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13 Jul 2009

Volume 95, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 023701 (2009); http://dx.doi.org/10.1063/1.3173808 (3 pages)

G. Devès, S. Roudeau, A. Carmona, S. Lavielle, K. Gionnet, G. Déléris, and R. Ortega
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Opening the light extraction cone of high index substrates with plasmonic gratings: Light emitting diode applications

A. Drezet, F. Przybilla, E. Laux, O. Mahboub, C. Genet, T. W. Ebbesen, J. S. Bouillard, A. Zayats, I. S. Spevak, A. V. Zayats, A. Yu Nikitin, and L. Martín-Moreno

Appl. Phys. Lett. 95, 021101 (2009); http://dx.doi.org/10.1063/1.3176435 (3 pages) | Cited 8 times

Online Publication Date: 13 July 2009

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The opening of the light extraction cone of a high index substrate (GaP) is demonstrated using plasmonic gratings. We show that the excitation of surface plasmons on the metal grating leads to the extraction of light otherwise undergoing total internal reflection in the substrate with high efficiency. This effect has an immediate application in the context of light emitting diodes, where resonant metal gratings are promising for the design of dual purpose electric contact/extraction structures.
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42.79.Dj Gratings
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
85.60.Jb Light-emitting devices

AlGaN membrane grating reflector

Jaehoon Kim, Dong-Uk Kim, Joonhee Lee, Heonsu Jeon, Yeonsang Park, and Y.-S. Choi

Appl. Phys. Lett. 95, 021102 (2009); http://dx.doi.org/10.1063/1.3168552 (3 pages) | Cited 5 times

Online Publication Date: 13 July 2009

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We report on AlGaN grating reflectors for short-wavelength applications, an alternative to conventional distributed Bragg reflectors that are difficult to make in a GaN-based system. An array of air-bridge AlGaN grating reflectors, with a period and filling factor of 430 nm and 0.55, was fabricated through holographic lithography and photoelectrochemical etching. Polarization-dependent microreflectance spectra were measured to confirm their consistency with simulation results. The reflectance measured at 532 nm for transverse-electric polarization was as high as ∼ 90%. We also found that the spectral range for high reflection correlates with the photonic Bloch band-edge modes.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
07.60.Hv Refractometers and reflectometers
42.40.Kw Holographic interferometry; other holographic techniques
42.79.Dj Gratings
82.45.Vp Semiconductor materials in electrochemistry

Three-dimensional localization with nanometer accuracy using a detector-limited double-helix point spread function system

Sri Rama Prasanna Pavani, Adam Greengard, and Rafael Piestun

Appl. Phys. Lett. 95, 021103 (2009); http://dx.doi.org/10.1063/1.3158923 (3 pages) | Cited 17 times

Online Publication Date: 13 July 2009

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Accurate estimation of the three-dimensional (3D) position of particles is critical in applications like biological imaging, atom/particle-trapping, and nanomanufacturing. While it is well-known that localization accuracy better than the Rayleigh resolution limit is possible, it was recently shown that, for photon-limited cases, 3D point spread functions (PSFs) can be shaped to increase accuracies over a 3D volume [ Pavani and Piestun, Opt. Express 16, 22048 (2008) ]. Here, we show that in the detector-limited regime, the gain in accuracy occurs in all three dimensions throughout the axial range of interest. The PSF is shaped as a double helix, resulting in a system with fundamentally better 3D localization accuracies than standard PSF systems, capable of achieving single-image subnanometer accuracies.
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71.55.Jv Disordered structures; amorphous and glassy solids
42.30.Lr Modulation and optical transfer functions

Schottky contact surface-plasmon detector integrated with an asymmetric metal stripe waveguide

Ali Akbari and Pierre Berini

Appl. Phys. Lett. 95, 021104 (2009); http://dx.doi.org/10.1063/1.3171937 (3 pages) | Cited 19 times

Online Publication Date: 13 July 2009

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A silicon-based Schottky contact photodetector integrated into a finite width asymmetric metal stripe supporting short-range surface plasmon polaritons is presented. Input optical energy is coupled into a bound mode supported by the stripe, leading to total absorption of in-coupled energy. The absorbed energy excites carriers in the metal stripe, some of which cross the Schottky barrier (internal photoemission) leading to a photocurrent under reverse bias. Significant enhancement in the quantum efficiency is observed for a thin metal stripe due to multiple internal reflections of excited carriers. The device holds promise for short-reach high-speed optical interconnects and silicon-based photonic circuitry.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.30.+y Surface double layers, Schottky barriers, and work functions
85.30.Kk Junction diodes
42.82.Et Waveguides, couplers, and arrays
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

A widely voltage-tunable quantum cascade laser based on “two-step” coupling

Yu Yao, Kale J. Franz, Xiaojun Wang, Jen-Yu Fan, and Claire Gmachl

Appl. Phys. Lett. 95, 021105 (2009); http://dx.doi.org/10.1063/1.3179165 (3 pages) | Cited 3 times

Online Publication Date: 14 July 2009

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A novel quantum cascade laser design with “two-step” coupling between the injector and the upper laser state is demonstrated to achieve a widely voltage-tunable laser spectrum. Electroluminescence from this design can be tuned over a range of more than 200 cm−1 with a tuning coefficient of ∼ 700 cm−1/V per stage. Lasers based on this design provide a tuning range of ∼ 100 cm−1 (8.3–9 μm) above threshold with a tuning coefficient of ∼ 900 cm−1/V per stage at a constant temperature of 295 K.
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42.55.Px Semiconductor lasers; laser diodes
78.60.Fi Electroluminescence

Saturated small-signal gain of Si quantum dots embedded in SiO2/SiOx/SiO2 strip-loaded waveguide amplifier made on quartz

Gong-Ru Lin, Chung-Lun Wu, Cheng-Wei Lian, and Hung-Chun Chang

Appl. Phys. Lett. 95, 021106 (2009); http://dx.doi.org/10.1063/1.3179413 (3 pages) | Cited 6 times

Online Publication Date: 14 July 2009

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A SiO2/SiOx/SiO2 strip-loaded waveguide with buried Si quantum dots is optically pumped to provide amplified spontaneous emission centered at 805 nm with spectral linewidth of 140 nm. By top-pumping the 350-nm-thick SiOx with He–Cd laser of 40 mW at 325 nm, the optical gain of 65 cm−1 and loss coefficient of 5 cm−1 are determined. Under a 785 nm small-signal injection diagnosis, the power-dependent gain curve fitting with gain-saturated amplifier model reveals a peak gain of 27 dB (not including waveguide loss) and a net power gain of 9.5 dB for the Si-rich SiOx waveguide amplifier with a length of 5 mm.
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78.67.Hc Quantum dots
78.45.+h Stimulated emission
42.79.Gn Optical waveguides and couplers

Optical rectification in self-assembled monolayers probed at surface plasmon resonance condition

Ryohei Uzawa, Daisuke Tanaka, Haruki Okawa, Kazuhiko Hashimoto, and Kotaro Kajikawa

Appl. Phys. Lett. 95, 021107 (2009); http://dx.doi.org/10.1063/1.3179466 (3 pages) | Cited 2 times

Online Publication Date: 14 July 2009

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Optical rectification in a self-assembled monolayer containing nonlinear optical choromophore of hemicyanine adsorbed on a gold surface was observed in the attenuated total reflection geometry under the surface plasmon resonance condition. The effective second-order susceptibility χeff(2) was evaluated to be 43 pm V−1, which is consistent with the χ(2) values measured by linear electro-optic effect.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
42.65.An Optical susceptibility, hyperpolarizability
68.43.Mn Adsorption kinetics

Microstrip circuit analog of a complex diffraction phenomenon

A. Fernández-Prieto, F. Medina, and F. Mesa

Appl. Phys. Lett. 95, 021108 (2009); http://dx.doi.org/10.1063/1.3176436 (3 pages)

Online Publication Date: 14 July 2009

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This letter presents a methodology to reproduce at microwave frequencies the physical behavior of certain diffraction structures that have been investigated in the optics community. The methodology will be exemplified with a microstrip circuit implementation of a transmission line system exhibiting an electromagnetic response that mimics the response of simple and compound diffraction gratings. The identification of such “bridge” circuit analogies could be very fruitful for the understanding and development of design strategies to devise practical components based on phenomena employed in the affine areas of optics and microwave engineering.
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84.40.Az Waveguides, transmission lines, striplines
84.40.Ua Telecommunications: signal transmission and processing; communication satellites
42.79.Dj Gratings

Vertical-geometry all-optical switches based on InAs/GaAs quantum dots in a cavity

C. Y. Jin, O. Kojima, T. Kita, O. Wada, M. Hopkinson, and K. Akahane

Appl. Phys. Lett. 95, 021109 (2009); http://dx.doi.org/10.1063/1.3180704 (3 pages) | Cited 13 times

Online Publication Date: 16 July 2009

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Self-assembled InAs/GaAs quantum dots (QDs) incorporated in an asymmetric GaAs/Al0.8Ga0.2As vertical cavity have been employed as an optical nonlinear medium for reflection-type all-optical switches. Switching time down to 23 ps together with wavelength tuning range over 30 nm have been achieved in this structure. An angle-dependent behavior of the switching time has been observed, which suggests there is a coupling mechanism between the ground and excited states in QDs with different sizes.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.65.Pc Optical bistability, multistability, and switching, including local field effects
73.21.La Quantum dots
42.82.Gw Other integrated-optical elements and systems

Midinfrared electroluminescence from pentanary-quaternary heterojunction light-emitting diodes

N. B. Cook and A. Krier

Appl. Phys. Lett. 95, 021110 (2009); http://dx.doi.org/10.1063/1.3177193 (3 pages) | Cited 6 times

Online Publication Date: 16 July 2009

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InAs-GaInAsSbP-InAsSbP double heterojunction light-emitting diodes were fabricated which exhibit electroluminescence near 3.7 μm at room temperature. Radiative recombination from band-tail states associated with alloy disorder and localized potential fluctuations was observed, as well as emission from states localized at the InAs-pentanary heterointerface.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
73.20.Fz Weak or Anderson localization
73.20.At Surface states, band structure, electron density of states

Employing two distinct photonic crystal resonances to improve fluorescence enhancement

Patrick C. Mathias, Hsin-Yu Wu, and Brian T. Cunningham

Appl. Phys. Lett. 95, 021111 (2009); http://dx.doi.org/10.1063/1.3184573 (3 pages) | Cited 6 times

Online Publication Date: 17 July 2009

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Surface-bound fluorescence assays such as microarrays have emerged as a prominent technology in current life sciences research and are currently performed on optically passive substrates such as glass microscope slides. We present an alternative approach using photonic crystal substrates exhibiting resonant reflections. In this work, we design and fabricate a photonic crystal with a TM-polarized resonance at the cyanine-5 excitation wavelength and a TE-polarized resonance spectrally overlapping this fluorophore’s emission spectrum. The former resonance increases the excitation of the fluorophore through enhanced electric field intensities, while the latter resonance redirects a proportion of emitted light toward the detection instrumentation. Spots of cyanine-5 conjugated streptavidin on the photonic crystal demonstrate a 60-fold increase in fluorescence intensity and a 42-fold increase in signal-to-noise ratio relative to a glass slide.
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42.70.Qs Photonic bandgap materials
78.60.Fi Electroluminescence
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Photonic stopband tuning of organic semiconductor distributed feedback lasers by oblique angle deposition of an intermediate high index layer

M. Stroisch, C. Teiwes-Morin, T. Woggon, M. Gerken, U. Lemmer, K. Forberich, and A. Gombert

Appl. Phys. Lett. 95, 021112 (2009); http://dx.doi.org/10.1063/1.3184591 (3 pages)

Online Publication Date: 17 July 2009

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We modified the photonic band structure of organic distributed feedback lasers by introducing a patterned high index intermediate layer of tantalum pentoxide. This layer was oblique angle evaporated onto one dimensional surface gratings with a periodicity of 400 nm. The dielectric broadened the stopband due to its high refractive index compared to both the substrate and the active layer. By tuning the layer thickness we could increase the stopband from 3 to 16 nm.
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42.55.Px Semiconductor lasers; laser diodes
42.79.Dj Gratings
42.60.Fc Modulation, tuning, and mode locking
42.70.Qs Photonic bandgap materials
42.60.By Design of specific laser systems
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Magnetized microplasmas generated in a narrow quartz tube

Hiroyuki Yoshiki

Appl. Phys. Lett. 95, 021501 (2009); http://dx.doi.org/10.1063/1.3174915 (3 pages) | Cited 1 time

Online Publication Date: 13 July 2009

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Magnetized He and Ar microplasmas in a narrow quartz tube having an inner diameter of 1 mm (referred to as magnetized capillary microplasmas) are reported. A capillary microplasma can be magnetized by the occurrence of a radio frequency (rf) oscillating E×B drift motion along the tube axis, provided that the external magnetic field is perpendicular to both the rf electric field and the tube axis and that the Larmor radius of an electron is sufficiently smaller than both the electron mean free path and the tube radius. When a magnetic flux density of 0.4 T was applied, a magnetized capillary microplasma could be generated at gas pressures lower than 1.5 kPa because the electron cyclotron frequency exceeds the electron-neutral collision frequency. However, plasma ignition at low gas pressure below 4 kPa was hardly taken place without a strong magnetic field. The Ar atomic excitation temperature was estimated by optical emission spectroscopy and found to increase dramatically from 5000 to 15 000 K when the gas pressure was reduced from 4 to 0.2 kPa. This implies an increase in the electron temperature. Furthermore, Ar ionic emission (Ar II) lines were clearly observed under the magnetized plasma conditions.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.25.Xz Magnetized plasmas
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma

Kinetics of the initial stage of silicon surface oxidation: Deal–Grove or surface nucleation?

I. Levchenko, U. Cvelbar, and K. Ostrikov

Appl. Phys. Lett. 95, 021502 (2009); http://dx.doi.org/10.1063/1.3179557 (3 pages) | Cited 10 times

Online Publication Date: 14 July 2009

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The nucleation-initiated oxidation of a Si surface at very low temperatures in plasmas is demonstrated experimentally, in contrast to the Deal–Grove mechanism, which predicts Si oxidation at a Si/SiO interface and cannot adequately describe the formation of SiO nanodots and oxidation rates at very low (several nanometers) oxide thickness. Based on the experimental results, an alternative oxidation scenario is proposed and supported by multiscale numerical simulations suggesting that saturation of micro- and nanohillocks with oxygen is a trigger mechanism for initiation of Si surface oxidation. This approach is generic and can be applied to describe the kinetics of low-temperature oxidation of other materials.
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81.05.Cy Elemental semiconductors
81.65.Mq Oxidation
82.20.-w Chemical kinetics and dynamics

On the surface roughness development of hydrogenated amorphous silicon deposited at low growth rates

M. A. Wank, R. A. C. M. M. van Swaaij, and M. C. M. van de Sanden

Appl. Phys. Lett. 95, 021503 (2009); http://dx.doi.org/10.1063/1.3179151 (3 pages) | Cited 3 times

Online Publication Date: 15 July 2009

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The surface roughness evolution of hydrogenated amorphous silicon (a-Si:H) films has been studied using in situ spectroscopic ellipsometry for a temperature range of 150–400 °C. The effect of external rf substrate biasing on the coalescence phase is discussed and a removal/densification of a hydrogen-rich layer is suggested to explain the observed roughness development in this phase. After coalescence we observe two distinct phases in the roughness evolution and highlight trends which are incompatible with the idea of dominant surface diffusion. Alternative, nonlocal mechanisms such as the re-emission effect are discussed, which can partly explain the observed incompatibilities.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition
68.35.Fx Diffusion; interface formation
68.55.ag Semiconductors
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Diameter dependent strength of carbon nanotube reinforced composite

Ying Sun and Quanfang Chen

Appl. Phys. Lett. 95, 021901 (2009); http://dx.doi.org/10.1063/1.3168520 (3 pages) | Cited 8 times

Online Publication Date: 14 July 2009

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Experimental results of carbon nanotube (CNT) reinforced copper composites (Cu/CNT) have shown that the resultant tensile strength of Cu/CNT composite is CNT diameter dependent, in a form of parabolic relationship that the smaller the CNT diameters the greater the resultant strength of the Cu/CNT composites. The largely increased strength of Cu/CNT composited is attributed to the good CNT dispersion in both the electrolyte and in composite after electrochemical deposition, as well as to the good interfacial bonding formed by the electrochemical deposition process. Smaller CNT diameters result in greater total interfacial bonding area thus the greater resultant strength of the composite.
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61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
82.45.Qr Electrodeposition and electrodissolution
82.45.Gj Electrolytes
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
62.25.-g Mechanical properties of nanoscale systems

Stabilization of liquid crystal photoaligning layers by reactive mesogens

O. Yaroshchuk, V. Kyrychenko, Du Tao, V. Chigrinov, H. S. Kwok, H. Hasebe, and H. Takatsu

Appl. Phys. Lett. 95, 021902 (2009); http://dx.doi.org/10.1063/1.3168526 (3 pages) | Cited 10 times

Online Publication Date: 14 July 2009

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Via passivation of liquid crystal (LC) photoaligning layers by thin layers of reactive mesogens, strong enhancement in LC alignment stability is achieved. Simultaneously, the passivation layers improve alignment uniformity and chemical stability of photoaligning layers and widely change pretilt angle of liquid crystal.
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61.30.-v Liquid crystals
81.65.Rv Passivation

Morphological instability of spherical soft particles induced by surface charges

Bo Li, Xi-Qiao Feng, Yue Li, and Gang-Feng Wang

Appl. Phys. Lett. 95, 021903 (2009); http://dx.doi.org/10.1063/1.3177189 (3 pages) | Cited 4 times

Online Publication Date: 14 July 2009

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We here demonstrate that surface charges on a spherical soft particle may induce its morphology instability. It is found that various patterns can be obtained by varying the surface charge density. The critical condition for the occurrence of surface instability and the wavelength of the induced surface patterns are derived analytically and, thereby, the morphological phase diagram of soft particles can be provided easily. Besides the electric stress, surface tension also plays a significant role in the surface evolution process. In addition, the morphological evolution behavior of a soft particle is demonstrated to exhibit distinct dependence on its size.
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73.25.+i Surface conductivity and carrier phenomena
68.03.Cd Surface tension and related phenomena
82.70.Dd Colloids

Thermal stability and formation barrier of a high-energetic material N8 polymer nitrogen encapsulated in (5,5) carbon nanotube

Wei Ji, V. Timoshevskii, H. Guo, Hakima Abou-Rachid, and Louis-Simon Lussier

Appl. Phys. Lett. 95, 021904 (2009); http://dx.doi.org/10.1063/1.3162334 (3 pages) | Cited 4 times

Online Publication Date: 15 July 2009

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We report the density functional theory total energy calculations of thermal stability and formation barrier of polymer nitrogen confined in carbon nanotubes (CNT). The analysis suggests that N8 polymer nitrogen encapsulated in (5,5) carbon nanotube [N8@CNT(5,5)] is thermally (meta)stable at a finite temperature up to energy scale of at least 5000 K, similar to nitrogen molecule gas phase confined in CNT [N2@CNT(5,5)]. The energetic difference between these two phases of N does not significantly change with temperature. A barrier of 1.07 eV was found for the formation of N8@CNT(5,5) from N2@CNT(5,5), while the dissociation barrier was found to be 0.2 eV. Snapshots of the reaction pathway show that the transition state is composed by a N2 and a N6 inside a CNT(5,5).
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71.15.Nc Total energy and cohesive energy calculations
82.20.Db Transition state theory and statistical theories of rate constants
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Enhancement of heterogeneous nucleation of β-Sn phases in Sn-rich solders by adding minor alloying elements with hexagonal closed packed structures

Moon Gi Cho, Hyun You Kim, Sun-Kyoung Seo, and Hyuck Mo Lee

Appl. Phys. Lett. 95, 021905 (2009); http://dx.doi.org/10.1063/1.3177335 (3 pages) | Cited 5 times

Online Publication Date: 15 July 2009

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The measured undercooling of pure Sn was about 30 °C due to the difficulty of nucleating a solid β-Sn phase from a liquid phase. To promote the heterogeneous nucleation of β-Sn phases, the addition of impurity elements to the solders was suggested. Among the impurity elements, alloying elements with hexagonal closed packed (hcp) structures, such as Co, Zn, Ti, and Mg, were found effective to enhance heterogeneous nucleation of β-Sn phases in Sn-rich solders. Calculations of the density functional theory indicate that the interfacial energy between β-Sn and Zn was relatively low. Minor alloying elements with hcp crystals are expected to provide more favorable heterogeneous nucleation sites for β-Sn phases.
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64.60.Q- Nucleation
61.72.S- Impurities in crystals
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Microstructure and infrared spectral properties of porous polycrystalline and nanocrystalline cubic silicon carbide

J. Y. Fan, H. X. Li, and W. N. Cui

Appl. Phys. Lett. 95, 021906 (2009); http://dx.doi.org/10.1063/1.3180706 (3 pages) | Cited 6 times

Online Publication Date: 16 July 2009

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We investigated the structural and infrared spectral properties of porous polycrystalline 3C-SiC and 3C-SiC nanoparticles produced via electrochemical method. The porous sample consisted of parallel nanowires with periodic beadlike structures. It exhibited infrared spectral features quite different from that of single crystal. The 3C-SiC crystallites with an average size of 4 nm showed simple surface chemistry with the surfaces well passivated by dissociation of surrounding water molecules. Our result explains the distinctive optical properties in porous polycrystalline and nanocrystalline 3C-SiC and reveals the crucial conditions for quantum confinement photoluminescence to arise.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.07.Bc Nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.55.Mb Porous materials
78.30.Hv Other nonmetallic inorganics
81.16.-c Methods of micro- and nanofabrication and processing
81.65.Rv Passivation
82.45.Bb Corrosion and passivation

Energy current imaging method for time reversal in elastic media

Brian E. Anderson, Robert A. Guyer, Timothy J. Ulrich, Pierre-Yves Le Bas, Carène Larmat, Michele Griffa, and Paul A. Johnson

Appl. Phys. Lett. 95, 021907 (2009); http://dx.doi.org/10.1063/1.3180811 (3 pages) | Cited 6 times

Online Publication Date: 16 July 2009

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An energy current imaging method is presented for use in locating sources of wave energy during the back propagation stage of the time reversal process. During the back propagation phase of an ideal time reversal experiment, wave energy coalesces from all angles of incidence to recreate the source event; after the recreation, wave energy diverges in every direction. An energy current imaging method based on this convergence/divergence behavior has been developed. The energy current imaging method yields a smaller spatial distribution for source reconstruction than is possible with traditional energy imaging methods.
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46.25.-y Static elasticity

Dislocation structures of Σ3 {112} twin boundaries in face centered cubic metals

J. Wang, O. Anderoglu, J. P. Hirth, A. Misra, and X. Zhang

Appl. Phys. Lett. 95, 021908 (2009); http://dx.doi.org/10.1063/1.3176979 (3 pages) | Cited 21 times

Online Publication Date: 16 July 2009

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High resolution transmission electron microscopy of nanotwinned Cu films revealed Σ3 {112} incoherent twin boundaries (ITBs), with a repeatable pattern involving units of three {111} atomic planes. Topological analysis shows that Σ3 {112} ITBs adopt two types of atomic structure with differing arrangements of Shockley partial dislocations. Atomistic simulations were performed for Cu and Al. These studies revealed the structure of the two types of ITBs, the formation mechanism and stability of the associated 9R phase, and the influence of stacking fault energies on them. The results suggest that Σ3 {112} ITBs may migrate through the collective glide of partial dislocations.
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61.72.Mm Grain and twin boundaries
61.72.Nn Stacking faults and other planar or extended defects
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Fractal network dimension determining the relation between the strength of bulk metallic glasses and the glass transition temperature

D. J. Klein, N. H. March, and J. A. Alonso

Appl. Phys. Lett. 95, 021909 (2009); http://dx.doi.org/10.1063/1.3183520 (3 pages) | Cited 2 times

Online Publication Date: 16 July 2009

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[ Ma et al., Nat. Mater. 8, 30 (2009) ] have uncovered the fractal dimension Df = 2.31 associated with the medium-range order in a variety of bulk metallic glasses, reflected in the first sharp diffraction peak q1 determined from neutron and x-ray measurements. Here, based on the proposal in this journal of [ Yang et al., Appl. Phys. Lett. 88, 221911 (2006) ], which related the strength σy of bulk metallic glasses to the glass transition temperature Tg, we show that the product q1Dfσy is linear in Tg.
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64.70.pe Metallic glasses
64.60.al Fractal and multifractal systems
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties
62.20.-x Mechanical properties of solids
61.43.Fs Glasses

Phase separation and nanocrystal formation in GeO

Christoph J. Sahle, Christian Sternemann, Heiko Conrad, Alexej Herdt, Omid M. Feroughi, Metin Tolan, Achim Hohl, Ralph Wagner, Dirk Lützenkirchen–Hecht, Ronald Frahm, Arto Sakko, and Keijo Hämäläinen

Appl. Phys. Lett. 95, 021910 (2009); http://dx.doi.org/10.1063/1.3183581 (3 pages) | Cited 10 times

Online Publication Date: 16 July 2009

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The temperature-induced phase separation (disproportionation) and Ge nanocrystal formation in bulk amorphous germanium monoxide (a-GeOx,x ≈ 1) are studied both in situ and ex situ by measurements of the x-ray absorption near edge structure at the Ge K-edge and x-ray diffraction. The considerable amount of suboxides contained in the native a-GeO samples decreases with increasing annealing temperature. The phase separation sets in at a temperature of 260±20 °C and is almost completed at a temperature of 450±18 °C before nanocrystal formation occurs. Ge nanocrystals of a few nanometers in diameter are observed for an annealing temperature of 509±15 °C. The time dependence of the phase separation and the effect of different annealing procedures are discussed. The presented results provide important information for the production of Ge nanocrystals embedded in amorphous oxide matrices which are relevant for optoelectronic applications.
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81.16.-c Methods of micro- and nanofabrication and processing
64.75.-g Phase equilibria
81.05.Gc Amorphous semiconductors
61.72.Cc Kinetics of defect formation and annealing
78.70.Dm X-ray absorption spectra
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.07.Bc Nanocrystalline materials
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