bluuebunny/crossref_metadata_2025_split huggingface dataset:
Natural Poly(Hydroxybutyrate-Hydroxyvalerate) Polymers as Degradable Biomatertals.
Authors: Chaput Cyril , Yahia L'Hocine , Selmani Amine , Rivard Charles-Hilaire 
Published: April 2011

AbstractPoly(ß-hydroxybutyrate-co-13-hydroxyvalerate) have been recently proposed as degradable biomaterials for drug delivery systems, sutures, bone plates and short-term implants. Three P-B\HV (7, 14 & 22 % HV) films were analyzed for in vitro cytotoxicity and aqueous accelerated degradation, in vivo degradation and tissue reactions. The PHB/HV materials and extracts elicit few or mild toxic responses, do not lead in vivo to tissue necrosis or abscess formation, but provoke acute inflammatory reactions slightly decreasing with the time. The degradation of PHB/HV polymers present low rates in vitro as well as in vivo. The weight loss rate generally increases with the copolymer composition (HV content) and ranges from 0.15- 0.30 (in vitro) to 0.25 %/day (in vivo). Compositional and physico-chemical changes in PHB/HV materials were rapidly detected during the accelerated hydrolysis, but were much slower to appear in vivo. The structural and mechanical integrity of PHB/HV materials tend to disappear early in vitro as well as in vivo. After 90 wks in dorsal muscular tissues of adult sheep, there was no significant dissolution of the PHB/HV polymer, 50–60% of the initial weight still remaining. PHB/HV polymers are biodegradable materials, either by hydrolysis or implantation, but with extremely low dissolution or degradation rates.
Tissue Engineering of Tendon
Authors: Caoa Y. , Vacanti J. P. , Ma P. X. , Ibarra C. , Paige K.T. , Upton J. , Langer R. , Vacanti C. A. 
Published: April 2011

AbstractWe studied the feasibility of creating new tissue engineered tendons, using bovine tendon fibroblasts (tenocytes) attached to synthetic biodegradable polymer scaffolds in athymic mice. Calffore- and hind-limbs were obtained from a local slaughterhouse within 6 hours of sacrifice. Tenocytes were isolated from the calf tendons. Cells were seeded onto an array of fibers composed of polymer (PGA) configured either as a random mesh of fibers, or as an array of parallel fibers. Fifty cell-polymer constructs were implanted subcutaneously in athymic mice and harvested at 3, 6, 8, 10 and 12 weeks. Grossly, all excised specimens resembled the tendons from which the cells had been isolated. Histologic sections stained with hematoxylin and eosin (H&E) and Masson's trichrome showed cells arranged longitudinally within parallel collagen fibers in the periphery. Centrally, collagen fibers were more randomly arranged, although they seemed to attain a parallel arrangement of cells and fibers over time. By 10 weeks, specimens showed very similar histologic characteristics to normal tendon. Histologically, 12-week samples were virtually identical to normal tendon. When longitudinal polymer fibers seeded with cell had been implanted, the collagen fibers seen in the neo-tendons became organized at an earlier interval of time. Biomechanical tests demonstrated linear increase in tensile strength of the neo-tendons over time. Eight-week specimens showed 30% the tensile strength of normal tendon samples of similar size. By 12 weeks, tensile strength was already 57% that of normal bovine tendon.
Elastic Constants and Related Properties of the Group III-Nitrides
Authors: Kim Kwiseon , Lambrecht Walter R. L. , Segall B. 
Published: April 2011

ABSTRACTThe elastic constants of the Group-III nitrides, c-BN, AlN and GaN were calculated from first-principles using the full-potential linear muffin-tin orbital method and local density approximation. The relation between the elatic constants in zincblende and wurtzite is studied by means of a tensor coordinate transformation approach. The latter combined with a correction for the internal displacement of the rotated tetrahedra is found to provide good results for the Ch11Ch12 and Ch44 but not for Ch13 and Ch33. These two require explicit calculations involving distortions along the c-axis. The calculations also provide information on the transverse optical phonons. By deriving Keating model parameters we show that BN is much stiffer against bond-angle distortions than the other nitrides.
The Phonon Densities of States of AlN and ZrN
Authors: Loong C.-K. 
Published: April 2011

ABSTRACTPhonons are thought to play a crucial role in the high thermal conductivity of AIN and ZrN. Using time-of-flight neutron spectroscopy, we have measured the phonon spectra of A1N and ZrN up to 300 meV (2400 cm−1). The one-phonon density of states (DOS) of AIN exhibits relatively sharp bands at about 33, 63, 83 and 91 meV. In addition, distinct multiple-phonon excitations were observed at ∼173 and 255 meV. The phonon DOS of ZrN displays similar features with the corresponding phonon energies shifted toward lower energies. The measured DOS of AIN is compared with results of molecular-dynamics simulations.
Structure and Quasiparticle Energies of Cubic, Wurtzite and Hexagonal BN
Authors: Cappellini Giancarlo , Fiorentini Vincenzo , Tenelsen Katrin , Bechstedt Friedhelm 
Published: April 2011

ABSTRACTWe present local density functional theory (DFT-LDA) studies of the structural properties of boron nitride in the layered hexagonal (h-BN), zincblende (c-BN), and wurtzite (w-BN) structures, performed using a fast implementation of the norm-conserving pseud-opotential plane-wave method. Quasiparticle band structures are then calculated for all phases by means of an efficient GW self-energy scheme. To our knowledge, these are the first GW quasiparticle calculations for wurtzite BN including local-field and dynamical screening effects. DFT-LDA band gaps as functions of pressure and uniaxial distorsion for h-BN are also discussed.
Growth and Optical Properties of GaN Grown by MBE on Novel Lattice-Matched Oxide Substrates
Authors: Nicholls J.F.H. , Gallagher H. , Henderson B. , Trager-cowan C. , Middleton P.G. , O'Donnell K.P. , Cheng T.S. , Foxon C.T. , Chai B.H.T. 
Published: April 2011

ABSTRACTIn this paper we demonstrate the feasibility of growing III-N semiconductors on novel lattice-matched oxide substrates. Although the growth parameters are not yet optimal, acceptable GaN layers have been grown.
Spatially-Resolved Photoluminescence and Raman Study on the GaN/Substrate Interface
Authors: Siegle H , Thurian P. , Eckey L. , Hoffmann A. , Thomsen C. , Meyer B K. , Detchprohm T. , Hiramatsu K. , Amano H. , Akasaki I. 
Published: April 2011

ABSTRACTWe performed spatially-resolved photoluminescence and Raman experiments on the substrate interface region of wurtzite GaN layers. We found that the broad ”yellow” photoluminescence band is strong only near the interface. Our investigations reveal that both the substrate interface and a region of structural reorientation of the layer near the interface act as source of the photoluminescence. The Raman-scattering experiments show that at least a portion of the GaN layer near the substrate interface is oriented in such a way that the c-axis of the layer is parallel to the substrate interface. At a distance about 30 µm away from the interface the layer reorients by turning the c-axis by 90° into a direction perpendicular to the substrate interface.
Spin-Dependent Transport in GaN Light Emitting Diodes
Authors: Brandt M. S. , Reinacher N. M. , Ambacher O. , Stutzmann M. 
Published: April 2011

ABSTRACTElectrically detected magnetic resonance (EDMR) is used to study recombination processes in two types of gallium nitride light emitting diodes: in m/i/n/n+- and InGaN/AlGaN double-heterostructure devices. In the MIS-diodes, two resonances at g=1.96 and 2.00, corresponding to the effective mass donor and a deep defect are observed at room temperature. At low temperatures, an acceptor-related resonance at g=2.06 is visible as well. After current degradation, the spectra are dominated by the defect resonance, indicating that the creation of this defect is responsible for the decreased electroluminescence efficiency. In the double-heterostrucrure devices, EDMR can only be observed below 60 K showing the g=2.00 defect resonance. The same defect resonance is also observed in conventional electron spin resonance experiments under illumination (light-induced ESR).
Ex Situ and in Situ Methods for Oxide and Carbon Removal from AlN and GaN Surfaces
Authors: King Sean W. , Smith Laura L. , Barnak John P. , Ku Ja-Hum , Christman Jim A. , Benjamin Mark C. , Bremser Michael D. , Nemanich Robert J. , Davis Robert F. 
Published: April 2011

ABSTRACTExposure to numerous acids and bases and UV/O3 oxidation were used to determine the best ex situ cleaning techniques for the (0001) surfaces of AIN and GaN. HF and HCI were the most effective in removing the oxide from AIN and GaN, respectively. However, AES and XPS revealed the surfaces to be terminated with F and CI which inhibited re-oxidation prior to loading into vacuum. TPD showed mat temperatures of 650 and 850°C are necessary to thermally desorb the CI and F, respectively. UV/O3 oxidation in air was not effective in removing hydrocarbons from either surface but was effective for oxide growth. In situ remote hydrogen plasma exposure at 450°C removed halogens and hydrocarbons remaining after ex situ cleaning of both AIN and GaN surfaces; however, oxide free surfaces could not be achieved. Thermal desorption of hydrocarbons from GaN in UHV was achieved at 650°C. Complete thermal desorption of the surface oxide in UHV was only achieved at temperatures > 800°C where some GaN decomposition occurred. Annealing GaN in NH3 at 700°C reduced the surface oxide without loss of surface stoichiometry.
Annealing Study of Ion Implanted MOCVD and MBE Grown GaN
Authors: Silkowski E. , Yeo Y. K. , Hengehold R. L. , Khan M. A. , Lei T. , Evans K. , Cerny C. 
Published: April 2011

ABSTRACTMOCVD and MBE grown GaN were implanted with Ar, Mg, Si, Be, C, and O, and annealed in a conventional oven under flowing NH3 or N2 gas. Absorption measurements confirmed that implantation damage was annealed out after 90 minutes at a temperature of 1000 °C. Surface damage caused by NH3 annealing was evident in absorption and photoluminescence measurements for annealing temperatures of over 1000 °C. Although most of the implants showed no unique luminescence peaks, systematic changes in the relative intensities of the exciton, donor-acceptor pair, and yellow peaks were noted. The Mg implanted samples showed evidence of the acceptor bound exciton line at 3.44 eV, and a unique peak at 3.3 eV possibly due to a Mg free-to-bound transition.
Schottky Barriers on p-GaN
Authors: Kuznetsov N.I. , Kalinina E.V. , Soloviev V.A. , Dmitriev V.A. 
Published: April 2011

ABSTRACTSchottky barriers were formed on p-GaN. p-GaN layers doped with Mg were grown by metalorganic chemical vapor deposition (MOCVD). 6H-SiC wafers were used as substrates. The barriers were made by vacuum thermal evaporation of Au. Capacitance-voltage (C-V) and current-voltage (I-V) characteristics of the barriers were investigated. The concentration of the ionized acceptors in the p-layers was measured to be about ∼1017 cm−3. The barrier height was determined to be 2.48 eV by C - V measurements at room temperature. The forward current flow mechanism through the barriers is discussed.
The Surface Chemistry of Triallylamine on Si(111) and its Coadsorption with Triethylgallium
Authors: Freundt Dirk , Landmesser Georg , Rizzi Angela , Lüth Hans 
Published: April 2011

ABSTRACTThe surface chemistry of Triallylamine (TAA), (C3H5)3N on Si(111) has been studied by adsorption under UHV conditions and in-situ characterization. High Resolution Electron Energy Loss Spectroscopy (HREELS) yields the spectrum of vibration modes at the surface, and X-ray Photoelectron Spectroscopy (XPS) yields the chemical bonding and the partial concentration of the different adsorbates in the near surface region. The tertiary amine TAA physisorbs at RT without dissociation. Successive annealing steps of the physisorbed phase induce the dissociation of the amine at 400 °C. At higher temperatures the allyl groups are partially desorbed and the rest fully dissociated at 600 °C, where the hydrogen leaves the surface and the nitrogen and carbon start to diffuse into the Si substrate. A very similar behaviour is observed for the adsorption of TAA on a heated Si substrate. The coadsorption with Triethylgallium (TEG) in the temperature range 500–800 °C does not induce significant changes in the reaction at the Si surface. A negligible quantity of Ga is detected at the surface after codeposition in the whole investigated temperature range. The growth of a GaN phase has not been observed, neither on Si(111) nor on Al2O3(0001) substrates.
Correlation of surface morphology and optical properties of GaN by conventional and selective-area MOCVD
Authors: Li X. , Jones A. M. , Roh S. D. , Turnbull D. A. , Reuter E. E. , Gu S. Q. , Bishop S. G. , Coleman J. J. 
Published: April 2011

ABSTRACTWe have studied GaN films grown by atmospheric pressure metalorganic chemical vapor deposition (MOCVD) on sapphire substrates using different buffer layer structures. Surface morphology was characterized by scanning electron microscopy (SEM). Optical properties were measured using photoluminescence (PL), cathodoluminescence (CL) spectroscopy and catho-luminescence wavelength imaging (CLWI) method. It is found that the hexagonal pit-like defects in morphology are associated with the D-A/e-A transition band in the PL and CL spectra. The same correlation of morphology with optical properties is observed for the GaN films grown by selective area epitaxy (SAE). In addition, the possibility of improving optical quality by SAE is investigated. The SAE depth profile is simulated for the first time, and satisfactory results are obtained.
Spectral Response of GaN P-N Junction Photovoltaic Structures
Authors: Walker D. , Zhang X. , Kung P. , Saxler A. , Xu J. , Razeghi M. 
Published: April 2011

ABSTRACTGaN ultraviolet photovoltaic and photoconductive detectors were grown on sapphire substrates by metalorganic chemical vapor deposition. The spectral response was analyzed considering the detector structure of a p-n junction connected back-to-back with a Schottkty barrier. Based on the one-dimensional model of abrupt p-n junctions, the diffusion length of minority carriers was derived to be about 0.1 μm in n-GaN. To further characterize the n-GaN material, photoconductivity experiments have also been realized. The majority carrier lifetime of about 0.1 ms was obtained by analyzing the voltage-dependent responsivity of GaN photoconductors The current-responsivity under a bias of 8 V was about 1 A/W.
Gas Phase Adduct Reactions in MOCVD Growth of GaN
Authors: Thon A. , Kuech T.F. 
Published: April 2011

ABSTRACTGas phase reactions between trimethylgallium (TMG) and ammonia were studied at high temperatures, characteristic to MOCVD of GaN reactors, by means of insitu mass spectroscopy in a flow tube reactor. It is shown, that a very fast adduct formation followed by elimination of methane occurs. The decomposition of TMG and the adduct - derived compounds are both first order and have similar apparent activation energy. The pre-exponential factor of the adduct decomposition is smaller, and hence is responsible for the higher full decomposition temperature of the adduct relative to that of TMG.
Effect of Ambient Gas Pressure on Pulsed Laser Ablation Plume Dynamics and Znte Film Growth
Authors: Rouleau CM. , Lowndes D.H. , Strauss M.A. , Cao S. , Pedraza A.J. , Geohegan D.B. , Puretzky A.A. , Allard L.F. 
Published: April 2011

ABSTRACTEpitaxial thin films of nitrogen-doped p-ZnTe were grown on single-crystal, semi-insulating GaAs substrates via pulsed laser ablation of a stoichiometric ZnTe target. Both low pressure nitrogen ambients and high vacuum were used. Results of in situ reflection high energy electron diffraction (RHEED) and time-resolved ion probe measurements have been compared with ex situ Hall effect and transmission electron microscopy (TEM) measurements. A strong correlation was observed between the nature of the film's surface during growth (2-D vs. 3-D, assessed via RHEED) and the ambient gas pressures employed during deposition. The extended defect content (assessed via cross-sectional TEM) in the region >150 nm from the film/substrate interface was found to increase with the ambient gas pressure during deposition, which could not be explained by lattice mismatch alone. At sufficiently high pressures, misoriented, columnar grains developed which were not only consistent with the RHEED observations but also were correlated with a marked decrease in Hall mobility and a slight decrease in hole concentration. Ion probe measurements, which monitored the attenuation and slowing of the ion current arriving at the substrate surface, indicated that for increasing nitrogen pressure the fast (vacuum) velocity-distribution splits into a distinct fast and two collisionally-slowed components or modes. Gas-controlled variations in these components mirrored trends in electrical properties and microstructural measurements.
Fabrication of A Barium Titanate-Strontium Titanate Strained Layer Superlattice
Authors: Harkness S.D. , Singh R.K. 
Published: April 2011

ABSTRACTA thin film superlattice heterostructure composed of alternating BaTiO3 and SrTiO3 layers was grown on a thin YBa2Cu3O7 electrode templated on a (100) SrTiO3 wafer using the pulsed laser deposition method. Stranski-Krastanov nucleation of the layers was demonstrated using atomic force microscopy (AFM) when processing conditions were maintained at 6 millitorr oxygen partial pressure, and 550 °C substrate temperatures. High-resloution x-ray diffraction (HRXRD) measurements indicate that all the deformation was concentrated in the BaTiO3 layers with c/a extension to approximately 1.08. Rutherford backscattering spectroscopy (RBS) results indicate excellent crystallinity in the heterostructure. The microstructural data suggests that the theoretical critical thickness of the film has been surpassed by an order of magnitude.
Positive Ion Emission Accompanying UV Irradiation of Single Crystal Mgo and NanO3
Authors: Ermer D. R. , Shin J. J. , Langford S. C. , Dickinson J. T. 
Published: April 2011

ABSTRACTAlthough MgO is much more resistant to radiolysis by 248-nm photons than NaNO3, the ion emission processes at low fluence have much in common: both materials yield high energy ions (> 5 eV kinetic energy) with a strongly nonlinear fluence dependence. We report time-of-flight measurements of quadrupole mass-selected Mg+ from polished, single crystal MgO and Na+ from cleaved, single crystal NaNO3. At fluences between 10 and 1000 mJ/cm2, the Mg+ intensities show a strongly nonlinear fluence dependence which decreases to roughly second order behavior at fluences above 100 mJ/cm2. The Na+ intensities display third or fourth order emission kinetics throughout the experimental range of fluences. We attribute these emissions to cations adsorbed atop surface electron traps where the cation is ejected when the underlying trap is photo-ionized. The potential energy of this defect configuration accounts for the observed ion kinetic energies. However, the direct photo-ionization of surface vacancy/adsorbed ion defects with 5 eV photons should not be possible. Thus we propose that emission requires the photo-ionization of nearby electron traps, followed by photo-induced charge transfer to the empty traps. We show that a sequence of single-photon absorption events [involving photo-ionization, charge transfer, and electron retrapping] accounts for the strongly nonlinear fluence dependence.
A Non-Reactive Excimer-Based Surface Preparation and Cleaning Tool for Broad-Based Industrial Applications
Authors: Harvey E. C. , Fletcher J. , Engelsberg A. C. 
Published: April 2011

ABSTRACTA surface-cleaning and preparation method that uses high-energy photons and a laminar flowing inert gas has been demonstrated as a feasible technology for broad-based industrial applications such as semiconductors, electronics, optics, coated optical and magnetic media, automotive, aerospace and art restoration. This technology is flexible in tool embodiment and is environmentally friendly because no water and chemicals are not used.
CO2 Laser Cleaning of Hydrophilic Oxidized Silicon Surfaces
Authors: Boughaba S. , Sacher E. , Meunier M. 
Published: April 2011

ABSTRACTThe removal of particles as small as 0.1 μm was achieved using a pulsed CO2 laser to induce the explosive vaporization of condensed water. The surfaces used were hydrophilic oxidized silicon. The contaminant particles were 0.1 μm alumina, 0.1-0.2 μm fumed silica, and 0.1 μm polystyrene latex; their zeta potentials in water vary from positive to negative. The effect of the laser beam energy flux on the cleaning efficiency was thoroughly investigated. It was varied between 0.5 and 3 J/cm2. Whatever the nature of the contaminants, the cleaning process was characterized by an upper limit, the surface damage threshold energy density, determined to be 1.5 J/cm2. If the removal efficiency drops for the lowest beam energy flux, i.e., 0.5 J/cm2, and 0.1 μmAl2O3 particles, no single, sharp removal threshold was observed. Another parameter of importance investigated was the thickness of the condensed water. It was varied by changing the time of exposure of the substrate surface to water vapor before laser irradiation, the vapor flow being fixed to 4700 ml/min. Exposure times ranging from 1.5 to 2.5 s were evaluated to be the most effective.
Structure-Property Relationship of Ceramic Coatings Produced by Laser Processing
Authors: De Hosson J.Th.M. , Zhou X.B. 
Published: April 2011

ABSTRACTThis paper deals with a well known puzzling observation that wetting in some instances is improved by a chemical reaction between a liquid and a solid substrate in laser processing while in other systems just the opposite effect takes place. Here, contact angles of liquid Al on SiO2 and liquid Ti on Al2O3 are reported and some results of laser melt injection of SiO2 particles into molten Al.The surface and interface structures were explored by scanning electron microscopy and energy dispersive X-ray spectrometry. According to the experimental observations, it appears that the volume change of ceramic substrates during reaction plays a key role in the effect of chemical reaction on wetting.
Use of an Excimer Lamp for Photochemical Resistless Etching of Thermal Silicon Oxide Substrate
Authors: Kamata N. , Murahara M. 
Published: April 2011

ABSTRACTPhotochemical resistless etching was carried out by using a Xe2* excimer lamp and a KrF excimer laser. The decomposition method with Xe2* excimer lamp increases the decomposition efficiency by 100 times than that of using ArF excimer laser and etchant gas, CHClF2. Xe2* excimer lamp irradiation allowed decomposition of CHClF2 gas to produce CF2 radical with a small quantity of gas. The CF2 radical was polymerized to form fluorocarbon layer on the SiO2 substrate. Simultaneously, circuit patterned KrF excimer laser was vertically irradiated the fluorocarbon layer on the substrate for resistless etching. The etching depth was about 1,000Â.