bluuebunny/crossref_metadata_2025_split huggingface dataset:
In Situ Monitoring and Model Simulation of BaTiO3 Pulsed Laser Thin Film Deposition
Authors: Paul Albert J. , Schenck Peter K. , Bonnell David W. , Hastie John W. 
Published: April 2011

AbstractWe have applied intensified Charge Coupled Detector (ICCD) imaging to real-time, in situ monitoring of excited vapor species emission during the pulsed excimer (248 nm wavelength) laser deposition (PLD) of BaTiO3 ferroelectric thin films. Molecular beam mass spectrometry (MS) was used for species identification and velocity distribution analysis. Gasdynamic model simulations of the plume formation and transport process are tested by comparison with the ICCD and MS results. Particular attention is given to the time scale during and immediately following the laser pulse (0 - 460 ns), and also to the effects of added 02. atomic oxygen was found to be the predominant species present at the leading edge of the vapor plume. Other, slower species found included neutral Ti, TiO, Ba, and BaO.
Dielectric Susceptibility and Strain in Sr1-XBaXTio3 Ferroelectric Thin Films Grown by Pulsed Laser Deposition
Authors: Knauss L.A. , Horwitz J.S. , Chrisey D.B. , Pond J.M. , Grabowski K.S. , Qadri S.B. , Donovan E.P. , Mueller C.H. 
Published: April 2011

AbstractThin films of Srl-xBaxTiO3 (SBT) with x = 0 to 0.80 have been grown in situ by pulsed laser deposition onto single crystals of (001) LaAlO3. the films were grown to thicknesses of 0.6 μ.m and found to be single phase, highly oriented, and characterized by x-ray ω scan widths of ≤ 0.5°. the temperature dependence of the dielectric constant and the relative dissipation factor were measured at 1 kHz using au interdigital capacitors deposited on top of the ferroelectric films. the capacitance measurements indicate that the temperature dependence of the dielectric constant of the film is broad and the maximum is shifted relative to the bulk material. the differences between thin film and bulk properties are attributed to strain in the film resulting from film -substrate lattice mismatch. Thick films (∼7 μm) gave direct evidence for strain through cracking and delamination. X-ray diffraction measurements have been made to determine the non-uniform strain in the thin films which was approximately 0.1%.
Analysis of the Effects of Interior Aperture Angle on Print Quality in Solder Paste Stenciling
Authors: Monaghan K. , Head L. , Sahay C. , Constable J. 
Published: April 2011

ABSTRACTStencil apertures of various interior angle, i.e. angle between two sides of a polygon, are analyzed for print performance. Aperture size and sidewall taper are also examined for their individual and combined effects on printing. The results show no effect of interior angle within the bounds of the experiment. Sidewall taper becomes relevant when aperture geometry is nearly square.
Indium-Copper Multilayer Composite Solder for Fluxless Bonding
Authors: Lee Chin C. , Chen Yi-Chia 
Published: April 2011

ABSTRACTA 200°C fluxless process is developed to produce In-Cu joints. The fluxless feature is achieved by the prevention of indium oxidation during the solder fabrication and the bonding process. Indium and copper are deposited on an object in high vacuum to inhibit indium oxidation. Copper interacts with indium to form CuIn compound that further protects the inner indium from oxidation. For a specific design, the resulting joints consist of mainly CuIn intermetallic grains surrounded by a small amount of pure indium as revealed by SEM with EDX. Scanning acoustic microscope examination indicates that the joints are nearly void-free. This technology enables versatile control of the alloy composition, thus leading to several remelting temperatures and various physical properties.
New Synthetic Approaches to Self-Assembled Chromophoric Multilayers as Second-Order Nonlinear Optical Materials
Authors: Lin Wenbin , Marks Tobin J. , Yitzchaik Shlomo , Lin Weiping , Wong George K. 
Published: April 2011

AbstractThis contribution describes the synthesis and properties of NLO-active self-assembled chromophoric multilayers. The stilbazolium self-assembled multilayers were prepared by new topotactic approaches based on siloxane self-assembly technology. X-ray photoelectron spectroscopy (XPS), advancing aqueous contact angle (θa) measurements, transmission optical spectroscopy, polarized second harmonic generation (SHG), and specular X-ray rellectivity (XRR) show that the resulting self-assembled chromophoric superlattices have very high structural regularity and very large second-order nonlinear optical susceptibility.
Spatially Reversible Electric Field-Induced Permeation in Pure and Mixed Langmuir-Blodgett Layers of Hemicyanine Dyes and Octadecanoic Acid on Poly(2-Vinylpyridine)
Authors: Lu W. , Song Q. , Bohn P.W. 
Published: April 2011

AbstractLangmuir-Blodgett (LB) films of the hemicyanine dyes 4-(4-dihexadecylaminostyryl)- N-methylpyridinium iodide and 4-(4-dioctylaminostyryl)-N-propylsulfonate pyridinium mixed with octadecanoic acid have been deposited onto H2O-swollen poly(2-vinylpyridine) (P2VP) as mass transport barriers. The transport properties of these structures have been studied both with and without the application of an electric field in the range 0 ≤ E ≤ 100 V/cm, by observing the rate of permeation of both anionic (fluorescein) and zwitterionic (rhodamine B) fluorophores. The apparent diffusion coefficient at E = 0 decreases exponentially with the number of monolayers through which the probe molecule must permeate, in agreement with a hole-mediated permeation model. Application of an external electric field is observed to control the rate and direction of the mass transport of the probe molecule across the barrier layer. The electric field effect is both spatially reversible, i.e. the probe can be transported in either direction across the barrier layer, and temporally reversible, i.e. the permeability cycles with the field between large values when the field is on and small values when it is not applied. The results are consistent with an interpretation in which electroporation is the dominant mechanism for transport in the field-on state.
β-Glycosylamide Glycopolymers: Synthesis, Physical Properties, Chemical and Enzymatic Stability
Authors: Spevak Wayne , Tropper Frangois D. 
Published: April 2011

AbstractA method is described for the preparation β-glycosylamide monomers from reducing carbohydrates. The glycosylamide monomers were copolymerized with acrylamide to formhigh molecular weight, water soluble polymers. The chemical and enzymatic stability of the β-N-glycosidic linkage was investigated. In addition, the glycopolymers were characterized by their interactions with lectins.
NH3 as Nitrogen Source in MBE growth of GaN
Authors: Kamp M. , Mayer M. , Pelzmann A. , Thies A. , Chung H. Y. , Sternschulte H. , Marti O. , Ebeling K. J. 
Published: April 2011

ABSTRACTWe report on the growth of GaN in GSMBE using NH3 as nitrogen source. Special focus will be on the NH3 cracking, where we applied an On Surface Cracking technique (OSC). Using OSC we achieve photoluminescence linewidths as narrow as 5.5meV (5K) and mobilities of 220 cm2/Vs at room temperature.
Growth and Properties of Bulk Single Crystals of GaN
Authors: Suski T. , Perlin P. , Leszczyński M. , Teisseyre H. , Grzegory I. , Jun J. , Boćkowski M. , Porowski S. , Pakuła K. , Wysmołek A. , Baranowski J.M. 
Published: April 2011

ABSTRACTIn this paper we review recent developments in the growth of bulk GaN crystals by a high-pressure, high-temperature method. We also provide information on various physical properties of bulk GaN material. Then, some preliminary results on the homoepitaxial growth of GaN are given. In the second part of this paper we discuss the following problems: the possible origin of the large free electron concentration in undoped GaN material, the parasitic effect of yellow luminescence and the nature of Zn- and Mg-acceptors.
Defect Microstructure of Thin Wurtzite GaN Films Grown by MBE
Authors: Sverdlov B.N. , Botchkarev A. , Martin G.A. , Salvador A. , MorkoÇ H. , Tsen S.-C.Y. , Smith David J. 
Published: April 2011

ABSTRACTThin films of wurtzite GaN have been grown by molecular beam epitaxy on 6H SiC (basal plane), Si {111} and sapphire (c-plane) substrates with and without various buffer layers. The defect microstructure of the films and the substrate/buffer/GaN interfacial quality have been characterized by cross-sectional transmission electron microscopy. The morphology was dominated by threading defects that originated at the substrate/buffer and/or buffer/film interfaces. Typical defect densities dropped rapidly with distance from the substrate but remained ∼108–109/cm2, depending on the particular substrate, for film thicknesses approaching one micron or more. The best quality films were grown at 770°C on sapphire with A1N buffer layers, and had X-ray rocking curve full-width at half-maximum values of ∼ 55arc-sec.
High-Quality III-V Nitrides Grown by Metalorganic Chemical Vapor Deposition
Authors: Dupuis R.D. , Holmes A.L. , Grudowski P.A , Fertitta K.G. , Ponce F.A. 
Published: April 2011

ABSTRACTWe report the growth of high-quality III-V nitride heteroepitaxial films on (0001) sapphire substrates by low-pressure metalorganic chemical vapor deposition (MOCVD). These films have exhibited narrow X-ray diffraction rocking curves with full-width-at-half-maximum values as low as ΔΘ∼37 arc sec. Photoluminescence and transmission electron microscopy analysis further indicate the samples to be of high quality.
MOVPE Growth of High Electron Mobility AlGaN/GaN Heterostructures
Authors: Redwing J.M. , Flynn J.S. , Tischler M.A. , Mitchel W. , Saxler A. 
Published: April 2011

ABSTRACTWe have fabricated AlxGa1−xN/GaN heterostructures with high two-dimensional electron gas (2DEG) mobilities and high sheet carrier densities by metalorganic vapor phase epitaxy (MOVPE). The 2DEG sheet density and mobility exhibit a compositional dependence on the Al fraction of the electron donor layer. The highest mobility (5750 cm2/Vs at 16K) was measured in a sample with x=0.15 that had a sheet carrier density of 8.5×1012 cm−2. The undoped AlxGa1−xN layers have low background carrier concentrations and can be intentionally doped n-type using SiH4. The effect of intentional n-type doping of the AlxGa1−xN donor layer on the electrical properties of the 2DEG was studied in structures that included an undoped AlxGa1−xN spacer layer of varying thickness. Higher 2DEG mobilities were obtained when a 100Å thick undoped layer was included in the structure due to spatial separation of the 2DEG from ionized impurities in the doped AlxGa1−xN. These initial results demonstrate that the electrical properties of AlxGa1−xN/GaN heterostructures can be controlled by intentional doping and appropriate layer design.
Growth of Cubic GAN on (001) GAAS
Authors: Brandt O. , Yang H. , Trampert A. , Ploog K. H. 
Published: April 2011

ABSTRACTWe present a study of the growth of cubic GaN films on (001) GaAs by molecular beam epitaxy. Our investigations focus on the nucleation stage as well as on the subsequent growth of GaN. The phenomenon of epitaxial growth at this extreme mismatch (20%) is demonstrated to arise from a coincidence lattice between GaAs and GaN. The presence of a high-density of stacking faults in the GaN layer is explained within this understanding as being a natural consequence of the coalescence of perfectly relaxed nuclei. We furthermore analyze the growth kinetics of GaN via the surface reconstruction transitions observed upon an impinging Ga flux, from which we obtain both the desorption rate of Ga as well as the diffusion coefficient of Ga adatoms on the Ga-stabilized GaN surface. The diffusivity of Ga is found to be very low at the growth temperatures commonly used during molecular beam epitaxy, which provides an explanation for the microscopic surface roughness observed on our samples.
Issues and Examples Regarding Growth of AlN, GaN and AlxGa1−xN Thin Films via OMVPE and Gas Source MBE
Authors: Davis Robert F. , Weeks T. W. , Bremser M. D. , Tanaka S. , Kern R. S. , Sitar Z. , Ailey K. S. , Perry W. G. , Wang C. 
Published: April 2011

ABSTRACTOrganometallic vapor phase epitaxy (OMVPE) and molecular beam epitaxy (MBE) are the most common methods for the growth of thin films of A1N and GaN. Sapphire is the most common substrate; however, a host of materials have been used with varying degrees of success. Both growth techniques have been employed by the authors to grow AIN, GaN and AlxGa1−xN thin films primarily on 6H-SiC(0001). The mismatch in atomic layer stacking sequences along the growth direction produces double positioning boundaries in A1N and the alloys at the SiC steps; this sequence problem appears to discourage the two-dimensional nucleation of GaN. Films of these materials grown by MBE at 650°C are textured; monocrystalline films are achieved between 850°C (pure GaN) and 1050°C (pure A1N) by this technique and OMVPE. Donor and acceptor doping of GaN has been achieved via MBE without post growth annealing. Acceptor doping in CVD material requires annealing to displace the H from the Mg and eventually remove it from the material. High brightness light emitting diodes are commercially available; however, numerous concerns regarding metal and nitrogen sources, heteroepitaxial nucleation, the role of buffer layers, surface migration rates as a function of temperature, substantial defect densities and their effect on film and device properties, ohmic and rectifying contacts, wet and dry etching and suitable gate and field insulators must and are being addressed. Selected issues surrounding the growth of these materials with particular examples drawn from the authors' research are presented herein.
Alternative Routes to the MOVPE Growth of GaN and Aln
Authors: Roberts V. , Roberts J. S. , Jones A. C. , Rushworth S. 
Published: April 2011

ABSTRACTAlternative precursors to group-in nitrides have been studied based on two schemes: 1) The reaction Me3M (M=Al,Ga) with t-BuNH2 and 2) the decomposition of NH3 based adducts. Polycrystalline growth of AIN has been demonstrated by both routes. Decomposition of the adduct Me3Al:NH3 has been used to prepare epitaxial AIN on (0001) sapphire with an X-ray FWHM (full width at half maximum) of 16 arcrnin at a growth temperature of 1050C. Similar growth using analogous gallium precursors always resulted in gallium droplets. We have attributed this difference in chemical reactivities to the lower electronegativity of gallium compounds, thus leading to dissociation rather than sequential methane loss to form the nitride.
Understanding the Pyramidal Growth of GaN
Authors: Rouviere J.-L. , Arlery M. , Bourret A. , Niebuhr R. , Bachem K.-H. 
Published: April 2011

ABSTRACTBy a combination of conventional, HREM and CBED TEM experiments we have studied wurtzite GaN layers grown by Metal-Organic Chemical Vapour Deposition (MOCVD) on (0001)Al2O3. We experimentally determine the structure of the macroscopic hexagonal pyramids that are visible at the surface of the layers when no optimised buffer is introduced. These pyramids look like hexagonal volcanoes with one hexagonal microscopic chimney (up to 75nm wide) at their core. The crystal inside the chimney is a pure GaN crystal with a polarity opposed to the one of the neighbouring material : the GaN layers grown on (0001)Al2O3 are everywhere Ga-terminated except in the chimneys where they are N-terminated. Some of the N-terminated chimneys grow faster and form macroscopic hexagonal pyramids. Chimneys bounded by Inversion Domains Boundaries (IDBs) originate from steps at the surface of the substrate and may be suppressed by an adapted buffer layer.
Electronic and Optical Properties of the Group-III Nitrides, their Heterostructures and Alloys
Authors: Lambrecht Walter R. L. , Kim Kwiseon , Rashkeev Sergey N. , Segall B. 
Published: April 2011

ABSTRACTVarious aspects of the electronic structure of the group III nitrides are discussed. The relation between band structures and optical response in the vacuum ultraviolet is analyzed for zincblende and wurtzite GaN and for wurtzite A1N and compared with available experimental data obtained from reflectivity and spectroscopic ellipsometry. The spin-orbit and crystal field splittings of the valence band edges and their relations to exciton fine structure are discussed including substrate induced biaxial strain effects. The band-offsets between the III-nitrides and some relevant semiconductor substrates obtained within the dielectric midgap energy model are presented and strain effects which may alter these values are discussed. The importance of lattice mismatch in bandgap bowing is exemplified by comparing AlxGa1−xN and InxGa1−xN.
Structural and Electronic Properties of AlN, GaN And InN, and Band Offsets at AlN/GaN (1010) and (0001) Interfaces
Authors: Satta A. , Fiorentini Vincenzo , Bosin Andrea , Meloni F. , Vanderbilt David 
Published: April 2011

ABSTRACTAb initio local-density-functional calculations are presented for bulk A1N, GaN, and InN in the wurtzite, zincblende, and rocksalt structures. Structural transition pressures and deformation potentials of electronic gaps are investigated. In addition, we study the band offset at the polar (0001) and non-polar (1010) AIN/GaN interfaces. Within AIN-on-GaN epitaxial conditions, we obtain valence-band offset values close to 0.7 eV for both interfaces. From the macroscopic field appearing along the growth direction of the polar interface (tentatively attributed to AIN macroscopic polarization), an estimate of the macroscopic dielectric constant of GaN is extracted. All calculations employed conjugate-gradient total-energy minimizations, ultrasoft pseudopotentials, and plane waves at 25 Ryd cutoff.
Epitaxial Growth of GaN on Lattice-Matched Hafnium Substrates
Authors: Beresford R. , Stevens K.S. , Briant C. , Bai R. , Paine D.C. 
Published: April 2011

ABSTRACTA method of producing epitaxial GaN on single-crystal Hf has been developed. The metal substrate is formed by a strain-anneal process yielding macroscopic (5-mm) grain sizes, followed by polishing, chemical etching, and Ar ion sputtering at elevated temperature in ultrahigh vacuum. The growth is conducted by plasma-assisted molecular beam epitaxy using an initial passivation layer deposited at low temperature and subsequent growth at 700 °C. The resulting films are in registry with the hep substrate lattice as observed by reflection high-energy electron diffraction during growth and verified by plan-view transmission electron microscopy. High-resolution x-ray rocking curve linewidths of the GaN and Hf [1012] peaks are as narrow as 900 and 180 arc seconds, respectively. The [0002] peak separation confirms the approximately 2.7% mismatch in the c axis spacing. Initial photo]uminescence observations at 20 K of a (donor-bound exciton) peak at 3.467 eV are consistent with the assumption of a nearly strain-free film resulting from the exact basal-plane lattice match and close thermal coefficient match between GaN and Hf.
Near-Bandgap Photoluminescence Decay Time in GaN Epitaxial Layers Grown on Sapphire
Authors: Hangleiter A. , Im J. S. , Forner T. , Härle V. , Scholz F. 
Published: April 2011

ABSTRACTUsing picosecond time-resolved photoluminescence we have studied the decay time of excess carriers in GaN epitaxial layers over a wide range of temperatures from 4 K up to 400 K. At low temperature, a thermal dissociation of donor-bound excitons is observed. At higher temperatures up to room temperature, the luminescence decay at moderate excitation is governed by trapping of photogenerated electrons in ionized shallow donor levels. Using measured luminescence intensities to determine the quantum efficiency, we obtain the radiative lifetime of free excitons from low temperature up to room temperature. We use these data to determine the radiative recombination coefficient and the interband momentum matrix element.
Selective Dynamical Study of Luminescences Near the Surface and the Interface of Epitaxial GaN
Authors: Eckey L. , Hoffmann A. , Heitz R. , Broser I. , Meyer B.K. , Detchprohm T. , Hiramatsu K. , Amano H. , Akasaki I. 
Published: April 2011

ABSTRACTRecombination processes and their dynamics are selectively studied (a) near the interface betweeen a 400μm thick GaN epilayer and its Al2O3 substrate and (b) in the structurally relaxed regions near the surface of this sample. Strong radiative excitonic recombination is observed in the relaxed regions. However, the recombination dynamics of free and shallow-bound excitons here are strongly influenced by shallow and deep defects. Near the substrate the presence of dislocations suppresses radiative recombination of free and shallow bound excitons. Deeper emissions appear which we attribute to excitons deeply bound to dislocation-related defects. They exhibit ps-recombination dynamics effected by strong nonradiative contributions.
On Compensation and Impurities in State-of-the-Art GaN Epilayers Grown on Sapphire
Authors: Wickenden A.E. , Gaskill D.K. , Koleske D.D. , Doverspike K. , Simons D.S. , Chi P.H. 
Published: April 2011

ABSTRACTA comparison between 300 K electron transport data for state-of-the-art wurtzite GaN grown on sapphire substrates and corresponding theoretical calculations shows a large difference, with experimental mobility less than the predicted mobility for a given carrier concentration. The comparison seems to imply that GaN films are greatly compensated, but the discrepancy may also be due to the poorly known values of the materials parameters used in the calculations. In this work, recent analysis of transport and SIMS measurements on silicon-doped GaN films are shown to imply that the compensation, NA/ND, is less than 0.3. In addition, the determination of an activation energy of 34 meV in a GaN film doped to a level of 6×1016 cm−3 suggests either that a second, native donor exists in the doped films at a level of between 6×1017 cm−3 and 1×1017 cm−3, or that the activation energy of Si in GaN is dependent on the concentration, being influenced by impurity banding or some other physical effect. GaN films grown without silicon doping are highly resistive.
A New Single Source Precursor Approach to Gallium and Aluminum Nitride
Authors: Neumayer Deborah A. , Carmalt C.J. , Arendt M.F. , White J.M. , Cowley A.H. , Jones R.A. , Ekerdt J.G. 
Published: April 2011

ABSTRACTSingle source precursors which contain preformed gallium-nitrogen and aluminum-nitrogen bonds are being considered for the growth of gallium and aluminum nitride because of their potential for overcoming problems associated with conventional precursors. Presented is the evaluation of dimethylgallium azide, Me2GaN3(1), bisdimethylamidogallium azide, (Me2N)2GaN3(2), and bisdimethylamidoaluminum azide, (Me2N)2AlN3(3) as potential precursors for A1N and GaN film growth. The compounds were evaluated for stability, ease of transport, temperature of decomposition and quality of film deposited. Amorphous thin films of GaN with a band gap of 3.4 eV were deposited with 2 at 250 °C. Increasing the substrate temperature to 580 °C resulted in the deposition of epitaxial GaN films. Polycrystalline A1N films were grown with 3 at 600 °C.