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15 Feb 2010

Volume 107, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 107, 041101 (2010); http://dx.doi.org/10.1063/1.3318287 (13 pages)

Y. C. Tao and J. G. Hu
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Superconducting spintronics: Spin-polarized transport in superconducting junctions with ferromagnetic semiconducting contact

Y. C. Tao and J. G. Hu

J. Appl. Phys. 107, 041101 (2010); http://dx.doi.org/10.1063/1.3318287 (13 pages) | Cited 2 times

Online Publication Date: 25 February 2010

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Superconducting spintronics is one of the most attractive subjects of spintronics. This article reviews superconducting spintronics based on the superconducting junctions with ferromagnetic semiconducting contact. The authors summarize recent theoretical developments with an emphasis on the interplay between ferromagnetic semiconductor (FS) and superconductor (SC). It is found that the spin-polarized transport in the superconducting junctions exhibits a rich dependence on hole types of FS, mismatches in the effective mass and Fermi velocity of holes between the FS and SC, as well as strengths of potential scattering at the interface. These systems have great intrinsic scientific importance and potential device applications including signal processing and general purpose computing.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
72.25.Mk Spin transport through interfaces
72.25.Dc Spin polarized transport in semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
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back to top Lasers, Optics, and Optoelectronics

Comparison of the performance of photonic band-edge liquid crystal lasers using different dyes as the gain medium

Carrie Mowatt, Stephen M. Morris, Myoung Hoon Song, Timothy D. Wilkinson, Richard H. Friend, and Harry J. Coles

J. Appl. Phys. 107, 043101 (2010); http://dx.doi.org/10.1063/1.3284939 (9 pages) | Cited 12 times

Online Publication Date: 16 February 2010

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The primary concern of this work is to study the emission characteristics of a series of chiral nematic liquid crystal lasers doped with different laser dyes (DCM, pyrromethene 580, and pyrromethene 597) at varying concentrations by weight (0.5–2 wt %) when optically pumped at 532 nm. Long-wavelength photonic band-edge laser emission is characterized in terms of threshold energy and slope efficiency. At every dye concentration investigated, the pyrromethene 597-doped lasers exhibit the highest slope efficiency (ranging from 15% to 32%) and the DCM-doped lasers the lowest (ranging from 5% to 13%). Similarly, the threshold was found to be, in general, higher for the DCM-doped laser samples in comparison to the pyrromethene-doped laser samples. These results are then compared with the spectral properties, quantum efficiencies and, where possible, fluorescence lifetimes of the dyes dispersed in a common nematic host. In accordance with the low thresholds and high slope efficiencies, the results show that the molar extinction coefficients and quantum efficiencies are considerably larger for the pyrromethene dyes in comparison to DCM, when dispersed in the liquid crystal host.
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42.55.Mv Dye lasers
42.55.Tv Photonic crystal lasers and coherent effects
42.60.By Design of specific laser systems
42.70.Hj Laser materials

Generation of a dynamic polarized laser beam for applications in laser welding

Stephan Gräf, Gisbert Staupendahl, Carlo Seiser, Bernd-Jürgen Meyer, and Frank A. Müller

J. Appl. Phys. 107, 043102 (2010); http://dx.doi.org/10.1063/1.3295911 (6 pages)

Online Publication Date: 18 February 2010

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The temporal control and optimization of laser beam parameters, e.g., the beam power, can be employed to enhance the quality and reliability of the welding process. Until now, the influence of a time-dependent beam polarization has been less investigated in welding. The publication describes a new experimental arrangement allowing the fast variation of the polarization of CO2 laser radiation [“dynamic polarization” (DP)]. The key element of the setup is a high power interference laser beam modulator for cw laser power rating of up to 4 kW. Weld seams were produced with different process parameters in the technically relevant steels St37 and Ck45 and in the precoated steel 22MnB5 (USIBOR 1500P). The welds were subsequently characterized by roughness measurements of the top bead surfaces and by the preparation of cross sections and their macroscopic analysis. The experiments on welding with DP showed a significant influence on the keyhole and melt pool dynamics, especially a reduction in the top bead roughness at certain DP frequencies up to a factor of about 3. In addition, a threshold behavior for this effect was observed. It was shown that the cross sectional shape and thus the degree of energy coupling to the material was unaffected by the DP. Finally, during welding USIBOR 1500P with DP an enhanced melt pool stirring was achieved. The results show that the temporal modulation of energy coupling to the material caused by DP is suitable to enhance the quality and reliability of the welding process.
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42.62.Cf Industrial applications

Highly efficient blue organic light emitting device using indium-free transparent anode Ga:ZnO with scalability for large area coating

Liang Wang, Dean W. Matson, Evgueni Polikarpov, James S. Swensen, Charles C. Bonham, Lelia Cosimbescu, Joseph J. Berry, David S. Ginley, Daniel J. Gaspar, and Asanga B. Padmaperuma

J. Appl. Phys. 107, 043103 (2010); http://dx.doi.org/10.1063/1.3282526 (8 pages) | Cited 5 times

Online Publication Date: 19 February 2010

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Organic light emitting devices have been achieved with an indium-free transparent anode, Ga doped ZnO (GZO). A large area coating technique was used (RF magnetron sputtering) to deposit the GZO films onto glass. The respective organic light emitting devices exhibited an operational voltage of 3.7 V, an external quantum efficiency of 17%, and a power efficiency of 39 lm/W at a current density of 1 mA/cm2. These parameters are well within acceptable standards for blue OLEDs to generate a white light with high enough brightness for general lighting applications. It is expected that high-efficiency, long-lifetime, large area, and cost-effective white OLEDs can be made with these indium-free anode materials.
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85.60.Jb Light-emitting devices
81.05.Dz II-VI semiconductors
81.15.Cd Deposition by sputtering

Shape measurement of objects using an ultrafast optical Kerr gate of bismuth glass

Wenjiang Tan (谭文疆), Yi Yang (杨毅), Jinhai Si (司金海), Junyi Tong (佟俊仪), Wenhui Yi (易文辉), Feng Chen (陈烽), and Xun Hou (侯洵)

J. Appl. Phys. 107, 043104 (2010); http://dx.doi.org/10.1063/1.3310492 (3 pages) | Cited 4 times

Online Publication Date: 22 February 2010

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An ultrafast optical Kerr gate of Bi2O3–B2O3–SiO2 oxide glass (BI glass) was used in an ultrafast time-resolved imaging system for shape measurement of objects. The experimental results showed that the longitudinal resolution of the imaging system using the ultrafast optical Kerr gate was less than 20 μm and the measurements of object shape using the ultrafast optical Kerr gate of BI glass had more advantages compared with that using CS2.
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06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.79.-e Optical elements, devices, and systems
06.60.Jn High-speed techniques (microsecond to femtosecond)

Increasing the coupling efficiency of a microdisk laser to waveguides by using well designed spiral structures

Danyu Liu, Haroldo T. Hattori, Lan Fu, Hark Hoe. Tan, and Chennupati Jagadish

J. Appl. Phys. 107, 043105 (2010); http://dx.doi.org/10.1063/1.3309748 (8 pages) | Cited 1 time

Online Publication Date: 23 February 2010

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In this article, we optimize the coupling efficiency from a GaAs microdisk resonator into a single mode spiral waveguide. A classical microdisk resonator coupling light into a nonevanescent straight waveguide reaches a typical coupling efficiency of 67%. We show that the introduction of a spiral waveguide that works both as a waveguide and circular Bragg reflector can improve such efficiency to almost 90%. The same structure with the addition of a taper can couple up to 80% of the generated power into a slot waveguide.
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42.55.Sa Microcavity and microdisk lasers

Interaction of a high-power laser beam with metal sheets

C. D. Boley, K. P. Cutter, S. N. Fochs, P. H. Pax, M. D. Rotter, A. M. Rubenchik, and R. M. Yamamoto

J. Appl. Phys. 107, 043106 (2010); http://dx.doi.org/10.1063/1.3284204 (5 pages) | Cited 1 time

Online Publication Date: 24 February 2010

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Experiments with a high-power laser beam directed onto thin aluminum sheets, with a large spot size, demonstrate that airflow produces a strong enhancement of the interaction. The enhancement is explained in terms of aerodynamic effects. As laser heating softens the material, the airflow-induced pressure difference between front and rear faces causes the metal to bulge into the beam. The resulting shear stresses rupture the material and remove it at temperatures well below the melting point. The material heating is shown to conform to an elementary model. We present an analytic model of elastic bulging. Scaling with respect to spot size, wind speed, and material parameters is determined.
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79.20.Ds Laser-beam impact phenomena
78.47.J- Ultrafast spectroscopy (<1 psec)
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
64.70.dj Melting of specific substances

Near infrared quantum cutting in heavy Yb doped Ce0.03Yb3xY(2.97−3x)Al5O12 transparent ceramics for crystalline silicon solar cells

Hui Lin, Shengming Zhou, Hao Teng, Yukun Li, Wenjie Li, Xiaorui Hou, and Tingting Jia

J. Appl. Phys. 107, 043107 (2010); http://dx.doi.org/10.1063/1.3298907 (4 pages) | Cited 10 times

Online Publication Date: 25 February 2010

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Near infrared (NIR) quantum cutting involving the conversion of an absorbed blue photon into two NIR photons emission has been realized in heavy Yb doped Ce0.03Yb3xY(2.97−3x)Al5O12 (x = 0.1, 0.25, and 0.5) transparent ceramics. Upon the 467 nm excitation, the energy transfer process was dominated by the cooperative downconversion from the 5d1 state of one Ce3+ ion to the math5/2 state of two Yb3+ ions. The influence of the Ce4+–Yb2+ charge transfer state (CTS) should not contribute much to the energy transfer process for the large energy gap between Ce3+:5d1 and the CTS. The calculated quantum yield of Yb3+ for the x = 0.25 sample without concentration quenching was 175.4%.
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88.40.H- Solar cells (photovoltaics)
71.20.Mq Elemental semiconductors
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions

Highly nonlinear tellurite microstructured fibers for broadband wavelength conversion and flattened supercontinuum generation

Guanshi Qin, Xin Yan, Chihiro Kito, Meisong Liao, Takenobu Suzuki, Atsushi Mori, and Yasutake Ohishi

J. Appl. Phys. 107, 043108 (2010); http://dx.doi.org/10.1063/1.3311566 (4 pages) | Cited 2 times

Online Publication Date: 25 February 2010

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We demonstrate four-wave mixing-based broadband (>68 nm) wavelength conversion and flattened supercontinuum generation spanning from 900 to 2800 nm in a 36-cm-long tellurite microstructured fiber which has a high nonlinearity. By reducing the size of air holes of the tellurite microstructured fibers, single mode propagation and small dispersion slope are obtained without the propagation loss enhancement. Our results show that chromatic-dispersion controlled tellurite microstructured fibers are promising candidates for nonlinear applications.
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42.81.Bm Fabrication, cladding, and splicing
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.81.Dp Propagation, scattering, and losses; solitons

Rate equations analysis of external-cavity quantum cascade lasers

Q. K. Yang, B. Hinkov, F. Fuchs, W. Bronner, K. Köhler, J. Wagner, R. Maulini, and J. Faist

J. Appl. Phys. 107, 043109 (2010); http://dx.doi.org/10.1063/1.3309764 (7 pages) | Cited 1 time

Online Publication Date: 26 February 2010

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We present a comprehensive analysis of an external-cavity (EC) quantum cascade (QC) laser system, which is based on a coupled-mode system with the length of the EC set equal to that of the laser chip and accommodating the large difference in physical cavity length by introducing an effective speed of light for light propagating in the EC. By analyzing the rate equations and discussing the cross sections and losses of the EC QC lasers, numerical results as well as suggestions for a further optimization of the spectral tuning range of the EC system are presented. Besides, the delayed onset of the EC modes with respect to that of the internal Fabry–Perot modes in pulsed operation has been simulated using the rate equations, yielding a good agreement with the experimental data.
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42.55.Px Semiconductor lasers; laser diodes
42.25.Bs Wave propagation, transmission and absorption
07.60.Ly Interferometers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Superintense fields from multiple ultrashort laser pulses retroreflected in circular geometry

C. H. Raymond Ooi

J. Appl. Phys. 107, 043110 (2010); http://dx.doi.org/10.1063/1.3296128 (5 pages) | Cited 1 time

Online Publication Date: 26 February 2010

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Laser field with superintensity beyond 1029 W/cm2 can be generated by coherent superposition of multiple 100 fs laser pulses in circular geometry setup upon retroreflection by a ring mirror. We have found the criteria for attaining such intensities using broadband ring mirror within the practical damage threshold and paraxial focusing regime. Simple expressions for the intensity enhancement factor are obtained, providing insight for achieving unlimited laser intensity. Higher intensities can be achieved by using few-cycle laser pulses.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
back to top Plasmas and Electrical Discharges

Microwave breakdown in waveguide filters, numerical simulation, and comparison to experiments

K. Frigui, D. Baillargeat, A. Catherinot, S. Bila, S. Verdeyme, J. Puech, and D. Pacaud

J. Appl. Phys. 107, 043301 (2010); http://dx.doi.org/10.1063/1.3298458 (11 pages)

Online Publication Date: 16 February 2010

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Microwave breakdowns in output multiplexer filters, boarded on telecommunications satellites, can affect the device and damage it. During tests at atmospheric pressure, these breakdowns are generally initiated in the vicinity of a noble metal coated frequency adjustment screw. A modeling of the microwave breakdown ignition is developed taking into account the thermoelectronic emission from the screw and the noble metal atom vaporization. The influence of field strength is particularly investigated to predict the breakdown delay after the application of the microwave power. Then, a specific structure has been designed and built and a dedicated measurement procedure has been proposed. As it will be shown, the test structure experimental behavior agrees well with the theoretical one. Finally, the results given by the numerical modeling of microwave breakdown are compared to the measurements performed in a five-pole filter of an output multiplexer.
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84.30.Vn Filters
02.60.-x Numerical approximation and analysis
84.40.Az Waveguides, transmission lines, striplines

Prediction of UV spectra and UV-radiation damage in actual plasma etching processes using on-wafer monitoring technique

Butsurin Jinnai, Seiichi Fukuda, Hiroto Ohtake, and Seiji Samukawa

J. Appl. Phys. 107, 043302 (2010); http://dx.doi.org/10.1063/1.3313924 (6 pages) | Cited 4 times

Online Publication Date: 19 February 2010

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UV radiation during plasma processing affects the surface of materials. Nevertheless, the interaction of UV photons with surface is not clearly understood because of the difficulty in monitoring photons during plasma processing. For this purpose, we have previously proposed an on-wafer monitoring technique for UV photons. For this study, using the combination of this on-wafer monitoring technique and a neural network, we established a relationship between the data obtained from the on-wafer monitoring technique and UV spectra. Also, we obtained absolute intensities of UV radiation by calibrating arbitrary units of UV intensity with a 126 nm excimer lamp. As a result, UV spectra and their absolute intensities could be predicted with the on-wafer monitoring. Furthermore, we developed a prediction system with the on-wafer monitoring technique to simulate UV-radiation damage in dielectric films during plasma etching. UV-induced damage in SiOC films was predicted in this study. Our prediction results of damage in SiOC films shows that UV spectra and their absolute intensities are the key cause of damage in SiOC films. In addition, UV-radiation damage in SiOC films strongly depends on the geometry of the etching structure. The on-wafer monitoring technique should be useful in understanding the interaction of UV radiation with surface and in optimizing plasma processing by controlling UV radiation.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
61.82.Ms Insulators
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.40.Ha Other nonmetallic inorganics
77.55.-g Dielectric thin films

Laser wavelength effects on the charge state resolved ion energy distributions from laser-produced Sn plasma

Russell A. Burdt, Yezheng Tao, Mark S. Tillack, Sam Yuspeh, Nek M. Shaikh, Eli Flaxer, and Farrokh Najmabadi

J. Appl. Phys. 107, 043303 (2010); http://dx.doi.org/10.1063/1.3309413 (8 pages) | Cited 5 times

Online Publication Date: 22 February 2010

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The effects of laser wavelength on the charge state resolved ion energy distributions from laser-produced Sn plasma freely expanding into vacuum are investigated. Planar Sn targets are irradiated at laser wavelengths of 10.6 and 1.064 μm and intensities of 1.8×1010 and 3.4×1011 W/cm2, respectively. These parameters are relevant to the extreme ultraviolet x-ray source application. An electrostatic deflection probe and single channel electron multiplier are used to record the charge state resolved ion energy distributions 100 cm from the laser plasma source. At the longer laser wavelength, higher charge state ions are observed. At both laser wavelengths, the peak ion energies increase approximately linearly as a function of charge state, and all ion energies greatly exceed the initial thermal electron temperature. The differences in the ion energy distributions are attributed to the laser wavelength dependence of the laser energy absorption, the resulting plasma density in the corona, and the subsequent recombination after the laser pulse. Numerical simulations of the plasma expansion from a collisional-radiative steady state model support the experimental results.
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42.62.-b Laser applications
47.85.M- Material processing flows; industrial applications
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
02.60.-x Numerical approximation and analysis

Role of metastable atoms in the propagation of atmospheric pressure dielectric barrier discharge jets

Qing Li, Xi-Ming Zhu, Jiang-Tao Li, and Yi-Kang Pu

J. Appl. Phys. 107, 043304 (2010); http://dx.doi.org/10.1063/1.3295914 (7 pages) | Cited 4 times

Online Publication Date: 22 February 2010

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In the experiment of plasma jets generated in a tube dielectric barrier discharge configuration, three distinguishable modes, namely, laminar, transition, and turbulent jet modes, have been identified. Flows of helium, neon, and argon gases shared the hydrodynamic law when their plasma jets spraying into ambient air of atmospheric pressure and room temperature. Aiming to reveal the basic processes, we propose that plasma jet length is mainly determined by reactions involving metastable atoms. These processes are responsible for the variation in plasma jet length versus gas flow rate and working gas species. To investigate this proposal in detail, we have obtained three significant experimental results, i.e., (1) the plasma jet lengths of helium, neon, and argon are different; (2) the plasma jet length of krypton slightly changes with gas flow rate, with three modes indistinguishable; and (3) there are large differences between optical emission spectra of helium, neon, argon, and krypton flow gases. These observations are in good agreement with our proposal.
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52.30.-q Plasma dynamics and flow
52.35.Ra Plasma turbulence
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.20.-j Elementary processes in plasmas

Dynamics of reactive high-power impulse magnetron sputtering discharge studied by time- and space-resolved optical emission spectroscopy and fast imaging

M. Hala, N. Viau, O. Zabeida, J. E. Klemberg-Sapieha, and L. Martinu

J. Appl. Phys. 107, 043305 (2010); http://dx.doi.org/10.1063/1.3305319 (9 pages) | Cited 11 times

Online Publication Date: 24 February 2010

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Time- and space-resolved optical emission spectroscopy and fast imaging were used for the investigation of the plasma dynamics of high-power impulse magnetron sputtering discharges. 200 μs pulses with a 50 Hz repetition frequency were applied to a Cr target in Ar, N2, and N2/Ar mixtures and in a pressure range from 0.7 to 2.66 Pa. The power density peaked at 2.2–6 kW cm−2. Evidence of dominating self-sputtering was found for all investigated conditions. Up to four different discharge phases within each pulse were identified: (i) the ignition phase, (ii) the high-current metal-dominated phase, (iii) the transient phase, and (iv) the low-current gas-dominated phase. The emission of working gas excited by fast electrons penetrating the space in-between the electrodes during the ignition phase spread far outwards from the target at a speed of 24 km s−1 in 1.3 Pa of Ar and at 7.5 km s−1 in 1.3 Pa of N2. The dense metal plasma created next to the target propagated in the reactor at a speed ranging from 0.7 to 3.5 km s−1, depending on the working gas composition and the pressure. In fact, it increased with higher N2 concentration and lower pressure. The form of the propagating plasma wave changed from a hemispherical shape in Ar, to a droplike shape extending far from the target in N2. An important N2 emission rise in the latter case was detected during the transition at the end of the metal-dominated phase.
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52.80.Pi High-frequency and RF discharges
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Measurement of interfacial shear strength in single wall carbon nanotubes reinforced composite using Raman spectroscopy

Debdulal Roy, Sanjib Bhattacharyya, A. Rachamim, A. Plati, and Marie-Louise Saboungi

J. Appl. Phys. 107, 043501 (2010); http://dx.doi.org/10.1063/1.3295907 (6 pages) | Cited 2 times

Online Publication Date: 16 February 2010

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A novel method of measuring interfacial shear strength using Raman peak shift is reported. Carbon nanotubes (CNT) functionalized with biomolecules have been used to form a composite with polyvinyl alcohol. Type I collagen has proven to improve the load transfer from the matrix to the tubes leading to improvement of interfacial shear strength. Collagen interacts with single wall CNTs and probably wraps around it. When a composite structure is formed with the collagen, load transfer takes place through the collagen molecule. The interfacial strength of the nanotubes-matrix interface was found to be larger than 160 MPa, which is significantly higher than that observed before. A similar shear strength is estimated using a simple analytical calculation.
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62.25.-g Mechanical properties of nanoscale systems
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties
78.30.-j Infrared and Raman spectra
78.67.Sc Nanoaggregates; nanocomposites

Nitridation behavior of sapphire using a carbon-saturated N2–CO gas mixture

Hiroyuki Fukuyama, Katsuhito Nakamura, Toshiaki Aikawa, Hidekazu Kobatake, Akira Hakomori, Kazuya Takada, and Kenji Hiraga

J. Appl. Phys. 107, 043502 (2010); http://dx.doi.org/10.1063/1.3272692 (7 pages) | Cited 2 times

Online Publication Date: 16 February 2010

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The authors previously developed a sapphire nitridation method using carbon-saturated N2–CO gas mixture to form a high-quality AlN film for III-nitride-based optoelectronic devices. In this study, the nitridation behavior of (0001) (c) plane and (11math0) (a) plane sapphire was studied to elucidate and optimize the process at temperatures of 1823 and 1873 K. The AlN film thickness, surface morphology, crystal quality, and interfacial phenomena were investigated as functions of nitridation time and temperature. Fundamentally, the AlN film grows as a result of the diffusion process that occurs in the AlN film. The voids found at the AlN/sapphire interface indicate that the Al2O3 dissociates into Al3+ and O2− ions, and that the ions diffuse in the AlN film. However, the growth rate of AlN film does not obey the simple diffusion model. The AlN film thickness has a maximum and decreases slightly with time, which indicates that the thermal decomposition of AlN film must be considered when comprehensively describing the nitridation process.
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81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
81.05.Cy Elemental semiconductors
61.72.Qq Microscopic defects (voids, inclusions, etc.)
78.66.Fd III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.ag Semiconductors

Anomalous and normal Hall effect in hydrogenated amorphous Si prepared by plasma enhanced chemical vapor deposition

I. Crupi, S. Mirabella, D. D’Angelo, S. Gibilisco, A. Grasso, S. Di Marco, F. Simone, and A. Terrasi

J. Appl. Phys. 107, 043503 (2010); http://dx.doi.org/10.1063/1.3305805 (6 pages) | Cited 2 times

Online Publication Date: 17 February 2010

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The double sign anomaly of the Hall coefficient has been studied in p-doped and n-doped hydrogenated amorphous silicon grown by plasma enhanced chemical vapor deposition and annealed up to 500 °C. Dark conductivity as a function of temperature has been measured, pointing out a conduction mechanism mostly through the extended states. Anomalous Hall effect has been observed only in the as-deposited n-doped film, disappearing after annealing at 500 °C, while p-doped samples exhibit normal Hall effect. When Hall anomaly is present, a larger optical band gap and a greater Raman peak associated with Si–H bond are measured in comparison with the cases of normal Hall effect. The Hall anomaly will be related to the hydrogen content and implication on photovoltaic applications will be discussed.
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73.61.Jc Amorphous semiconductors; glasses
73.61.Cw Elemental semiconductors
73.50.Pz Photoconduction and photovoltaic effects
78.66.Jg Amorphous semiconductors; glasses
78.66.Db Elemental semiconductors and insulators
78.56.-a Photoconduction and photovoltaic effects
78.30.Am Elemental semiconductors and insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Phononic gaps in thin semiconductor superlattices

S. P. Hepplestone and G. P. Srivastava

J. Appl. Phys. 107, 043504 (2010); http://dx.doi.org/10.1063/1.3285415 (9 pages) | Cited 3 times

Online Publication Date: 17 February 2010

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We have studied one-dimensional phononic gaps in thin semiconductor superlattices. A general methodology has been developed for predicting the locations of these gaps in both thin and thick superlattices. Quantitative analysis of results for the phonon dispersions of Si/Ge[001] and GaAs/AlAs[001] superlattices are presented as both a function of period and composition. The effect of interface mixing is studied and its effects are found to be smaller than previously guessed. The introduction of the defects is shown to not change the phononic gap characteristics significantly. Finally, we present a discussion on the merits and uses of one-dimensional phononic structures.
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63.20.dd Measurements

Polarization mechanisms and structural rearrangements in thermally poled sodium-alumino phosphate glasses

Marc Dussauze, Vincent Rodriguez, Leoni Velli, Christos P. E. Varsamis, and Efstratios I. Kamitsos

J. Appl. Phys. 107, 043505 (2010); http://dx.doi.org/10.1063/1.3305318 (6 pages) | Cited 2 times

Online Publication Date: 18 February 2010

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Thermally poled glasses of composition 0.20Na2O–0.15Al2O3–0.65P2O5 were investigated by second harmonic generation (SHG) to characterize the induced second order optical nonlinearities (χ2), and by infrared reflectance and micro-Raman spectroscopy to probe structural rearrangements in the nonlinear optical (NLO) layer. The SHG signals showed anodic and bulk χ2 contributions, with the anodic response being one order of magnitude stronger. Also, a good agreement was found between the thickness of the NLO anodic layer (approximately 3 μm) and the depth where structural changes were detected. The latter include the destruction of bonds between phosphorus and nonbridging oxygen atoms, this process leads to the release and migration of sodium cations and oxide anions and to the enhancement of glass network connectivity in the anodic NLO layer.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
61.43.Fs Glasses
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Dynamic yielding in lithium fluoride and aluminum

Yukio Sano and Tomokazu Sano

J. Appl. Phys. 107, 043506 (2010); http://dx.doi.org/10.1063/1.3275503 (6 pages)

Online Publication Date: 18 February 2010

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At a time immediately after shock loading, a kink (a weak discontinuity or a discontinuity in slope) occurs at a position in an unsteady portion in a smooth plane wave front in a lithium fluoride single crystal (material IIIb) or in 1060-0 aluminum due to the instability of the wave front. After the occurrence of the kink, a zone is produced and broadened with time between a near steady precursor ahead of the kink and a plastic wave behind it in a weak-discontinuity plane wave by the difference in the propagation velocity between them. Stress relaxes in the zone, which is called a follower, and the precursor decay takes place due to the stress relaxation. During the decay process, the large increase in plastic flow occurs in the vicinity of the leading edge of the follower, causes yielding at the leading edge, and stabilizes the weak-discontinuity wave. The stress-strain (σ-ε) history caused by the follower rotates clockwise with time around the yield point. The rotation yields different σ-ε histories behind the point and therefore different types of the dynamic σ-ε relation. Dynamic yield phenomena are illustrated by showing the schematic diagrams of three different types of the dynamic σ-ε relation, which are caused by weak-discontinuity plane waves composed of a precursor C, a follower (i) C, (ii) I or II, or (iii) R′ or Rb, and a plastic wave C behind the follower. Here C is the contraction (compression) wave, I and II are the degenerate contraction waves I and II, R′ is the subrarefaction wave, and Rb is the rarefaction wave.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
62.50.Ef Shock wave effects in solids and liquids
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.F- Deformation and plasticity

Thermal expansion of skutterudites

G. Rogl, L. Zhang, P. Rogl, A. Grytsiv, M. Falmbigl, D. Rajs, M. Kriegisch, H. Müller, E. Bauer, J. Koppensteiner, W. Schranz, M. Zehetbauer, Z. Henkie, and M. B. Maple

J. Appl. Phys. 107, 043507 (2010); http://dx.doi.org/10.1063/1.3284088 (10 pages) | Cited 3 times

Online Publication Date: 18 February 2010

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The current paper gives an overview of the newly obtained thermal expansion coefficients of skutterudites as well as those so far available in literature. Thermal expansion was determined for CoSb3, Pt4Sn4.4Sb7.6, for As- and Ge-based skutterudites as well as for various high-ZT skutterudites (micro- and nanostructured) with didymium (DD) and mischmetal (Mm) as filler atoms in frameworks of (Fe1−xCox)4Sb12 and (Fe1−xNix)4Sb12, and for double and triple-filled skutterudites such as Ca0.07Ba0.23Co3.95Ni0.05Sb12 and Sr0.025Ba0.075Yb0.1Co4Sb12. For low temperatures, a capacitance dilatometer was used (4–300 K), whereas for temperatures 300<T<750 K, a dynamic mechanical analyzer was employed. For a set of Ge-, P-, and Sb-based skutterudites, lattice parameters of single crystals, measured at three different temperatures, were used to derive the thermal expansion coefficient. The semiclassical model of Mukherjee [Phys. Rev. Lett. 76, 1876 (1996) ] has been successfully used to quantitatively describe the thermal expansion coefficient in terms of Einstein and Debye temperatures, which compare well with the corresponding results from specific heat, electrical resistivity, or temperature dependent x-ray measurements.
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65.40.De Thermal expansion; thermomechanical effects
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
61.66.Dk Alloys
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
65.40.Ba Heat capacity

Accurate measurements of the thermal diffusivity of thin filaments by lock-in thermography

Agustín Salazar, Arantza Mendioroz, Raquel Fuente, and Ricardo Celorrio

J. Appl. Phys. 107, 043508 (2010); http://dx.doi.org/10.1063/1.3309328 (7 pages)

Online Publication Date: 18 February 2010

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In lock-in (modulated) thermography the lateral thermal diffusivity can be obtained from the slope of the linear relation between the phase of the surface temperature and the distance to the heating spot. However, this slope is greatly affected by heat losses, leading to an overestimation of the thermal diffusivity, especially for thin samples of poor thermal conducting materials. In this paper, we present a complete theoretical model to calculate the surface temperature of filaments heated by a focused and modulated laser beam. All heat losses have been included: conduction to the gas, convection, and radiation. Monofilaments and coated wires have been studied. Conduction to the gas has been identified as the most disturbing effect preventing from the direct use of the slope method to measure the thermal diffusivity. As a result, by keeping the sample in vacuum a slope method combining amplitude and phase can be used to obtain the accurate diffusivity value. Measurements performed in a wide variety of filaments confirm the validity of the conclusion. On the other hand, in the case of coated wires, the slope method gives an effective thermal diffusivity, which verifies the in-parallel thermal resistor model. As an application, the slope method has been used to retrieve the thermal conductivity of thin tubes by filling them with a liquid of known thermal properties.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
66.30.Xj Thermal diffusivity
44.10.+i Heat conduction

Size distributions of nanoscopic holes in Ti/h-BN and Ti/B nanocomposites

J. Čížek, I. Procházka, O. S. Morozova, C. Borchers, and A. Pundt

J. Appl. Phys. 107, 043509 (2010); http://dx.doi.org/10.1063/1.3305790 (11 pages)

Online Publication Date: 19 February 2010

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Positron annihilation spectroscopy was employed for defect studies of “Ti”-based nanocomposites prepared by high-energy ball milling and consisting of Ti nanoparticles separated by hexagonal boron nitride (h-BN) or boron (B) additive. The size distribution of nanoscopic holes in nanocomposites was determined directly from measurement of ortho-positronium (Ps) lifetimes. Chemical environment of defects was characterized using coincidence Doppler broadening. It was found that size of nanoscopic holes is reduced with increasing milling time in H2/He atmosphere and also probability of Ps formation in holes decreases. At the same time the Ti content in the vicinity of holes increases. This can be explained by (i) increased intermixing of Ti particles with h-BN or B additive and by (ii) filling the nanoscopic holes with absorbed hydrogen. Analysis of obtained results showed that both these processes take place during milling of nanocomposites. In addition, it was found that the effect of filling the nanoscopic pores with hydrogen is enhanced in TiH2 milled with h-BN or B in He atmosphere. Comparison of nanocomposites with h-BN and B additive showed that sufficiently long milling time leads to a similar size distribution of nanoscopic holes in Ti/h-BN and Ti/B, despite the fact that it differs substantially in the initial powders. However, density of nanoscopic holes in Ti/B is significantly lower than in Ti/h-BN nanocomposites.
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72.80.Tm Composite materials
61.72.-y Defects and impurities in crystals; microstructure
81.16.-c Methods of micro- and nanofabrication and processing
78.70.Bj Positron annihilation
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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