is that the metal should not react with the substrate material. On subsequent irradiation at a laser energy density of 1.5 J/cm2, ablation of silica partially exposes the metallic particles. Strong bonding between a new film deposited after irradiation and the substrate is obtained because these particles anchor the freshly deposited film. Anchoring is clearly revealed by cross sectional TEM. The mechanisms of encapsulation are discussed using results from TEM and adhesion testing.
Laser-Assisted Dry Etching Ablation for Microstructuring of III-V Semiconductors
Authors: Dubowski J.J. , Julier M. , Sproule G.I. , Mason B. 
Published: April 2011

ABSTRACTLaser-assisted dry etching ablation (LADEA) has been reviewed with an emphasis on its applicability for the microstructuring of III-V semiconductor compounds. The method is based on the application of an excimer laser ( λ= 308 nm) for pulsed heating of a wafer which is placed in a stream of Cl2/He gas. Both the products of chemical reaction and the depth to which a laser-induced reaction takes place depend on laser fluence. This makes possible the ablation of a well defined volume of the material. Little or no structural damage to the surface is observed because ablation is carried out with laser fluences below those required to melt the matrix material. The laser fluence dependence of the etch rate indicates that the process is primarily temperature driven with a characteristic energy for desorption. We have investigated LADEA as a method for in-situ processing of III-V semiconductors and the fabrication of nanostructures. An atomic force microscopy study has shown that atomically smooth surfaces can be obtained if the etch rate is near 1/2 atomic layer per laser pulse. The lateral resolution of LADEA has been found to be at least 20 nm. This, as well as the results of in-situ photoluminescence and Auger electron spectroscopy measurements, indicate that LADEA can be used for the direct (photoresist-free) fabrication of high quality microstructures and, ultimately, for the nanostructuring of III-V semiconductor compounds.
Three-Dimensional Laser Chemical Vapor Deposition of Nickel-Iron Alloys
Authors: Maxwell J.L. , Pegna J. , Deangelis D.A. , Messia D.V. 
Published: April 2011

ABSTRACTA systematic study of the composition of Ni-Fe steel microstructures grown from iron pentacarbonyl and nickel tetracarbonyl by direct laser-induced pyrolysis is presented. The partial pressures of both precursors were varied from 2 to 40 mbar, resulting in needles of iron, nickel, and iron-nickel alloys. An Ar+ laser was employed at incident powers of 100 to 600 mW. Auger Spectroscopy and a microprobe were used to determine the composition of the needles vs. partial pressure and laser power. Composition was also measured along the length of the rods to determine temperature changes during needle growth. This latter effect is useful in modelling the heat flow mechanisms during 3-dimensional laser CVD, as the threshold decomposition temperatures of Fe(CO)5 and Ni(CO)4 differ and the composition of the rods affects their thermal conductivity. In some iron samples, periodic banded structures were observed along the length of the rods, indicative of periodic melting. Axial deposition rates were also measured relative to laser power density, and rates up to 40 μm/s were achieved. Photolysis in the gas phase was observed for the iron-nickel carbonyl mixture, and was largely eliminated with a high-pass UV filter at 420nm. Additional disassociation of the carbonyl groups produced carbon soot near the reaction zone, but only for high nickel carbonyl concentrations. Convective cooling of the needles during growth was determined to be the primary heat transfer mechanism.
2d Modeling of Laser Induced Plasma Expansion
Authors: Le H.C. , Zeitoun D. , Burtschell Y. , Marine W. , Sentís M. , Dreyus R.W. 
Published: April 2011

ABSTRACTAn axisymmetric two-dimensional modeling of plasma expansion in background gas is carried out to provide a better understanding of pulsed laser deposition (PLD) processes. This model takes into account the plasma plume dynamics just after the laser ablation pulse. It is shown that hydrodynamic behaviour and thermal relaxation of the plasma are strongly dependent on the nature and the pressure of background gas. In good agreement with experimental results backward movement of particles is clearly identified at a late expansion stage (≥ 2 μs).
Diagnostics of Pulsed Plasma Fluxes in Laser Deposition of Thin Films
Authors: Ozegowski M. , Metev S. , Sepold G. , Burmester S. 
Published: April 2011

ABSTRACTThis paper presents the main results of an experimental study of the dependence of some important plasma parameters (plasma flux density, multicharge ion content, degree of ionization, energy distribution of the ions) on some laser parameters (light flux density, wavelength) for two laser types (TEA-CO2- and excimer laser). A special experimental method has been developed for an absolute and simultaneous measurement of the plasma parameters. The results obtained show the possibility to control the parameters of plasma fluxes over the deposition conditions and herewith to control the properties of the deposited films.
Thick-Film Processing of Pb5Ge3O11-Based Ferroelectric Glass-Ceramics
Authors: Cornejo Iván A. , Haun Michael J. 
Published: April 2011

ABSTRACTProcessing techniques were investigated to produce c-axis orientation, or texture, of ferroelectric Pb5Ge3O11-based glass-ceramic compositions during crystallization of amorphous thick-film printed samples from the Pb5Ge3O11-PbTiO3 (PG-PT) and Pb5Ge3O11Pb(Zr1/2Ti1/2)O3 (PG-PZT) systems. In these systems the PG crystallized into a ferroelectric phase, producing a multiple ferroelectric phase composite at low temperatures, PG-PT or PG-PZT. In this way the non-ferroelectric component of traditional ferroelectric glass-ceramics was eliminated.
Pressure-Induced Structural Transformation in Cristobalite Studied by Molecular Dynamic Simulations
Authors: Duffrene Lucas , Kjeffer John 
Published: April 2011

ABSTRACTThe phase transformation between the α- and β-cristobalite modifications of SiO2 were studied using molecular dynamic simulations. The transformation was induced isothermally by control of the pressure within the structure, either through an externally applied constant stress or by changing the simulation box volume. The atomic scale mechanisms of the transformation can best be observed by means of a time-correlation function describing the spatial orientation of the planes containing the Si-O-Si bonds. These planes rotate by 90° over the course of the transition. Both, the bulk modulus, calculated for static structures, as well as the vibrational spectra of the Si-O-Si planes, reflect the softening of acoustic modes in the midst of the transition, which is characteristic of displacive phase transformations. Although the aperiodic shift of atomic positions upon passage of the transformation front could be responsible for a momentary softening of the structure, this is not the only reason, since this behavior persists when maintaining the structure at intermediate densities, which corresponds neither to α-, nor to β- cristobalite.
A Monte-Carlo Study of B2 Ordering and Precipitation on a Bcc Lattice
Authors: Athènes M. , Bellon P. , Martin G. , Haider F. 
Published: April 2011

ABSTRACTAtomistic Monte-Carlo simulations of precipitation and B2 ordering in a binary alloy on a BCC lattice via vacancy mechanism are presented. Evolution of simulated patterns is in good agreement with the experimentally observed morphologies. Moreover, it is observed that the very early stages of ordering are strongly dependent on atomic mobility parameters. Depending on the relative exchange frequency of vacancies with A and B atoms, two extreme regimes oiordering are identified, leading either to localized or delocalized ordering.
Hysteresis of Long-Range Ordering in CuAu
Authors: Chalupa B. , Chmelik F. , Sima V. , Sprusil B. , Spanl M. , Lang H. , Pfeiler W. 
Published: April 2011

ABSTRACTThe effect of heating and cooling on the long-range order transformation in stoichiometric CuAu is investigated by several complementary measuring methods. Measurements of heat flow, resistometry and acoustic emission are done dynamically by linear heating/cooling. It is shown that measuring dynamically yields the expected effect of undercooling, which decreases with decreasing cooling rate. The dependence of undercooling on cooling rate is compared with the concept of continuous cooling for glass forming. A small influence of heating rate on disordering temperature is reported (retro-effect).
Growth of Transition Metal Films on AL(110) Surfaces
Authors: Smith R.J. , Saleh Adli A. , Shutthanandan V. , Shivaparan N.R. , Krasemann V. 
Published: April 2011

ABSTRACTThe growth of thin Pd, Ni, Fe and Ti films on Al(110) surfaces has been studied using high-energy ion scattering (HEIS), x-ray photoemission spectroscopy and photoelectron diffraction techniques. Of these four metals, only Ti grows as an epitaxial overlayer, while the other metals mix with the substrate to form surface alloys. In the HEIS experiments the backscattered ion yield from Al surface atoms is measured as a function of metal coverage on the Al surface. A decrease in the Al scattering is observed for Ti deposition while the other metals result in increased Al scattering, attributed to alloy formation. An explanation for the exceptional growth behavior of Ti on Al is provided using a model of surface strain associated with aluminide formation.
Morphological Transition of Epitaxial Rhodium (111)
Authors: Tsui Frank , Wellman Joanne , Uher Ctirad , Clarke Roy 
Published: April 2011

ABSTRACTWe report a global morphological transition in the nucleation and growth of epitaxial Rh (111). The transition occurs near 600 K, about 1/4 of the Rh melting temperature, and is signaled by a change in the shape of the surface features from fingered to compact. The transition appears to be related to a change in the critical nucleation size from 1 to 2 atoms. On both sides of the transition, there lies a regime of persistent layer-by-layer growth indicated by a minimum in surface roughness and by the presence of RHEED oscillations. The general surface features exhibit well defined length scales that are not self-affine, and as growth proceeds they increase in size following a power-law dependence on film thickness with a temperature-independent exponent of 0.33 ± 0.03. The results suggest a general pathway to the layer-by-layer growth of close-packed metals.
Correlation between Extended Defects and Surface Morphology in MBE Grown InAs/GaAs Heterostructures
Authors: Bruni M.R. , Padeletti G. , Simeone M.G. , Francesio L. , Franzosi P. , Gennari S. , Nasi L. , Salviati G. 
Published: April 2011

ABSTRACTInAs single layers were grown by Molecular Beam Epitaxy on nominally (001) oriented GaAs substrates at growth temperatures ranging from 350 °C to 500 °C and thicknesses between 1 nm and 6 μm. A systematic study of the influence of growth temperature and thickness on crystal defects and surface morphology is discussed by comparing High Resolution X-Ray Diffraction, Transmission Electron Microscopy and Atomic Force Microscopy investigations.Surface hexagonal shaped holes were observed to develop at the lowest temperatures starting from an heterolayer thickness of 50 nm. Both misfit and threading dislocations were revealed; moreover the correlation between hexagonal shaped surface holes and mixed dislocations, with the component of the Burgers vector (b) along the growth axis larger than the minimum interatomic distance, is discussed. The holes increase in size and decrease in density by increasing the layer thickness. An almost complete surface planarization is observed at a thickness of 6 μm by increasing the growth temperature up to 500 °C.
Crossover from Dimer Nucleation to Adatom Exchange During Submonolayer Epitaxy
Authors: Bales G.S. 
Published: April 2011

ABSTRACTThe nucleation and growth of islands in the early stages of epitaxial growth is studied with kinetic Monte Carlo Simulations and self-consistent mean field rate equations. Specifically, adatom exchange and irreversible dimer formation are allowed to compete equally as the origin of two-dimensional islands. The island size distribution and number density are found to satisfy a dynamic crossover scaling form. The critical island size evolves from one to zero with increasing temperature, decreasing flux, and increasing coverage.
Morphological Evolution During Ge/Si(100) Heteroepitaxy
Authors: Espada Loren I. , Chaparro Sergio , Aguilar Jose , Dorrance Melissa , McKay Michael , Payne Ken , Drucker Jeff 
Published: April 2011

ABSTRACTWe have investigated the morphological evolution of islanded Ge/Si(100) samples formed by > 3 monolayer (ML) Ge deposition. Ge was deposited onto Si(100) surfaces cleaned by flash desorption of the native oxide at rates near 1/2 ML per minute. Growths were performed in an ultra-high vacuum system with a base pressure of < 10−9 Torr. Substrate temperature during growth was 500 °C. Post-deposition processing ranged from no additional treatment to 1 hour at 560 °C anneals. Samples removed from the growth chamber were processed using standard transmission electron microscopy (TEM) specimen preparation techniques and characterized using plan-view TEM. Micrographs were computer analyzed to generate island size distributions (histograms of island size). These size distributions fall into general classes. First, samples with only coherent Ge islands exhibit relatively narrow size distributions. Secondly samples with both coherent and incoherent islands presented bi-modal size distributions with coherent islands populating the smaller radii. These results will be discussed in the context of a model which includes elastic as well as surface and interface energies as driving forces for ripening.
Strain Relaxation in GaAs on Si by Two Groups of Misfit Dislocations
Authors: Tamura M. , Saitoh T. , Yodo T. 
Published: April 2011

ABSTRACTHigh-resolution cross-sectional and conventional plan-view transmission electron microscope observations have been carried out for molecular beam epitaxially grown GaAs films on vicinal Si (001) as a function of film thicknesses and observation directions between two orthogonal <110> directions before and after annealing. Two groups of misfit dislocations are characterized by analyzing whether their extra half planes exist in the film and the substrate side. The group I misfit dislocations due to a stress caused by a lattice misfit between GaAs and Si consist of partial and, 60° and 90° complete dislocations in an as-grown state. After annealing partial dislocations almost disappear and 90° perfect dislocations are predominantly observed. The group II misfit dislocations due to a thermal-expansion misfit-induced stress are all of the 60° type complete dislocations, independent of film thickness and annealing.
Phase Evolution During Crystallization of Amorphous Titanium Aluminide Thin Films: Effect Mn and Nb Additions
Authors: Banerjee R. , Swaminathan S. , Wheeler R. , Fraser H. L. 
Published: April 2011

AbstractThin films of Ti-aluminides have been sputter deposited using a binary γ-TiAl based target and a quaternary γ-TiAl based target containing alloying additions of Nb and Mn. The as-deposited binary film consisted of microcrystalline agglomerates of α-Ti(Al) embedded in an amorphous matrix whereas the as-deposited quaternary film was found to be amorphous. These films have been annealed in a furnace under a protective Ar atmosphere (referred to as ex situ annealing) as well as on a hot stage in a transmission electron microscope (TEM), referred to as in situ annealing, to study the crystallization behavior of these films and also the effect of Nb and Mn additions on the same. Ex situ annealing of both binary and quaternary films resulted in a nanocrystalline microstructure consisting of primarily γ-TiAl with a small amount of finely dispersed α2-Ti3Al. During in situ annealing of the binary film, at 753 K (stage temperature), growth of the α-Ti(Al) phase was observed together with crystallization of a second phase in relatively thicker regions of the specimen. The first crystalline phase to appear during in situ annealing of the quaternary film was a surface crystallized metastable tetragonal phase at 873 K. Prolonged annealing at the same temperature resulted in the transformation of the amorphous region between grains of the tetragonal phase into γ-TiAl. Formation of the tetragonal and intergranular γ-TiAl phases were also observed in the thin regions of the binary film when it was heated to 873 K.