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17 May 2004

Volume 84, Issue 20, pp. 3957-4121

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 4104 (2004); http://dx.doi.org/10.1063/1.1753068 (3 pages)

Tetsuya Akasaka, Toshio Nishida, Toshiki Makimoto, and Naoki Kobayashi
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Conducting fluorocarbon coatings for organic light-emitting diodes

S. W. Tong, C. S. Lee, Y. Lifshitz, D. Q. Gao, and S. T. Lee

Appl. Phys. Lett. 84, 4032 (2004); http://dx.doi.org/10.1063/1.1751220 (3 pages) | Cited 13 times

Online Publication Date: 5 May 2004

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Conducting fluorocarbon coatings (CFx) have recently been used as an anode buffer layer in organic light-emitting diode (OLEDs) for enhancement of stability and carrier injection. The effect of CFx on OLEDs was related to its conductivity. We found the resistivity of poorly conducting (about 1010 Ω cm) CFx coatings can be substantially decreased to 105 Ω cm by either near UV or Ar ion irradiation. OLEDs were prepared on untreated and treated CFx for performance comparison. The UV treatment of CFx improved the device performance, while the Ar ion treatment led to deterioration. X-ray photoelectron spectroscopy analysis showed the UV treatment created graphitic regions leading to the higher conductivity of the CFx layer but the underlying indium tin oxide (ITO) anode remained intact. In contrast, argon ion bombardment caused damage to the ITO anode which contributed to poor device performance, although the CFx conductivity was similarly increased. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
81.15.Kk Vapor phase epitaxy; growth from vapor phase
85.30.De Semiconductor-device characterization, design, and modeling
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Excimer laser nanostructuring of nickel thin films for the catalytic growth of carbon nanotubes

S. J. Henley, C. H. P. Poa, A. A. D. T. Adikaari, C. E. Giusca, J. D. Carey, and S. R. P. Silva

Appl. Phys. Lett. 84, 4035 (2004); http://dx.doi.org/10.1063/1.1751226 (3 pages) | Cited 16 times

Online Publication Date: 5 May 2004

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Pulse laser ablation and subsequent laser nanostructuring at room temperature has been employed to produce nanostructured Ni on SiO2/Si substrates for catalytic growth of carbon nanotubes. The resultant nanostructured surface is seen to consist of nanometer sized hemispherical droplets whose mean diameter is controlled by the initial metal thickness, which in turn is readily controlled by the number of laser pulses. Vertically aligned multiwall carbon nanotube mats were then grown using conventional plasma enhanced chemical vapor deposition. We show that within a single processing technique it is possible to produce the initial metal-on-oxide thin film to a chosen thickness but also to be able to alter the morphology of the film to desired specifications at low macroscopic temperatures using the laser parameters. The influence of the underlying oxide is also explored to explain the mechanism of nanostructuring of the Ni catalyst. © 2004 American Institute of Physics.
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81.07.De Nanotubes
81.16.Mk Laser-assisted deposition

Self-assembled magnetic nanostripes by organic patterning

X. Ma, H. L. Meyerheim, J. Barthel, J. Kirschner, S. Schmitt, and E. Umbach

Appl. Phys. Lett. 84, 4038 (2004); http://dx.doi.org/10.1063/1.1751228 (3 pages) | Cited 7 times

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Selective adsorption of Fe deposited on the organic molecule 3,4,9,10-perylene-tetracarboxylic-3, 4,9,10-dianhydride (PTCDA) is used to prepare a self assembled magnetic nanostripe structure on a vicinal Ag surface. Scanning tunneling microscopy reveals that after PTCDA deposition on the Ag(10 8 7) surface a grating-like domain pattern is formed. It consists of alternating stripes of molecule-covered facets and uncovered (111) terraces. Fe adsorption takes place selectively on the molecule-covered stripes forming disk-shaped super-paramagnetic islands with a polar easy magnetization axis. © 2004 American Institute of Physics.
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81.16.Dn Self-assembly
75.75.-c Magnetic properties of nanostructures
81.16.Rf Micro- and nanoscale pattern formation
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Formation chemistry of high-density nanocraters on the surface of sapphire substrates with an in situ etching and growth mechanism of device-quality GaN films on the etched substrates

M. Hao, H. Ishikawa, and T. Egawa

Appl. Phys. Lett. 84, 4041 (2004); http://dx.doi.org/10.1063/1.1751607 (3 pages) | Cited 3 times

Online Publication Date: 5 May 2004

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An efficient method has been investigated to grow GaN films with sapphire substrates being treated in situ metalorganic chemical vapor deposition reactor for a special effect rather than simple thermal cleaning. First, a thin GaN layer is grown on the sapphire substrate. And then it is almost etched away by thermal decomposition. It is found that the decomposition of GaN induces the decomposition of sapphire resulting in the formation of high-density nanocraters on its surface. Finally the device-quality GaN film is regrown on the etched substrate with residual gallium droplets as nucleation sites. The chemistry of the etching process and the mechanism of the final GaN growth process have been discussed. The distinct feature of this method is the in situ formation of high-density nanocraters on the surface of the substrate. A rough interface between the substrate and GaN can improve the efficiency of the light-emitting diode built on it greatly. © 2004 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
68.55.-a Thin film structure and morphology
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Measurement of guided light-mode intensity: An alternative waveguide sensing principle

Róbert Horváth, Nina Skivesen, and Henrik C. Pedersen

Appl. Phys. Lett. 84, 4044 (2004); http://dx.doi.org/10.1063/1.1751610 (3 pages) | Cited 16 times

Online Publication Date: 5 May 2004

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An alternative transduction mechanism for planar optical waveguide sensors is reported. Based on a simple measurement of the mode intensity, the presented transduction is an interesting alternative to the conventional mode-angle transduction, because the expensive, high-precision angular rotation usually employed may be avoided. © 2004 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.79.Pw Imaging detectors and sensors
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Coulomb blockade in a silicon/silicon–germanium two-dimensional electron gas quantum dot

L. J. Klein, K. A. Slinker, J. L. Truitt, S. Goswami, K. L. M. Lewis, S. N. Coppersmith, D. W. van der Weide, Mark Friesen, R. H. Blick, D. E. Savage, M. G. Lagally, Charlie Tahan, Robert Joynt, M. A. Eriksson, J. O. Chu, et al.

Appl. Phys. Lett. 84, 4047 (2004); http://dx.doi.org/10.1063/1.1751612 (3 pages) | Cited 34 times

Online Publication Date: 5 May 2004

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We report the fabrication and electrical characterization of a single electron transistor in a modulation doped silicon/silicon–germanium heterostructure. The quantum dot is fabricated by electron beam lithography and subsequent reactive ion etching. The dot potential and electron density are modified by laterally defined side gates in the plane of the dot. Low temperature measurements show Coulomb blockade with a single electron charging energy of 3.2 meV. © 2004 American Institute of Physics.
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85.35.Gv Single electron devices
81.07.Ta Quantum dots
81.16.Nd Micro- and nanolithography
73.23.Hk Coulomb blockade; single-electron tunneling
73.61.Le Other inorganic semiconductors
73.61.Cw Elemental semiconductors
81.65.Cf Surface cleaning, etching, patterning
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Femtosecond-laser-activated fluorescence from silver oxide nanoparticles

T. Gleitsmann, B. Stegemann, and T. M. Bernhardt

Appl. Phys. Lett. 84, 4050 (2004); http://dx.doi.org/10.1063/1.1751613 (3 pages) | Cited 21 times

Online Publication Date: 5 May 2004

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A method for fast spatially resolved photoactivation of fluorescence from silver oxide nanoparticle films is presented. High activation rates are achieved through fast scanning of a focused high repetition rate 800 nm femtosecond laser with a peak power of 6.5 MW/cm2 over the sample. The activated areas of the thin films show fluorescence after subsequent excitation with an Ar+/Kr+ laser. The fluorescent properties were investigated by means of scanning laser microscopy at ambient conditions. Depending on excitation wavelengths (488 or 568 nm) strong fluorescence in the green or red domain was observed. The activation efficiencies were examined both as a function of exposure time and femtosecond laser power. Sensitivity, reliability and possible mechanisms for the photoactivation process are discussed. © 2004 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.66.Nk Insulators
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Influence of misfit dislocations on the electrical properties of CdTe layers grown by molecular beam epitaxy on InSb

G. M. Khattak, G. W. Matthews, C. G. Scott, and M. Yousaf

Appl. Phys. Lett. 84, 4053 (2004); http://dx.doi.org/10.1063/1.1751615 (3 pages) | Cited 2 times

Online Publication Date: 5 May 2004

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The electrical properties of n-CdTe films grown by molecular beam epitaxy on (001) InSb substrates have been studied with a view to examining the influence of dislocations arising from strain relaxation in these materials. It is shown that the observed nonuniformity in free carrier density as a function of depth through the films can be explained by electron trapping at dislocations assuming that the density of dislocations diminishes with distance from the substrate surface in proportion to the spatially distributed strain within the films. From a comparison of the experimentally deduced and theoretically derived values for the maximum dislocation density, it is concluded that CdTe layers grown using a stoichiometric Cd/Te flux are characterized by an interfacial layer, probably In2Te3, consistent with independent evidence from x-ray diffraction studies. © 2004 American Institute of Physics.
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73.61.Ga II-VI semiconductors
61.72.Lk Linear defects: dislocations, disclinations
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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Strong quantum-confinement effects in the conduction band of germanium nanocrystals

C. Bostedt, T. van Buuren, T. M. Willey, N. Franco, L. J. Terminello, C. Heske, and T. Möller

Appl. Phys. Lett. 84, 4056 (2004); http://dx.doi.org/10.1063/1.1751616 (3 pages) | Cited 53 times

Online Publication Date: 5 May 2004

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Quantum-confinement effects in the conduction band of deposited germanium nanocrystals are measured to be greater than in similar-sized silicon nanocrystals. The germanium particles are condensed out of the gas phase and their electronic properties are determined with x-ray absorption spectroscopy. The conduction band edge shifts range from 0.2 eV for 2.7 nm particles up to 1.1 eV for 1.2 nm particles. © 2004 American Institute of Physics.
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73.63.Bd Nanocrystalline materials
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
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All-optical switching due to state filling in quantum dots

R. Prasanth, J. E. M. Haverkort, A. Deepthy, E. W. Bogaart, J. J. G. M. van der Tol, E. A. Patent, G. Zhao, Q. Gong, P. J. van Veldhoven, R. Nötzel, and J. H. Wolter

Appl. Phys. Lett. 84, 4059 (2004); http://dx.doi.org/10.1063/1.1751617 (3 pages) | Cited 31 times

Online Publication Date: 5 May 2004

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We report all-optical switching due to state filling in quantum dots (QDs) within a Mach–Zehnder interferometric switch (MZI). The MZI was fabricated using InGaAsP/InP waveguides containing a single layer of InAs/InP QDs. A 1530–1570 nm probe beam is switched by optical excitation of one MZI arm. By exciting below the InGaAsP band gap, we prove that the refractive index nonlinearity is entirely due to the QDs. The switching efficiency is 5 rad/(μW absorbed power), corresponding to a 6 fJ switching energy. Probe wavelength insensitivity was obtained using a broad size distribution of QDs. © 2004 American Institute of Physics.
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78.67.Hc Quantum dots
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
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Thermophysical properties of a highly superheated and undercooled Ni–Si alloy melt

H. P. Wang, C. D. Cao, and B. Wei

Appl. Phys. Lett. 84, 4062 (2004); http://dx.doi.org/10.1063/1.1751618 (3 pages) | Cited 20 times

Online Publication Date: 5 May 2004

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The surface tension of superheated and undercooled liquid Ni–5 wt % Si alloy was measured by an electromagnetic oscillating drop method over a wide temperature range from 1417 to 1994 K. The maximum undercooling of 206 K (0.13 TL) was achieved. The surface tension of liquid Ni–5 wt % Si alloy is 1.697 N m−1 at the liquidus temperature 1623 K, and its temperature coefficient is −3.97×10−4 N m−1 K−1. On the basis of the experimental data of surface tension, the other thermophysical properties such as the viscosity, the solute diffusion coefficient, and the density of liquid Ni–5 wt % Si alloy were also derived. © 2004 American Institute of Physics.
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68.03.Cd Surface tension and related phenomena
66.20.-d Viscosity of liquids; diffusive momentum transport
66.10.C- Diffusion and thermal diffusion
61.25.Mv Liquid metals and alloys
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Surface effects in Mn L3,2 x-ray absorption spectra from (Ga,Mn)As

K. W. Edmonds, N. R. S. Farley, R. P. Campion, C. T. Foxon, B. L. Gallagher, T. K. Johal, G. van der Laan, M. MacKenzie, J. N. Chapman, and E. Arenholz

Appl. Phys. Lett. 84, 4065 (2004); http://dx.doi.org/10.1063/1.1751619 (3 pages) | Cited 45 times

Online Publication Date: 5 May 2004

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We have identified a Mn-rich layer on the surface on (Ga,Mn)As thin films which significantly influences soft x-ray absorption measurements. The Mn L3,2 x-ray absorption spectra of the untreated films show a strong multiplet structure, consistent with earlier observations and characteristic of MnO. After removal of the surface layer, the multiplet structure is less pronounced and the spectrum is shifted to ∼0.5 eV lower photon energy. Comparison with calculated spectra imply a localized Mn ground state for the untreated sample and a hybridized ground state after etching. In addition, a large x-ray magnetic circular dichroism is observed at the Mn L3,2 edge in the etched film. These results may explain several peculiarities of previously reported x-ray absorption studies from (Ga,Mn)As. © 2004 American Institute of Physics.
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78.70.Dm X-ray absorption spectra
81.65.Cf Surface cleaning, etching, patterning
75.70.Ak Magnetic properties of monolayers and thin films
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Terahertz quantum-well photodetector

H. C. Liu, C. Y. Song, A. J. SpringThorpe, and J. C. Cao

Appl. Phys. Lett. 84, 4068 (2004); http://dx.doi.org/10.1063/1.1751620 (3 pages) | Cited 62 times

Online Publication Date: 5 May 2004

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The design and projected performance of quantum-well infrared photodetectors (QWIP) for the terahertz (1–10 THz) or the very-far-infrared region are presented together with our initial demonstration of a GaAs/AlGaAs QWIP working at photon energies below the optical phonons. We point out the problem with this initial device, discuss possible causes, and suggest areas of improvement.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
78.67.De Quantum wells
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
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Nonuniform twin-boundary motion in Ni–Mn–Ga single crystals

Miguel A. Marioni, Samuel M. Allen, and Robert C. O’Handley

Appl. Phys. Lett. 84, 4071 (2004); http://dx.doi.org/10.1063/1.1751621 (3 pages) | Cited 16 times

Online Publication Date: 5 May 2004

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The twin-boundary motion in Ni–Mn–Ga single crystals has been studied with 620 μs magnetic-field pulses on samples of 5 mm×5 mm cross section and 10 mm in length. A sequence of pulses applied on a single variant induces an extension. It is close to linear with the pulse’s peak generated driving forces, for peaks in excess of 0.68×Ku, where Ku ≃ 1.9×105 J/m3 is the magnetocrystalline anisotropy. The extension is caused by the motion of a few distinct twin boundaries, which exhibit differing driving-force thresholds for motion between 1.3 and 1.8×105 J/m3. Pulses applied without restoring the single-variant initial condition, cause discrete twin boundaries to expand in a stochastic manner consistent with the existence of obstacles to their motion. The number of obstacles is broadly distributed in pinning strengths, except for a peak near 0.56×Ku ≃ 1.06×105 J/m3. © 2004 American Institute of Physics.
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61.72.Mm Grain and twin boundaries
75.30.Gw Magnetic anisotropy
75.50.Cc Other ferromagnetic metals and alloys
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Bistable nanoelectromechanical devices

Kirk J. Ziegler, Daniel M. Lyons, Justin D. Holmes, Donats Erts, Boris Polyakov, Håkan Olin, Krister Svensson, and Eva Olsson

Appl. Phys. Lett. 84, 4074 (2004); http://dx.doi.org/10.1063/1.1751622 (3 pages) | Cited 25 times

Online Publication Date: 5 May 2004

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A combined transmission electron microscopy-scanning tunneling microscopy (TEM-STM) technique has been used to investigate the force interactions of silicon and germanium nanowires with gold electrodes. The I(V) data obtained typically show linear behavior between the gold electrode and silicon nanowires at all contact points, whereas the linearity of I(V) curves obtained for germanium nanowires were dependent on the point of contact. Bistable silicon and germanium nanowire-based nanoelectromechanical programmable read-only memory (NEMPROM) devices were demonstrated by TEM-STM. These nonvolatile NEMPROM devices have switching potentials as low as 1 V and are highly stable making them ideal candidates for low-leakage electronic devices. © 2004 American Institute of Physics.
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84.30.Sk Pulse and digital circuits
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.30.Hi Surface barrier, boundary, and point contact devices
82.37.Gk STM and AFM manipulations of a single molecule
68.37.Lp Transmission electron microscopy (TEM)
73.40.Mr Semiconductor-electrolyte contacts

Initial growth of vertically aligned carbon nanofibers

Hongtao Cui, Xiaojing Yang, Michael L. Simpson, Douglas H. Lowndes, and Maria Varela

Appl. Phys. Lett. 84, 4077 (2004); http://dx.doi.org/10.1063/1.1751624 (3 pages) | Cited 37 times

Online Publication Date: 5 May 2004

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Samples of vertically aligned carbon nanofibers (VACNFs) were viewed transverse to the growth direction and studied using both scanning and transmission electron microscopy. The VACNFs are composed of graphite layers nearly parallel to the substrate at their bottom end, gradually formed graphite “cups” in the main body, and a catalyst particle on the tip. The formation of such structure is due to the corresponding transformation of the shape of the catalyst particle during initial VACNF growth. A model for their initial growth is proposed. © 2004 American Institute of Physics.
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81.07.De Nanotubes
81.16.Hc Catalytic methods
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
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Longitudinal compression of short laser pulses in air

I. Alexeev, A. Ting, D. F. Gordon, E. Briscoe, J. R. Penano, R. F. Hubbard, and P. Sprangle

Appl. Phys. Lett. 84, 4080 (2004); http://dx.doi.org/10.1063/1.1753051 (3 pages) | Cited 12 times

Online Publication Date: 5 May 2004

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We have performed laboratory experiments to study long distance propagation of large bandwidth ultrashort laser pulses in air. Initial pulse length, frequency chirping, and laser pulse energy were varied where the maximum propagation distance was up to 105 m. We have demonstrated the compression of initially negatively chirped low intensity laser pulses due to the linear group velocity dispersion of air. The characteristics of the compressed pulse such as pulse duration and spectral chirping were found to be significantly affected by the laser pulse intensity, with higher intensities corresponding to longer minimum compressed pulse duration. © 2004 American Institute of Physics.
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42.60.Fc Modulation, tuning, and mode locking
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

High contrast polymer-dispersed liquid crystal in a 90° twisted cell

Yi-Hsin Lin, Hongwen Ren, and Shin-Tson Wu

Appl. Phys. Lett. 84, 4083 (2004); http://dx.doi.org/10.1063/1.1753052 (3 pages) | Cited 27 times

Online Publication Date: 5 May 2004

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A polymer-dispersed liquid crystal confined in a 90° twisted cell (T-PDLC) is demonstrated. In comparison to a conventional PDLC, the T-PDLC is also polarization independent while exhibiting a higher contrast ratio. Potential applications of the T-PDLC are in polarizer-free reflective display and light switch. A black and white segmented-alphabet reflective display using a dye-doped T-PDLC is demonstrated. © 2004 American Institute of Physics.
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61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems
61.72.S- Impurities in crystals
42.79.Kr Display devices, liquid-crystal devices
42.70.Df Liquid crystals
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Effects of the one-dimensional quantum barriers in pyramidal quantum dots

F. Michelini, M.-A. Dupertuis, and E. Kapon

Appl. Phys. Lett. 84, 4086 (2004); http://dx.doi.org/10.1063/1.1753054 (3 pages) | Cited 9 times

Online Publication Date: 5 May 2004

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We investigated theoretically the effects of the one-dimensional barriers on the electronic states in a quantum dot grown on a nonplanar substrate. These peculiar barriers drastically modify the confined carrier wave functions and their energies. Connecting the quantum wire to the pyramidal quantum dot leads to an enhancement in the ground to first excited state separation energy and a simultaneous large reduction of the energy size sensitivity. © 2004 American Institute of Physics.
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73.21.La Quantum dots
73.63.Kv Quantum dots
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The normal-state resistivity of grain boundaries in YBa2Cu3O7−δ

J. H. T. Ransley, S. H. Mennema, K. G. Sandeman, G. Burnell, E. J. Tarte, J. E. Evetts, M. G. Blamire, J. I. Kye, and B. Oh

Appl. Phys. Lett. 84, 4089 (2004); http://dx.doi.org/10.1063/1.1753055 (3 pages) | Cited 7 times

Online Publication Date: 5 May 2004

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Using an optimized bridge geometry, we have been able to make accurate measurements of the properties of YBa2Cu3O7−δ grain boundaries above Tc. The results show a strong dependence of the change of resistance with temperature on grain boundary angle. Analysis of our results in the context of band bending at the boundary allows us to estimate the height of the potential barrier present at the grain boundary interface. © 2004 American Institute of Physics.
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61.72.Mm Grain and twin boundaries
74.25.F- Transport properties
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.72.-h Cuprate superconductors
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Persistent photocurrent and surface trapping in GaN Schottky ultraviolet detectors

O. Katz, G. Bahir, and J. Salzman

Appl. Phys. Lett. 84, 4092 (2004); http://dx.doi.org/10.1063/1.1753056 (3 pages) | Cited 25 times

Online Publication Date: 5 May 2004

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GaN-based Schottky detectors were implemented and their photoresponse as a function of the incident power and time was measured. The measured photoresponse shows gain saturation and persistent photoconductivity behavior. These effects are shown here to be related to each other, arising from a nonideal semiconductor surface. A microscopic model of the gain mechanism to explain these observations is presented. Trap density at the semiconductor metal interface, characteristic lifetime, and carrier capture coefficient are extracted from our measurements. © 2004 American Institute of Physics.
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85.30.Hi Surface barrier, boundary, and point contact devices
85.30.Kk Junction diodes
72.40.+w Photoconduction and photovoltaic effects
85.60.Gz Photodetectors (including infrared and CCD detectors)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
85.60.Dw Photodiodes; phototransistors; photoresistors
79.60.-i Photoemission and photoelectron spectra
79.60.Jv Interfaces; heterostructures; nanostructures
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SU-8 for real three-dimensional subdiffraction-limit two-photon microfabrication

W. H. Teh, U. Dürig, G. Salis, R. Harbers, U. Drechsler, R. F. Mahrt, C. G. Smith, and H.-J. Güntherodt

Appl. Phys. Lett. 84, 4095 (2004); http://dx.doi.org/10.1063/1.1753059 (3 pages) | Cited 38 times

Online Publication Date: 5 May 2004

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We report the inherent utility of two-photon-absorption (TPA) in the fabrication of real three-dimensional (3D) structures with subdiffraction-limit resolution, based on SU-8 as the threshold polymer media. We exploit the nonlinear velocity dependence of TPA photopolymerization as the shutter mechanism for disruptive 3D lithography. We show that low numerical aperture optics can be used for the rapid microfabrication of ultrahigh-aspect ratio photoplastic pillars, planes, and cage structures. © 2004 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography

Formation of highly aligned ZnO tubes on sapphire (0001) substrates

B. P. Zhang, N. T. Binh, K. Wakatsuki, Y. Segawa, Y. Yamada, N. Usami, M. Kawasaki, and H. Koinuma

Appl. Phys. Lett. 84, 4098 (2004); http://dx.doi.org/10.1063/1.1753061 (3 pages) | Cited 84 times

Online Publication Date: 5 May 2004

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ZnO tubes were epitaxially grown on sapphire (0001) substrates by metalorganic chemical vapor deposition. The tubes grew along the substrate normal and were characterized by hexagon-shaped cross sections. All of the tubes possessed the same epitaxial relationships with respect to the substrate. Both reactor pressure and growth temperature were found to play an important role in the formation of ZnO tubes. Spiral column growth mode was found to be responsible for the formation of ZnO tubes. © 2004 American Institute of Physics.
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81.07.De Nanotubes
81.05.Dz II-VI semiconductors
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Raman characterization of 0.4 nm single-wall carbon nanotubes using the full-symmetry line group

Z. M. Li, Z. K. Tang, G. G. Siu, and I. Bozovic

Appl. Phys. Lett. 84, 4101 (2004); http://dx.doi.org/10.1063/1.1753066 (3 pages) | Cited 15 times

Online Publication Date: 5 May 2004

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Raman spectra of single-wall carbon nanotubes produced in the channels of zeolite AFI single crystals have been analyzed in the light of the full symmetry group, the line group. The phonon dispersion curves of the tubes (5,0), (3,3), and (4,2) are calculated based on the lattice dynamical model and the phonon branches are assigned to their quantum numbers (irreducible representations). The structures of Raman spectra of different samples are reproduced well by the density of states of relevant Raman-active phonons. The result is useful to evaluate the contents of these tubes in real crystals where the contents are not well defined before. © 2004 American Institute of Physics.
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78.67.Ch Nanotubes
78.30.Hv Other nonmetallic inorganics
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
61.46.-w Structure of nanoscale materials
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
73.22.-f Electronic structure of nanoscale materials and related systems
73.22.Lp Collective excitations
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An InGaN-based horizontal-cavity surface-emitting laser diode

Tetsuya Akasaka, Toshio Nishida, Toshiki Makimoto, and Naoki Kobayashi

Appl. Phys. Lett. 84, 4104 (2004); http://dx.doi.org/10.1063/1.1753068 (3 pages)

Online Publication Date: 5 May 2004

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An InGaN-based horizontal-cavity surface-emitting laser diode (HCSELD) was fabricated by dry-etching of an InGaN-based multilayer on a SiC substrate and selective-area regrowth of a Mg-doped GaN layer. The InGaN-based HCSELD is a Fabry–Perot laser diode equipped with outer micromirrors that reflect the laser beams upward. The cavity mirrors and outer micromirrors are vertical {11math0} and inclined {11math2} facets of the regrown Mg-doped GaN layers, respectively. These grown facets are very smooth and had little angle misalignment. The InGaN-based HCSELD lased by current injection at room temperature. Current-injection lasing for group-III-nitride-based surface-emitting lasers is reported. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
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