bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theoretical Study of Electron Initiated Impact Ionization Rate in Bulk GaN using a Wave Vector Dependent Numerical Transition Rate Formulation
Authors: Kolnik J. , Oguzman I.H. , Brennan K.F. , Wang R. , Ruden P.P. 
Published: April 2011

ABSTRACTIn this paper, we present ensemble Monte Carlo based calculations of electron initiated impact ionization in bulk zincblende GaN using a wavevector dependent formulation of the interband impact ionization transition rate. These are the first reported estimates, either theoretical or experimental, of the impact ionization rates in GaN. The transition rate is determined from Fermi’s golden rule for a two-body screened Coulomb interaction using a numerically determined dielectric function as well as by numerically integrating over all of the possible final states. The Monte Carlo simulator includes the full details of the first four conduction bands derived from an empirical pseudopotential calculation as well as all of the relevant phonon scattering mechanisms. It is found that the ionization rate has a relatively "soft" threshold.
Effects of Reactive Ion Etching on the Electrical Properties of n-GaN Surfaces
Authors: Ping A. T. , Schmitz A. C. , Asif Khan M. , Adesida I. 
Published: April 2011

ABSTRACTDry etch damage on n-GaN has been investigated using Pd Schottky diodes fabricated on surfaces etched by conventional reactive ion etching with SiCl4 plasma. The Schottky barrier height and ideality factor were investigated as a function of the plasma self-bias voltage. Current-voltage measurements revealed severe degradation of both the forward and reverse characteristics for plasma self-bias voltages in excess of -150 V.
Electrical Properties of Nichia AlGaN/InGaN/GaN Blue LEDs in a Wide Current/Temperature Range
Authors: Zeller Joachim , Eliseev Petr G. , Sartori Philippe , Perlin Piotr , Osiński Marek 
Published: April 2011

ABSTRACTStudies of electrical characteristics of nitride-based light emitting diodes (LEDs) are of interest as they can shed light on carrier transport across the p-n heterojunction. In addition, they provide a convenient way of investigating degradation processes associated with high electrical stress. We present electrical characteristics of Nichia NLPB500 blue LEDs based on AlGaN/InGaN/GaN material system in the temperature range of 9-340 K. Two components of current are identified. High-density current stress leads to diode degradation by shunt formation caused by metal electromigration. At 8 K, blue emission was observed at currents as small as 20 nA.
In-Situ Plume Diagnosis During Pulsed Laser Deposition of Epitaxial-Oxide Thin Films
Authors: Fenner David B. , Kung Pang-Jen , Gores Jörn , Li Qi 
Published: April 2011

ABSTRACTThe visible plume, induced during pulsed-laser deposition (PLD) of epitaxial La0.5.jSr0.5 5CoO3/Ba0.4Sr0.6TiO3/La0.5Sr05CoO3/YBa2Cu3O7/YSZ heterostructures on silicon (100) wafers, was studied by optical-emission spectroscopy (OES). These films are suitable for the fabrication of ferroelectric capacitors and pyroelectric-sensor devices. A YAG laser, at 266 nm, is used for ablation. A collection lens transfers the PLD-plume emission into an optical fiber and onto a diffraction grating and a CCD array, for time-averaged spectroscopy from 410 to 640 nm. Plume emissions from ablated targets in the presence of an oxygen ambient, due to various atomic (Ba, Co, Cu, Sr, Ti, Y, Zr), ionic (Ba+, La+, Sr+, Y+), and a diatomic oxide (YO) species were identified. Emission intensity and evolution of ablated species are reported for distance away from the target surface, oxygen pressures, and laser fluences (1 to 4 J/cm2). The behavior of reactive-product species, especially YO for plumes from yttria-stabilized zirconia (YSZ) and YBCO targets, is discussed. This simple and inexpensive OES system is suitable for use as a plume-quality monitor on routine PLD film synthesis.
Pulsed Laser Deposition of Poly(Tetrafluoroethylene) Films
Authors: Kjendal D.L. , Kumar Ashok , Inturi R.B. , Barnard J. A. 
Published: April 2011

ABSTRACTThin films of poly(tetrafluoroethylene) have been deposited on amorphous (7059 Corning Glass) and silicon(l00) substrates at various temperatures by the Pulsed Laser Deposition technique. The deposition was carried out at high vacuum (˜10-6 torr)at temperatures ranging from room temperature to 350°C. The mechanical properties of these films at the varying process temperatures have been evaluated by nano-indentation techniques and compositional properties of the films have been characterized by Fourier Transform Infrared spectroscopy. The deposition parameters have been optimized in order to produce good quality films.
Liquid-Target Pulsed Laser Deposition and Its Application to Grow Diamond and Diamond-Like Carbon Films
Authors: Xiao Rong-Fu 
Published: April 2011

ABSTRACTA liquid-target pulsed laser deposition system has been designed to grow diamond and diamond-like carbon films using an organic liquid. The system has overcome the problem of target deterioration under high power laser irradiation and has prevented splashing of large particulares on the substrate. The technique is simple and safe to operate and the cost of source materials is much lower than in chemical vapor deposition experiments. With the introduction of oxygen (O2) gas during deposition, only diamond-like carbon is produced. Crystalline diamond films can be obtained when H2O2 is added along with O2 gas. The results provide a evidence that hydroxyl ions, OH-, together with atomic oxygen can indeed promote diamond growth.
Coupled Peritectic Growth of the α- and Γ- Phases in Binary Titanium Aluminides
Authors: Meissen F. , Busse P. , Laakmann J. 
Published: April 2011

ABSTRACTCoupled growth during three phase equilibrium solidification is well known from directionally solidified eutectic systems, and was recently generated in monotectic systems. Several theories predict a stationary peritectic reaction and coupled growth of the properitectic and the peritectic phases therefore should be possible. In spite of these theories coupled growth has not been observed up to now. The TiAl system was selected for further investigation on this topic because of its technical relevance and the fact that it meets the condition mentioned for coupled growth.In a Bridgman laboratory furnace, TiAl with 53.4 at.% Al was directionally solidified with solidification rates v between 0.025 mm/min and 0.1 mm/min and a temperature gradient up to 20 K/mm. The resulting microstructures, analyzed using optical and scanning microscopy with EDX and WDX, consist of two phases parallel to the growth direction. At v = 0.05 to 0.1 mm/min, the alloy solidifies as properitectical α, which subsequently eutectoidally transforms to a substructure of α2-Ti3Al and γ-TiAl, and peritectic γ. The lamellar α2/γ-substructure is oriented parallel to the growth direction.The experimental results were compared with the existing theoretical models of a stationary peritectic reaction and the possibility of metastable eutectic growth was discussed.
Ion Assisted Nucleation in Amorphous Silicon: Mechanism and Theoretical Description
Authors: Spinella C. , Lombardo S. , Priolo F. , Campisano S.U. 
Published: April 2011

ABSTRACTWe present new results on the ion-assisted amorphous to polycrystal transition in silicon. The grain growth velocity vg and the nucleation rate r exhibit quite different behaviours: i) ion irradiation enhances r by a factor which is several orders of magnitude larger than that observed for vg; ii) irradiation with lighter ions produces a decrease of vg and a strong increase of r; iii) the increase of dose rate produces a decrease of both vg and r, but is particulary severe for r. These results have been explained by assuming that ion irradiation produces three fundamental effects: i) generation of long living defects which increase the free energy of the amorphous phase to the value of the fully unrelaxed amorphous silicon, causing the decrease of the thermodynamic barrier to nucleation; ii) generation of defects promoting the transition kinetics at concentrations well above the thermal equilibrium value; iii) prompt amorphization of a small volume at the surface of each crystalline grain.
Low Temperature Oxidation of Silicon After Copper Ion Implantation
Authors: Jaquez E.J. , Alford T.L. , Theodore N.D. , Adams D. , Li Jian , Russell S.W. , Anders Simone 
Published: April 2011

ABSTRACTSilicon oxide films ( > 1μm ) were grown at room-temperature after low-energy copper-ion implantation of Si(100) substrates. The structural properties of the silicon oxide layer and the implanted silicon were characterized by Rutherford backscattering spectrometry and transmission-electron microscopy. During room temperature oxidation a portion of the implanted copper resided on the surface and a portion moved with the advancing Si/SiOx interface. This study revealed that the oxide growth rate was dependent on the amount of Cu present at the moving interface. The resulting oxide formed was approximately stoichiometric silicon dioxide.
Solid-State Alloying in Binary Systems with a Positive Heat of Mixing
Authors: Ma E. , He J.-H. , Schilling P.J. , Pan F. , Liu B.X. 
Published: April 2011

ABSTRACTThe Extended X-ray Absorption Fine Structure (EXAFS) technique has been employed to monitor the formation of metastable alloys by mechanical alloying in two positive-heat-of-mixing systems, Cu-Fe and Ag-Fe. With its unique atom selectivity and local atomic environment sensitivity, EXAFS provides clear evidence of atomic-level alloying forming bcc (Fe80Cu20) and fee (Fe50Cu50) solid solutions in the Cu-Fe system. In contrast, such alloying appears to be absent in Ag-Fe. The possible availability of a thermodynamic driving force for alloying in certain nanostructured mixtures of immiscible elements is discussed. A preliminary study was performed on the possibility of alloying and amorphization in vacuum-deposited Cu/Ta multilayer films.
Thermal Activation of the Crystallization Kinetics of Amorphous Silicon
Authors: Mohammed-Brahim T. , Briand D. , Kis-Sion K. , Guillet D. , Salaün A.C. , Bonnaud O. 
Published: April 2011

ABSTRACTSolid Phase Crystallization of amorphous silicon films, deposited by the Low Pressure Chemical Vapor Deposition technique, is studied by in-situ monitoring the film conductance. The crystal growth rate VG, deduced from this measurement, was found to be thermally activated. The activation energy E behaviour for films with different doping varying in a great range, from undoped to 4×1019 cm−3, was then deduced. This behaviour, described for the first time in this work, shows a constant E for undoped and weak doping, then a high decrease after a doping value threshold. The undoped films show a decreasing E when the deposition rate increases i.e. when the structure of the amorphous deposited film tends to correspond to the relaxed amorphous network. All these new results are used to introduce a crystallization model based on a crystalline-amorphous double phase and on the charge of defects at the crystal-amorphous interface.
Calculation of Phase Competition and Selection in Solidification Using a Combined Nucleation and Calphad Approach
Authors: Shao G. , Tsakiropoulos P. 
Published: April 2011

ABSTRACTThermodynamic data derived by the CALPHAD method has been extended to undercooled melts to study phase competition and the role of time dependent and steady state nucleation in rapidly solidified materials. The theoretical predictions made about phase competition between hcp α, bcc β and Ll0 γ in some Al(Ti,V) alloys are compared with experimental results. It is shown that high melt cooling rates introduce significant transient nucleation effects on phase nucleation.
Partial Reduction of NiAl2O4 - Mechanism and the Influence of Doping
Authors: Zhang Z. , Üstündag E. , Sass S.L. 
Published: April 2011

ABSTRACTMetal-ceramic microstructures were formed in situ by partial reduction of the spinel compound NiAl2O4. At 1300°C the reduction reaction passed through an intermediate stage involving the formation of Ni and metastable “defect spinel” phases, before the appearance of the equilibrium phases, Ni + α-Al2O3. At 1100°C, depending on the reduction time, the products of the reduction reaction were Ni and the metastable “defect spinel” for less than 24 hours; Ni + θ-Αl2Ο3 for 24-48 hours; and Ni + GI-AI2O3 for 144-168 hours. The effects of dopants, such as Cr2O3, MgO, TiO2 and Y2O3, on the reduction mechanism and kinetics were examined and shown, in the case of TiO2, to have a controlling influence. A reduction reaction mechanism is proposed.
High dielectric SrGeO3 perovskite prepared by high pressure synthesis
Authors: Grzechnik Andrzej , McMillan Paul F. , Petuskey William 
Published: April 2011

ABSTRACTHigh pressure synthesis of SrGeO3 perovskite and its properties are reported. The metastable material recovered to room pressure shows a high dielectric constant (>100), due to a “stretched” crystal lattice.
Studies of Ordering in Small Particles
Authors: Herr U. , Poilack M. , Olynick D.L. , Gibson J.M. , Averback R.S. 
Published: April 2011

ABSTRACTDisordered clusters of the intermetallic compounds Ni3Al and Cu3Au have been produced using a high pressure sputtering technique. The clusters are either embedded in a film or studied, in-situ in an UHV electron microscope. The evolution of the ordered structure upon annealing is studied. Using a scanning transmission electron microscope, electron diffraction is obtained from individual clusters. Partial ordering is observed in Cu3Au clusters which have been annealed below the bulk order-disorder transition temperature. Under the experimental conditions, only clusters with sizes of 10–15 nm or larger show ordering.
Influence of Interfacial Copper on the Ti-SiO2 Reaction During Nitridation of Cu-Ti Films
Authors: Adams Daniel , Alford T.L. , Theodore N.D. , Laursen T. , Russell S.W. , Kim M.J. 
Published: April 2011

ABSTRACTCu(90 nm)/Ti(20 nm) bilayers and Cu(Ti 27 at.%) alloy films were deposited on SiO2 and annealed in an NH3 ambient at temperatures 400–700° C for 30 min. During annealing Ti segregated to both the free surface and the alloy/SiO2 interface. At the surface Ti reacted with NH3 to form TiN, whereas at the interface the Ti reacted with the SiO2 to form a TiO/Ti5Si3 structure. High resolution energy dispersive x-ray analysis revealed the presence of interfacial Cu between the Ti-silicide and Ti-oxide layers at temperatures greater than 450°C. Using Cu-Ti alloy films enhanced the Si02 consumption rate by a factor of 3-4 compared to that of pure Ti. It is suggested that the interfacial Cu is responsible for the increased rate. It is plausible that an interfacial Cu2O component has a catalytic effect on the Ti- SiO2 reaction.
Heteroepitaxial Si1-x-yGex Cy Layer Growth on (100)Si by Atmospheric Pressure Chemical Vapor Deposition
Authors: Atzmon Z. , Bair A. E. , Alford T. L. , Chandrasekhar D. , Smith David J. , Mayer J.W. 
Published: April 2011

ABSTRACTThin heteroepitaxial films of Si1-x-yGexCy have been grown on (100)Si substrates using atmospheric pressure chemical vapor deposition at 550 and 700°C. The crystallinity, composition and microstructure of the SiGeC films were characterized using Rutherford backscattering spectrometry (ion channeling), secondary-ion-mass-spectrometry and cross-sectional transmission electron microscopy. SiGeC films with up to 2% C were grown at 700°C with good crystallinity and very few interracial defects, while misfit dislocations at the SiGe/Si interface were observed for SiGe films grown under the same conditions. This difference indicates that the presence of carbon in the SiGe matrix increases the critical thickness of the grown layers. SiGeC thin films (>110 nm) with up to 3.5% C were grown at 550°C with good crystallinity. The crystallinity of the films grown at lower temperature (550°C) was less sensitive to the flow rate of the C source (C2H4), which enabled growth of single crystal SiGeC films with higher C content.
Surfactant-Mediated Growth of SiGe/Si Quantum-Well Structures Studied by Photoluminescence Technique and Secondary Ion Mass Spectrometry
Authors: Nilsson S. , Zeindl H. P. , Krüger D. , Klatt J. , Kurps R. 
Published: April 2011

ABSTRACTIn this investigation, surfactant-mediated growth of SiGe/Si single quantum-well structures is studied by photoluminescence and secondary ion mass spectrometry. The samples were grown by molecular-beam epitaxy and Sb was used as a surfactant. The photon energy of the SiGe-related near-band-edge photoluminescence was used to probe the action of Sb as a surfactant to promote two-dimensional growth and to reduce segregation of Ge during growth. First, the "growth-temperature window" at which Sb acts preferentially as a surfactant was determined. Then, at this optimized temperature of 700°C, the influence of different Sb coverages was investigated and it was found that 0.5 monolayer was a sufficient coverage to obtain full surfactant action. Ge concentration depth profiles obtained by secondary ion mass spectrometry confirmed the effect of surfactant-mediated growth and, in addition, the unintentional incorporation of the Sb surfactant during growth was determined quantitatively. In a final experiment the effect of deposition of Sb on either the lower or the upper heterointerface is addressed.
The use of Rheed Intensities for the Quantitative Characterization of Surfaces
Authors: Ma Y. , Lordi S. , Eades J. A. 
Published: April 2011

ABSTRACTRHEED is an important method for the in situ characterization of surfaces. Until recently, this characterization has not used the intensities of RHEED reflections. Improved methods of calculation have made it possible to simulate RHEED patterns from bulk-terminated, reconstructed and stepped surfaces. From the comparison between simulated and experimental patterns, it is now possible to refine the positions of atoms in surfaces and to determine the density of steps on surfaces (well almost).
Orientation Dependence of CdTe/Si Grown by MBE
Authors: Almeida L. A. , Chen Y. P. , Faurie J. P. , Smith David J. , Tsen S.-C. Y. , Sivananthan S. 
Published: April 2011

ABSTRACTIn this study CdTe (111)B was grown by molecular beam epitaxy on vicinal Si(001) substrates, with a variety of substrate tilt angles (θ), and tilt directions (φ) relative to [110]. Layer quality, and content of double-domain and microtwin defects were evaluated by double crystal rocking curve (DCRC) full width at half maximum (FWHM) and x-ray diffraction, respectively. Transmission electron microscopy (TEM) was used to study interface quality and the nature of structural defects as a function of epilayer thickness. In the present investigation, substrate preparation and growth conditions, particularly initiation conditions, are correlated with Si (001) tilt. It has been found that oxide desorption processes can depend strongly on θ, especially for larger values of θ (> 4°). Currently, we routinely produce single domain, twin-free CdTe(111)B epilayers on vicinal Si (001) substrates.
Defect Structures in GaP/Si
Authors: Samavedam Srikanth B. , Kvam Eric P. , Ford Greg , Wessels Bruce W. , Chin T. P. , Woodall Jerry M. 
Published: April 2011

ABSTRACTThe heteroepitaxial growth of gallium phosphide on silicon (GaP/Si) is a useful step towards integration of III-V based devices onto silicon. GaP layers grown on silicon substrates of different orientations using metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) were characterized using transmission electron microscopy (TEM) with an attempt to understand the epilayer growth characteristics. Despite the fact that the GaP/Si system has a low misfit (≈0.4 %), a high density of crystal stacking defects was commonly observed. Inversion domain boundaries (IDBs) were another common defect observed in regions where the fault density was reduced.
Formation of Interfacial Dislocations in Hetero-Epitaxial Layers Grown in Two-Dimensional Mode
Authors: Oktyabrsky S. , Narayan J. 
Published: April 2011

ABSTRACTHigh-resolution transmission electron microscopy has been used to study formation of interfacial defects related to misfit strain accommodation in Ge/Si heterostructures (mismatch 4%) grown in the two-dimensional mode. Special emphasis is placed on the conditions leading to a two-dimensional (layer-by-layer) growth mode. We discuss general features of a dislocation tangle resulted from glide-limited plastic relaxation, typical for highly mismatched (001)-diamond and zinc-blende heterostructures. The evolution of the dislocation network as a function of film thickness and thermal annealing is controlled by growth instabilities and dislocation interactions. The observed correlation in distribution of parallel misfit dislocations including pairing (at <2 nm) of misfit segments from intersecting glide planes and rearrangements in a nonequilibrium dislocation network driven by elastic interaction between 60° dislocation segments in the almost relaxed heterostructures are discussed in detail. Pairing of the 60° glide dislocations results either in their combination to form pure edge 90° dislocations or in the dissociation into partials. We propose and experimentally verify a model for the latter process involving the formation of extrinsic stacking faults in the heterolayers under compressive strain.
Twinning in epilayers of CdTe on <211> Si: Influence of ZnTe buffer layer and substrate misorientation
Authors: Gray A. , Dhar N.K. , Clark W. , Charlton P. , Dinan J.H. , Segnan R. , Mayo W.E. 
Published: April 2011

ABSTRACTX-ray diffraction spectra of CdTe epilayers grown with and without ZnTe buffer layers on <211> Si substrates by molecular beam epitaxy consist of 422 and 331 reflections. We interpret these as evidence for the existence of twins within the volume of a <211> oriented epilayer and show that twin volume is dependent on the ZnTe buffer layer and substrate misorientation.
Characterization of Particles Synthesized by Aerosol Processes for Various Pb:Si Molar Feed Ratios
Authors: Owens Timothy M. , Biswas Pratim 
Published: April 2011

AbstractA detailed characterization was performed of the particles produced under various Pb:Si molar feed ratios in a flow reactor at a maximum temperature of 1000 °C. The silica particles formed in the high temperature region coagulated and only partially coalesced to form large agglomerate structures of high specific surface area. For a lead only feed, the resulting particles were hydrocerussite with small but detectable amounts of massicot. As the silica precursor was inlet in excess amounts (Pb:Si ≤ 1:12), the crystalline lead compounds disappeared and amorphous lead-silica complexes predominated. The particle morphology also changed from cylindrical, polygonal and spherical shapes to large agglomerate structures composed of several size modes of primary particles. At Pb:Si molar feed ratios of 1:12 and 1:29, the particles making up the chain-like agglomerate structure were primarily spherical with larger lead silicate spherical particles (≈ 0.5 μm) attached to the agglomerate. The lead was found to be distributed throughout the large agglomerate structures.