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Journal of Applied Physics

Issue 8 • Date Oct 2003

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Displaying Results 1 - 25 of 120
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Fluorescence intensity ratio technique for optical fiber point temperature sensing

    Page(s): 4743 - 4756
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    The fluorescence intensity ratio technique for optical fiber-based point temperature sensing is reviewed, including the materials suitable for this technique. The temperature dependence of the fluorescence intensity ratio has been studied using thermally coupled energy levels in seven different rare earth ions doped into a variety of glasses and crystals. Sensor prototypes developed using Pr3+:ZBLANP, Nd3+-doped silica fiber and Yb3+-doped silica fiber as the sensing material have been used to measure temperatures covering the range of approximately -50 to 600 °C with a resolution of the order of 1 °C. © 2003 American Institute of Physics. View full abstract»

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  • Perfect two-dimensional porous alumina photonic crystals with duplex oxide layers

    Page(s): 4757 - 4762
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    A perfect two-dimensional porous alumina photonic crystal with 500 nm interpore distance was fabricated on an area of 4 cm2 via imprint methods and subsequent electrochemical anodization. By comparing measured reflectivity with theory, the refractive indices in the oxide layers were determined. The results indicate that the porous alumina structure is composed of a duplex oxide layer: an inner oxide layer consisting of pure alumina oxide of 50 nm in thickness, and an outer oxide layer of a nonuniform refractive index. We suggest that the nonuniform refractive index of the outer oxide arises from an inhomogeneous distribution of anion species concentrated in the intermediate part of the outer oxide. © 2003 American Institute of Physics. View full abstract»

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  • Beam fanning reversal in the ferroelectic relaxor Sr0.61Ba0.39Nb2O6 at high external electric fields

    Page(s): 4763 - 4771
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    Beam fanning has been studied in the cerium-doped ferroelectric relaxor strontium–barium–niobate (Sr0.61Ba0.39Nb2O6:Ce, SBN:Ce) under the application of high external electric fields. Spatial reversal in the distribution of the scattered light is achieved both below and above the phase transition. It is shown that the photorefractive response in SBN strongly depends on the state of the polar structure of the crystal, which can be controlled by external fields. Coherent illumination of the crystal greatly facilitates the repoling process, causes a considerable refinement of the domain order in the ferroelectric phase and assists the stabilization of the polar structure in the relaxor regime. The model of scattering centers associated with refractive index anomalies located on domain walls is applied to receive detailed information about the distribution of initial seed scattering in the crystal bulk and the efficiency of nonlinear amplification of the scattering. © 2003 American Institute of Physics. View full abstract»

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  • Optical nonlinear properties and optical limiting for [(n-Bu)4N]4[MoS4Cu]4

    Page(s): 4772 - 4775
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    We report the nonlinear optical properties of one metal cluster [(n-Bu)4N]4[MoS4Cu]4 by picosecond and nanosecond laser pulses. The optical limiting response is measured by a transmission technique and the nonlinear absorption by a Z-scan technique. The experimental data are theoretically fitted, the mechanism for the optical nonlinearities and the optical limiting properties is discussed, and the absorption cross sections of the ground states and the excited states are evaluated by a rate equation model. © 2003 American Institute of Physics. View full abstract»

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  • Simultaneous, multilayer plasma etching and deposition of fluorocarbon layers on silicon

    Page(s): 4776 - 4780
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    The plasma etching and deposition of a fluorocarbon layer on a silicon substrate are modeled by the simultaneous etching and deposition of a stack of fluorocarbon monolayers. Langmuir kinetics apply in each of the monolayers to a depth where the energy of the bombarding ions exceeds or equals the threshold energy for breaking carbon fluorine bonds. The ion energy controls many of the terms in the etch rate and deposition rate expressions. The model is based on the diffusion of fluorine etchant through the fluorocarbon layer to the silicon substrate. The deposition and etching of the fluorocarbon layer are ion assisted; the etching of the silicon is thermal and is assumed self-similar based on experiments. The model covers three regimes: reactive sputtering, fluorocarbon suppression, and fluorocarbon deposition. Etch and deposition curves model CF+ ion beam deposition and etch on silicon and CHF3 and C2F6 etch and deposition on fluorocarbon covered silicon substrates. © 2003 American Institute of Physics. View full abstract»

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  • Prebreakdown phenomena and formation processes of low pressure glow discharges in N2, O2, and N2/O2 mixtures

    Page(s): 4781 - 4787
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    The prebreakdown phenomena and the resulting transient processes from the prebreakdown phenomena to the glow discharge in low-pressure N2, O2 gases, and N2/O2 mixtures were investigated. When the applied voltage was a lower overvoltage ratio less than about 2%, nonprebreakdown phenomenon was observed, and the overvoltage ratio was independent of the gas materials. This phenomenon, however, was observed at the overvoltage ratio of higher than about 3%. The prebreakdown phenomenon in N2 gas differed from those in O2 gas, and formed pulseless components. On the other hand, those in O2 gas formed pulsed components. The prebreakdown phenomenon in N2 gas changed to a pulsed discharge by mixing it with a small amount of more than 0.3% O2 gas. These transient processes from the prebreakdown phenomena to the glow discharges were also observed by a high-speed video camera. As a result, the formation processes of the glow discharge became clear. © 2003 American Institute of Physics. View full abstract»

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  • Analytical fit of the I–V characteristic for cylindrical and spherical Langmuir probes

    Page(s): 4788 - 4795
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    A unified radial model of the collisionless sheath for both cylindrical and spherical Langmuir probes is developed. The I–V characteristics are obtained and analytically fitted, taking into account both the probe radius and the probe biasing potential as parameters of the model. This parameterization allowed us to obtain an analytical approach for the potential profile, the floating potential and the sheath edge according to the Nachmann and Tahn criterion [M. Nachmann and P. C. Tahn, IEEE Trans. Plasma Sci. 19, 423 (1991)]. An alternative criterion for the sheath edge is established. This is referred to as the curvature criterion and it matches the Bohm criterion in the limiting case of planar Langmuir probes. The case of a planar sheath is obtained as a limiting case of the model when the probe radius is large enough. © 2003 American Institute of Physics. View full abstract»

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  • Influence of the expansion dynamics of laser-produced gold plasmas on thin film structure grown in various atmospheres

    Page(s): 4796 - 4802
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    The expansion dynamics of plasma produced by excimer laser ablation of a gold target was measured by means of spatially resolved real time emission spectroscopy. The emission line of the Au(I) neutral gold species at 267.65 nm was used to monitor the expansion dynamics of the plasma in several background gases (He, N2, O2, and Ar). The measurements were performed as a function of the gas pressure (from 4×10-5 to 4 Torr) and target-to-substrate distance (from 1.5 to 11 cm). Gold thin films were prepared in the same conditions and their structure was analyzed by x-ray diffraction. All films prepared fall into one of three categories: highly (111) oriented, mixed, or polycrystalline. All the films prepared herein show a transition from highly (111) oriented to mixed and then to polycrystalline as the velocity of the Au(I) neutral gold species decreases. In the case of inert background gases (He, N2, and Ar), the velocity at which the transition between the various types of structure occurs is remarkably constant. Highly (111) oriented films are obtained for Au(I) neutral gold species exceeding v1=2.4 km s-1 (5.8 eV), while a polycrystalline (nanocrystalline) film is formed when the velocity falls below v2=0.8 km s-1 (0.6 eV). The conditions of distance and pressure at which these velocities are attained differ greatly from one atmosphere to the other, reflecting the fact that the interaction between the expanding plasma and the background gases varies with the molar mass of the gas. In the case of O2, the transition velocities between the different structures are higher than those observed in He, N2, and Ar [v1=8.3 km s-1 (70.4 eV) and v2=3.4 km s-1 (11.8 eV)]. This reflects a significant difference in the growth mechanism of these films compared to those prepared in an inert atmosphere. © 2003 American Institute of Physics. View full abstract»

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  • Aluminum oxynitride at pressures up to 180 GPa

    Page(s): 4803 - 4806
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    Hugoniot equation-of-state data of shock compressed aluminum oxynitride (AlON), consisting of 64.1 mol% Al2O3∙35.9 mol% AlN with a density of ∼3.68 g/cm3, have been determined to 180 GPa. The relationship between shock velocity (Us) and particle velocity (Up) is expressed by a straight line: Us(km/s)=8.08+0.761Up(km/s). Although there is no evidence of phase transition in the data, the determined Hugoniot of AlON has been compared with those of oxide spinels such as MgAl2O4 and Fe3O4. We discuss the systematics of high pressure phase transitions of spinels that indicate a phase transition to CaTi2O4-type phases. The phase transition to CaTi2O4-type structures implies that the recently discovered Si3N4 spinel also may be transformed into a CaTi2O4-type phase with increasing pressure. © 2003 American Institute of Physics. View full abstract»

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  • Postgrowth annealing of defects in ZnO studied by positron annihilation, x-ray diffraction, Rutherford backscattering, cathodoluminescence, and Hall measurements

    Page(s): 4807 - 4812
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    Defects in hydrothermal grown ZnO single crystals are studied as a function of annealing temperature using positron annihilation, x-ray diffraction, Rutherford backscattering, Hall, and cathodoluminescence measurements. Positron lifetime measurements reveal the existence of Zn vacancy related defects in the as-grown state. The positron lifetime decreases upon annealing above 600 °C, which implies the disappearance of Zn vacancy related defects, and then remains constant up to 900 °C. The Rutherford backscattering and x-ray rocking curve measurements show the improvement of crystal quality due to annealing above 600 °C. Although the crystal quality monitored by x-ray diffraction measurements is further improved after annealing at above 1000 °C, the positron lifetime starts to increase. This is due to either the formation of Zn vacancy related defects, or the change of the Zn vacancy charge state occupancy as a result of the Fermi level movement. The electron concentration increases continuously with increasing annealing temperature up to 1200 °C, indicating the formation of excess donors, such as oxygen vacancies or zinc interstitials. The cathodoluminescence measurements reveal that the ultraviolet emission is greatly enhanced in the same temperature range. The experimental results show that the ZnO crystal quality, electrical and optical characteristics are improved by postgrowth annealing from 600 to 1200 °C. The disappearance of Zn vacancy related defects contributes to the initial stage of improved crystal quality. © 2003 American Institute of Physics. View full abstract»

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  • Optical characterization of AlN/GaN heterostructures

    Page(s): 4813 - 4818
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    AlN/GaN/sapphire heterostructures with AlN gate film thickness of 3–35 nm are characterized using photoreflectivity (PR) and photoluminescence (PL) spectroscopy. Under a critical AlN film thickness, the luminescence from the GaN channel layer near the interface proves to be excitonic. No luminescence related to the recombination of the two-dimensional electron gas (2DEG) is observed, in spite of high 2DEG parameters indicated by Hall-effect measurements. The increase of the AlN gate film thickness beyond a critical value leads to a sharp decrease in exciton resonance in PR and PL spectra as well as to the emergence of a PL band in the 3.40–3.45 eV spectral range. These findings are explained taking into account the formation of defects in the GaN channel layer as a result of strain-induced AlN film cracking. A model of electronic transitions responsible for the emission band involved is proposed. © 2003 American Institute of Physics. View full abstract»

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  • Experimental findings in support of atomic transport of hydrogen in silica

    Page(s): 4819 - 4823
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    Data supporting a view of both molecular and atomic transport of hydrogen in quartz is presented. By studying isotopic equilibration, it is shown that virtually all of the molecules diffusing through a 1.5 mm thick quartz membrane at 900 °C have undergone dissociation. The catalytic properties of platinum for the dissociation of H2 are used to increase the surface concentration of atomic hydrogen on a quartz membrane. It is found that the high surface concentration increases the total flux of hydrogen through the membrane. It is also found by comparison with literature data that diatomic molecules probably diffuse in two modes in quartz. We suggest that these two modes are one atomic and one molecular. © 2003 American Institute of Physics. View full abstract»

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  • Fictive temperature dependence of density fluctuation in SiO2 glass

    Page(s): 4824 - 4827
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    Fictive temperature dependence of density fluctuation in SiO2 glass was investigated by the small-angle x-ray scattering measurement. The density fluctuation in SiO2 glass varies linearly to the fictive temperature. Contribution of structural relaxation to the density fluctuation is larger than that of phonons. Isothermal compressibility, relaxational isothermal compressibility and high-frequency adiabatic compressibility are estimated. If N,  ¯, and Δ represent the number of SiO4/2 unit, average and difference from average, respectively, the density fluctuation in SiO2 glass is less than 3.6% as (ΔN)2/N¯. © 2003 American Institute of Physics. View full abstract»

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  • Enhancement of sp3 hybridized C in amorphous carbon films by Ar ion bombardment and Si incorporation

    Page(s): 4828 - 4834
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    We report an effective method of increasing the sp3 hybridization fraction in sputtered amorphous carbon (a-C) film by the combination of Ar ion bombardment and Si incorporation. In the deposition of an a-C film, Ar ion bombardment by controlling the applied bias voltage plays a role in creating high stress in film and causes the local bonding configuration to change to a sp3 hybridized bond. Simultaneously, the incorporated Si in an a-C network breaks the sp2 hybridized bonded ring and promotes the formation of a sp3 hybridized bond. This enhancement of the sp3 hybridized bonding characteristic is maximized for an a-C film with 23 at. % of Si and 100–150 V of applied bias voltage. In this region, the increase of resistivity, optical band gap, and mechanical hardness of a-C is attributed to the reduction of the sp2 hybridized bonded ring and increased fraction of the sp3 hybridized bond. However, at a higher bias voltage above 150 V, the enhancement effect is reduced due to the resputtering and thermally activated reconversion of a sp3 to a sp2 hybridized bond. © 2003 American Institute of Physics. View full abstract»

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  • Modeling the absorption spectra of Er3+ and Yb3+ in a phosphate glass

    Page(s): 4835 - 4840
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    Absorption spectra of Er3+ and Yb3+ ions, codopants in a phosphate glass, are reported at 8 K and at wavelengths between 350 and 1600 nm. Detailed structure appearing in the spectra, associated with individual multiplet states, 2S+1LJ, of Er3+(4f11) and Yb3+(4f13) is interpreted using a ligand-field coordination sphere model to characterize the microscopic environment surrounding the rare earth ions in multiple sites. Inhomogeneous broadening of the spectra is likely due to different configurations of PO4 tetrahedra clustered about a caged rare earth ion in the amorphous host. Similarity between the Er3+ spectrum in the glass and in the spectrum of single-crystal LiErP4O12, where Er3+ occupies sites of C2 symmetry, suggests that an averaged site symmetry of C2 is a reasonable approximation for Er3+ and Yb3+ ions in the phosphate glass. Calculated splitting of multiplet states by the ligand-field cluster model are compared with energy levels derived from the observed absorption peaks and well-defined shoulders. Inhomogeneous broadening of the spectra limit the precision in establishing the energy of the multiplet splittings, but the analysis is useful for modeling studies of the Er:Yb:phosphate glass as an eye-safe laser (1.53 μm). The splitting of the Yb3+(4f13)2FJ - states is determined using parameters obtained from the Er3+ set by means of the three-parameter theory. No adjustments were made to the Yb3+ parameters that predict multiplet splittings in reasonable agreement with experimental data. © 2003 American Institute of Physics. View full abstract»

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  • Formation of self-assembled epitaxial nickel nanostructures

    Page(s): 4841 - 4846
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    Highly orientated nickel magnetic nanoparticles were obtained by pulsed laser deposition technique on silicon (100) substrate using epitaxial titanium nitride film as the template. These nanoparticles have been characterized by conventional and high-resolution transmission electron microscopy, scanning transmission electron microscopy Z-contrast imaging, and x-ray diffraction techniques. The results have shown that the growth of nickel on epitaxially grown titanium nitride follows a three-dimensional island growth mechanism. The predominant orientation of nickel islands observed is Ni(100)||TiN(100)||Si(100), the so-called “cube-on-cube” orientation relation. The islands are faceted with a truncated pyramidal shape and bounded by (111) planes at sides and (100) plane at the top. Islands with nontruncated pyramidal shape were also found in some samples, but with rotational orientation relations, where the nickel crystal rotates with an approximate angle of 90° with respect to one of TiN <110> directions parallel to the interface. The appearance of this rotational epitaxial growth did not show any obvious deposition temperature dependence in the range of 400–650 °C, rather it seemed to be closely related to the crystalline quality of TiN template. The actual size of islands varies from a few nanometers to tens of nanometers, depending on the deposition time and temperature. The three-dimensional growth of nickel islands and the island faceting could be explained by the surface energy anisotropy of both nickel and titanium nitride. © 2003 American Institute of Physics. View full abstract»

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  • Gd on GaN(0001) surface: Growth, interaction, and Fermi level movement

    Page(s): 4847 - 4852
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    Growth, interfacial reaction, and Fermi level movement of Gd on n-type GaN(0001)-(1×1) surface are studied using x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and low-energy-electron diffraction. Gd grows in a layer-by-layer-like mode and reacts with the substrate at the interface, leading to formation of metallic Ga at room temperature. A downward Fermi level movement is observed, and the resultant Schottky barrier height is 1.5 eV. Annealing promotes further diffusion and an interfacial Gd–Ga exchange reaction, reducing the Schottky barrier height. © 2003 American Institute of Physics. View full abstract»

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  • Stress development in sputtered NiO thin films during heat treatment

    Page(s): 4853 - 4858
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    Nickel oxide thin films with a thickness of 100 nm were deposited on oxidized silicon wafers by rf magnetron sputtering from a NiO target in an Ar (nonreactive case) and an Ar+O2 atmosphere with various oxygen contents (reactive cases). The as-deposited films possess high compressive stresses (up to 3700 MPa) which decrease irreversibly during annealing between 150 and 500 °C. Compositional and microstructural analyses were performed on as-deposited and annealed films by means of electron probe microanalysis, transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, thermal-desorption spectrometry, and magnetization measurements. All as-deposited thin films consist of NiOx with x ranging between about 1.15 and 1.27. These oxygen-excess films are thermally unstable. They decompose during heat treatment into thermally more stable, oxygen-poorer NiO and/or metallic Ni. This decomposition is the reason for the observed irreversible stress changes. © 2003 American Institute of Physics. View full abstract»

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  • Atomic structure of random and c-axis oriented YMnO3 thin films deposited on Si and Y2O3/Si substrates

    Page(s): 4859 - 4862
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    We have studied the atomic structure of YMnO3 deposited on Si and Y2O3 with high-resolution transmission electron microscopy and fast Fourier transforms-filtered lattice image analysis during furnace and rapid thermal annealing (RTA) processes. For the YMnO3/Si, it is found that the YMnO3 layer is c-axis oriented with an amorphous bottom region after furnace annealing at 850 °C for 1 h. In contrast, after RTA at 850 °C for 3 min the bottom region forms YMnO3 polycrystalline layer with the {1¯21¯2} plane parallel to the surface. When an Y2O3 layer is interposed between YMnO3 and Si, a c-axis oriented YMnO3 layer grows on a [111]-oriented Y2O3 layer. Memory window and leakage current density of the c-axis YMnO3/[111] Y2O3 bilayers are strongly improved due to an aligned [0001] unipolar axis. © 2003 American Institute of Physics. View full abstract»

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  • Selectively excited photoluminescence of GaAs1-xNx single quantum wells

    Page(s): 4863 - 4865
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    GaAsN bulk and GaAsN/GaAs single quantum wells grown by molecular beam epitaxy are studied by selectively excited photoluminescence (PL) measurements. A significant difference is observed in the PL spectra when the excitation energy is set below or above the band gap of GaAs for the GaAsN/GaAs quantum well samples, while the spectral features of GaAsN bulk are not sensitive to the excitation energy. The observed difference in PL of the GaAsN/GaAs quantum well samples is attributed to the exciton localization effect at the GaAsN/GaAs interfaces, which is directly correlated with the transfer and trap processes of the photogenerated carriers from GaAs into GaAsN through the heterointerfaces. This interface-related exciton localization effect can be greatly reduced by a rapid thermal annealing process, making the PL be dominated by the intrinsic delocalized transition in GaAsN/GaAs. © 2003 American Institute of Physics. View full abstract»

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  • Temperature and thickness dependence of molecular orientation of α-sexithienyl on Cu(111)

    Page(s): 4866 - 4870
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    Atomic and electronic structures of α-sexithienyl(6 T) films grown on Cu(111) were studied by near edge x-ray absorption fine structure (NEXAFS) and S 1s x-ray photoemission spectroscopies. The polarization dependent NEXAFS indicated highly ordered arrays of 6 T molecules, with their molecular long axes parallel to the surface, at substrate temperatures lower than 300 K. On the other hand, their molecular long axes became normal to the surface at 360 K, while they initially adsorbed with their long axes parallel to the surface. The film thickness and substrate temperature dependence of the molecular orientation is discussed in terms of the van der Waals interaction between 6 T and Cu(111) and the kinetics of the growth process. It is demonstrated that the molecular orientation of the promising organic semiconductor 6 T can be controlled by substrate temperature. © 2003 American Institute of Physics. View full abstract»

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  • Observation of reflection high-energy electron diffraction oscillation during metalorganic-molecular-beam epitaxy of AlAs and control of carbon incorporation

    Page(s): 4871 - 4875
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    The in situ observation of reflection high-energy electron diffraction (RHEED) oscillations during the metalorganic-molecular-beam epitaxy deposition of AlAs and AlGaAs epitaxial layers is reported. In situ RHEED oscillations as well as atomic force microscopy measurements confirmed the layer-by-layer growth of the AlAs as well as the AlGaAs layers on GaAs substrates. RHEED oscillation was successfully applied to the precise control of the AlAs/GaAs superlattices and of the alloy compositions in the AlGaAs alloys. High-resolution x-ray diffraction and Hall effect measurements revealed the unintentional doping of carbon into the AlGaAs layers, but it was found that the increase in the V/III ratio is able to reduce the carbon incorporation. © 2003 American Institute of Physics. View full abstract»

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  • Brillouin scattering in planar waveguides. I. Numerical model

    Page(s): 4876 - 4881
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    A model for the calculation of Brillouin spectra in planar waveguides is presented. The electromagnetic field in a mode of a planar waveguide is a current wave along the guide and a standing wave across the guide with an evanescent tail in the substrate. The modal electromagnetic field can be calculated if the refractive index profile across the waveguide is known. The model for the calculation of Brillouin spectra considers the spatial distribution of the exciting field in the mode, a simple spatial dependence of the elasto-optic coefficients, through the value of the refractive index, and neglects the refraction of phonons. A single parameter, i.e., the sound velocity, is necessary to calculate as many spectra as is the number of modes in the waveguide. Examples of step index waveguides of different thicknesses and of graded-index waveguides are calculated and the results are compared with those of a simpler model based on a ray-tracing approach. In multimode waveguides with a step index profile, it turns out that longitudinal phonons produce two main peaks with an energy separation which increases with the mode index m. In graded-index waveguides, m-1 peaks of comparable intensities may appear. © 2003 American Institute of Physics. View full abstract»

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  • Brillouin scattering in planar waveguides. II. Experiments

    Page(s): 4882 - 4889
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    Silica–titania planar waveguides of different thicknesses and compositions have been produced by radio-frequency sputtering and dip coating on silica substrates. Waveguides were also produced by silver exchange on a soda-lime silicate glass substrate. Brillouin scattering of the samples has been studied by coupling the exciting laser beam with a prism to different transverse-electric (TE) modes of the waveguides, and collecting the scattered light from the front surface. In multimode waveguides, the spectra depend on the m mode of excitation. For waveguides with a step index profile, two main peaks due to longitudinal phonons are present, apart from the case of the TE0 excitation, where a single peak is observed. The energy separation between the two peaks increases with the mode index. In graded-index waveguides, m-1 peaks of comparable intensities are observed. The spectra are reproduced very well by a model which considers the space distribution of the exciting field in the mode, a simple space dependence of the elasto-optic coefficients, through the value of the refraction index, and neglects the refraction of phonons. A single-fit parameter, i.e., the longitudinal sound velocity, is used to calculate as many spectra as is the number of modes in the waveguide. © 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