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17 Aug 2009

Volume 95, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 073703 (2009); http://dx.doi.org/10.1063/1.3152768 (3 pages)

Mohammud R. Noor, Swati Goyal, Shawn M. Christensen, and Samir M. Iqbal
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Demonstration of nonpolar a-plane InGaN/GaN light emitting diode on r-plane sapphire substrate

Sung-Min Hwang, Yong Gon Seo, Kwang Hyeon Baik, In-Sung Cho, Jong Hyeob Baek, Sukkoo Jung, Tae Geun Kim, and Meoungwhan Cho

Appl. Phys. Lett. 95, 071101 (2009); http://dx.doi.org/10.1063/1.3206666 (3 pages) | Cited 26 times

Online Publication Date: 17 August 2009

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High crystalline a-plane (11math0) GaN epitaxial layers with smooth surface morphology were grown on r-plane (1math02) sapphire substrate by metalorganic chemical vapor deposition. The full width at half maximum of x-ray rocking curve was measured as 407 arc sec along c-axis direction, and the root mean square roughness was 1.23 nm. Nonpolar a-plane InGaN/GaN light emitting diodes were subsequently grown on a-plane GaN template, and the optical output power of 0.72 mW was obtained at drive current of 20 mA (3.36 V) and 2.84 mW at 100 mA (4.62 V) with the peak emission wavelength of 477 nm.
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85.60.Jb Light-emitting devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.bg Semiconductors

Experimental verification of extraordinary transmission without surface plasmons

F. Medina, J. A. Ruiz-Cruz, F. Mesa, J. M. Rebollar, J. R. Montejo-Garai, and R. Marqués

Appl. Phys. Lett. 95, 071102 (2009); http://dx.doi.org/10.1063/1.3206738 (3 pages) | Cited 11 times

Online Publication Date: 17 August 2009

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This letter provides an experimental demonstration of extraordinary transmission in a closed waveguide system loaded with an electrically small diaphragm. This is a situation where the standard surface plasmon polariton (SPP) theory does not apply. The theoretical explanation is then based on the concept of impedance matching. This concept has previously been applied by some of the authors to account for enhanced transmission in situations where surface plasmon theory can be used: periodic arrays of small holes or slits in flat metal screens. The experiment in this letter supports the impedance matching model, valid for when SPPs are present or not.
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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
42.79.Gn Optical waveguides and couplers

InGaN laser diodes with 50 mW output power emitting at 515 nm

Adrian Avramescu, Teresa Lermer, Jens Müller, Sönke Tautz, Désirée Queren, Stephan Lutgen, and Uwe Strauß

Appl. Phys. Lett. 95, 071103 (2009); http://dx.doi.org/10.1063/1.3206739 (3 pages) | Cited 33 times

Online Publication Date: 17 August 2009

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We demonstrate direct green laser operation from InGaN based diodes at wavelengths as long as 515.9 nm with 50 mW output power in pulse operation. A factor of ∼ 10 defect reduction for the In-rich InGaN quantum wells based on improvements of the epitaxial growth process and design of the active layers on c-plane GaN-substrates makes it possible to demonstrate laser operation at room temperature. Micrometer-scale photoluminescence mappings and electro-optical measurements confirm the reduction of nonradiative defects in the emitting layers. The 11 μm broad-area gain-guided laser structures were driven in pulse operation to minimize thermal effects and to accurately measure the laser temperature dependence. The threshold current density was ∼ 9 kA/cm2 and the fitted slope efficiency had a value of ∼ 130 mW/A for an optical output up to 50 mW.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.79.-e Optical elements, devices, and systems

Laser-direct photoetching of metal thin film for the electrode of transistor

Hyeongjae Lee, Hyunkwon Shin, Youngmin Jeong, Jooho Moon, and Myeongkyu Lee

Appl. Phys. Lett. 95, 071104 (2009); http://dx.doi.org/10.1063/1.3207823 (3 pages) | Cited 8 times

Online Publication Date: 17 August 2009

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We report that metal thin films can be directly photoetched by a pulsed neodymium doped yttrium aluminum garnet laser beam irradiating the film surface. This process utilizes a laser-induced thermoelastic force, which plays a role to detach the film from the underlying layer. High-fidelity patterns at the micrometer scales have been fabricated using a spatially modulated laser beam. A zinc-tin-oxide thin film transistor with photoetched Al source and drain electrodes exhibited an on/off ratio higher than 105 and a very low off-current level. This indicates that the metallic layer is completely etched out by this process, making an additional cleaning or etching step unnecessary.
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42.60.Fc Modulation, tuning, and mode locking
85.30.Tv Field effect devices
81.65.Cf Surface cleaning, etching, patterning
85.40.Ls Metallization, contacts, interconnects; device isolation

Plasmonic light enhancement in the near-field of metallic nanospheroids for application in intermediate band solar cells

Manuel J. Mendes, Antonío Luque, Ignacio Tobías, and Antonio Martí

Appl. Phys. Lett. 95, 071105 (2009); http://dx.doi.org/10.1063/1.3205470 (3 pages) | Cited 10 times

Online Publication Date: 18 August 2009

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In order to enhance infrared light absorption in sub-bandgap transitions in an intermediate band solar cell, the scattered near-field potential from uncoated and coated metallic nanoparticles with a spheroidal shape is calculated with the electrostatic model. The absorption enhancement produced at the surface plasmon frequency of the nanoparticles can be of several orders of magnitude in some cases.
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78.66.Bz Metals and metallic alloys
78.68.+m Optical properties of surfaces
73.22.Lp Collective excitations
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Temperature dependent optical properties of (002) oriented ZnO thin film using surface plasmon resonance

Shibu Saha, Navina Mehan, K. Sreenivas, and Vinay Gupta

Appl. Phys. Lett. 95, 071106 (2009); http://dx.doi.org/10.1063/1.3206954 (3 pages) | Cited 8 times

Online Publication Date: 18 August 2009

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Temperature dependent optical properties of c-axis oriented ZnO thin film were investigated using surface plasmon resonance (SPR) technique. SPR data for double layer (prism-Au-ZnO-air) and single layer (prism-Au-air) systems were taken over a temperature range (300–525 K). Dielectric constant at optical frequency and real part of refractive index of the ZnO film shows an increase with temperature. The bandgap of the oriented ZnO film was found to decrease with rise in temperature. The work indicates a promising application of the system as a temperature sensor and highlights an efficient scientific tool to study optical properties of thin film under varying ambient conditions.
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78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
68.55.ag Semiconductors
77.22.Ch Permittivity (dielectric function)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
07.20.Dt Thermometers
71.20.Nr Semiconductor compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Simultaneous two-level lasing in GaInAsSb/GaSb strained quantum-well lasers

Kristijonas Vizbaras, Kaveh Kashani-Shirazi, and Markus-Christian Amann

Appl. Phys. Lett. 95, 071107 (2009); http://dx.doi.org/10.1063/1.3207826 (3 pages)

Online Publication Date: 18 August 2009

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Simultaneous two-level lasing, corresponding to ground level and excited level transitions in GaInAsSb/GaSb quantum well lasers under continuous wave operation is reported. The effect is attributed to a slowed-down intersubband relaxation in the quantum wells due to buildup of hot phonon population resulting in an incomplete clamping of the excited state population above the ground level lasing threshold.
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42.55.Px Semiconductor lasers; laser diodes

Effect of efficiency “droop” in violet and blue InGaN laser diodes

S. Grzanka, P. Perlin, R. Czernecki, L. Marona, M. Boćkowski, B. Łucznik, M. Leszczyński, and T. Suski

Appl. Phys. Lett. 95, 071108 (2009); http://dx.doi.org/10.1063/1.3211129 (3 pages) | Cited 6 times

Online Publication Date: 20 August 2009

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We have studied two types of InGaN laser diodes emitting at 410 and 440 nm. Each device was characterized by measuring light-current characteristics in two geometries for which the light was collected: along the resonator and perpendicularly to the cavity. In the first configuration, the 410 nm device displays no reduction of differential efficiency while 440 nm laser shows evidence of droop. In the perpendicular configuration both devices show the pronounced droop. We associate the suppression of the droop for 410 nm laser in the “along cavity” configuration with the appearance of the stimulated recombination.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Effects of backward-propagating waves and lumped mirror losses on self-induced transparency modelocking in quantum cascade lasers

Muhammad Anisuzzaman Talukder and Curtis R. Menyuk

Appl. Phys. Lett. 95, 071109 (2009); http://dx.doi.org/10.1063/1.3206741 (3 pages) | Cited 2 times

Online Publication Date: 20 August 2009

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Work to date on self-induced transparency modelocking in quantum cascade lasers (QCLs) has neglected backward-propagating waves and lumped mirror losses. In this work, we remove these unrealistic assumptions. The qualitative features of the modelocking are unaffected by this improvement in the model, but the parameter regime in which stable modelocked pulses may be found is reduced. This reduction is due to incomplete gain recovery near the edges of the QCL when pulses pass through after reflecting from the mirrors, coincident with the loss of pulse energy at the mirrors. Spatial hole burning is observed in parameter regimes in which continuous waves can grow, but it does not affect the stability of the modelocking.
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42.60.Fc Modulation, tuning, and mode locking
42.25.Bs Wave propagation, transmission and absorption
42.55.Px Semiconductor lasers; laser diodes

Ghost “pinhole” imaging in Fraunhofer region

Wenlin Gong, Pengli Zhang, Xia Shen, and Shensheng Han

Appl. Phys. Lett. 95, 071110 (2009); http://dx.doi.org/10.1063/1.3207832 (3 pages) | Cited 15 times

Online Publication Date: 20 August 2009

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For an aperture with transverse size D, Fraunhofer region is named when the distance between the aperture and the detector is larger than D2/λ, where λ is the wavelength of the illuminating light. For a lensless system, when both reference detector and the object are located in Fraunhofer region relative to the thermal source, we demonstrate that a ghost “pinhole” camera with magnification M = z/z1 can be obtained by the second-order correlation of two light fields even if the test detector is a single pointlike detector. Effects determining the quality of ghost pinhole imaging and its potential applications are also discussed.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
42.79.Pw Imaging detectors and sensors

Trapped rainbow effect in visible light left-handed heterostructures

X. P. Zhao, W. Luo, J. X. Huang, Q. H. Fu, K. Song, X. C. Cheng, and C. R. Luo

Appl. Phys. Lett. 95, 071111 (2009); http://dx.doi.org/10.1063/1.3211867 (3 pages) | Cited 22 times

Online Publication Date: 21 August 2009

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We experimentally demonstrate the trapped rainbow in tapered left-handed heterostructures (LHHs) at visible frequencies. The employed left-handed metamaterials (LHMs) are isotropic with the size of hundreds of square millimeter. Specifically, the LHMs sample at visible frequencies has a broad spectral range and low loss, making it an intrinsic optical response for the LHHs. It is found that the frequency components of the wave packet separate at positions with different guide thicknesses only if the inclination of tapered LHHs is greater than zero and smaller than the critical value.
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42.70.-a Optical materials
78.40.-q Absorption and reflection spectra: visible and ultraviolet

Planar metallic nanoscale slit lenses for angle compensation

Lieven Verslegers, Peter B. Catrysse, Zongfu Yu, and Shanhui Fan

Appl. Phys. Lett. 95, 071112 (2009); http://dx.doi.org/10.1063/1.3211875 (3 pages) | Cited 17 times

Online Publication Date: 21 August 2009

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We demonstrate numerically, using a modified total-field/scattered-field formalism, that metallic lenses, based on arrays of nanoscale slits with varying widths in a planar metallic film, can be used to focus light and compensate for various angles of incidence. These structures could be used as integrated microlenses to improve the efficiency of pixels in solid-state image sensors. Our design guidelines simultaneously accomplish a prism and focusing action. Our results also indicate the importance of the aperture effect for such far-field focusing devices.
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42.79.Bh Lenses, prisms and mirrors
42.79.Pw Imaging detectors and sensors

A ring artifact suppression algorithm based on a priori information

Sofya Titarenko, Valeriy Titarenko, Albrecht Kyrieleis, and Philip J. Withers

Appl. Phys. Lett. 95, 071113 (2009); http://dx.doi.org/10.1063/1.3211956 (3 pages) | Cited 6 times

Online Publication Date: 21 August 2009

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In this letter, ring artifacts in two-dimensional (2D) tomographic slices are considered. For a parallel beam geometry we propose an interactive algorithm, which removes the artifacts while preserving fine image details. The algorithm comprises two stages and is based on a priori information about the true attenuation coefficient in some areas of a 2D slice. Even in the absence of any a priori information the initial stage of the algorithm can already provide good ring artifact suppression.
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42.30.Wb Image reconstruction; tomography

Study on the formation of dodecagonal pyramid on nitrogen polar GaN surface etched by hot H3PO4

S. L. Qi, Z. Z. Chen, H. Fang, Y. J. Sun, L. W. Sang, X. L. Yang, L. B. Zhao, P. F. Tian, J. J. Deng, Y. B. Tao, T. J. Yu, Z. X. Qin, and G. Y. Zhang

Appl. Phys. Lett. 95, 071114 (2009); http://dx.doi.org/10.1063/1.3211970 (3 pages) | Cited 12 times

Online Publication Date: 21 August 2009

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Hot phosphor acid (H3PO4) etching is presented to form a roughened surface with dodecagonal pyramids on laser lift-off N face GaN grown by metalorganic chemical vapor deposition. A detailed analysis of time evolution of surface morphology is described as a function of etching temperature. The activation energy of the H3PO4 etching process is 1.25 eV, indicating the process is reaction-limited scheme. And it is found that the oblique angle between the facets and the base plane increases as the temperature increases. Thermodynamics and kinetics related factors of the formation mechanism of the dodecagonal pyramid are also discussed. The light output power of a vertical injection light-emitting-diode (LED) with proper roughened surface shows about 2.5 fold increase compared with that of LED without roughened surface.
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68.35.bg Semiconductors
81.65.Cf Surface cleaning, etching, patterning
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.60.Jb Light-emitting devices
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Carbon nanotube induced enhancement of electroluminescence of phosphor

Min Jong Bae, Shang Hyeun Park, Tae Won Jeong, Jeong Hee Lee, In Taek Han, Yong Wan Jin, Jong Min Kim, Jin-Young Kim, Ji Beom Yoo, and Se Gi Yu

Appl. Phys. Lett. 95, 071901 (2009); http://dx.doi.org/10.1063/1.3196430 (3 pages) | Cited 7 times

Online Publication Date: 17 August 2009

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Electroluminescence (EL) was observed on conventional cathodoluminescent (CL) phosphor with the incorporation of carbon nanotube (CNT) at ambient air. The role of CNT can be understood as enhancing the local electrical field, which allows electron injection to the active center of phosphor at relatively low operating voltages. In this EL device, the brightness of CL phosphor was significantly improved from no light emission in the case of no addition of CNT to 35 cd/m2 with 1 wt % CNT at 10 kHz of ac 300 V.
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61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
78.60.Fi Electroluminescence
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.63.Fg Nanotubes
78.67.Ch Nanotubes
78.60.Hk Cathodoluminescence, ionoluminescence

Tailoring UV cure depth profiles for optimal mechanical properties of organosilicate thin films

Taek-Soo Kim, Dmytro Chumakov, Ehrenfried Zschech, and Reinhold H. Dauskardt

Appl. Phys. Lett. 95, 071902 (2009); http://dx.doi.org/10.1063/1.3190198 (3 pages) | Cited 2 times

Online Publication Date: 18 August 2009

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The adhesive and cohesive properties of organosilicate thin films are remarkably insensitive to UV curing. We demonstrate how to maximize these properties with UV standing waves together with an optical spacer underlying layer. Using a simulation of the UV cure profile through the film thickness, we demonstrate how a UV transparent SiN optical spacer layer can be selected to maximize curing at both sides of the organosilicate film with marked increases in interfacial fracture energy. On the contrary, a UV absorbing SiCN underlying layer resulted in significantly reduced UV intensities and small improvements of the interfacial fracture energies.
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68.60.Wm Other nonelectronic physical properties
68.55.am Polymers and organics
82.50.-m Photochemistry
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.25.Mn Fracture/brittleness
62.20.mm Fracture

Quasifree Mg–H thin films

A. Baldi, V. Palmisano, M. Gonzalez-Silveira, Y. Pivak, M. Slaman, H. Schreuders, B. Dam, and R. Griessen

Appl. Phys. Lett. 95, 071903 (2009); http://dx.doi.org/10.1063/1.3210791 (3 pages) | Cited 14 times

Online Publication Date: 19 August 2009

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The thermodynamics of hydrogen absorption in Pd-capped Mg films are strongly dependent on the magnesium thickness. In the present work, we suppress such dependency by inserting a thin Ti layer between Mg and Pd. By means of optical measurements, we show that the surface energy contribution to the destabilization of MgH2 is negligible. The inserted Ti layer prevents Mg–Pd alloy formation at the Mg/Pd interface, leading to quasifree Mg films and enhancing the kinetics of hydrogen desorption. Our observations are important for the development of thin film devices.
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68.55.jd Thickness
68.43.Nr Desorption kinetics
65.40.gp Surface energy

Nucleation tendency and crystallizing phase in silicate glasses: A structural aspect

Yoshihiro Takahashi, Hirokazu Masai, and Takumi Fujiwara

Appl. Phys. Lett. 95, 071904 (2009); http://dx.doi.org/10.1063/1.3206931 (3 pages) | Cited 6 times

Online Publication Date: 19 August 2009

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We consider the relationship of nucleation tendency with crystallizing-phase structures in silicate glasses using glassy sanbornite (1BaO–2SiO2) that shows homogeneous nucleation resulting crystallization of Ba5Si8O21 and β-BaSi2O5 phases with a layered structure of a network modifier and a network former. This trend is also confirmed in other silicate glasses with homogeneous nucleation tendency, which has been assessed by Zanotto and other researchers. It is suggested that the structural dimension of the crystallizing phase governs the nucleation tendency in silicate glasses.
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61.43.Fs Glasses
64.60.qj Studies of nucleation in specific substances
64.70.kj Glasses

Indium migration paths in V-defects of InAlN grown by metal-organic vapor phase epitaxy

Th. Kehagias, G. P. Dimitrakopulos, J. Kioseoglou, H. Kirmse, C. Giesen, M. Heuken, A. Georgakilas, W. Neumann, Th. Karakostas, and Ph. Komninou

Appl. Phys. Lett. 95, 071905 (2009); http://dx.doi.org/10.1063/1.3204454 (3 pages) | Cited 25 times

Online Publication Date: 20 August 2009

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InAlN thin films grown on GaN/Al2O3 (0001) templates by metal-organic vapor phase epitaxy were studied by transmission electron microscopy techniques. V-defects in the form of hexagonal inverted pyramids with {10math1} sidewalls were observed on the films’ surfaces linked to the termination of threading dislocations. Their origin is explained by the different surface atom mobility of In and Al and the built-in strain relaxation. Indium segregation in the films is influenced by the formation of V-defects, the edges and the apexes of which function as paths of migrating indium atoms diffusing along nanopipes formed at the open-core threading dislocations.
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66.30.Lw Diffusion of other defects
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.ag Semiconductors
68.35.Dv Composition, segregation; defects and impurities
71.55.Eq III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Enhancing plasticity of Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk metallic glass by precompression

J. L. Zhang, H. B. Yu, J. X. Lu, H. Y. Bai, and C. H. Shek

Appl. Phys. Lett. 95, 071906 (2009); http://dx.doi.org/10.1063/1.3211112 (3 pages) | Cited 10 times

Online Publication Date: 21 August 2009

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Precompression treatments on Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk metallic glass rods with tapered ends induced controllable stress distributions and resulted in residual stress accompanied with a few tiny shear bands after unloading. The built-in stress state increased macroscopic plasticity dramatically and produced predictable distributions of shear bands in the cylindrical samples cut from the taper-ended samples. The macroscopic plasticity was interpreted in terms of the competition among different types of shear bands.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
46.35.+z Viscoelasticity, plasticity, viscoplasticity
81.05.Kf Glasses (including metallic glasses)
46.70.Hg Membranes, rods, and strings

Strong and ductile nanostructured Cu-carbon nanotube composite

Hongqi Li, Amit Misra, Zenji Horita, Carl C. Koch, Nathan A. Mara, Patricia O. Dickerson, and Yuntian Zhu

Appl. Phys. Lett. 95, 071907 (2009); http://dx.doi.org/10.1063/1.3211921 (3 pages) | Cited 12 times

Online Publication Date: 21 August 2009

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Nanocrystalline carbon nanotube (CNT)—reinforced Cu composite (grain size <25 nm) with high strength and good ductility was developed. Pillar testing reveals that its strength and plastic strain could be as large as 1700 MPa and 29%, respectively. Compared with its counterpart made under the same condition, an addition of 1 wt % CNTs leads to a dramatic increase in strength, stiffness and toughness without a sacrifice in ductility. Microstructural analysis discloses that in the Cu matrix, CNTs could be distributed either at grain boundaries or inside grains and could inhibit dislocation nucleation and motion, resulting in an increase in the strength.
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62.23.Pq Composites (nanosystems embedded in a larger structure)
61.46.-w Structure of nanoscale materials
81.40.Lm Deformation, plasticity, and creep
62.20.fk Ductility, malleability
62.20.fq Plasticity and superplasticity
61.72.Mm Grain and twin boundaries
61.46.Fg Nanotubes
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
62.25.-g Mechanical properties of nanoscale systems

Intermediate-band material based on GaAs quantum rings for solar cells

Jiang Wu, Dali Shao, Zhenhua Li, M. O. Manasreh, Vasyl P. Kunets, Zhiming M. Wang, and G. J. Salamo

Appl. Phys. Lett. 95, 071908 (2009); http://dx.doi.org/10.1063/1.3211971 (3 pages) | Cited 13 times

Online Publication Date: 21 August 2009

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The intermediate-band concept is invoked to explain the photoresponse spectra obtained for unbiased devices fabricated from GaAs quantum rings grown by a droplet epitaxy technique on lattice-matched Al0.3Ga0.7As barriers. The photoresponse spectra where measured at room temperature in the visible-near-infrared spectral range. The presence of the intermediate band in the device active region is confirmed by measuring the mid-infrared photoresponse, which is attributed to the intersubband transitions in the conduction band. The photocurrent was measured at room temperature and found to be about four orders of magnitude larger than the dark current in the voltage range of ± 4.0 V.
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84.60.Jt Photoelectric conversion
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.63.Bd Nanocrystalline materials
73.63.Kv Quantum dots
78.30.Fs III-V and II-VI semiconductors
73.22.-f Electronic structure of nanoscale materials and related systems
72.40.+w Photoconduction and photovoltaic effects
78.67.Hc Quantum dots
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Precursive stage of nanocrystallization in niobium oxide-containing glass

Yoshihiro Takahashi, Hirokazu Masai, Minoru Osada, and Takumi Fujiwara

Appl. Phys. Lett. 95, 071909 (2009); http://dx.doi.org/10.1063/1.3211989 (3 pages) | Cited 9 times

Online Publication Date: 21 August 2009

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In situ observation of inelastic light scattering in Raman and Boson regions was performed in a niobiogermanate glass with a high nucleation ability during heating in order to examine its nanocrystallization dynamics. The relation of structural heterogeneity to the precursive stage of crystallization is also discussed. It is suggested that evolution of nuclei occurs in a nanometric niobate-rich region due to density fluctuation in the supercooled liquid phase prior to nanocrystallization.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
64.60.Q- Nucleation
64.70.ph Nonmetallic glasses (silicates, oxides, selenides, etc.)
42.65.-k Nonlinear optics
42.70.Ce Glasses, quartz
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Crystallization times of Ge–Te phase change materials as a function of composition

S. Raoux, H.-Y. Cheng, M. A. Caldwell, and H.-S. P. Wong

Appl. Phys. Lett. 95, 071910 (2009); http://dx.doi.org/10.1063/1.3212732 (3 pages) | Cited 28 times

Online Publication Date: 21 August 2009

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The crystallization times of Ge–Te phase change materials with variable Ge concentrations (29.5–72.4 at. %) were studied. A very strong dependence of the crystallization time on the composition for as-deposited, amorphous films was confirmed, with a minimum for the stoichiometric composition GeTe. The dependence is weaker for melt-quenched, amorphous material and crystallization times are between one to almost four orders of magnitude shorter than for as-deposited materials. This is promising for applications because recrystallization from the melt-quenched phase is the relevant process for optical and solid state memory, and fast crystallization and weak dependence on compositional variations are desirable.
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64.70.kg Semiconductors
42.70.Gi Light-sensitive materials
68.60.-p Physical properties of thin films, nonelectronic
61.66.Bi Elemental solids
61.66.Dk Alloys
81.40.Gh Other heat and thermomechanical treatments

Grain boundary complexions: The interplay of premelting, prewetting, and multilayer adsorption

Jian Luo

Appl. Phys. Lett. 95, 071911 (2009); http://dx.doi.org/10.1063/1.3212733 (3 pages) | Cited 8 times

Online Publication Date: 21 August 2009

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A thermodynamic model for coupled adsorption and disordering transitions at grain boundaries is developed by combining diffuse-interface and lattice-gas models and incorporating colloidal type interfacial forces. This model produces a systematical spectrum of interfacial phenomena for grain boundaries, including first-order and continuous coupled prewetting and premelting transitions, critical points, multilayer adsorption, layering and roughening, and complete wetting and drying, and it produces a series of grain boundary “phases” (complexions) with character similar to those observed by [ Dillon et al., Acta Mater. 55, 6208 (2007) ]. The presence of dispersion and electrostatic forces in ceramic materials can appreciably change grain boundary transitions.
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61.72.Mm Grain and twin boundaries
64.70.K- Solid-solid transitions
64.60.Cn Order-disorder transformations
68.43.Mn Adsorption kinetics
68.08.Bc Wetting
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