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Applied Physics Letters

Issue 13 • Date Sep 1999

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Displaying Results 1 - 25 of 59
  • Issue Cover

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

    Page(s): toc1
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  • A continuous-wave tunable solid-state blue laser based on intracavity sum-frequency mixing and pump-wavelength tuning

    Page(s): 1821 - 1823
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    We report on continuous-wave tunable blue-light generation from a Nd:Y3Al15O12 laser by intracavity sum-frequency mixing of its fundamental laser line at 946 nm with the pump light from a tunable Ti:sapphire laser by use of cadmium–mercury–thiocyanate nonlinear crystal. The tunable range of the blue light was 434.4–437.5 nm, and the maximum output power at 436 nm was measured to be 310 μW. © 1999 American Institute of Physics. View full abstract»

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  • Scanning near-field optical spectroscopy and imaging using nanofabricated probes

    Page(s): 1824 - 1826
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    We have designed and constructed a scanning near-field optical microscopy (SNOM) system which is based on batch-fabricated aperture probes fabricated using micromachining and direct-write electron-beam lithography. The aperture is situated at the hollow tip apex of a modified silicon nitride atomic force microscope (AFM) cantilever. The SNOM/AFM probes are used both for excitation and collection of luminescence due to their excellent optical efficiency. The integration of a cantilever with the aperture allows better control of the aperture–sample distance and also results in considerable simplification of the SNOM system. Using this system, we have obtained near-field luminescence spectra and imaging of GaAs/AlGaAs quantum wires and wells, and have demonstrated spectrally resolved luminescence imaging with a spatial resolution of ∼50 nm. © 1999 American Institute of Physics. View full abstract»

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  • Blue-green variable light-emitting diode based on organic–molecule-doped polymer

    Page(s): 1827 - 1829
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    Monolayer organic light-emitting diodes based on the organic molecule [(3,4-dimethoxybenzyldehycle-2-hydroxy naphthylimine)dimethyl gallium]-doped [poly(2-mehtyoxy-5-ethyloxy)-4-di-(2-methyoxy-5-octaoxy)phenylene vinylene] have been fabricated by a spin-coating method. Color variation from green to blue has been observed. The results have been attributed to the variation of the recombination zone and the charge transfer between the materials. © 1999 American Institute of Physics. View full abstract»

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  • Raman scattering enhancement in porous silicon microcavity

    Page(s): 1830 - 1832
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    We have measured an enhancement factor of Raman signal up to 30 times using a Fabry-Pérot structure made of porous silicon (PS) layers of different porosity. The obtained enhancement was due to the coupling of the laser radiation and Stokes photons of porous silicon with the microcavity mode at the optimal laser beam incidence and scattering angles. Our results provide a way to increase the sensitivity of Raman spectroscopy for studying the species inside porous silicon which can considerably influence the properties of this material and hence of PS based devices. © 1999 American Institute of Physics. View full abstract»

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  • Upconversion luminescence of Er-implanted GaN films by focused-ion-beam direct write

    Page(s): 1833 - 1835
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    Upconversion luminescence has been obtained from Er-implanted GaN films by focused-ion-beam (FIB) direct write. FIB implantation was performed on GaN films grown by molecular beam epitaxy, hydride vapor phase epitaxy, and metalorganic chemical vapor deposition. After implantation, the GaN samples were annealed at 1100 °C for 1 h in various ambients (Ar, N2, and O2). Strong green upconversion was observed at 523 and 546 nm under red (840 nm) and infrared (1.0 μm) excitation. Upconversion intensity was measured for Er doses ranging from 4.3×1012 to 2.4×1016atoms/cm2. Maximum upconversion intensity at 546 nm was observed at a dose of 1–2×1015atoms/cm2, which corresponds to an atomic percentage of 0.3%–0.6%. © 1999 American Institute of Physics. View full abstract»

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  • Selective electroluminescence from a single stack of sidewall quantum wires on patterned GaAs (311)A substrates

    Page(s): 1836 - 1838
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    A p-i-n light-emitting diode (LED) with a single stack of sidewall quantum wires in the center of the intrinsic region has been fabricated by molecular-beam epitaxy on patterned GaAs (311)A substrates with all-Si n- and p-type doping. For small injection currents, the electroluminescence (EL) measured at low temperatures solely originates from the quantum wires without emission from the surrounding quantum wells within the patterned LED of 220 μm diameter. The selectivity of the EL emission is gradually reduced with increasing temperature, but the emission intensity per unit area in the wire regions is still two orders of magnitude larger than that in the well regions at room temperature. A model based on the lateral diffusion of injected electrons and holes is proposed to explain the selective carrier injection into the quantum wires. © 1999 American Institute of Physics. View full abstract»

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  • Effects of broad-waveguide structure in 0.8 μm high-power InGaAsP/InGaP/AlGaAs lasers

    Page(s): 1839 - 1841
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    Systematic study on the effects of the waveguide thickness Wg has been carried out for 200-μm-wide stripe separate-confinement-heterostructure lasers in the range of Wg=0.22–1.2 μm while the width of single quantum well is kept constant at 10 nm. The internal loss αi is reduced from 1.7 to 1 cm-1 when Wg is increased from 0.22 to 1.2 μm. It is shown that αi is not determined by the free-carrier absorption of clad layers, but primarily by Γ, the optical confinement factor, most probably due to scattering at the quantum well/waveguide interfaces. The external differential quantum efficiency ηd monotonically increases with Wg for pulsed operation. By contrast, ηd is maximum at Wg=0.8 μm for continuous-wave (cw) operation. Both the threshold carrier density and the threshold temperature sensitivity increases with Wg for Wg≥0.8 μm, which decreases ηd in cw operation. When 200-μm-wide devices (20%/97% coated) were life tested at 2 W and 30 °C, the median degradation rate shows a minimal value of 3×10-6h-1 at Wg=0.8 μm, which is 7 times smaller than that at Wg=0.22 μm. The facet temperature measured by the modulation reflectance is also minimized at Wg=0.8 μm. In broad-waveguide lasers with increasing Wg, the increase in carrier overflow competes with the reduction of optical power density, and thus self-absorption in the quantum well, which determine- - s the optimal Wg. © 1999 American Institute of Physics. View full abstract»

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  • Diameter modification of silicon nanowires by ambient gas

    Page(s): 1842 - 1844
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    Si nanowires (SINWs) with different diameters have been synthesized by laser ablation in different ambient gases. SINWs with the diameter distribution peaks at ∼13.2 and ∼9.5 nm have been obtained respectively in He and Ar (5% H2). SINWs produced in N2 had the smallest peak diameter at 6 nm, and are mixed in with some spherical particles with diameters ranging from ∼9 nm to several hundreds nm. Elements from the ambient gas were not detected in the SINWs. SINWs produced in Ar(5% H2) and N2 atmospheres exhibited photoluminescence and spectral blue-shift with diameter reduction, which are attributable to two-dimensional quantum confinement effects in crystalline nanowires. © 1999 American Institute of Physics. View full abstract»

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  • Third-order nonlinear optical properties of didodecyldimethylammonium–Au(dmit)2

    Page(s): 1845 - 1847
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    The third-order optical nonlinearity of metal(dmit)2 was investigated with femtosecond optical Kerr effect at 830 nm wavelength. The nonresonant second-order hyperpolarizability for the didodecyldimethylammonium–Au(dmit)2 (2C12–Au) molecule was estimated to be as large as 2.2×10-32esu. © 1999 American Institute of Physics. View full abstract»

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  • Band gap and wave guiding effect in a quasiperiodic photonic crystal

    Page(s): 1848 - 1850
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    A two-dimensional octagonal quasiperiodic photonic crystal composed of alumina cylinders is prepared. The transmission spectra of the quasicrystal are measured in the microwave region for the TM wave. We find that the position and width of the band gap do not depend on the incident direction, while the band structure can appear for quite a small piece of the quasicrystal. Two types of waveguide, a straight guide and a bending guide with two sharp 90° corners, are fabricated by removing three rows of cylinders. The measured transmittances show that the guiding efficiency for both waveguides is high. © 1999 American Institute of Physics. View full abstract»

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  • The interplay of sputtering and oxidation during plasma diffusion treatment

    Page(s): 1851 - 1853
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    Metals that form dense native surface oxide layers challenge plasma diffusion treatment techniques. Experimental results obtained during nitriding of stainless steel from real-time depth-resolved compositional analysis by elastic recoil detection give insight into the transport kinetics. In agreement with semiquantitative considerations on the oxide removal and the oxide growth, the interplay of sputtering and oxidation emerges as a key parameter. On this background, suggestions for practical applications and optimization of the modification processes are given for different plasma diffusion treatment techniques. © 1999 American Institute of Physics. View full abstract»

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  • Thermal and electrical transport properties of the single-phase quasicrystalline material: Al70.8Pd20.9Mn8.3

    Page(s): 1854 - 1856
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    The electrical and thermal transport properties of a single-phase quasicrystalline material of composition Al70.8Pd20.9Mn8.3 have been measured as a function of temperature (T) over a range of 10 K≪T≪320 K. The following room-temperature values were found: electrical conductivity [640 (Ω cm)-1], Seebeck coefficient (85 μV/K), and thermal conductivity (1.6 W/m K). As the temperature was decreased from room temperature, the electrical conductivity decreased undergoing a minimum at T≈50 K after which it increased slightly and the Seebeck coefficient decreased monotonically. The thermal conductivity decreased with temperature and exhibited a broad plateau region between 50 K≪T≪150 K. This class of materials is being investigated for potential thermoelectric applications. © 1999 American Institute of Physics. View full abstract»

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  • Absorption spectra of nanocrystalline silicon embedded in SiO2 matrix

    Page(s): 1857 - 1859
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    Nanocrystalline silicon embedded SiO2 matrix is formed by annealing the SiOx films fabricated by plasma enhanced chemical vapor deposition technique. Absorption coefficient and photoluminescence of the films have been measured at room temperature. The experimental results show that there exists an exponential absorption in the spectral range of 2.0–3.0 eV. The relationship of (αhν)1/2∝(hν-Eg) demonstrates that the luminescent nanocrystalline silicon has an indirect band structure. The existence of Stokes shift between photoluminescence and absorption edge indicates that radiative combination can take place not only between shallow trap states of electrons and holes but also between quantized states of electrons and holes. © 1999 American Institute of Physics. View full abstract»

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  • Grain growth in thin-film strontium sulfide electroluminescent phosphors

    Page(s): 1860 - 1862
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    A comprehensive study of grain growth in strontium sulfide (SrS) thin-film electroluminescent (TFEL) phosphors is reported. It is suggested that the grain growth during annealing is influenced by the migration of the dopant ion from the grain boundary into a lattice position. The difference in the free energy of formation between SrS and the sulfur compounds of the dopants changes the activation energy for the grain boundary movement and promotes the grain growth. This understanding has successfully been used to explain the grain growth phenomena observed in SrS TFEL phosphors with different dopants, such as Cu, Ag, Mn, and Ga. © 1999 American Institute of Physics. View full abstract»

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  • Solid-state gadolinium–magnesium hydride optical switch

    Page(s): 1863 - 1865
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    The optical switching properties of gadolinium–magnesium hydride have been demonstrated in a solid-state electrochromic device. With positive polarization of the hydride electrode, the visible reflectance approaches 35% with virtually zero transmission, while with negative polarization, the visible transmission exceeds 25% at 650 nm. The switching is reversible, with intermediate optical properties between the transparent and reflecting states. © 1999 American Institute of Physics. View full abstract»

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  • Evolution of the energy levels in quantum dot ensembles with different densities

    Page(s): 1866 - 1868
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    Ensembles of self-assembled InAs/GaAs quantum dots (QDs) have been obtained with different densities by molecular beam epitaxy. The evolution of the structural and optical properties with coverage shows that lateral interactions are present for QD spacings of hundreds of nanometers (coverage≫∼109QDs/cm2). Clear evidence for transfer of InAs from the wetting layer to the QDs is observed at the onset of the Stranski–Krastanow’s island formation for 1.83 monolayers (MLs). QDs with sharp electronic shell structures are observed by state-filling spectroscopy for the low density ensembles (1.83–1.91 ML). A decrease in the photoluminescence intensity is observed for more than 1.96 ML and is associated with the coalescence of the islands. © 1999 American Institute of Physics. View full abstract»

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  • Microscopical aspects of boron diffusion in ultralow energy implanted silicon

    Page(s): 1869 - 1871
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    The transient enhanced diffusion of ultralow energy implanted B is reported in this letter. The mechanism giving rise to an enhancement of the diffusion during postimplantation anneal is investigated in detail by monitoring the diffusion of B as a function of temperature in the range 600–750 °C, for implant energies of 500 eV and 1 keV. The contribution of several classes of defect clusters to the anomalous diffusion phenomenon has been detected and interpreted. Both an ultrafast diffusion, occurring during the ramp-up of the thermal process, and a transient enhancement of the diffusion with characteristic decay times shorter by orders of magnitude than the known transient enhanced diffusion lifetimes, have been evidenced. The activation energy for the enhanced diffusion has been measured and found to be 1.7 eV. © 1999 American Institute of Physics. View full abstract»

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  • Amplified stain-rate dependence of deformation in polymer-dispersed liquid-crystal materials

    Page(s): 1872 - 1874
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    The mechanical properties of polymer-dispersed liquid crystals (PDLCs) are investigated to elucidate their fundamental microstructural and mechanistic underpinnings, and overall structural integrity under deformation. High strain-rate loading experiments and quasistatic compression tests on PDLC materials reveal an amplified strain-rate dependence relative to the matrix material. A finite-element micromechanical model of PDLC materials explains this behavior in terms of strain-rate concentrations at the equators of the spherical liquid-crystal droplets. The model also predicts a weak dependence of the aspect ratio of deforming liquid-crystal droplets on their volume fraction. © 1999 American Institute of Physics. View full abstract»

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  • Synthesizing boron nitride nanotubes filled with SiC nanowires by using carbon nanotubes as templates

    Page(s): 1875 - 1877
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    A method is described to synthesize silicon carbide (SiC)-filled boron nitride (BN) nanotubes (NT) simultaneously in high yield by using carbon nanotubes (CNTs) as templates. This method combines both carbon nanotube-substitution reaction and confined reaction. Through the CNT-substitution reaction, CNTs react with boron oxide vapor in the presence of nitrogen gas to form BN NTs, whose diameters and lengths are similar to those of the starting CNTs. The formation of the SiC filling is proceeded by the penetration of SiO vapor into the cavity of the nanotubes and subsequent reaction of SiO vapor with the inner carbon layers or volatile carbon mono-oxide in the interior to form SiC nanowires. The filled length can be up to the entire length of the nanotubes. SiC-filled (BN)xCy nanotubes also form in the product. © 1999 American Institute of Physics. View full abstract»

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  • Photoinduced surface relief gratings on azopolymer films: Analysis by a fluid mechanics model

    Page(s): 1878 - 1880
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    Photoinduced surface relief grating (SRG) formation on azopolymer films is discussed precisely using a fluid mechanics model which takes depth dependence of photoinduced driving force and velocity distribution in the film surface into account. Formulation for the SRG dynamics is derived analytically as a function of film thickness and interference wave number. The film thickness dependence of diffraction efficiency, which is observed experimentally, agrees well with the theoretical value in the entire range of film thickness. The dependence of SRG driving force on interference wave number is also discussed in terms of the experimental data using proposed model. © 1999 American Institute of Physics. View full abstract»

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  • Macroscopic residual stress in chemical-vapor-deposition free-standing diamond films by x-ray diffraction analyses

    Page(s): 1881 - 1883
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    We present a structural analysis of plasma-assisted chemical-vapor-deposition self-supporting diamond films with different qualities, black, gray and white. Experimental results show a weak fiber texture and a large average grain size at the growth side, consistent with the model usually used to described chemical-vapor-deposition growth with a preferred orientation of the grains. Macroscopic residual stresses have been determined by means of x-ray measurements, through the sin2 ψ” method. Compressive and tensile stresses are reported at both faces of the samples. We show that stresses present at both growth face and nucleation face cannot be explained by the usual models involving the average grain size. For some samples, a closer analysis of the sin2 ψ curves reveals a shift from the linear behavior. This effect comes from various stress states and/or lattice parameters between the grains belonging to the texture and the randomly oriented grains. © 1999 American Institute of Physics. View full abstract»

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  • Radiation damage to fullerite (C60) in the transmission electron microscope

    Page(s): 1884 - 1886
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    Electron energy-loss spectroscopy was used to monitor structural damage to solid C60 as a function of electron exposure. The characteristic dose was found to be in the range 300–700 C/cm2 for incident energies in the range 100–200 keV and specimen temperatures between 100 and 300 K. The absolute value of this dose, and its energy and temperature dependence, suggest that the damage mechanism is predominantly electronic rather than knock-on displacement. © 1999 American Institute of Physics. View full abstract»

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  • Structural and optical quality of GaN/metal/Si heterostructures fabricated by excimer laser lift-off

    Page(s): 1887 - 1889
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    Gallium nitride (GaN) thin films grown on sapphire substrates were successfully bonded and transferred onto Si substrates using a Pd–In metallic bond. After bonding, a single 600 mJ/cm2, 38 ns KrF (248 nm) excimer laser pulse was directed through the transparent sapphire followed by a low-temperature heat treatment to remove the substrate. Channeling-Rutherford backscattering measurements revealed the thickness of the defective interfacial region to be approximately 350 nm. The full width at half maximum, low-temperature (4 K), donor-bound exciton photoluminescence (PL) peak was larger by 25% on the exposed interfacial layer compared to the original GaN surface. Ion milling of the exposed interface to a depth of 400 nm was found to remove the interfacial layer and associated defects. The minimum channeling yield and PL linewidths from the exposed interface were found to be comparable to those obtained from the original GaN surface after ion milling. © 1999 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