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Journal of Applied Physics

Issue 11 • Date Jun 2005

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Displaying Results 1 - 25 of 161
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Ultrafast electron microscopy in materials science, biology, and chemistry

    Page(s): 111101 - 111101-27
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    The use of pump-probe experiments to study complex transient events has been an area of significant interest in materials science, biology, and chemistry. While the emphasis has been on laser pump with laser probe and laser pump with x-ray probe experiments, there is a significant and growing interest in using electrons as probes. Early experiments used electrons for gas-phase diffraction of photostimulated chemical reactions. More recently, scientists are beginning to explore phenomena in the solid state such as phase transformations, twinning, solid-state chemical reactions, radiation damage, and shock propagation. This review focuses on the emerging area of ultrafast electron microscopy (UEM), which comprises ultrafast electron diffraction (UED) and dynamic transmission electron microscopy (DTEM). The topics that are treated include the following: (1) The physics of electrons as an ultrafast probe. This encompasses the propagation dynamics of the electrons (space-charge effect, Child’s law, Boersch effect) and extends to relativistic effects. (2) The anatomy of UED and DTEM instruments. This includes discussions of the photoactivated electron gun (also known as photogun or photoelectron gun) at conventional energies (60–200 keV) and extends to MeV beams generated by rf guns. Another critical aspect of the systems is the electron detector. Charge-coupled device cameras and microchannel-plate-based cameras are compared and contrasted. The effect of various physical phenomena on detective quantum efficiency is discussed. (3) Practical aspects of operation. This includes determination of time zero, measurement of pulse-length, and strategies for pulse compression. (4) Current and potential applications in materials science, biology, and chemistry. UEM has the potential to make a significant impact in future science and technology. Understanding of reaction pathways of complex transient phenomena in materials science, biology, and chemistry will provid- e fundamental knowledge for discovery-class science. View full abstract»

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  • Optical detection of chemical warfare agents and toxic industrial chemicals: Simulation

    Page(s): 113101 - 113101-11
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    We present an analysis of optical techniques for the detection of chemical warfare agents and toxic industrial chemicals in real-world conditions. We analyze the problem of detecting a target species in the presence of a multitude of interferences that are often stochastic and we provide a broadly applicable technique for evaluating the sensitivity, probability of false positives (PFP), and probability of false negatives (PFN) for a sensor through the illustrative example of a laser photoacoustic spectrometer (L-PAS). This methodology includes (1) a model of real-world air composition, (2) an analytical model of an actual field-deployed L-PAS, (3) stochasticity in instrument response and air composition, (4) repeated detection calculations to obtain statistics and receiver operating characteristic curves, and (5) analyzing these statistics to determine the sensor’s sensitivity, PFP, and PFN. This methodology was used to analyze variations in sensor design and ambient conditions, and can be utilized as a framework for comparing different sensors. View full abstract»

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  • Nonlinear harmonic generation in high-gain free-electron lasers

    Page(s): 113102 - 113102-7
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    We reconsider the derivation of semianalytical expressions providing the most significant aspects of the high-gain free-electron laser dynamics. We obtain new expressions for the growth of the laser power, of the e-beam-induced energy spread, and of the higher-order nonlinearly generated harmonics. The procedure we employ, based on theoretical ansatz and fitting methods, allows the determination of crucial quantities like the expected harmonic output power and its dependences on the e-beam parameters. View full abstract»

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  • Time-resolved optical emission studies on the laser ablation of a graphite target: The effects of ambient gases

    Page(s): 113103 - 113103-5
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    Time-resolved optical emission spectroscopy was employed to examine the temporal properties of a plume formed by laser ablation of a graphite target in He, N2, and Ar background gases. Time-dependent spectroscopic temperatures of electronically excited C2 and CN molecules generated in the plume at different background gases and pressures were derived by simulation of the emission spectra. The rotational temperature of CN molecules was significantly higher than the vibrational temperature. This indicates that they are formed in the gas phase by the chemical reaction C2+N2CN. At pressure above 0.5 Torr, the temperature in each background gas was apparently in the order of ArN2He while there was no such gas dependence at 0.1 Torr. The expansion dynamics and cooling rate of the plume turned out to be highly dependent on the background gas and its pressure. View full abstract»

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  • Atomically designed precursors in optical fiber amplifiers: The thermal stability of the heterobimetallic ErAl3(OPri)12 in a solution-coated silica soot

    Page(s): 113104 - 113104-7
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    The thermal stability of the bimetallic alkoxide ErAl3(OPri)12 doped in an unsintered silica (soot) has been investigated. Samples have been heated to different temperatures (up to 1500 °C and analyzed by using ultraviolet-visible-near infrared absorption spectroscopy, infrared spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, thermal gravimetric analysis, and powder x-ray diffraction. It is seen that the doped samples heated up to 1000 °C show broad glasslike absorption spectra, indicating an amorphous structure, while the high-temperature sample shows an ordered crystallinelike structure with sharp characteristic absorption peaks. X-ray diffraction measurements indicate the formation of an ordered structure at temperatures of 1500 °C, revealing a crystal phase of silica and phases of erbium and aluminosilicate. A comparison is also made with a sample doped with aqueous ErCl3 and Al(NO3)3. It is concluded that the local structure of the ErAl3 precursor is not preserved at temperatures above 1000 °C. Alternative doping procedures are discussed. View full abstract»

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  • Periodically poled LiNbO3: Optical parametric oscillation at wavelengths larger than 4.0 μm with strong idler absorption by focused Gaussian beam

    Page(s): 113105 - 113105-4
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    Coupled-wave equations for focused Gaussian beams in an optical superlattice are derived. By solving the coupled equations, we investigate theoretically the optimum design parameters for the middle-infrared wavelength generation under the configuration of a singly resonating optical parametric oscillation with strong idler absorption. A positive dephasing is required due to the Gouy effect for optimal idler generation. For idler wavelengths of up to 5.0 μm, the threshold power can be kept at a lower level over a wider range of dephasing. Beyond this, the threshold power increases with the absorption coefficient of the idler wave. This model accurately predicts the current experimental results with weaker idler absorption. Validation with strong idler absorption is also verified. View full abstract»

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  • Effect of carrier loss through waveguide layer recombination on the internal quantum efficiency in large-optical-cavity laser diodes

    Page(s): 113106 - 113106-5
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    An analytical treatment for carrier distribution in optical confinement layers (OCLs) of semiconductor lasers with bimolecular recombination is developed. On the basis of this approach, the effect of OCL recombination on the internal quantum efficiency of a laser is evaluated. It is shown that this effect can lead to a rapid deterioration in efficiency with increased waveguide thickness at high enough currents, and also contributes to the efficiency decrease with current in a given structure. An asymmetric, narrow waveguide structure is shown to avoid this problem while still providing a good-quality beam. View full abstract»

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  • Enhanced temporal resolution in femtosecond dynamic-grating experiments

    Page(s): 113107 - 113107-5
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    Recording of gratings by interference of two pump pulses and diffraction of a third probe pulse is useful for investigating ultrafast material phenomena. We demonstrate, in theory and experiment, that the temporal resolution in such configurations does not degrade appreciably even for large angular separation between the pump pulses. Transient Kerr gratings are generated inside calcium fluoride (CaF2) crystals by two interfering femtosecond (pump) pulses at 388 nm and read out by a Bragg-matched probe pulse at 776 nm. The solution to the relevant coupled-mode equations is well corroborated by the experimental results, yielding a value of the Kerr coefficient of ≈4.4×10-7 cm2/GW for CaF2. View full abstract»

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  • The effects of photorefraction on electro-optic field sensors

    Page(s): 113108 - 113108-5
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    We have measured the electro-optic response of LiNbO3 and SrxBa1-xNb2O6 crystals to be used for electric-field sensors. Our results indicate that optically induced refractive index variations (photorefractivity) in the crystals affect the temporal stability and sensitivity of the sensors. Spatial distributions of the refractive indices produced from the photorefractivity create incoherence in the polarization of the probing laser passing through the crystal (optical probe). In LiNbO3 crystals, this spatial incoherence was negligible and sensor responsivities close to the theoretical maximum were attained. However, in SrxBa1-xNb2O6 crystals, strong spatial variations of the principal refractive indices resulted in an extremely incoherent polarization of the optical probe and reduced the electro-optic responsivity dramatically. The photorefractive-induced sensitivity loss is modeled using a distribution function (rather than a constant value) to describe the phase of the optical probe. These results emphasize the importance of an optically stable material, with little or no photorefractivity, when designing an electro-optic field sensor. View full abstract»

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  • Experimental investigation of hybrid-evaporation-glow discharge plasma immersion ion implantation

    Page(s): 113301 - 113301-5
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    High-voltage pulsed glow discharge is applied to plasma immersion ion implantation (PIII). In the glow discharge, the target constitutes the cathode and the gas tube forms the anode under a relatively high working gas pressure of 0.15–0.2 Pa. The characteristics of the glow discharge and ion density are measured experimentally. Our results show resemblance to hollow-anode glow discharge and the anode fall is faster than that of general glow discharge. Because of electron focusing in the anode tube orifice, ions are ionized efficiently and most of them impact the negatively biased samples. The resulting ion current density is higher than that in other PIII modes and possible mechanisms of the glow discharge PIII are proposed and discussed. View full abstract»

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  • Impact of reductive N2/H2 plasma on porous low-dielectric constant SiCOH thin films

    Page(s): 113302 - 113302-8
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    Porous low-dielectric constant (low-κ) SiCOH thin films deposited using a plasma-enhanced chemical-vapor deposition have been comprehensively characterized before and after exposure to a reactive-ion-etch-type plasma of N2 and H2 chemistry. The low-κ film studied in this work is a carbon-doped silicon oxide film with a dielectric constant (κ) of 2.5. Studies show that a top dense layer is formed as a result of significant surface film densification after exposure to N2/H2 plasma while the underlying bulk layer remains largely unchanged. The top dense layer is found to seal the porous bulk SiCOH film. SiCOH films experienced significant thickness reduction, κ increase, and leakage current degradation after plasma exposure, accompanied by density increase, pore collapse, carbon depletion, and moisture content increase in the top dense layer. Both film densification and removal processes during N2/H2 plasma treatment were found to play important roles in the thickness reduction and κ increase of this porous low-κ SiCOH film. A model based upon mutually limiting film densification and removal processes is proposed for the continuous thickness reduction during plasma exposure. A combination of surface film densification, thickness ratio increase of top dense layer to bulk layer, and moisture content increase results in the increase in κ value of this SiCOH film. View full abstract»

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  • Influence of dielectric barrier discharges on low Mach number shock waves at low to medium pressures

    Page(s): 113303 - 113303-6
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    For shock wave propagation in nonequilibrium plasmas, it has been shown that when the electron Debye length exceeds the shock wave discontinuity dimension, strong double layers are generated, propagating with the shock wave. Strong double layer formation leads to the enhancement of the local excitation, ionization, and local neutral gas heating which increases the shock wave velocity. It is shown that dielectric barrier discharges (DBD) in pure N2 also increase the shock wave velocity and broaden the shock wave. The DBD is considerably more energy efficient in producing these effects compared to a dc glow discharge and can operate over a wide pressure range. It is shown that these effects are also operative in the pure N2 discharge afterglow, allowing a wide range of pulse repetition frequencies. View full abstract»

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  • Microbubble-based model analysis of liquid breakdown initiation by a submicrosecond pulse

    Page(s): 113304 - 113304-10
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    An electrical breakdown model for liquids in response to a submicrosecond (∼100 ns) voltage pulse is presented, and quantitative evaluations carried out. It is proposed that breakdown is initiated by field emission at the interface of pre-existing microbubbles. Impact ionization within the microbubble gas then contributes to plasma development, with cathode injection having a delayed and secondary role. Continuous field emission at the streamer tip contributes to filament growth and propagation. This model can adequately explain almost all of the experimentally observed features, including dendritic structures and fluctuations in the prebreakdown current. Two-dimensional, time-dependent simulations have been carried out based on a continuum model for water, though the results are quite general. Monte Carlo simulations provide the relevant transport parameters for our model. Our quantitative predictions match the available data quite well, including the breakdown delay times and observed optical emission. View full abstract»

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  • Role of dissociative recombination in the excitation kinetics of an argon microwave plasma at atmospheric pressure

    Page(s): 113305 - 113305-11
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    A collisional radiative model was developed in order to investigate the influence of dissociative recombination on the Saha–Boltzmann plasma equilibrium. As the dissociative recombination products are not well known, their relative importance was tested through comparison with the distribution of line intensities obtained in a microwave argon discharge produced at atmospheric pressure by a surface wave. It was found that the main dissociation products are the ground state and the 4s levels, the 5p and upper levels playing a negligible role. Because the higher levels are only weakly affected by dissociative recombination, they remain in partial local thermodynamic equilibrium. Therefore, the excitation temperature determined from these levels adequately describes the electron temperature. The model well reproduces experimental measurements of excitation temperature, rotational temperature, electron density, and absolute populations of the excited levels. View full abstract»

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  • Measurement and modeling of a diamond deposition reactor: Hydrogen atom and electron number densities in an Ar/H2 arc jet discharge

    Page(s): 113306 - 113306-15
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    A combination of experiment [optical emission and cavity ring-down spectroscopy (CRDS) of electronically excited H atoms] and two-dimensional (2D) modeling has enabled a uniquely detailed characterization of the key properties of the Ar/H2 plasma within a ≤10-kW, twin-nozzle dc arc jet reactor. The modeling provides a detailed description of the initial conditions in the primary torch head and of the subsequent expansion of the plasma into the lower pressure reactor chamber, where it forms a cylindrical plume of activated gas comprising mainly of Ar, Ar+, H, ArH+, and free electrons. Subsequent reactions lead to the formation of H2 and electronically excited atoms, including H(n=2) and H(n=3) that radiate photons, giving the plume its characteristic intense emission. The modeling successfully reproduces the measured spatial distributions of H(n≫1) atoms, and their variation with H2 flow rate, FH20. Computed H(n=2) number densities show near-quantitative agreement with CRDS measurements of H(n=2) absorption via the Balmer-β transition, successfully capturing the observed decrease in H(n=2) density with increased FH20. Stark broadening of the Balmer-β transition depends upon the local electron density in close proximity to the H(n=2) atoms. The modeling- reveals that, at low FH20, the maxima in the electron and H(n=2) atom distributions occur in different spatial regions of the plume; direct analysis of the Stark broadening of the Balmer-β line would thus lead to an underestimate of the peak electron density. The present study highlights the necessity of careful intercomparisons between quantitative experimental data and model predictions in the development of a numerical treatment of the arc jet plasma. The kinetic scheme used here succeeds in describing many disparate observations—e.g., electron and H(n=2) number densities, spatial distributions of optical emission from the plume, the variation of these quantities with added flow of H2 and, when CH4 is added, absolute number densities and temperatures of radicals such as C2 and CH. The remaining limitations of the model are discussed. View full abstract»

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  • Parameters of the plasma produced at the surface of a ferroelectric cathode by different driving pulses

    Page(s): 113307 - 113307-13
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    Spectroscopic investigations of the properties of a plasma produced by a ferroelectric-plasma source are presented. The electron plasma density, the electron and ion temperature, and the density of desorbed neutrals near the ferroelectric surface are determined from spectral line intensities and profiles. Three different methods of surface plasma formation are analyzed using a simplified model for the plasma production. The model predicts the total amount of charge in the plasma to be proportional to the dielectric constant of the ferroelectric material. Also, the model shows a strong dependence of the plasma parameters on the resistivity of the plasma transition layer. A maximal plasma density of ∼1015 cm-3 is achieved when the electrons that were attached by the driving field to the ferroelectric surface are released from the surface owing to driving pulse sharp decay and ionized heavy atoms desorbed from the ferroelectric. View full abstract»

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  • White organic light-emitting devices with CdSe/ZnS quantum dots as a red emitter

    Page(s): 113501 - 113501-4
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    White hybrid organic/inorganic light-emitting devices (LEDs) have been fabricated by using stable red-emitting CdSe/ZnS core-shell quantum dots (QDs) covered with a trioctylphosphine oxide organic ligand. The device-active structure consists in a host/guest system with a blue-emitting poly[(9,9-dihexyloxyfluoren-2,7-diyl)-alt-co-(2-methoxy-5-{2-ethylhexyloxy}phenylen-1,4-diyl)] (PFH-MEH) polymer doped with red-emitting QDs and a green emitting metal chelate complex Alq3, with improved electron injection and transfer properties. A fairly pure white OLED with Commission Internationale de l’Eclairage coordinates of (0.30,0.33) is fabricated by accurate control of the Förster energy and charge-transfer mechanisms between the different device constituents obtained by tuning the concentration ratio of the QDs/PFH-MEH blend. In particular, charge-transfer processes to CdSe/ZnS core-shell quantum dots are found to be the key element for well-balanced white emission. Maximum external quantum efficiency up to 0.24% at 1 mA cm-2 and 11 V in air atmosphere are reported, showing that hybrid LEDs can be a promising route towards more stable and efficient light-emitting devices for lighting applications. View full abstract»

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  • Vibrational spectroscopy study of Ar+-ion irradiated Si-rich oxide films grown by plasma-enhanced chemical vapor deposition

    Page(s): 113502 - 113502-11
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    SiOx thin films with different stoichiometry degree were obtained by plasma-enhanced chemical vapor deposition on crystalline silicon substrates from SiH4 and N2O gas mixtures. Two twin sets of samples were irradiated by 380 keV Ar+ ions at a fluence of 5×1016 ions/cm2 at room temperature and at 500 °C, respectively, and then annealed in vacuum at different temperatures, between 500 and 1100 °C. A set of unirradiated samples has been annealed in the same conditions in order to discriminate the contribution of ion irradiation and of thermal treatments to the changes of the film microstructure. The structural modification of the oxide network and the growth of Si nanoclusters have been studied by vibrational spectroscopy techniques. Fourier transform infrared absorption spectra evidenced that ion irradiation induces a hydrogen loss of about 50%, and that postirradiation thermal treatments lead to the recovery of the irradiation defects and to the out diffusion of the residual hydrogen. After heating at 800 °C, irradiated and unirradiated samples exhibit substantially the same structure from the point of view of infrared-absorption spectra. In the meanwhile, the Si–O–Si stretching peak blue shifts, but never reaches the wavenumber value of pure silica owing to the presence of nitrogen into the network. Raman spectra of as-irradiated films reveal the presence of an amorphous silicon phase within the damaged layer of the oxide matrix. Raman spectra of irradiated samples undergoing thermal treatments at high temperature indicate a rearrangement of the film microstructure with the progressive clustering of the amorphous silicon phase. Howeve- r, no clear spectroscopic evidence is gained about the crystallization of silicon nanoclusters, even after annealing at the highest temperature. In fact, the Raman scattering from silicon nanocrystals is partially hidden by the Raman peak of the c-Si substrate. View full abstract»

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  • A physically based lifetime model for stress-induced voiding in interconnects

    Page(s): 113503 - 113503-6
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    We use a simple closed-form lifetime model for stress-induced voiding (SIV) or stress migration for Al- or Cu-based interconnects. Stress-induced voiding is treated as a process of void nucleation/growth and stress relaxation through atomic diffusion driven by a stress gradient. We developed a physically based method of modeling atomic diffusion and void growth, which explicitly accounts for the dependence of void growth on several factors including stress, temperature, diffusivity, and effective modulus. Based on basic physics associated with void growth, we define zones as SIV plate, SIV long line, and SIV short line, respectively, i.e., the three sequential stages for the process of void growth, depending on a nondimensional time-dependent parameter ψ and the aspect ratio of the interconnect. Simple form solutions to the governing equations that describe void growth are then sought for each scenario separately. Time to failure (TTF) is calculated as a function of stressing temperature, mechanical stress, interlayer dielectrics property, and line dimension based on an explicit formulation. The model provides insight into the separate impact of each input factor upon the SIV rate. We find that TTF is invariant with line width in the early zone (SIV plate), while void generation rate is linear with time. TTF is a strong function of line width for both the later zones. The void generation rate varies as the square root of time in the SIV long-line realm, but is constant with time in the SIV short-line zone. View full abstract»

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  • Skeletal silica characterization in porous-silica low-dielectric-constant films by infrared spectroscopic ellipsometry

    Page(s): 113504 - 113504-5
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    Porous-silica low-dielectric-constant (low-k) films were prepared using a sol-gel method based on the self-assembly of surfactant templates. No change in the refractive index at 633 nm nor in the infrared-absorption intensities of C–H and O–H stretching vibrations at around 2900 and 3400 cm-1 of porous-silica low-k films were observed after annealing at each temperature from 523 to 723 K. On the other hand, the Young’s elastic modulus and hardness increased with the increase of annealing temperature. The structure in the complex dielectric function of porous-silica low-k films observed in between 1000 and 1400 cm-1 is assigned as the asymmetric stretching vibration mode of the Si–O–Si bond. By applying the effective-medium theory by Bruggeman to the experimental results from infrared spectroscopic ellipsometry, we analyzed the skeletal silica structures. The peak positions of transverse TO) and longitudinal LO) vibration modes for Si–O–Si network in the silica skeleton of porous-silica films changed from 1061 to 1068 cm-1 and from 1219 to 1232 cm-1, respectively, with the annealing temperature. It is shown that the ωLO2TO2 of skeletal silica correlates with Young’s elastic modulus of porous-silica low-k films. View full abstract»

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  • Investigation of surface acoustic wave fields in silicon crystals by x-ray diffraction: A dynamical theory approach

    Page(s): 113505 - 113505-5
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    X-ray diffraction spectra at different x-ray energies from a Si crystal subjected to a deformation produced by surface acoustic wave propagation have been modeled using the general framework of dynamical diffraction theory. The simulations have been successfully compared with the corresponding experimental results confirming the accuracy of the elastic model describing the acoustic wave fields inside the crystal. View full abstract»

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  • Reduction of acoustic-phonon deformation potential in one-dimensional array of Si quantum dot interconnected with tunnel oxides

    Page(s): 113506 - 113506-6
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    The scattering potential for the acoustic deformation potential scattering in a one-dimensional silicon quantum dot array interconnected by thin oxide layers is theoretically investigated. One-dimensional phonon normal modes are numerically obtained using the linear atomic chain model. The strain caused by an acoustic-phonon vibration is absorbed by the oxide layers, resulting in the reduction of the strain in the Si dots. This effect eventually leads to ∼40% reduction of the scattering potential all over the structure. The amount of the reduction does not depend on the phonon energy, but rather on the ratio of the Si dot size to the oxide thickness. View full abstract»

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  • Atomic structure of Al88Y7Fe5 metallic glass

    Page(s): 113507 - 113507-8
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    The structure of Al88Y7Fe5 metallic glass has been investigated by differential scanning calorimetry, x-ray powder diffraction, and x-ray absorption fine structure (XAFS) techniques. The amorphous alloy crystallizes according to the following scheme: amorphous →α-Al+ residual amorphous →α-Al+Al3Y+AlFeY. The atomic structure of the amorphous alloy was modeled by reverse Monte Carlo methods. The resulting structure indicates that the prepeak (at 1.42 Å-1) in the static structure factor S(Q) is caused by contributions of distinct Y-Y, Y-Fe pairs. From the analysis of our XAFS spectra at the Fe and Y K edge the following characteristics of the local structure are found: The interatomic distance between Fe and coordinated Al atoms in the amorphous state is significantly (8.9%) shorter than the sum of the nominal metallic-state radii. The average coordination number is anomalously 36% reduced compared to the value derived from the dense-random-packing (DRP) model, using again the nominal metallic-state radii. On the other hand, the Y-Al distance as well as the number of Al atoms coordinating Y is close to the values predicted by the DRP model. These anomalous changes around the Fe atoms indicate a strong interaction between Fe and Al, which corroborate a covalent bonding. In connection with the values obtained from the XAFS data analysis, the effective atomic radii in the amorphous phase have been calculated. Consequently, applying them to the calculation of the atomic size factor (λ=0.1076) confirms that Al88Y7Fe5 follows the rule of atomic size ratio for glass formation. View full abstract»

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  • Production efficiency of thin metal flyers formed by laser ablation

    Page(s): 113508 - 113508-6
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    Thin metal plates (flyers) were launched from an aluminum-coated glass support using nanosecond and picosecond Nd: yttrium aluminum garnet laser pulses at 1.06 μm. The velocity of the flyers was measured as a function of incident fluence and of the delay between two consecutive laser pulses using a time-of-flight method. Profilometric scans of the craters formed on the substrate provided an accurate mapping of the crater’s morphology and enabled a realistic estimation of the flyer’s mass. The combination of these measurements allowed the determination of the flyer’s kinetic energy and hence the efficiency of the launching process as a function of the initiating laser’s energy. Threshold fluences of 1.3–2.0 J/cm2 and acceleration efficiencies up to 0.45 were measured under our experimental conditions. The results show that acceleration efficiency rises with the energy of initiating laser and drops when the delay time between two pulses of 10-ns full width at half maximum becomes larger. The acceleration efficiency is also reduced (relative to a 10-ns laser pulse) when the process is initiated by a single 20-ps pulse. On the basis of these data we assume that the launching efficiency may be optimized by using 2-ps laser pulses with a subnanosecond delay time between them. 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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P. James Viccaro
Argonne National Laboratory