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14 Mar 2013

Volume 113, Issue 10, Articles (10xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 113, 103506 (2013); http://dx.doi.org/10.1063/1.4794002 (9 pages)

J. P. Escobedo, E. N. Brown, C. P. Trujillo, E. K. Cerreta, and G.T. Gray, III
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back to top Lasers, Optics, and Optoelectronics
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The effect of blast wave re-focusing on a laser-induced plasma

Stefan Brieschenk, Harald Kleine, and Sean O'Byrne

J. Appl. Phys. 113, 103101 (2013); http://dx.doi.org/10.1063/1.4794017 (8 pages)

Online Publication Date: 8 March 2013

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The effect of laser-induced plasma confinement on lifetime and temperature is reported using cylindrical reflectors. This is determined experimentally in a gas cell, with hydrogen as test gas, and cylindrical shock reflectors of different diameters. The temperature evolution of confined and unconfined laser-induced plasma has been measured using plasma emission spectroscopy. Temperatures were determined through the plasma line-to-continuum thermometry technique in the hydrogen Balmer series using the Hα and Hβ transitions at λ = 656 nm and λ = 486 nm, respectively. The experiments found that re-focusing the blast wave can significantly increase temperatures during the exponential decay of the plasma. The experimental results also show that confinement increases peak plasma temperatures, and that plasma lifetimes are only marginally affected by the confinement.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.70.-m Plasma diagnostic techniques and instrumentation
52.25.-b Plasma properties
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams

Study of sensitization process on mid-infrared uncooled PbSe photoconductive detectors leads to high detectivity

Jijun Qiu, Binbin Weng, Zijian Yuan, and Zhisheng Shi

J. Appl. Phys. 113, 103102 (2013); http://dx.doi.org/10.1063/1.4794492 (5 pages)

Online Publication Date: 11 March 2013

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For nearly a century, oxygen has been widely accepted as the key element that triggers photo-response in polycrystalline PbSe photoconductive detectors. Our photoluminescence and responsivity studies on PbSe samples, however, suggest that oxygen only serves as an effective sensitization improver and it is iodine rather than oxygen that plays the key role in triggering the photo-response. These studies shed light on the sensitization process for detector applications and ways to passivate defects in IV–VI semiconductors. As a result, high peak detectivity of 2.8 × 1010 cm·Hz1/2·W−1 was achieved at room temperature.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Holographic formation of compound photonic crystal and nano-antenna templates through laser interference

Jeff Lutkenhaus, David George, David Garrett, Hualiang Zhang, and Yuankun Lin

J. Appl. Phys. 113, 103103 (2013); http://dx.doi.org/10.1063/1.4795119 (5 pages)

Online Publication Date: 12 March 2013

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This paper presents a holographic formation of compound photonic crystal and nano-antenna templates through a reflective optical element based laser interference. The reflective optical element consists of four Si facets where a circularly polarized single beam impinges at the Brewster angle and is reflected into four linearly s-polarized beams for the inference lithography. By tuning the phase delay in one of the interfering beams, dual-lattice photonic crystal, and nano-antenna templates are fabricated and compared with theoretic simulation. The design conditions for the nano-antenna formation are discussed.
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42.40.-i Holography
42.70.Qs Photonic bandgap materials

Propagation of magnetically controllable lasers and magneto-optic dual switching using nitrogen-vacancy centers in diamond

J.-H. Li, R. Yu, and Y. Wu

J. Appl. Phys. 113, 103104 (2013); http://dx.doi.org/10.1063/1.4795275 (10 pages)

Online Publication Date: 13 March 2013

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We study coherent laser-induced optical behaviors in weak twin-light propagation through strained diamond nitrogen-vacancy (NV) centers via switching on and off an external magnetic field. By numerically solving the coupled Bloch-Maxwell equations for NV center and field simultaneously in space and time, we address dynamic control of pulse propagation and magneto-optic dual switching in such a laser-driven NV center system. The proposed scheme may have applications in the design of magneto-optic switching and magneto-optic storage devices.
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42.60.-v Laser optical systems: design and operation
78.20.Ls Magneto-optical effects
79.20.Ds Laser-beam impact phenomena
61.72.jd Vacancies
41.20.-q Applied classical electromagnetism

Measurement of ionization in direct frequency comb spectroscopy

B. Lomsadze, C. W. Fehrenbach, and B. D. DePaola

J. Appl. Phys. 113, 103105 (2013); http://dx.doi.org/10.1063/1.4794813 (4 pages)

Online Publication Date: 13 March 2013

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Direct frequency comb spectroscopy is currently one of the most precise techniques for studying the internal structure of atomic and molecular systems. In this technique, a train of ultrafast laser pulses excites states in the target system which then relax, emitting fluorescence. The measured fluorescence is then plotted as a function of the comb parameters. But according to recent theory, the ultrashort pulses from the comb laser can also significantly ionize the target. Here, we test this theory by measuring the ion signal from direct frequency comb spectroscopy. Furthermore, instead of actively controlling the frequency comb parameters, we allow them to drift passively, measuring them and the ion signal simultaneously. The experiments were found to be in satisfactory agreement with theory, and the passive comb approach was found to be functional, though not as convenient as the conventional actively locked comb.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)
34.50.Gb Electronic excitation and ionization of molecules

A novel way to improve the quantum efficiency of silicon light-emitting diode in a standard silicon complementary metal–oxide–semiconductor technology

Kaikai Xu and G. P. Li

J. Appl. Phys. 113, 103106 (2013); http://dx.doi.org/10.1063/1.4795170 (6 pages)

Online Publication Date: 13 March 2013

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Silicon diode at avalanche breakdown has visible light emission in the depletion region. It is believed that this optical radiation comes from the kinetic energy loss of carriers generated by impact ionization colliding with immobile charge centers in the avalanche region. A theoretical model is presented to show the correlation of the hot carrier effect with the related photonic emission in high field. Meanwhile, a PMOSFET-like silicon light source device fabricated completely in the standard silicon CMOS process technology is measured to demonstrate that avalanching current is linearly proportional to optical emission power whether this light source acts as a two-terminal device (i.e., diode, the “p+ Source/Drain to n-Substrate junction” with floating the gate) or acts as a three-terminal device (i.e., gate-diode, the “p+ Source/Drain to n-Substrate junction” in the course of varying the gate voltage). Such linearity implies that control of the increasing current is a significant way to enhance the quantum efficiency of this light source device no matter what the physical structure (i.e., two terminals or three terminals) of this device is. For the first time, it has been discovered that, at the same avalanching current, the optical output power in gate-diode structure is higher than the optical output power in diode structure. In other words, for this PMOSFET-like device, the three-terminal operating mode is more efficient than the two-terminal operating mode.
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85.60.Jb Light-emitting devices
85.30.De Semiconductor-device characterization, design, and modeling
85.30.Kk Junction diodes

Laser direct writing of GaN-based light-emitting diodes—The suitable laser source for mesa definition

Rüdiger Moser, Christian Goßler, Michael Kunzer, Klaus Köhler, Wilfried Pletschen, Jens Brunne, Ulrich T. Schwarz, and Joachim Wagner

J. Appl. Phys. 113, 103107 (2013); http://dx.doi.org/10.1063/1.4794844 (13 pages)

Online Publication Date: 14 March 2013

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The development of a process chain allowing for rapid prototyping of GaN-based light-emitting diodes (LEDs) is presented, which does not rely on photolithography. Structuring of the epitaxial layers is realized by direct-writing laser ablation, allowing a flexible chip layout that can be changed rapidly and at low cost. Besides contact metallization and trench formation, mesa definition is the most critical processing step. For mesa formation and to expose the n-GaN contact layer, the epitaxial grown p-GaN layer together with the active region has to be removed completely without forming cracks or crystal defects in the n-GaN layer or the mesa sidewalls, which would cause sidewall leakage currents. In developing an appropriate laser ablation process that meets these requirements, three different laser systems have been employed in a comparative study. These are a frequency-tripled picosecond (ps) Nd:YVO4 laser emitting at a wavelength of 355 nm and a pulse length of 10 ps and two 20 nanosecond (ns) pulse length laser systems, operating at a wavelength of 248 nm (Excimer laser) and 355 nm (frequency-tripled Nd:YVO4 laser), respectively. First, the laser sources are compared regarding the morphological properties of the resulting laser trenches. Due to band filling effects resulting in optical bleaching of the GaN material when irradiating with ps-laser pulses at 355 nm, the resulting ablation process suffers from cracking. Laser ablation using ns-pulses at both 355 nm and 248 nm leads to crack-free material removal up to a well-defined depth. To keep reverse-bias leakage currents at a level comparable to that of conventional dry-etched mesa-LEDs, subsequent wet etching is essential to remove residues in the mesa-trenches irrespective of the laser source used. Besides wet etching, an additional annealing step has to be applied to mesa-trenches fabricated using ns- and ps-laser pulses at a wavelength of 355 nm. Due to the larger penetration depth at 355 nm, defects causing an increased leakage current are generated in the quantum well region during laser irradiation, which manifest themselves by a spectrally broad defect luminescence. To separate and quantify the contributions from the mesa sidewall leakage and from the areal leakage through the p-n-junction, a series of LEDs have been fabricated and analyzed for which the mesa perimeter length was varied while keeping the mesa area constant. In this way, it is shown that laser ablation with ns-pulses at 248 nm results in the lowest sidewall leakage current as well as forward bias voltage-current and output power-current characteristics very similar to those of conventionally dry etched reference LEDs.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.40.Ls Metallization, contacts, interconnects; device isolation

Large electroluminescence excitation cross section and strong potential gain of erbium in ErYb silicate

Bing Wang, Ruimin Guo, Xingjun Wang, Lei Wang, Bing Yin, and Zhiping Zhou

J. Appl. Phys. 113, 103108 (2013); http://dx.doi.org/10.1063/1.4795153 (5 pages)

Online Publication Date: 14 March 2013

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1.53 μm electroluminescence of erbium was observed in ErYb silicate metal-insulator-silicon light emitting device (MISLED). The erbium ions were excited by direct impact of hot carriers at electric field higher than 7 MV/cm. The conduction and carrier injection mechanisms were investigated. The impact excitation cross section of Er ions was measured to be 3 × 10−14 cm2, three times of Er-doped SiO2 MISLED. Rate equation modeling suggests that strong potential material's gain of more than 23 dB/cm from the ErYb silicate may be achieved by electrical pumping.
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85.60.Jb Light-emitting devices
back to top Plasmas and Electrical Discharges

Characterization of the supersonic flowing microwave discharge using two dimensional plasma tomography

M. Nikolić, A. Samolov, F. Čučkov, S. Popović, L. Vušković, and A. Godunov

J. Appl. Phys. 113, 103301 (2013); http://dx.doi.org/10.1063/1.4793494 (6 pages)

Online Publication Date: 11 March 2013

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A tomographic numerical method based on the two-dimensional Radon formula for a cylindrical cavity has been employed for obtaining spatial distributions of the argon excited levels. The spectroscopy measurements were taken at different positions and directions to observe populations of excited species in the plasmoid region and the corresponding excitation temperatures. Excited argon states are concentrated near the tube walls, thus, confirming the assumption that the post discharge plasma is dominantly sustained by travelling surface wave. An automated optical measurement system has been developed for reconstruction of local plasma parameters of the plasmoid structure formed in an argon supersonic flowing microwave discharge. The system carries out angle and distance measurements using a rotating, flat mirror, as well as two high precision stepper motors operated by a microcontroller-based system and several sensors for precise feedback control.
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52.80.Pi High-frequency and RF discharges
02.30.Uu Integral transforms
02.60.-x Numerical approximation and analysis
47.40.Ki Supersonic and hypersonic flows
52.25.-b Plasma properties
52.70.-m Plasma diagnostic techniques and instrumentation

Characterization of nanosecond pulse driven dielectric barrier discharge plasma actuators for aerodynamic flow control

Robert Dawson and Jesse Little

J. Appl. Phys. 113, 103302 (2013); http://dx.doi.org/10.1063/1.4794507 (10 pages)

Online Publication Date: 12 March 2013

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Positive polarity nanosecond pulse driven dielectric barrier discharge (ns-DBD) plasma actuators are studied experimentally in quiescent atmosphere. Pulse energy and instantaneous pulse power (hereafter referred to as energy and power) are calculated using simultaneous voltage and current measurements. Electrical characteristics are evaluated as a function of peak voltage, pulse frequency, discharge length, and dielectric thickness. Schlieren imaging is used to provide a relative estimate of discharge energy that is coupled to the near surface gas as heat for the same parameters. Characteristics of the DBD load have a substantial effect on the individual voltage and current traces which are reflected in the energy and power values. Power is mainly dependent on actuator length which is inconsistent with schlieren data as expected. Higher per unit length energy indicates a stronger compression wave for a given actuator geometry, but this is not universally true across different actuators suggesting some constructions more efficiently couple energy to the gas. Energy and compression wave strength are linearly related. Higher pulse frequency produces higher energy but is primarily attributed to heating of the actuator and power supply components and not to an optimal discharge frequency. Both energy and wave strength increase as peak voltage to the power of approximately 3.5 over a substantial range similar to ac-DBD plasma actuators.
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52.75.-d Plasma devices
52.80.-s Electric discharges
47.85.L- Flow control
52.70.-m Plasma diagnostic techniques and instrumentation

A new method for removing the blackout problem on reentry vehicles

R. L. Stenzel and J. M. Urrutia

J. Appl. Phys. 113, 103303 (2013); http://dx.doi.org/10.1063/1.4795148 (5 pages)

Online Publication Date: 13 March 2013

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Supersonic vehicles are surrounded by a plasma layer which produces a cutoff layer for electromagnetic waves. Methods to remove the layer by gas releases, dc magnetic fields, and E×B flows have been proposed earlier. The present work suggests a new approach which is based on laboratory observations. Ions are expelled by a time varying magnetic field which creates a Hall electric field. The ion expulsion opens up a window of transparency for wave communications.
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95.30.Qd Magnetohydrodynamics and plasmas
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.40.Hf Plasma-material interactions; boundary layer effects
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Temperature and pressure dependent geometry optimization and elastic constant calculations for arbitrary symmetry crystals: Applications to MgSiO3 perovskites

Bin Wen, Tianjiao Shao, Roderick Melnik, Yoshiyuki Kawazoe, and Yongjun Tian

J. Appl. Phys. 113, 103501 (2013); http://dx.doi.org/10.1063/1.4794360 (12 pages)

Online Publication Date: 8 March 2013

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To optimize lattice parameters for arbitrary symmetry crystals under high temperature and high pressure conditions, a new “geometry optimization method for arbitrary symmetry crystals” has been proposed in this work. By minimizing non-equilibrium Gibbs energy functions for a series of deformed crystal configurations, the components of deformation tensors have been obtained, and allowing the optimized crystal lattice parameters to be determined. Based on our method and Zhao's method, a new method for calculating high temperature and high pressure elastic constants in arbitrary symmetry crystals has been deduced. To verify the effectiveness of the new method, the high temperature and high pressure lattice parameters and elastic constants of orthorhombic symmetry MgSiO3 pv have been studied, and a good agreement between calculated and experimental results has been obtained.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.dq Other elastic constants
62.20.F- Deformation and plasticity
62.50.-p High-pressure effects in solids and liquids
61.66.Fn Inorganic compounds

Internal friction associated with the premartensitic transformation and twin boundary motion of Ni50+xMn25−xGa25 (x = 0−2) alloys

Junyi Liu, Jingmin Wang, Chengbao Jiang, and Huibin Xu

J. Appl. Phys. 113, 103502 (2013); http://dx.doi.org/10.1063/1.4794509 (4 pages)

Online Publication Date: 8 March 2013

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The internal friction (IF) during the martensitic transformation (MT) has been extensively studied in NiMnGa alloys. In this paper, temperature dependence of the IF associated with the premartensitic transformation (PMT) and twin boundary motion (TBM) was investigated in Ni50+xMn25−xGa25 (x = 0−2) alloys. Both the composition and frequency had no obvious effect on the IF peak position of the PMT and TBM. With increasing frequency from 0.1 Hz to 5 Hz, the IF peak height corresponding to the TBM was significantly decreased, but was kept constant during the PMT. The observed phenomena were discussed in terms of the different microscopic mechanisms of the TBM and PMT.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
64.70.K- Solid-solid transitions
61.72.Mm Grain and twin boundaries
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.30.Kf Martensitic transformations

Shape memory metamaterials with tunable thermo-mechanical response via hetero-epitaxial integration: A molecular dynamics study

Karthik Guda Vishnu and Alejandro Strachan

J. Appl. Phys. 113, 103503 (2013); http://dx.doi.org/10.1063/1.4794819 (5 pages)

Online Publication Date: 8 March 2013

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We show that nanoscale epitaxial superlattices (SLs) can be used to engineer the energy landscape that governs the martensitic transformation in shape memory alloys and tune their thermo-mechanical response. We demonstrate the approach using large-scale molecular dynamics simulations of a SL material consisting of alternate layers of a shape memory Ni-rich NiAl alloy and NiAl B2 alloy. The non-martensitic NiAl alloy was chosen to reduce the energy barrier that separates the martensite and austenite phases of the SL and its incorporation leads to a reduction in the thermal hysteresis of the transition. This is a desirable feature in applications involving actuation and our approach represents a generally applicable and powerful avenue to engineer desired behavior in mechanically active materials.
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81.30.Kf Martensitic transformations
64.70.K- Solid-solid transitions
68.65.Cd Superlattices

Compensation effects in GaN:Mg probed by Raman spectroscopy and photoluminescence measurements

Ronny Kirste, Marc P. Hoffmann, James Tweedie, Zachary Bryan, Gordon Callsen, Thomas Kure, Christian Nenstiel, Markus R. Wagner, Ramón Collazo, Axel Hoffmann, and Zlatko Sitar

J. Appl. Phys. 113, 103504 (2013); http://dx.doi.org/10.1063/1.4794094 (5 pages)

Online Publication Date: 8 March 2013

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Compensation effects in metal organic chemical vapour deposition grown GaN doped with magnesium are investigated with Raman spectroscopy and photoluminescence measurements. Examining the strain sensitive E2(high) mode, an increasing compressive strain is revealed for samples with Mg-concentrations lower than 7 × 1018 cm−3. For higher Mg-concentrations, this strain is monotonically reduced. This relaxation is accompanied by a sudden decrease in crystal quality. Luminescence measurements reveal a well defined near band edge luminescence with free, donor bound, and acceptor bound excitons as well as a characteristic donor acceptor pair (DAP) luminescence. Following recent results, three acceptor bound excitons and donor acceptor pairs are identified. Along with the change of the strain, a strong modification in the luminescence of the dominating acceptor bound exciton and DAP luminescence is observed. The results from Raman spectroscopy and luminescence measurements are interpreted as fingerprints of compensation effects in GaN:Mg leading to the conclusion that compensation due to defect incorporation triggered by Mg-doping already affects the crystal properties at doping levels of around 7 × 1018 cm−3. Thereby, the generation of nitrogen vacancies is introduced as the driving force for the change of the strain state and the near band edge luminescence.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.jd Vacancies
71.35.-y Excitons and related phenomena
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors

Effects of oxidation on reaction front instabilities and average propagation speed in Ni/Ti multilayer foils

Joel P. McDonald, Robert V. Reeves, Eric D. Jones, Jr., Kathryn A. Chinn, and David P. Adams

J. Appl. Phys. 113, 103505 (2013); http://dx.doi.org/10.1063/1.4794183 (7 pages)

Online Publication Date: 8 March 2013

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Vapor-deposited, equiatomic Ni/Ti multilayer foils exhibit low-speed, self-propagating formation reactions that are characterized by a spin-like reaction front instability. In addition to the intermetallic reaction between Ni and Ti, reactions performed in air can also exhibit a discrete combustion wave associated with the oxidation of Ti. In general, the oxidation wave trails the complex intermetallic reaction front. Multilayers that have a large reactant layer periodicity (≥200 nm) exhibit a decrease in net reaction speed as air pressure is reduced. Oxidation has a much smaller effect on the net propagation speed of multilayers with small layer periodicity (<100 nm). The net propagation speed of the multilayers is increased when air is present, due to the added energy release of Ti oxidation. High-speed optical microscopy shows that the increased front speed is associated with an increased nucleation rate of the reaction bands that typify the spinning reaction instability of the Ni/Ti system.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.05.Cy Elemental semiconductors
81.65.Mq Oxidation
64.60.qj Studies of nucleation in specific substances
73.21.Ac Multilayers

The effect of shock-wave profile on dynamic brittle failure

J. P. Escobedo, E. N. Brown, C. P. Trujillo, E. K. Cerreta, and G.T. Gray, III

J. Appl. Phys. 113, 103506 (2013); http://dx.doi.org/10.1063/1.4794002 (9 pages)

Online Publication Date: 8 March 2013

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The influence of shock-wave-loading profile on the failure processes in a brittle material has been investigated. Tungsten heavy alloy (WHA) specimens have been subjected to two shock-wave loading profiles with a similar peak stress of 15.4 GPa but different pulse durations. Contrary to the strong dependence of strength on wave profile observed in ductile metals, for WHA, specimens subjected to different loading profiles exhibited similar spall strength and damage evolution morphology. Post-mortem examination of recovered samples revealed that dynamic failure for both loading profiles is dominated by brittle cleavage fracture, with additional energy dissipation through crack branching in the more brittle tungsten particles. Overall, in this brittle material, all relevant damage kinetics and the spall strength are shown to be dominated by the shock peak stress, independent of pulse duration.
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62.50.Ef Shock wave effects in solids and liquids
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mj Brittleness
62.20.mm Fracture
62.20.mt Cracks

Shock-induced phase transitions of α-Ce3Al

Yuankan Fang, Chuanmin Meng, Wenjun Zhu, Duanwei He, Gaohui Du, and Jianzhong Jiang

J. Appl. Phys. 113, 103507 (2013); http://dx.doi.org/10.1063/1.4793282 (5 pages)

Online Publication Date: 11 March 2013

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A series of shock compression experiments on hexagonal α-Ce3Al have been carried out using a two-stage light gas gun. No phase transition was observed in the recovered sample shock compressed at 23.5 GPa. However, as the shock pressure was increased to 27.3 GPa, a face-centered cubic Ce3Al phase was detected in the samples recovered at ambient conditions. Furthermore, a Ce2Al phase was found in the 37.1 GPa shocked sample with a space group Fd-3m and lattice parameter a = 8.26(1) Å. These Ce-based alloys may have potential industrial applications due to the heavy-fermion related properties.
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62.50.Ef Shock wave effects in solids and liquids
64.70.K- Solid-solid transitions
61.66.Dk Alloys
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Origin of ultrafast Ag radiotracer diffusion in shear bands of deformed bulk metallic glass Pd40Ni40P20

K. L. Ngai and Hai Bin Yu

J. Appl. Phys. 113, 103508 (2013); http://dx.doi.org/10.1063/1.4795260 (7 pages)

Online Publication Date: 13 March 2013

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Measurements of Ag radiotracer diffusion in shear bands of deformed bulk metallic glass, Pd40Ni40P20 [Bokeloh et al., Phys. Rev. Lett. 107, 235503 (2011)], have found a colossal enhancement of diffusion coefficient by more than eight orders of magnitude than in undeformed Pd40Ni40P20. Suggestion was made by Bokeloh et al. that enhanced diffusion occurs in high-mobility pathways originating from some excess free volume distribution inside the shear bands. Although plausible, this qualitative suggestion does not allow quantitative calculation of the enhancement. The impasse is avoided by using the coupling model to calculate the maximum of the enhancement of diffusivity possible in high-mobility pathways of the shear bands. Within the range of eight to ten orders of magnitude, the calculated maximum enhancement is capable to account for the experimental observation.
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66.30.-h Diffusion in solids
72.15.Gd Galvanomagnetic and other magnetotransport effects
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.43.Fs Glasses

Defects in N, O and N, Zn implanted ZnO bulk crystals

J. E. Stehr, X. J. Wang, S. Filippov, S. J. Pearton, I. G. Ivanov, W. M. Chen, and I. A. Buyanova

J. Appl. Phys. 113, 103509 (2013); http://dx.doi.org/10.1063/1.4795261 (9 pages)

Online Publication Date: 13 March 2013

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Comprehensive characterization of defects formed in bulk ZnO single crystals co-implanted with N and Zn as well as N and O atoms is performed by means of optically detected magnetic resonance (ODMR) complemented by Raman and photoluminescence (PL) spectroscopies. It is shown that in addition to intrinsic defects such as Zn vacancies and Zn interstitials, several N-related defects are formed in the implanted ZnO. The prevailed configuration of the defects is found to depend on the choices of the co-implants and also the chosen annealing ambient. Specifically, co-implantation with O leads to the formation of (i) defects responsible for local vibrational modes at 277, 511, and 581 cm−1; (ii) a N-related acceptor with the binding energy of 160 ± 40 meV that is involved in the donor-acceptor pair emission at 3.23 eV; and (iii) a deep donor and a deep NO acceptor revealed from ODMR. Activation of the latter defects is found to require post-implantation annealing in nitrogen ambient. None of these defects are detected when N is co-implanted with Zn. Under these conditions, the dominant N-induced defects include a deep center responsible for the 3.3128 eV PL line, as well as an acceptor center of unknown origin revealed by ODMR. Formation mechanisms of the studied defects and their role in carrier recombination are discussed.
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61.72.uj III-V and II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
61.72.jd Vacancies
61.72.jj Interstitials

Gate modulation on angle-resolved photoabsorption spectra of zigzag-edge graphene nanoribbons

Wen-Huan Zhu, Guo-Hui Ding, and Bing Dong

J. Appl. Phys. 113, 103510 (2013); http://dx.doi.org/10.1063/1.4795124 (5 pages)

Online Publication Date: 13 March 2013

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Graphene nanoribbons (GNRs) exhibit novel and special electronic and optical properties with promising technological applications. The gate modulation on angle-resolved photoabsorption spectra of zigzag-edge GNRs (ZGNRs) is investigated based on the Hubbard model in the Hartree-Fock approximation. By examining the electron transition processes and the optical selection rules taking into account the Coulomb interaction effect, we demonstrate that the excitations from the edge states of ZGNRs are essential for the optical properties in the neutral case, and show the energy of the absorption peaks has the dispersion and splitting effects with increasing momentum transfer from the incident light. By modulating the chemical potential of ZGNRs, the intraband transitions which are forbidden for the neutral ZGNRs at zero temperature become important for the low energy optical properties, and a Drude peak of the optical conductivity emerges in the low frequency region.
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78.67.Wj Optical properties of graphene
61.46.-w Structure of nanoscale materials
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Atomic resolution mapping of interfacial intermixing and segregation in InAs/GaSb superlattices: A correlative study

Honggyu Kim, Yifei Meng, Jean-Luc Rouviére, Dieter Isheim, David N. Seidman, and Jian-Min Zuo

J. Appl. Phys. 113, 103511 (2013); http://dx.doi.org/10.1063/1.4794193 (6 pages)

Online Publication Date: 13 March 2013

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We combine quantitative analyses of Z-contrast images with composition analyses employing atom probe tomography (APT) correlatively to provide a quantitative measurement of atomic scale interfacial intermixing in an InAs/GaSb superlattice (SL). Contributions from GaSb and InAs in the Z-contrast images are separated using an improved image processing technique. Correlation with high resolution APT composition analyses permits an examination of interfacial segregation of both cations and anions and their incorporation in the short period InAs/GaSb SL. Results revealed short, intermediate, and long-range intermixing of In, Ga, and Sb during molecular beam epitaxial growth and their distribution in the SL.
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68.35.Dv Composition, segregation; defects and impurities
68.47.Fg Semiconductor surfaces
68.65.Cd Superlattices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors

Pressure induced phase transitions in TiH2

Guoying Gao, Aitor Bergara, Guangtao Liu, and Yanming Ma

J. Appl. Phys. 113, 103512 (2013); http://dx.doi.org/10.1063/1.4795164 (4 pages)

Online Publication Date: 13 March 2013

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Recent room temperature experiments on TiH2 [Kalita et al., J. Appl. Phys. 108, 043511 (2010)], an important compound in hydrogen storage research, revealed a cubic (fcc, Fm-3m) to tetragonal (bct, I4/mmm) phase transition at around 0.6 GPa, which was suggested to remain stable up to at least 90 GPa. However, the simulated X-ray diffraction (XRD) pattern of the I4/mmm structure cannot explain all the diffraction peaks observed at 90 GPa. In this article, we apply the recently developed particle swarm optimization algorithm for crystal structure prediction to propose that at 63 GPa TiH2 presents a further phase transition from I4/mmm to P4/nmm, which we have also confirmed is dynamically and enthalpically stable up to 294 GPa. Moreover, the XRD patterns and calculated lattice parameters of the P4/nmm structure are in good agreement with the experimental available data. Above 294 GPa, we predict a monoclinic P21/m structure to be stable.
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64.70.K- Solid-solid transitions
61.66.Fn Inorganic compounds
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
62.50.-p High-pressure effects in solids and liquids

Effects of flexural and extensional excitation modes on the transmission spectrum of phononic crystals operating at gigahertz frequencies

Seyedhamidreza Alaie, Mehmet F. Su, Drew F. Goettler, Ihab El-Kady, and Zayd Leseman

J. Appl. Phys. 113, 103513 (2013); http://dx.doi.org/10.1063/1.4790485 (8 pages)

Online Publication Date: 13 March 2013

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Phononic crystals (PnCs) are a class of materials that are capable of manipulating elastodynamic waves. Much of the research on PnCs, both theoretical and experimental, focus on studying the transmission spectrum of PnCs in an effort to characterize and engineer their phononic band gaps. Although most studies have shown acceptable agreement between the theoretical and experimental bandgaps, perfect matches are elusive. A framework is presented wherein two and three dimensional harmonic finite element analyses are utilized to study their mechanical behavior for the purpose of more accurately predicting the spectral properties of PnCs. Discussions on a Harmonic Finite Elements Analysis formulation of a perfectly matched layer absorbing boundary and how reflections from absorbing boundaries can be inferred via standing wave ratios are provided. Comparisons between 2D and 3D analyses are presented that show the less computationally intensive 2D models are equally accurate under certain conditions. Finally, it is shown that a surface excitation boundary condition in a 3D model can significantly improve understanding of the experimental results for PnCs excited by surface mounted excitation sources.
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63.20.-e Phonons in crystal lattices
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
02.60.-x Numerical approximation and analysis

Helium at elevated pressures: Quantum liquid with non-static shear rigidity

D. Bolmatov, V. V. Brazhkin, and K. Trachenko

J. Appl. Phys. 113, 103514 (2013); http://dx.doi.org/10.1063/1.4795340 (4 pages)

Online Publication Date: 14 March 2013

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The properties of liquid helium have always been a fascinating subject to scientists. The phonon theory of liquids, taking into account liquid non-static shear rigidity, is employed here for studying internal energy and heat capacity of compressed liquid 4He. We demonstrate the good agreement of calculated and experimental heat capacity of liquid helium at elevated pressures and supercritical temperatures. Unexpectedly, helium remains a quantum liquid at elevated pressures for a wide range of temperature supporting both longitudinal and transverse-like phonon excitations. We have found that in the very wide pressure range of 5 MPa-500 MPa, liquid helium near melting temperature is both solid-like and quantum.
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67.25.bd Thermodynamic properties
62.10.+s Mechanical properties of liquids
65.20.Jk Studies of thermodynamic properties of specific liquids
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