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Journal of Applied Physics

Issue 3 • Date Aug 2005

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Displaying Results 1 - 25 of 132
  • Issue Cover

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

    Page(s): toc1
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  • Phase-matched generation of a terahertz surface wave by a subluminous optical strip

    Page(s): 033101 - 033101-7
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    We show that a weakly focused ultrashort laser pulse with tilted intensity front can efficiently excite a terahertz surface wave via phase-matched optical rectification at the surface of a semiconductor. The surface wave is excited by a strip of nonlinear polarization moving along the semiconductor surface with subluminous velocity. The amplitude and power of the radiated surface wave are calculated. For a 90-fs optical pulse with a peak intensity of 2 GW/cm2, we estimate the energy conversion coefficient to be 10-7 at the surface of GaAs. The direct excitation of surface waves at terahertz frequencies can be particularly attractive for terahertz spectroscopy of semiconductor surfaces. View full abstract»

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  • Displacement sensing using evanescent tunneling between guided resonances in photonic crystal slabs

    Page(s): 033102 - 033102-4
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    Using both analytic theory and first-principles finite-difference time-domain simulations, we introduce a displacement sensing mechanism using photonic crystal slabs coupled in the near-field regime. In this regime, the operating characteristics are completely different from conventional resonant optical sensors, and high sensitivity can be obtained without the use of highly reflecting mirrors. This enables high displacement sensitivity combined with low sensitivity to wavelength and to structural disorders, thereby simplifying operation and fabrication of high-sensitivity displacement sensors. View full abstract»

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  • On the resonances and polarizabilities of split ring resonators

    Page(s): 033103 - 033103-9
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    In this paper, the behavior at resonance of split ring resonators (SRRs) and other related topologies, such as the nonbianisotropic SRR and the broadside-coupled SRR, are studied. It is shown that these structures exhibit a fundamental resonant mode (the quasistatic resonance) and other higher-order modes which are related to dynamic processes. The excitation of these modes by means of a properly polarized time varying magnetic and/or electric fields is discussed on the basis of resonator symmetries. To verify the electromagnetic properties of these resonators, simulations based on resonance excitation by nonuniform and uniform external fields have been performed. Inspection of the currents at resonances, inferred from particle symmetries and full-wave electromagnetic simulations, allows us to predict the first-order dipolar moments induced at the different resonators and to develop a classification of the resonances based on this concept. The experimental data, obtained in SRR-loaded waveguides, are in agreement with the theory and point out the rich phenomenology associated with these planar resonant structures. View full abstract»

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  • Ultrasound generated by a femtosecond and a picosecond laser pulse near the ablation threshold

    Page(s): 033104 - 033104-7
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    We have investigated high-frequency ultrasound generated by single laser pulses in thin (50 μm) aluminum foils as a function of the laser fluence. Laser-pulse durations of 80 fs and 270 ps were used to compare the ultrasound generated in two very different regimes: thermoelastic and ablation. The measured rear-surface displacement induced by the ultrasound pulse is similar after 50-μm propagation through the foils for the two laser-pulse durations in the fluence range of 0.1–0.7 J/cm2. For fluences greater than the ablation threshold (0.25 and 0.63 J/cm2 for the 80-fs and 270-ps pulses, respectively), the ultrasound amplitude generated by the 270-ps laser pulse is increased significantly due to absorption of laser energy by the ablating plasma. This is not observed for the 80-fs laser pulse since ablation is produced well after the laser-pulse irradiation of the target. The measured surface displacement as a function of laser fluence is compared to the calculations of a one-dimensional fluid code for both laser-pulse durations. The model calculations agree in many ways with the experimental results, but some discrepancies are observed. View full abstract»

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  • Microwave diagnostics of small plasma objects

    Page(s): 033301 - 033301-3
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    We suggest an approach for using microwave radiation in collisional, weakly ionized plasma diagnostics when plasma dimensions are relatively small compared with the microwave wavelength. We show that in this case the microwave diagnostics can be based on the measurement of the radiation scattered by an oscillating plasma dipole, similar to the Rayleigh scattering of an atom in light. Examples considered show possibilities of obtaining the decaying plasma parameters (time dependence of charge density and information about loss rates, for instance) from the measured scattered signal. View full abstract»

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  • Double-pulse machining as a technique for the enhancement of material removal rates in laser machining of metals

    Page(s): 033302 - 033302-6
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    Several nanosecond 0.53-μm laser pulses separated by several tens of nanoseconds have been shown to significantly enhance (three to ten times) material removal rates while minimizing redeposition and heat-affected zones. Economic, high-quality, high-aspect ratio holes (≫10:1) in metals are produced as a result. A phenomenological model whereby the second laser pulse interacts with the ejecta produced by the first laser pulse and in close proximity to the material surface is consistent with the observations. Incident laser wavelengths of 1.05 and 0.35 μm also benefit from this pulse format. View full abstract»

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  • Study of the sputtered Cu atoms and Cu+ ions in a hollow cathode glow discharge using a hybrid model

    Page(s): 033303 - 033303-11
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    The role of the Cu atoms sputtered from the cathode material in a cylindrical hollow cathode discharge (HCD) and the corresponding Cu+ ions are studied with a self-consistent model based on the principle of Monte Carlo (MC) and fluid simulations. In order to obtain a more realistic view of the discharge processes, this model is coupled with other submodels, which describe the behavior of electrons, fast Ar atoms, Ar+ ions, and Ar metastable atoms, also based on the principles of MC and fluid simulations. Typical results are, among others, the thermalization profile of the Cu atoms, the fast Cu atom, the thermal Cu atom and Cu+ ion fluxes and densities, and the energy distribution of the Cu+ ions. It was found that the contribution of the Ar+ ions to the sputtering was the most significant, followed by the fast Ar atoms. At the cathode bottom, there was no net sputtered flux but a net amount of redeposition. Throughout the discharge volume, at all the conditions investigated, the largest concentration of Cu atoms was found in the lower half of the HCD, close to the bottom. Penning ionization was found the main ionization mechanism for the Cu atoms. The ionization degree of copper atoms was found to be in the same order as for the argon atoms (10-4). View full abstract»

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  • Polarization-resolved measurements of picosecond laser-ablated plumes

    Page(s): 033304 - 033304-5
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    We discuss the ablation of aluminum plasma using picosecond pulsed laser in vacuum and in ambient atmosphere of nitrogen. The plume dynamics of picosecond and nanosecond laser-ablated plumes in ambient atmosphere is discussed. The degree of polarization is measured using optical emission spectroscopy for the Al III transition 4s 2S1/2-4p 2P3/2o at 569.6 nm. Strong anisotropy is observed using picosecond laser pulse as compared to nanosecond laser pulse. View full abstract»

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  • Improved quality factors of magneto-optical imaging calculated for heteroepitaxial iron garnet multilayers

    Page(s): 033501 - 033501-4
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    We suggest to modify the usual iron garnet sensor film for magneto-optical imaging by introducing a Bragg mirror consisting of heteroepitaxial garnet layers between the substrate and sensor film. For the example situation of a hexagonal vortex lattice in a type II superconductor, we show by calculation that the quality factors of image contrast and optical efficiency can be higher for the proposed heteroepitaxial garnet multilayers than for the single-layer garnet films currently in use as sensor films. View full abstract»

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  • Size and emission wavelength control of InAs/InP quantum wires

    Page(s): 033502 - 033502-5
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    For a certain heteroepitaxial system, the optical properties of self-assembled nanostructures basically depend on their size. In this work, we have studied different ways to modify the height of InAs/InP quantum wires (QWrs) in order to change the photoluminescence emission wavelength. One procedure consists of changing the QWr size by varying the amount of InAs deposited. The other two methods explored rely on the control of As/P exchange process, in one case during growth of InAs on InP for QWr formation and in the other case during growth of InP on InAs for QWr capping. The combination of the three approaches provides a fine tuning of QWr emission wavelength between 1.2 and 1.9 μm at room temperature. View full abstract»

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  • Nucleation of pores in brittle solids under load

    Page(s): 033503 - 033503-12
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    The microscopic mechanism of appearance and evolution of pores and cracks is proposed to investigate the process of micropore nucleation in solids under impact and fixed loadings. The size distribution function and the critical size of pores are defined. The dependencies between the rate of pore nucleation and the rate of pore accumulation in solids under loading are specified. The temperature influence on the pore appearance process is examined. View full abstract»

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  • The mechanism of linear and nonlinear optical effects in fluoride crystals

    Page(s): 033504 - 033504-7
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    Electronic structure calculations of Na2SbF5, BaMgF4, and BaZnF4 are performed from first principles based on a plane-wave pseudopotential method. The linear optical properties and the static second-harmonic generation coefficients are also calculated. Furthermore, a real-space atom-cutting method is employed to analyze the respective contributions of the anionic groups and cations in Na2SbF5 to the optical response. The results show that the anionic groups (SbF5)2- in the crystal are quite favorable for producing larger microscopic second-order susceptibilities. View full abstract»

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  • Indentation stress dependence of the temperature range of microscopic superelastic behavior of nickel-titanium thin films

    Page(s): 033505 - 033505-4
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    The microscopic superelastic behavior of thin-film NiTi is investigated by instrumented indentation experiments conducted at different temperatures. The indentation-induced superelastic effect is found to be persistent to about 100 K above the austenite transformation finish temperature (Af). In contrast, the upper temperature where superelastic effect exists is only around Af plus 40 K in uniaxial tension and compression tests, beyond which the plasticity of the austenite phase overwhelms the transformation-induced superelasticity. By combining the Clausius-Clapeyron equation and spherical cavity model for indentation, we show that the high hydrostatic pressure under the indenter is capable of elevating the transformation temperatures and increase the upper temperature limit of indentation-induced superelastic behavior. View full abstract»

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  • ZrO2 film interfaces with Si and SiO2

    Page(s): 033506 - 033506-6
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    The interface formed by the thermal oxidation of sputter-deposited Zr metal onto Si(100)- and SiO2-coated Si(100) wafers was studied in situ and in real time using spectroscopic ellipsometry (SE) in the 1.5–4.5 photon energy range and mass spectrometry of recoiled ions (MSRI). SE yielded optical properties for the film and interface and MSRI yielded film and interface composition. An optical model was developed and verified using transmission electron microscopy. Interfacial reaction of the ZrO2 was observed for both substrates, with more interaction for Si substrates. Equivalent oxide thicknesses and interface trap levels were determined on capacitors with lower trap levels found on samples with a thicker SiO2 underlayer. In addition to the optical properties for the intermixed interface layer, the optical properties for Zr metal and unreacted ZrO2 are also reported. View full abstract»

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  • Phase-separated Al–Si thin films

    Page(s): 033507 - 033507-7
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    Phase-separated Al–Si films composed of Al nanocylinders embedded in an amorphous-Si matrix have been prepared by a sputtering method. By controlling the deposition rate, substrate temperature, and film composition, the average diameter of the Al cylinders can be varied systematically from less than 5 to 13 nm with a cylinder density ranging from 1015 to in excess of 1016 cylinders m-2. A three-dimensional simulation of phase separation in binary thin films was performed using a modified Cahn-Hilliard [J. Chem. Phys. 28, 258 (1958)] equation to understand the growth mechanism. The simulation studies indicate that the surface diffusion length and film composition are important factors which determine film morphology. Experimental and simulation studies are compared and discussed. View full abstract»

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  • Donor-acceptor pair emission enhancement in mass-transport-grown GaN

    Page(s): 033508 - 033508-8
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    A dominating donor-acceptor pair (DAP) emission at about 3.27 eV is observed in the photoluminescence and cathodoluminescence spectra of intentionally undoped mass-transport (MT)-grown GaN, while only a weak presence of the DAP emission is recorded in the as-grown hydride vapor phase epitaxial GaN. A comparative study of impurity and native defect incorporation in the as-grown and MT GaN was performed, showing a significant increase of oxygen and empty clusters involving Ga vacancy and oxygen in the MT GaN. Based on the observed results as well as on doping analysis of the structure and kinetic analysis of the emission intensities, we propose an acceptorlike complex, creating a state as a semiclassical potential well near the valence-band top due to the local tensile strain caused by the empty clusters to be responsible for the dominating behavior of the DAP emission. View full abstract»

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  • Structural aspects of synthetic zeolite: A comparative assay through positron annihilation and gas adsorption methods

    Page(s): 033509 - 033509-7
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    Structural arrangement in alumino-silicate compounds (synthetic zeolite species), which encompasses large cavities and channels, have been discussed on the basis of their molecular organization and is further illustrated with the help of micrographs as perceived through transmission electron microscopic studies. The crystallinity aspects and structural defects were investigated through line broadening in x-ray diffraction and the grain sizes through the Debye-Scherrer method. Further, assays of the void size (micro- as well as mesopores) have been performed through positronium annihilation lifetime spectroscopy (PALS) and Brunauer-Emmett-Teller adsorption-desorption isotherm and compared. Despite of some of the limitations of the latter, the final results are in close agreement. The utility of PALS as a microprobe is illustrated through our models. Finally, it has been justified that PALS not only probes the subnanometer micropore sizes efficiently but it also senses the mesopores. View full abstract»

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  • Resonant excitation of plasma oscillations in a partially gated two-dimensional electron layer

    Page(s): 033510 - 033510-7
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    We have solved the problem of diffraction of terahertz radiation on a perfectly conductive gate strip that partially screens a two-dimensional (2D) electron layer located at some distance from the gate. Scattering and absorption spectra of such a structure reveal the fundamental plasma resonance excited under the gate. We have shown that the absorption enhancement factor at plasma resonance may reach very high values (up to 60). However, for narrow gate strips (with the width less than 100 nm) the resonant scattering length of such a scatterer is shorter than its resonant absorption length by four orders of magnitude, which means that the gated plasmons in this case weakly couple to the terahertz radiation. We discuss the effects of interaction between plasma oscillations in gated and ungated regions of 2D electron layer and provide a qualitative explanation of the rather intensive terahertz emission from unstable gated plasmons in a 60-nm gate field-effect transistor observed recently. View full abstract»

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  • The lower boundary of the hydrogen concentration required for enhancing oxygen diffusion and thermal donor formation in Czochralski silicon

    Page(s): 033511 - 033511-4
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    Hydrogen-enhanced thermal donor formation is achieved in p-type Czochralski silicon after exposure to hydrogen plasma and posthydrogenation annealing. Hydrogen diffusivities for the temperatures between 350 and 450 °C are determined based on spreading resistance probe measurement. The hydrogen diffusion is found to be trap limited. Two relationships (for different temperature ranges) are established to describe the lower boundary of the hydrogen concentration required for enhancing oxygen diffusion and thermal donor formation in silicon. The result reveals that hydrogen atoms both in free and in trapped states can enhance the oxygen diffusion. View full abstract»

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  • Growth and characterization of Si1-xMnx alloys on Si(100)

    Page(s): 033512 - 033512-6
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    Si1-xMnx alloy films of 50 nm thickness with 0.005≤x≤0.035 were grown by low-temperature molecular-beam epitaxy onto Si(100) substrates held at temperatures T in the range of 150 °C≤T≤350 °C. All films exhibit surface roughness with ∼20-nm-lateral and ∼1-nm-vertical length scales. This roughness is random for films with small x grown at the lower end of the temperature range. Films with larger x grown at higher T exhibit roughness organized into <110>-oriented cluster arrays centered on shallow surface depressions. This organized roughness correlates with the formation of subsurface complexes of four {111} planar defects or “funnel” defects. Mn-rich, nanometer-sized nodules form near the bottom of the Si1-xMnx film and seed the formation of vertical, amorphous nanopipes. For growth of small x films at the lower end of the temperature range, these vertical nanopipes extend to the surface. In contrast, films with larger x grown at higher T form funnel defects which appear to emanate from the vertical nanopipes. Regardless of growth conditions, the Mn-rich nodules appear crystalline and do not correlate to any known Si–Mn phase. Ion channeling indicates that up to 90% of the Mn is substitutionally incorporated for samples with x=0.005. Although the substitutional fraction decreases with increasing x, the substitutional content increases. Our results indicate that Mn may be substitutionally incorp- orated in epitaxial thin films at concentrations of several orders of magnitude greater than its equilibrium solubility. View full abstract»

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  • Lattice vibrations and phase-transition soft mode in near stoichiometric lithium niobate crystals

    Page(s): 033513 - 033513-6
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    At room temperature, Raman-scattering investigations of near stoichiometric lithium niobate (S-LN) crystals theoretically and experimentally reveal an effect of the lattice vacant positions on the Raman spectra. At high temperature, Raman peaks of the mode ν5 vary sensitively and intensely with the increase of the temperature. A condensed soft optical-phonon mode originates from the triply degenerate symmetric in-plane O–Nb–O bending. The paraelectric-ferroelectric structural transition occurs at about 1170 °C. The composition homogeneity and optical uniformity of the S-LN crystals are demonstrated to be excellent compared with those of the congruent lithium niobate. View full abstract»

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  • Angle dependence of acoustic phonon-assisted tunneling in a weakly coupled superlattice: Evidence for terahertz phonon amplification

    Page(s): 033514 - 033514-5
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    We investigate nonequilibrium acoustic phonon-assisted tunneling in a weakly coupled GaAs/AlAs superlattice (SL). Previously it had been predicted that, in such structures, the conditions for terahertz acoustic phonon amplification can be achieved [B. A. Glavin, V. A. Kochelap, and T. L. Linnik, Appl. Phys. Lett. 74, 3525 (1999)]. We present experimental measurements of the change in current ΔI due to an incident nonequilibrium phonon pulse generated by thermalizing a laser pulse in a metal film. In particular, we measure the dependence on the angle of incidence θ of the phonons relative to the SL growth direction. The results are compared with numerical calculations made using the two-well model. It is found that good agreement between the measurements and calculations can be obtained for all θ if we assume that amplification is occurring for phonons propagating in a direction near θ=0. Due to the amplification of phonons with energy ħωq>~Δ, where Δ is the energy drop per period of the SL, the nonequilibrium phonon distribution in the vicinity of the SL is different from the expected Planck spectrum of the phonon source. We show that this can explain the experimental measurements of ΔI at θ=0. We present these results as evidence for phonon amplification in the 400-GHz–1-THz frequency range. View full abstract»

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  • TmZn: A possible regenerator material for low-temperature cryocoolers

    Page(s): 033515 - 033515-7
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    The intermetallic compound TmZn has two low-temperature magnetic phase transitions and is a potential regenerator material. Application of a magnetic field to regulate the phase-transition temperature by influencing the specific heat cp(T) dependence in TmZn was investigated. The low-temperature heat capacity of a monocrystalline TmZn sample was measured as a function of magnetic field (up to 30 kOe). The anisotropy of the transition temperature in the applied magnetic field was modeled using ac susceptibility measurements. From the measured values, the TmZn regenerator specific heat was calculated taking into account both the temperature regulation and the anisotropy. A numerical simulation study of the TmZn regenerator was made. The results show an improvement in TmZn regenerator performance by the application of a magnetic field and employment of the transition anisotropy. The minimal cold chamber temperature was lowered from 11.76 to 9.77 K by the application of a magnetic field of 30 kOe. The performance of the TmZn regenerator is compared with the existing regenerator materials, Er3Ni, Pb, HoCu2, and Er50Pr50. 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