bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Susceptor Geometry on GaN Growth on SI(111) with a New Mocvd Reactor
Authors: Gao Yungeng , Gulino Daniel A. , Higgins Ryan 
Published: April 2011

AbstractHigh quality GaN films on AIN buffer layers were grown on Si(111) with a new, commercial, two-injector vertical rotating disk MOCVD reactor (CVD, Inc.). It was found that the geometry of the susceptor greatly affected the structural quality of the epilayers on Si. For the original susceptor geometry, though single crystal GaN films could be obtained, the films were dark gray in appearance with a rough morphology, and the best x-ray rocking curve FWHM was 2.33°. After modifying the susceptor geometry, transparent, mirror-like single crystal GaN films were obtained with the best x-ray rocking curve FWHM being 0.24°. Photoluminescence (PL) and infrared reflectance (IR) spectra of the grown films were compared. The film growth rate was found to increase with decrease of the growth pressure. A 2-D simulation of the flow, heat transfer, and chemical species transport in the reactor showed a more symmetric flow, larger velocity gradient, and lower upward velocity with the modified susceptor, which may be the main reason for the improvement of the structural quality of the films.
Process Routes for Low Defect-Density GaN on Various Substrates Employing Pendeo-Epitaxial Growth Techniques
Authors: Linthicum K.J. , Gehrke T. , Thomson D.B. , Tracy K.M. , Carlson E.P. , Smith T. P. , Zheleva T.S. , Zorman C.A. , Mehregany M. , Davis R.F. 
Published: April 2011

AbstractGaN films have been grown on 6H-SiC substrates employing a new form of selective lateral epitaxy, namely pendeo-epitaxy. This technique forces regrowth to start exclusively on sidewalls of GaN seed structures. Both discrete pendeo-epitaxial microstructures and coalesced single crystal layers of GaN have been achieved. SEM and TEM analysis are used to evaluate the morphology of the resulting GaN films. Process routes leading to GaN pendeo-epitaxial growth using silicon substrates have also been achieved and the preliminary results are discussed.
Absorption Coefficient and Refractive Index of GaN, AIN and AlGaN Alloys
Authors: Muth J. F. , Brown J. D. , Johnson M. A. L. , Yu Zhonghai , Kolbas R. M. , Cook J. W. , Schetzina J. F. 
Published: April 2011

AbstractThe design of optoelectronic devices fabricated from III-nitride materials is aided by knowledge of the refractive index and absorption coefficient of these materials. The optical properties of GaN, AIN and A1GaN grown by MOVPE on sapphire substrates were investigated by means of transmittance and reflectance measurements. Thin (less than 0.5 μm) single crystal films were employed to insure that transmission measurements could be obtained well above the optical band gap. The influence of alloy broadening on the absorption edge was investigated by using a series of AlGaN alloy samples with a range of Al compositions. The optical absorption coefficient above the band gap was obtained for AIGaN having up to 38% Al composition. The refractive index below the band gap was determined for the same series of samples. These properties provide information critical to the optimal design of solar blind detectors or other optoelectronic devices.
Role of the Substitutional Oxygen Donor in the Residual N-Type Conductivity in GaN
Authors: Chen W.M. , Buyanova I.A. , Wagner Mt. , Monemar B. , Lindstrom J.L. , Amano H. , Akasaki I. 
Published: April 2011

AbstractA detailed photoluminescence (PL) study reveals a striking similarity in local vibrational properties of a defect center in GaN as compared to that for the substitutional Op donor in GaP. This observation could be interpreted as if the center is in fact related to the substitutional oxygen donor in GaN. The deep-level nature experimentally determined for the defect center calls for caution of a commonly referred model that the substitutional oxygen donor is responsible for the residual n-type conductivity in GaN.
Electrical Characterization of Defects Introduced in n-GaN During High Energy Proton and He-Ion Irradiation
Authors: Goodman S. A. , Auret F. D. , Koschnick F. K. , Spaeth J.-M. , Beaumont B. , Gibart P. 
Published: April 2011

AbstractWe report on the electrical properties of defects as determined by deep level transient spectroscopy (DLTS) introduced in epitaxially grown n-GaN by 2.0 MeV protons and 5.4 MeV He-ions. After He-ion bombardment three electron traps ER3 (Ec - 0.196 eV), ER4 (Ec - 0.78 eV), and ER5 (Ec - 0.95 eV) were introduced uniformly in the region profiled by DLTS with introduction rates of 3270 ± 200, 1510 ± 300, and 3030 ± 500 cm-1 respectively. Capture cross section measurements revealed that the electron capture kinetics of ER5 is similar to that of a line defect. A defect with similar electronic properties as ER3 is observed after 2.0 MeV proton irradiation. The emission rate of ER3 depends on the electric field strength in the space-charge region. This emission rate is modelled according to the Poole-Frenkel distortion of a square well with a radius of 20 ± 2 Å or alternatively, a Gaussian well with a characteristic width of 6.0 ± 1 Å. Hence, we conclude that ER1 is a point defect which appears to have an acceptor like character. Two additional electron traps, ER1 (Ec -0.13 eV) and ER2 (Ec - 0.16eV) with introduction rates of 30 ± 10 and 600 ± 100 cm-1 not thusfar observed after electron or He-ion bombardment were observed after proton irradiation.
Inductively Coupled Plasma Etching of III-Nitrides in Cl2/Xe, Cl2/Ar AND Cl2/He
Authors: Cho Hyun , Hahn Y.B. , Hays D.C. , Jung K.B. , Donovan S.M. , Abernathy C.R. , Pearton S.J. , Shul R.J. 
Published: April 2011

AbstractThe role of additive noble gases He, Ar and Xe to Cl2-based Inductively Coupled Plasmas for etching of GaN, AIN and InN were examined. The etch rates were a strong function of chlorine concentration, rf chuck power and ICP source power. The highest etch rates for InN were obtained with Cl2/Xe, while the highest rates for AIN and GaN were obtained with Cl2/He. Efficient breaking of the III-nitrogen bond is crucial for attaining high etch rates. The InN etching was dominated by physical sputtering, in contrast to GaN and AIN. In the latter cases, the etch rates were limited by initial breaking of the III-nitrogen bond. Maximum selectivities of ∼ 80 for InN to GaN and InN to AIN were obtained.
Scanning Tunneling Microscopy Studies of InGaN Growth by Molecular Beam Epitaxy
Authors: Chen Huajie , Smith A. R. , Feenstra R. M. , Greve D. W. , Northrup J. E. 
Published: April 2011

AbstractInGaN alloys with indium compositions ranging from 0–40% have been grown by molecular beam epitaxy. The dependence of the indium incorporation on growth temperature and group III/group V ratio has been studied. Scanning tunneling microscopy images, interpreted using first-principles theoretical computations, show that there is strong indium surface segregation on InGaN. Based on this surface segregation, a qualitative model is proposed to explain the observed indium incorporation dependence on the growth parameters.
Fiber Debonding Along a Crack Front in Paper
Authors: Kettunen H. , Niskanen K. J. 
Published: April 2011

AbstractWe follow the accumulation of microscopic damage ahead the crack tip in paper. The fiber debonding process varies even within each specimen because of large variation in fiber and bond properties. In general, stiff and weakly bonded fibers tend to debond as a rigid body while ductile or well bonded fibers pull out gradually in a process that propagates from the crack line to the fiber ends. Particularly in the latter case the network ruptures coherently rather than through debonding of single fibers. Experimental analysis and simulations show that fracture energy correlates closely with the size of the fracture process zone (FPZ) irrespective the nature of the debonding process. Only the cases of low bonding and stiff fibers seem to make an exception in that FPZ can grow in size without a corresponding increase in fracture energy.
Cracks in Nano-Ceramic thin Layers Produced by Laser Treatments
Authors: De Hosson J.Th.M. , Teeuw D.H.J. 
Published: April 2011

AbstractSol-gel derived thin nano-ceramic layers of TiO2 and Al2O3 are studied using scanning electron microscopy to reveal the microstructure and morphologies of the layers. The low-voltage scanning electron microscope with a field emission gun is equipped with an especially designed lens, where the specimen is placed at the location where the magnetic field is the largest. In such a way a maximum resolving power could be attained of 1.5 nm at 3kV accelerating voltage. The melt-spun layers were treated differently afterwards, i.e. by furnace and by laser curing. These heat treatments appeared to dictate the final morphologies of the layers to a large extent. Grain growth is observed for the furnace as well as the laser cured layers. The activation energy for grain growth of these layers is determined. Homogeneous dense layers may be obtained if the parameters in the curing process are selected adequately. If the parameters are chosen incorrectly, severely debonded layers may be obtained. Pre-heating the layers resulted in less blister formation. The mechanisms which may cause the layers to fail were examined in more detail.
Long Distance Roughness of Fracture Surfaces in Heterogeneous Materials
Authors: Hinojosa M. , Bouchaud E. , Nghiem B. 
Published: April 2011

AbstractThe long distance roughness of fatigue fracture surfaces of a nickel-based superalloy is reported for two samples of different grain size. Statistical analysis over a wide range of length scales, from a few nanometers to a few millimeters, using scanning electron microscopy and atomic force microscopy allows to obtain accurately the self-affine correlation length. Long distance fracture profiles of 14,000 points were obtained and digitized from overlapping electron micrographs at a resolution of 0.22 micrometers/point. We have also analyzed the long distance roughness of the mirror zone on a soda-lime glass using atomic force microscopy. In the case of the nickel superalloy, correlation lengths are found to correspond well to the grain size. This result gives information about the mechanism of crack propagation in heterogeneous materials and shows that the correlation length of fracture surfaces is of the order of the largest microstructural heterogeneity.
Quantitative Modeling and Measurement of Copper Thin Film Adhesion
Authors: Volinsky A.A. , Tymiak N.I. , Kriese M.D. , Gerberich W.W. , Hutchinson J.W. 
Published: April 2011

AbstractNumerous mechanisms have been identified as fundamental to the adhesion of thin metallic films. The primary mechanism is the thermodynamic work of adhesion of the interface, which in its most basic description is the difference between the surface energies of the two materials and that of the interface. This quantity is often described as leveraging the contributions of other mechanisms. One of the more important mechanisms is that of plasticity occurring in a process zone in the vicinity of the delamination boundary. A quantitative model to characterize the contributions of plastic energy dissipation has been developed and used to rationalize experimental adhesion assessments. This model incorporates the functional dependence of the film thickness and constitutive properties. Orders of magnitude increases in the practical work of adhesion were both observed and predicted. Experimentally, the films used for model comparison were sputter-deposited copper ranging from 40 to 3300 nm in thickness, with and without a thin 10 nm Ti underlayer. Nanoindentation induced delamination of the Cu from SiO2/Si wafers were evaluated in the context of composite laminate theory to determine adhesion energies ranging from 0.6 to 100 J/m2 for bare Cu and from 4 to 110 J/m2 for Cu with the Ti underlayer.
Novel Precursors for MOCVD of Thin Films of Metal Oxides Containing Early Transition Metals
Authors: Davies Hywel O. , Fleeting Kirsty A. , Leedham Timothy J. , Jones Anthony C. , O'Brien Paul , Otway David J. 
Published: April 2011

AbstractMOCVD is a useful method for the deposition of thin films of metal oxides containing early transition metals,e.g., lead zirconium titanate, (PZT), because of its good step coverage and control of composition. Results are presented on a number of novel compounds which may be, or are, good MOCVD precursors. The compounds studied are in several general classes and include M(←diket)x, M(OR)x, M(←diket)x(OR)y[where M = Ti, Zr, Hf, Ta; ←-diket = tmhd (2,2,6,6-tetramethylheptane-3,5-dione), acac (acetylacetonate), hfac (1,1,1,5,5,5-hexafluoroacetylacetonate); R = Me, Et, Pr1, Butt]. We have sought to modify the precursors through chemical methods and have synthesized a number of novel, volatile, and intrinsically thermally stable MOCVD precursors. Full chemical characterization of the precursors (NMR, IR, MS, CHN, TGA/DSC, Single Crystal X-ray diffraction) has been undertaken.
Crystallization Kinetics and Texture of Sol-Gel PZT Thin Films
Authors: Shur V.Ya. , Blankova E.B. , Subbotin A.L. , Borisova E.A. , Bolten D. , Gerhardt R. , Waser R. 
Published: April 2011

AbstractThe morphology and phase evolution of sol-gel PZT thin films during rapid thermal annealing are investigated by in situ recording of scattered light intensity measured in reflected mode and momentary patterns visualized by optical microscope. In addition the texture and fractions of growing phases and the angular dependence of the scattered light are studied in partly annealed films. The kinetic parameters characterizing the transition from pyrochlore to perovskite phase are extracted by mathematical treatment of experimental data. It is shown that the film's texture and the transformation kinetics strongly depend on pyrolysis temperature. A mechanism of texture formation is proposed.
Pyroelectric Effects on 1T-1C Fram and 1Tr Fram
Authors: Yoo In Kyeong , Chung I.S. , Kim C.J. , Lee J.K. , Jeon B.K. , Desu S.B. 
Published: April 2011

AbstractPyroelectric effect on ferroelectricity was examined for PZT capacitors with diodes in series. It was observed that the magnitude of the polarization reversal increases as heating rate increases. The polarization reversal begins to decrease as heating rate becomes very high, which may stem from the fact that pyroelectric charges flow through the PZT film at high temperature as the film loses its resistance at the elevated temperature. A pure remanent polarization reversal model is suggested for the polarization reversal caused by pyroelectric charges. Based on the above results, a thermal shock test method is proposed for quality control of FRAM products. The thermal shock test reveals that pyroelectric effect can be minimized by controlling process for 1T-1C FRAM. It was also observed, by the thermal shock test, that imprint dominates pyroelectric effect in 1Tr cell with MFIS structure.
Low-Frequency Dielectric Properties of Sol-Gel Derived BaTiO3 Thin Films
Authors: Lee Su-Jae , Kang Kwang-Yong , Kim Jin-Woo , Han Seok Kil , Jeong Sang-Don 
Published: April 2011

AbstractFerroelectric BaTiO 3 thin films with perovskite structure were grown by sol-gel spin-on processing onto (111)Pt/Ti/SiO2/Si substrates. In order to investigate the effects of space charge in BaTiO3 thin films, we measured the relative dielectric constant and the ac conductivity of the films as a function of frequency, ac oscillation amplitude and temperature. Dielectric constant and dielectric loss were 147 and 0.03 at 100 kHz, respectively. Also, BaTiO3 thin films exhibited marked dielectric relaxation above the Curie temperature and in the low frequency region below 100 Hz. This low frequency dielectric relaxation is attributed to the ionized space charge carriers such as oxygen vacancies and defects in BaTiO3 film and the interfaical polarization. The thermal activation energy for the relaxation process of the ionized space charge carriers was 0.72 eV.
X-Ray Diffraction Method for Determining Textured Volume Fractions in PZT Thin Films
Authors: Fox G.R. 
Published: April 2011

AbstractThe crystallographic texture of PZT thin films has been proven to play a critical role in the electrical performance of PZT used in non-volatile FRAM. During both development and production of FRAM, PZT texture must be monitored to assure ferroelectric performance. A common method for monitoring texture is to use normalized intensities collected from X-ray diffraction 2-theta scans. Although this method can reveal thin film texture, it does not give a quantitative measure of the volume of textured and/or random material. In addition, this method can only be used to compare films with constant thickness since differences in X-ray absorption are not taken into account. A new method for calculating the volume fractions of textured and randomly oriented material in PZT thin films has been developed. This new method for calculating textured volume fractions still utilizes integrated intensities from 2-theta scans, but the calculations include corrections for film thickness and geometrical factors. The calculated volume fractions obtained from this new method of data analysis can be used directly for physical evaluation of PZT thin film ferroelectric performance.
Electromechanical Properties of Pb(Mg1/3Nb2/3)O3 Thin Film Capacitors
Authors: Catalan G. , Corbett M.H. , Bowman R.M. , Gregg J.M. 
Published: April 2011

AbstractPulsed Laser Deposition was used to grow Pb(Mg1/3Nb2/3)O3 (PMN) thin film planar capacitor structures. PMN crystallography was verified by x-ray diffraction and plan-view Transmission Electron Microscopy (TEM). Capacitance of the thin film structures was measured as a function of temperature and frequency. Leakage current was also measured for each capacitor. A DC field was subsequently applied and crystallographic strain was monitored in-situ by X-ray diffraction. The electromechanical strain was found to strongly depend on the deposition conditions for each capacitor. Tensile strains of ∼0.2% and compressive strains of ∼0.3% parallel to the applied field were measured for capacitors of different oxygen contents and thicknesses. We propose that the compressive strain is caused by the combined effect of joule heating of the capacitor structure, caused by large leakage currents, and epitaxial coupling between substrate and films. Electrostrictive tensile strains are of the same order as observed inbulk.
Evidence for the Presence of a Twist-Grain-Boundary Structure in Confined Hybrid Non-Chiral Smectic Liquid Crystal Films
Authors: Hu Y. , Martinez-Miranda L. J. 
Published: April 2011

AbstractWe have used Grazing Incidence X-ray Scattering to study the depth dependence of the interfacial structure of smectic liquid crystal (8CB) hybrid films. These films are bounded by a grated glass substrate and air, and have been studied as a function of both temperature and thickness. Our measurements indicate the presence of both a chevron structure and a structure similar to the helical twist-grain-boundary (TGB) phase. Our measurements constitute the first to show that this structure can also be observed in hybrid smectic liquid crystal films. The twisted structure is the result of anchoring at two dissimilar competing confining surfaces.
A Direct Method of Studying Polymer Adsorption on to Mica Surfaces Using a Commercial Mettler Ultramicrobalance
Authors: Terashima H. 
Published: April 2011

AbstractA simple and direct method has been developed of determining absolute values of adsorbance, i.e. mass per unit area, of polymers adsorbed from solution on to mica surfaces. A commercially available Mettler UMT2 ultramicrobalance is used to measure the weight of mica sheets before and after the immersion of the mica sheets into polymer solution for a given period of time. The increase in weight of mica sheets is divided by the total area of mica surfaces to derive the adsorbance. Practically measurable change in adsorbance was evaluated to be 0.1 mg m2. As an example of the practical application of the present method, an experimental result is presented of the adsorption kinetics of polystyrene (M=66,000) adsorbed from cyclohexane on to mica surfaces at the 0 -temperature.
Energy Transfer in Organic Dendrimer Antenna Funnel and Anti-Funnel Supermolecules
Authors: Swallen Stephen F. , Kopelman Raoul , Moore Jeffrey S. 
Published: April 2011

AbstractThe photophysics of exciton localization and energy transfer are examined in two unique classes of phenylacetylene dendrimers. One set of supermolecules is observed to efficiently and rapidly funnel absorbed radiation toward the molecular locus, while a slight change in molecular structure creates an effective “anti-funnel”, greatly reducing the efficiency of energy trapping. Lifetime-based and steady state fluorescence studies are used to determine the rates of intramolecular energy transfer and to glean information on molecular geometry and intermolecular interactions in two solvents.
Friction Based Segregation Of 2D Granular Assembly
Authors: Kondic L. , Tennakoon S. G. K. , Painter B. , Behringer R. 
Published: April 2011

AbstractWe present theoretical, computational (molecular dynamics), and experimental results describing the dynamical properties of a set of monodisperse, spherical particles confined to a two dimensional surface. An interaction model, which includes the interaction between the particles via collisions as well as the interaction with the substrate, shows that the properties of this granular system are influenced significantly by the latter. In particular, we analyze in detail the effects of slipping and rolling friction, which are usually overlooked. Theoretically, we explore the possibility of formulating a continuum, hydrodynamic-like theory applicable to this system. Further, we apply our model to the particular problem of a system of two kinds of particles with different frictional properties. Our experiments have found that friction-based segregation of particles moving on a horizontally shaken substrate can be achieved. Computational results give further insight into this novel segregation mechanism and confirm that careful and realistic modeling is needed in order to understand this effect.
Structure Stability in Plasma Chemistry
Authors: Wang Ji-Tao , Zhang David Wei , Liu Zhi-Jie , Zhang Jian-Yun , Ding Shi-Jin , Wang Peng-Fei 
Published: April 2011

AbstractDiamond is a metastable phase, while graphite is a stable phase in low pressure equilibrium phase diagrams of carbon. However, diamond with saturated structure of π bonds is more stable than graphite with unsaturated structure of n bonds during the existence of activated particles generated by plasma. That provides an excellent explanation for the plasma and other activated CVD diamond growth under low pressure taking place with simultaneous graphite etching.
Plasma Polymerization of Low Dielectric Constant Fluoro-Hydrocarbon Film
Authors: Lee Wei William , Tyndall George , Zehringer Raymond , Crowder Mark 
Published: April 2011

AbstractLow dielectric constant fluoro-hydrocarbon polymer films were deposited using an electron cyclotron resonance (ECR) plasma source with pentafluorostyrene as a precursor. The pentafluorostyrene is a cyclic liquid monomer with relative high vapor pressure. The chemical structure of the deposited films were characterized by X-ray photoelectron spectroscopy, infrared spectroscopy and Rutherford backscattering spectroscopy. The structure of deposited films studies gave an insight of the fluorohydrocarbon polymer formation regarding to deposition conditions. The dielectric constant of the film was found in the range of 2.2 to 2.4. The influence of deposition conditions on chemical, physical and electrical properties of the resulting films were evaluated.