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Applied Physics Letters

Issue 22 • Date May 2007

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Displaying Results 1 - 25 of 107
  • 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
  • Optofluidic ring resonator based dye laser

    Page(s): 221101 - 221101-3
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    The authors demonstrate a microfluidic dye laser using a liquid core optical ring resonator (LCORR). The LCORR is made of a fused silica capillary with a wall thickness of a few microns. The circular cross section of the capillary forms a ring resonator that supports whispering gallery modes (WGMs) and provides an optical feedback for lasers. Due to the high Q factor of the WGM (107), a low lasing threshold is achieved (1 μJ/mm2). In addition, they show that the laser can be coupled out via a tapered fiber in touch with the LCORR, thus providing a mechanism for easy laser delivery. View full abstract»

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  • In situ observation of Zn-induced etching during CdSe quantum dot formation using time-resolved ellipsometry

    Page(s): 221102 - 221102-3
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    A combined segregation and desorption process has been observed in situ by ellipsometry in real-time during overgrowth of a CdSe layer by a ZnSe cap layer using migration enhanced epitaxy. This segregation enhanced etching of CdSe during Zn deposition is known to play an important role in the formation process of CdSe quantum dots. The time-resolved ellipsometry data can be fitted assuming a rapid thickness reduction of about 68% of the CdSe layer, consistent with results obtained by high-resolution x-ray diffraction after growth. Furthermore, a significant change in growth rate during deposition of CdSe has been observed. View full abstract»

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  • Red light emission from controlled multilayer stack comprising of thin amorphous silicon and silicon nitride layers

    Page(s): 221103 - 221103-3
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    The authors demonstrate photoluminescence from a multilayer stack comprising of thin amorphous silicon/silicon nitride multilayer stack. The peak emission wavelength is in the visible wavelength range (λ=674–706 nm). The authors show that emission originates from the quantum confinement of the amorphous silicon layers. They demonstrate the tunability of the peak emission wavelength by controlling the amorphous silicon layer thickness. Postdeposition annealing was carried out to enhance the photoluminescence without recrystallization of the amorphous silicon layers as confirmed by transmission electron microscopy and Raman spectroscopy. Such multilayer structure should be advantageous for electrical injection of carriers due to the thin dielectric layers View full abstract»

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  • Deviations from the reciprocity theory of McCumber at low temperature in Nd3+-doped glasses

    Page(s): 221104 - 221104-3
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    The reciprocity theory of McCumber [Phys. Rev. 136, A954 (1964)], which relates optical absorption and emission spectra between two energy level manifolds, was tested at temperatures down to 130 K on the 4F3/24I9/2 transition in Nd-doped glass. Deviations between calculated and measured spectra were observed for temperatures below 230 K in Nd:silicate and below 170 K in Nd:fluorozirconate glass. Below these temperatures, the calculated absorption is skewed to shorter wavelength and the calculated emission is skewed to longer wavelength. The magnitude of the deviation depends on the ratio of inhomogeneous linewidth to thermal energy kBT. View full abstract»

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  • Growth and photoluminescence studies of a-plane AlN/AlxGa1-xN quantum wells

    Page(s): 221105 - 221105-3
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    Both a-plane and c-plane AlN/Al0.65Ga0.35N quantum wells (QWs) have been grown by metal organic chemical vapor deposition and their photoluminescence (PL) emission properties were studied and compared. It was found that the low temperature PL characteristics of a-plane QWs are primarily governed by the quantum size effect, whereas those of c-plane QWs are significantly affected by the polarization fields. The PL decay time was found to be only weakly dependent on the well width Lw for a-plane QWs, whereas a strong dependence of the PL decay time on Lw was observed for c-plane QWs. Moreover, Lw dependence studies also revealed that structures with Lw≫2 nm and Lw≈2 nm provide highest emission efficiency in a-plane and c-plane AlN/Al0.65Ga0.35N QWs, respectively. View full abstract»

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  • Contrast in transmission spectroscopy of a single quantum dot

    Page(s): 221106 - 221106-3
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    The authors perform transmission spectroscopy on single quantum dots and examine the effects of a resident carrier’s spin, the incident laser spot size, polarization, and power on the experimental contrast. They demonstrate a factor of 5 improvement in the maximum contrast by using a solid immersion lens to decrease the spot area. This increase yields a maximum signal to noise ratio of ∼2000 Hz-1/2, which will allow for megahertz detection frequencies. The authors anticipate that this improvement will allow further investigation of spectral fluctuation and open up the feasibility for an all-optical readout of an electron spin in a quantum dot. View full abstract»

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  • Luminescence and absorption analysis of undoped organic materials

    Page(s): 221107 - 221107-3
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    The authors model and analyze the electroluminescence and absorption properties of organic semiconductors using Alq3 as example. Instead of using a typical quasiparticle approach based on singlet and triplet excitons, they obtain the absorption and electroluminescence spectra by solving the equation of motion for the linear microscopic polarization in a hierarchical many-body framework. A special focus is put on Coulomb effects. The electronic structure input parameters for this model are obtained by molecular orbital calculations. In particular for Alq3, they find a (Coulomb) exciton binding energy of about 0.9 eV and discuss the impact of the strong carrier density induced Coulomb exchange shift on electroluminescence and absorption spectra. View full abstract»

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  • 40 J class laser oscillation of Nd-doped silica glass with high thermal shock parameter

    Page(s): 221108 - 221108-3
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    The authors demonstrated a 40 J class laser oscillation from a bulk-type Nd-doped silica glass with a high thermal shock parameter. A maximum output energy of 37.3 J was obtained from a laser oscillator that consisted of a 30% output coupler with a 30 mm diameter and 300 mm length laser medium. The thermal shock parameter, a figure of merit for the thermal toughness of the materials, was estimated to be 12.0 W/cm, which is 1.5 times larger than neodymium-doped yttrium aluminum garnet (7.9 W/cm). These results show that the Nd-doped silica glass has the potential to be installed in high-average-power or high-peak-power lasers. View full abstract»

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  • Air-suspended two-dimensional polymer photonic crystal slab waveguides fabricated by nanoimprint lithography

    Page(s): 221109 - 221109-3
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    Air-suspended membrane-type photonic crystals were fabricated in polystyrene. The two-dimensional photonic crystal slab nanostructures were replicated by a thermal nanoimprint process, and then air-suspended membrane structures were generated by a selective sacrificial layer etch process. The optical transmission showed clear band gap characteristics at 1550 nm wavelength, which is in good agreement with the theoretical calculations. View full abstract»

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  • Field-induced and polymer-stabilized two-dimensional cholesteric liquid crystal gratings

    Page(s): 221110 - 221110-3
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    The authors experimentally demonstrate an electrically switchable gratings based on polymer-stabilized, field-induced two-dimensional square-lattice pattern of a cholesteric liquid crystal. A dependence of the two-dimensional diffraction patterns with the magnitude of applied voltage is observed for before and after the polymer stabilization. The diffraction efficiency reaches 84% calculated for the zero order light intensity at the applied voltage of 0.23 Vm for a 10 μm thick sample. View full abstract»

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  • Transflective liquid crystal display using commonly biased reflectors

    Page(s): 221111 - 221111-3
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    A normally black single cell gap transflective liquid crystal display (LCD) using vertical alignment and commonly biased patterned reflectors is developed. In the transmissive region, continuous and uniform vertical electric fields are formed throughout the LC cell. On the other hand, in the reflective region, the electric fields are mainly confined near the substrate surfaces. As a result, the phase retardation in the transmissive region is approximately two times as that of the reflective region. Such a transflective LCD shows a high light efficiency (≫90%) for both transmissive and reflective modes and well matched gray scales. View full abstract»

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  • Contactless electroreflectance investigation of energy levels in a 1.3 μm emitting laser structure with the gain medium composed of InAsN quantum dots embedded in GaInNAs/GaAs quantum wells

    Page(s): 221112 - 221112-3
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    Laser structures designed for the emission at 1.3 μm and based on an active region containing InAsN quantum dots (QDs) embedded in GaInNAs/GaAs quantum wells (QWs) have been investigated by contactless electroreflectance. Optical transitions related to both the dots and the wells have been observed and the energies of the latter have been calculated using the effective mass approach. It has been shown that QW confines one electron, one light-hole, and three heavy-hole states only and the energy separation between the QD and QW ground state transitions is approximately 250 meV, which is ten times higher than the thermal energy at room temperature. View full abstract»

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  • Low threshold, high gain AlGaInAs quantum dot lasers

    Page(s): 221113 - 221113-3
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    The properties of AlGaInAs quantum dot (QD) lasers are reported and compared to GaInAs QD lasers emitting at a similar wavelength (∼920 nm). It is found that Al0.15Ga0.23In0.62As QD lasers show an ∼2.1 times higher material gain and lower threshold current densities than Ga0.57In0.43As lasers (a factor of ∼1.4 for 1.0 mm long and 100 μm wide devices). Both laser samples display comparable high internal quantum efficiencies of 0.79 (AlGaInAs) and 0.83 (GaInAs). The AlGaInAs devices exhibit a high characteristic temperature of 174 K between 15 and 85 °C. View full abstract»

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  • Optical properties of helical Ag nanostructures calculated by discrete dipole approximation method

    Page(s): 221501 - 221501-3
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    The extinction spectra and field distribution of Ag helical nanostructures have been calculated using the discrete dipole approximation method. The plasmon peak of the Ag helix can be tuned not only by the structural parameters but also by the polarizations of the incident light, especially the circular polarizations. In addition, the polarization direction of the incident light can change the spatial distribution of the maximum E field, which provides a simple way to spatially resolve analyte’s distribution on the nanostructures for sensing applications. View full abstract»

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  • Enhanced performance of cylindrical Hall thrusters

    Page(s): 221502 - 221502-3
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    The cylindrical thruster differs significantly in its underlying physical mechanisms from the conventional annular Hall thruster. It features high ionization efficiency, quiet operation, ion acceleration in a large volume-to-surface ratio channel, and performance comparable with the state-of-the-art conventional Hall thrusters. Very significant plume narrowing, accompanied by the increase of the energetic ion fraction and improvement of ion focusing, led to 50%–60% increase of the thruster anode efficiency. These improvements were achieved by overrunning the discharge current in the magnetized thruster plasma. View full abstract»

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  • Spherical carbon liquids generated in a low pressure CH4/Ar plasma

    Page(s): 221503 - 221503-3
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    The authors present a study on spherical carbon particles of micron sizes grown in the plasma sheath as spherical liquids that can be agglomerated by capillary force based on the Laplace pressure. In addition, it is suggested that those spherical carbon liquids with negative charges that are levitating in the sheath region begin to display a collective behavior of Coulomb crystals. View full abstract»

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  • Self-organized pattern formation of an atmospheric pressure plasma jet in a dielectric barrier discharge configuration

    Page(s): 221504 - 221504-3
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    This letter reports the observation of self-organized patterns formed in a 29 mm wide atmospheric pressure plasma jet. By altering the gas flow rate and/or the applied voltage, the plasma jet is seen to have at least three different modes, namely, a diffuse-looking discharge, a self-organized discharge, and an unstable discharge with randomly occurring plasma channels. The self-organized discharge mode is characterized by several bright plasma channels embedded in a diffuse and dim plasma background. These plasma channels are regularly spaced from each other and their self-organized patterns are shown to evolve abruptly. View full abstract»

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  • Segregation and precipitation of Er in Ge

    Page(s): 221901 - 221901-3
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    Although Er-doped Ge nanomaterials are attractive for photonic applications, very little is known about the basic properties of Er in Ge. Here, the authors study the annealing behavior of Ge implanted with keV Er ions to doses resulting in >~1 at. % of Er. Large redistribution of Er, with segregation at the amorphous/crystalline interface, starts at ≳500 °C, while lower temperatures are required for material recrystallization. However, even at 400 °C, Er forms precipitates. The concentration of Er trapped in the bulk after recrystallization decreases with increasing temperature but is independent of the initial bulk Er concentration for the range of ion doses studied here. View full abstract»

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  • Structural studies of single crystalline In2O3 films epitaxially grown on InN(0001)

    Page(s): 221902 - 221902-3
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    Single crystalline In2O3 is a prospective material to be used as a gate dielectric in InN based field effect transistors (FETs). This work addresses structural investigations of In2O3/InN heterostuctures for metal-oxide-semiconductor FET devices. Single crystalline cubic In2O3 (111) films were epitaxially grown on hexagonal InN (0001) epilayers. The epitaxial relationship between the film and the template was determined as In2O3[111]||InN[0001] and In2O3[101]||InN<1120> with an effective lattice mismatch of 2.14%. On the basis of the structural investigations, a phenomenological model for the growth of In2O3 on InN (0001) is proposed. View full abstract»

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  • Quantitative Landau potentials for the martensitic transformation in Ni–Al

    Page(s): 221903 - 221903-3
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    The martensitic phase transformation in Ni–Al (63.5 at. % Ni) is described by a Landau-type Gibbs free energy G(Q)=1/2AΘs(coths/T)-coths/TC))Q2+1/4BQ4+1/6CQ6, with A=5.6 J K-1 mol-1, B=-3493 J mol-1, C=4901 J mol-1, TC=86 K, and Θs=257 K. The dispersion (Ginzburg) energy was estimated to be g=60 J mol-1 nm2. This potential was determined from high resolution diffraction data to determine the spontaneous strain as proxy for the order parameter Q and differential scanning calorimetry measurements for the calibration of the excess entropy of the martensitic phase transformation. The Gibbs free energy is compared with equivalent functions of Ni–Ti, quartz, KMnF3, BaTiO3, and SrTiO3. View full abstract»

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  • Dynamics of bound excitons versus thickness in freestanding GaN wafers grown by halide vapor phase epitaxy

    Page(s): 221904 - 221904-3
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    The bound exciton recombination properties in freestanding GaN layers of various thicknesses grown by halide vapor phase epitaxy have been characterized by time-resolved spectroscopy. Improvement of the donor bound exciton (D0X) lifetime was observed with increasing GaN layer thickness up to ∼400 μm, while for thicker layers the recombination time of D0X shows a tendency to saturate. The thickness-dependent behavior of the D0X decay can be understood in terms of competition between two nonradiative mechanisms: one of which is connected to structural defects, and consequently more important for thinner layers, while for layers with thickness above 400 μm with low structural defect density the recombination time is limited by point defects such as impurities and vacancies. View full abstract»

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  • Cellular solids with tunable positive or negative thermal expansion of unbounded magnitude

    Page(s): 221905 - 221905-3
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    Material microstructures are presented with a coefficient of thermal expansion larger in magnitude than that of either constituent. Thermal expansion can be large positive, zero, or large negative. Three-dimensional lattices with void space exceed two-phase bounds but obey three-phase bounds; lattices and normal materials have a trend of expansion decreasing with modulus. Two-phase composites with a negative stiffness phase exceed bounds that assume positive strain energy density. The author determined Young’s modulus and its relation to thermal expansion. Behavior of these composites is compared with that of homogeneous solids in expansion-modulus maps. View full abstract»

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  • Thermal stability of metal organic vapor phase epitaxy grown AlInN

    Page(s): 221906 - 221906-3
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    AlInN layers with a thickness of 100 nm were grown by metal organic vapor phase epitaxy on GaN buffer layers on Si(111) substrates. By varying the growth temperature, In and NH3 flows, and reactor pressure, three series with different In contents were produced and thermally treated in the temperature range from 30 to 960 °C. The as grown and annealed layers were investigated by x-ray diffraction in standard and grazing incidence geometry. Nearly lattice matched samples with an indium concentration of 17%–18% show long time stability at annealing temperatures as high as 960 °C. At higher temperatures, the onset of severe Ga–Si meltback etching prevents further measurements. Nonlattice matched samples consist of pseudomorphic and relaxed parts. In the latter, a redistribution and loss of indium is observed upon annealing. 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