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23 Apr 2012

Volume 100, Issue 17, Articles (17xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 171903 (2012); http://dx.doi.org/10.1063/1.4704193 (3 pages)

Y. Peng and K. Kempa
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Improved lasing characteristics of ZnO/organic-dye random laser

Kurniawan Firdaus, Toshihiro Nakamura, and Sadao Adachi

Appl. Phys. Lett. 100, 171101 (2012); http://dx.doi.org/10.1063/1.4705471 (4 pages) | Cited 1 time

Online Publication Date: 23 April 2012

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We investigate the random lasing characteristics of ZnO nanopowder suspended in methanol with the addition of organic-dye molecules. At a certain dye concentration, the random lasing intensity is enhanced, and the excitation threshold power is reduced. These improvements are explained by Förster-type resonant energy transfer from the dye-molecule donor to the ZnO-nanopowder acceptor.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.55.Zz Random lasers

Perpendicular coupling to in-plane photonics using arc waveguides fabricated via two-photon polymerization

Chee-Wei Lee, Stefano Pagliara, Ulrich Keyser, and Jeremy J. Baumberg

Appl. Phys. Lett. 100, 171102 (2012); http://dx.doi.org/10.1063/1.4704358 (3 pages) | Cited 1 time

Online Publication Date: 23 April 2012

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We demonstrate the concept of vertically standing arc waveguides to couple normally incident light into the plane of a photonic circuit or sensor array. The simple one-step direct write fabrication uses a low power picosecond microchip laser for two-photon polymerization with high-speed and low-cost. Arc waveguides with different arc radii and waveguide port diameters are obtained, with insertion loss down to 1.5 dB. This demonstration of a distinctly different architecture employing unsupported arc waveguides adds another dimension to photonic integration and opens up applications for environmental sensors, integrated microfluidics, bio-assay chips, as well as offering an alternate way of input/output-coupling to planar waveguides.
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42.82.Et Waveguides, couplers, and arrays
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.62.-b Laser applications
42.55.Rz Doped-insulator lasers and other solid state lasers

High-efficiency acousto-optical interaction in phoxonic nanobeam waveguide

Fu-Li Hsiao, Cheng-Yi Hsieh, Hao-Yu Hsieh, and Chien-Chang Chiu

Appl. Phys. Lett. 100, 171103 (2012); http://dx.doi.org/10.1063/1.4705295 (4 pages) | Cited 1 time

Online Publication Date: 23 April 2012

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We demonstrate the simultaneous existence of slow photonic and phononic modes in phoxonic nanobeam. The phoxonic nanobeam is formed by arranging air semi-cylinders along lateral sides of a suspended silicon waveguide. Because of the slow group velocities, the acousto-optical interactions are dramatically enhanced. The efficiencies of interaction are strongly related to the polarizations of both slow photonic and phononic modes. Our proposed structure is a potential high-efficiency acousto-optical modulator with ultra-small footprint size. The operating optical wavelength is about 1550 nm, while the acoustic frequency is about 6.8 GHz.
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42.82.Et Waveguides, couplers, and arrays
42.79.-e Optical elements, devices, and systems
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

Temperature curve of magnetization and left-handed properties of La0.775Sr0.225MnO3

D. P. Belozorov, T. V. Kalmykova, S. I. Tarapov, A. M. Pogorily, A. I. Tovstolytkin, A. G. Belous, and S. A. Solopan

Appl. Phys. Lett. 100, 171104 (2012); http://dx.doi.org/10.1063/1.4705729 (4 pages) | Cited 1 time

Online Publication Date: 24 April 2012

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The left-handed features of Sr doped manganite lanthanum ceramics La0.775Sr0.225MnO3 in the vicinity of its Curie temperature are studied. The left-handed features are responsible for appearance of the additional transparency peak in the forbidden band of the photonic crystal bounded with the above manganite. The magnitude of the critical exponent β (β ∼ 0.50) determined in the work agrees with results reported in the literature and allows supposing that long-range interactions play an important role in the phase transition from conductive ferromagnetic to nonconductive dielectric paramagnetic state of the manganite in its Curie point.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.20.Ck Nonmetals
75.50.Dd Nonmetallic ferromagnetic materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Double embedded photonic crystals for extraction of guided light in light-emitting diodes

Jason Jewell, Dobri Simeonov, Shih-Chieh Huang, Yan-Ling Hu, Shuji Nakamura, James Speck, and Claude Weisbuch

Appl. Phys. Lett. 100, 171105 (2012); http://dx.doi.org/10.1063/1.4705735 (4 pages) | Cited 8 times

Online Publication Date: 24 April 2012

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Light-emitting diodes (LEDs) were fabricated in gallium nitride with two embedded photonic crystals (PhCs), creating a waveguide with a highly confined, strongly excited, and well-extracted fundamental mode. This structure improves upon previous PhC LED designs by reducing the extraction length of the fundamental mode and establishing a path to designs with very low absorption losses. Optical output was measured with angular-resolved electroluminescence. The extraction length of the fundamental mode was measured to be 21–39 μm along the PhCs’ Γ-M directions, which is much shorter than values reported for single-PhC devices. This structure opens the way to more efficient LEDs and lasers.
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85.60.Jb Light-emitting devices
42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials
42.15.Eq Optical system design

Effect of magnetic field on polariton emission characteristics of a quantum-well microcavity diode

Pallab Bhattacharya, Ayan Das, Sishir Bhowmick, Marc Jankowski, and Chi-sen Lee

Appl. Phys. Lett. 100, 171106 (2012); http://dx.doi.org/10.1063/1.4707155 (4 pages)

Online Publication Date: 24 April 2012

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The effect of an applied magnetic field on the polariton emission characteristics of a In0.1Ga0.9As/GaAs multi-quantum well microcavity diode in the strong coupling regime has been investigated. It is observed that the relaxation bottleneck is suppressed due to an enhancement of the polariton-phonon scattering rates in the presence of the magnetic field. A distinct non-linearity is also observed in the light-current characteristics.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

High-speed waveguide-coupled graphene-on-graphene optical modulators

Steven J. Koester and Mo Li

Appl. Phys. Lett. 100, 171107 (2012); http://dx.doi.org/10.1063/1.4704663 (4 pages) | Cited 3 times

Online Publication Date: 24 April 2012

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An electro-absorption optical modulator concept based upon a dual-graphene layer is presented. The device consists of a silicon-on-insulator waveguide upon which two graphene layers reside, separated by a thin insulating region. The lower graphene acts as a tunable absorber, while the upper layer functions as a transparent gate electrode. Calculations based upon realistic graphene material properties show that 3-dB bandwidths over 120 GHz (30 GHz) are achievable at near- (λ = 1.55 μm) and mid- (λ = 3.5 μm) infrared bands. The effect of background doping and potential fluctuations on the bandwidth, modulation depth, and insertion loss are also quantified.
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42.79.Hp Optical processors, correlators, and modulators
42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers

Deflection switching of a laser beam by the Pockels effect of water

Shunpei Yukita, Naoyuki Shiokawa, Hiroki Kanemaru, Hajime Namiki, Takayoshi Kobayashi, and Eiji Tokunaga

Appl. Phys. Lett. 100, 171108 (2012); http://dx.doi.org/10.1063/1.4705154 (3 pages) | Cited 1 time

Online Publication Date: 24 April 2012

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Deflection of a laser beam in response to an electric field was detected with a Sagnac interferometer. A laser beam was aligned to travel between two electrodes immersed in aqueous electrolyte solution. When the alternating electric field was applied perpendicular to the beam axis, the direction of the beam deflection was switched synchronously with the field alternation as expected for the Pockels effect. Broken inversion symmetry is prerequisite to the linear electrooptic effect, but surprisingly the effect was observed even when the laser beam travels through the bulk water a few millimeters away from the electrode surface.
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79.20.Ds Laser-beam impact phenomena
78.20.Jq Electro-optical effects
07.60.Ly Interferometers

Ultraviolet electroluminescence from ordered ZnO nanorod array/p-GaN light emitting diodes

J. J. Dong, X. W. Zhang, Z. G. Yin, J. X. Wang, S. G. Zhang, F. T. Si, H. L. Gao, and X. Liu

Appl. Phys. Lett. 100, 171109 (2012); http://dx.doi.org/10.1063/1.4706259 (4 pages) | Cited 6 times

Online Publication Date: 25 April 2012

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The highly ordered and aligned ZnO nanorod arrays were grown on p-GaN substrates via a facile hydrothermal process assisted by the inverted self-assembled monolayer template, from which the ZnO nanorod/p-GaN heterojunction light emitting diodes (LEDs) were fabricated. The ZnO nanorod-based LEDs exhibit a stronger ultraviolet emission of 390 nm than the ZnO film-based counterpart, which is attributed to the low density of interfacial defects, the improved light extraction efficiency, and carrier injection efficiency through the nano-sized junctions. Furthermore, the LED with the 300 nm ZnO nanorods has a better electroluminescence performance compared with the device with the 500 nm nanorods.
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85.60.Jb Light-emitting devices
85.30.Kk Junction diodes

Large two dimensional Coulomb crystals in a radio frequency surface ion trap

B. Szymanski, R. Dubessy, B. Dubost, S. Guibal, J.-P. Likforman, and L. Guidoni

Appl. Phys. Lett. 100, 171110 (2012); http://dx.doi.org/10.1063/1.4705153 (4 pages) | Cited 4 times

Online Publication Date: 25 April 2012

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We designed and operated a surface ion trap with an ion-substrate distance of 500 μm, realized with standard printed-circuit-board techniques. The trap has been loaded with up to a few thousand Sr+ ions in the Coulomb-crystal regime. An analytical model of the pseudo-potential allowed us to determine the parameters that drive the trap into anisotropic regimes in which we obtain large (N>150) purely two dimensional (2D) ion Coulomb crystals. These crystals may open a simple and reliable way to experiments on quantum simulations of large 2D systems.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles

Integrated high frequency aluminum nitride optomechanical resonators

Chi Xiong, Xiankai Sun, King Y. Fong, and Hong X. Tang

Appl. Phys. Lett. 100, 171111 (2012); http://dx.doi.org/10.1063/1.4707898 (4 pages) | Cited 6 times

Online Publication Date: 26 April 2012

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Aluminum nitride (AlN) has been widely used in microeletromechanical resonators for its excellent electromechanical properties. Here, we demonstrate the use of AlN as an optomechanical material that simultaneously offers low optical and mechanical loss. Integrated AlN microring resonators in the shape of suspended rings exhibit high optical quality factor (Q) with loaded Q up to 125 000. Optomechanical transduction of the Brownian motion of a GHz contour mode yields a displacement sensitivity of 6.2 × 10−18 m/Hz1/2 in ambient air.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
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Impact and wetting behaviors of impinging microdroplets on superhydrophobic textured surfaces

Dae Hee Kwon and Sang Joon Lee

Appl. Phys. Lett. 100, 171601 (2012); http://dx.doi.org/10.1063/1.4705296 (4 pages) | Cited 1 time

Online Publication Date: 24 April 2012

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The impact and wetting behaviors of impinging microdroplets on textured surfaces are investigated using high-speed imaging. Microdroplets with diameters less than 50 μm are ejected using a piezoelectric printhead with controlled Weber numbers. The impact behaviors are clearly observed, and the detailed mechanisms are explained according to the Weber number and wetting states of the impinging droplets. Moreover, the transition phenomena from bouncing to non-bouncing are clearly observed. The impalement transition, which has been explained by wetting pressures, is also examined in this study.
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68.08.Bc Wetting
68.35.B- Structure of clean surfaces (and surface reconstruction)
77.65.-j Piezoelectricity and electromechanical effects

Lateral heating of SiO2/Si: Interfacial Si structure change causing tunneling current reduction

Zhi Chen, Pang-Leen Ong, Yichun Wang, and Lei Han

Appl. Phys. Lett. 100, 171602 (2012); http://dx.doi.org/10.1063/1.4709418 (4 pages) | Cited 2 times

Online Publication Date: 27 April 2012

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Lateral heating processing of SiO2/Si samples can reduce the tunneling current of SiO2 by 5 orders of magnitude with very good reproducibility. There is a strong correlation between the flatband voltage shift of metal-oxide-semiconductor capacitors and the tunneling current reduction. Analysis of the flatband voltage shift suggests that origin of the tunneling current reduction after lateral heating is caused by the structure change of Si, most likely tensor strained Si, near the SiO2/Si interface.
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85.30.Tv Field effect devices
84.32.Tt Capacitors

Observation of UV-induced Auger features in catechol adsorbed on anatase TiO2 (101) single crystal surface

Andrew G. Thomas and Karen L. Syres

Appl. Phys. Lett. 100, 171603 (2012); http://dx.doi.org/10.1063/1.4709616 (4 pages) | Cited 1 time

Online Publication Date: 27 April 2012

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We have investigated the electronic structure of catechol adsorbed on the anatase TiO2 (101) surface under illumination with ultraviolet (UV) light (4.75 eV) using resonant photoemission spectroscopy. UV illumination results in the appearance of a strong Ti MVV (M refers to photoionization of 3p level and VV the Auger decay process via the valence levels) feature at a kinetic energy of 26.2 eV. This is attributed to the creation of localised states following catechol to Ti-3d excitation by the UV source. A sharp resonance attributed to excitation from Ti 3p states into these localised states is observed in constant final state spectra.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
68.43.Mn Adsorption kinetics
71.20.Nr Semiconductor compounds
79.20.Fv Electron impact: Auger emission
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
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Relaxation of a metallic glass to the metastable equilibrium: Evidence for the existence of the Kauzmann pseudocritical temperature

Yu. P. Mitrofanov, V. A. Khonik, A. V. Granato, D. M. Joncich, S. V. Khonik, and A. M. Khoviv

Appl. Phys. Lett. 100, 171901 (2012); http://dx.doi.org/10.1063/1.4705407 (4 pages) | Cited 3 times

Online Publication Date: 23 April 2012

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High-precision isothermal measurements on strongly preannealed metallic glass reveal a decrease of the shear modulus to the metastable equilibrium value both in the glassy state far below the glass transition and in the supercooled liquid state near Tg. The results obtained point out the existence of a low-temperature limit for the supercooled liquid, which is known as the Kauzmann pseudocritical temperature [W. Kauzmann, Chem. Rev. 43, 219 (1948)]. This finding experimentally questions the existence of the “Kauzmann paradox,” which is widely discussed in the literature.
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61.43.Fs Glasses
81.40.Gh Other heat and thermomechanical treatments
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
64.70.P- Glass transitions of specific systems

Identification of polymer stabilized blue-phase liquid crystal display by chromaticity diagram

Yi-Fen Lan, Cheng-Yeh Tsai, Ling-Yung Wang, Po-Jen Ku, Tai-Hsiang Huang, Chu-Yu Liu, and Norio Sugiura

Appl. Phys. Lett. 100, 171902 (2012); http://dx.doi.org/10.1063/1.4705432 (4 pages) | Cited 2 times

Online Publication Date: 23 April 2012

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We reported an identification method of blue phase liquid crystal (BPLC) display status by using Commission International de l’Éclairage (CIE) chromaticity diagram. The BPLC was injected into in-plane-switch (IPS) cell, polymer stabilized (PS) by ultraviolet cured process and analyzed by luminance colorimeter. The results of CIE chromaticity diagram showed a remarkable turning point when polymer stabilized blue phase liquid crystal II (PSBPLC-II) formed in the IPS cell. A mechanism of CIE chromaticity diagram identify PSBPLC display status was proposed, and we believe this finding will be useful to application and production of PSBPLC display.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems
FREE

Controlling light propagation with nanowires

Y. Peng and K. Kempa

Appl. Phys. Lett. 100, 171903 (2012); http://dx.doi.org/10.1063/1.4704193 (3 pages) | Cited 1 time

Online Publication Date: 23 April 2012

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We study the interaction of electromagnetic waves (EM) with metallic nanowire systems for frequencies not far from the surface plasma frequency (polaritonic range). We employ calculation and simulation to show that when excited at one end with axially polarized EM waves, nanowires can function as efficient waveguides of surface plasmon polaritons (SPPs). From the Fabry-Perot resonances of standing SPP waves, we study their dispersion relation and show that for a vanishing SPP wavelength it is identical to that for a planar metallic surface. Nanowire systems can be employed in various nanophotonic applications, and we assess this potential by studying propagation characteristics of these nano-waveguides and their interactions.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.22.Lp Collective excitations
78.68.+m Optical properties of surfaces
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Eu luminescence center created by Mg codoping in Eu-doped GaN

Dong-gun Lee, Atsushi Nishikawa, Yoshikazu Terai, and Yasufumi Fujiwara

Appl. Phys. Lett. 100, 171904 (2012); http://dx.doi.org/10.1063/1.4704920 (3 pages) | Cited 4 times

Online Publication Date: 23 April 2012

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We investigated the photoluminescence properties of Eu,Mg-codoped GaN grown by organometallic vapor phase epitaxy. Some emission due to intra-4f shell transition of 5D0-7F2 in Eu3+ ions in a center with Eu and Mg was observed together with typical Eu emission. The peak intensity of the Eu-Mg emission was about five times higher than that of the typical Eu emission. The Eu-Mg emission exhibited a maximum at around 180 K, while the typical Eu emission intensity decreased monotonically with increasing temperature. It was found that only one type of Eu-Mg center contributed to the enhanced intensity up to 180 K.
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78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.U- Doping and impurity implantation
61.72.uj III-V and II-VI semiconductors
78.66.Fd III-V semiconductors

Dimensional transition and carrier dynamics in CdxZn1−xTe/ZnTe nanostructures on Si substrates

K.-D. Park, S.-Y. Yim, and H. S. Lee

Appl. Phys. Lett. 100, 171905 (2012); http://dx.doi.org/10.1063/1.4705413 (4 pages) | Cited 1 time

Online Publication Date: 24 April 2012

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We investigate the dimensional transition and carrier dynamics in CdxZn1−xTe/ZnTe nanostructures with various Cd mole fractions, grown on Si substrates. Atomic force microscopy images show that the dimensional transition from quantum dots (QDs) to quantum wires occurs with increasing Cd mole fraction. The activation energy of the electrons confined in CdxZn1−xTe QDs with a Cd mole fraction of 0.6 is higher than that of electrons confined in CdxZn1−xTe nanostructures. In addition, the radiative recombination rate shows a linear dependence on the length of the CdxZn1−xTe nanostructures, which is well explained in terms of the “coherence volume” of the bound excitons.
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81.05.Dz II-VI semiconductors
81.07.Ta Quantum dots
81.07.Vb Quantum wires
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
64.70.kg Semiconductors
61.46.-w Structure of nanoscale materials

Strain-induced composition limitation in nitrogen δ-doped (In,Ga)As/GaAs quantum wells

R. Gargallo-Caballero, E. Luna, F. Ishikawa, and A. Trampert

Appl. Phys. Lett. 100, 171906 (2012); http://dx.doi.org/10.1063/1.4705731 (4 pages)

Online Publication Date: 24 April 2012

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The local element distribution across tensile-strained N δ-doped (In,Ga)As/GaAs quantum wells (QWs) is investigated by transmission electron microscopy. The sub-monolayer (ML) insertion results in a several monolayers thick (In,Ga)(As,N) layer with lateral composition fluctuations. We also find an inhomogeneous In incorporation across the QW, with a minimum In content, [In]min, exactly at the position of the N-insertion, where N content is maximum, [N]max. Regardless of the position along the QW, [N]max corresponds to [In]min so that an (In,Ga)(As,N) layer of this composition has a lattice parameter close to aGaAs. The impact of tensile strain on this complex chemical configuration is discussed.
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81.05.Ea III-V semiconductors
81.07.St Quantum wells
68.65.Fg Quantum wells
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
61.66.Fn Inorganic compounds

Employing pre-stress to generate finite cloaks for antiplane elastic waves

William J. Parnell, Andrew N. Norris, and Tom Shearer

Appl. Phys. Lett. 100, 171907 (2012); http://dx.doi.org/10.1063/1.4704566 (4 pages) | Cited 1 time

Online Publication Date: 24 April 2012

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It is shown that nonlinear elastic pre-stress of neo-Hookean hyperelastic materials can be used as a mechanism to generate finite cloaks and thus render objects near-invisible to incoming antiplane elastic waves. This approach appears to negate the requirement for special cloaking metamaterials with inhomogeneous and anisotropic material properties in this case. These properties are induced naturally by virtue of the pre-stress. This appears to provide a mechanism for broadband cloaking since dispersive effects due to metamaterial microstructure will not arise.
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62.30.+d Mechanical and elastic waves; vibrations

Correlation between local structure and electrical resistivity in gallium-antimony melts

Tingkun Gu (谷廷坤)

Appl. Phys. Lett. 100, 171908 (2012); http://dx.doi.org/10.1063/1.4706253 (4 pages)

Online Publication Date: 25 April 2012

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First-principles molecular dynamics simulations on the structural and electronic properties of liquid gallium-antimony alloys (GaxSb1−x) were performed. Analysis of the calculated results revealed that changes in the local structure of liquid GaxSb1−x depend on composition. The coordination tendencies of Ga-Ga, Ga-Sb, and Sb-Sb showed different trends as a function of the concentration of Sb, and the electronic structures of liquid GaxSb1−x were consistent with this finding. Further analysis confirmed that there is an explicit correlation between the structural parameters and electrical resistivity of liquid GaxSb1−x.
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71.22.+i Electronic structure of liquid metals and semiconductors and their alloys
72.80.Ph Liquid semiconductors
61.25.-f Studies of specific liquid structures

Enhanced adhesion with pedestal-shaped elastomeric stamps for transfer printing

Seok Kim, Andrew Carlson, Huanyu Cheng, Seungwoo Lee, Jung-Ki Park, Yonggang Huang, and John A. Rogers

Appl. Phys. Lett. 100, 171909 (2012); http://dx.doi.org/10.1063/1.4706257 (4 pages) | Cited 2 times

Online Publication Date: 25 April 2012

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Microscale elastomeric relief structures with “pedestal” shapes provide enhanced operation in stamps designed for deterministic materials assembly via transfer printing. Experimental measurements of adhesion and finite element analysis both show that for certain geometries, exceptionally large enhancements in adhesion strength (over 15×) can be achieved. Transfer printing of microscale platelets of silicon and ultrathin gallium nitride light emitting diodes onto a silicon substrate without adhesive coatings demonstrates some capabilities in assembly that result from this type of stamp, of interest in diverse applications, including those that involve heterogeneous materials integration.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.16.-c Methods of micro- and nanofabrication and processing
85.60.Jb Light-emitting devices
68.35.Np Adhesion

The contribution of quantum confinement to optical anisotropy of a-plane Cd0.06Zn0.94O/ZnO quantum wells

Hiroaki Matsui and Hitoshi Tabata

Appl. Phys. Lett. 100, 171910 (2012); http://dx.doi.org/10.1063/1.4707384 (4 pages) | Cited 1 time

Online Publication Date: 25 April 2012

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We investigated quantum size effects on polarized photoluminescence (PL) from a-plane Cd0.06Zn0.94O/ZnO quantum wells (QWs) with different well widths (LW). The degree of polarized PL at 300 K increased with a narrowing of LW, which obeyed the polarization selection rule based on a Boltzmann-like distribution. Furthermore, the narrowing of LW enhanced the anisotropic lattice distortions in well layers along the growing direction, which resulted in an increase of energy separation between the two topmost valence band levels. The effect of quantum confinement on polarized PL of QWs was accompanied by a change of structural symmetry of the well layers.
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78.67.De Quantum wells
81.07.St Quantum wells
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
71.20.Nr Semiconductor compounds
73.21.Fg Quantum wells

Photoluminescence induced by twinning interface in CdS nanocrystals

P. Q. Zhao, S. J. Xiong, X. L. Wu, and Paul K. Chu

Appl. Phys. Lett. 100, 171911 (2012); http://dx.doi.org/10.1063/1.4707388 (4 pages) | Cited 1 time

Online Publication Date: 25 April 2012

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The photoluminescence (PL) spectra acquired from CdS nanocrystals encapsulated with oleic acid synthesized by a two-phase approach exhibit two fine features, including a narrow peak arising from near-band edge emission and a broader one composed of two subpeaks at slightly lower energy. Solvent effects suggest that the surface defect states on the nanocrystals are not the origin of this broad PL band. High-resolution transmission electron microscopy examinations and density function theory calculation reveal that the broad low-energy PL band stems from twinning interfaces in the CdS nanocrystals.
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78.55.Et II-VI semiconductors
61.72.Mm Grain and twin boundaries
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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