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9 May 2011

Volume 98, Issue 19, Articles (19xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 193103 (2011); http://dx.doi.org/10.1063/1.3571437 (3 pages)

T. van der Sar, J. Hagemeier, W. Pfaff, E. C. Heeres, S. M. Thon, H. Kim, P. M. Petroff, T. H. Oosterkamp, D. Bouwmeester, and R. Hanson
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Diffractive optical elements based on plasmonic metamaterials

B. Walther, C. Helgert, C. Rockstuhl, and T. Pertsch

Appl. Phys. Lett. 98, 191101 (2011); http://dx.doi.org/10.1063/1.3587622 (3 pages) | Cited 5 times

Online Publication Date: 9 May 2011

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The dispersive properties of plasmonic metamaterials and the ability to tailor their complex transmission strongly suggest their use in versatile optical elements. Here we introduce the idea of such an application in diffractive elements and describe, as a proof-of-principle, two numerical implementations of computer-generated holograms at visible wavelengths that are based on fishnet metamaterials. These holograms consist of large arrays of metamaterial unit cells which have locally varying geometrical parameters into which the desired far-field optical response is encoded. We describe the entire design process for such holograms, discuss their efficiency and critically assess their limitations.
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42.40.Eq Holographic optical elements; holographic gratings
42.40.Jv Computer-generated holograms
42.15.Eq Optical system design
42.79.Wc Optical coatings

Femtosecond Z-scan measurement of third-order nonlinear refractive indices of BaMgF4

Junjie Chen, Xianfeng Chen, Anhua Wu, Hongjun Li, Yuanlin Zheng, Yanzhi Ma, Linwen Jiang, and Jun Xu

Appl. Phys. Lett. 98, 191102 (2011); http://dx.doi.org/10.1063/1.3587642 (3 pages) | Cited 2 times

Online Publication Date: 9 May 2011

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The BaMgF4 single crystal is grown by Bridgman method. The third-order nonlinear refractive indices along three crystallographic axes are determined by Z-scan technique with femtosecond laser. The largest one that has a value of 2.35×10−18 m2/W is along the c-axis and the corresponding third-order nonlinear susceptibility is 1.24×10−12 esu. This value is compared with LiNbO3 through self-phase modulation effect. Furthermore, the mechanism and the possible applications of the relatively large third-order nonlinear refractive indices are also discussed at last.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.47.J- Ultrafast spectroscopy (<1 psec)
77.80.-e Ferroelectricity and antiferroelectricity
81.10.Fq Growth from melts; zone melting and refining

Impact of dispersion, free carriers, and two-photon absorption on the generation of intense terahertz pulses in ZnTe crystals

S. Vidal, J. Degert, M. Tondusson, J. Oberlé, and E. Freysz

Appl. Phys. Lett. 98, 191103 (2011); http://dx.doi.org/10.1063/1.3588411 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2011

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We study the evolution of the energy and the spectrum of a terahertz wave generated by optical rectification of an ultrashort laser pulse in ZnTe crystals with different thicknesses. As the pump intensity increases, we observe a shift in the terahertz spectrum toward lower frequencies. Moreover, at high pump intensities, in disagreement with common sense, thin crystals have a better conversion efficiency than thicker ones. These phenomena are accounted for by the pump depletion induced by two-photon absorption, pulse broadening and the impact of the photoinduced free carriers on the complex refractive index of the crystal in the terahertz range.
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42.25.Bs Wave propagation, transmission and absorption
42.25.-p Wave optics

High power Sb-free quantum cascade laser emitting at 3.3 μm above 350 K

A. Bismuto, M. Beck, and J. Faist

Appl. Phys. Lett. 98, 191104 (2011); http://dx.doi.org/10.1063/1.3589355 (3 pages) | Cited 7 times

Online Publication Date: 9 May 2011

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The design and implementation of a short wavelength strain-compensated quantum cascade laser based on In0.72Ga0.28As/In0.52Al0.48As–AlAs on InP is presented. We demonstrate watt-level room temperature emission at 3.3 μm. Lasers operate in pulsed mode above 350 K. Threshold current densities of 3.6 kA/cm2 and slope efficiencies of more than 600 mW/A are observed at room temperature. The laser performance is comparable with Sb-containing quantum cascade lasers.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Ultrashort laser pulse energy deposition in metal films with phase changes

Yunpeng Ren, J. K. Chen, Yuwen Zhang, and Jing Huang

Appl. Phys. Lett. 98, 191105 (2011); http://dx.doi.org/10.1063/1.3579539 (3 pages) | Cited 2 times

Online Publication Date: 9 May 2011

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Four optical models of reflectivity and absorption coefficient are investigated in this letter. After compared with existing experimental data, the extended Drude model is incorporated into a two-temperature model to simulate laser energy deposition and thermal response, including solid–liquid and liquid–vapor phase change, in a gold film irradiated by a femtosecond laser pulse. Dynamic reflectivity and absorption coefficient should be employed in modeling ultrafast laser heating except for very low laser fluencies.
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81.15.Fg Pulsed laser ablation deposition
64.70.D- Solid-liquid transitions
64.70.F- Liquid-vapor transitions
68.55.A- Nucleation and growth
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Bz Metals and metallic alloys

Multimodal coherent anti-Stokes Raman spectroscopic imaging with a fiber optical parametric oscillator

Yan-Hua Zhai, Christiane Goulart, Jay E. Sharping, Huifeng Wei, Su Chen, Weijun Tong, Mikhail N. Slipchenko, Delong Zhang, and Ji-Xin Cheng

Appl. Phys. Lett. 98, 191106 (2011); http://dx.doi.org/10.1063/1.3589356 (3 pages) | Cited 2 times

Online Publication Date: 10 May 2011

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We report on multimodal coherent anti-Stokes Raman scattering (CARS) imaging with a source composed of a femtosecond fiber laser and a photonic crystal fiber (PCF)-based optical parametric oscillator (FOPO). By switching between two PCFs with different zero dispersion wavelengths, a tunable signal beam from the FOPO covering the range from 840 to 930 nm was produced. By combining the femtosecond fiber laser and the FOPO output, simultaneous CARS imaging of a myelin sheath and two-photon excitation fluorescence imaging of a labeled axons in rat spinal cord have been demonstrated at the speed of 20 μs per pixel.
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42.62.Be Biological and medical applications
87.19.lh Optical imaging of neuronal activity
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.55.Wd Fiber lasers
42.65.Yj Optical parametric oscillators and amplifiers
87.64.kp Raman

Energy efficient microcavity lasers with 20 and 40 Gb/s data transmission

F. Tan, C. H. Wu, M. Feng, and N. Holonyak, Jr.

Appl. Phys. Lett. 98, 191107 (2011); http://dx.doi.org/10.1063/1.3589363 (3 pages) | Cited 2 times

Online Publication Date: 10 May 2011

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Microcavity lasers (μCLs), reduced-size (≲3 μm aperture) vertical cavity surface-emitting lasers (VCSELs) defined by the buried-oxide process for current and field confinement (thus wide mode spacing), are demonstrated with low threshold current, sharp turn-on L-I characteristics, and wide bandwidth operation. Due to the enhanced spontaneous recombination rate at reduced mode and improved photon density, μCLs exhibit lower charge-field resonance peaks at a modulation bandwidth f−3 dB = 18.7 GHz, thus permitting open-“eye” operation at 20 and 40 Gb/s data rates (I≲3 mA). The energy efficiency for 20 Gb/s data transmission is measured to be 4.84 Gb/s/mW, which is eight times better than 7 μm aperture VCSELs.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
42.55.Sa Microcavity and microdisk lasers
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Energy transition characterization of 1.18 and 1.3 μm bands of bismuth fiber by spectroscopy of the transient oscillations

Regina Gumenyuk, Konstantin Golant, and Oleg G. Okhotnikov

Appl. Phys. Lett. 98, 191108 (2011); http://dx.doi.org/10.1063/1.3590266 (3 pages) | Cited 2 times

Online Publication Date: 11 May 2011

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The experimental evidence of laser transition type in bismuth-doped silica fibers operating at different spectral bands is presented. Spectrally resolved transient (relaxation) oscillations studied for a Bi-doped fiber laser at room and liquid-nitrogen temperatures allow to identify the three- and four-level energy bands. 1.18 μm short-wavelength band is found to be a three-level system at room temperature with highly populated terminal energy level of laser transition. The depopulation of ground level by cooling the fiber down to liquid-nitrogen temperature changes the transition to four-level type. Four-level energy transition distinguished at 1.32 μm exhibits the net gain at room temperature.
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42.55.Wd Fiber lasers
42.60.By Design of specific laser systems
81.05.Kf Glasses (including metallic glasses)

Total funneling of light in high aspect ratio plasmonic nanoresonators

Patrick Bouchon, Fabrice Pardo, Benjamin Portier, Laurence Ferlazzo, Petru Ghenuche, Gulnar Dagher, Christophe Dupuis, Nathalie Bardou, Riad Haïdar, and Jean-Luc Pelouard

Appl. Phys. Lett. 98, 191109 (2011); http://dx.doi.org/10.1063/1.3588393 (3 pages) | Cited 12 times

Online Publication Date: 12 May 2011

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We demonstrate the total extinction of the reflectivity for a transverse magnetic polarized wave on a gold surface etched on 6% of its area by both narrow (150 nm) and deep (2 μm) grooves. These high aspect ratio metallic grooves were fabricated using a mold cast technique based on an electrolytic growth of gold. They exhibit two resonance peaks corresponding to the first and second cavity modes inside the grooves. We also evidence the incidence-invariance of their spectral response, which undoubtedly shows the localized nature of the resonances. These experimental results confirm the prediction of total funneling of light in very narrow grooves.
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42.79.-e Optical elements, devices, and systems
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Imaging resonant modes in photonic crystal nanocavity by atomic force microscope nano-oxidation

W.-Y. Chen, M.-J. Chen, C.-C. Cheng, T. M. Hsu, C.-J. Wang, and J.-I. Chyi

Appl. Phys. Lett. 98, 191110 (2011); http://dx.doi.org/10.1063/1.3589372 (3 pages)

Online Publication Date: 12 May 2011

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Electric field distributions of resonant modes in a photonic crystal nanocavity were imaged using atomic force microscope nano-oxidation. A grid pattern of nanosize oxides was grown on the nanocavity to perturb the resonant modes. The perturbation caused a shift in the resonant wavelength that was proportional to the local electric field intensity of the resonant mode. The experimentally obtained field intensity images agreed excellently with the finite-difference time-domain calculations. The measured resonant mode images had high spatial resolution and image contrast, owing to the extremely local perturbation of the atomic force microscope oxidation technique.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
68.37.Ps Atomic force microscopy (AFM)
02.70.Bf Finite-difference methods
81.65.Mq Oxidation

In-plane manipulation of quantum dots in high quality laterally contacted micropillar cavities

J. Beetz, C. Kistner, M. Lermer, C. Schneider, S. Reitzenstein, S. Höfling, M. Kamp, and A. Forchel

Appl. Phys. Lett. 98, 191111 (2011); http://dx.doi.org/10.1063/1.3589975 (3 pages) | Cited 1 time

Online Publication Date: 12 May 2011

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We report on the realization and study of laterally contacted quantum dot (QD)-micropillars. The lateral contacts are formed by ion beam induced deposition and allow for the application of in-plane electric fields. The processing was optimized to preserve high optical quality of the QD-micropillars and to minimize detrimental leakage currents while providing a good electrical control of the QD properties. Under variation of the applied voltage we are able to Stark-tune the emission energy of the QDs up to 0.12 meV and to reduce their fine structure splitting by up to a factor of 5.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.20.Jq Electro-optical effects

Anomalous transmission of terahertz waves in arrays of double-ring resonators induced by a 400 nm pump pulse

Yulei Shi, Qing-li Zhou, Wei Liu, Jianfeng Liu, and Cunlin Zhang

Appl. Phys. Lett. 98, 191112 (2011); http://dx.doi.org/10.1063/1.3589977 (3 pages)

Online Publication Date: 12 May 2011

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In this letter, we describe detailed femtosecond-pump–terahertz-probe studies of the electromagnetic response of arrays of double-ring and complementary double-ring resonators. A surprising result is that an increase in the terahertz transmission is observed when a double-ring structure is excited by a 400 nm pump pulse. To explain this anomalous transmission, we propose a mechanism in which the photogenerated carriers play two competing roles. In other cases, for instance, when the wavelength of the pump pulse is 800 nm or in the case of a complementary double-ring structure, the normal transmission can also be understood in terms of this mechanism.
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42.70.-a Optical materials
42.79.-e Optical elements, devices, and systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Hydrodynamic modeling of surface plasmon enhanced photon induced current in a gold grating

Alex English, Cheng-Wen Cheng, Lloyd Lowe, II, Min-Hsiung Shih, and Wan Kuang

Appl. Phys. Lett. 98, 191113 (2011); http://dx.doi.org/10.1063/1.3590200 (3 pages) | Cited 2 times

Online Publication Date: 12 May 2011

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The current induced by incident photons on an gold grating slab is investigated numerically and experimentally. A semiclassical electrodynamic model is developed under the weak nonlinearity approximation. Electrons in the conduction band are treated as an electron gas in the presence of a self-consistent electromagnetic field. The model is solved by the finite element method and compared with measurements. The calculated current density as a function of incident angle and wavelength is found to be in qualitative agreement with the experimental measurements. The results show that increasing surface plasmon spatial variation enhances photon induced current.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
42.79.Dj Gratings
71.10.Ca Electron gas, Fermi gas
72.40.+w Photoconduction and photovoltaic effects

Gouy phase anomaly in photonic nanojets

Myun-Sik Kim, Toralf Scharf, Stefan Mühlig, Carsten Rockstuhl, and Hans Peter Herzig

Appl. Phys. Lett. 98, 191114 (2011); http://dx.doi.org/10.1063/1.3591175 (3 pages) | Cited 6 times

Online Publication Date: 13 May 2011

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We investigate in real space amplitude and phase distributions of light in photonic nanojets emerging from micrometer-sized dielectric spheres with a high-resolution interference microscope. Strong localization of light and a Gouy phase anomaly are witnessed. We show that the phase advance of photonic nanojets significantly deviates from a plane wave due to the sudden transition from a converging to a diverging wave front. Understanding such phase anomalies and verifying the presence of photonic nanojets promises to pave the way to prospective applications that may exploit the ability to localize light in spatial domains smaller than the usual resolution limit.
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42.79.-e Optical elements, devices, and systems
42.25.Bs Wave propagation, transmission and absorption
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
07.60.Ly Interferometers
07.60.Pb Conventional optical microscopes

Optical bistability in InGaN-based multisection laser diodes

J. Dorsaz, D. L. Boïko, L. Sulmoni, J.-F. Carlin, W. G. Scheibenzuber, U. T. Schwarz, and N. Grandjean

Appl. Phys. Lett. 98, 191115 (2011); http://dx.doi.org/10.1063/1.3591977 (3 pages) | Cited 2 times

Online Publication Date: 13 May 2011

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Optical bistability is observed in cw-operating InGaN-based laser diodes including a saturable absorber (SA) section. The dependence of the light-current hysteresis on the SA section length and reverse bias (VSA) has been studied. An analytical approach is developed to estimate the carrier lifetime τa in the SA section from the measurements of the hysteresis width, which leads to τa = 1.9 ns at zero bias. τa is found to decrease rapidly for higher reverse biases and a minimum of τa = 0.4 ns is interpolated for flatband conditions. We explain the dependence of the carrier lifetime on VSA via the modification of the quantum-confined Stark effect.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
42.79.-e Optical elements, devices, and systems
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Mass spectrometric study on inactivation mechanism of spore-forming bacteria by low-pressure surface-wave excited oxygen plasma

Ying Zhao, Akihisa Ogino, and Masaaki Nagatsu

Appl. Phys. Lett. 98, 191501 (2011); http://dx.doi.org/10.1063/1.3588036 (3 pages) | Cited 4 times

Online Publication Date: 9 May 2011

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In this letter, the etching phenomena of the spore-forming bacteria by oxygen plasma were investigated by using quadrupole mass spectrometry. The etching by-products of H2O and CO2 were obviously detected during the oxygen plasma irradiation by the multiple ion detection measurement. Inactivation of roughly 106 spores population was achieved under almost the same reduced spore shapes for three different incident microwave powers. It is considered from the present results that the oxygen radical etching could cause damage to the germinant receptors located in the inner membrane inevitable for germination of spores, without any damage of the DNA in the cores.
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87.85.-d Biomedical engineering
33.15.Ta Mass spectra
52.77.Bn Etching and cleaning
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Martensite transformation of epitaxial Ni–Ti films

J. Buschbeck, J. K. Kawasaki, A. Kozhanov, R. D. James, and C. J. Palmstrøm

Appl. Phys. Lett. 98, 191901 (2011); http://dx.doi.org/10.1063/1.3589361 (3 pages) | Cited 1 time

Online Publication Date: 10 May 2011

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The structure and phase transformations of thin Ni–Ti shape memory alloy films grown by molecular beam epitaxy are investigated for compositions from 43 to 56 at. % Ti. Despite the substrate constraint, temperature dependent x-ray diffraction and resistivity measurements reveal reversible, martensitic phase transformations. The results suggest that these occur by an in-plane shear which does not disturb the lattice coherence at interfaces.
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81.30.Kf Martensitic transformations
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
68.55.at Other materials
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Picosecond acoustic response of a laser-heated gold-film studied with time-resolved x-ray diffraction

Matthieu Nicoul, Uladzimir Shymanovich, Alexander Tarasevitch, Dietrich von der Linde, and Klaus Sokolowski-Tinten

Appl. Phys. Lett. 98, 191902 (2011); http://dx.doi.org/10.1063/1.3584864 (3 pages) | Cited 8 times

Online Publication Date: 11 May 2011

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We apply time-resolved x-ray diffraction using ultrashort x-ray pulses from a laser-produced plasma to probe the picosecond acoustic response of a thin laser-heated gold film. Measurements of the temporal changes in the angular distribution of diffracted x-rays provide direct quantitative information on the transient evolution of lattice strain. This allows to disentangle electronic and thermal pressure contributions driving lattice expansion after impulsive laser excitation. The electron-lattice energy equilibration time τE = (5±0.3) ps as well as the electronic Grüneisen parameter γe = (1.48±0.3) have been determined.
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78.47.J- Ultrafast spectroscopy (<1 psec)
61.05.cp X-ray diffraction
68.60.Bs Mechanical and acoustical properties
42.62.-b Laser applications

Atom probe analysis of interfacial abruptness and clustering within a single InxGa1−xN quantum well device on semipolar (10mathmath) GaN substrate

T. J. Prosa, P. H. Clifton, H. Zhong, A. Tyagi, R. Shivaraman, S. P. DenBaars, S. Nakamura, and J. S. Speck

Appl. Phys. Lett. 98, 191903 (2011); http://dx.doi.org/10.1063/1.3589370 (3 pages) | Cited 13 times

Online Publication Date: 11 May 2011

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Pulsed laser atom probe tomography (APT) of InxGa1−xN single quantum well (SQW) grown on semipolar (10mathmath) GaN orientation estimates the interior atomic composition within the SQW at 6.5±0.7 at. % In, 46.2±0.7 at. % Ga, and 47.3±0.7 at. % N. The atom probe analysis is performed in both “top-down” and “cross-section” orientations. Self-consistent Schrödinger–Poisson simulation employing structural and compositional parameters obtained from APT results estimates the polarization field within the SQW at 720 kV/cm. A statistical method for the evaluation of indium homogeneity within the SQW is also considered.
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81.07.St Quantum wells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
68.65.Fg Quantum wells
68.35.Ct Interface structure and roughness
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

The influence of impurities and planar defects on the infrared properties of silicon carbide films

S. Rajasekhara, B. H. Neuner, III, C. A. Zorman, N. Jegenyes, G. Ferro, G. Shvets, P. J. Ferreira, and D. Kovar

Appl. Phys. Lett. 98, 191904 (2011); http://dx.doi.org/10.1063/1.3585098 (3 pages)

Online Publication Date: 12 May 2011

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Two cubic, single crystal silicon carbide (3C-SiC) films with similar thickness are shown to exhibit significantly different optical properties at mid-infrared wavelengths. Depth profiling by time-of-flight secondary ion mass spectroscopy indicates that these two films have substantially different n-type impurity concentrations that are responsible for the observed differences in optical absorption. The influence of impurities manifests as substantially different planar defect morphologies.
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61.72.sd Impurity concentration
78.30.Hv Other nonmetallic inorganics
78.66.Li Other semiconductors
82.80.Rt Time of flight mass spectrometry
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Thermal conductivity degradation induced by point defects in irradiated silicon carbide

Jean-Paul Crocombette and Laurent Proville

Appl. Phys. Lett. 98, 191905 (2011); http://dx.doi.org/10.1063/1.3589358 (3 pages) | Cited 2 times

Online Publication Date: 12 May 2011

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Irradiations are known to decrease the thermal conductivity of ceramics. This phenomenon is tackled by molecular dynamics simulation of the thermal resistance of point defects in cubic silicon carbide. The additional thermal resistivity due to point defects proves to vary linearly with their concentration. Large variations in the proportionality coefficient with the nature of the defects are observed. From these calculations, an approximate scale for the concentration of vacancies in irradiated SiC is built.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
61.72.jd Vacancies

Enhanced optical performance of amber emitting quantum dots incorporated InGaN/GaN light-emitting diodes with growth on UV-enhanced electrochemically etched nanoporous GaN

C. B. Soh, W. Liu, H. Hartono, Norman S. S. Ang, S. J. Chua, S. Y. Chow, C. B. Tay, and A. P. Vajpeyi

Appl. Phys. Lett. 98, 191906 (2011); http://dx.doi.org/10.1063/1.3589969 (3 pages) | Cited 1 time

Online Publication Date: 12 May 2011

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Phosphor-free amber light emitting quantum dots with bimodal size distribution have been effectively incorporated in InGaN/GaN light emitting diodes (LEDs). With overgrowth of the LEDs structure on electrochemically etched nanoporous GaN templates, a reduction in density of threading dislocations and lower biaxial stress are achieved. A higher density of smaller quantum dots ∼ 4.5×109 cm−2 is incorporated in the multiple quantum well of LEDs on the nanoporous GaN template, generating higher energy emission, and enhanced light output by 1.45 times over LEDs grown on conventional GaN. The carrier capture kinetic by the bimodal distributed quantum dots is discussed with its energy band profile.
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85.60.Jb Light-emitting devices

Conversion of strain state from biaxial to uniaxial in strained silicon

Fei Ma, Tian-Wei Zhang, Ke-Wei Xu, and Paul K. Chu

Appl. Phys. Lett. 98, 191907 (2011); http://dx.doi.org/10.1063/1.3589981 (3 pages) | Cited 3 times

Online Publication Date: 12 May 2011

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The Raman shift of Δω3 in (001) strained silicon is found to be independent of the azimuthal angle of the patterned structures but exhibits shape dependence in strain relaxation. The tensile strain is reduced from 0.85% in the unpatterned thin film to 0.16% in the cylindrical pillars showing 82% relaxation. It becomes more significant along the width direction of the patterned gratings due to Poisson’s effect and only a tensile strain of 0.07% remains. Consequently, the strain state changes from biaxial into uniaxial and is expected to enhance the carrier mobility. Finite element analysis is conducted to elucidate the mechanism.
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78.30.Am Elemental semiconductors and insulators
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
81.16.-c Methods of micro- and nanofabrication and processing
81.05.Cy Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
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Metallic and insulating adsorbates on graphene

K. M. McCreary, K. Pi, and R. K. Kawakami

Appl. Phys. Lett. 98, 192101 (2011); http://dx.doi.org/10.1063/1.3588035 (3 pages) | Cited 6 times

Online Publication Date: 9 May 2011

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We directly compare the effect of metallic titanium (Ti) and insulating titanium dioxide (TiO2) on the transport properties of single layer graphene. The deposition of Ti results in substantial n-type doping and a reduction in graphene mobility by charged impurity scattering. Subsequent exposure to oxygen largely reduces the doping and scattering by converting Ti into TiO2. In addition, we observe evidence for short-range scattering by TiO2 impurities. These results illustrate the contrasting scattering mechanisms for identical spatial distributions of metallic and insulating adsorbates.
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81.05.ue Graphene
72.80.Vp Electronic transport in graphene
68.43.Mn Adsorption kinetics
61.72.up Other materials

Copper oxide transistor on copper wire for e-textile

Jin-Woo Han and M. Meyyappan

Appl. Phys. Lett. 98, 192102 (2011); http://dx.doi.org/10.1063/1.3589374 (3 pages) | Cited 3 times

Online Publication Date: 10 May 2011

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A Cu2O-based field effect transistor was fabricated on Cu wire. Thermal oxidation of Cu forms Cu–Cu2O core-shell structure, where the metal-semiconductor Schottky junction was used as a gate barrier with Pt Ohmic contacts for source and drain. The device was coated with polydimethylsiloxane (PDMS) to protect from contamination and demonstrated as a humidity sensor. The cylindrical structure of the Cu wire and the transistor function enable embedding of simple circuits into textile which can potentially offer smart textile for wearable computing, environmental sensing, and monitoring of human vital signs.
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85.30.Tv Field effect devices
73.30.+y Surface double layers, Schottky barriers, and work functions
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