bluuebunny/crossref_metadata_2025_split huggingface dataset:
Epitaxial Multilayers of (Sr,Ba)Nb2O6 and Conducting Films on (001) Mgo Substrates
Authors: Huang T. F. , Youden K. E. , Schwyn Thöny S. , Hesselink L. , Harris J. S. 
Published: April 2011

Abstract(Sr,Ba)Nb2O6 (SBN) is a very promising material for nonlinear optical applications because of its high electro-optic and nonlinear optical coefficients. For these applications, SBN requires ferroelectric poling along the optical axis. Conducting layers such as Pt or YBCO must therefore be deposited to provide electrodes above and below the SBN film.We have investigated the epitaxial growth of multilayers of Sr0.61Ba0.39Nb2O6/Pt and Sr0.61Ba0.39Nb2O6/YBCO thin films on (001) MgO substrates by pulsed laser deposition. X-ray diffraction 2θ scans indicate epitaxial growth of SBN/Pt/MgO and SBN/YBCO/MgO heterostructures with their c-axes perpendicular to the substrate plane. X-ray phi scans indicate single crystal Pt and YBCO growth with one in plane orientation. atomic Force Microscopy shows surface roughness of 2.19 nm, and no evidence of particles is observed.
High-Performance Thermoplastics for Rigid-Flex Printed Circuit Boards
Authors: Lin Wendy W. , Savrun Ender 
Published: April 2011

ABSTRACTAdhesive failure of rigid-flex printed circuit boards (RF-PCBs) during use has degraded the performance of military avionics systems. Adhesive failure is often caused by differences in the coefficient of thermal expansion (CTE) between the materials used in RF-PCBs and by moisture absorption by the adhesives and polyimide (PI) films. High-performance thermoplastics were investigated to replace the epoxies, PIs, and adhesives currently used in RF-PCBs. Because thermoplastic materials are remeltable, adhesive bonding may be replaced by fusion bonding to join RF-PCBs. Fusion bonding would eliminate problems with material compatibility and differences in the CTE encountered with adhesive bonding. Industries that would benefit from this research are manufacturers of aerospace instrumentation, medical equipment, automotive systems, computers, telecommunications equipment, industrial instrumentation and controls, and consumer products, such as stereo systems and calculators.An extensive survey of high-performance-engineering thermoplastic materials was performed, and samples of the more promising materials (both films and chopped fiber reinforced) were obtained for preliminary screening tests. The tests performed were chemical resistance, water absorption, tensile strength, flexibility, and solder resistance of bare dielectric. From these tests, a glass-filled liquid crystal polymer film made by Hoescht Celanese Performance Films best met the performance criteria compared with the thermoplastics tested.
Corrosion Behaviour of Aluminum Metallization During Aqueous Exposure
Authors: Koo Y. C. , Walzak T. L. , Davidson R. D. 
Published: April 2011

ABSTRACTIt is known that aluminum will readily form aluminum hydroxide during aqueous exposures. Thick oxide layers with a typical pseudoboehmite (fibre-like network) structure and bayerite crystals were observed on the aluminum metallization after the aqueous cleaning process. The study investigated the effect of a deionized (DI) water cleaning process (recently implemented to replace CFC-based cleaning technology) on the surface chemistry and corrosion behaviour of aluminum wire bond pads. The study also correlated the wire bond yield and oxide thickness with various water cleaning process parameters. The wire bond yield and reliability issues are discussed briefly.
Determination of the Adhesive Strength of Film-Substrate Interfaces Using the Constant Depth Scratch Test
Authors: Dutta I. , Campbell J. C. 
Published: April 2011

ABSTRACTA constant depth scratch test (CDST) has been recently developed to quantify the shear strength of film-substrate interfaces. This test is capable of measuring interfacial adhesion as a function of position on the sample surface during a continuous scratch. Unlike many of the currently available tests which are applicable to a limited array of materials systems, or are experimentally complex, this test is quite versatile, and is relatively straightforward to conduct and interpret because of the constant depth geometry. The theoretical basis and the experimental set-up for the test have been previously presented. In this paper, extensions of the theoretical formulation to account for different debonding behaviors of different film-substrate systems are discussed. Experimental results generated with a number of systems, including chromium on glass, gold on aluminum nitride, gold on aluminum nitride with a chromium inter-layer, and polycrystalline diamond on aluminum nitride are presented.
Stability and Performance Issues for Nonlinear Optical Chromophores, Polymers and Devices
Authors: Twieg R. J. , Burland D. M. , Jurich M. , Lee V. Y. , Miller R. D. , Moylan C. R. , Siemens R. , Skumanich A. , Thackara J. I. , Verbeist T. , Volksen W. , Knoesen A. , Hill R. A. , Yankelevich D. 
Published: April 2011

AbstractIn the course of development of any new technology the issues of device stability and reliability are inevitably encountered and must be summarily dealt with. The development of organic and polymeric nonlinear optical media has been no exception and has now evolved to a stage wherein solutions to a few performance issues are of crucial importance. Discussions here focus on just two of these critical problems. First, we describe a preliminary study intended to identify some of the variables involved in optical damage. The goal here is to identify suitable photochemically stable chromophores and polymers and to elucidate any processing and environmental influences which contribute to damage. Second, the thermal stability of nonlinear optical chromophores has already attracted much attention and significant progress has been made in enhancing the thermal stability of many systems. Our most recent effort has concentrated on chromophores with a variety of different configurations and combinations of nitrile acceptor groups, some of which possess both large nonlinearities and excellent thermal stability. Some newer aspects of a thermal stability screening protocol which are particularly useful for these thermally stable chromophores and polymers are also described.
Ferroelectric Thin Films and Their Applications
Authors: Neurgaonkar R. R. , Oliver J. R. , Nelson J. G. , Santha I. S. 
Published: April 2011

AbstractFerroelectric morphotropic phase boundary (MPB) materials based on Pb2+ - containing compositions are potentially important for optical and electronic applications because they exhibit high switchable polarization near this boundary with superior electro-optic and piezoelectric properties. In this paper we discuss these MPB materials, substrate issues, and the growth of MPB film compositions based on the PZT and PSKNN systems.
Degradation, Structure and Properties of Fibrous Nonwoven Poly(Glycolic Acid) Scaffolds for Tissue Engineering
Authors: Ma Peter X. , Langer Robert 
Published: April 2011

AbstractBiodegradable polymer scaffolds have been used to engineer new tissues or organs by culturing cells on them. The degradation, structure and properties of fibrous nonwoven poly(glycolic acid) (PGA) scaffolds (2 mm thick and 10 mm in diameter) were studied over 9 weeks in tissue culture medium at 37°C under mixing condition. After 3 days of in vitro culture, the mass of the scaffolds increased slightly (5.6%) due to hydration and/or adsorption, but it decreased thereafter. After 9 weeks, only 12.5% of the mass were retained. The melting point of the scaffolds decreased from 218.1°C to 186.0°C in the first 3 weeks, as measured with differential scanning calorimetry (DSC). No melting peak could be identified for later times (6 weeks and 9 weeks). The crystallinity of the scaffolds doubled over the first 11 days, but decreased thereafter. The glass transition temperature of the degrading scaffolds (36–39°C) was lower than that of the dry starting scaffolds (40°C) presumably due to the plasticizing effect of absorbed water and other low molecular weight molecules. The PGA scaffolds without cells lost their structural integrity and mechanical strength completely in 2 to 3 weeks. In contrast, the neocartilage constructs regenerated from the PGA scaffolds and bovine chondrocytes kept their structural integrity throughout the in vitro culture study. After 12 weeks of in vitro culture, the biomechanical properties of the neocartilage constructs reached the same orders of magnitude as those of normal bovine cartilage.
The Effect of a GaN Nucleation Layer on GaN Film Properties Grown by Metalorganic Chemical Vapor Deposition
Authors: Van Der Stricht W. , Moerman I. , Demeester P. , Crawley J.A , Thrush E.J. , Middleton P.G. , Trager Cowan C. , O'donnell K.P. 
Published: April 2011

ABSTRACTIn this paper GaN films are examined, which are grown on basal plane (0001) sapphire substrates. Growth is performed in a novel type of vertical rotating disk reactor. Results on the effect of a GaN nucleation layer on the properties of the overgrown GaN epilayer are presented. Characterisation includes surface morphology studies, DC X-ray diffraction and optical characterisation. Best film quality so far has a double crystal X-ray half width of 85 arcsec at approximately 1 μm thickness.
Halide Vapor Phase Epitaxy of Gallium Nitride Films on Sapphire and Silicon Substrates
Authors: Perkins N.R. , Horton M.N. , Bandic Z.Z. , McGill T.C. , Kuech T.F. 
Published: April 2011

ABSTRACTA major limitation of the current technology for GaN epitaxy is the availability of suitable substrates matched in both lattice constant and thermal expansion coefficient. One alternative for the development of GaN substrates rests in the application of halide vapor phase epitaxy (HVPE) to produce GaN films at high growth rates. In this paper, we describe the growth of thick GaN films via the HVPE technique on (0001) sapphire and (111) Si substrates. At a temperature of 1030°C, films are grown at rates between 70 and 90 μm/hr, yielding total thicknesses exceeding 200 μm on sapphire. DCXRD measurements of GaN/sapphire indicate FWHM values less than 220 arcsec on 180 μm thick films. Room temperature PL measurements of GaN/sapphire indicate strong emission at 3.41 eV, with a FWHM value of 65 meV. Moreover, no detectable deep level emission was found in room temperature PL measurement. Under optimized conditions, films are morphologically smooth and optically clear. The GaN morphology appears to be a strong function of the initial nucleation conditions, which in turn are strongly affected by the partial pressure of GaCl. HVPE growth on (111) Si substrates is accomplished using an AlN MOVPE buffer layer.
Supersonic Jet Epitaxy: An Improved Method for Nitride Deposition
Authors: Norris Peter E. , Zhu Long D. , Paul Maruska H. , HO Wilson , Ustin Scott , Lauhon L. 
Published: April 2011

ABSTRACTGaN was grown by supersonic jet epitaxy(SSJE), seeding triethylgallium in helium carrier gas. Activated nitrogen was supplied by a microwave plasma source. Single crystalline GaN films were deposited on the Si-face 6H-SiC and the c-plane sapphire substrates at 600–670°C. A cubic SiC buffer layer was grown onSi(111) at 800°C by SSJE using dichlorosilane, acetylene, and a high quality GaN crystal was grown on this template at 630°C. The materials high quality was proved by hard rectifying characteristics of a diode with an N-GaN/β-SiC/P-Si(111) structure.
XPS Measurement of the SiC/AlN Band-Offset at the (0001) Interface
Authors: King Sean W. , Benjamin Mark C. , Nemanich Robert J. , Davis Robert F. , Lambrecht Walter R. L. 
Published: April 2011

ABSTRACTX-ray photoelectron spectroscopy is used to determine the band-offset at the SiC/AIN (0001) interface. First, the valence band spectra are determined for bulk materials and analyzed with the help of calculated densities of states. Core levels are then measured across the interface for a thin film of 2H-AIN on 6H-SiC and allow us to extract a band offset of 1.4 ±0.3 eV. The analysis of the discrepancies between measured peak positions and densities of states obtained within the local density approximation provides information on self-energy corrections in good agreement with independent calculations of the latter.
Lattice-Matching Growth of InGaAIN Systems
Authors: Matsuoka Takashi 
Published: April 2011

ABSTRACTThe development and device applications of the InGaAIN system have progressed dramatically with improvements in crystalline quality by achieved through a buffer layer, the realization of p-type doping, and the growth of ternary alloys. As a substrate, sapphire is mainly used for epitaxial growth because of the lack of a GaN bulk crystal. However, many cracks in GaN film can still be observed and its X-ray rocking curve width is less than 100 arc seconds. This is are thought to be due to the lattice constants and thermal expansion coefficients of GaN and sapphire differ by 13.8% and by -34.2%, respectively. These values are extremely large in comparison with the corresponding values for InP and GaAs. Lattice-matching growth thus remains a basic problem in growing the high-quality epitaxial films necessary for high-performance devices.This paper reviews attempts at lattice-matching growth. Lattice-matching growth of InGaN on a house-made ZnO substrate and near-lattice-matching growth of GaN on SiC and NdGaO3 substrates have been proposed and performed, and the effects of lattice-matching have been confirmed. Various types of surface planes commercially available sapphire substrates are also discussed.
The Role of Impurities in LP-MOCVD Grown Gallium Nitride
Authors: Hwang C.Y. , Li Y. , Schurman M. J. , Mayo W. E. , Lu Y. , Stall R. A. 
Published: April 2011

ABSTRACTWe have investigated the relationship of the Hall electron mobility to the background carrier concentration in low pressure MOCVD grown GaN. The highest electron mobility (400 cm2 /V•s) of the unintentionally doped GaN was obtained at a carrier concentration of 1×1017 cm−3 and samples with carrier concentrations lower than this exhibited lower mobilities. SIMS analysis shows C and O concentrations in the range of 2–3×1016 cm−3 and H in the 2–3×1017 cm−3 range. Structural defects, stoichiometry and impurities in the GaN films grown under different conditions are investigated to understand their relationship to the electron Hall mobilities. In particular, different growth temperatures and pressures were used to grow undoped GaN and modify the background doping effect of the impurities.
Optical Properties of Wurtzite-and Zincblende-GaN Films Grown by RF Plasma-MBE
Authors: Semendy F. , Bambha N. , Kim J.G. , Liu H. , Park R.M. 
Published: April 2011

ABSTRACTBoth wurtzite-and zincblende-GaN films have been grown on sapphire and MgO substrates, respectively, and examined by photoluminescence and x-ray analysis. GaN films were grown on suitably prepared Al2O3 and MgO substrates by molecular beam epitaxy employing a rf plasma discharge, nitrogen free radical source. The wurtzite-and zincblende-GaN films exhibited dominant near band-edge emission, the nature of which will be compared and contrasted for both phases in this paper. X-ray diffraction data for both phases will also be discussed.
Dielectric Functions of Wurtzite and Zincblende Structure GaN
Authors: Wang R. , Ruden P.P. , Kolnik J. , Oguzman I. , Brennan K.F. 
Published: April 2011

ABSTRACTWe present calculated longitudinal frequency and wavevector dependent dielectric functions of zincblende and wurtzite structure GaN using band energies and wavefunctions generated in the framework of the empirical pseudopotential method. We discuss the anisotropy of the static dielectric function and find that our results are in satisfactory agreement with experimental data for |q| ₒ 0.
Detection of Magnetic Resonance on Shallow Donor - Shallow Acceptor and Deep (2.2 eV) Recombination from GaN Films Grown on 6H-SiC
Authors: Glaser E.R. , Kennedy T.A. , Brown S.W. , Freitas J.A. , Perry W.G. , Bremser M.D. , Weeks T.W. , Davis R.F. 
Published: April 2011

ABSTRACTPhotoluminescence (PL) and optically-detected magnetic resonance (ODMR) experiments have been performed on undoped GaN epitaxial layers grown on 6H-SiC substrates. The defects observed in these films are compared with those found from previous ODMR studies of undoped GaN layers grown on sapphire substrates. Strong, sharp donor-bound exciton bands at 3.46 -3.47 eV and weak, broad emission bands at 2.2 eV were observed from several 0.7 and 2.6 μm-thick films. In addition, fairly strong shallow donor - shallow acceptor (SD-SA) recombination with a zero-phonon-line at 3.27 eV was found for GaN layers less than 1 μm-thick. The first observation of magnetic resonance on this SD-SA recombination from undoped GaN is reported in this work. Two magnetic resonance features attributed to effective-mass (EM) and deep-donor (DD) states were detected on the 2.2 eV emission bands from all the GaN/6H-SiC films. These resonances were observed previously on similar emission from undoped GaN layers grown on sapphire substrates. The same EM donor resonance, though much weaker, was also found on the SD-SA recombination. However, a resonance associated with shallow acceptor states was not observed on this emission. The weakness of the donor resonance arises from the weak spin-dependence of the recombination mechanism involving spin-thermalized shallow acceptors. The absence of an EM acceptor is due to the broadening of the resonance through the spreading of the acceptor g-values by random strains in these films.
Role of C, O and H in III-V Nitrides
Authors: Abernathy C. R. , Pearton S. J. , MacKenzie J. D. , Lee J. W. , Vartuli C. B. , Wilson R. G. , Shul R. J. , Zolper J. C. , Zavada J. M. 
Published: April 2011

ABSTRACTThe light ion impurities C, O and H have been implanted or diffused into GaN and related compounds and their effect on the electrical properties of these materials measured by Hall, C-V and SIMS as a function of annealing temperatures from 300-1100ºC. While C in as-grown GaN appears to create an acceptor under MOMBE conditions, implanted C shows no measurable activity. Similarly, implanted O does not show any shallow donor activity after annealing at ≤ 700°C, but can create high resistivity regions (106 Ω/□) in GaN, AlInN and InGaN for device isolation when annealed at 500–700°C. Finally, hydrogen is found to passivate shallow donor and acceptor states in GaN, InN, InAIN and InGaN, with dissociation of the neutral complexes at >450°C. The liberated hydrogen does not leave the nitride films until much higher annealing temperatures (>800°C). Typical reactivation energies are ∼2.0eV for impurity-hydrogen complexes.
Infrared Absorption and Electron Spin Resonance Studies of Nanocrystalline Cubic Boron Nitride/Amorphous Hydrogenated Boron Nitride Mixed Phase Thin Films
Authors: Lin Shu-han , Brown Ian M. , Feldman Bernard J. 
Published: April 2011

ABSTRACTBoth infrared absorption (IR) and electron spin resonance (ESR) spectroscopies have been used to investigate the complicated structure of nanocrystalline cubic boron nitride/amorphous hydro-genated boron nitride thin films. The ESR spectra from this material consist of a component with a four-line hyperfine structure and/or a component with a ten-line hyperfine structure superimposed upon a broad central line. The hyperfine structures are associated with defect centers located in the nanocrystalline phase, whereas the broad line is attributed to dangling bonds in the amorphous phase. The IR spectra consist of three lines around 1400 cm−1: the lines at 1263 and 1505 cm−1 originate in a boron-poor amorphous hydrogenated boron nitride region; the line at 1371 cm−1, in a boron-rich amorphous hydrogenated boron nitride region. These results, together with previously reported electron diffraction spectra, suggest the following picture: small (2.5 nm) nanocrys-tallites of cubic boron nitride (about 5% of the material) are imbedded in a mixed amorphous phase. The amorphous region can be approximated by a mixture of boron-rich and boron-poor amorphous hydrogenated boron nitride.
Magneto-Optic Studies of GaN Films and GaN/AlGaN Heterostructures
Authors: Wang Y.J. , Ng H.K. , Kaplan R. , Doverspike K. , Gaskill D.K. , Ikedo T. , Amano H. , Akasaki I. 
Published: April 2011

ABSTRACTMagneto-studies have been carried out for several MOCVD grown GaN thin films and GaN/AlGaN heterostructures at magnetic fields up to 30 T and at temperatures between 4.2 K to 100 K. Electron cyclotron resonance was observed in two heterostructures with high mobilities (μ > 2000 cm2/V-s), the effective mass obtained from the cyclotron resonance measurement is 0.23±0.01 m0, where m0 is the mass of free electron. For Si-doped thin film GaN there was no sign of electron cyclotron resonance even when samples were heated up to 100 K. However, a Is to 2p+ absorption line was observed for Si-doped GaN samples. A binding energy of 29 meV and low frequency dielectric constant of 10.4 is obtained.
Deep States in GaN Studied by Thermally Stimulated Current Spectroscopy
Authors: Huang Z.C. , Chen J.C. , Mott D.B. 
Published: April 2011

ABSTRACTDeep levels in insulating GaN grown by metalorganic chemical vapor deposition have been studied using thermally stimulated current (TSC) and photocurrent (PC) spectroscopies. Five main traps were observed by TSC measurement in the as-grown undoped GaN in the range of 0-0.75 eV below the conduction band edge or above the valence band edge. Their activation energies were 0.11, 0.24, 0.36, 0.53 and 0.62 eV, respectively. PC measurements showed three deep levels located within the bandgap at 1.32, 1.70 and 2.36 eV, respectively. Furnace annealing was carried out on GaN for identifying all the observed deep levels. We have found that the 0.24, 0.36 and 0.53 eV traps were eliminated by annealing at 1000°C under N2for six hours, whereas the 0.62 eV trap density increased after annealing. The three deep levels detected by the PC measurement were not affected by annealing. The 1.70 eV trap, which is located at the midgap, does not seem to compensate with narrow donors. We attribute the 0.11 eV trap to surface states, and the 0.62 eV trap to nitrogen vacancies.
Plasma Chemistry Dependent ECR Etching of GaN
Authors: Shul R. J. , Ashby C. I. H. , Rieger D. J. , Howard A. J. , Pearton S. J. , Abernathy C. R. , Vartuli C. B. , Barnes P. A. , Davis P. 
Published: April 2011

ABSTRACTElectron cyclotron resonance (ECR) etching of GaN in Cl2/H2/Ar, Cl2/SF6/Ar, BCl3/H2Ar and BCl3/SF6/Ar plasmas is reported as a function of percent H2 and SF6. GaN etch rates were found to be 2 to 3 times greater in Cl2/H2/Ar discharges than in BCl3/H2/Ar discharges independent of the H2 concentration. In both discharges, the etch rates decreased as the H2 concentration increased above 10%. When SF6 was substituted for H2, the GaN etch rates in BCl3-based plasmas were greater than those for the Cl2-based discharges as the SF6 concentration increased. GaN etch rates were greater in Cl2/H2/Ar discharges as compared to Cl2/SF6/Ar discharges whereas the opposite trend was observed for BCl3,-based discharges. Variations in surface morphology and near-surface stoichiometry due to plasma chemistries were also investigated using atomic force microscopy and Auger spectroscopy, respectively.