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Applied Physics Letters

Issue 6 • Date Feb 2001

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Displaying Results 1 - 25 of 57
  • Issue Cover

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

    Page(s): toc1
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    Freely Available from IEEE
  • Near-field images of the AgOx-type super-resolution near-field structure

    Page(s): 685 - 687
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    As a promising disk structure for ultrahigh density optical data storage, super-resolution near-field structure of AgOx type has been studied by the tapping-mode tuning-fork near-field scanning optical microscope as well as the transmission electron microscope. This structure presents strong near-field intensity enhancement and nonlinear optical effect, compared with the ordinary material. Numerical calculations confirm that the localized surface plasmon and the nonuniform material structures are the main causes for these unusual characteristics. © 2001 American Institute of Physics. View full abstract»

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  • Photorefractive chiral smectic A phases

    Page(s): 688 - 690
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    We present results of the photorefractive properties of a chiral smectic A liquid-crystalline phase. In our approach, the mesophase is sandwiched between two photoconducting layers. In contrast to the effect due to the dielectric anisotropy typical of nematic phases, the refractive-index modulation is due to the electroclinic effect. We measured the grating spacing and the field dependence of the gain coefficient and obtained a net two-beam coupling gain of 600 cm-1 at 35 V/μm. © 2001 American Institute of Physics. View full abstract»

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  • Strong luminescence from Tamm states in modulation-doped superlattices

    Page(s): 691 - 693
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    Calculations are presented for the photoluminescence spectrum of InP/In0.53Ga0.47As superlattices doped with Si. When doping is confined to the inner barriers, the photoluminescence is dominated by transitions between Tamm states in the electron and valence bands, which contribute with an optical band at energies higher than the In0.53Ga0.47As band gap. These results are in good agreement with experimental observations. © 2001 American Institute of Physics. View full abstract»

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  • Gratings in indium oxide film overlayers on ion-exchanged waveguides by excimer laser micromachining

    Page(s): 694 - 696
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    Relief Bragg gratings were imprinted by 248 nm interferometric excimer laser ablation on potassium ion-exchanged channel waveguides in BK-7 glass overlaid with a thin high-index InOx film. Using five pulses of energy density 60 mJ/cm2, a spectral transmittance notch of depth 66% and ΔλFWHM≪0.1 nm was obtained at 1547 nm in the TE polarization for a waveguide having a nominal width of 8 μm and a 135-nm-thick InOx overlayer. In waveguides coated with 100 nm InOx, with widths increasing from 3 to 8 μm, the reflection wavelength shifted by 0.12 nm/μm and the reflectivity increased monotonically. © 2001 American Institute of Physics. View full abstract»

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  • Influence of disorder and a parallel magnetic field on a quantum cascade laser

    Page(s): 697 - 699
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    The luminescence spectra of a quantum cascade laser (QCL) in a strong magnetic field is influenced significantly by the presence of disorder (charged or neutral) in the system. An externally applied magnetic field parallel to the electron plane causes a redshift of the luminescence peak in the absence of any disorder potential. Our results indicate that the disorder potential tends to cancel that redshift and causes a rapid decrease of the luminescence peak. A similar behavior was observed in a recent experiment on a QCL in a parallel magnetic field by S. Blaser, L. Diehl, M. Beck, and J. Faist [Physica E 7, 33 (2000)]. © 2001 American Institute of Physics. View full abstract»

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  • Efficient molecular photorefractive materials based on methine dyes

    Page(s): 700 - 702
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    This letter reports a series of molecular materials that shows efficient photorefractive effect. The materials which consist of monolithic methine dye molecules can form amorphous films. A net photorefractive gain of 215 cm-1 and a diffraction efficiency of 87.6% at a semiconductor laser wavelength of 780 nm are observed. These materials are the simplest molecular materials and possess the best photorefractive performances. Due to the large photorefractive effect, optical self-defocusing and instability of the laser beam are observed in these materials when the applied electric field is above a threshold. © 2001 American Institute of Physics. View full abstract»

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  • Optically induced pulse delay in a solid-state Raman amplifier

    Page(s): 703 - 705
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    The pump-induced group velocity reduction of subnanosecond pulses is calculated and measured in a Ba(NO3)2 solid-state Raman amplifier. 1.197 μm probe pulses with 90 ps duration were generated using a Raman-shifted mode-locked and Q-switched Nd:YAG laser, and propagated through a Ba(NO3)2 crystal synchronously pumped by 7-ns-long 1.06 μm pulses. The time delay of the pulse peak was measured with varying pump intensity and was compared with theoretical calculation up to the point where amplified spontaneous Raman emission becomes dominant. The maximum time delay was found to be 105 ps. © 2001 American Institute of Physics. View full abstract»

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  • Extraction of ions from the matrix sheath in ablation-plasma ion implantation

    Page(s): 706 - 708
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    A simple one-dimensional theory is presented to assess the implantation of ions from the ion matrix sheath (IMS) in an ablated plasma plume that is approaching a negatively biased substrate. Under the assumption that the plume geometry, the electron and ion density distributions, and the potential distribution are frozen during the IMS extraction, the implanted ion current is calculated as a function of time for various substrate-plume separations. This model accurately recovers Lieberman’s classic results when the plume front is initially in contact with the substrate. © 2001 American Institute of Physics. View full abstract»

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  • Excitation of a microdischarge with a reverse-biased pn junction

    Page(s): 709 - 711
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    Excitation of cylindrical microdischarges, 300–360 μm in diameter, by a reverse-biased, Si pn junction has been demonstrated. Devices fabricated from commercial diodes have been operated with Ne gas pressures in the 200–700 Torr range and dc voltages as low as 120 V. For a Ne gas pressure of 700 Torr, the wavelength-integrated (300–800 nm) output power—emitted into a solid angle of ∼6×10-2 sr—of a 360-μm-diam device is 48±1 μW for an operating current and voltage of 5.7±0.1 mA and 134 V, respectively. This hybrid solid state/gas device represents the demonstration of the generation of a gas discharge by a pn junction and lends itself to the fabrication of large arrays. © 2001 American Institute of Physics. View full abstract»

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  • Molecular-beam epitaxial growth and surface characterization of GaAs(311)B

    Page(s): 712 - 714
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    Reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM) are used to study the surface and growth of GaAs (311)B. The RHEED pattern reveals a lateral periodicity of 3.2 nm along the [011¯] direction, which is confirmed in real space by STM images. Pronounced RHEED intensity oscillations during the homoepitaxial growth on GaAs(311)B were observed in a wide substrate temperature range. © 2001 American Institute of Physics. View full abstract»

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  • Influence of crystallite size distribution on the micro-Raman analysis of porous Si

    Page(s): 715 - 717
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    First-order Raman spectra from nanocrystalline semiconductors reflect the influence of crystallite sizes on the Raman shifts and line shapes. A Gaussian distribution in crystallite sizes is explicitly included to calculate the Raman spectra of porous silicon. Several porous-silicon samples were prepared using electrochemical anodization, and Raman as well as photoluminescence measurements were carried out on the same spots using a micro-Raman probe. The size distribution obtained from fitting the Raman data using our procedure is able to predict the photoluminescence accurately in the quantum-confinement models. © 2001 American Institute of Physics. View full abstract»

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  • Anomalously increased effective thermal conductivities of ethylene glycol-based nanofluids containing copper nanoparticles

    Page(s): 718 - 720
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    It is shown that a “nanofluid” consisting of copper nanometer-sized particles dispersed in ethylene glycol has a much higher effective thermal conductivity than either pure ethylene glycol or ethylene glycol containing the same volume fraction of dispersed oxide nanoparticles. The effective thermal conductivity of ethylene glycol is shown to be increased by up to 40% for a nanofluid consisting of ethylene glycol containing approximately 0.3 vol % Cu nanoparticles of mean diameter ≪10 nm. The results are anomalous based on previous theoretical calculations that had predicted a strong effect of particle shape on effective nanofluid thermal conductivity, but no effect of either particle size or particle thermal conductivity. © 2001 American Institute of Physics. View full abstract»

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  • Fabrication of CaS:Pb blue phosphor by incorporating dimeric Pb2+ luminescent centers

    Page(s): 721 - 723
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    The CaS:Pb phosphor emitting blue electroluminescence (EL) induced by dimeric Pb2+ luminescent centers was deposited using the controlled atomic layer deposition technique. The effect of the incorporation method and concentration of Pb2+ ions on the color of high luminance CaS:Pb phosphor was investigated at the deposition temperatures of 350 and 400 °C. The blue EL emission at 440–445 nm could be maintained with the Pb concentration ranging from 0.6 to 2.5 mol % contrary to the earlier works that had demonstrated very sensitive dependence of color on Pb2+ concentration. The selective incorporation of dimeric Pb2+ ions was attributed to the reactivity of tetraethyl lead as Pb precursor as well as the controlled deposition technique. © 2001 American Institute of Physics. View full abstract»

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  • Raman scattering studies on single-crystalline bulk AlN under high pressures

    Page(s): 724 - 726
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    We report on the Raman analysis of wurtzite single-crystalline bulk AlN under hydrostatic pressures up to 10 GPa. The pressure dependence of the AlN phonon frequencies was investigated. Mode Grüneisen parameters of 1.39, 1.57, 1.71, 0.93, and 1.26 were determined for the A1(TO), E1(TO), E2(high), A1(LO), and the quasi-longitudinal optical phonons, respectively. Recent theoretical calculations underestimate the pressure-induced frequency shift of the AlN phonons by about 20%–30%. Mode Grüneisen parameters of AlN were compared to those of GaN. © 2001 American Institute of Physics. View full abstract»

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  • Maskless epitaxial lateral overgrowth of GaN layers on structured Si(111) substrates

    Page(s): 727 - 729
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    GaN layers are laterally overgrown by metalorganic chemical vapor deposition on structured Si(111) substrates in a single growth process. The substrates are structured with parallel grooves along the Si 〈1–10〉 or perpendicular to the Si 〈1–10〉 direction by standard photolithography and subsequent dry etching. Due to the anisotropic chemical dry etch process, the remaining Si ridges are underetched. The GaN layer grows nearly exclusively on the bottom of the grooves and on the top of the ridges between the grooves. These two growth fronts are completely separated from each other. As a consequence, the GaN layer growing from the ridge area between grooves can extend over the grooves. This process is similar to the so called pendeo-epitaxy process, but is completely mask free during growth and does not require any growth interruption. The improvement of the crystalline and the optical quality of the GaN layer is demonstrated by atomic force microscopy and cathodoluminescence spectroscopy. © 2001 American Institute of Physics. View full abstract»

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  • Structural modification of single-axis-oriented yttria-stabilized-zirconia films under zirconium ion bombardment

    Page(s): 730 - 732
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    Crystal size and orientation control of yttria-stabilized-zirconia (YSZ) films produced by pulsed-laser deposition under zirconium-ion bombardment are reported. A structure development mechanism is proposed based on the correlation between ablated plasma chemistry, velocity distributions of atomic and molecular species in the plasma, bombardment energy, time, incidence angle, film crystal size, and orientation. A near-room-temperature growth of single-axis-oriented YSZ films with (002) texture on randomly oriented polycrystalline substrates is demonstrated. © 2001 American Institute of Physics. View full abstract»

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  • Hanle effect measurements of spin lifetimes in InAs self-assembled quantum dots

    Page(s): 733 - 735
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    Transverse spin lifetimes of spin-polarized photogenerated carriers in InAs self-assembled quantum dots are extracted from the depolarization of their photoluminescence in a magnetic field perpendicular to the spin (the Hanle effect). Hanle measurements on a series of samples reveal that the dot dimensions influence the spin lifetime and its dependence on temperature. The spin lifetime as a function of excitation intensity is qualitatively distinct for carrier spins created in the GaAs host as compared to in the InAs wetting layer. © 2001 American Institute of Physics. View full abstract»

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  • Fast through-bond diffusion of nitrogen in silicon

    Page(s): 736 - 738
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    We report first-principles total energy calculations of interaction of nitrogen in silicon with silicon self-interstitials. Substitutional nitrogen captures a silicon interstitial with 3.5 eV binding energy forming a 〈100〉 split interstitial ground-state geometry, with the nitrogen forming three bonds. The low-energy migration path is through a bond bridge state having two bonds. Fast diffusion of nitrogen occurs through a pure interstitialcy mechanism: the nitrogen never has less than two bonds. Near-zero formation energy of the nitrogen interstitialcy with respect to the substitutional rationalizes the low solubility of substitutional nitrogen in silicon. © 2001 American Institute of Physics. View full abstract»

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  • Defect-induced tetragonalization of the orthorhombic TiSi2 C49 phase: X-ray diffraction and first principles calculations

    Page(s): 739 - 741
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    We discuss the rather scattered predictions on the orthorhombic lattice parameters for the C49 TiSi2 phase, which are reported in the literature. New and accurate x-ray diffraction measurements and ab initio calculations are presented. Both agree in indicating that the density is higher than the one commonly assumed and it is close to the stable C54 phase. An unexpected tetragonalization of the orthorhombic cell has been observed and the theoretical analysis shows that this phenomenon could be originated by the massive presence of stacking faults. © 2001 American Institute of Physics. View full abstract»

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  • Sharp band edge photoluminescence of high-purity CuInS2 single crystals

    Page(s): 742 - 744
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    Temperature-dependent photoluminescence measurements were carried out between 8 and 300 K on CuInS2 single crystals grown by a traveling heater method. Ten distinct peaks were present in the near-band edge region. Four unknown peaks, observed at 8 K, were found to be due to bound exciton emission. Moreover, the luminescence remained stable up to room temperature. © 2001 American Institute of Physics. View full abstract»

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  • Carrier-type reversal in Pb–Ge–Se glasses: Photopyroelectric measurements of thermal conductivity and heat capacity

    Page(s): 745 - 747
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    The thermal conductivity and heat capacity of Pb modified Ge–Se glasses, Pb20GexSe80-x (x=17–24) and PbyGe42-ySe58 (y=0–20), which exhibit carrier-type reversal from p type to n type at specific compositions, have been measured simultaneously by the photopyroelectric technique. The thermal conductivity as well as the heat capacity show anomalous variations at the compositions at which carrier-type reversals are reported to occur in these glasses. The results are explained in terms of the enhancement in electron concentration during p- to n-type changeover in these materials. © 2001 American Institute of Physics. View full abstract»

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  • Structural changes during annealing of GaInAsN

    Page(s): 748 - 750
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    The alloy GaInAsN has great potential as a lower-band-gap material lattice matched to GaAs, but there is little understanding of what causes its poor optoelectronic properties and why these improve with annealing. This study provides information about the structural changes that occur when GaInAsN is annealed. The Fourier transform infrared spectra exhibit two primary features: a triplet at ∼470 cm-1 (Ga–N stretch) and two or three bands at ∼3100 cm-1 (N–H stretch). The change in the Ga–N stretch absorption can be explained if the nitrogen environment is converted from NGa4 to NInGa3 after annealing. The N–H stretch is also changed after annealing, implying a second, and unrelated, structural change. © 2001 American Institute of Physics. View full abstract»

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  • Improved performance of amorphous silicon thin film transistors by cyanide treatment

    Page(s): 751 - 753
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    We have examined the impact of a simple, wet chemical postgrowth treatment of “immersing in KCN solution” on the performance of inverted staggered amorphous silicon n-channel thin film transistors. Results show that the cyanide treatment significantly improves the overall transistor performance by the elimination of defect states. © 2001 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