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Applied Physics Letters

Issue 4 • Date Jul 2001

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Displaying Results 1 - 25 of 38
  • 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
  • Highly efficient electroluminescent materials based on fluorinated organometallic iridium compounds

    Page(s): 449 - 451
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    We report a class of highly efficient electroluminescent materials based on fluorinated iridium compounds. Using aluminum as the cathode, a device, using fac-tris[5-fluoro-2(5-trifluoromethyl-2-pyridinyl)phenyl-C,N]iridium (Ir-2h) as the luminescent layer, displayed intense electroluminescence at 525 nm with an efficiency of 20 cd/A and a maximum radiance of 4800 cd/m2. Differing from the previously reported Ir(ppy)3, Ir-2h can be used in the undiluted form without the use of a charge-transporting host. This indicates that Ir-2h by itself has good enough charge-transporting properties. Photoluminescence studies at room temperature and 77 K revealed that electroluminescence originates from the metal-to-ligand charge transfer state with a quantum yield of 0.56 for Ir-2h and 0.5 for Ir(ppy)3 in toluene at room temperature. In the thin-film form, photoluminescence quantum yield of Ir-2h is a factor of 10 greater than that of Ir(ppy)3 due to the larger self-quenching effect of Ir(ppy)3. © 2001 American Institute of Physics. View full abstract»

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  • High-repetition-rate polymeric solid-state dye lasers pumped by a copper-vapor laser

    Page(s): 452 - 454
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    We report on the laser action of pyrromethene 567 incorporated into polymeric matrices and pumped longitudinally with the green line of a copper-vapor laser. When the dye was dissolved in a copolymer of methyl methacrylate and pentaerythritol triacrylate, 290 mW average power at 1 kHz (37% lasing efficiency) was obtained. The laser output decreased to 150 mW after 30 min irradiation time (1.8×106shots) and to 32 mW after 70 min of operation (4.2×106shots). Output power of up to 1 W at 6.2 kHz was obtained for short periods of time. Polymeric matrices incorporating rhodamine 6G were also studied. © 2001 American Institute of Physics. View full abstract»

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  • Infrared absorption of an In0.2Ga0.8As/GaAs quantum-well infrared photodetector employing a p–n–p camel diode structure

    Page(s): 455 - 457
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    Far-infrared absorption of an In0.2Ga0.8As/GaAs multiple-quantum-well infrared photodetector employing a p–n–p camel diode structure is studied. The detector showed a photocurrent response to normal incident light at approximately 3 μm due to the intersubband hole transition, which is attributed to the strong hole–band mixing of the strained multiple quantum well. Application of the camel diode structure to the photodetector substantially reduced the dark hole current, resulting in an improved detectivity. © 2001 American Institute of Physics. View full abstract»

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  • Ultraviolet single-frequency pulses with high average power using frequency-converted passively Q-switched quasimonolithic Nd:yttrium–aluminum–garnet ring lasers

    Page(s): 458 - 460
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    We demonstrate a compact ultraviolet light source based on frequency-converted diode-pumped passively Q-switched miniature Nd:yttrium–aluminum–garnet (YAG) ring lasers. A unique pulse-to-pulse stability in single-frequency operation is obtained by diffusion-bonding the Nd:YAG crystal with the Cr4+:YAG saturable absorber crystal to form an all-solid-state quasimonolithic ring laser cavity. Amplified in a longitudinally pumped Nd:vanadate (YVO4) crystal and single-pass frequency quadrupled in periodically poled potassium titanyl phosphate and barium borate crystals, an average output power of 485 mW at 266 nm with 25 μJ pulse energy is achieved with an overall efficiency of 3.3% with respect to the diode pump power. © 2001 American Institute of Physics. View full abstract»

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  • Optical control of an integrated interferometer using a photochromic polymer

    Page(s): 461 - 463
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    An integrated optical interferometer has been fabricated using ion exchange technology in glass. Using a photochromic polymer, we show that it is possible to reversibly modulate the phase of the guided wave with an optical control beam. This constitutes a demonstrator of an optically controlled integrated optical device. © 2001 American Institute of Physics. View full abstract»

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  • Zero-point oscillations in the vicinity of atoms

    Page(s): 464 - 466
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    It is shown that the vacuum fluctuations of an electromagnetic field are concentrated near atoms. This effect worsens the quantum limit of precision of the measurements in atomic systems. © 2001 American Institute of Physics. View full abstract»

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  • Ion-irradiation-induced mixing, interface broadening and period dilation in Pt/C multilayers

    Page(s): 467 - 469
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    Pt/C multilayers of nanometric dimension have been irradiated with 2-MeV-Au ions to a fluence of 1×1014ions/cm2 and analyzed by x-ray reflectivity and x-ray standing wave measurements. The multilayer period has expanded by ∼9%, the expansion of the Pt layers being larger than that of the C layers. Ion-induced displacement of atoms across the interfaces led to an increased interface roughness and an increase of 2 at. % Pt in C layers. Monte Carlo simulations for ion-induced atomic displacement have been used to explain the observed effects. © 2001 American Institute of Physics. View full abstract»

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  • Single-crystalline rocksalt CdO layers grown on GaAs (001) substrates by metalorganic molecular-beam epitaxy

    Page(s): 470 - 472
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    In this letter, we report the growth of single-crystalline rocksalt CdO layers on (001) GaAs substrates using ZnS buffer layers. The growth processes of CdO layers were studied by reflection high-energy electron diffraction (RHEED), and the grown CdO layers were evaluated with atomic force microscopy (AFM), and x-ray diffraction (XRD) measurements. After an initial growth delay, the formation of polycrystalline CdO was observed in RHEED measurements during the initial growth of very thin CdO layers. With the increase of the CdO layer thicknesses, streaky RHEED patterns were observed, which indicate the formation of single-crystalline cubic-phase CdO layers. Surface morphology of the CdO layers observed by AFM was atomically flat with root-mean-square roughness of ∼1 nm. The crystalline structures were elucidated from XRD measurements by the determination of the lattice constant to be 4.686±0.001 Å, indicating the single-phase rocksalt CdO structure. © 2001 American Institute of Physics. View full abstract»

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  • Determination of the dispersion of the index of refraction and the elastic moduli for molecular-beam-epitaxy-grown Zn1-xBexSe alloys

    Page(s): 473 - 475
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    The prism coupler technique, together with reflectivity channeled spectra, were used to determine the dispersion of the indices of refraction for a series of ternary alloys of Zn1-xBexSe grown by molecular-beam epitaxy on GaAs substrates. The measurements covered the wavelength range of 400–1300 nm, and the entire Be concentration range, from x=0 to 1.00. The availability of accurate values of the index-of-refraction then enabled us to determine the elastic moduli c11 for the Zn1-xBexSe and its dependence on the Be concentration x from frequency shifts in Brillouin scattering spectra observed on the epilayers of these ternary alloys. The c11 results clearly indicate that the bonding in Zn1-xBexSe becomes more robust as the Be concentration increases. © 2001 American Institute of Physics. View full abstract»

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  • Fabrication of strain-balanced Si0.73Ge0.27/Si distributed Bragg reflectors on Si substrates

    Page(s): 476 - 478
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    Strain-balanced Si0.73Ge0.27/Si distributed Bragg reflectors (DBRs) which were designed to overcome the limitation of the number of pairs originating from the strain accumulation were fabricated. Raman spectra of Si0.73Ge0.27/Si DBRs with 11 and 25 mirror pairs showed that SiGe and Si layers were under compressive and tensile strain on SiGe virtual substrates as designed. A record reflectivity of 80% was achieved at 1.44 μm in SiGe/Si DBRs with 25 pairs. The surface roughness of the 25 pair sample, however, was increased to about 46 nm compared with 6.3 nm of the 11 pair sample. © 2001 American Institute of Physics. View full abstract»

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  • Ti3SiC2 and ice

    Page(s): 479 - 481
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    Despite vast differences in their other properties, the responses of Ti3SiC2 and ice to stress are quite similar in that they are quite strain-rate sensitive; if loaded rapidly, both are brittle, but if loaded slowly they are quite plastic. This stems from the fact that both are plastically very anisotropic; deformation occurs overwhelmingly, if not exclusively, by slip along basal planes. In both cases, stress concentrations and the rate at which they are relaxed dictate the nature of the mechanical response. In the brittle regime, microcracks and their linkage play a dominant role in both cases. © 2001 American Institute of Physics. View full abstract»

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  • Direct correlation between microstructure and mechanical tensile properties in Pb-free solders and eutectic SnPb solder for flip chip technology

    Page(s): 482 - 484
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    The relationship between the microstructure and the mechanical tensile properties of lead-free solders and eutectic SnPb solders is presented for flip chip scale interconnects. Eutectic Sn–37Pb and Sn–0.7Cu solder (in wt %) exhibited a ductile fracture after tensile testing. Eutectic Sn–3.5Ag solder (in wt %) had greater strength and exhibited a brittle fracture at the interface. The different fracture behavior of the lead-free solders was attributed to the grain size and configuration of the intermetallics. Minor additions of alloying elements to the high Sn lead-free solder dramatically affected the microstructure and mechanical properties. © 2001 American Institute of Physics. View full abstract»

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  • Local structure of amorphous Zr70Pd30 alloy studied by electron diffraction

    Page(s): 485 - 487
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    The structures of melt-spun, and subsequently annealed, Zr70Pd30 alloys, which form a nanosized icosahedral quasicrystalline phase during the primary crystallization of the amorphous phase, have been investigated by means of electron-diffraction pair-distribution-function (PDF) analysis. The PDF analysis for this alloy was performed by precise measurements of elastic halo-electron-diffraction intensities. Possible structure models for as-quenched and annealed amorphous structures were constructed with the help of reverse Monte Carlo simulations. In order to obtain the local atomic structures, the Voronoi-polyhedra analysis was performed. A considerable number of icosahedral clusters with Zr atoms in the center are present in the simulated structure of the as-quenched state, and the number of the clusters increases by annealing. © 2001 American Institute of Physics. View full abstract»

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  • Visible luminescence from a-SiN films doped with Er and Sm

    Page(s): 488 - 490
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    Relatively strong and narrow red and green light emission has been achieved from amorphous (a-) SiN films independently doped with Er3+ and Sm3+ ions. The films were deposited by cosputtering a Si target partially covered with small pieces of metallic Er (and Sm) in an atmosphere of pure nitrogen. As a consequence of the deposition method and conditions, the films have an amorphous structure, and contents of Er (and Sm) in the low 0.5 at. %. All characterizations were accomplished on as-deposited samples and at room temperature and included: ion-beam analysis (Rutherford backscattering spectrometry and nuclear reaction analysis) and optical techniques (light absorption, Raman scattering, and photoluminescence and cathodoluminescence). A detailed examination of the experimental results allowed the identification of all luminescence features existing in the films. © 2001 American Institute of Physics. View full abstract»

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  • Optical constants of ice Ih crystal at terahertz frequencies

    Page(s): 491 - 493
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    Terahertz time-domain spectroscopy was used to measure the refractive indices of Ih crystalline ice in the frequency range of 0.25–1.0 THz. With increasing frequency, the real part, n, of the refractive index increases from 1.787 to 1.793 at 243 K, and the imaginary part, n, increases from 0.005 to 0.020. The temperature dependence of n is less than 0.01%/K and that of n is ∼1%/K. Our results connect smoothly to the data of Matsuoka and co-workers [T. Matsuoka, S. Fujita, and S. Mae, J. Appl. Phys. 80, 5884 (1996)] in the microwave range and the data in the far IR range, and can be well described by the existing theoretical models. © 2001 American Institute of Physics. View full abstract»

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  • Low-temperature selective deposition of silicon on silicon nitride by time-modulated disilane flow and formation of silicon narrow wires

    Page(s): 494 - 496
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    The low-temperature (410 °C) selective deposition of Si on silicon nitride has been achieved by means of the time-modulated flow of disilane while a very small amount of Si is deposited on SiO2. Very narrow (21 nm width and 28 nm thick) Si wires have been fabricated using the selective deposition. The resistivity of the Si wires fabricated by the selective deposition is much smaller (∼1/5) than that fabricated by the conventional reactive ion etching followed by annealing. This technique will be applicable to the formation of a polycrystalline silicon gate with small resistivity for the high-performance ultrasmall metal–oxide–semiconductor transistors and quantum effect devices. © 2001 American Institute of Physics. View full abstract»

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  • Greatly enhanced detection sensitivity for carbon, nitrogen, and oxygen in silicon by secondary-ion-mass spectrometry

    Page(s): 497 - 499
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    The detection limits of secondary-ion-mass spectrometry for carbon, nitrogen, and oxygen in silicon are determined and are shown to be as low as about 1×1014 atoms/cm3 for nitrogen and 2×1015 atoms/cm3 for carbon and oxygen. This very high sensitivity is achieved by an analytical approach: to suppress the interference from residual-gas adsorption onto the sputtered surface, the elemental concentrations are extrapolated to a zero contribution from these adsorbed species by an incremental increase of the applied ion-beam erosion rate. © 2001 American Institute of Physics. View full abstract»

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  • Dynamical behaviors of GaCl on the GaAs(001) 4×6 surface by pulsed molecular beam scattering

    Page(s): 500 - 502
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    We studied dynamical behaviors of gallium chloride (GaCl) on a GaAs(001) 4×6 surface using pulsed molecular beam scattering. The angular distribution of reflected GaCl consists of two parts; inelastic direct scattering contribution and thermal desorption of trapped molecules on the GaAs(001) 4×6 surface. We divided the time of flight spectra of thermally desorbed GaCl into two components with activation energies of 22.0 and 10.5 kcal/mol corresponding to GaCl trapping wells. These wells were associated with two comparatively large domains on the GaAs(001) 4×6 surface. The relatively large activation energy is responsible for the strong dipole-electrostatic interaction between GaCl, which has a large dipole moment, and the ionic GaAs crystal. © 2001 American Institute of Physics. View full abstract»

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  • Atomic scale investigations of the Co/Pt(111) interface structure and magnetic properties

    Page(s): 503 - 505
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    The interface structure of an ultrathin Co overlayer on a Pt(111) crystal was investigated with atomic-layer resolution medium-energy ion scattering spectroscopy and surface magneto-optical Kerr effect (SMOKE). For a 7 ML Co, interdiffusion begins at 673 K to form a heavily distorted Co–Pt surface alloy layer with little change in SMOKE intensity. However, annealing at 773 K formed a 30 atomic-layer-thick Co–Pt substitutional alloy with 3.7% maximum tensile strain, at which the SMOKE intensity increased more than 200%. The enhancement of the Kerr intensity is discussed with the interface alloy formation. © 2001 American Institute of Physics. View full abstract»

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  • Colossal magnetoresistance in doped manganites: A consequence of percolation and phase separation

    Page(s): 506 - 508
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    We report measurements of the resistivity and magnetization of high-quality melt-processed La0.67Ca0.33MnO3 (LCM) and Sr-doped LCM materials that exhibit a sharp and enhanced metal–insulator transition (TMI) with significant colossal magnetoresistance (CMR) and two competing magnetic phases in the vicinity of TMI. Our results can well be explained using percolation in combination with the phase-separation scenario proposed for CMR. We propose that the spin polarization through grain boundaries and the enhanced grain connectivity between the ferromagnetic domains facilitate better percolation through a junction and filament-like resistor network. © 2001 American Institute of Physics. View full abstract»

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  • Scaling behavior of higher harmonic responses in textured (Bi,Pb)2Sr2Ca2Cu3Oy/Ag tapes

    Page(s): 509 - 511
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    A silver-sheathed (Bi,Pb)2Sr2Ca2Cu3Oy tape was studied in terms of harmonic responses χnn-iχn (n=3, 5, 7) to reveal the angular dependence of its physical properties. In the screening method higher harmonic responses are directly related to the nonlinear voltage–current [E(J)] relation of the sample. Therefore, the effect of the silver sheath on the harmonic measurements can be neglected. We performed measurements of the harmonic responses as a function of applied magnetic field or angle between the magnetic field and the tape plane at various temperatures. The measured data could be scaled onto a single curve by using the three-dimensional scaling relation. The derived anisotropic parameter γ ranged from 5.1 to 5.6 at the measured temperature region. Such a small γ value was attributed to the misalignment of the grains in the tape. © 2001 American Institute of Physics. View full abstract»

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  • Correlation of power handling capability and intermodulation distortion in YBa2Cu3O7-δ thin films

    Page(s): 512 - 514
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    The nonlinearity of the microwave properties of coplanar thin-film YBa2Cu3O7-δ resonators are examined by measurements of the degradation of the quality factor QL and the increase of the two-tone third-order intermodulation distortion signal with increasing microwave power. A linear correlation between the data of the characteristic microwave powers, which are obtained for the degradation of QL and the intermodulation signal, is experimentally observed and explained in terms of a theoretical model based solely on well-known expressions for the nonlinear surface resistance. Due to these experimental observations and the theoretical model, we conclude, that the degradation of the resonator Q factor and the generation of intermodulation distortion are determined by the same physical mechanism and that thermal effects can most likely be excluded. © 2001 American Institute of Physics. View full abstract»

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  • Atomic-scale observation of polarization switching in epitaxial ferroelectric thin films

    Page(s): 515 - 517
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    The thin-film x-ray standing wave (XSW) technique is used for an atomic-scale study of polarization switching in ferroelectric Pb(Zr0.3Ti0.7)O3 (PZT)/electrode heterostructures grown on SrTiO3(001). The XSW is selectively generated in the PZT by the interference between the incident x-ray wave and the weak (001) Bragg diffracted wave from the film. The XSW excites a fluorescence signal from the Pb ions in the PZT film, that is used to determine their subangström displacements after polarization switching has occurred. This experimental method yields unique information on the underlying atomic configurations for different polarization domain 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