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Applied Physics Letters

Issue 22 • Date Dec 2003

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Displaying Results 1 - 25 of 69
  • 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
  • Waveguide tapers and waveguide bends in AlGaAs-based two-dimensional photonic crystals

    Page(s): 4471 - 4473
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    In transmission studies of two-dimensional AlGaAs-based photonic crystal waveguide structures, we demonstrate high coupling efficiencies from ridge waveguides to photonic crystal waveguides using photonic crystal waveguide tapers. Enhanced bending efficiencies and bend bandwidths are achieved by use of modified waveguide bends. © 2003 American Institute of Physics. View full abstract»

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  • Ridge waveguide as a near-field optical source

    Page(s): 4474 - 4476
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    We investigate the feasibility of using a ridge waveguide at optical frequencies as a near-field optical transducer, using the finite difference time domain method. The complete electromagnetic field picture of the ridge waveguide, in the absence and presence of the irradiated medium, is presented. A power efficiency of 7% and an optical spot with full width half maximum of 50 nm×80 nm is obtained in the medium. We show that impedance considerations play a major role in the transducer-medium optical coupling. © 2003 American Institute of Physics. View full abstract»

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  • Measurement of the electro-optic properties of poled polymers at λ=1.55 μm by means of sandwich structures with zinc oxide transparent electrode

    Page(s): 4477 - 4479
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    We report on the measurement of the electro-optic properties of poled polymers at λ=1.55 μm via the Teng and Man technique. Measurements of the electro-optic coefficient obtained for two different sandwich structures, using either indium tin oxide (ITO) or aluminum doped zinc oxide (ZnO:Al) semitransparent electrodes, are compared. The experimental results show that the use of ITO electrodes can lead to a largely wrong evaluation of the electro-optic coefficient r33, with respect to that obtained when using ZnO:Al electrodes, whose plasma resonance is shifted to longer wavelengths. Results on the disperse red 1/methyl-metacrylate based sidechain benchmark system are reported. © 2003 American Institute of Physics. View full abstract»

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  • Three-dimensional simple cubic woodpile photonic crystals made from chalcogenide glasses

    Page(s): 4480 - 4482
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    Construction of three-dimensional photonic crystals for optical wavelengths presents many technological and material science challenges. The submicron-feature-size sculpturing must be performed in high-refractive-index materials. We present the fabrication and optical characterization of ∼750 nm feature-size simple cubic woodpile photonic crystals from As2S3 (n≈2.2). The process is based on interference lithography and the layer-by-layer construction. © 2003 American Institute of Physics. View full abstract»

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  • High extraction efficiency InGaN micro-ring light-emitting diodes

    Page(s): 4483 - 4485
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    Light-emitting diodes (LEDs) based on an interconnected array of GaN/InGaN micro-ring elements have been demonstrated. The devices have electrical characteristics similar to those of conventional broad-area devices. However, due to the large surface areas provided by the sidewalls, the extraction efficiency is greatly enhanced. Intense light emission at the periphery of the micro-rings is observed upon excitation by an electron beam, suggesting scattering of the photons which are extracted through the sidewalls. The devices provide a doubling in total light output compared to a broad-area reference LED of equal light-generation area. © 2003 American Institute of Physics. View full abstract»

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  • Optical waveguide focusing system with short free-working distance

    Page(s): 4486 - 4487
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    In photonics, light usually diffracts in all directions when it emerges from a planar optical waveguide. Besides this fact, in this letter we show that a waveguide with a rectangular cross section can be turned to a focusing system by using three-dimensional self-imaging technique. We obtained a configuration where the focus of the field lies outside the waveguide, in air, with a spot size of approximately the resolution limit of half a wavelength. This type of waveguide could be used as a coupling element in integrated optics or in high numerical aperture optical systems. © 2003 American Institute of Physics. View full abstract»

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  • Optical amplification of the cutoff mode in planar asymmetric polymer waveguides

    Page(s): 4488 - 4490
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    Modes with low threshold for optical gain were observed at wavelengths close to the cutoff in experiments probing the amplified spontaneous emission of light-emitting polymer thin films. The polymer was the semiconductor layer in a multilayer semiconductor–insulator–metal structure that simulates the one-dimensional waveguide characteristics in the channel of a field-effect transistor. The “cutoff” mode propagates at the polymer/gate-insulator interface, has an optical gain threshold of approximately 10 kW/cm2, and is not influenced by absorption of the gate electrode. The wavelength of the amplified emission tracks the cutoff wavelength of the asymmetric double-waveguide structure and the cutoff mode is, therefore, tunable in wavelength. Our results suggest that the light-emitting field-effect transistor architecture is a promising route for the construction of an injection laser. © 2003 American Institute of Physics. View full abstract»

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  • Tuning the microcavity resonant wavelength in a two-dimensional photonic crystal by modifying the cavity geometry

    Page(s): 4491 - 4493
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    High-quality-factor microcavities in two-dimensional photonic crystals at optical frequencies have a number of technological applications, such as cavity quantum electrodynamics, optical switching, filtering, and wavelength multiplexing. For such applications, it is useful to have a simple approach to tune the microcavity resonant wavelength. In this letter, we propose a microcavity design by which we can tune the resonant wavelength by changing the cavity geometry while still obtaining a high quality factor. © 2003 American Institute of Physics. View full abstract»

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  • Unusually narrowed emission lines from a single crystal of thiophene/phenylene co-oligomer

    Page(s): 4494 - 4496
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    We have observed unusually narrowed emission lines from a single crystal of thiophene/phenylene co-oligomer. Very narrow lines (0.07 nm of linewidth) arise around 493 and 466 nm by photopumping a long slender region of the crystal. The relevant emissions are due to the lasing caused by high gain media. The photopumping configuration of the crystal in the present studies is useful in examining how the relevant lines are gain narrowed under each specific measurement. © 2003 American Institute of Physics. View full abstract»

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  • Room temperature terahertz phase shifter based on magnetically controlled birefringence in liquid crystals

    Page(s): 4497 - 4499
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    We present the use of magnetically controlled birefringence in a nematic liquid crystal cell for phase shifting of electromagnetic waves in the range of terahertz frequencies. This device can be operated at room temperature. A maximum phase shift of 141° has been demonstrated at 1.025 THz and the results are in good agreement with theoretical predictions. © 2003 American Institute of Physics. View full abstract»

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  • Focusing light with a single subwavelength aperture flanked by surface corrugations

    Page(s): 4500 - 4502
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    In this letter, we show theoretically how a single subwavelength aperture surrounded by a finite array of grooves made on a metallic film can act as a “lens” for electromagnetic radiation within a certain frequency range. The dependence of this resonant focusing ability with the geometrical parameters defining the structure is extensively analyzed. Universal curves for the depth, length and width of the focus as a function of the number of grooves are also given. © 2003 American Institute of Physics. View full abstract»

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  • Sonoplasma generated by a combination of ultrasonic waves and microwave irradiation

    Page(s): 4503 - 4505
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    Plasma chemical vapor deposition (plasma CVD) is a generic term for methods in which a precursor containing a material to be deposited is dissociated in a plasma where it is subject to chemical reactions, and is then deposited as a film on the surface of a heated substrate. A drawback of plasma CVD is that this process cannot be used to synthesize large amounts of adsorbate, or to deposit onto substrates that are vulnerable to high temperatures. As liquids are much denser than gases, synthesis rates are thought to be much higher in the former. The authors have observed the ignition and maintenance of a stable plasma in a liquid hydrocarbon exposed to a combination of ultrasonic waves and microwave radiation. Microwave energy is effectively injected into the interior of acoustic cavitation bubbles, which act as nuclei for the ignition and maintenance of the plasma. Because the plasma is formed in a liquid environment, it is possible to obtain much higher film deposition rates at much lower plasma temperatures than ever before. In addition, this process can be carried out at normal temperatures and pressures. © 2003 American Institute of Physics. View full abstract»

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  • On the negative value of dielectric permittivity of the water surface layer

    Page(s): 4506 - 4508
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    The present letter reports on experimental measurements of a resonant frequency shift of a radially two-layer quasioptical dielectric resonator with whispering gallery wave modes when the internal layer is water or benzine. The sign of the shift indicates that the real part of dielectric permittivity of the water surface layer adjacent to a solid-state dielectric becomes negative (ε≪0). The measurements were carried out at room temperature in microwave K band. © 2003 American Institute of Physics. View full abstract»

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  • Temperature-dependent spectral generalized magneto-optical ellipsometry

    Page(s): 4509 - 4511
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    We present a setup for temperature-dependent spectral generalized magneto-optical ellipsometry (SGME). This technique gives access to the electronic as well as the magnetic properties of ferromagnetic materials within one single magneto-optical measurement. It also allows the determination of the orientation of the magnetization. We show spectra of the real and the imaginary part of the refractive index N as well as the magneto-optical coupling parameter Q of permalloy and iron films for in-plane magnetization. Our findings demonstrate the relevance of SGME for the understanding of the interplay between electronic and magnetic properties of ferromagnetics. © 2003 American Institute of Physics. View full abstract»

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  • Correlation between the volume change during crystallization and the thermal stability of supercooled liquids

    Page(s): 4512 - 4514
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    We have measured the density of Pd40Ni40-xCuxP20 (x=0–40) alloys in the amorphous and crystalline states. For x≫30, the alloys are denser in the amorphous than in the crystalline states, which is contrary to the behavior of all known metallic glasses. For Pd40Ni40-xCuxP20 and all other bulk metallic glasses where density data are available in both the amorphous and crystalline states, we find a correlation between the stability of the supercooled liquids and the difference between the molar volumes of the glassy and crystalline phases. The supercooled liquid region is largest for those alloys that show no change in molar volume upon crystallization. © 2003 American Institute of Physics. View full abstract»

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  • Interface stability and solid-state amorphization in an immiscible Cu–Ta system

    Page(s): 4515 - 4517
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    Assisted by ab initio calculation, a realistic Cu–Ta potential is derived and applied to determine the energies of Cu/Ta interfaces with various orientations by molecular dynamics simulations. It turns out that the (111) Cu/(100) Ta and (111) Cu/(110) Ta interfaces are thermally stable at a temperature of 873 K and that for the other Cu/Ta interfaces, the interface energies are sufficiently high to drive interfacial reaction and solid-state amorphization, which features an asymmetric behavior, i.e., the amorphous interlayer grows faster toward Cu than that toward Ta. © 2003 American Institute of Physics. View full abstract»

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  • Step instability and island formation during annealing of pseudomorphic InGaAs/GaAs layers

    Page(s): 4518 - 4520
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    The morphological stability of compressively strained In0.27Ga0.73As/GaAs pseudomorphic layers has been investigated during annealing. Large three-dimensional islands form at the beginning of annealing on initially flat surfaces, likely to relieve strain energy. The islands disappear with increasing annealing, being reabsorbed into the terraces. At the same time, the step line destabilizes forming cusps that inject two-dimensional vacancy islands into the terrace. At high temperatures, this process leads to a severe deterioration of the morphology that is not due to decomposition. The island dissolution and the development of the step instability are likely alternative paths towards the reduction of surface energy. © 2003 American Institute of Physics. View full abstract»

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  • Room-temperature electroluminescence properties of Er,O-codoped GaAs injection-type light-emitting diodes grown by organometallic vapor phase epitaxy

    Page(s): 4521 - 4523
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    Room-temperature Er-related electroluminescence (EL) properties have been investigated in Er,O-codoped GaAs (GaAs:Er,O) light-emitting diodes grown by organometallic vapor phase epitaxy. Under forward bias, characteristic emission due to a luminescence center consisting of Er coordinated by O and As was clearly observed at room temperature. The injection current density dependence of the EL intensity and its dynamics revealed extremely large excitation cross section of 1–2×10-15cm2. The excitation cross section for current injection c) is by five orders of magnitude larger than that for optical excitation o) in Er-doped fiber amplifiers (10-21–10-20cm2). © 2003 American Institute of Physics. View full abstract»

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  • Improvement of InAs quantum-dot optical properties by strain compensation with GaNAs capping layers

    Page(s): 4524 - 4526
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    Two kinds of self-assembled InAs quantum dots (QDs) grown on GaAs (001) substrates were studied. One is capped with GaAs layers and the other with GaNAs strain-compensating layers. Photoluminescence (PL) measurements on the two kinds of InAs QDs showed distinct dependence on the selection of the capping layers. The homogeneity and luminescence efficiency of the InAs QDs were much improved when the net strain was reduced with GaNAs layers. These results demonstrate the importance of net strain compensation for the improved optical quality of InAs QDs. © 2003 American Institute of Physics. View full abstract»

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  • Pareto-optimal alloys

    Page(s): 4527 - 4529
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    Large databases that can be used in the search for new materials with specific properties remain an elusive goal in materials science. The problem is complicated by the fact that the optimal material for a given application is usually a compromise between a number of materials properties and the cost. In this letter we present a database consisting of the lattice parameters, bulk moduli, and heats of formation for over 64 000 ordered metallic alloys, which has been established by direct first-principles density-functional-theory calculations. Furthermore, we use a concept from economic theory, the Pareto-optimal set, to determine optimal alloy solutions for the compromise between low compressibility, high stability, and cost. © 2003 American Institute of Physics. View full abstract»

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  • Heteroepitaxy of GaN on Si(111) realized with a coincident-interface AlN/β-Si3N4(0001) double-buffer structure

    Page(s): 4530 - 4532
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    We present a stacked buffer mechanism for heteroepitaxial growth with large lattice mismatch. The stacked buffer consists of constituent layers, which can form coincident lattices at layer/layer and layer/substrate interfaces. For the case of GaN-on-Si(111) heteroepitaxy, we utilize the 1:2 and 5:2 coincident lattices formed at the β-Si3N4(0001)/Si(111) and AlN(0001)/β-Si3N4(0001) interfaces, respectively, to facilitate the double-buffer layer for GaN-on-Si heteroepitaxial growth. By using this buffer technique, we resolve the issue of autodoping resulting from Si outdiffusion when grown with a single AlN(0001) buffer. As a result, the epitaxial quality of GaN film is also significantly improved. © 2003 American Institute of Physics. View full abstract»

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  • Optical properties of gallium oxide films deposited by electron-beam evaporation

    Page(s): 4533 - 4535
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    Thin films of gallium oxide were deposited by electron-beam evaporation on unheated substrates. Samples were deposited either without oxygen, or under an oxygen partial pressure of 5×10-4 mbar. The films were amorphous. Films deposited with oxygen were stoichiometric, whereas those deposited without oxygen were substoichiometric. The optical properties of the films were derived from measurements, at normal incidence, of transmittance and reflectance. Films deposited without oxygen had higher values of the refractive index and extinction coefficient. The energy gaps were 5.04 and 4.84 eV for films deposited with and without oxygen, respectively. © 2003 American Institute of Physics. View full abstract»

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  • Epitaxial growth of quaterphenyl thin films on gold(111)

    Page(s): 4536 - 4538
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    The crystal structure and molecular arrangement of para-quaterphenyl (4P) grown on single crystalline Au(111) was investigated over a wide thickness range. The molecular arrangement in the first monolayer, as investigated with low energy electron diffraction, shows a highly regular structure. This wetting layer is defined by adsorbate–substrate interactions and forms a prestage for the epitaxial growth of 4P single crystalline islands, as observed in x-ray diffraction. Two similar orientations of the 4P bulk phase are observed, with the (211) and (311) planes parallel to the Au(111) surface. The alignment of the molecules was kept unchanged from the first monolayers up to a film thickness of 200 nm. © 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