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15 Feb 2010

Volume 96, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 96, 072501 (2010); http://dx.doi.org/10.1063/1.3314301 (3 pages)

T. Hesjedal and T. Phung
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Multi-gigahertz operation of photon counting InGaAs avalanche photodiodes

Z. L. Yuan, A. W. Sharpe, J. F. Dynes, A. R. Dixon, and A. J. Shields

Appl. Phys. Lett. 96, 071101 (2010); http://dx.doi.org/10.1063/1.3309698 (3 pages) | Cited 21 times

Online Publication Date: 16 February 2010

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We report a 2 GHz operation of InGaAs avalanche photodiodes for efficient single photon detection at telecom wavelengths. Employing a self-differencing circuit that incorporates tuneability in both frequency and arm balancing, extremely weak avalanches can now be sensed so as to suppress afterpulsing. The afterpulse probability is characterized as 4.84% and 1.42% for a photon detection efficiency of 23.5% and 11.8%, respectively. The device will further increase the secure bit rate for fiber wavelength quantum key distribution.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)
42.50.Ar Photon statistics and coherence theory

One-step generation of cluster state by adiabatic passage in coupled cavities

Jie Song, Yan Xia, and He-Shan Song

Appl. Phys. Lett. 96, 071102 (2010); http://dx.doi.org/10.1063/1.3299005 (3 pages) | Cited 10 times

Online Publication Date: 16 February 2010

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We propose a scheme to generate an N-qubit cluster state by adiabatic passage in coupled cavities. The required interaction time keeps unchanged with the increasing of the number of qubits and need not be accurately controlled. In addition, the scheme is robust against the fluctuations of some experimental parameters.
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03.67.Mn Entanglement measures, witnesses, and other characterizations
03.67.Lx Quantum computation architectures and implementations

Whispering gallery mode lasing in high quality GaAs/AlAs pillar microcavities

P. Jaffrennou, J. Claudon, M. Bazin, N. S. Malik, S. Reitzenstein, L. Worschech, M. Kamp, A. Forchel, and J.-M. Gérard

Appl. Phys. Lett. 96, 071103 (2010); http://dx.doi.org/10.1063/1.3315869 (3 pages) | Cited 9 times

Online Publication Date: 17 February 2010

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We report whispering gallery mode (WGM) lasing from high quality GaAs/AlAs micropillars with embedded InAs quantum dots, under continuous optical pumping. For temperatures ranging from 5 to 100 K, simultaneous lasing from TE1,1,m WGMs is observed for pillar diameters in the 3–4 μm range. Spectral linewidths and energy shifts of the lasing modes are analyzed as a function of the pump power. Thanks to the efficient heat sinking provided by the micropillar geometry, a clear line narrowing is observed above threshold. Moreover, the lasing mode energy remains stable for pump power as large as six times the lasing threshold.
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42.55.Sa Microcavity and microdisk lasers
42.60.By Design of specific laser systems

Soliton gating and switching in liquid crystal light valve

Armando Piccardi, Alessandro Alberucci, Umberto Bortolozzo, Stefania Residori, and Gaetano Assanto

Appl. Phys. Lett. 96, 071104 (2010); http://dx.doi.org/10.1063/1.3301261 (3 pages) | Cited 12 times

Online Publication Date: 17 February 2010

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Using a photoconductive light valve with nematic liquid crystals, we introduce a versatile platform for the excitation and routing of spatial optical solitons, with external beams controlling the whereabouts of the underlying all-optically induced waveguides and their spatial dynamics. Using this all-optical control of soliton trajectory, we demonstrate a NOR gate, an XNOR, and a Boolean half-adder.
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42.79.Kr Display devices, liquid-crystal devices
84.40.Az Waveguides, transmission lines, striplines
84.30.Sk Pulse and digital circuits
42.70.Df Liquid crystals
42.81.Dp Propagation, scattering, and losses; solitons

Extended Kerr effect of polymer-stabilized blue-phase liquid crystals

Jin Yan, Hui-Chuan Cheng, Sebastian Gauza, Yan Li, Meizi Jiao, Linghui Rao, and Shin-Tson Wu

Appl. Phys. Lett. 96, 071105 (2010); http://dx.doi.org/10.1063/1.3318288 (3 pages) | Cited 45 times

Online Publication Date: 17 February 2010

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Electric-field-induced birefringence of a polymer-stabilized blue-phase liquid crystal (BPLC) is investigated. In the low field region, conventional Kerr effect holds. As the electric field increases, the induced birefringence gradually saturates and deviates from Kerr effect. An exponential convergence model, called extended Kerr effect, is proposed to fit the experimental data. Good agreement between experiment and model is obtained. This extended Kerr effect will make a significant impact to the optimization of emerging BPLC display devices.
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42.70.Df Liquid crystals
42.25.Lc Birefringence
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Quasi-phase-matched probe-energy electro-optic sampling as a method of narrowband terahertz detection

G. Kh. Kitaeva, S. P. Kovalev, I. I. Naumova, R. A. Akhmedzhanov, I. E. Ilyakov, B. V. Shishkin, and E. V. Suvorov

Appl. Phys. Lett. 96, 071106 (2010); http://dx.doi.org/10.1063/1.3309688 (3 pages) | Cited 6 times

Online Publication Date: 17 February 2010

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Implementation of free-space quasi-phase-matched electro-optic detection is reported, based on measuring the energy variation of a femtosecond laser pulse induced by a terahertz field. Narrowband probe-energy type of detection is demonstrated using wide-aperture periodically poled Mg:Y:LiNbO3 crystals with as-grown domain gratings. Spectra of air plasma generation measured by this method are compared with the spectrum measured by the conventional ZnTe-based probe-phase ellipsometry scheme. Besides, the conventional method was performed for both types of sources, for the air plasma generation, and for the quasi-phase-matched optical rectification in the same periodically poled Mg:Y:LiNbO3 crystals.
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78.20.Jq Electro-optical effects
78.47.J- Ultrafast spectroscopy (<1 psec)
78.70.Gq Microwave and radio-frequency interactions

Surface plasmon enhanced band edge luminescence of ZnO nanorods by capping Au nanoparticles

C. W. Cheng, E. J. Sie, B. Liu, C. H. A. Huan, T. C. Sum, H. D. Sun, and H. J. Fan

Appl. Phys. Lett. 96, 071107 (2010); http://dx.doi.org/10.1063/1.3323091 (3 pages) | Cited 37 times

Online Publication Date: 17 February 2010

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The author observe sixfold enhancement in the near band gap emission of ZnO nanorods by employing surface plasmon of Au nanoparticles, while the defect-related emission is completely suppressed. Time-resolved photoluminescence indicates that the decay process becomes much faster by Au capping. The remarkable enhancement of the ultraviolet emission intensities and transition rates is ascribed to the charge transfer and efficient coupling between ZnO nanorods and Au surface plasmons. The suppression of the green emission might be due to a combined effect of Au surface plasmon and passivation of the ZnO nanorod surface traps.
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78.67.Qa Nanorods
78.55.Et II-VI semiconductors
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
78.47.jd Time resolved luminescence
71.55.Gs II-VI semiconductors
81.07.Bc Nanocrystalline materials
81.05.Dz II-VI semiconductors

Lasing characteristics at different band edges in GaN photonic crystal surface emitting lasers

S. W. Chen, T. C. Lu, Y. J. Hou, T. C. Liu, H. C. Kuo, and S. C. Wang

Appl. Phys. Lett. 96, 071108 (2010); http://dx.doi.org/10.1063/1.3313947 (3 pages) | Cited 5 times

Online Publication Date: 17 February 2010

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We have investigated the lasing characteristics of GaN-based two-dimensional photonic crystal surface emitting lasers (PCSELs) with different PC lattice constants by using angled resolved spectroscopy. Due to the Bragg diffraction theory, normalized frequency of lasing wavelength of PCSELs can be exactly matched with three distinct band-edge frequencies (Γ1, K2, and M3) in the photonic band diagram. The three band-edge frequencies (Γ1, K2, and M3) have different emission angles corresponding to the normal direction of the sample (0°, 29°, and 59.5°).
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.70.Qs Photonic bandgap materials

Temperature scaling of hot electrons produced by a tightly focused relativistic-intensity laser at 0.5 kHz repetition rate

Aghapi G. Mordovanakis, Paul-Edouard Masson-Laborde, James Easter, Konstantin Popov, Bixue Hou, Gérard Mourou, Wojciech Rozmus, Malcolm G. Haines, John Nees, and Karl Krushelnick

Appl. Phys. Lett. 96, 071109 (2010); http://dx.doi.org/10.1063/1.3306730 (3 pages) | Cited 2 times

Online Publication Date: 18 February 2010

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The energy spectrum of hot electrons emitted from the interaction of a relativistically intense laser with an Al plasma is measured at a repetition rate of 0.5 kHz by accumulating ∼ 103 highly reproducible laser shots. In the 1017–2×1018 W/cm2 range, the temperature of electrons escaping the plasma along the specular direction scales as (Iλ2)0.64±0.05 for p-polarized pulses incident at 45°. This scaling is in good agreement with three-dimensional particle-in-cell simulations and a simple model that estimates the hot-electron temperature by considering the balance between the deposited laser intensity and the energy carried away by those electrons.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Determination of the intrinsic temperature dependent thermal conductivity from analysis of surface temperature of laser irradiated materials

Selim Elhadj, Manyalibo J. Matthews, Steven T. Yang, Diane J. Cooke, James S. Stolken, Ryan M. Vignes, Vaughn G. Draggoo, and Scott E. Bisson

Appl. Phys. Lett. 96, 071110 (2010); http://dx.doi.org/10.1063/1.3291665 (3 pages) | Cited 7 times

Online Publication Date: 18 February 2010

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An experimental and analytical approach is described to determine the temperature dependent intrinsic lattice thermal conductivity, k(T), for a broad range of materials. k(T) of silica, sapphire, spinel, and lithium fluoride were derived from surface temperature measurements. Surfaces were heated from room temperature up to 3000 K using a CO2-laser irradiance ≤ 5 kW/cm2. The solution of the nonlinear heat flow equation was used to extract parameters of k(T) = A×Tε, where −1.13 ≤ ε ≤ 0 depending on the material. Results generally show good agreement with reported k(T). Below evaporation, the phonon-only k remains the dominant heat transport mechanism during laser heating.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
63.20.-e Phonons in crystal lattices
81.40.Gh Other heat and thermomechanical treatments
79.20.Ds Laser-beam impact phenomena

Toward determinism in surface damaging of dielectrics using few-cycle laser pulses

N. Sanner, O. Utéza, B. Chimier, M. Sentis, P. Lassonde, F. Légaré, and J. C. Kieffer

Appl. Phys. Lett. 96, 071111 (2010); http://dx.doi.org/10.1063/1.3309700 (3 pages) | Cited 9 times

Online Publication Date: 18 February 2010

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We introduce a quantitative measurement of the determinism of laser-induced damaging at the surface of a dielectric material, e.g., fused silica. Using laser pulses ranging from 7 to 300 fs, we demonstrate that laser damage occurrence tends to be dramatically deterministic at 7 fs, which is attributed to the increasing importance of tunneling ionization as the major channel for the generation of free-carriers in the conduction band.
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79.20.Ds Laser-beam impact phenomena
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Submegahertz frequency stabilization of a terahertz quantum cascade laser to a molecular absorption line

H. Richter, S. G. Pavlov, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, D. A. Ritchie, and H.-W. Hübers

Appl. Phys. Lett. 96, 071112 (2010); http://dx.doi.org/10.1063/1.3324703 (3 pages) | Cited 11 times

Online Publication Date: 19 February 2010

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The frequency of a terahertz quantum-cascade laser is stabilized to the absorption line of methanol gas at a frequency of 2.55 THz. The method is based on frequency modulation of the laser emission across the absorption line. The resulting derivativelike signal is used as an error signal for a control loop that keeps the laser frequency at maximum absorption. The unstabilized laser that is operated in a pulse tube cooler has frequency fluctuations of 15 MHz, which are reduced to 300 kHz with the control loop in action. The line shape of the locked signal is Gaussian.
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42.55.Px Semiconductor lasers; laser diodes
07.05.Dz Control systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
42.60.By Design of specific laser systems

Enhancement of the 1.54 μm Er3+ emission from quasiperiodic plasmonic arrays

A. Gopinath, S. V. Boriskina, S. Yerci, R. Li, and L. Dal Negro

Appl. Phys. Lett. 96, 071113 (2010); http://dx.doi.org/10.1063/1.3327827 (3 pages) | Cited 12 times

Online Publication Date: 19 February 2010

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Periodic and Fibonacci Au nanoparticle arrays of varying interparticle separations were fabricated on light emitting Er:SiNx films using electron beam lithography. A 3.6 times enhancement of the photoluminescence (PL) intensity accompanied by a reduction in the Er3+ emission lifetime at 1.54 μm has been observed in Fibonacci quasiperiodic arrays and explained with radiating plasmon theory. Our results are further supported by transmission measurements through the Fibonacci and periodic nanoparticle arrays with interparticle separation in the 25–500 nm range. This work demonstrates the potential of quasiperiodic nanoparticle arrays for the engineering of light emitting devices based on the silicon technology.
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78.55.-m Photoluminescence, properties and materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Cryogenic temperatures as a path toward high-Q terahertz metamaterials

Ranjan Singh, Zhen Tian, Jiaguang Han, Carsten Rockstuhl, Jianqiang Gu, and Weili Zhang

Appl. Phys. Lett. 96, 071114 (2010); http://dx.doi.org/10.1063/1.3313941 (3 pages) | Cited 17 times

Online Publication Date: 19 February 2010

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Optical properties of planar thin film metamaterials were measured at room and liquid nitrogen temperatures using terahertz time-domain spectroscopy. The operation of metamaterials at cryogenic temperatures is anticipated to be a promising path toward low-loss metamaterials since nonradiative losses are strongly suppressed due to higher charge mobility. A 14% increase in the quality factor of the resonances was experimentally observed. It was limited by the high electron scattering rate due to defects in thin films. Supplementary simulations assuming metamaterials made of thick films reveal a temperature controlled behavior and a 40% increase in the quality factor at 10 K.
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78.66.Nk Insulators
79.20.Kz Other electron-impact emission phenomena
78.47.J- Ultrafast spectroscopy (<1 psec)
42.79.Wc Optical coatings
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
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Effects of rf-bias power on plasma parameters in a low gas pressure inductively coupled plasma

Hyo-Chang Lee, Min-Hyong Lee, and Chin-Wook Chung

Appl. Phys. Lett. 96, 071501 (2010); http://dx.doi.org/10.1063/1.3293295 (3 pages) | Cited 17 times

Online Publication Date: 17 February 2010

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Remarkable changes of the electron temperature and the plasma density by increasing bias power were observed in low gas pressure inductively coupled plasma (ICP) by the measurement of electron energy distribution function (EEDF). As the bias power increases, the electron temperature increased with accompanying the evolution of the EEDF from a bi-Maxwellian to a Maxwellian distribution. However, a different trend of the plasma density was observed with a dependence on the ICP powers. When the ICP power was relatively small or the discharge is in capacitive mode (E mode), the plasma density increased considerably with the bias power, while decrease of the plasma density was observed when the discharge is in inductive mode (H mode). The change of the plasma density can be explained by the balance between total power absorption and power dissipation.
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52.25.-b Plasma properties
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.80.-s Electric discharges

A high current density plasma cathode electron gun

Wenjie Fu, Yang Yan, Wenxu Li, Xiaoyun Li, and Jianqiang Wu

Appl. Phys. Lett. 96, 071502 (2010); http://dx.doi.org/10.1063/1.3310280 (3 pages) | Cited 1 time

Online Publication Date: 17 February 2010

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The design, performance, and characteristics of a plasma cathode electron gun are presented. The plasma cathode is based on a hollow cathode direct current discharge, and the electron beam is accelerated by pulse voltage. By discharging at high gas pressure and operating at low gas pressure, both the maximum accelerating voltage and maximum emitting current could be increased. Utilizing argon, with the accelerating voltage up to 9 kV and gas pressure down to 52 mPa, the gun is able to generate an electron beam of about 4.7 A, and the corresponding emitting current density is about 600 A/cm2.
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52.50.-b Plasma production and heating
52.80.-s Electric discharges
52.75.-d Plasma devices

O2(a mathg) production in flowing Ar–O2 surface-wave microwave discharges: Possible use for oxygen-iodine laser excitation

Vasco Guerra, Kinga Kutasi, and Paulo A. Sá

Appl. Phys. Lett. 96, 071503 (2010); http://dx.doi.org/10.1063/1.3318253 (3 pages) | Cited 6 times

Online Publication Date: 18 February 2010

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Herein we present the calculations conducted on an Ar–O2 surface-wave microwave discharge and its afterglow, and show that this system can be effectively used for the oxygen-iodine laser excitation. It is demonstrated that at pressures higher than 10 mbar O2(a) yields higher than the threshold yield required for positive gain can be achieved along the afterglow. Additionally, the density of O(math) atoms, which can quench the I(math1/2) excited state, can be tuned to the desired level.
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52.80.Pi High-frequency and RF discharges
52.80.Hc Glow; corona
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.25.-b Plasma properties
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The cubic to tetragonal phase transition in SrTiO3 single crystals near its surface under internal and external strains

R. Loetzsch, A. Lübcke, I. Uschmann, E. Förster, V. Große, M. Thuerk, T. Koettig, F. Schmidl, and P. Seidel

Appl. Phys. Lett. 96, 071901 (2010); http://dx.doi.org/10.1063/1.3324695 (3 pages) | Cited 7 times

Online Publication Date: 16 February 2010

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The displacive phase transition in SrTiO3 was investigated by means of x-ray diffraction. We used 4.5 keV photons thus probing only a very thin region near the surface. In the low temperature phase the lattice parameters evolve substantially different than in bulk material. We also investigated the phase transition under the influence of an epitaxial coating with YBaCu2O7 and found the nature of the phase transition changed. The near-surface region behaves like an epitaxial thin SrTiO3 film.
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64.70.K- Solid-solid transitions
61.50.Ks Crystallographic aspects of phase transformations; pressure effects
61.66.Fn Inorganic compounds

Three-dimensional photovoltaics

Bryan Myers, Marco Bernardi, and Jeffrey C. Grossman

Appl. Phys. Lett. 96, 071902 (2010); http://dx.doi.org/10.1063/1.3308490 (3 pages) | Cited 6 times

Online Publication Date: 16 February 2010

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The concept of three-dimensional (3D) photovoltaics is explored computationally using a genetic algorithm to optimize the energy production in a day for arbitrarily shaped 3D solar cells confined to a given area footprint and total volume. Our simulations demonstrate that the performance of 3D photovoltaic structures scales linearly with height, leading to volumetric energy conversion, and provides power fairly evenly throughout the day. Furthermore, we show that optimal 3D structures are not simple box-like shapes, and that design attributes such as reflectivity could be optimized using three-dimensionality.
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88.40.H- Solar cells (photovoltaics)
84.60.Jt Photoelectric conversion

Electronic structure of ZnTe:O and its usability for intermediate band solar cell

Byounghak Lee and Lin-Wang Wang

Appl. Phys. Lett. 96, 071903 (2010); http://dx.doi.org/10.1063/1.3298553 (3 pages) | Cited 7 times

Online Publication Date: 16 February 2010

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The electronic structures of lattice highly mismatched ZnTe1−xOx alloys are calculated with the linear scaling three-dimensional fragment method. We found that the intermediate band states should be described as a result of the coupling between O impurity states rather than the coupling of the impurity state with the conduction band states. We also found that this system can be used for intermediate band state solar cell with a theoretical efficiency of 63%.
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71.20.Nr Semiconductor compounds
71.55.Gs II-VI semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
88.40.J- Types of solar cells

Electrical failure in blends of chemically identical, soft thermoplastic elastomers with different elastic stiffness

Matthias Kollosche and Guggi Kofod

Appl. Phys. Lett. 96, 071904 (2010); http://dx.doi.org/10.1063/1.3319513 (3 pages) | Cited 15 times

Online Publication Date: 16 February 2010

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Investigations on the effect of stiffness on breakdown strength in polymer materials are typically performed indirectly by variation of temperature. Here, the stiffness is varied directly using blends of chemically identical, physically crosslinking elastomers, thus avoiding possible temperature-induced variations in electric and ionic conductivity. Avoiding a chemically crosslinking system rules out variations due to crosslinkers or initiators. Measurements were carried out with a hemispherical indenter resting on a slab of the material with constant load. A theory recently proposed by Zhao and Suo was adapted to the experimental conditions and found to apply well, with no free fitting parameters.
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77.22.Jp Dielectric breakdown and space-charge effects
77.84.Jd Polymers; organic compounds
62.20.dq Other elastic constants
81.40.Jj Elasticity and anelasticity, stress-strain relations

Reaction rate in reversible A↔B reaction-diffusion processes

M. Sinder, V. Sokolovsky, and J. Pelleg

Appl. Phys. Lett. 96, 071905 (2010); http://dx.doi.org/10.1063/1.3319840 (2 pages) | Cited 1 time

Online Publication Date: 16 February 2010

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The reversible A↔B reaction-diffusion process, where species A and B are initially mixed and diffuse with different diffusion coefficients, is usually simulated in the framework of the quasiequilibrium approximation. In this paper the reaction rate of such process is investigated. It is shown that despite the fact that a reaction-diffusion process is considered as the quasiequilibrium process the contribution of the reaction in changes of the species concentration is comparable with the diffusion contribution. Moreover, the ratio of the reaction to diffusion contributions is independent of time and coordinate. Using published experimental data the reaction rate and its profile are calculated.
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82.20.-w Chemical kinetics and dynamics
66.30.Dn Theory of diffusion and ionic conduction in solids

Surface plasmon enhanced energy transfer between type I CdSe/ZnS and type II CdSe/ZnTe quantum dots

C. H. Wang, C. W. Chen, Y. T. Chen, C. M. Wei, Y. F. Chen, C. W. Lai, M. L. Ho, P. T. Chou, and M. Hofmann

Appl. Phys. Lett. 96, 071906 (2010); http://dx.doi.org/10.1063/1.3315876 (3 pages) | Cited 7 times

Online Publication Date: 17 February 2010

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Fluorescence resonant energy transfer (FRET) has been investigated between donor-acceptor pairs of type I CdSe/ZnS and type II CdSe/ZnTe quantum dots (QDs). An Au nanoparticles assisted FRET enhancement was clearly demonstrated. It is found that the efficiency of the energy transfer depends on the excitation wavelength and is largest when in resonance with the Au surface plasmon mode. With the large tunability of the emission intensity in near infrared region, our finding paves an excellent route for creating highly efficient optoelectronic devices and bioimaging labels derived from type II QDs.
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78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
73.21.La Quantum dots
73.22.Lp Collective excitations
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.20.Nr Semiconductor compounds

Gate voltage dependence of nuclear spin relaxation in an impurity-doped semiconductor quantum well

M. Ono, H. Kobayashi, S. Matsuzaka, Y. Ohno, and H. Ohno

Appl. Phys. Lett. 96, 071907 (2010); http://dx.doi.org/10.1063/1.3309687 (3 pages) | Cited 4 times

Online Publication Date: 17 February 2010

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We investigated the gate voltage dependence of the nuclear spin relaxation in a Schottky-gated n-GaAs/AlGaAs (110) quantum well by the time-resolved Kerr rotation measurement combined with the nuclear magnetic resonance technique. The Fermi contact hyperfine interaction is enhanced by decreasing the background electron density, as the electrons become localized at impurity site. The energy relaxation time T1 and the decay time of the Rabi oscillation T2Rabi can be controlled by more than a factor of 10 and a factor of ∼ 2, respectively.
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76.60.Es Relaxation effects
78.20.Jq Electro-optical effects
78.67.De Quantum wells
73.21.Fg Quantum wells
71.70.Jp Nuclear states and interactions
61.72.U- Doping and impurity implantation

Role of negatively charged defects in the lattice contraction of Al–Si–N

C. A. Pignedoli, D. Passerone, H. J. Hug, A. Pélisson-Schecker, and J. Patscheider

Appl. Phys. Lett. 96, 071908 (2010); http://dx.doi.org/10.1063/1.3323093 (3 pages) | Cited 1 time

Online Publication Date: 17 February 2010

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Experiments reveal that incorporation of substitutional Si in wurtzite AlN up to 6 at. % results in a lattice contraction in the [0001] direction. The contraction is linear and, for higher silicon contents, the lattice parameters remain constant. We investigate the geometric and electronic properties of Al–Si–N compounds with Si content varying from 0 to 9 at. % by means of ab initio simulations based on density functional theory. We demonstrate that charged defects are necessary to support the experimental evidence of a shrinking cell parameter: an ideal Al–Si–N wurtzite structure with delocalized charges would undergo lattice expansion due to Coulomb repulsion upon Si incorporation. Charged defects that act as acceptors and compensate the excess charge coming from Si overcompensate the lattice expansion and therefore promote a lattice contraction.
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61.66.Fn Inorganic compounds
61.72.jd Vacancies
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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