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Journal of Applied Physics

Issue 2 • Date Jul 2003

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Displaying Results 1 - 25 of 73
  • Issue Cover

    Page(s): c1
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    Freely Available from IEEE
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Lattice symmetry applied in transfer-matrix methods for photonic crystals

    Page(s): 811 - 821
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    Transfer-matrix methods have been routinely used to calculate the transmission and reflection spectra of electromagnetic waves propagating through a photonic crystal slab. In this article we show that the intrinsic lattice symmetries within a photonic crystal can be used to reduce numerical computations of the electromagnetic problem. We have employed this lattice-symmetry enhanced transfer-matrix method to handle two-dimensional photonic crystal slabs of square and triangular lattices and three-dimensional layer-by-layer photonic crystal slabs. The calculated transmission spectra agree excellently with the photonic band structures in predicting the photonic band gap positions, indicating the accuracy and efficiency of this proposed approach. © 2003 American Institute of Physics. View full abstract»

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  • Emission, thermocouple, and electrical measurements in SF6/Ar/O2 SiC etching discharges

    Page(s): 822 - 830
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    In SiC etching plasma devices, we have recorded plasma emission from Ar, F, and O atoms in SF6/Ar/O2 rf discharges as a function of pressure, input power, and mixture fraction. At fixed power, the emission intensities rise nearly linearly with increasing pressure between 100 and 300 mTorr; with pressure increases to 600 mTorr, the emission intensity rolls off due to the increase in collisional de-excitation. At fixed pressure, Ar and O atom emission shows a similar functional dependence on input power with a roll off at the higher powers due to decreasing reduced electric field strength (E/n, where n denotes the number density). In contrast, the F atom emission increase with increasing power is nearly linear. This reflects the fact that F atoms are produced by dissociative attachment of SF6 (for lower E/n conditions) in addition to direct electron impact dissociation. Electrical measurements, with a variable interelectrode gap discharge, indicate that the electric field to pressure (E/p) ratio does drop with increasing input power. Thermocouple measurements show that the ground electrode temperature increases with increasing power. The dissociative attachment of SF6 increases with increasing temperature as well. The SiC etch rate increases nearly linearly with input power up until the polymer buildup becomes the rate limiting process. At fixed pressure, the Ar emission from the 750 nm line decreases with increasing additions (up to 10%) of O2. This is due to resonantly enhanced quenching of the 4p (13.5 eV) manifold by oxygen atoms. In marked contrast, the F atom emission intensity increases suggesting F atom production by neutral species chemistry. Over the pressure (10- 0–600 mTorr) and power (20–60 W) range studied, the Ar 750 nm emission line serves as a good actinometer for the 704 nm F line provided that there is not a high degree (or changing degree) of O2 dissociation. Resonant deactivation of the 750 nm line through collisional interaction with O atoms, can make the 750 nm line problematic. Under such conditions our previous work indicates that the Ar 641 nm line can provide an alternative actinometer. The excited state of the 641 nm transition lies above the O atom ionization limit making it immune from resonant quenching.© 2003 American Institute of Physics. View full abstract»

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  • Dynamics of steady and unsteady operation of inductive discharges with attaching gases

    Page(s): 831 - 843
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    Relaxation oscillations in charged particle densities are seen in low-pressure inductive discharges, if attaching gases such as SF6 and Ar/SF6 mixtures are used, such that the plasma contains negative ions. These oscillations occur in the neighborhood of the transition between lower power capacitive operation and higher power inductive operation. An instability, which occurs around this transition, can be described by a global model, that consists of time-dependent equations for the electrons, ions, and electron temperature. The model qualitatively agrees with experimental observations, but leaves significant quantitative differences to be explained. To understand the reasons for the model’s inability to make quantitative predictions, the local conditions for instability are determined for a model somewhat simplified from the one that approximates the experiment, but retains most of the important physics. The simplified model allows explicit determination for the local transition to instability and identifies two parameters that govern the transition. The local criteria are related to the global criterion that all fixed points are unstable. The importance for the instability of the physical parameters of the ion wall loss and of the ratio of capacitive to inductive power transfer has led to a reexamination of the size of these factors, and gives better quantitative agreement of the model to experiments. © 2003 American Institute of Physics. View full abstract»

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  • Distribution of gas temperature in an unconfined glow discharge plasma

    Page(s): 844 - 851
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    An analysis is carried out to determine radial temperature distributions in the cylindrical positive column of a glow discharge formed in air in free space without confining walls. The analysis considers discharge with current densities lower than 100 mA/cm2 and at gas pressures of several tens of Torr. The plasma is represented by a set of hydrodynamic equations that include the balances for electron number density, translational energy, and the vibrational energy. The equations are solved using an iterative method to obtain gas temperatures for a range of plasma conditions. The results show that increasing discharge current densities lead to higher gas temperatures on plasma axis, however, unlike in the case with glow discharge restricted by dielectric walls, increased current densities also lead to wider radial profiles of temperature. Increased gas pressure, while leading to higher on-axis gas temperatures, results in narrower temperature profiles, mainly due to the reduced diffusion rates and vibrational-translational energy relaxation times. At low gas pressures and current densities, the electron density profiles are found to be significantly narrower than those for temperature while at higher values of these parameters, the width of the two are comparable. The characteristic radius of the predicted gas temperature distribution is in a good agreement with recent experimental findings. © 2003 American Institute of Physics. View full abstract»

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  • Enhanced ionization in the cylindrical Hall thruster

    Page(s): 852 - 857
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    Conventional annular Hall thrusters do not scale efficiently to low power. An alternative approach, a cylindrical Hall thruster with a cusp-type magnetic field distribution, has been investigated. A relatively large 9-cm-diam version of a cylindrical thruster, operated in 300–1000 W power range, and the 2.6 cm miniaturized cylindrical Hall thruster, operated in the power range 50–300 W, exhibited performance comparable with conventional annular Hall thrusters of the similar size. The cylindrical thrusters have unusually high propellant utilization, compared to conventional Hall thrusters. Numerical simulations, performed within the framework of a quasi-one-dimensional stationary thruster model, show that the increase in the propellant utilization does not appear to be quantitatively explained by a reduction of plasma wall losses. A more complete theoretical model, likely including kinetic effects, will be necessary to explain the observed propellant utilization effect. © 2003 American Institute of Physics. View full abstract»

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  • Simultaneous measurement of laser-induced shock wave and released particle velocities at Mbar pressure

    Page(s): 858 - 862
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    We show the feasibility of simultaneous measurement of shock velocity and released particle velocity after shock at Mbar pressure. The shock wave is driven by a laser pulse of 1.2 ps duration (full width at half maximum), with the intensity of ∼1014 W/cm2 at 785 nm, irradiating a 500-nm-thick aluminum foil. A chirped laser pulse split from the main pulse is applied to detect the shock breakout process at the rear surface of the target based on frequency domain interferometry. The mean shock velocity determination benefits from the precise synchronization (≪100 fs resolution) of the shock pump and probe laser pulse, which is calculated from the time the shock takes to travel the 500-nm-thick aluminum. The released particle velocity determination takes advantage of the chirped pulse frequency domain interferometry. The two measured parameters are self-consistent. © 2003 American Institute of Physics. View full abstract»

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  • Phonon-assisted cooperative energy transfer and frequency upconversion in a Yb3+/Tb3+ codoped fluoroindate glass

    Page(s): 863 - 866
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    We report large thermal enhancement of the frequency upconversion (UC) process due to cooperative energy transfer (CET) in a Yb3+/Tb3+ codoped fluoroindate glass obtained by heating the sample from 308 to 530 K. To study the influence of multiphonon transitions in the UC process we chose anti-Stokes quasiresonant excitation of Yb3+ ions which were used as sensitizers. UC of radiation at 1064 nm into blue and green light was obtained. Various emission lines of Tb3+ were observed between 400 and 700 nm due to CET from Yb3+ to Tb3+ ions. A rate equation model was used to describe the temperature dependence of the UC emission intensities and the theoretical results are in good agreement with the experimental data. © 2003 American Institute of Physics. View full abstract»

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  • Optical absorption and electronic structure of Zn1-xMnxO alloys studied by spectroscopic ellipsometry

    Page(s): 867 - 869
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    Dielectric functions of Zn1-xMnxO (x≤0.19) thin films were obtained by spectroscopic ellipsometry at room temperature in the 1.5–5 eV photon energy region. A strong absorption structure is observed near 3.1 eV, below the optical band-gap absorption (E0) edge, and it does not shift with x. It is interpreted as due to transitions between the crystal-field-split 3d5 multiplet levels of the tetrahedral Mn2+ ion that substitute for Zn2+. A redshift is observed for the E0 edge near x=0.06 from that of pure ZnO, interpreted as due to the spin–exchange interaction between d electrons of the Mn2+ ion and sp electrons near the band gap. The E0 edge shows a blueshift for larger x. The excitonic character of the E0 edge is gradually reduced and replaced by a three-dimensional shape as x increases, and this is attributed to increased disorder. © 2003 American Institute of Physics. View full abstract»

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  • Amorphous carbon films prepared by the “dip” technique: Deposition and film characterization

    Page(s): 870 - 878
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    Several nondestructive characterization techniques (optical and photothermal deflection spectroscopy in the visible photon energy range, Raman spectroscopy, profilometry, photoluminescence, electron-spin-resonance characterization of the paramagnetic centers, etc.) are used to study the properties of the a-C:H:OH films deposited by the “dip” technique. With such a preparation method, the substrates are dipped in viscous mixtures of liquid carbon compounds. The subsequent baking in an oven at different temperatures (300–500 °C) allows the formation on a substrate of submicrometric thin solid films. The as-prepared material exhibits several characteristics that are comparable to that of floppy, polymer-like amorphous carbons. Transitions on many film properties (thicknesses, optical gaps, photoluminescence intensities, spin densities, g factors, relaxation times, etc.) were found between 300 and 350 and between 450 and 500 °C. © 2003 American Institute of Physics. View full abstract»

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  • Optical characterization of CuIn1-xGaxSe2 alloy thin films by spectroscopic ellipsometry

    Page(s): 879 - 888
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    Optical constants of polycrystalline thin film CuIn1-xGaxSe2 alloys with Ga/(Ga+In) ratios from 0 to 1 have been determined by spectroscopic ellipsometry over an energy range of 0.75–4.6 eV. CuIn1-xGaxSe2 films were deposited by simultaneous thermal evaporation of elemental copper, indium, gallium and selenium. X-ray diffraction measurements show that the CuIn1-xGaxSe2 films are single phase. Due to their high surface roughness, the films are generally not suitable for ellipsometer measurements. A method is presented in which spectroscopic ellipsometer measurements were carried out on the reverse side of the CuIn1-xGaxSe2 films immediately after peeling them from Mo-coated soda lime glass substrates. A detailed description of multilayer optical modeling of ellipsometric data, generic to ternary chalcopyrite films, is presented. Accurate values of the refractive index and extinction coefficient were obtained and the effects of varying Ga concentrations on the electronic transitions are presented. © 2003 American Institute of Physics. View full abstract»

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  • Numerical simulations of pattern-directed phase decomposition in a stressed, binary thin film

    Page(s): 889 - 898
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    Two-dimensional simulations of the microstructural evolution of stressed, epitaxial, binary thin films on a geometrically patterned substrate using a Cahn–Hilliard equation are presented. Substrate and film are differentiated using a phase field parameter and both epitaxial and compositional strains for a cubic system under plane strain are treated. Numerical simulations show that arrays of nanoparticles can self-assemble in the decomposing film, especially near the film–substrate interface. The size and distribution of the precipitates in the film are sensitive to the geometry of the substrate interface, compositional and epitaxial strains, the film composition and thickness, and the interfacial interaction of the film with the substrate and with the surface. The simulations show the possibility of creating particle spacings considerably smaller than the substrate pattern periodicity, allowing a “demagnification” beyond the resolution of the imposed pattern. © 2003 American Institute of Physics. View full abstract»

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  • Contactless electroreflectance, in the range of 20 K≪T≪300 K, of freestanding wurtzite GaN prepared by hydride-vapor-phase epitaxy

    Page(s): 899 - 903
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    We have performed a detailed contactless electroreflectance study of the interband excitonic transitions on both the Ga and N faces of a 200-μm-thick freestanding hydride-vapor-phase-epitaxy grown wurtzite GaN sample with low defect concentration in the temperature range between 20 and 300 K. The transition energies of the A, B, and C excitons and broadening parameters of the A and B excitons have been determined by least-square fits to the first derivative of a Lorentzian line shape. The energy positions and separations of the excitonic transitions in the sample reveal the existence of residual strain. At 20 K the broadening parameter of A exciton deduced for the Ga (5×105dislocation cm-2) and N (1×107dislocation cm-2) faces are 3 and 7 meV, respectively, indicating a lower defect concentration on the former face. The parameters that describe the temperature dependence of the interband transition energies of the A, B, and C excitons as well as the broadening function of the A and B features are evaluated. The results from an analysis of the temperature dependence of the broadening function of excitons A and B indicate that GaN exhibits a very large exciton-phonon coupling. © 2003 American Institute of Physics. View full abstract»

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  • Shear bands and cracking of metallic glass plates in bending

    Page(s): 904 - 911
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    The thickness dependence of yielding and fracture of metallic glass plates subjected to bending is considered in terms of the shear band processes responsible for these properties. We argue that the shear band spacing (and length) scales with the thickness of the plate because of strain relaxation in the vicinity of the shear band at the surface. This is consistent with recent measurements of shear band spacing versus sample size. We also argue that the shear displacements in the shear band scale with the shear band length and plate thickness, thus causing cracks to be initiated in thicker plates at smaller bending strains. This leads to fracture bending strains that decrease markedly with increasing plate thickness, consistent with recent experiments. These results suggest that amorphous metals in the form of foams might have superior ductility and toughness. © 2003 American Institute of Physics. View full abstract»

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  • Epitaxial growth of yttrium-stabilized HfO2 high-k gate dielectric thin films on Si

    Page(s): 912 - 915
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    Epitaxial yttrium-stabilized HfO2 thin films were deposited on p-type (100) Si substrates by pulsed laser deposition at a relatively lower substrate temperature of 550 °C. Transmission electron microscopy observation revealed a fixed orientation relationship between the epitaxial film and Si; that is, (100)Si//(100)HfO2 and [001]Si//[001]HfO2. The film/Si interface is not atomically flat, suggesting possible interfacial reaction and diffusion. X-ray photoelectron spectrum analysis also revealed the interfacial reaction and diffusion evidenced by Hf silicate and Hf–Si bond formation at the interface. The epitaxial growth of the yttrium stabilized HfO2 thin film on bare Si is via a direct growth mechanism without involving the reaction between Hf atoms and SiO2 layer. High-frequency capacitance–voltage measurement on an as-grown 40-Å yttrium-stabilized HfO2 epitaxial film yielded an effective dielectric constant of about 14 and equivalent oxide thickness to SiO2 of 12 Å. The leakage current density is 7.0×10-2A/cm2 at 1 V gate bias voltage. © 2003 American Institute of Physics. View full abstract»

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  • Influence of the elastic strain on the band structure of ellipsoidal SiGe coherently embedded in the Si matrix

    Page(s): 916 - 920
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    We report on a theoretical investigation of the elastic strain in an ellipsoidal SiGe inclusion coherently embedded in Si and its influence on the band structure of SiGe. The strain was calculated as a function of the Ge fraction in SiGe and the aspect ratio of the ellipsoid, and utilized to derive the shift of the band edge. When the principal axis of the ellipsoid was chosen to be parallel to [001], the band structure of SiGe was predicted to be Si like regardless of the aspect ratio. The band gap of strained SiGe was also calculated, and the deviation of the aspect ratio from unity was found to be effective to decrease the band gap due to the breaking of the crystal symmetry. These results suggest the importance of controlling strain, shape, and local Ge fraction in multicrystalline SiGe, which we propose as a promising material for solar cell applications. © 2003 American Institute of Physics. View full abstract»

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  • Growth and physical properties of epitaxial CeN layers on MgO(001)

    Page(s): 921 - 927
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    While NaCl-structure transition-metal nitrides have been widely studied over the past two decades, little is known about the corresponding NaCl-structure rare-earth nitrides. Polycrystalline CeN, for example, has been reported by different groups to be both a wide band-gap semiconductor and a metal. To address this controversy, we have grown epitaxial CeN layers on MgO(001) and measured their physical properties. The films were grown at 700 °C by ultrahigh vacuum reactive magnetron sputter deposition in mixed Ar/N2 discharges maintained at 4 mTorr (0.53 Pa). X-ray diffraction and transmission electron microscopy results establish the film/substrate epitaxial relationship as cube-on-cube, (001)CeN∥(001)MgO with [100]CeN∥[100]MgO, while Rutherford backscattering spectroscopy shows that the layers are stoichiometric with N/Ce=0.99±0.02. CeN is metallic with a positive temperature coefficient of resistivity and a temperature-independent carrier concentration, as determined by Hall effect measurements, of 2.8±0.2×1022cm-3 with a room temperature mobility of 0.31 cm2V-1s-1. At temperatures between 2 and 50 K, the resistivity is limited by defect scattering and remains constant at 29 μΩ cm, while at higher temperatures it increases linearly, limited primarily by phonon scattering, to reach a room-temperature value of 68.5 μΩ cm. The hardness and elastic modulus of C- eN(001) were determined from nanoindentation measurements to be 15.0±0.9 and 330±16 GPa. © 2003 American Institute of Physics. View full abstract»

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  • Thermal decomposition behavior of the HfO2/SiO2/Si system

    Page(s): 928 - 934
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    We report on the thermal decomposition of uncapped, ultrathin HfO2 films grown by chemical vapor deposition on SiO2/Si(100) substrates. Medium energy ion scattering, x-ray photoelectron spectroscopy, scanning electron microscopy and atomic force microscopy were used to examine the films after they had been annealed in vacuum to 900–1050 °C. Film decomposition is a strong function of the HfO2 overlayer thickness at a given temperature, but the underlying SiO2 layer thickness does not significantly affect the thermal stability of the HfO2 film. Oxygen diffusion in the system was monitored by 16O/18O isotopic labeling methods. Direct evidence of silicide formation is observed upon decomposition. © 2003 American Institute of Physics. View full abstract»

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  • Nondestructive characterization of nanopore microstructure: Spatially resolved Brunauer–Emmett–Teller isotherms using nuclear magnetic resonance imaging

    Page(s): 935 - 941
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    This article presents the results of nuclear magnetic resonance imaging (MRI) studies of gas adsorption/desorption in nanoporous solids. MR images obtained as a function of the equilibrium pressure, at constant temperature, form a pixel-by-pixel map of adsorption isotherms. Analysis of these isotherms using Brunauer–Emmett–Teller (BET) theory results in spatial maps of the specific surface area, the net energy of adsorption, and the pore morphology. Results obtained using MRI for γ-Al2O3 and ZnO powders and partially sintered ceramics of these materials, as well as Vycor® porous glass, compare well to results for bulk samples obtained using conventional N2 BET adsorption. MRI studies of gas adsorption are shown to provide statistical averages of the pore microstructure parameters, resolved on a macroscopic scale. © 2003 American Institute of Physics. View full abstract»

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  • Polarity determination of a-plane GaN on r-plane sapphire and its effects on lateral overgrowth and heteroepitaxy

    Page(s): 942 - 947
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    Achieving nitride-based device structures unaffected by polarization-induced electric fields can be realized with nonpolar GaN, although polarity plays a key role in the growth. (1120) a-plane GaN films were grown on (1102) r-plane sapphire substrates and subsequently laterally overgrown using metalorganic chemical vapor deposition. Convergent beam electron diffraction analysis was used to determine the a-GaN polarity to explicitly define the film/substrate relationship, and subsequently to identify various growth features and surfaces observed throughout our studies of a-plane GaN. In particular, the effects of polarity on (1) lateral overgrowth from mask stripe openings aligned along [1100]GaN and (2) pit formation in heteroepitaxial films grown under nonoptimized conditions were investigated. The fundamental differences between the polar surfaces are clearly observed; analysis of the lateral epitaxial overgrowth stripes revealed that (0001) surfaces grew faster than (0001¯) surfaces by approximately an order of magnitude, and these stable, slow-growing (0001¯) surfaces are a likely cause of pitting in a-GaN films. The growth features under investigation were imaged using scanning and transmission electron microscopy. © 2003 American Institute of Physics. View full abstract»

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  • Intrinsic compressive stress in polycrystalline films with negligible grain boundary diffusion

    Page(s): 948 - 957
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    The model developed here describes compressive stress evolution during the growth of continuous, polycrystalline films (i.e., beyond the point where individual islands have coalesced into a continuous film). These stresses are attributed to the insertion of excess adatoms at grain boundaries. Steady state occurs when the strain energy at the top of the film is balanced by the local excess chemical potential of surface adatmos. Strain gradients associated with this compressive stress mechanism depend on the kinetics of the process. In the absence of grain boundary diffusion, these strain profiles are determined by the ratio of the atom insertion and growth rates. The steady-state strain and the strain evolution kinetics also depend on the two key length scales, the grain size, and the film thickness. The ratio of these two lengths (i.e., the grain aspect ratio) can also have a significant influence on the thermodynamic driving force for strain evolution if the grain sizes are sufficiently small. The model is fit to existing data for the growth of AlN films. However, more detailed comparisons will require experiments that are specifically designed to test this model. © 2003 American Institute of Physics. View full abstract»

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  • Response of chromium-doped alumina screens to soft x rays using synchrotron radiation

    Page(s): 958 - 962
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    We have measured the response of chromium-doped alumina screens to soft x-ray radiation and derived quantum efficiency curves for the energy range from 2.5 to 4.5 keV. Persistent luminescence (or afterglow) from this material is observed for several minutes following the removal of the x-ray source. It is also observed that the luminescence output rises gradually for several minutes before maximizing during x-ray irradiation. In the article we discuss possible sources of this delayed luminescence and its consequences for application of these screens as soft x-ray detectors. Such screens have found application as narrow-band radiation detectors for a hot fusion plasma diagnostic. © 2003 American Institute of Physics. View full abstract»

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  • Evidence of a density grating under light induced formation of surface relief gratings at polymers containing azobenzene moieties

    Page(s): 963 - 967
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    The formation of a surface relief grating (SRG) on polymer films containing azobenzene moieties has been inspected during exposure with counter-rotating circularly polarized light of λwrite=488 nm by probing the diffracting efficiency of a second low power laser. In particular, the growing SRG was observed at films of different film thickness and with low and high light power of the writing laser. Using probe lasers of two different wavelength probe=514 and 670 nm) the grating formation was inspected near the film surface and within the whole film, respectively. At low writing power (P=50 mW) and small film thickness (d≪100 nm) only a SRG appears while at higher laser power and thicker films (d≫300 nm) a density grating is also created within the film. The observations confirm the trends suggested by finite element calculations. © 2003 American Institute of Physics. View full abstract»

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  • Brillouin scattering study of ZnO

    Page(s): 968 - 972
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    Polarized Brillouin scattering measurements were carried out for a bulk ZnO single crystal. The whole set of elastic stiffness constants was determined to be c11=19.0, c12=11.0, c13=9.0, c33=19.6, c44=3.9, and c66=4.0 in units of 1011dyn/cm2. The relationships between photoelastic constants at wavelength of 514.5 nm were also obtained: p11, p13, p44, and p66=1.8, 2.3, 0.50, and 0.38, respectively, relative to p12. © 2003 American Institute of Physics. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Editor
P. James Viccaro
Argonne National Laboratory