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21 Jul 2008

Volume 93, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 031101 (2008); http://dx.doi.org/10.1063/1.2959092 (3 pages)

Di Xu, Kevin P. Chen, Kris Ohlinger, and Yuankun Lin
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Holographic fabrication of diamondlike photonic crystal template using two-dimensional diffractive optical elements

Di Xu, Kevin P. Chen, Kris Ohlinger, and Yuankun Lin

Appl. Phys. Lett. 93, 031101 (2008); http://dx.doi.org/10.1063/1.2959092 (3 pages) | Cited 8 times

Online Publication Date: 21 July 2008

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This letter demonstrates holographic fabrication of three-dimensional diamondlike photonic crystal templates in SU8 photoresist using a single diffractive optical element. Five coherent laser beams produced by a two-dimensional phase mask were used to construct face-centered-cubic or tetragonal interference patterns. The superposition of two interference patterns through double exposures yields diamondlike photonic crystal templates in SU8. Photonic bandgap calculation reveals a full bandgap in inverse structures based on the template. The utilization of the two-dimensional phase mask simplifies the fabrication configuration in multiple beam holographic lithography for three-dimensional photonic fabrication.
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42.40.Eq Holographic optical elements; holographic gratings
42.86.+b Optical workshop techniques
42.70.Qs Photonic bandgap materials
42.40.Kw Holographic interferometry; other holographic techniques

Estimating threshold reduction for spin-injected semiconductor lasers

I. Vurgaftman, M. Holub, B. T. Jonker, and J. R. Meyer

Appl. Phys. Lett. 93, 031102 (2008); http://dx.doi.org/10.1063/1.2957656 (3 pages) | Cited 5 times

Online Publication Date: 21 July 2008

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The magnitude of threshold reduction in a semiconductor laser with electron spin injection is shown to depend on such intrinsic properties of the active region as the dominant recombination mechanism, the ratio of hole-to-electron densities of states, the active-region doping, and the available material gain as well as cavity properties such as the optical loss. The threshold reduction is expected to be greatest when the laser’s active region is undoped, the recombination is strongly dominated by Auger processes, and the threshold gain is low. It can approach a factor of 3.5 for fully spin-polarized electrons in the active region.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Simultaneous closure of multiple high voltage parallel spark channels without switch: A parametric study

Pallavi Raote, Gautam Patil, J. Padma Nilaya, and Dhruba J. Biswas

Appl. Phys. Lett. 93, 031103 (2008); http://dx.doi.org/10.1063/1.2960997 (3 pages) | Cited 3 times

Online Publication Date: 21 July 2008

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Results of a detailed parametric study of a self-switched mutually inductively coupled high voltage parallel spark preionizer are presented. The maximal behavior exhibited by the breakdown voltage of the parallel gaps with respect to the number of mutually coupled turns has been explained. It has been found that there exists a threshold rise time of the current pulse beyond which simultaneous closure of the parallel gaps is not possible and that this threshold value is independent of the nature and geometry of the cores used for the mutual coupling. The degree of simultaneity of the closure of the self-switched parallel gaps matched that of the conventional operation of such gaps.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity

Effect of waveguide sidewall roughness on the threshold current density and slope efficiency of quantum cascade lasers

Fatima Toor, Deborah L. Sivco, Hao E. Liu, and Claire F. Gmachl

Appl. Phys. Lett. 93, 031104 (2008); http://dx.doi.org/10.1063/1.2962984 (3 pages) | Cited 5 times

Online Publication Date: 21 July 2008

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We report on a study to determine the effect of waveguide sidewall roughness on quantum cascade (QC) laser performance using two two-wavelength heterogeneous QC laser structures, one with emission wavelengths of 7.0 μm/11.2 μm, and the other with 8.7 μm/12.0 μm. For the range of roughness standard deviation values from about 0.4 to 1.0 μm, for which all four QC lasers were operating, the threshold current density increases by 12%–15% and the slope efficiency decreases by 30%–70% with stronger performance degradation for the shorter wavelength lasers, which is in agreement with a model based on Rayleigh scattering.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Transient carrier transfer in tunnel injection structures

V. G. Talalaev, J. W. Tomm, N. D. Zakharov, P. Werner, U. Gösele, B. V. Novikov, A. S. Sokolov, Y. B. Samsonenko, V. A. Egorov, and G. E. Cirlin

Appl. Phys. Lett. 93, 031105 (2008); http://dx.doi.org/10.1063/1.2963973 (3 pages) | Cited 9 times

Online Publication Date: 23 July 2008

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InGaAs tunnel injection nanostructures consisting of a single quantum well as injector and a quantum dot layer as emitter are studied by time-resolved photoluminescence spectroscopy. The quantum dot photoluminescence undergoes substantial changes when proceeding from direct quantum dot excitation to quantum well excitation, which causes an indirect population of the dot ground states. This results in a lowered effective carrier temperature within the dots. Results on the carrier transfer versus barrier thickness are discussed within the Wentzel–Kramers–Brillouin approximation. Deviations for barrier thicknesses <5 nm are assigned to the formation of nanobridges that are actually detected by transmission electron microscopy.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.63.Hs Quantum wells
73.63.Kv Quantum dots
73.40.Gk Tunneling
78.67.De Quantum wells
78.67.Hc Quantum dots

Real-time optical reflectometry enabled by amplified dispersive Fourier transformation

Keisuke Goda, Daniel R. Solli, and Bahram Jalali

Appl. Phys. Lett. 93, 031106 (2008); http://dx.doi.org/10.1063/1.2963974 (3 pages) | Cited 9 times

Online Publication Date: 23 July 2008

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The axial scan rate of optical frequency-domain reflectometry and optical coherence tomography can be increased to megahertz frequencies by dispersive Fourier transformation. However, the fundamental connection between dispersion and loss creates a trade-off between detection sensitivity and acquisition speed. Here we circumvent this predicament by using distributed Raman postamplification of the reflection from the sample. The Raman amplification enables measurement of weak signals, which are otherwise buried in detector noise. It extends the depth range without sacrificing the acquisition speed. Single-shot imaging with improved sensitivity at an axial scan rate of 36.6 MHz is demonstrated.
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07.60.Hv Refractometers and reflectometers
42.30.Kq Fourier optics

The effect of doping the M-barrier in very long-wave type-II InAs/GaSb heterodiodes

Darin Hoffman, Binh-Minh Nguyen, Edward Kwei-wei Huang, Pierre-Yves Delaunay, Manijeh Razeghi, Meimei Z. Tidrow, and Joe Pellegrino

Appl. Phys. Lett. 93, 031107 (2008); http://dx.doi.org/10.1063/1.2963980 (3 pages) | Cited 5 times

Online Publication Date: 23 July 2008

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A variation on the standard homodiode type-II superlattice with an M-barrier between the π-region and the n-region is shown to suppress the dark currents. By determining the optimal doping level of the M-superlattice, dark current densities of 4.95 mA/cm2 and quantum efficiencies in excess of 20% have been demonstrated at the moderate reverse bias of 50 mV; allowing for near background-limted performance with a Johnson-noise detectivity of 3.11×1010 cm math/W at 77 K for 14.58 μm cutoff wavelength for large area diodes without passivation. This is comparable to values for the state-of-the-art HgCdTe photodiodes.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.40.Ry Impurity doping, diffusion and ion implantation technology

Thermally assisted magnetic recording on a bit-patterned medium by using a near-field optical head with a beaked metallic plate

Takuya Matsumoto, Kimio Nakamura, Tetsuya Nishida, Hiroyuki Hieda, Akira Kikitsu, Katsuyuki Naito, and Tetsunori Koda

Appl. Phys. Lett. 93, 031108 (2008); http://dx.doi.org/10.1063/1.2960344 (3 pages) | Cited 6 times

Online Publication Date: 23 July 2008

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A near-field optical head with a beaked metallic plate was used for writing marks on a Co/Pd bit-patterned medium with a diameter of 20–25 nm and a pitch of 30 nm. Magnetic-force-microscope images of the medium show that the magnetizations of single bits were selectively reversed by the head. The light-utilization efficiency (defined as the ratio of the absorbed power in the medium to the incident light power) was estimated from the writing condition used and thermal modeling as about 5%.
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75.50.Ss Magnetic recording materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

A high speed, postprocessing free, quantum random number generator

J. F. Dynes, Z. L. Yuan, A. W. Sharpe, and A. J. Shields

Appl. Phys. Lett. 93, 031109 (2008); http://dx.doi.org/10.1063/1.2961000 (3 pages) | Cited 34 times

Online Publication Date: 23 July 2008

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A quantum random number generator (QRNG) based on gated single photon detection of an In–GaAs photodiode at gigahertz frequency is demonstrated. Owing to the extremely long coherence time of each photon, each photons’ wave function extends over many gating cycles of the photodiode. The collapse of the photon wave function on random gating cycles as well as photon random arrival time detection events are used to generate sequences of random bits at a rate of 4.01 Mbit/s. Importantly, the random outputs are intrinsically biasfree and require no postprocessing procedure to pass random number statistical tests, making this QRNG an extremely simple device.
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03.67.Lx Quantum computation architectures and implementations
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors

Fabry–Pérot microcavities with controllable resonant wavelengths in periodic dielectric waveguides

Yao Zhang, Wanwen Huang, and Baojun Li

Appl. Phys. Lett. 93, 031110 (2008); http://dx.doi.org/10.1063/1.2964188 (3 pages) | Cited 3 times

Online Publication Date: 24 July 2008

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Fabry–Pérot microcavities with controllable resonant wavelengths and constant quality factors are constructed by introducing defects in periodic dielectric waveguides. Two-dimensional finite-difference time-domain method is used to simulate the field distributions in the cavities. The simulated electric field profile fits a cosine-Gaussian curve. The quadratic relation between the resonant wavelength and the defect length is theoretically discussed and numerically proved. Simulations show that the resonant wavelength can be simply controlled by shifting cylinders in the defects, and the value of quality factor keeps a constant of about 103.
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42.79.Gn Optical waveguides and couplers

Single-frequency, Yb-free, resonantly cladding-pumped large mode area Er fiber amplifier for power scaling

Mark Dubinskii, Jun Zhang, and Igor Kudryashov

Appl. Phys. Lett. 93, 031111 (2008); http://dx.doi.org/10.1063/1.2964189 (3 pages) | Cited 5 times

Online Publication Date: 25 July 2008

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We report results for a single-frequency (SF) resonantly cladding-pumped Yb-free large mode area (LMA) erbium-doped fiber amplifier (EDFA) with nearly 50% slope efficiency based on a commercial 20/125 μm Er-doped double-clad LMA fiber with a core numerical aperture of 0.07. We believe that this is the original demonstration of a SF resonantly cladding-pumped LMA EDFA. We obtained a diffraction-limited SF output of 9.3 W, which is also a record power output obtained for resonantly cladding-pumped LMA EDFA.
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42.55.Wd Fiber lasers
42.60.By Design of specific laser systems
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Development of a trielectrode plasma curtain at atmospheric pressure

H. Zastawny, R. Sosa, D. Grondona, A. Márquez, G. Artana, and H. Kelly

Appl. Phys. Lett. 93, 031501 (2008); http://dx.doi.org/10.1063/1.2960996 (3 pages) | Cited 2 times

Online Publication Date: 23 July 2008

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The development of a nonequilibrium, low-power, trielectrode plasma curtain at atmospheric pressure is presented. The discharge is based on the combination of an ac dielectric barrier discharge with a dc corona discharge in a three electrode system, and can be sustained for large time periods and over interelectrode air gaps up to 20 mm and with an electrode length of ∼ 10 cm in the transversal direction. The discharge is composed of a train of streamers, with a repetition frequency in the range 50–200 kHz, and carrying an average current in the range 0.1–0.4 mA. The geometry of the discharge makes it appropriate for gas decontamination.
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52.50.Dg Plasma sources
52.80.Hc Glow; corona

Multiple substrate microwave plasma-assisted chemical vapor deposition single crystal diamond synthesis

J. Asmussen, T. A. Grotjohn, T. Schuelke, M. F. Becker, M. K. Yaran, D. J. King, S. Wicklein, and D. K. Reinhard

Appl. Phys. Lett. 93, 031502 (2008); http://dx.doi.org/10.1063/1.2961016 (3 pages) | Cited 4 times

Online Publication Date: 23 July 2008

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A multiple substrate, microwave plasma-assisted chemical vapor deposition synthesis process for single crystal diamond (SCD) is demonstrated using a 915 MHz reactor. Diamond synthesis was performed using input chemistries of 6–8% of CH4/H2, microwave input powers of 10–11.5 kW, substrate temperatures of 1100–1200 °C, and pressures of 110–135 Torr. The simultaneous synthesis of SCD over 70 diamond seeds yielded good quality SCD with deposition rates of 14–21 μm/h. Multiple deposition runs totaling 145 h of deposition time added 1.8–2.5 mm of diamond material to each of the 70 seed crystals.
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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
68.55.aj Insulators

Influence of operating pressure on surface dielectric barrier discharge plasma aerodynamic actuation characteristics

Yun Wu, Yinghong Li, Min Jia, Huimin Song, Zhigang Guo, Ximing Zhu, and Yikang Pu

Appl. Phys. Lett. 93, 031503 (2008); http://dx.doi.org/10.1063/1.2964193 (3 pages) | Cited 2 times

Online Publication Date: 24 July 2008

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This letter reports an experimental study of surface dielectric barrier discharge plasma aerodynamic actuation characteristics’ dependence on operating pressure. As the pressure decreases, the N2(C 3Пu) rotational temperature decreases, while its vibrational temperature decreases initially and then increases. In addition, the discharge mode changes from a filamentary type to a glow type at 45 Torr. In the filamentary mode, the electron density decreases with pressure, while the electron temperature remains almost unchanged. In the glow mode, however, both the electron density and the electron temperature increase while the pressure decreases. The induced velocity shows a maximum value at 445 Torr.
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52.30.-q Plasma dynamics and flow
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.80.Hc Glow; corona
47.85.Gj Aerodynamics

Modulating effects of the low-frequency source on ion energy distributions in a dual frequency capacitively coupled plasma

Xiao-Song Li, Zhen-Hua Bi, Da-Lei Chang, Zhi-Cheng Li, Shuai Wang, Xiang Xu, Yong Xu, Wen-Qi Lu, Ai-Min Zhu, and You-Nian Wang

Appl. Phys. Lett. 93, 031504 (2008); http://dx.doi.org/10.1063/1.2945890 (3 pages) | Cited 19 times

Online Publication Date: 24 July 2008

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With the energy resolved quadrupole mass spectrometer and hybrid simulation, the influence of low-frequency (LF) source parameters on the ion energy distributions (IEDs) of argon ions impinging on the grounded electrode was studied, both experimentally and numerically, in a dual frequency capacitively coupled plasma. It was shown that for decreasing LF or increasing LF power, the high energy peak in IEDs shifts toward the high energy region significantly. The simulation results were in general agreement with the experimental data.
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52.25.-b Plasma properties
52.50.Dg Plasma sources
52.65.Ww Hybrid methods
52.70.Nc Particle measurements

Design of fine phosphor system for the improvement in the luminescent properties of the phosphor layer in the plasma display panel: Theoretical and experimental analysis

Chae-Woong Cho, Ungyu Paik, Do-Hyung Park, Yoon-Chang Kim, and Dong-Sik Zang

Appl. Phys. Lett. 93, 031505 (2008); http://dx.doi.org/10.1063/1.2963477 (3 pages) | Cited 10 times

Online Publication Date: 25 July 2008

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Improvement in the luminescent properties of plasma display panels via phosphor size control was theoretically and experimentally investigated. From theoretical analyses of photon extraction and plasma efficiency, fine phosphor system was designed, which was compared with experimental data. The denser microstructure of finer phosphor-based layer promoted photon extraction efficiency by higher reflectivity. Also, the finer phosphor increased vacuum-ultraviolet discharge space and corresponding plasma efficiency via decrease in layer thickness. Based on the results, the phosphor size control improved the panel efficiency by the synergistic effect of improvements in photon extraction and plasma efficiency.
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85.60.Pg Display systems
52.75.-d Plasma devices
78.60.-b Other luminescence and radiative recombination

Experimental observation of the inductive electric field and related plasma nonuniformity in high frequency capacitive discharge

S. K. Ahn and H. Y. Chang

Appl. Phys. Lett. 93, 031506 (2008); http://dx.doi.org/10.1063/1.2965118 (3 pages) | Cited 4 times

Online Publication Date: 25 July 2008

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To elucidate plasma nonuniformity in high frequency capacitive discharges, Langmuir probe and B-dot probe measurements were carried out in the radial direction in a cylindrical capacitive discharge driven at 90 MHz with argon pressures of 50 and 400 mTorr. Through the measurements, a significant inductive electric field (i.e., time-varying magnetic field) was observed at the radial edge, and it was found that the inductive electric field creates strong plasma nonuniformity at high pressure operation. The plasma nonuniformity at high pressure operation is physically similar to the E-H mode transition typically observed in inductive discharges. This result agrees well with the theories of electromagnetic effects in large area and/or high frequency capacitive discharges.
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52.70.Ds Electric and magnetic measurements
52.80.Pi High-frequency and RF discharges
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Phase transformation accommodated plasticity in nanocrystalline nickel

X. Y. Zhang, X. L. Wu, Q. Liu, R. L. Zuo, A. W. Zhu, P. Jiang, and Q. M. Wei

Appl. Phys. Lett. 93, 031901 (2008); http://dx.doi.org/10.1063/1.2953545 (3 pages) | Cited 3 times

Online Publication Date: 21 July 2008

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Based on detailed x-ray diffraction and transmission electron microscopy we have found body-centered-cubic (bcc) Ni upon room-temperature rolling of nanocrystalline (nc) face-centered-cubic (fcc) Ni. The bcc phase forms via the Kurdjumov–Sachs (KS) martensitic transformation mechanism when the von Mises equivalent strain exceeds ∼ 0.3, much higher than accessible in tensile testing. The fcc and bcc phases keep either the KS or the Nishiyama–Wasserman orientation relationship. Our results provide insights into the deformation physics in nc Ni, namely, the fcc-to-bcc phase transformation can also accommodate plasticity at large plastic strains.
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81.30.Kf Martensitic transformations
64.70.kd Metals and alloys
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
62.25.-g Mechanical properties of nanoscale systems
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

In situ metal-organic chemical vapor deposition atomic-layer deposition of aluminum oxide on GaAs using trimethyaluminum and isopropanol precursors

Cheng-Wei Cheng and Eugene A. Fitzgerald

Appl. Phys. Lett. 93, 031902 (2008); http://dx.doi.org/10.1063/1.2960574 (3 pages) | Cited 20 times

Online Publication Date: 21 July 2008

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In situ atomic-layer deposition (ALD) of Al2O3 on p-GaAs in metal-organic chemical vapor deposition system is demonstrated in this article. Isopropanol was chosen as the oxygen source for Al2O3 ALD, instead of common H2O. The ALD mechanism is discussed and it is proposed that water does not form in the process. The saturation growth rate of Al2O3 is about 0.8 Å/cycle. X-ray photoetectron spectroscopy depth profiles were performed and no arsenic oxide is observed at the interface. The capacitance-voltage measurements show a small accumulation capacitance dispersion and voltage shift in the depletion region. The interfacial defect density near the midgap of the GaAs bandgap has been determined with the conductance-frequency method. The interfacial defect density is determined as 2.5×1011 eV−1 cm−2 at the midgap of the GaAs.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.at Other materials
81.15.Kk Vapor phase epitaxy; growth from vapor phase
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Giant effective g-factor in PbxEu1−xTe epitaxial films

E. Heredia, P. H. de Oliveira Rappl, P. Motisuke, A. L. Gazoto, F. Iikawa, and M. J. S. P. Brasil

Appl. Phys. Lett. 93, 031903 (2008); http://dx.doi.org/10.1063/1.2961018 (3 pages) | Cited 4 times

Online Publication Date: 21 July 2008

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We investigated PbxEu1−xTe films with x ⩽ 0.2 by magneto-optical measurements. For x ∼ 0.01, the optical emission is similar to high quality EuTe films with two narrow lines attributed to excitonic recombinations associated with magnetic polarons. For increasing x, the emission becomes dominated by a broader lower energy band, which is very efficient as compared to the binary emission. The magneto-optical properties of the ternary films show various similarities with EuTe results, such as quenchings at similar temperatures and magnetic fields. Most remarkably, they also present a giant effective g-factor that makes this material a strong candidate for spintronic applications.
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78.66.Li Other semiconductors
78.20.Ls Magneto-optical effects
75.70.Ak Magnetic properties of monolayers and thin films
78.55.Hx Other solid inorganic materials
71.38.-k Polarons and electron-phonon interactions
71.35.-y Excitons and related phenomena

Evolution of valence-band alignment with nitrogen content in GaNAs/GaAs single quantum wells

Jun Shao, Wei Lu, M. Sadeghi, Xiang Lü, S. M. Wang, Lili Ma, and A. Larsson

Appl. Phys. Lett. 93, 031904 (2008); http://dx.doi.org/10.1063/1.2958232 (3 pages) | Cited 5 times

Online Publication Date: 21 July 2008

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We report on experimental evidence for the transition of valence-band alignment from type I to type II in GaNxAs1−x/GaAs single quantum wells by photoreflectance measurements. The substitutional nitrogen content covers a range of 1.4%–5.9%. The turning point of the type I–type II transition occurs at x≳4.7%. The experimental observations can be well interpreted by a combination of band anticrossing model and model-solid theory when nonlinear behavior of either the shear deformation potential or the average valence-band energy is taken into account. The effect of dilute nitrogen on the valence-band offset of GaNAs/GaAs quantum well structure is hence clarified.
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73.21.Fg Quantum wells
78.67.De Quantum wells

Modulus mapping of nanoscale closure variants in Ni–Mn–Ga

Yaniv Ganor and Doron Shilo

Appl. Phys. Lett. 93, 031905 (2008); http://dx.doi.org/10.1063/1.2961023 (3 pages) | Cited 3 times

Online Publication Date: 21 July 2008

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The twinned magnetic microstructure of Ni2MnGa ferromagnetic shape-memory alloy is investigated by high resolution nanoscale modulus mapping. A surprisingly fine near-surface nanoscale substructure of closure magnetic twin variants was observed. The lateral distance between adjacent closure variants was found to be 100 nm. The small size of twin variant prisms provides a unique opportunity for evaluating the twin boundary energy by considering the competition between the magnetic field and interface energies. Our estimate shows a relatively small twin boundary energy of 3 ergs/cm2, which suggests the ability of Ni2MnGa to form nanoscale structures of magnetic twin variants.
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61.72.Mm Grain and twin boundaries
75.50.Cc Other ferromagnetic metals and alloys
81.40.Lm Deformation, plasticity, and creep
68.35.Md Surface thermodynamics, surface energies
62.20.F- Deformation and plasticity

Improved GaN film overgrown with a molybdenum nanoisland mask

Chaotong Lin, Guanghui Yu, Xinzhong Wang, Mingxia Cao, Hang Gong, Ming Qi, and Aizhen Li

Appl. Phys. Lett. 93, 031906 (2008); http://dx.doi.org/10.1063/1.2962983 (3 pages) | Cited 3 times

Online Publication Date: 21 July 2008

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We report the improved crystalline and optical quality of GaN film overgrown by hydride vapor phase epitaxy adopting a molybdenum (Mo) nanoisland mask (MNM). The MNM is fabricated following thermal annealing of the nanometer-thick Mo film deposited by electron-beam evaporation. The full width at half maximum values of high-resolution x-ray diffraction (HRXRD) rocking curves for the GaN film with MNM are 188 arc sec (002 reflection) and 219 arc sec (102 reflection), while those for the GaN film without MNM are 256 and 364 arc sec, respectively. This result indicates a significant reduction of dislocation density in the overgrown GaN film with MNM. Photoluminescence spectra measurements reveal the compressive strain relaxation and improvement in the quality of the overgrown GaN film with MNM as compared to the regrown GaN film without MNM, which is consistent with the trend observed by HRXRD.
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81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.ag Semiconductors
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Shear band melting and serrated flow in metallic glasses

K. Georgarakis, M. Aljerf, Y. Li, A. LeMoulec, F. Charlot, A. R. Yavari, K. Chornokhvostenko, E. Tabachnikova, G. A. Evangelakis, D. B. Miracle, A. L. Greer, and T. Zhang

Appl. Phys. Lett. 93, 031907 (2008); http://dx.doi.org/10.1063/1.2956666 (3 pages) | Cited 34 times

Online Publication Date: 23 July 2008

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Scanning electron microscopy observations of shear steps on Zr-based bulk metallic glasses show direct evidence of shear band melting due to heat generated by elastic energy release. The estimated range of attained temperatures and the observed morphologies are consistent with shear steps forming at a subsonic speed limited by a required redistribution of local microscopic stresses. The calculations indicate that a 0.2 μm layer melts in the vicinity of a shear band forming a 1 μm shear step. The plastic part of the stress strain curve is serrated but a majority of shear events are not associated to serrations.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
62.20.de Elastic moduli
61.43.Fs Glasses
81.40.Jj Elasticity and anelasticity, stress-strain relations
64.70.dj Melting of specific substances

Mechanical twinning and omega transition by ⟨111⟩ {112} shear in a metastable β titanium alloy

H. Xing and J. Sun

Appl. Phys. Lett. 93, 031908 (2008); http://dx.doi.org/10.1063/1.2959183 (3 pages) | Cited 7 times

Online Publication Date: 23 July 2008

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{112} ⟨111⟩ mechanical twinning and stress-induced omega transition were observed by high-resolution transmission electron microscope in a metastable β titanium alloy with chemical composition of Ti-23Nb-0.7Ta-2Zr-1.2O at. % after deformation. The orientation relationships between the ω phase and β parent matrix are (math010)ω‖(211)β, [1math10]ω‖[0math1]β and [0001]ω‖[math11]β, and the habit plane of (math010)ω‖(211)β for the stress-induced ω transition is different from that of (0001)ω‖(111)β often observed for the thermal ω transition. Both mechanical twinning and ω transition arise from the shear along ⟨111⟩ {112}. A dislocation mechanism for mechanical twinning and stress-induced ω transition was discussed additionally.
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61.72.Mm Grain and twin boundaries
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.kd Metals and alloys
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
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