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Applied Physics Letters

Issue 11 • Date Sep 2003

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Displaying Results 1 - 25 of 71
  • Issue Cover

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

    Page(s): toc1
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  • Submicron diamond-lattice photonic crystals produced by two-photon laser nanofabrication

    Page(s): 2091 - 2093
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    Diamond-lattice photonic crystal structures consisting of around 500-nm-diameter 〈111〉 rods and 580-nm-diameter photonic atoms were realized by two-photon photopolymerization. In the course of laser nanofabrication, it was found that the surface quality of elements depended on the crystal geometry, which was then interpreted as voxel floating effect arising from insufficient overlapping degree of voxels. With the solution of this issue, nearly perfect photonic lattices were obtained, from which single-period power rejection of approximately 35% was achieved. This work is an important step toward arbitrarily tailoring the density of photon states of photonic crystals according to end use by engineering cavity or crystalline geometry. © 2003 American Institute of Physics. View full abstract»

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  • Enhanced blue emission from Tm-doped AlxGa1-xN electroluminescent thin films

    Page(s): 2094 - 2096
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    Electroluminescent (EL) emission from Tm-doped AlxGa1-xN (AlxGa1-xN:Tm) has been observed with various Al compositions (0≤x≤1). AlxGa1-xN:Tm thin films were grown by molecular beam epitaxy with in situ doping of Tm. At lower Al composition (x≪0.15), blue emission at 478 nm dominates, corresponding to the Tm 1G43H6 transition. For x≫0.15, however, a second blue emission peak was observed at 465 nm, becoming dominant with increasing Al composition. The 465 nm emission is attributed to the higher level Tm transition 1D23F4, which was not observed in GaN:Tm. Blue EL emission from Tm was enhanced with Al content in the films. The ratio of EL intensity at blue (465 nm plus 478 nm) to infrared (801 nm) wavelengths increased monotonically with Al composition, from ∼2 for GaN:Tm to ∼30 for AlN:Tm. © 2003 American Institute of Physics. View full abstract»

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  • Ultraviolet light selective photodiode based on an organic–inorganic heterostructure

    Page(s): 2097 - 2099
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    We show a perfect ultraviolet (UV) light selective and sensitive photovoltaic cell easily fabricated. The device consists of a water-soluble p-type semiconducting polymer PEDOT-PSS: poly(3,4-ethylenedioxythiophene) doped by poly(4-styrenesulfonate) film deposited on a Nb-doped titanium oxide (SrTiO3:Nb) substrate. For the PEDOT-PSS/SrTiO3:Nb heterostructure, the photosensitivity at zero bias for the UV light with L=1 mW/cm2 is estimated to be 0.05 A/W, corresponding to a quantum yield of 16% electron/photon. This device is only activated in the UV region (λ≪390 nm), and then, it exhibits a large response to the UV–B light (290–320 nm). © 2003 American Institute of Physics. View full abstract»

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  • Distribution of density of photonic states in amorphous photonic materials

    Page(s): 2100 - 2102
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    The density of states (DOS) and local density of states (LDOS) for an amorphous photonic material (APM) with a finite size and constructed by hexagonal basic cells are simulated. It is found that there is a frequency interval in which the total DOS is very small, i.e., a photonic gap exists. Near the gap-center frequency, the LDOS drops rapidly from the edge to the center area of the sample. However, at the gap-edge frequency, some discrete spots with high LDOS spread in the sample and corresponding electric field distributions show the occurrence of localized modes. This phenomenon can be attributed to the disordered distribution of the scatterers. © 2003 American Institute of Physics. View full abstract»

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  • Simultaneous production of spin-polarized ions/electrons based on two-photon ionization of laser-ablated metallic atoms

    Page(s): 2103 - 2105
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    We demonstrate the simultaneous production of spin-polarized ions/electrons using two-color, two-photon ionization of laser-ablated metallic atoms. Specifically, we have applied the developed technique to laser-ablated Sr atoms, and found that the electron-spin polarization of Sr+ ions, and accordingly, the spin polarization of photoelectrons is 64%±9%, which is in good agreement with the theoretical prediction we have recently reported [T. Nakajima and N. Yonekura, J. Chem. Phys. 117, 2112 (2002)]. Our experimental results open up a simple way toward the construction of a spin-polarized dual ion/electron source. © 2003 American Institute of Physics. View full abstract»

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  • Infrared passbands from fractal slit patterns on a metal plate

    Page(s): 2106 - 2108
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    We show that a fractal pattern of submicron wide slits, etched on a 0.1-μm-thick gold film, exhibit multiple pass and stop bands in the wavelength regime of 2–200 μm. In the midinfrared regime, the passbands show ∼36% transmission (three orders of magnitude higher than the reference), and the stop bands exhibit ∼80% reflection. In the far infrared regime, the passband transmittances are 25%, 29%, and 14%, respectively, at wavelengths of 34, 62, and 111 μm. These transmittances are rather high in view of the fact that supporting substrate is itself only about 40% transmitting, and a control pattern of holes with similar void-to-metal ratio is 3000 times less transmitting in all frequencies. We attribute the high transmittance from subwavelength slits to geometric resonances. © 2003 American Institute of Physics. View full abstract»

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  • Room-temperature type-II interband cascade lasers near 4.1 μm

    Page(s): 2109 - 2111
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    Operation of type-II interband cascade lasers has been demonstrated in pulsed mode at room temperatures at wavelengths near 4.1 μm. These lasers fabricated with 150 μm wide mesa stripes also operated in cw mode at temperatures up to 145 K. Threshold current densities as low as 9 A/cm2 and output powers exceeding 100 mW/f have been achieved in cw mode at 80 K. © 2003 American Institute of Physics. View full abstract»

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  • Experimental evidence of carrier leakage in InGaAsN quantum-well lasers

    Page(s): 2112 - 2114
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    Carrier leakage processes are shown experimentally as one of the factors contributing to the temperature sensitivity of InGaAsN quantum well lasers. The utilization of the direct barriers of GaAs0.85P0.15 instead of GaAs, surrounding the InGaAsN quantum-well (QW)-active region, leads to significant suppression of carrier leakage at elevated temperatures of 90–100 °C. Threshold current densities of only 390 and 440 A/cm2 was achieved for InGaAsN QW lasers (Lcav=2000 μm) with GaAs0.85P0.15-direct barriers at temperature of 80 and 90 °C, respectively. © 2003 American Institute of Physics. View full abstract»

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  • Ultrafast nonresonant third-order optical nonlinearity of fullerene-containing polyurethane films at telecommunication wavelengths

    Page(s): 2115 - 2117
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    High-optical-quality polyurethane films containing a high load of (60)fullerene (C60) were prepared by reaction of the hydroxy-containing C60 and triisocyanate with the goal of obtaining enhanced nonresonant third-order optical nonlinearity. Optical nonlinearity was measured using the Z-scan technique in the wavelength range 1150–1600 nm. This revealed a positive Kerr coefficient with nonresonant n2 equal to 2.0(±0.6)×10-3cm2/GW and excellent linear-absorption and nonlinear-absorption figures of merit at 1550 nm. The technique reported herein is a new approach to obtain fullerene films with the capacity to realize a high number density of C60 moieties. These resulted in more than 2 orders of enhancement in the third-order susceptibility over recently reported C60 sol and gel, and an enlarged second-order hyperpolarizability resulting from further enhanced charge transfer processes. © 2003 American Institute of Physics. View full abstract»

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  • Blue, surface-emitting, distributed feedback polyfluorene lasers

    Page(s): 2118 - 2120
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    We report the fabrication of optically-pumped solid-state distributed feedback lasers utilizing two blue-light-emitting semiconducting polyfluorenes as gain media. The lasers were readily fabricated by solution deposition of thin polymer films on top of gratings etched into fused silica substrates. A compact Nd:YVO4 microchip laser was used as the pump source for the two polymers studied, and lasing was achieved at 455 and 465 nm. Low threshold energies, ≥4 nJ per pulse, were obtained. The emission characteristics of the lasers are described along with the results of additional experiments that investigate in more detail the effect of the grating microstructure on polymer light emission. © 2003 American Institute of Physics. View full abstract»

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  • Room-temperature GaN vertical-cavity surface-emitting laser operation in an extended cavity scheme

    Page(s): 2121 - 2123
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    A GaN-based vertical-cavity surface-emitting laser (VCSEL) has been demonstrated in an extended cavity structure. A VCSEL device had a long extended cavity, which consisted of a sapphire substrate as well as a GaN epilayer and had an integrated microlens on one side. High-reflection dielectric mirrors were deposited on both sides of the laser cavity. The laser was optically pumped and operated at room temperature. The VCSEL device lased at a low threshold excitation intensity of 160 kW/cm2. In contrast to a conventional microcavity-VCSEL structure, the VCSEL operated in multiple longitudinal modes with mode spacing consistent with its physical thickness. © 2003 American Institute of Physics. View full abstract»

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  • Terahertz quantum-cascade laser at λ≈100 μm using metal waveguide for mode confinement

    Page(s): 2124 - 2126
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    We report lasing at ∼3.0 THz (λ≈98–102 μm) in a quantum-cascade structure in which mode confinement is provided by a double-sided metal waveguide. The depopulation mechanism is based on resonant phonon scattering, as in our previous work. Lasing takes place in pulsed mode up to a heat-sink temperature of 77 K. The waveguide consists of metallic films placed above and below the 10-μm-thick multiple-quantum-well gain region, which gives low losses and a modal confinement factor of nearly unity. Fabrication takes place via low-temperature metallic wafer bonding and subsequent substrate removal using selective etching. This type of waveguide is expected to be increasingly advantageous at even longer wavelengths. © 2003 American Institute of Physics. View full abstract»

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  • Subfemtosecond pulse generation by nonadiabatic molecular modulation

    Page(s): 2127 - 2129
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    We suggest a technique to generate subfemtosecond pulse train in a Raman generator driven by three sufficiently intense single-mode laser beams whose carrier frequencies are tuned off the Raman resonance with two different two-photon detunings. The Raman interaction establishes a molecular modulation through a nonadiabatic process. The simulation based on the first fundamental vibrational Raman transition of solid hydrogen indicates that subfemtosecond pulse train can be generated when the signs of the two-photon detunings are opposite. This opens an experimentally feasible way to observe enhanced generation of broadband Raman sidebands as well as compression of the phase-locked Raman sidebands into subfemtosecond pulse trains in the same Raman media with above- and below-resonance Raman excitations. © 2003 American Institute of Physics. View full abstract»

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  • Giant dielectric permittivity and electromechanical strain in thin film materials produced by pulsed-laser deposition

    Page(s): 2130 - 2132
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    Thin film materials with a giant dielectric permittivity εr≈10 000 and an electromechanical strain of Δh/h≈8% are produced by pulsed-laser deposition. Composite targets containing various different oxides such as BaTiO3, BaO2, BaCO3, and TiO2 powder embedded in the polymer polytetrafluoroethylen (PTFE) are employed for laser ablation. The dielectric permittivities of the films show strong relaxation at frequencies above 10 kHz, a pronounced dependence on layer thickness, and a frequency-dependent activation at lower temperatures. Composite targets as well as films produced from BaF2/PTFE targets show only low permittivities with εr≪20 and do not reveal such phenomena. © 2003 American Institute of Physics. View full abstract»

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  • Continuous-wave millimeter wave generation at 94 GHz in a lithium niobate nonlinear optical waveguide using modulated optical input

    Page(s): 2133 - 2135
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    Continuous-wave millimeter wave signals are generated at 94 GHz in a LiNbO3 nonlinear optical waveguide. Optical light with two frequency components is introduced into an optical waveguide, and the generated millimeter waves are obtained from a terminal connected to the metallic traveling waveguide. The configuration is made with a LiNbO3 commercial phase modulator. The generated signals have square-law characteristics between the output and the input power. Experimentally obtained results show that the probable candidate of this physical mechanism is difference frequency generation in nonlinear optical materials. © 2003 American Institute of Physics. View full abstract»

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  • Recording and readout mechanisms of super-resolution near-field structure disk with a silver oxide mask layer

    Page(s): 2136 - 2138
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    The chemical decomposition of AgOx sandwiched between two ZnS–SiO2 protective layers was an irreversible process. We confirmed that a hollow Ag cylinder, or ring, serving as an aperture, was formed and small Ag particles were precipitated in the center region during the recording process. The small aperture can significantly reduce the laser spot size during the readout process and the strong near-field interaction between precipitated Ag particles and subwavelength marks can effectively enhance the readout signal. That clarifies both the super-resolution effect and the near-field interaction in the super-resolution near-field structure disk. © 2003 American Institute of Physics. View full abstract»

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  • Two stage oxidation in epitaxial Ni (111)/GaN (0001) thin films

    Page(s): 2139 - 2141
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    We present the oxidation process of epitaxial Ni (111)/GaN (0001) thin films studied by in situ synchrotron x-ray scattering, scanning electron microscopy, and transmission electron microscopy. By monitoring the evolution of the Ni (111) Bragg reflection, we reveal that two distinct oxidation processes occur. Initially, a continuous NiO layer of about 50 Å thickness is formed on the surface of Ni. The planar oxide layer saturates immediately and passivates the film from further surface oxidation. From this stage, the oxidation proceeds by means of the growth of surface oxide islands. The Ni atoms diffuse out through the defect sites running vertically through the initial oxide layer to form the oxide islands. Voids are generated underneath the oxide layer in this process. The oxide in the second stage grows logarithmically in time with the activation energy of about 0.15 eV. © 2003 American Institute of Physics. View full abstract»

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  • Thermoelectric cooling at cryogenic temperatures

    Page(s): 2142 - 2144
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    Experimental results demonstrating Peltier cooling below 10 K are reported, using crystals of the thermoelectric cerium hexaboride (CeB6). Direct measurements of the Peltier cooling showed δT up to ∼0.2 K in magnitude at T∼4–5 K. All three kinetic parameters: resistivity (ρ), heat conductivity (k), and Seebeck coefficient (S), characterizing the thermoelectric figure of merit ZT=S2T/ρk, were measured, giving high-confidence results. © 2003 American Institute of Physics. View full abstract»

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  • Intense ultraviolet cathodoluminescence at 318 nm from Gd3+-doped AlN

    Page(s): 2145 - 2147
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    We present investigations of Gd-implanted aluminum nitride, studied with cathodoluminescence (CL) as well as time-resolved CL in the temperature range 12–300 K. Luminescence due to intra-4f electron transitions of Gd3+ is dominated by the 6P7/28S7/2 transition between the first excited state and the ground state of Gd3+ detected at around 318 nm. Time-resolved CL of the 6P7/2 level monitoring the 6P7/28S7/2 transition shows a temperature-dependent lifetime which decreases from 0.76 ms at 12 K to 0.69 ms at 300 K, in contrast to an increasing intensity of the 6P7/28S7/2 transition by a factor of more than 3.5 in the same temperature range. The decay is of the Inokuti–Hirayama-type indicating energy transfer between Gd3+ ions. Due to the overall weak splitting of the 6P7/2 and 8S7/2 multiplets phonon replica with energies of 100 and 588 cm-1 can be assigned. © 2003 American Institute of Physics. View full abstract»

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  • Monitoring the formation of Sb nanocrystals in SiO2 by grazing incidence x-ray techniques

    Page(s): 2148 - 2150
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    We investigate the formation, crystallinity, size, and depth distribution of Sb nanoclusters in thin SiO2 matrix by grazing incidence x-ray diffraction (GIXRD) and reflectivity (GIXRR). The complementarity of these two techniques reveals the formation of Sb nanocrystals after a rapid thermal treatment at 1000 °C and their depth distribution. The implantation profile is found to have its maximum centered in the middle of the SiO2 layer. After thermal treatment, the Sb atom redistribution, monitored by the variation in the electron density profile obtained by GIXRR, corresponds to the formation of metallic Sb nanoclusters, as confirmed by transmission electron microscopy (TEM) and GIXRD. The cluster distribution within the SiO2 layer presents a maximum at the center of the layer and their average diameter is 67±3 Å. The results are in agreement with TEM analyses. © 2003 American Institute of Physics. View full abstract»

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  • Evidence for energy coupling from the Si–D vibration mode to the Si–Si and Si–O vibration modes at the SiO2/Si interface

    Page(s): 2151 - 2153
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    In order to verify Van de Walle and Jackson’s theory on the isotope effect of the Si–H/D bonds resistant to hot-electron excitation [C. G. Van de Walle and W. B. Jackson, Appl. Phys. Lett., 69, 2441 (1996)], we measured the Si–H, Si–D, and other vibrational modes in the oxidized silicon wafers annealed in hydrogen and deuterium using Fourier-transform infrared (FTIR) spectrometry. Our FTIR data suggest that the frequency for the Si–D bending mode at the SiO2/Si interface is 490 cm-1. Our experimental data support Van de Walle and Jackson’s theory with some modification. Their theory is correct for the experiments of breaking Si–H/D bonds using scanning tunneling microscope where no oxide involves. In the SiO2/Si case, the de-excitation of the Si–D bond may be due to the energy coupling from the Si–D bending mode to two vibrational modes, i.e., Si–O TO mode and the Si–Si TO phonon mode. Van de Walle and Jackson only pointed out coupling to Si–Si TO phonon mode. The strongest coupling might happen between the Si–D mode and the Si–O TO mode. Therefore, the oxide may play a crucial role in energy dissipation of the Si–D bond in metal–oxide–semiconductor devices. © 2003 American Institute of Physics. View full abstract»

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  • Long-wavelength optical phonon properties of ternary MgZnO thin films

    Page(s): 2154 - 2156
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    Far-infrared (FIR) reflection measurements have been employed to study the long-wavelength optical phonon properties in cubic MgZnO thin films grown by reactive electron beam evaporation on sapphire substrates. The frequencies of the optical phonons with T2 symmetry are obtained by calculating the FIR reflection spectra using a multioscillator model and Kramers–Kronig dispersion analysis. The modified random-element-isodisplacement model has been used to analyze the long-wavelength optical mode behavior in both cubic and hexagonal MgZnO alloys. It is found that cubic MgZnO exhibits a two-mode behavior, while for hexagonal MgZnO, the E1 mode displays a two-mode behavior and the A1 mode a one-mode behavior. The effects of structural transition on the optical phonon frequency, optical mode behavior, and force constant have also been clearly revealed. © 2003 American Institute of Physics. View full abstract»

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  • Micropipe evolution in silicon carbide

    Page(s): 2157 - 2159
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    Micropipe bundling and twisting in SiC crystals was revealed using synchrotron x-ray phase sensitive radiography. The computer simulation of micropipe evolution during the crystal growth suggests that the bundled and twisted micropipes arise under the influence of stress fields from other neighboring micropipes. The annihilation of twisted dipoles is attributed to their transformation into semiloops. Reactions of micropipe coalescence lead to the generation of micropipes and/or the annihilation of initial micropipes, resulting in the decrease in their average density. © 2003 American Institute of Physics. View full abstract»

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Applied Physics Letters, published by the American Institute of Physics, features concise, up-to-date reports on significant new findings in applied physics.

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Nghi Q. Lam
Argonne National Laboratory