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6 Dec 2004

Volume 85, Issue 23, pp. 5499-5791

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 5694 (2004); http://dx.doi.org/10.1063/1.1828575 (3 pages)

M. Y. Shen, C. H. Crouch, J. E. Carey, and E. Mazur
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Pairing space-charge field conditions with self-guiding for the attainment of circular symmetry in photorefractive solitons

E. DelRe, G. De Masi, A. Ciattoni, and E. Palange

Appl. Phys. Lett. 85, 5499 (2004); http://dx.doi.org/10.1063/1.1830075 (3 pages) | Cited 26 times

Online Publication Date: 8 December 2004

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By means of a comparative study, we identify a specific physical mechanism that leads to circular-symmetric two-dimensional photorefractive solitons, and determine the conditions for their observation. For a given photorefractive crystal, this allows the control of the transition from an elliptical soliton-supporting regime to a round soliton-supporting one. This indicates a basic recipe to generate electro-optic devices in three-dimensional crystals compatible with single-mode fiber.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Tg Optical solitons; nonlinear guided waves
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
77.22.Jp Dielectric breakdown and space-charge effects

Distributed feedback regime of photonic crystal waveguide lasers at 1.5 μm

X. Checoury, P. Boucaud, J-M. Lourtioz, F. Pommereau, C. Cuisin, E. Derouin, O. Drisse, L. Legouezigou, F. Lelarge, F. Poingt, G. H. Duan, D. Mulin, S. Bonnefont, O. Gauthier-Lafaye, J. Valentin, et al.

Appl. Phys. Lett. 85, 5502 (2004); http://dx.doi.org/10.1063/1.1832731 (3 pages) | Cited 4 times

Online Publication Date: 8 December 2004

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Lasing of W3 and W2∕3 triangular lattice photonic crystal waveguides on InP substrate is investigated around 1.5 μm by optical pumping. The lattice period of the fabricated structures is varied from 320 to 540 nm by steps of 20 nm, thereby leading to a detailed exploration of the lasing mechanism over a large frequency range. A distributed-feedback-laser- (DFB-) like-emission is observed above the gap (W3), while a genuine DFB laser emission is obtained in the gap (W2∕3). Side-mode suppression ratios can reach 40 dB when an antireflecting coating is used on the cleaved output facet. Experimental results including light–light characteristics are analyzed in the framework of two-dimensional plane-wave calculations.
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42.55.Tv Photonic crystal lasers and coherent effects
42.55.Px Semiconductor lasers; laser diodes

Spectrally resolved dynamics of inhomogeneously broadened gain in InAs∕InP 1550 nm quantum-dash lasers

D. Hadass, R. Alizon, H. Dery, V. Mikhelashvili, G. Eisenstein, R. Schwertberger, A. Somers, J. P. Reithmaier, A. Forchel, M. Calligaro, S. Bansropun, and M. Krakowski

Appl. Phys. Lett. 85, 5505 (2004); http://dx.doi.org/10.1063/1.1832761 (3 pages) | Cited 8 times

Online Publication Date: 8 December 2004

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We report spectrally resolved dynamical properties of 1550 nm quantum-dash lasers. The dynamics are governed by the inhomogeneous broadening of the gain medium and by wavelength-dependent carrier capture and escape rates.
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42.55.Px Semiconductor lasers; laser diodes
78.67.Hc Quantum dots

Optical coupling and transport phenomena in chains of spherical dielectric microresonators with size disorder

V. N. Astratov, J. P. Franchak, and S. P. Ashili

Appl. Phys. Lett. 85, 5508 (2004); http://dx.doi.org/10.1063/1.1832737 (3 pages) | Cited 59 times

Online Publication Date: 8 December 2004

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The optical transmission properties of chains or circuits of touching polystyrene microspheres with sizes in the 3–20 μm range and a size dispersion of ∼1% are studied. The dye-doped spheres with fluorescent peaks due to whispering gallery modes were attached to one end of the chains. The effects of optical transport were detected using spatially resolved scattering spectroscopy. The attenuation was shown to be ∼3 to 4 dB per sphere for the modes with the best transport properties. A mechanism for the observed transport is suggested based on the formation of strongly coupled photonic modes in the systems of randomly detuned resonators with size disorder. It is shown that such circuits possess broad bandpass waveguiding characteristics essential for applications in integrated all-optical network devices.
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42.79.Gn Optical waveguides and couplers
78.40.Me Organic compounds and polymers
78.40.Pg Disordered solids
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
78.55.Kz Solid organic materials
78.55.Qr Amorphous materials; glasses and other disordered solids

Bistable chiral tilted-homeotropic nematic liquid crystal cells

Jy-Shan Hsu, Bau-Jy Liang, and Shu-Hsia Chen

Appl. Phys. Lett. 85, 5511 (2004); http://dx.doi.org/10.1063/1.1830681 (3 pages) | Cited 13 times

Online Publication Date: 8 December 2004

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A bistable chiral tilted-homeotropic nematic cell which uses dual-frequency liquid crystal is demonstrated. This cell can be switched between the tilted homeotropic state and the twisted state. The switching mechanisms are achieved by the backflow effect together with the anisotropic properties of the dual-frequency liquid crystal material. The experimental results of this bistable cell are described explicitly.
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42.79.Kr Display devices, liquid-crystal devices
64.70.M- Transitions in liquid crystals

Two-photon-induced photoenhancement of densely packed CdSe∕ZnSe∕ZnS nanocrystal solids and its application to multilayer optical data storage

James W. M. Chon, Peter Zijlstra, Min Gu, Joel van Embden, and Paul Mulvaney

Appl. Phys. Lett. 85, 5514 (2004); http://dx.doi.org/10.1063/1.1829392 (3 pages) | Cited 16 times

Online Publication Date: 8 December 2004

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We report on a two-photon absorption-induced photoenhancement effect on a densely packed CdSe∕ZnSe∕ZnS core-shell semiconductor nanocrystal solid film. The enhancement is found to be irreversible without a noticeable blueshift in emission spectra, hence we attribute the enhancement to the photoannealing of interface defects rather than to the photo-oxidation or surface passivation by other molecules. The two-photon enhancement allows us to record the enhanced spots three dimensionally, hence demonstrating the feasibility of its application to multilayered optical data storage based on nanocrystal solids.
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42.79.Vb Optical storage systems, optical disks
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.65.Mq Oxidation
81.65.Rv Passivation
73.20.-r Electron states at surfaces and interfaces

Bistable emission of a black-body radiator

S. M. Redmond, S. C. Rand, and S. L. Oliveira

Appl. Phys. Lett. 85, 5517 (2004); http://dx.doi.org/10.1063/1.1825068 (3 pages) | Cited 5 times

Online Publication Date: 8 December 2004

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Bistable black-body emission is reported from resonantly excited Er3+,Yb3+:Y2O3 nanopowders. A simple model based on thermo-optic nonlinear response in the strongly scattering random medium explains the observed behavior.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials
42.65.Pc Optical bistability, multistability, and switching, including local field effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects

Single-molecule signal enhancement using a high-impedance ground plane substrate

Krishanu Ray, Michael D. Mason, Celeste Yang, Zhipan Li, and Robert D. Grober

Appl. Phys. Lett. 85, 5520 (2004); http://dx.doi.org/10.1063/1.1830271 (3 pages) | Cited 1 time

Online Publication Date: 8 December 2004

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We introduce a “high-impedance ground plane” (HIGP) substrate for use in single-molecule imaging applications. The HIGP is a quarter-wave-thick layer of dielectric material is deposited over a regular metallic mirror. Comparison of confocal fluorescence images of single DiI molecules on HIGP substrates and on glass substrates indicates a dramatic increase in the number of collected photons for the HIGP substrate. Signal enhancement ranges from a factor of 8 at low excitation powers to a lifetime-limited factor of 2 at higher powers.
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78.55.Kz Solid organic materials

Polarization-independent optical racetrack resonators using rib waveguides on silicon-on-insulator

William R. Headley, Graham T. Reed, Simon Howe, Ansheng Liu, and Mario Paniccia

Appl. Phys. Lett. 85, 5523 (2004); http://dx.doi.org/10.1063/1.1827337 (3 pages) | Cited 34 times

Online Publication Date: 8 December 2004

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In an effort to find low-cost alternatives for components currently used in dense wavelength division multiplexing, optical ring resonators fabricated on silicon on insulator are currently being investigated. Their performance can be further enhanced if they are polarization independent. Herein we use rib waveguides to control the polarization properties of the devices and hence produce polarization-independent racetrack ring resonators. Transverse electric and transverse magnetic resonant peaks are measured to within 2 pm of one another over four cycles of the free spectral range. The racetrack resonators also exhibit measured Q factors of approximately 90 000 and finesse values of 12.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.79.Gn Optical waveguides and couplers

Nonequilibrium gain in optically pumped GaInNAs laser structures

A. Thränhardt, S. Becker, C. Schlichenmaier, I. Kuznetsova, T. Meier, S. W. Koch, J. Hader, J. V. Moloney, and W. W. Chow

Appl. Phys. Lett. 85, 5526 (2004); http://dx.doi.org/10.1063/1.1831570 (3 pages) | Cited 12 times

Online Publication Date: 8 December 2004

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A theory is presented which couples a dynamical laser model to a fully microscopic calculation of scattering effects. Calculations for two optically pumped GaInNAs laser structures show how this approach can be used to analyze nonequilibrium and dynamical laser properties over a wide range of system parameters.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
72.10.Di Scattering by phonons, magnons, and other nonlocalized excitations

High-performance distributed feedback quantum cascade lasers grown by metalorganic vapor phase epitaxy

R. P. Green, L. R. Wilson, E. A. Zibik, D. G. Revin, J. W. Cockburn, C. Pflügl, W. Schrenk, G. Strasser, A. B. Krysa, J. S. Roberts, C. M. Tey, and A. G. Cullis

Appl. Phys. Lett. 85, 5529 (2004); http://dx.doi.org/10.1063/1.1830072 (3 pages) | Cited 20 times

Online Publication Date: 8 December 2004

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We report the operation of distributed feedback quantum cascade lasers, grown by metalorganic vapor phase epitaxy. Single-mode laser emission at λ∼10.3 μm and λ∼7.8 μm is observed from two different samples, with 300 K threshold current densities of Jth∼3 and ∼2.4 kA cm−2, respectively. Structural investigation by x-ray diffraction and transmission electron microscopy, and the close correlation between the predicted and observed emission wavelengths indicate exceptional control of the layer thicknesses, including ultrathin (∼8 math) barrier layers in the active region. These results confirm metalorganic vapor phase epitaxy as a viable technology for the growth of high-performance quantum cascade lasers.
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42.55.Px Semiconductor lasers; laser diodes
68.65.Fg Quantum wells
42.60.By Design of specific laser systems
68.37.Lp Transmission electron microscopy (TEM)

AlGaN-based 280 nm light-emitting diodes with continuous-wave power exceeding 1 mW at 25 mA

J. P. Zhang, X. Hu, Yu. Bilenko, J. Deng, A. Lunev, M. S. Shur, R. Gaska, M. Shatalov, J. W. Yang, and M. A. Khan

Appl. Phys. Lett. 85, 5532 (2004); http://dx.doi.org/10.1063/1.1831557 (3 pages) | Cited 5 times

Online Publication Date: 8 December 2004

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Optimization of the migration-enhanced metalorganic chemical vapor deposition and further optimization of the contact and active layer design for 280 nm light-emitting diodes resulted in large improvement of cw and pulsed output power and in a superior spectrum purity. The ratio of the main peak to the background luminescence determined by the detection system is higher than 2000:1 at 20 mA dc. The on-wafer cw power was measured to be 255 μW at 20 mA dc. The power popped up exceeding 1 mW for a packaged device under 25 mA dc and 9 mW under pulse 200 mA. The maximum wall-plug-efficiency of 0.67% was obtained for the packaged device at 25 mA dc.
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85.60.Jb Light-emitting devices
78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
78.60.Fi Electroluminescence
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Terahertz study of 1,3,5-trinitro-s-triazine by time-domain and Fourier transform infrared spectroscopy

Feng Huang, Brian Schulkin, Hakan Altan, John F. Federici, Dale Gary, Robert Barat, David Zimdars, Minghan Chen, and D. B. Tanner

Appl. Phys. Lett. 85, 5535 (2004); http://dx.doi.org/10.1063/1.1829793 (3 pages) | Cited 43 times

Online Publication Date: 8 December 2004

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This letter describes the use of THz time-domain spectroscopy (TDS) applied in transmission to the secondary explosive 1,3,5 trinitro-s-triazine. Samples were also subjected to Fourier transform infrared spectroscopy over the same range for comparison. A detailed spectroscopy study is presented. General agreement between results from both methods confirms the absorption features found. A comparison study with computer molecular simulations shows that THz-TDS is sensitive to collective modes or vibrational modes of material.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.47.-p Spectroscopy of solid state dynamics
78.30.Jw Organic compounds, polymers
78.70.Gq Microwave and radio-frequency interactions
82.33.Vx Reactions in flames, combustion, and explosions

Collection-mode near-field scanning infrared microscope based on silver halide probes

K. Roodenko, P. Ephrat, L. Nagli, and A. Katzir

Appl. Phys. Lett. 85, 5538 (2004); http://dx.doi.org/10.1063/1.1830674 (3 pages) | Cited 5 times

Online Publication Date: 8 December 2004

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We developed a collection-mode scanning near field microscope for the midinfrared spectral range, employing probes fabricated from tapered silver halide fibers. The system was tested in the photon scanning tunneling regime, where a sample was illuminated under total internal reflection conditions. The experimental results agreed with the results obtained by an analytical theoretical model.
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07.79.Fc Near-field scanning optical microscopes
42.81.Gs Birefringence, polarization

All-fiber integrated ∼10 kW peak power ultrashort optical pulse source based on compression in aircore photonic band gap fiber

C. J. S de Matos, R. E. Kennedy, and J. R. Taylor

Appl. Phys. Lett. 85, 5541 (2004); http://dx.doi.org/10.1063/1.1826227 (3 pages)

Online Publication Date: 8 December 2004

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We demonstrate an all-fiber integrated, ∼10 kW peak power, ∼1 ps optical pulse source at a wavelength of 1.55 μm based on compression in aircore photonic band gap fiber. A 10 GHz pulse train was modulated at 10 MHz in a Mach–Zehnder amplitude modulator with a ∼1 ns transmission window before stretching in 100 m of dispersion compensating fiber, amplifying, and recompressing in 10 m of aircore photonic band gap fiber. Numerical simulations show that if the aircore fiber dispersion slope could be made negligible, the achievable peak power would be increased by a factor of approximately 2.
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42.55.Wd Fiber lasers
42.70.Qs Photonic bandgap materials
42.81.Dp Propagation, scattering, and losses; solitons
42.79.Hp Optical processors, correlators, and modulators
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Room-temperature “W” diode lasers emitting at λ≈4.0 μm

W. W. Bewley, I. Vurgaftman, C. S. Kim, M. Kim, C. L. Canedy, J. R. Meyer, J. D. Bruno, and F. J. Towner

Appl. Phys. Lett. 85, 5544 (2004); http://dx.doi.org/10.1063/1.1834714 (3 pages) | Cited 10 times

Online Publication Date: 8 December 2004

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Type-II “W” diode lasers with ten quantum-well periods operated in pulsed mode to 315 K, where the emission wavelength was 4.02 μm. The devices with uncoated facets had a threshold current density of 145 A∕cm2 and slope efficiency of 47 mW∕A per facet at 78 K, and displayed a characteristic temperature T0≈46 K in the range 78–300 K.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.By Design of specific laser systems

Pre-breakdown suppression in planar InP∕InGaAs avalanche photodiode using deep floating guard ring

Kyung-Sook Hyun, Youngmi Paek, Yong-Hwan Kwon, Sungmin Hwang, Jongin Shim, and Seong Joon Ahn

Appl. Phys. Lett. 85, 5547 (2004); http://dx.doi.org/10.1063/1.1835552 (3 pages)

Online Publication Date: 8 December 2004

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We propose a deep floating guard ring (DFGR) structure which effectively prevents the curvature breakdown of a central junction in a planar InGaAs∕InP avalanche photodiode (APD). In order to investigate the DFGR APD performance, the dark current, photocurrent, and radial dependence of gain were measured and analyzed. In addition, the relation between breakdown voltage and multiplication layer thickness was calculated using a nonlocal history-dependent model. Reliable operation in the device center region was examined by measuring the radial gain. As a result, it has been confirmed that the DFGR is very useful for an APD with a very thin multiplication layer.
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85.60.Dw Photodiodes; phototransistors; photoresistors
72.40.+w Photoconduction and photovoltaic effects
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Patterned growth of pentacene

Soeren Steudel, Dimitri Janssen, Stijn Verlaak, Jan Genoe, and Paul Heremans

Appl. Phys. Lett. 85, 5550 (2004); http://dx.doi.org/10.1063/1.1832732 (3 pages) | Cited 22 times

Online Publication Date: 8 December 2004

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We propose a way of patterning organic small molecule thin films without requiring a hardmask and therefore more compatible with printing technologies. Active and passive areas for transistors are predefined by different surface chemistries. The subsequent growth takes place under conditions that cause the formation of a high mobility two-dimensional film in the active area and a disconnected three-dimensional film or no film in the passive area. This concept is founded on the basic theory of nucleation of organic small molecules on inert substrates and applied to the growth of patterned pentacene layers.
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81.05.Hd Other semiconductors
68.55.A- Nucleation and growth
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
85.30.Tv Field effect devices

Near-infrared intersubband transitions in delta-doped InAs∕AlSb multi-quantum wells

S. Sasa, Y. Nakajima, M. Nakai, M. Inoue, D. C. Larrabee, and J. Kono

Appl. Phys. Lett. 85, 5553 (2004); http://dx.doi.org/10.1063/1.1833559 (3 pages) | Cited 2 times

Online Publication Date: 8 December 2004

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Intersubband transitions (ISBTs) in narrow InAs∕AlSb multiple quantum wells (MQWs) were investigated for well widths, d, ranging from 5 nm down to 1.8 nm with 10, 20, or 60 periods. In order to observe a strong ISBT signal, a heavy silicon doping was made in each InAs quantum well. Delta doping was employed for the narrowest wells to prevent silicon incorporation into the AlSb barrier layers. As the well width decreased, the ISBT signal of the MQWs decreased. However, it persisted down to d=2.1 nm with a sheet doping density in each quantum well of 9×1012 cm−2 and 60 periods. The ISBT signal observed for d=2.1 nm was peaked at an energy of 650 and 670 meV at 300 and 77 K, respectively. These are the highest energy values ever observed for ISBTs in InAs∕AlSb MQWs.
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78.67.De Quantum wells
73.63.Hs Quantum wells
78.30.Fs III-V and II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
61.72.S- Impurities in crystals
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Continuous liquid crystal pretilt control through textured substrates

Fuk Kay Lee, Baoshe Zhang, Ping Sheng, Hoi Sing Kwok, and Ophelia K. C. Tsui

Appl. Phys. Lett. 85, 5556 (2004); http://dx.doi.org/10.1063/1.1833552 (3 pages) | Cited 20 times

Online Publication Date: 8 December 2004

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Reliable control on the pretilt alignment of nematic liquid crystal (LC) in the 30°–50° range is a well-known challenge. An unconventional approach, involving microtextured surfaces with domains favoring dissimilar LC alignments, has recently demonstrated applicability in bi- and tristable displays. These textured domains realize the so-called frustrated boundary condition in which the LC elastic energy built-up (frustration) can drive the LC alignment into macroscopic uniformity. Here we show that one can harness the frustrated boundary to achieve variable LC pretilt control up to 40°.
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42.70.Df Liquid crystals
61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
81.40.Jj Elasticity and anelasticity, stress-strain relations
64.70.M- Transitions in liquid crystals
61.72.Mm Grain and twin boundaries
68.35.B- Structure of clean surfaces (and surface reconstruction)

Phase transformations induced in relaxed amorphous silicon by indentation at room temperature

B. Haberl, J. E. Bradby, M. V. Swain, J. S. Williams, and P. Munroe

Appl. Phys. Lett. 85, 5559 (2004); http://dx.doi.org/10.1063/1.1832757 (3 pages) | Cited 17 times

Online Publication Date: 8 December 2004

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The deformation behavior of self-ion-implanted amorphous-Si (a-Si) has been studied using spherical nanoindentation in both relaxed (annealed) and unrelaxed (as-implanted) a-Si. Interestingly, phase transformations were clearly observed in the relaxed state, with the load–unload curves from these samples displaying characteristic discontinuities and cross-sectional transmission electron microscopy images indicating the presence of high-pressure crystalline phases Si-III and Si-XII following pressure release. Thus, an amorphous to crystalline phase transformation has been induced by indentation at room temperature. In contrast, no evidence of a phase transformation was observed in unrelaxed a-Si, which appeared to deform via plastic flow of the amorphous phase. Furthermore, in situ electrical measurements clearly indicate the presence of a metallic Si phase during loading of relaxed a-Si but no such behavior was observed for unrelaxed a-Si
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81.05.Cy Elemental semiconductors
81.40.Lm Deformation, plasticity, and creep
64.70.K- Solid-solid transitions
62.50.-p High-pressure effects in solids and liquids
62.20.F- Deformation and plasticity
61.72.uf Ge and Si
61.72.Cc Kinetics of defect formation and annealing
68.37.Lp Transmission electron microscopy (TEM)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Depth distribution of the strain in the GaN layer with low-temperature AlN interlayer on Si(111) substrate studied by Rutherford backscattering/channeling

Y. Lu, G. W. Cong, X. L. Liu, D. C. Lu, Z. G. Wang, and M. F. Wu

Appl. Phys. Lett. 85, 5562 (2004); http://dx.doi.org/10.1063/1.1830679 (3 pages) | Cited 3 times

Online Publication Date: 8 December 2004

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The depth distribution of the strain-related tetragonal distortion eT in the GaN epilayer with low-temperature AlN interlayer (LT-AlN IL) on Si(111) substrate is investigated by Rutherford backscattering and channeling. The samples with the LT-AlN IL of 8 and 16 nm thickness are studied, which are also compared with the sample without the LT-AlN IL. For the sample with 16-nm-thick LT-AlN IL, it is found that there exists a step-down of eT of about 0.1% in the strain distribution. Meanwhile, the angular scan around the normal GaN 〈0001〉 axis shows a tilt difference about 0.01° between the two parts of GaN separated by the LT-AlN IL, which means that these two GaN layers are partially decoupled by the AlN interlayer. However, for the sample with 8-nm-thick LT-AlN IL, neither step-down of eT nor the decoupling phenomenon is found. The 0.01° decoupled angle in the sample with 16-nm-thick LT-AlN IL confirms the relaxation of the LT-AlN IL. Thus the step-down of eT should result from the compressive strain compensation brought by the relaxed AlN interlayer. It is concluded that the strain compensation effect will occur only when the thickness of the LT-AlN IL is beyond a critical thickness.
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68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

Wannier orbitals and bonding properties of interstitial and antisite defects in GaN

F. Gao, E. J. Bylaska, A. El-Azab, and W. J. Weber

Appl. Phys. Lett. 85, 5565 (2004); http://dx.doi.org/10.1063/1.1827932 (3 pages) | Cited 1 time

Online Publication Date: 8 December 2004

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Intrinsic interstitial and antisite defects in GaN have been studied using density functional theory (DFT), and their configurations, electronic structures, and bonding properties have been characterized using the Wannier function. All N interstitial configurations eventually transform into N–N split interstitials, between which two π orbitals exist. The relaxation of a Ga antisite defect also leads to the formation of a N–N split configuration; however, its local Wannier orbitals are remarkably different from the N–N split interstitial. The different local Wannier orbitals around Ga interstitial configurations demonstrate that Ga interstitials are critical defects in GaN. The most striking feature is that Ga–Ga〈11math0〉 split interstitials can bridge the gap between nonbonded Ga atoms, thereby leading to a chain of four metallic-like-bonded Ga atoms along the 〈11math0〉 direction in GaN, which may exhibit quantum properties.
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71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.J- Point defects and defect clusters
71.55.Eq III-V semiconductors

Structural and optical properties of 6,13-pentacenequinone thin films

D. K. Hwang, Kibum Kim, Jae Hoon Kim, Seongil Im, Duk-Young Jung, and Eugene Kim

Appl. Phys. Lett. 85, 5568 (2004); http://dx.doi.org/10.1063/1.1832759 (3 pages) | Cited 12 times

Online Publication Date: 8 December 2004

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We report on the structural and optical properties of 6,13-pentacenequinone thin films deposited on n-Si substrates by thermal evaporation at room temperature. X-ray diffraction data indicate excellent crystallinity but the films have two crystalline phases mixed. Photoluminescence (PL) spectra exhibited double peaks at 1.97 and 2.09 eV while the corresponding (double) peaks, associated with the highest occupied molecular orbital–lowest unoccupied molecular orbital transition, were also observed from direct absorption spectra at 2.94 and 3.11 eV. The yellow PL band was quite intense under UV illumination; the intensity was comparable to that from Tris-(8-hydroxyquinoline) aluminum (Alq3) thin films. A large Stokes shift of ∼1 eV found in our 6,13-pentacenequinone thin films suggests potential applications to UV-detectors and UV-detecting cards.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.05.Hd Other semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
78.66.Qn Polymers; organic compounds
78.66.Li Other semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.55.Kz Solid organic materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
61.82.Pv Polymers, organic compounds

Hardness of cubic spinel Si3N4

Julong He, Licong Guo, Dongli Yu, Riping Liu, Yongjun Tian, and Hui-Tian Wang

Appl. Phys. Lett. 85, 5571 (2004); http://dx.doi.org/10.1063/1.1832756 (3 pages) | Cited 20 times

Online Publication Date: 8 December 2004

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The hardness of cubic spinel Si3N4 was calculated by using our microscopic model of hardness combined with first principles calculation. The calculated Vickers hardness is only 33.3 GPa in good agreement with its experimental values reported recently, indicating that the cubic spinel Si3N4 is not a superhard material. Our calculation results also implicate a more important fact that predicting the hardness of a material based on its bulk modulus or shear modulus is impertinent.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
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