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16 Nov 2009

Volume 95, Issue 20, Articles (20xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 204101 (2009); http://dx.doi.org/10.1063/1.3238316 (3 pages)

Gengxin Zhang, Brandon Weeks, Richard Gee, and Amitesh Maiti
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Optical nanorod antennas as dispersive one-dimensional Fabry–Pérot resonators for surface plasmons

Ertugrul Cubukcu and Federico Capasso

Appl. Phys. Lett. 95, 201101 (2009); http://dx.doi.org/10.1063/1.3262947 (3 pages) | Cited 11 times

Online Publication Date: 16 November 2009

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Resonant optical nanoantennas exhibit a different length scaling due to the surface plasmons compared to their radio frequency counterparts. In this letter, we address this difference by calculating the wavelength-dependent effective mode index neff for a cylindrical one-dimensional gold nanowire waveguide. Our results show that nanorod optical antennas act as dispersive and lossy Fabry–Pérot resonators for surface plasmons.
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42.82.-m Integrated optics
42.79.Gn Optical waveguides and couplers

Blue light-emitting diodes with a roughened backside fabricated by wet etching

Chia-Feng Lin, Chun-Min Lin, Kuei-Ting Chen, Wan-Chun Huang, Ming-Shiou Lin, Jing-Jie Dai, Ren-Hao Jiang, Yu-Chieh Huang, and Chung-Ying Chang

Appl. Phys. Lett. 95, 201102 (2009); http://dx.doi.org/10.1063/1.3262968 (3 pages) | Cited 11 times

Online Publication Date: 16 November 2009

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The InGaN-based light-emitting diodes (LEDs) with a roughened patterned backside on the N-face GaN surface were fabricated through a crystallographic etching process to increase light-extraction efficiency. After laser decomposition, laser scribing, and a lateral crystallographic wet etching process at the GaN/Al2O3 interface, stable crystallographic etching planes were formed as the GaN {10math} planes that included an angle with the top GaN (0001) plane measured at 58°. The GaN buffer layer acted as the sacrificial layer for the laser decomposition process and the lateral wet etching process with a 26 μm/min etching rate. The LED with the inverted pyramidal N-face GaN surface close to the GaN/Al2O3 interface has a larger light-scattering process than the conventional LED. The light-output power of the LED with the backside roughened surface had a 47% enhancement when measured in LED chip form.
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85.60.Jb Light-emitting devices

Extended depth of focus in a particle field measurement using a single-shot digital hologram

Wen Chen, Chenggen Quan, and Cho Jui Tay

Appl. Phys. Lett. 95, 201103 (2009); http://dx.doi.org/10.1063/1.3263141 (3 pages) | Cited 12 times

Online Publication Date: 16 November 2009

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We propose a method to extend the depth of focus in a particle field measurement using a single-shot digital hologram. A focal plane is obtained for each pixel based on an entropy method, and a depth map is subsequently extracted. A synthesized extended focused image is determined correspondingly using the extracted depth map. In addition, a wavelet modulus maxima algorithm and Canny algorithm are further employed to detect the edges of each particle, and the sizes and a three-dimensional localization of the particles are also estimated. Preliminary results are presented to show the feasibility and effectiveness of the proposed technique.
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42.40.Kw Holographic interferometry; other holographic techniques
07.60.Ly Interferometers
42.30.Sy Pattern recognition

Randomly packed n-SnO2 nanorods/p-SiC heterojunction light-emitting diodes

H. Y. Yang, S. F. Yu, C. W. Cheng, S. H. Tsang, H. K. Liang, and H. J. Fan

Appl. Phys. Lett. 95, 201104 (2009); http://dx.doi.org/10.1063/1.3266523 (3 pages) | Cited 5 times

Online Publication Date: 17 November 2009

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A layer of randomly packed n-SnO2 nanorods is grown by vapor transport method on the p-SiC(4H) substrate to realize heterojunction light-emitting diodes. Diodelike rectifying current-voltage characteristics, with a turn-on voltage of ∼ 4.5 V and reverse leakage current density of <0.25 A/m2, are obtained at room temperature. Furthermore, electroluminescent spectra with emission peaks at around 395, 434, and 497 nm are observed from the heterojunction under forward bias. This is due to the relaxation of electrons in the conduction band of SnO2 to the surface defect states and subsequent radiative recombination with holes injected from the p-SiC substrate.
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85.60.Jb Light-emitting devices

Electrically switchable multiple volume hologram recording in polymer-dispersed liquid-crystal films

Hongyue Gao, Haihui Pu, Bin Gao, Dejin Yin, Jianhua Liu, and Fuxi Gan

Appl. Phys. Lett. 95, 201105 (2009); http://dx.doi.org/10.1063/1.3264955 (3 pages) | Cited 5 times

Online Publication Date: 17 November 2009

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Multiple Bragg hologram recording was investigated in trimethylolpropane triacrylate based polymer-dispersed liquid-crystal thin films. Ten volume holograms were stored at a single location of less than 0.8 mm2 area with the diffraction efficiencies of 6%–15%, by a simplified method of peristrophic multiplexing, and the formation process of multiple volume holograms was presented. Furthermore, volume hologram capacity was studied both experimentally and theoretically in this film. Based on the maximum of Δn, ∼ 2×10−2, the theoretical capacity of a location could be improved to 25 Bragg holograms with the relatively high diffraction efficiency of 1%, and the holographic storage density of more than 20 Gbits/in.2 was achieved just by peristrophic multiplexing. Finally, electrically switchability for multiple holograms with a low threshold voltage of ∼ 3 V/μm was realized, which demonstrates that this material is a potential medium for electrically controlled holographic storage or diffraction device.
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42.70.Ln Holographic recording materials; optical storage media
42.79.Vb Optical storage systems, optical disks
42.70.Df Liquid crystals
42.40.Lx Diffraction efficiency, resolution, and other hologram characteristics
42.40.Ht Hologram recording and readout methods
42.40.Pa Volume holograms

Intensity modulation of terahertz quantum cascade lasers under external light injection

Norihiko Sekine and Iwao Hosako

Appl. Phys. Lett. 95, 201106 (2009); http://dx.doi.org/10.1063/1.3264965 (3 pages) | Cited 1 time

Online Publication Date: 17 November 2009

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We investigated the light-current characteristics of terahertz (THz) quantum cascade lasers under external light injection, which excites interband transitions in the active materials. It was found that the amount of reduction in the THz power was constant for all injection currents above threshold, and the dependence of the reduction amount on the wavelength of the external light was observed to show a resonancelike feature. The dominant intensity modulation mechanism was found to be the loss change caused by interband transitions in the active region. Further, the effective coupling efficiency plays an important role in the intensity modulation.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Transient optical response of quantum well excitons to intense narrowband terahertz pulses

A. D. Jameson, J. L. Tomaino, Yun-Shik Lee, J. P. Prineas, J. T. Steiner, M. Kira, and S. W. Koch

Appl. Phys. Lett. 95, 201107 (2009); http://dx.doi.org/10.1063/1.3265735 (3 pages) | Cited 8 times

Online Publication Date: 17 November 2009

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Intense narrowband terahertz pulses are used to modify excitonic transitions in semiconductor quantum wells and to study the dephasing properties of the optically dark 2p states. Time-resolved terahertz-pump and optical-probe measurements exhibit strong nonlinear optical transients of the 1s heavy-hole and light-hole exciton resonances when the terahertz radiation is tuned near the 1s to 2p intraexciton transition. A microscopic theory attributes the observed nonlinearities to Rabi sidebands showing that the 2p-dephasing time is three times that of the 1s-state.
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73.21.Fg Quantum wells
71.35.-y Excitons and related phenomena
78.47.J- Ultrafast spectroscopy (<1 psec)
78.47.D- Time resolved spectroscopy (>1 psec)
81.07.St Quantum wells
78.70.Gq Microwave and radio-frequency interactions

Direct measurement of auger recombination in In0.1Ga0.9N/GaN quantum wells and its impact on the efficiency of In0.1Ga0.9N/GaN multiple quantum well light emitting diodes

M. Zhang, P. Bhattacharya, J. Singh, and J. Hinckley

Appl. Phys. Lett. 95, 201108 (2009); http://dx.doi.org/10.1063/1.3266520 (3 pages) | Cited 35 times

Online Publication Date: 18 November 2009

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The Auger recombination coefficient in In0.1Ga0.9N/GaN quantum wells, emitting at 407 nm has been determined from large signal modulation measurements on lasers in which these quantum wells form the gain region. A value of 1.5×10−30 cm6 s−1 is determined for the Auger coefficient at room temperature, which is used to analyze the reported efficiency characteristics of 410 nm In0.1Ga0.9N/GaN quantum wells light emitting diodes. The calculated efficiencies agree remarkably well with the measured ones. It is apparent that Auger recombination is largely responsible for limiting device efficiencies at high injection currents.
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73.63.Hs Quantum wells
85.60.Jb Light-emitting devices
78.67.De Quantum wells
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Shape-dependent nonlinear absorption and relaxation in CuInS2 nanocrystals

N. Venkatram, Sudip K. Batabyal, Lu Tian, Jagadese J. Vittal, and Wei Ji

Appl. Phys. Lett. 95, 201109 (2009); http://dx.doi.org/10.1063/1.3266518 (3 pages) | Cited 3 times

Online Publication Date: 18 November 2009

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We report the observation of nonlinear-optical response and relaxation in copper indium sulfide (CuInS2) crystalline nanoparticles and nanorods with femtosecond Z-scans and transient absorption measurements. Dependent on the size and shape, two-photon absorption and saturation in the one-photon absorption manifest themselves in these measurements as laser excitation wavelength of 780 nm is in the proximity of the lowest-lying excitonic energy, particularly for the nanorods. The transient absorption measurements by both one-photon and two-photon excitation reveal that electron-hole recombination is faster in smaller nanoparticles, or in nanorods with smaller aspect ratio. However, the decay to trapping states is independent of the size and aspect-ratio.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.63.Bd Nanocrystalline materials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.47.jb Transient absorption
78.40.Fy Semiconductors
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
71.35.-y Excitons and related phenomena

Terahertz lasing from silicon by infrared Raman scattering on bismuth centers

S. G. Pavlov, U. Böttger, R. Eichholz, N. V. Abrosimov, H. Riemann, V. N. Shastin, B. Redlich, and H.-W. Hübers

Appl. Phys. Lett. 95, 201110 (2009); http://dx.doi.org/10.1063/1.3266837 (3 pages) | Cited 4 times

Online Publication Date: 18 November 2009

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Stimulated emission at terahertz frequencies (4.5–5.8 THz) has been realized by electronic Raman scattering of infrared radiation on bismuth donor centers in silicon at low temperatures. The Stokes shift of the observed laser emission is 40.53 meV which corresponds to the bismuth intracenter transition between the 1s(A1) ground state and the excited 1s(E) state. The laser has a low optical threshold and the largest frequency coverage in comparison with other Raman silicon lasers based on shallow donor centers. Time-resolved pump spectra enable the separation of donor and Raman lasing.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Ye Raman lasers
78.30.-j Infrared and Raman spectra
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering

Reflection-mode sensing using optical microresonators

Barry Koch, Yasha Yi, Jun-Ying Zhang, Stephen Znameroski, and Terry Smith

Appl. Phys. Lett. 95, 201111 (2009); http://dx.doi.org/10.1063/1.3263143 (3 pages) | Cited 9 times

Online Publication Date: 19 November 2009

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The authors present an approach for applying optical microring resonators to sensing. The approach relies on the interaction of the resonator with a nanoparticle taggant, which can induce coupling between forward and backward propagating traveling-wave resonant modes of the device. In the conventional four-port Add/Drop filter configuration, such coupling results in significant build-up of output intensity at ports that would normally be “dark.” Because the increased intensity occurs across a wide range of device resonances, the sensor may be interrogated using broadband excitation and with a broadband detector, enabling a low-cost, robust system.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.82.Et Waveguides, couplers, and arrays

Control of free space propagation of Airy beams generated by quadratic nonlinear photonic crystals

Ido Dolev, Tal Ellenbogen, Noa Voloch-Bloch, and Ady Arie

Appl. Phys. Lett. 95, 201112 (2009); http://dx.doi.org/10.1063/1.3266066 (3 pages) | Cited 12 times

Online Publication Date: 20 November 2009

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We present experimentally the control of free space propagation of an Airy beam. This beam is generated by a nonlinear wave mixing process in an asymmetrically poled nonlinear photonic crystal. Changing the quasi-phase matching conditions, e.g., the crystal temperature or pump wavelength, alters the location of the Airy beam peak intensity along the same curved trajectory. We explain that the variation in the beam shape is caused by noncollinear interactions. Owing to the highly asymmetric shape of nonlinear crystal in the Fourier space, these noncollinear interactions are still relatively efficient for positive (nonzero) phase mismatch.
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42.70.Qs Photonic bandgap materials
42.25.Bs Wave propagation, transmission and absorption
42.70.Mp Nonlinear optical crystals
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.30.Kq Fourier optics

On carrier spillover in c- and m-plane InGaN light emitting diodes

J. Lee, X. Li, X. Ni, Ü. Özgür, H. Morkoç, T. Paskova, G. Mulholland, and K. R. Evans

Appl. Phys. Lett. 95, 201113 (2009); http://dx.doi.org/10.1063/1.3266833 (3 pages) | Cited 12 times

Online Publication Date: 20 November 2009

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The internal quantum efficiency (IQE) and relative external quantum efficiency (EQE) in InGaN light-emitting diodes (LEDs) emitting at 400 nm with and without electron blocking layers (EBLs) on c-plane GaN and m-plane GaN were investigated in order to shed some light on any effect of polarization charge induced field on efficiency killer carrier spillover. Without an EBL the EQE values suffered considerably (by 80%) for both orientations, which is clearly attributable to carrier spillover. Substantial carrier spillover in both polarities, therefore, suggests that the polarization charge is not the major factor in efficiency degradation observed, particularly at high injection levels. Furthermore, the m-plane variety with EBL did not show any discernable efficiency degradation up to a maximum current density of 2250 A cm−2 employed while that on c-plane showed a reduction by ∼ 40%. In addition, IQE of m-plane LED structure determined from excitation power dependent photoluminescence was ∼ 80% compared to 50% in c-plane LEDs under resonant and moderate excitation condition. This too is indicative of the superiority of m-plane LED structures, most probably due to relatively larger optical matrix elements for m-plane orientation.
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85.60.Jb Light-emitting devices
78.55.Cr III-V semiconductors

Surface-plasmon mode hybridization in subwavelength microdisk lasers

R. Perahia, T. P. Mayer Alegre, A. H. Safavi-Naeini, and O. Painter

Appl. Phys. Lett. 95, 201114 (2009); http://dx.doi.org/10.1063/1.3266843 (3 pages) | Cited 21 times

Online Publication Date: 20 November 2009

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Hybridization of surface-plasmon and dielectric waveguide whispering-gallery modes are demonstrated in a semiconductor microdisk laser cavity of subwavelength proportions. A metal layer is deposited on top of the semiconductor microdisk, the radius of which is systematically varied to enable mode hybridization between surface-plasmon and dielectric modes. The anticrossing behavior of the two cavity mode types is experimentally observed via photoluminescence spectroscopy and optically pumped lasing action at a wavelength of λ ∼ 1.3 μm is achieved at room temperature.
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42.55.Sa Microcavity and microdisk lasers
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Study of an organic-inorganic hybrid columinescence system by photoacoustic method

Yue-tao Yang, Xiao-jun Liu, and Shu-yi Zhang

Appl. Phys. Lett. 95, 201115 (2009); http://dx.doi.org/10.1063/1.3266850 (3 pages) | Cited 1 time

Online Publication Date: 20 November 2009

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In this work, a columinescence system is found for lanthanide complexes Ln(p-ABA)3⋅H2O (p-ABA: p-aminobenzoic acid) incorporated in silica matrix. It is found that the luminescence quantum yield of Tb3+ emissions increases remarkably when partly replacing Tb(p-ABA)3⋅H2O by Gd(p-ABA)3⋅H2O in silica glass. Moreover, through the ratio of the fast to the slow heat components derived from a photoacoustic method, the intrinsic luminescence quantum yield of Tb3+ and the ligand sensitization efficiency are determined for the samples. The luminescence quenching effect for Tb–Er(p-ABA)3⋅H2O complexes in silica matrix is also discussed.
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78.20.Pa Photoacoustic effects
62.65.+k Acoustical properties of solids
78.55.-m Photoluminescence, properties and materials

Resonant nanometric cross-shaped apertures: Single apertures versus periodic arrays

L. Lin, L. B. Hande, and A. Roberts

Appl. Phys. Lett. 95, 201116 (2009); http://dx.doi.org/10.1063/1.3267080 (3 pages) | Cited 9 times

Online Publication Date: 20 November 2009

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Here localized surface plasmon (LSP) resonances occurring inside cross-shaped apertures arranged in thin metallic films are investigated. It is shown that these resonances can be controlled by altering the geometry of the apertures, whereas surface plasmon polariton excitation and Wood anomalies arising as a consequence of the periodicity distorts the spectrum produced by isolated LSP resonances. Simulations showing the behavior of single apertures versus periodic arrays of apertures are compared with experimental results for periodic arrays.
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73.22.Lp Collective excitations
68.55.jd Thickness
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
78.66.Bz Metals and metallic alloys

Extremely broadened high-order harmonics generated by the femtosecond pulses propagating through the filaments in air

R. A. Ganeev and H. Kuroda

Appl. Phys. Lett. 95, 201117 (2009); http://dx.doi.org/10.1063/1.3267081 (3 pages) | Cited 2 times

Online Publication Date: 20 November 2009

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We demonstrate a considerable broadening of the harmonics generating in laser plasma using the laser pulses propagating through the filaments in air. A fourfold increase of harmonic bandwidth was achieved in the case of phase-modulated laser pulses, alongside with an increase in harmonic conversion efficiency (from 5×10−6 to 1.2×10−5). We also present the studies of harmonic generation using phase-modulated pulses at different ranges of ellipticity of the polarization of laser beam.
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52.38.Hb Self-focussing, channeling, and filamentation in plasmas
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Spectrally resolved confocal microscopy for laser mode imaging and beam characteristic investigations

W. Brezna and J. Smoliner

Appl. Phys. Lett. 95, 201118 (2009); http://dx.doi.org/10.1063/1.3264969 (3 pages) | Cited 1 time

Online Publication Date: 20 November 2009

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In this letter, confocal optical microscopy is used to investigate the intensity patterns of an infrared vertical cavity surface emitting laser in three dimensions with high spectral resolution. The measurements were performed between the near field (Fresnel) regime and the far field (Fraunhofer) regime. The calculated intensity patterns were found to be in good agreement with the measured intensity distribution. The calculations together with the measurements can be used to determine the phase relation between different positions inside the gain medium.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes
07.60.Pb Conventional optical microscopes

Hybrid InP-based photonic crystal lasers on silicon on insulator wires

Y. Halioua, T. J. Karle, F. Raineri, P. Monnier, I. Sagnes, G. Roelkens, D. Van Thourhout, and R. Raj

Appl. Phys. Lett. 95, 201119 (2009); http://dx.doi.org/10.1063/1.3265743 (3 pages) | Cited 10 times

Online Publication Date: 20 November 2009

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We report on InP-based photonic crystal lasers operating at 1.585 μm at room temperature, integrated with and evanescently coupled to silicon on insulator (SOI) waveguides. By optically pumping at 1.18 μm through the SOI wires, pulsed laser emission from line defect photonic crystal waveguides accurately aligned (<30 nm) to the silicon circuitry is demonstrated.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Tv Photonic crystal lasers and coherent effects
42.60.By Design of specific laser systems
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Characteristics of kilohertz-ignited, radio-frequency atmospheric-pressure dielectric barrier discharges in argon

Pei-Si Le, Guo Li, Sen Wang, He-Ping Li, and Cheng-Yu Bao

Appl. Phys. Lett. 95, 201501 (2009); http://dx.doi.org/10.1063/1.3263153 (3 pages) | Cited 2 times

Online Publication Date: 17 November 2009

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In this letter, ignited by a kilohertz atmospheric-pressure dielectric-barrier discharge (APDBD), the stable and uniform argon radio-frequency (rf) APDBDs are generated with lower rf ignition voltages compared to the conventional rf APDBDs without the aid of the kilohertz filamentary discharges. The experimental studies on the mechanisms of this dual-frequency APDBD method indicate that it is the filaments extending from the kilohertz electrode region to the rf electrode region that provide the seed electrons for the ignition of the rf APDBDs at the lower applied rf voltages. A 12-mm-long stable and uniform argon plasma jet is obtained using the coaxial-type plasma generator.
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52.80.Pi High-frequency and RF discharges
52.75.-d Plasma devices

Measurement of the electron density in a microwave plasma torch at atmospheric pressure

Qing Zhang, Guixin Zhang, Liming Wang, Xinxin Wang, Shumin Wang, and Yan Chen

Appl. Phys. Lett. 95, 201502 (2009); http://dx.doi.org/10.1063/1.3266923 (3 pages) | Cited 1 time

Online Publication Date: 20 November 2009

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The electron density in a microwave plasma torch at atmospheric pressure was measured with a Mach–Zehnder interferometer. The electron density is on the order of 1017/cm3, one order higher than that deduced from the Stark broadening of spectral lines, and increases with the increase in the microwave power. The spatial distribution of the electron density was obtained. The highest electron density locates at the symmetrical axis of the plasma torch and decreases radially. It was found that the electron density fluctuates within a range of 0.3 with the time under the same experimental conditions.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.75.Hn Plasma torches
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
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Measurement of anharmonicity of phonons in the negative thermal expansion compound Zn(CN)2 by high pressure inelastic neutron scattering

R. Mittal, S. L. Chaplot, and H. Schober

Appl. Phys. Lett. 95, 201901 (2009); http://dx.doi.org/10.1063/1.3264963 (3 pages) | Cited 2 times

Online Publication Date: 16 November 2009

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Zn(CN)2 is known to have an isotropic negative thermal expansion (NTE) coefficient (about −51×10−6 K−1) over 10–370 K that is twice as large as that of ZrW2O8. We have measured the pressure dependence of the phonon spectra up to 30 meV from a polycrystalline sample of Zn(CN)2 at pressures of 0, 0.3, 1.9, and 2.8 kbar at temperatures of 165 and 225 K. The measurements enabled us to estimate the energy dependence of the ratios Γi/B (Γi are Grüneisen parameters as a function of phonon energy Ei at ambient pressure and B is the bulk modulus), which reflect the anharmonicity of phonons. We conclude that the phonon modes of low energy below 15 meV play an important role in the understanding of the NTE behavior in Zn(CN)2 and the measured anharmonicity can quantitatively explain the NTE.
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63.20.-e Phonons in crystal lattices
65.40.De Thermal expansion; thermomechanical effects
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli

Synthesis and characterization of nanoporous Pt–Ni alloys

Hongqi Li, Amit Misra, Jon K. Baldwin, and S. T. Picraux

Appl. Phys. Lett. 95, 201902 (2009); http://dx.doi.org/10.1063/1.3265744 (3 pages) | Cited 3 times

Online Publication Date: 16 November 2009

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Two nanoporous Pt–Ni alloys were synthesized by dealloying ternary amorphous Si–Pt–Ni precursors. Both foams have nearly the same composition, ligament diameter size, and density. However, their ligament patterns are different, depending on the microstructure of precursors. The difference in morphology is shown to have a profound effect on mechanical properties. The structure with well-aligned long nanoligaments exhibited over 50% higher hardness and stiffness than the structure with short random-oriented nanoligaments. These nanoporous Pt–Ni structures are thermally stable at 300 °C.
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81.16.-c Methods of micro- and nanofabrication and processing
61.43.Gt Powders, porous materials
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
61.46.-w Structure of nanoscale materials
81.20.-n Methods of materials synthesis and materials processing

Dynamical and quasistatic structural relaxation paths in Pd40Ni40P20 glass

A. Kahl, T. Koeppe, D. Bedorf, R. Richert, M. L. Lind, M. D. Demetriou, W. L. Johnson, W. Arnold, and K. Samwer

Appl. Phys. Lett. 95, 201903 (2009); http://dx.doi.org/10.1063/1.3266828 (3 pages) | Cited 5 times

Online Publication Date: 19 November 2009

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By sequential heat treatment of a Pd40Ni40P20 metallic glass at temperatures and durations for which α-relaxation is not possible, dynamic, and quasistatic relaxation paths below the glass transition are identified via ex situ ultrasonic measurements following each heat treatment. The dynamic relaxation paths are associated with hopping between nonequilibrium potential energy states of the glass, while the quasistatic relaxation path is associated with reversible β-relaxation events toward quasiequilibrium states. These quasiequilibrium states are identified with secondary potential energy minima that exist within the inherent energy minimum of the glass, thereby supporting the concept of the sub-basin/metabasin organization of the potential-energy landscape.
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61.43.Fs Glasses
64.70.pe Metallic glasses
62.65.+k Acoustical properties of solids
81.40.Gh Other heat and thermomechanical treatments

Photoluminescence enhancement of Er-doped silica containing Ge nanoclusters

J. Guzman, S. J. Shin, C. Y. Liao, C. W. Yuan, P. R. Stone, O. D. Dubón, K. M. Yu, J. W. Beeman, M. Watanabe, J. W. Ager, III, D. C. Chrzan, and E. E. Haller

Appl. Phys. Lett. 95, 201904 (2009); http://dx.doi.org/10.1063/1.3266846 (3 pages) | Cited 2 times

Online Publication Date: 19 November 2009

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The photoluminescence (PL) of Er-doped silica films containing Ge nanoclusters synthesized by ion implantation was investigated. The area of the 1540 nm Er3+ PL peak was enhanced by up to a factor of 200 by the addition of Ge nanoclusters. The PL enhancement was found to be proportional to the concentration of Ge atoms. Control experiments with argon ion implantation were used to show that the enhancement is due to the presence of Ge and not radiation damage. Furthermore, the Er3+ PL was found to be strongly influenced by the postgrowth annealing and the crystallinity of the Ge nanoclusters.
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78.66.-w Optical properties of specific thin films
78.55.Hx Other solid inorganic materials
42.70.-a Optical materials
81.40.Gh Other heat and thermomechanical treatments
81.40.Tv Optical and dielectric properties related to treatment conditions
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
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