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14 Aug 2006

Volume 89, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 073501 (2006); http://dx.doi.org/10.1063/1.2335838 (3 pages)

Ingrid Graz, Martin Kaltenbrunner, Christoph Keplinger, Reinhard Schwödiauer, Siegfried Bauer, Stéphanie P. Lacour, and Sigurd Wagner
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Properties of an optical multipass surface plasmon resonance technique

Chin B. Su, Jun Kameoka, B. Ilic, Kung-Hui Chu, and Kuang-An Chang

Appl. Phys. Lett. 89, 071101 (2006); http://dx.doi.org/10.1063/1.2336625 (3 pages) | Cited 2 times

Online Publication Date: 14 August 2006

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A fiber optic four-pass surface plasmon resonance technique with an approach to increase the number of passes to any arbitrary number is described. Within multipass regime, reflections off the gold sample surface that reduce the reflectivity to less than 0.1% are achieved by using a fiber optic collimator, a reflector, and a corner cube prism. In this case, the optical beam emits from and returns to the collimator. This technique holds the potential for significantly increasing the detection sensitivity of surface plasmon resonance device.
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42.81.Pa Sensors, gyros
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.81.Wg Other fiber-optical devices
07.60.Vg Fiber-optic instruments
42.79.Ag Apertures, collimators
42.79.Bh Lenses, prisms and mirrors

Visible two-dimensional photonic crystal slab laser

Zhaoyu Zhang, Tomoyuki Yoshie, Xiaoliang Zhu, Jiajing Xu, and Axel Scherer

Appl. Phys. Lett. 89, 071102 (2006); http://dx.doi.org/10.1063/1.2336721 (3 pages) | Cited 13 times

Online Publication Date: 14 August 2006

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The authors describe the fabrication and performance of photonic crystal lasers fabricated within thin membranes of InGaP/InGaAlP quantum well material and emitting in the visible wavelength range. These lasers have ultrasmall mode volumes, emit red light, and exhibit low threshold powers. They can be lithographically tuned from 650 to 690 nm. Their cavity volumes of approximately 0.01 μm3 are ideally suited for use as spectroscopic sources.
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42.55.Tv Photonic crystal lasers and coherent effects
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.70.Qs Photonic bandgap materials
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.72.Bj Visible and ultraviolet sources

Traveling-wave photomixers fabricated on high energy nitrogen-ion-implanted GaAs

M. Mikulics, E. A. Michael, M. Marso, M. Lepsa, A. van der Hart, H. Lüth, A. Dewald, S. Stanček, M. Mozolik, and P. Kordoš

Appl. Phys. Lett. 89, 071103 (2006); http://dx.doi.org/10.1063/1.2337523 (3 pages) | Cited 8 times

Online Publication Date: 15 August 2006

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The authors report on fabrication and measurement of traveling-wave photomixers based on high energy and low dose nitrogen-ion-implanted GaAs. They used 3 MeV energy to implant N+ ions into GaAs substrates with an ion concentration dose of 3×1012 cm−2. The N+-implanted GaAs photomixers exhibit improvements in the output power in comparison with their counterparts, photomixers fabricated on low-temperature-grown GaAs. The maximal output power was 2.64 μW at 850 GHz. No saturation of the output power with increased bias voltage and optical input power was observed. These characteristics make N+-implanted GaAs the material of choice for efficient high power sources of terahertz radiation.
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84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
84.40.-x Radiowave and microwave (including millimeter wave) technology
61.80.Jh Ion radiation effects
61.72.uj III-V and II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Complementary thermoreflectance and micro-Raman analysis of facet temperatures of diode lasers

Tomasz J. Ochalski, Dorota Pierścińska, Kamil Pierściński, Maciej Bugajski, Jens W. Tomm, Tobias Grunske, and Anna Kozlowska

Appl. Phys. Lett. 89, 071104 (2006); http://dx.doi.org/10.1063/1.2335675 (3 pages) | Cited 15 times

Online Publication Date: 16 August 2006

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A methodological approach for advanced facet temperature characterization of operating diode lasers is presented. It relies on the concerted application of micro-Raman spectroscopy and thermoreflectance mapping. The latter technique allows for fast facet mapping, whereas the Raman data provide the temperature calibration. Residual effects, e.g., caused by the different reflectances of the materials involved into the laser structure, are discussed. Since both techniques provide rather complementary information, their concerted application appears as an effective tool for advanced device inspection.
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42.55.Px Semiconductor lasers; laser diodes

Fabrication of inorganic GeO2:SiO2 channel waveguides by ultraviolet imprinting technique

Rajni, K. Pita, S. F. Yu, S. C. Tjin, and C. H. Kam

Appl. Phys. Lett. 89, 071105 (2006); http://dx.doi.org/10.1063/1.2335965 (3 pages)

Online Publication Date: 16 August 2006

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The authors demonstrate the effective waveguiding channel formation inside an ∼ 3 μm thick photosensitive GeO2(20%):SiO2(80%) planar slab waveguide film prepared using the sol-gel technique by the direct ultraviolet (UV) imprinting technique. This is possible because of the ability to induce large refractive index change ( ∼ 10−3) in the films by the UV radiation. Channel waveguides with various refractive index values have been fabricated. The measured modal profiles of the waveguides match well with the simulation results. The simplicity of the direct UV imprinting technique is also shown by the fabrication of a 1×2 multimode-interference 3 dB light splitter in one single processing step.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.70.-a Optical materials
42.79.Fm Reflectors, beam splitters, and deflectors
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Actuation of cantilevers by optical trapping

Peter Domachuk, Eric Mägi, Benjamin J. Eggleton, and Mark Cronin-Golomb

Appl. Phys. Lett. 89, 071106 (2006); http://dx.doi.org/10.1063/1.2335983 (3 pages) | Cited 5 times

Online Publication Date: 16 August 2006

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Cantilevers are commonly used in microelectromechanical systems for sensing and optical switching applications. The authors demonstrate the use of optical tweezers for all optical actuation of a tapered optical fiber used as a cantilever and to drive it as a micromechanical oscillator. A fiber optic confocal detection system is used to monitor backscattered trapping light to sense the position and oscillation characteristics of the cantilever. Potential applications include optical switching and dynamic reconfigurability of photonic circuits.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
42.81.Wg Other fiber-optical devices
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Room temperature polariton luminescence from a GaN/AlGaN quantum well microcavity

E. Feltin, G. Christmann, R. Butté, J.-F. Carlin, M. Mosca, and N. Grandjean

Appl. Phys. Lett. 89, 071107 (2006); http://dx.doi.org/10.1063/1.2335404 (3 pages) | Cited 14 times

Online Publication Date: 16 August 2006

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The authors report on the demonstration of strong light-matter coupling at room temperature using a crack-free UV microcavity containing GaN/AlGaN quantum wells (QWs). Lattice-matched AlInN/AlGaN distributed Bragg reflectors (DBRs) with a maximum peak reflectivity of 99.5% and SiO2/Si3N4 DBRs were used to form high finesse hybrid microcavities. State-of-the-art GaN/Al0.2Ga0.8N QWs emitting at 3.62 eV with a linewidth of 45 meV at 300 K were inserted in these structures. For a 3λ/2 microcavity containing six QWs, the interaction between cavity photons and QW excitons is sufficiently large to reach the strong coupling regime. A polariton luminescence is observed with a vacuum field Rabi splitting of 30 meV at 300 K.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
42.82.Gw Other integrated-optical elements and systems
71.35.-y Excitons and related phenomena

Tailoring holes for improving the efficiency of single-mode photonic crystal waveguide lasers on InP substrate

X. Checoury, P. Boucaud, X. Li, J.-M. Lourtioz, E. Derouin, O. Drisse, F. Poingt, L. Legouezigou, O. Legouezigou, P. Pommereau, and G.-H. Duan

Appl. Phys. Lett. 89, 071108 (2006); http://dx.doi.org/10.1063/1.2335484 (3 pages)

Online Publication Date: 16 August 2006

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The authors show that the use of triangular lattice photonic crystals (PhCs) with wide holes can significantly improve the lasing performances of PhC waveguides in the InP substrate approach. The study is carried out on W2-3 waveguides made in PhCs whose air filling factor is varied from ∼ 25% to 55%. Intrinsically single-mode laser emissions with reduced threshold (/2) are obtained when the laser mode folds deeply into the gap. Concurrently, the slope of the light-light characteristic is increased by a factor of 14. The laser spectral behavior and threshold evolution are explained from three-dimensional finite difference time domain calculations.
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42.55.Tv Photonic crystal lasers and coherent effects
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.82.Gw Other integrated-optical elements and systems

High performance thin-film flip-chip InGaN–GaN light-emitting diodes

O. B. Shchekin, J. E. Epler, T. A. Trottier, T. Margalith, D. A. Steigerwald, M. O. Holcomb, P. S. Martin, and M. R. Krames

Appl. Phys. Lett. 89, 071109 (2006); http://dx.doi.org/10.1063/1.2337007 (3 pages) | Cited 91 times

Online Publication Date: 16 August 2006

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Data are presented on the operation of thin-film flip-chip InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs). The combination of thin-film LED concept with flip-chip technology is shown to provide surface brightness and flux output advantages over conventional flip-chip and vertical-injection thin-film LEDs. Performance characteristics of blue, white, and green thin-film flip-chip 1×1 mm2 LEDs are described. Blue ( ∼ 441 nm) thin-film flip-chip LEDs are demonstrated with radiance of 191 mW/mm2 sr at 1 A drive, more than two times brighter than conventional flip-chip LEDs. An encapsulated thin-film flip-chip blue LED lamp is shown to have external quantum efficiency of 38% at forward current of 350 mA. A white lamp based on a YAG:Ce phosphor coated device exhibits luminous efficacy of 60 lm/W at 350 mA with peak efficiency of 96 lm/W at 20 mA and luminance of 38 Mcd/m2 at 1 A drive current. Green ( ∼ 517 nm) devices exhibit luminance of 37 Mcd/m2 at 1 A.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Tunable silicon microring resonator with wide free spectral range

Magdalena S. Nawrocka, Tao Liu, Xuan Wang, and Roberto R. Panepucci

Appl. Phys. Lett. 89, 071110 (2006); http://dx.doi.org/10.1063/1.2337162 (3 pages) | Cited 36 times

Online Publication Date: 17 August 2006

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The authors present a silicon-on-insulator single ring resonator with a free spectral range equal to 47 nm, which is the widest known value for this type of resonators. The ring radius is 2 μm and is the smallest ring resonator ever reported, achieving experimentally such a wide spectral range. For this ring resonator, the authors demonstrate the quality factor to be equal to 6730±60. They thermally tune the resonant wavelength with 0.11 nm/°C, thus showing the ring resonator as an attractive component for on-chip ultracompact photonic add/drop filters and switches.
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42.79.Ci Filters, zone plates, and polarizers
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks

Nonlocality-controlled interaction of spatial solitons in nematic liquid crystals

Wei Hu, Tao Zhang, Qi Guo, Li Xuan, and Sheng Lan

Appl. Phys. Lett. 89, 071111 (2006); http://dx.doi.org/10.1063/1.2337268 (3 pages) | Cited 39 times

Online Publication Date: 18 August 2006

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The authors demonstrate experimentally that interaction between nonlocal solitons in nematic liquid crystals (NLCs) can be controlled by the degree of nonlocality. For a given beam width, the degree of nonlocality can be modulated by changing the pretilt angle θ0 of NLC molecules through bias voltage V. As V increases (so does θ0), the degree of nonlocality decreases. When the degree of nonlocality is below a critical value, the solitons behave in the way like their local counterpart, i.e., in-phase solitons attract while out-of-phase solitons repulse each other. Such a voltage-controlled interaction between the solitons can be readily implemented in experiments.
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42.70.Df Liquid crystals
61.30.-v Liquid crystals
42.65.Tg Optical solitons; nonlinear guided waves

1 μm saturable absorber with recovery time reduced by lattice mismatch

S. Suomalainen, M. Guina, T. Hakulinen, O. G. Okhotnikov, T. G. Euser, and S. Marcinkevicius

Appl. Phys. Lett. 89, 071112 (2006); http://dx.doi.org/10.1063/1.2337278 (3 pages) | Cited 4 times

Online Publication Date: 18 August 2006

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Metamorphic growth of lattice mismatched InGaP on GaAs has been used to fabricate a fast semiconductor saturable absorber mirror operating at the 1060 nm wavelength range. The absorption recovery time could be reduced to ∼ 5 ps without deteriorating the nonlinear absorption properties. The device was used to demonstrate self-starting operation of a mode-locked Yb-doped fiber laser and obtain high quality picosecond pulses.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Bh Lenses, prisms and mirrors
42.60.Fc Modulation, tuning, and mode locking
42.55.Wd Fiber lasers

InN nanoflowers grown by metal organic chemical vapor deposition

Ting-Ting Kang, Xianglin Liu, Ri Q. Zhang, Wei G. Hu, Guangwei Cong, Feng-Ai Zhao, and Qinsheng Zhu

Appl. Phys. Lett. 89, 071113 (2006); http://dx.doi.org/10.1063/1.2337875 (3 pages) | Cited 15 times

Online Publication Date: 18 August 2006

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Hexangular indium nitride nanoflower pattern is observed from scanning electron microscopy and atomic force microscopy. The sample is grown on c-plane (0001) sapphire by metal organic chemical vapor deposition with intentional introduction of hydrogen gas. With the aid of hydrogen, a stable existence of metallic indium is achieved. This will induce the growth of InN nanoflowers via self-catalysis vapor-liquid-solid (VLS) process. It is found that the VLS process is modulated by the interface kinetics and thermodynamics among the sapphire substrate, indium, and InN, which leads to the special morphology of the authors’ InN nanoflower pattern.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.Rf Micro- and nanoscale pattern formation
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.16.Hc Catalytic methods

Carrier lifetime reduction in 1.5 μm AlGaAsSb saturable absorbers with air and AlAsSb barriers

O. Ostinelli, W. Bächtold, H. Haiml, R. Grange, U. Keller, E. Gini, and G. Almuneau

Appl. Phys. Lett. 89, 071114 (2006); http://dx.doi.org/10.1063/1.2240742 (3 pages) | Cited 1 time

Online Publication Date: 18 August 2006

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The optical properties of different AlGaAsSb semiconductor saturable absorber mirrors and InP/AlGaAsSb heterostructures have been investigated by pump-probe and low temperature photoluminescence measurements. The results show that the type-II electron-hole recombination process at the InP–AlGaAsSb interface is responsible for the slow carrier decay time in the absorber. Nevertheless, this slow transition can be avoided by growing an AlAsSb barrier layer between InP and the absorber layer promoting the fast electron-hole recombination at the surface states on the absorber/air interface. This allows reducing the carrier decay time from several nanoseconds down to 20 ps.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
42.79.Bh Lenses, prisms and mirrors
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors

Observation of optical bistability in a ZnO powder random medium

Hideki Fujiwara and Keiji Sasaki

Appl. Phys. Lett. 89, 071115 (2006); http://dx.doi.org/10.1063/1.2338533 (3 pages) | Cited 4 times

Online Publication Date: 18 August 2006

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Optical bistability has been observed in photoluminescence from a ZnO powder random medium. The emission spectra and the excitation intensity dependence of 420 nm emission clearly exhibit the existence of bistable steady states with changing excitation intensity.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
78.55.Hx Other solid inorganic materials

Laser emission from GaN photonic crystals

Li-Ming Chang, Chia-Hung Hou, Yu-Chen Ting, Chii-Chang Chen, Che-Lung Hsu, Jenq-Yang Chang, Chien-Chieh Lee, Guan-Ting Chen, and Jen-Inn Chyi

Appl. Phys. Lett. 89, 071116 (2006); http://dx.doi.org/10.1063/1.2236107 (3 pages) | Cited 10 times

Online Publication Date: 18 August 2006

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In this study, photonic crystals have been designed, fabricated, and characterized in GaN bulk materials. The energy dependent measurement showed that the emission peak width can be significantly reduced as the pumping pulse energy was larger than 0.7 μJ at room temperature. The mode at the wavelength of 371 nm emitted from the defect due to the structure disorder unintentionally introduced during the fabrication process of the GaN photonic crystals can be obtained.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Tv Photonic crystal lasers and coherent effects
42.70.Qs Photonic bandgap materials
42.60.By Design of specific laser systems

High bandwidth Ge p-i-n photodetector integrated on Si

M. Oehme, J. Werner, E. Kasper, M. Jutzi, and M. Berroth

Appl. Phys. Lett. 89, 071117 (2006); http://dx.doi.org/10.1063/1.2337003 (3 pages) | Cited 29 times

Online Publication Date: 18 August 2006

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The authors present a germanium on silicon p-i-n photodiode for vertical light incidence. For a Ge p-i-n photodetector with a radius of 5 μm a 3 dB bandwidth of 25 GHz is measured at an incident wavelength of 1.55 μm and zero external bias. For a modest reverse bias of 2 V, the 3 dB bandwidth increases to 39 GHz. The monolithically integrated devices are grown on Si with solid source molecular beam epitaxy. The complete detector structure consisting of a highly p-doped Ge buried layer, an intrinsic absorption region, and a highly n-doped top contact layer of Ge/Si is grown in one continuous epitaxial run. A low growth temperature sequence was needed to obtain abrupt doping transitions between the highly doped regions surrounding the intrinsic layer. A theoretical consideration of the 3 dB bandwidth of the Ge detector was used to optimize the layer structure. For a photodiode with 5 μm mesa radius the maximum theoretical 3 dB frequency is 62 GHz with an intrinsic region thickness of 307 nm.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uf Ge and Si
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Silicon surface periodic structures produced by plasma flow induced capillary waves

I. P. Dojčinović, M. M. Kuraica, B. M. Obradović, and J. Purić

Appl. Phys. Lett. 89, 071501 (2006); http://dx.doi.org/10.1063/1.2336617 (3 pages) | Cited 5 times

Online Publication Date: 14 August 2006

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Silicon single crystal surface modification by the action of nitrogen quasistationary compression plasma flow generated by a magnetoplasma compressor is studied. It has been found that highly oriented silicon periodic cylindrical shape structures are produced during a single pulse surface treatment. The periodical structure formation can be related to the driven capillary waves quenched during fast cooling and resolidification phase of the plasma flow interaction with silicon surface. These waves are induced on the liquid silicon surface due to the compression plasma flow intrinsic oscillations.
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52.77.Fv High-pressure, high-current plasmas (plasma spray, arc welding, etc.)
81.05.Cy Elemental semiconductors
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.40.Hf Plasma-material interactions; boundary layer effects
81.30.Fb Solidification
64.70.D- Solid-liquid transitions
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Self-driven formation and structure of single crystal platelets of Zn3As2

N. Kouklin, S. Sen, and M. Gajdardziska-Josifovska

Appl. Phys. Lett. 89, 071901 (2006); http://dx.doi.org/10.1063/1.2335682 (3 pages) | Cited 3 times

Online Publication Date: 14 August 2006

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In this work the authors introduce and provide details on the stoichiometrically controlled self-driven formation of freestanding single crystal platelets in Zn3As2 by a direct self-catalytic vapor-solid growth mechanism. The platelets feature dimensions of up to ∼ 1 cm and mirrorlike microscopically flat top surfaces. A coherent formation of pyramids and wires has been further observed on some of the platelet top surfaces, the growth mechanism of which is discussed. This study might open pathways for facile engineering of high-performance semiconductor via a direct vapor-solid conversion of polycrystalline semiconductor powders into single crystal substrates on a large scale and with low cost.
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81.05.Hd Other semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Optimization of the surface and structural quality of N-face InN grown by molecular beam epitaxy

G. Koblmüller, C. S. Gallinat, S. Bernardis, J. S. Speck, G. D. Chern, E. D. Readinger, H. Shen, and M. Wraback

Appl. Phys. Lett. 89, 071902 (2006); http://dx.doi.org/10.1063/1.2335685 (3 pages) | Cited 54 times

Online Publication Date: 14 August 2006

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The authors demonstrate the impact of growth kinetics on the surface and structural properties of N-face InN grown by molecular beam epitaxy. Superior surface morphology with step-flow growth features is achieved consistently under In-rich conditions in a low-temperature region of 500–540 °C. Remarkably, off-axis x-ray rocking curve (ω scans) widths are found to be independent of the growth conditions. The band gap determined from optical absorption measurements of optimized InN is 0.651 eV, while photoluminescence peak emission occurs at even lower energies of ∼ 0.626 eV. Hall measurements show room temperature peak electron mobilities as high as 2370 cm2/V s at a carrier concentration in the low 1017 cm−3 region. Analysis of the thickness dependence of the carrier concentration demonstrates a n-type surface accumulation layer with a sheet carrier concentration of ∼ 3×1013 cm−2.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Fg Semiconductor surfaces
71.20.Nr Semiconductor compounds

On the solute coupling at the moving solid/liquid interface during equiaxed solidification

X. Yao

Appl. Phys. Lett. 89, 071903 (2006); http://dx.doi.org/10.1063/1.2336079 (3 pages)

Online Publication Date: 14 August 2006

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Integral mass conservation was widely accepted for the solute coupling to solve solute redistribution during equiaxed solidification so far. The present study revealed that the integral form was invalid for moving boundary problems as it could not represent the mass balance at the moving interface. Accordingly, differential mass conservation at the solid/liquid interface was used to solve solute diffusion for spherical geometry. The model was applied for hydrogen diffusion in solidification to validate that the hydrogen enrichment was significant and depended on the growth rate.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
64.70.D- Solid-liquid transitions

Shear-strain induced decomposition of 1,1-diamino-2,2-dinitroethylene

M. M. Kuklja, S. N. Rashkeev, and F. J. Zerilli

Appl. Phys. Lett. 89, 071904 (2006); http://dx.doi.org/10.1063/1.2335680 (3 pages) | Cited 8 times

Online Publication Date: 15 August 2006

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The structural and electronic features of shear strains in the molecular crystal 1,1-diamino-2,2-dinitroethylene and their effect on decomposition of the material are investigated. The authors demonstrate that shear strains lower the decomposition barrier and narrow the band gap of the solid and thus facilitate thermal chemistry in molecular materials. The appearance of defect-related electronic states in the band gap is consistent with previous results for dislocation modeling in molecular solids and with experiments on energetic materials. The dynamic behavior of the band gap contains a rich variety of information about the details of the decomposition processes at the initiation stage.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
64.75.-g Phase equilibria
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.66.Hq Organic compounds

Influence of N incorporation on In content in GaInNAs/GaNAs quantum wells grown by plasma-assisted molecular beam epitaxy

H. F. Liu, N. Xiang, and S. J. Chua

Appl. Phys. Lett. 89, 071905 (2006); http://dx.doi.org/10.1063/1.2335804 (3 pages) | Cited 7 times

Online Publication Date: 15 August 2006

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The authors investigated the synthesis of GaIn(N)As/Ga(N)As multiple quantum wells by molecular beam epitaxy. Introducing N into the GaInAs appears to suppress the incorporation of In as indicated by reflective high-energy electron diffraction (RHEED). This effect is mainly due to the N-induced enhancement of In surface segregation at the growth front and is evidenced by the increasing damping rate of RHEED oscillations with N incorporation. The N-induced enhancement of In segregation in the GaInNAs quantum wells is confirmed by secondary-ion-mass spectroscopy and high-resolution x-ray diffractions, and its origin is discussed.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Dv Composition, segregation; defects and impurities
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

High hydrogen content complex hydrides: A density-functional study

P. Vajeeston, P. Ravindran, A. Kjekshus, and H. Fjellvåg

Appl. Phys. Lett. 89, 071906 (2006); http://dx.doi.org/10.1063/1.2217159 (3 pages) | Cited 25 times

Online Publication Date: 15 August 2006

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Density-functional-theory calculations within the generalized-gradient approximation are used to establish the ground-state structure, optimized geometry, and electronic structure for Mg(AlH4)2 and Mg(BH4)2. Among 28 structural arrangements used as inputs for structural optimization calculations, the experimentally known framework is reproduced for Mg(AlH4)2 (space group Pmathm1) with positional and unit-cell parameters in good agreement with the experimental findings. The crystal structure of Mg(BH4)2 is predicted, the ground-state framework being orthorhombic (space group Pmc21; Pearson symbol oP22 with a fascinating two-dimensional arrangement of Mg2+ ions and [BH4]2− tetrahedra. The formation energy for the predicted Mg(BH4)2 phase is investigated along different reaction pathways. The electronic structures reveal that Mg(AlH4)2 and Mg(AlH4)2 are insulators with calculated band gaps of around 4.5 and 6.2 eV, respectively.
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71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Ps Other inorganic compounds
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
61.66.Fn Inorganic compounds
84.60.-h Direct energy conversion and storage

Thickness of shear bands in metallic glasses

Y. Zhang and A. L. Greer

Appl. Phys. Lett. 89, 071907 (2006); http://dx.doi.org/10.1063/1.2336598 (3 pages) | Cited 87 times

Online Publication Date: 15 August 2006

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A review of measurements and atomistic modeling shows that shear bands in metallic glasses have a characteristic thickness of ∼ 10 nm. Such extreme localization of plastic deformation, within a thicker liquidlike layer implied by fracture-surface morphology, cannot have a thermal origin. By analogy with granular materials, the thickness is linked to the local structural rearrangements required to generate dilatation. This analysis suggests that first-coordination-shell clusters may be significant structural units in metallic glasses.
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61.43.Fs Glasses
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
61.43.Bn Structural modeling: serial-addition models, computer simulation
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