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Journal of Applied Physics

Issue 12 • Date Dec 2001

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Displaying Results 1 - 25 of 123
  • 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
  • X-ray photoelectron spectroscopic study of KrF excimer laser nitrided InP surface

    Page(s): 5851 - 5855
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    Nitridation of InP is performed by KrF excimer laser irradiation in an NH3 ambient. The N–In and N–P bonds are formed in the irradiated area in proportion to the number of laser pulses. The x-ray photoelectron spectroscopy spectra of the nitrided samples contain a small concentration of oxide components after aging in an air atmosphere than nonirradiated samples © 2001 American Institute of Physics. View full abstract»

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  • Coherence collapse and redshifting in vertical-cavity surface-emitting lasers exposed to strong optical feedback

    Page(s): 5856 - 5858
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    The response of a commercial-grade, single-mode vertical-cavity surface-emitting laser to very strong optical feedback is investigated. With increasing feedback magnitude, the lasing spectrum broadens dramatically, eventually resulting in coherence collapse, and the lasing peak shifts to longer wavelengths. These effects became less severe with the onset of higher-order modes. A theoretical model is provided to explain the redshifting of the lasing spectrum with feedback. © 2001 American Institute of Physics. View full abstract»

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  • Effects of cell parameters on the properties of hybrid twisted nematic displays

    Page(s): 5859 - 5865
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    This article presents the results of an investigation of the electro-optical response for a hybrid twisted nematic (HTN) liquid crystal display. The device used both a hybrid alignment and a twisted director configuration. In comparison with the conventional twisted nematic mode, a faster response and a smaller operation voltage were obtained by using an appropriate amount of chiral dopant. The characteristics of the HTN cells were dependent on cell parameters such as the chemical nature of the polymer alignment layer, the cell thickness, the set twist angle, and the concentration of chiral dopant. Response times of 1.0 ms for turn-on and 16 ms for turn-off were achieved by the regulation of cell parameters. Computer simulations of the director configuration demonstrated that twist deformation plays an important role in the determination of the response characteristics. © 2001 American Institute of Physics. View full abstract»

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  • Nonlinearly optical–optical isomerization cycle in azobenzene liquid crystal polymers

    Page(s): 5866 - 5870
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    A nonlinearly optical method to induce the birefringence in azo liquid crystal polymers by the optical–optical isomerization cycle (O–O cycle) process is proposed in theory and implemented by experiments. In the O–O cycle, the two isomerization steps of trans-cis and cis-trans are both induced by light. In the nonlinearly O–O cycle, at least one step involves the nonlinearly optical absorption. It has been demonstrated that the permanent birefringence was induced in azo polymer P–CN films with a visible light source at 532 nm wavelength by the nonlinearly O–O cycle. The nonlinear nature of the photoisomerization process in P–CN was verified and a high nonlinear absorption coefficient of 40 cm/W was measured by use of the Z-scan technique. © 2001 American Institute of Physics. View full abstract»

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  • Energy distributions of electrons in a low-current self-sustained nitrogen discharge

    Page(s): 5871 - 5877
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    Electron energy distribution functions (EEDF) in N2 Townsend discharges for E/N between 1 and 30 kTd (1 Td=10-21 V m2) were measured using a multigridded energy analyzer behind a small (0.1 mm) aperture in the graphite anode. Experimental results are further analyzed by applying Monte Carlo simulations in order to describe nonequilibrium transport in steady state Townsend discharges and to determine the origin of the observed EEDF features. Boundary effects at electrodes are described by allowing exact representation of absorption, reflection, and secondary electron production at the anode. It was found that it is necessary to include electron reflection and secondary electron production in order to model the low energy part of the observed EEDF. © 2001 American Institute of Physics. View full abstract»

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  • Influence of charge exchange on the collection of the laser produced ions

    Page(s): 5878 - 5883
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    We evaluated influences of charge exchange on ion collection of laser isotope separation of uranium. We made a two-dimensional code based on fluid dynamics taking the charge exchange term into consideration. Parametric study was performed in terms of electric amplitude, ion density, and electron temperature. In addition to parallel electrode arrangement, calculations were performed for Π- and M-type arrangements. The ratio of charge exchanged ions is found to largely depend on the collection time. © 2001 American Institute of Physics. View full abstract»

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  • Collisional effects on the radio-frequency sheath dynamics

    Page(s): 5884 - 5888
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    Using the hydrodynamic model, we have derived a self-consistent model describing the dynamics of a collisional rf sheath driven by a sinusoidal current source. Numerical results have been obtained for the dependence of ion density, ion kinetic energy, sheath thickness, and sheath electric field, on the collision parameter and the current source parameter. © 2001 American Institute of Physics. View full abstract»

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  • Numerical simulation of laser induced plasma during pulsed laser deposition

    Page(s): 5889 - 5897
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    A numerical study of the laser induced evaporation and ionization process during pulsed laser deposition is presented. The process is separated into three domains: (i) conduction inside the solid, (ii) a discontinuity layer between solid and vapor, and (iii) expansion of high temperature vapor/plasma. A quasi-one-dimensional model is solved to predict the temperature field inside the solid. Mass, momentum, and energy are conserved across the discontinuity layer. Equations of mass, momentum, and energy conservation are solved simultaneously to provide boundary conditions for the expansion process. Euler equations are used to model the expansion of high temperature vapor/plasma. The Euler equations are integrated numerically using a Runge–Kutta scheme combined with flux vector splitting. The density, pressure, temperature, and velocity contours of the vapor phase are calculated and the results are analyzed. © 2001 American Institute of Physics. View full abstract»

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  • Transient charging effects on insulating surfaces exposed to a plasma during pulse biased dc magnetron sputtering

    Page(s): 5898 - 5903
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    Calculations of the transient charging currents to an insulating surface exposed to a dc discharge after the application of a pulse bias to the insulating surface are made based on a quasistatic treatment of the sheath’s impedance as a nonlinear dc resistance. Measurements of these transient charging currents are shown to correlate with the calculated transient currents for the experimental conditions used in this study. Discussion is then provided to indicate the limits on the pulse, plasma, and coupling conditions in which this quasistatic, dc treatment of the sheath’s response to the applied pulse remains valid. © 2001 American Institute of Physics. View full abstract»

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  • Elastic solution for liquid-bridging-induced microscale contact

    Page(s): 5904 - 5910
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    Microscale contact between two solid surfaces induced by the liquid-bridging force is studied in the present article. Attention is focused on the interaction between the size of the contact area and the magnitude of the liquid-bridging force. The liquid-bridging force is related to the contact size and the other parameters, such as the filling angle, the contact angles, and the surface tension of the liquid, by solving the Laplace–Young equation. A singular integral equation for the coupled contact equilibrium problem is established and solved. Two approximate solutions for the same problem are also given and compared with the solution of the singular integral equation. Parametric study reveals the dependence of the semicontact width and the liquid-bridging force on the filling angle and the dimensionless group in the microscale contact. © 2001 American Institute of Physics. View full abstract»

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  • Comparison of Poly(methylmethacrylate) and Novolak waveguide coatings for an acoustic biosensor

    Page(s): 5911 - 5914
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    In order to optimize the geometry of the acoustic waveguide biosensor, the performance of the device was assessed for two different guiding layers: a photeresist (Novolak) and a polymer Poly(methylmethacrylate) (PMMA) one. Initially, the effect of the thickness of each layer on the insertion loss of the device and frequency of the wave was monitored. The 1.5 and 1.7 μm Novolak and PMMA, respectively, coated devices were used to monitor the binding of Immunoglobulin G to the protein A activated device surface. Both devices were found to exhibit the same phase sensitivity to protein deposition. However, Novolak waveguides showed a higher stability in contact with water, making them more suitable for biosensing applications than PMMA waveguides. Finally, the reproducibility of the Novolak-coated waveguide was studied during the formation of the polymer layer, addition of buffer, and antibody binding. © 2001 American Institute of Physics. View full abstract»

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  • Subpicosecond carrier dynamics in low-temperature grown GaAs as measured by time-resolved terahertz spectroscopy

    Page(s): 5915 - 5923
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    The transient photoconductivity in a 1 μm layer of low temperature grown GaAs (LT-GaAs) on a GaAs substrate was measured using time-resolved terahertz spectroscopy. When photoexcitation occurs at 400 nm we find a time-dependent mobility that increases from 400±100 to 1100±100 cm2V-1s-1 with a time constant of 2 ps. Photoexcitation at 800 nm produces a time-independent mobility of 3000±500 cm2V-1s-1. We determine the carrier lifetime in LT-GaAs to be 1.1 ± 0.1 ps. © 2001 American Institute of Physics. View full abstract»

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  • Growth of epitaxial CoSi2 on 6H-SiC(0001)Si

    Page(s): 5924 - 5927
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    Epitaxial growth of (111)-oriented CoSi2 has been achieved on a scratch-free 6H-SiC(0001)Si substrate. The surface was prepared using atmospheric hydrogen etching and ultrahigh vacuum Si cleaning. A high-quality CoSi2 thin film was obtained by a modified template method and co-deposition of Co and Si at 550 °C. The structure and morphology of the film is studied by means of reflection high electron energy diffraction, x-ray absorption fine structure, x-ray diffraction, and atomic force microscopy. © 2001 American Institute of Physics. View full abstract»

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  • Electrical properties of electron irradiated thin polycrystalline CdSe layers

    Page(s): 5928 - 5932
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    Electrical properties of nonirradiated and electron-irradiated thin layers of CdSe, sandwiched between two gold electrodes, were investigated. Thin films of CdSe, prepared by thermal-vacuum evaporation on glass substrate at a temperature of 220 °C, were subjected to two sessions of irradiation with 7 MeV electrons to the fluences of 2×1015 and 4×1015 e/cm2, respectively. The current–voltage characteristics, recorded at temperatures in the range 150–350 K, showed that the Ohm’s law is followed at low-applied voltages, in both nonirradiated and irradiated CdSe layers. In the range of high-applied voltages, the space-charge-limited current (SCLC), controlled by a Gaussian trap distribution, placed in the vicinity of the Fermi level, has been identified as the dominant conduction mechanism. An analysis in the frame of SCLC theory allowed us to obtain the parameters characterizing the trap distribution and their changes induced by electron irradiation. © 2001 American Institute of Physics. View full abstract»

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  • Oriented growth of β-SiC on diamond crystals at high pressure

    Page(s): 5933 - 5935
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    Interaction between diamond crystals and liquid silicon at pressures of 2 and 9 GPa and various temperatures was studied by Raman spectroscopy, x-ray single crystal diffractometry, and scanning electron microscopy. The mechanism of growth of silicon carbide (SiC) film on diamond crystals depended on the magnitude of applied pressure. At low pressures, in the graphite stable region, only disoriented, fine grain β-SiC crystals were formed inside silicon surrounding diamond crystals. At higher pressures corresponding to the diamond stable region, oriented growth of β-SiC film on both {111} and {100} faces of diamond crystals was observed, even at high growth rates. © 2001 American Institute of Physics. View full abstract»

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  • Color of red mercuric iodide at cryogenic temperatures

    Page(s): 5936 - 5939
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    We investigated a red to yellow color change observed in α-HgI2 when cooled below 150 K. A phase transformation to β-HgI2, which has a yellow color, was ruled out by a variable temperature x-ray diffraction study. Instead the color change at cryogenic temperatures is caused by a shift in the transmission edge to shorter wavelengths which we attribute to a widening band gap at low temperatures. Using optical transmission spectroscopy the width of the band gap was measured between 10 and 330 K. At room temperature the gap was 2.11±0.03 eV, which is significantly smaller than the most recently published values of ∼2.3 eV. This smaller band gap was further verified by measuring the thermoelectric current at elevated temperatures. © 2001 American Institute of Physics. View full abstract»

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  • Crystallization of lithium cobalt oxide thin films by radio-frequency plasma irradiation

    Page(s): 5940 - 5945
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    The crystallinity of lithium cobalt oxide thin films deposited by the radio-frequency (rf) reactive magnetron sputtering method has been improved by the rf plasma irradiation method. Compared with conventional thermal annealing, reaction to form crystalline lithium cobalt oxide via rf plasma irradiation is fast and does not need any additional external heat supply. It is found that the nucleation and the growth reactions are determined during the film deposition and the rf irradiation, respectively. The film composition does not change significantly, and severe mechanical damages such as resputtering or etching phenomena do not appear after the irradiation. A model showing the process of the crystallization by rf plasma irradiation is suggested on the basis of phenomenological analyses using secondary electron microscopy, high-resolution transmission electron microscopy, etc. © 2001 American Institute of Physics. View full abstract»

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  • Cr3+(I) and Cr3+(II) centers in alexandrite single crystal

    Page(s): 5946 - 5950
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    Nuclear magnetic resonance spectra of the 9Be and 27Al nuclei as well as electron paramagnetic resonance spectra of Cr3+ ion in an alexandrite single crystal (BeAl2O4:Cr) have been investigated by employing a pulse nuclear magnetic resonance spectrometer and an X-band electron paramagnetic resonance spectrometer, respectively. Be has two magnetically inequivalent sites. While Al(I) at inversion symmetry has four magnetically inequivalent Al sites, Al(II) at mirror symmetry has two. The Cr3+(I) center has four magnetically inequivalent sites, whereas the Cr3+(II) center has two. All resonance sets of nuclear magnetic resonance for 9Be and 27Al nuclei and electron paramagnetic resonance for Cr3+ ion are analyzed in terms of crystal symmetry, ionic size, and charge state. It is concluded that the Cr3+(I) and Cr3+(II) ions substitute for Al3+(I) at inversion symmetry and Al3+(II) at mirror symmetry, respectively, intact of Be2+ sites. © 2001 American Institute of Physics. View full abstract»

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  • Optical functions, phonon properties, and composition of InGaAsN single layers derived from far- and near-infrared spectroscopic ellipsometry

    Page(s): 5951 - 5958
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    We study the optical properties of compressively strained InxGa1-xAs1-yNy (x≪0.13, y≪0.03) single layers for photon energies from 0.75 to 1.3 eV (near infrared), and for wave numbers from 100 to 600 cm-1 (far infrared) using spectroscopic ellipsometry. The intentionally undoped InGaAsN layers were grown pseudomorphically on top of undoped GaAs buffer layers deposited on Te-doped (001) GaAs substrates by metalorganic vapor-phase epitaxy. We provide parametric model functions for the dielectric function spectra of InGaAsN for both spectral ranges studied here. The InGaAsN layers show a two-mode phonon behavior in the spectral range from 100 to 600 cm-1. We detect the transverse GaAs- and GaN-sublattice phonon modes at wave numbers of about 267 and 470 cm-1, respectively. The polar strength f of the GaN sublattice resonance changes with nitrogen composition y and with the biaxial strain Єxx resulting from the lattice mismatch between InGaAsN and GaAs. This effect is used to derive the nitrogen and indium content of the InGaAsN layers combining the observed f dependence with results from high-resolution double-crystal x-ray diffractometry and using Vegard’s law for the lattice constants and the elastic coefficients C11 and C12. The calculated nitrogen concentrations reflect growth properties such as increasing N incorporation in InGaAsN with decreasing growth temperature, with increasing concentration of nitrogen in the gas phase, and with decreasing indium concentration in InGaAsN. © 2001 American Institute of Physics. View full abstract»

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  • Mechanism of the reduction of dislocation density in epilayers grown on compliant substrates

    Page(s): 5959 - 5962
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    A simplified model of the mechanism of dislocation reduction in epilayers grown on compliant substrates by molecular-beam epitaxy has been developed based on the dislocation theory and detailed experiments. Theoretical results calculated with this model indicate that up to 100-fold defect reduction can be achieved by using a silicon-on-insulator compliant substrate for the thick epilayer growth as compared to that of using a conventional Si substrate. The advantage of growing thick epilayers on compliant substrates can be predicted quantitatively. The mechanism of a nearly dislocation-free SiGe alloy, as well as GaAs epilayers grown on silicon-on-insulator compliant substrates, is explained and the dislocation density calculated with this model is in good agreement with our experimental results. © 2001 American Institute of Physics. View full abstract»

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  • Surface-mediated light-controlled Friedericksz transition in a nematic liquid crystal cell

    Page(s): 5963 - 5967
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    Surface-mediated director reorientation in a pure nematic liquid crystal (LC) cell in the presence of both a dc and low-power optical field has been observed. A surface-dependent lowering of the Friedericksz transition voltage in a planar cell upon light irradiation was found. It is believed that this effect is due to a light-induced change in the near-surface ion concentration in the presence of a dc field and a photosensitive surface. Enrichment in the ion concentration near the surface causes a redistribution of the electric field in the cell and its localization near the surface. As a consequence, the energy of interaction between the LC and the dc field near the surface overcomes the anchoring energy and results in the director reorientation. © 2001 American Institute of Physics. View full abstract»

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  • Temperature-dependent roughness of electronically excited InP surfaces

    Page(s): 5968 - 5972
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    Topographical evolution of 100 MeV Au8+-ion-irradiated InP surfaces was studied using atomic-force microscopy (AFM). The surfaces were roughened under dense electronic excitations. Root-mean-square roughness measured from AFM studies showed an exponential saturation behavior with fluence. Sample temperature during irradiation was found as a parameter to control the amount of roughness on the surface and the evolution of irradiated surface topography is discussed in terms of thermal spike model. © 2001 American Institute of Physics. View full abstract»

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  • Photoemission study of the solid-state interdiffusion in hybrid Fe/ZnSe/GaAs(001) heterostructures

    Page(s): 5973 - 5978
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    We report the chemical stability of the hybrid Fe/ZnSe/GaAs heterostructure prepared by molecular-beam epitaxy. Analyses of photoemission spectra show a remarkable chemical stability of the Fe/ZnSe(001) interface up to 380 °C, where the effective disruption of the heterostructure occurs, together with the appearance of Ga atoms near the film surface. This suggests that the ZnSe/GaAs interface is surprisingly less stable than the Fe/ZnSe one. © 2001 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