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1 Jul 2010

Volume 108, Issue 1, Articles (01xxxx)

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J. Appl. Phys. 108, 011101 (2010); http://dx.doi.org/10.1063/1.3457141 (19 pages)

Xunlin Qiu
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Patterned piezo-, pyro-, and ferroelectricity of poled polymer electrets

Xunlin Qiu

J. Appl. Phys. 108, 011101 (2010); http://dx.doi.org/10.1063/1.3457141 (19 pages) | Cited 12 times

Online Publication Date: 12 July 2010

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Polymers with strong piezo-, pyro-, and ferroelectricity are attractive for a wide range of applications. In particular, semicrystalline ferroelectric polymers are suitable for a large variety of piezo- and pyroelectric transducers or sensors, while amorphous polymers containing chromophore molecules are particularly interesting for photonic devices. Recently, a new class of polymer materials has been added to this family: internally charged cellular space-charge polymer electrets (so-called “ferroelectrets”), whose piezoelectricity can be orders of magnitude higher than that of conventional ferroelectric polymers. Suitable patterning of these materials leads to improved or unusual macroscopic piezo-, pyro-, and ferroelectric or nonlinear optical properties that may be particularly useful for advanced transducer or waveguide applications. In the present paper, the piezo-, pyro-, and ferroelectricity of poled polymers is briefly introduced, an overview on the preparation of polymer electrets with patterned piezo-, pyro-, and ferroelectricity is provided and a survey of selected applications is presented.
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81.20.-n Methods of materials synthesis and materials processing
77.65.-j Piezoelectricity and electromechanical effects
77.70.+a Pyroelectric and electrocaloric effects
77.80.-e Ferroelectricity and antiferroelectricity
77.22.-d Dielectric properties of solids and liquids
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back to top Lasers, Optics, and Optoelectronics

Radiation efficiency of heavily doped bulk n-InP semiconductor

Oleg Semyonov, Arsen Subashiev, Zhichao Chen, and Serge Luryi

J. Appl. Phys. 108, 013101 (2010); http://dx.doi.org/10.1063/1.3455874 (7 pages) | Cited 1 time

Online Publication Date: 1 July 2010

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Recombination of minority carriers in heavily doped n-InP wafers has been investigated using spectral and time-resolved photoluminescence at different temperatures. Studies of the transmitted luminescence were enabled by the partial transparency of the samples due to the Moss–Burstein effect. Temporal evolution of the transmitted luminescence shows virtually no effect of surface recombination but is strongly influenced by photon recycling. Temperature dependence of the decay time suggests Auger recombination as the dominant nonradiative process at room temperature. Radiative quantum efficiency has been evaluated at different doping levels and at 2×1018 cm−3 it is found to be as high as 97%, which makes n-InP suitable for scintillator application.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.Cr III-V semiconductors
79.20.Fv Electron impact: Auger emission
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Silicon based microfluidic cell for terahertz frequencies

A. J. Baragwanath, G. P. Swift, D. Dai, A. J. Gallant, and J. M. Chamberlain

J. Appl. Phys. 108, 013102 (2010); http://dx.doi.org/10.1063/1.3456175 (8 pages) | Cited 1 time

Online Publication Date: 6 July 2010

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We present a detailed analysis of the design, fabrication and testing of a silicon based, microfluidic cell, for transmission terahertz time-domain spectroscopy. The sensitivity of the device is tested through a range of experiments involving primary alcohol/water mixtures. The dielectric properties of these solutions are subsequently extracted using a Nelder–Mead search algorithm, and are in good agreement with literature values obtained via alternative techniques. Quantities in the order of 2 μmol can be easily distinguished for primary alcohols in solution, even with the subwavelength optical path lengths used. A further display of the device sensitivity is shown through the analysis of commercial whiskeys, where there are clear, detectable differences between samples. Slight absorption variations were identified between samples of the same commercial brand, owing to a 2.5% difference in their alcoholic content. Results from data taken on subsequent days after system realignment are also presented, confirming the robustness of the technique, and the data extraction algorithm used. One final experiment, showing the possible use of this device to analyze aqueous biological samples is detailed; where biotin, a molecule known for its specific terahertz absorptions, is analyzed in solution. The device sensitivity is once again displayed, where quantities of 3 nmol can be clearly detected between samples.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
47.85.Np Fluidics
84.40.-x Radiowave and microwave (including millimeter wave) technology

Extrinsic contributions to photocurrents from quantum-wells

Rakshyakar Giri, Sandy Schwirzke-Schaaf, and Jens W. Tomm

J. Appl. Phys. 108, 013103 (2010); http://dx.doi.org/10.1063/1.3457148 (6 pages) | Cited 1 time

Online Publication Date: 6 July 2010

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Photocurrent (PC) spectra representing the in-plane absorption of the quantum-wells (QWs) in diode lasers are monitored. Spectra from pristine and systematically aged devices are analyzed and aging-induced changes are explained within the frame of rate-equation models for nonequilibrium carriers. We conclude from the analysis of the PC phase behavior and from aging-induced changes in the QW PCs, these currents to be actually of extrinsic nature. This finding, however, does not prohibit the use of PC spectra for analytical purposes, e.g., when employing PC peak-positions or their shifts because the spectral shape of the extrinsic QW PCs is still governed by QW absorption. This holds for all photoelectric techniques if applied to the vertical transport in pin-structures, such as diode laser structures.
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42.55.Px Semiconductor lasers; laser diodes
81.05.Ea III-V semiconductors
78.67.De Quantum wells
78.66.Fd III-V semiconductors
79.60.Jv Interfaces; heterostructures; nanostructures
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Intersubband absorption in modulation doped heterostructures

J. Yao, W. Zheng, H. Opper, J. Cai, and G. W. Taylor

J. Appl. Phys. 108, 013104 (2010); http://dx.doi.org/10.1063/1.3436595 (10 pages) | Cited 2 times

Online Publication Date: 8 July 2010

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Intersubband absorption is reported in a new modulation doped structure using strained InGaAs quantum wells (QWs) that support transistor operation. Well defined absorption peaks (1000 to 1700 cm−1) from 8 to 11.5 μm have been obtained using either n-type or p-type modulation doped wells. Both n and p well responses show strong polarization dependence with maximum values at incident angles of 65°–70° and peak positions which are adjusted by the QW parameters. The p well shows a double peaked response with a peak separation of about 1.5 μm which results from heavy and light hole contributions. The absorption data are compared with a theoretical model developed on the basis of variable k conservation and excellent agreement is obtained. It is shown that a mass difference between the upper and lower states is essential to predict a finite spectral width of the response.
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78.67.De Quantum wells
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

The role of quantum confinement and crystalline structure on excitonic lifetimes in silicon nanoclusters

L. J. Borrero-González, L. A. O. Nunes, M. R. B. Andreeta, J. Wojcik, P. Mascher, Y. A. Pusep, D. Comedi, and F. E. G. Guimarães

J. Appl. Phys. 108, 013105 (2010); http://dx.doi.org/10.1063/1.3457900 (5 pages) | Cited 2 times

Online Publication Date: 8 July 2010

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The emission energy dependence of the photoluminescence (PL) decay rate at room temperature has been studied in Si nanoclusters (Si-ncl) embedded in Si oxide matrices obtained by thermal annealing of substoichiometric Si oxide layers SiyO1−y, y = (0.36,0.39,0.42), at various annealing temperatures (Ta) and gas atmospheres. Raman scattering measurements give evidence for the formation of amorphous Si-ncl at Ta = 900 °C and of crystalline Si-ncl for Ta = 1000 °C and 1100 °C. For Ta = 1100 °C, the energy dispersion of the PL decay rate does not depend on sample fabrication conditions and follows previously reported behavior. For lower Ta, the rate becomes dependent on fabrication conditions and less energy dispersive. The effects are attributed to exciton localization and decoherence leading to the suppression of quantum confinement and the enhancement of nonradiative recombination in disordered and amorphous Si-ncl.
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78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
61.72.Cc Kinetics of defect formation and annealing
71.35.-y Excitons and related phenomena
78.30.Am Elemental semiconductors and insulators

Temperature effect on the lasing from a dye-doped two-dimensional hexagonal photonic crystal made of holographic polymer-dispersed liquid crystals

D. Luo, X. W. Sun, H. T. Dai, H. V. Demir, H. Z. Yang, and W. Ji

J. Appl. Phys. 108, 013106 (2010); http://dx.doi.org/10.1063/1.3456991 (3 pages) | Cited 2 times

Online Publication Date: 12 July 2010

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Temperature dependent lasing was demonstrated in a dye-doped two-dimensional hexagonal photonic crystal made of holographic polymer-dispersed liquid crystals (LCs) along ΓM direction in TE polarization. A redshift in lasing peaks was observed as the temperature increased from 25 to 45 °C. The downward movement of photonic band of TE polarization, majorly caused by the decrease in the anisotropy of LC droplets with the increase in temperature, is responsible for the redshift in lasing peaks.
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42.55.Tv Photonic crystal lasers and coherent effects
42.55.Mv Dye lasers
42.70.Qs Photonic bandgap materials

Multiple-pulse laser dynamic forming of metallic thin films for microscale three dimensional shapes

Ji Li and Gary J. Cheng

J. Appl. Phys. 108, 013107 (2010); http://dx.doi.org/10.1063/1.3457869 (8 pages) | Cited 1 time

Online Publication Date: 13 July 2010

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Laser dynamic forming (LDF) is a novel high energy rate microfabrication technique, which makes use of the shock pressure induced by laser to generate dynamic high strain rate three dimensional (3D) forming of thin films. In LDF process, a high shock pressure accelerates the workpiece to a high velocity and deforms it into complex 3D shapes. The forming velocity of the workpiece imparted by a single laser pulse with high energy may exceed the critical forming velocity of the material, and thus causing it to fracture. This problem is more severe when 3D structure of large aspect ratio needs to be formed. To overcome this problem, multiple-pulse LDF is investigated in this study. The total laser energy is evenly distributed in different laser pulses to keep the forming velocity below the critical forming velocity of the material. The effects of the multiple-pulse LDF on the deformation behavior of ultrathin foils are investigated. The deformation depth and thickness variation distribution of the formed 3D features are characterized to reveal these effects. In addition, the effects of vacuum conditions on multiple-pulse LDF process are carried out. It is found that the bounce off of the foil can be effectively reduced by multiple-pulse LDF and the final shape could be controlled much more accurately. By extending single pulse LDF to multiple-pulse LDF, the forming capability of LDF is further enhanced, and thus enlarges the applicable range of this technique.
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42.62.Cf Industrial applications
81.10.Fq Growth from melts; zone melting and refining
81.16.Mk Laser-assisted deposition
89.20.Kk Engineering
89.20.Bb Industrial and technological research and development
81.40.Lm Deformation, plasticity, and creep

Direct measurement of micromotion speed in a linear quadrupole trap

B. Wang, J. W. Zhang, Z. H. Lu, and L. J. Wang

J. Appl. Phys. 108, 013108 (2010); http://dx.doi.org/10.1063/1.3457904 (5 pages)

Online Publication Date: 13 July 2010

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We demonstrate a simple method to directly measure the micromotion speed and amplitude of ions far away from the nodal line of the linear quadrupole trap using the cross-correlation technique. For the ions very close to the trap nodal line, the micromotion speed and amplitude of ions can also be deduced through linear fitting. This work gives us a direct picture to the ions’ micromotion modes at different displacements in the linear trap. With this work, an absolute measurement of the second-order Doppler effect in the research of atomic clocks based on large number of ions becomes possible.
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37.10.Ty Ion trapping
37.10.Rs Ion cooling

Microwave and plasma interaction in a rectangular waveguide: Effect of ponderomotive force

Hitendra K. Malik and Anil K. Aria

J. Appl. Phys. 108, 013109 (2010); http://dx.doi.org/10.1063/1.3452335 (8 pages) | Cited 3 times

Online Publication Date: 14 July 2010

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Studies on the propagation of high power microwave and its interaction with a plasma in a metallic waveguide are carried out. For this we consider the fundamental TE10 mode that propagates in an evacuated rectangular waveguide and encounters a plasma which is filled in another waveguide of the same size. Using Maxwell’s equations we evaluate the field components of the mode in the evacuated waveguide and then obtain coupled differential equations for the field components of the mode in the plasma filled waveguide, where the plasma effect enters in terms of its dielectric constant. These equations are solved numerically using the fourth-order Runge–Kutta method for the electric field amplitude of the microwave and its wavelength under the effect of plasma density, waveguide width, and microwave frequency. All the investigations are carried out for different initial plasma density profiles, namely homogeneous density, linear density with gradient in the propagation direction and the density with Gaussian profile along the waveguide width. The structure of the perturbed density due to the ponderomotive force exerted by the mode is also investigated under the effect of microwave parameters and waveguide width. Numerical studies are conducted for the isothermal plasma in the waveguide.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.25.Fi Transport properties
52.25.Mq Dielectric properties

Temperature dependence of superluminescence in InGaN-based superluminescent light emitting diode structures

Katarzyna Holc, Łucja Marona, Robert Czernecki, Michał Boćkowski, Tadeusz Suski, Stephen Najda, and Piotr Perlin

J. Appl. Phys. 108, 013110 (2010); http://dx.doi.org/10.1063/1.3459876 (4 pages) | Cited 2 times

Online Publication Date: 14 July 2010

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We have studied the temperature dependence of electroluminescence in superluminescent light emitting diode InGaN structures emitting light at 405 nm. Devices were fabricated in the “tilted ridge” geometry. We measured the superluminescence emission as a function of temperature from 263 to 295 K and observed a very pronounced power sensitivity with temperature. Simple modeling of the optical intensity reveals that the main temperature dependence is related to the spontaneous emission factor in the amplified spontaneous emission and the temperature dependence of gain is of secondary importance. This result strongly suggests the need for reducing nonradiative recombination in superluminescent devices.
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85.60.Jb Light-emitting devices
back to top Plasmas and Electrical Discharges

Electric probe investigations of microwave generated, atmospheric pressure, plasma jets

H. E. Porteanu, S. Kühn, and R. Gesche

J. Appl. Phys. 108, 013301 (2010); http://dx.doi.org/10.1063/1.3448034 (8 pages) | Cited 3 times

Online Publication Date: 2 July 2010

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We examine the applicability of the Langmuir-type of characterization for atmospheric pressure plasma jets generated in a millimeter-size cavity microwave resonator at 2.45 GHz. Wide range I-V characteristics of helium, argon, nitrogen, air and oxygen are presented for different gas fluxes, distances probe-resonator, and microwave powers. A detailed analysis is performed for the fine variation in the current around the floating potential. A simplified theory specially developed for this case is presented, considering the ionic and electronic saturation currents and the floating potential. Based on this theory, we conclude that, while the charge carrier density depends on gas flow, distance to plasma source, and microwave absorbed power, the electron temperature is quite independent of these parameters. The resulting plasma parameters for helium, argon, and nitrogen are presented.
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52.70.Ds Electric and magnetic measurements
52.50.Dg Plasma sources
52.75.-d Plasma devices
52.25.Fi Transport properties

Long-wavelength optical transmission of extremely narrow slits via hybrid surface-plasmon and Fabry–Pérot modes

X. F. Li and S. F. Yu

J. Appl. Phys. 108, 013302 (2010); http://dx.doi.org/10.1063/1.3457841 (5 pages) | Cited 3 times

Online Publication Date: 7 July 2010

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We have verified that extraordinary transmission of long-wavelength light through extremely narrow slits in a thick metal film can be achieved by hybrid surface-plasmon and Fabry–Pérot modes. Transmittance of these ultranarrow slits, which have width and thickness of 0.56 μm and 100 μm, respectively, for a terahertz light with wavelength of 225 μm can be 2.1×108 times higher than that predicted by using classic theory. Furthermore, the corresponding ratio between transmission wavelength and slit width can be up to 400, which is over 60 times larger than that the conventional grating-based surface-plasmon modes can provide.
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42.25.Bs Wave propagation, transmission and absorption
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
07.60.Ly Interferometers
42.79.Dj Gratings
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Oxygen deficiency defects in amorphous Al2O3

T. V. Perevalov, O. E. Tereshenko, V. A. Gritsenko, V. A. Pustovarov, A. P. Yelisseyev, Chanjin Park, Jeong Hee Han, and Choongman Lee

J. Appl. Phys. 108, 013501 (2010); http://dx.doi.org/10.1063/1.3455843 (4 pages) | Cited 5 times

Online Publication Date: 1 July 2010

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In the electron energy loss spectra for amorphous, atomic layer deposited (ALD) Al2O3 film, a peak at 6.4 eV was observed. First principle quantum chemical simulation shows that it relates to excitation of neutral oxygen vacancy in Al2O3. The 2.91 eV luminescence excited in a band near 6.0 eV in amorphous Al2O3 is similar to that in bulk crystals which is associated with neutral oxygen vacancy. Thus, the amorphous ALD Al2O3 film is oxygen deficient and the oxygen vacancy parameters are similar in crystalline and amorphous Al2O3.
Show PACS
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
61.72.jd Vacancies
79.20.Uv Electron energy loss spectroscopy
78.55.Qr Amorphous materials; glasses and other disordered solids
78.66.Nk Insulators

Carrier recombination process and magneto-photoluminescence in Zn1−xCoxO layers

Zhiyan Xiao, Hiroaki Matsui, Kouichi Katayama, Kensuke Miyajima, Tadashi Itoh, and Hitoshi Tabata

J. Appl. Phys. 108, 013502 (2010); http://dx.doi.org/10.1063/1.3455854 (6 pages) | Cited 1 time

Online Publication Date: 1 July 2010

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See Also: Publisher's Note | Publisher's Note

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High-quality Zn1−xCoxO layers were obtained with isolated Co ions in the host (x no more than 0.008). The photoluminescence properties of excitonic and Co-related emissions in the Zn1−xCoxO (x = 0.0015) layer were mainly investigated in both zero and up to 7 T magnetic fields in order to clear the energy transfer process from excitonic states to Co centers. It was found that Co emissions originated from 3d intraemissions in the Zn1−xCoxO (x = 0.0015) layer were remarkably enhanced with the suppression of excitonic emissions, indicating the presence of efficient energy transfer to the Co centers. Assignment of absorption and magnetoluminescence spectra revealed that the energy transfer to the Co centers was not derived from the excitonic states but from charge transfer (CT) states formed on the Co centers after a band-to-band excitation. Finally, we consider that the primary role for the energy transfer process of Zn1−xCoxO (x = 0.0015) layer is related to the phenomenon of impurity Auger recombination acting as a nonradiative energy transfer from the CT states to Co centers.
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81.05.Dz II-VI semiconductors
75.50.Pp Magnetic semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.61.Ga II-VI semiconductors
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors

Combined effects of Ga, N, and Al codoping in solution grown 3C–SiC

J. W. Sun, G. Zoulis, J. C. Lorenzzi, N. Jegenyes, H. Peyre, S. Juillaguet, V. Souliere, F. Milesi, G. Ferro, and J. Camassel

J. Appl. Phys. 108, 013503 (2010); http://dx.doi.org/10.1063/1.3455999 (10 pages) | Cited 1 time

Online Publication Date: 1 July 2010

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We report on Ga-doped 3C–SiC epitaxial layers grown on on-axis (0001) 6H–SiC substrates using the vapor-liquid-solid technique and different Si1−xGax melts. The resulting samples have been investigated using secondary ion mass spectroscopy (SIMS), micro-Raman spectroscopy (μ-R) and, finally, low temperature photoluminescence (LTPL) spectroscopy. From SIMS measurements we find Ga concentrations in the range of 1018 cm−3, systematically accompanied by high nitrogen content. In good agreement with these findings, the μ-R spectra show that the Ga-doped samples are n-type, with electron concentrations close to 2×1018 cm−3. As expected, the LTPL spectra are dominated by strong N–Ga donor-acceptor pair (DAP) transitions. In one sample, a weak additional N–Al DAP recombination spectrum is also observed, showing the possibility to have accidental codoping with Ga and Al simultaneously. This was confirmed on a non-intentionally doped 3C–SiC (witness) sample on which, apart of the usual N and Al bound exciton lines, a small feature resolved at 2.35 eV comings from neutral Ga bound excitons. Quantitative analyses of the DAP transition energies in the Ga-doped and witness sample gave 346 meV for the optical binding energy of Ga acceptors in 3C–SiC against 251 meV for the Al one. The conditions for the relative observa-tion of Ga and Al related LTPL features are discussed and the demonstration of room temperature luminescence using Ga doping is done.
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78.55.Hx Other solid inorganic materials
78.30.-j Infrared and Raman spectra
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.72.U- Doping and impurity implantation
68.55.ag Semiconductors

Mechanical behavior of twinned SiC nanowires under combined tension-torsion and compression-torsion strain

Zhijie Li, Shenjie Wang, Zhiguo Wang, Xiaotao Zu, Fei Gao, and William J. Weber

J. Appl. Phys. 108, 013504 (2010); http://dx.doi.org/10.1063/1.3456002 (5 pages)

Online Publication Date: 1 July 2010

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The mechanical behavior of twinned silicon carbide (SiC) nanowires under combined tension-torsion and compression-torsion is investigated using molecular dynamics simulations with an empirical potential. The simulation results show that both the tensile failure stress and buckling stress decrease under combined tension-torsional and combined compression-torsional strain, and they decrease with increasing torsional rate under combined loading. The torsion rate has no effect on the elastic properties of the twinned SiC nanowires. The collapse of the twinned nanowires takes place in a twin stacking fault of the nanowires.
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62.23.Hj Nanowires
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
61.72.Nn Stacking faults and other planar or extended defects
81.40.Lm Deformation, plasticity, and creep
62.20.mq Buckling

Effect of substrate roughness on the apparent surface free energy of sputter deposited superhydrophobic polytetrafluoroethylene coatings: A comparison of experimental data with different theoretical models

N. Selvakumar, Harish C. Barshilia, and K. S. Rajam

J. Appl. Phys. 108, 013505 (2010); http://dx.doi.org/10.1063/1.3456165 (9 pages) | Cited 2 times

Online Publication Date: 2 July 2010

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We have studied the effect of substrate roughness on the wettability and the apparent surface free energy (SFE) of sputter deposited polytetrafluoroethylene (PTFE) coatings deposited on untreated glass (average roughness, Ra = 2.0 nm), plasma etched glass (Ra = 7.4 nm), and sandblasted glass (Ra = 4500 nm) substrates. The wettability of the PTFE coatings deposited on substrates with varying roughnesses was evaluated by measuring the apparent contact angle (CA) using a series of probe liquids from nonpolar aprotic to polar protic. The wettability measurements indicate that an apparent water CA of 152° with a sliding angle of 8° was achieved for PTFE coatings deposited on a substrate with Ra = 4500 nm. The superhydrophobicity observed in these coatings is attributed to the presence of dual scale roughness, densely packed microstructure and the presence of CF3 groups. Unlike the bulk PTFE which is mainly dispersive, the sputter deposited PTFE coatings are expected to have some degree of polar component due to the plasma treatment. In order to calculate the dispersive SFE of PTFE coatings, we have used the Girifalco–Good–Fowkes (GGF) method and validated it with the Zisman model. Furthermore, the Owens–Wendt model has been used to calculate the dispersive and the polar components of the apparent SFE of the PTFE coatings. These results are further corroborated using the Fowkes method. Finally, an “equation of state” theory proposed by Neumann has been used to calculate the apparent SFE values of the PTFE coatings. The results indicate that the apparent SFE values of the PTFE coatings obtained from the Owens–Wendt and the Fowkes methods are comparable to those obtained from the Neumann’s method. The analyses further demonstrate that the GGF and the Zisman methods underestimate the apparent SFE values of the sputter deposited PTFE coatings.
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81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.03.Cd Surface tension and related phenomena
68.08.Bc Wetting
81.65.Cf Surface cleaning, etching, patterning

Photoluminescence enhancement and high gain amplification of ErxY2−xSiO5 waveguide

X. J. Wang, G. Yuan, H. Isshiki, T. Kimura, and Z. Zhou

J. Appl. Phys. 108, 013506 (2010); http://dx.doi.org/10.1063/1.3446822 (4 pages) | Cited 6 times

Online Publication Date: 2 July 2010

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ErxY2−xSiO5 (x = 0–2) films have been fabricated on Si(100) substrates by the sol-gel method. Enhanced Er3+ photoluminescence of around 30 times for the ErxY2−xSiO5 (x = 0.1) film was observed compared with pure Er2SiO5 film at the wavelength pump of 654 nm. Reduced upconversion effect and decreased nonradiative transient rate are two main reasons for the enhanced Er3+ luminescence in the new film of ErxY2−xSiO5. Above 10 dB optical gain can be achieved at the 1 mm length ErxY2−xSiO5 (x = 0.1) waveguide under 30 mW pumping power, indicating it is sought candidate material for compact waveguide amplifiers and emitters in silicon photonics integration.
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78.55.Hx Other solid inorganic materials
78.66.Nk Insulators
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Infrared study of the absorption edge of β-InN films grown on GaN/MgO structures

M. Pérez-Caro, A. G. Rodríguez, M. A. Vidal, and H. Navarro-Contreras

J. Appl. Phys. 108, 013507 (2010); http://dx.doi.org/10.1063/1.3456171 (6 pages)

Online Publication Date: 2 July 2010

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Infrared optical studies were carried out in a group of cubic InN samples grown by gas source molecular beam epitaxy on MgO (001) substrates. Room temperature (RT) reflectance and low-temperature (LT) transmittance measurements were performed by using fast Fourier transform infrared spectrometry. Reflectance fittings allowed to establish that β-InN films have large free-carrier concentrations present (>1019 cm−3), a result that is corroborated by Hall effect measurements. Each sample explored exhibited a different optical absorption edge. The Varshni parameters that describe adequately the optical absorption edge responses with temperature are obtained for the set of samples studied. The observed temperatures changes, from LT to RT, are the lowest reported for III-V semiconductor binary compounds. The temperature coefficient of the conduction band depends on the strength of the electron–phonon interaction (e-ph-i), as well as on the thermal expansion. It has been predicted that cubic InN has one of the smallest e-ph-i of all III-V compounds, which is corroborated by these results. The variation in values of absorption edges is clearly consistent with the Burstein–Moss and band renormalization effects, produced by high free electron concentrations. It is shown that the conduction band in β-InN, analogous to wurtzite InN, follows a nonparabolic behavior.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Heat flow model for pulsed laser melting and rapid solidification of ion implanted GaAs

Taeseok Kim, Manoj R. Pillai, Michael J. Aziz, Michael A. Scarpulla, Oscar D. Dubon, Kin M. Yu, Jeffrey W. Beeman, and Mark C. Ridgway

J. Appl. Phys. 108, 013508 (2010); http://dx.doi.org/10.1063/1.3457106 (7 pages) | Cited 3 times

Online Publication Date: 6 July 2010

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In order to further understand the pulsed-laser melting (PLM) of Mn and N implanted GaAs, which we have used to synthesize thin films of the ferromagnetic semiconductor Ga1−xMnxAs and the highly mismatched alloy GaNxAs1−x, we have simulated PLM of amorphous (a-) and crystalline (c-) GaAs. We present a numerical solution to the one-dimensional heat equation, accounting for phase-dependent reflectivity, optical skin depth, and latent heat, and a temperature-dependent thermal conductivity and specific heat. By comparing the simulations with experimental time-resolved reflectivity and melt depth versus laser fluence, we identify a set of thermophysical and optical properties for the crystalline, amorphous, and liquid phases of GaAs that give reasonable agreement between experiment and simulation. This work resulted in the estimation of thermal conductivity, melting temperature and latent heat of fusion of a-GaAs of 0.008 W/cm K at 300 K, 1350 K, and 2650 J/cm3, respectively. These materials properties also allow the prediction of the solidification velocity of crystalline and ion-amorphized GaAs.
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81.05.Ea III-V semiconductors
81.15.Fg Pulsed laser ablation deposition
75.50.Pp Magnetic semiconductors
81.30.Fb Solidification
66.70.Df Metals, alloys, and semiconductors
68.60.Wm Other nonelectronic physical properties

Variable percolation threshold of composites with fiber fillers under compression

Chuan Lin, Hongtao Wang, and Wei Yang

J. Appl. Phys. 108, 013509 (2010); http://dx.doi.org/10.1063/1.3457351 (5 pages) | Cited 4 times

Online Publication Date: 6 July 2010

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The piezoresistant effect in conducting fiber-filled composites has been studied by a continuum percolation model. Simulation was performed by a Monte Carlo method that took into account both the deformation-induced fiber bending and rotation. The percolation threshold was found to rise with the compression strain, which explains the observed positive piezoresistive coefficients in such composites. The simulations unveiled the effect of the microstructure evolution during deformation. The fibers are found to align perpendicularly to the compression direction. As the fiber is bended, the effective length in making a conductive network is shortened. Both effects contribute to a larger percolation threshold and imply a positive piezoresistive coefficient according the universal power law.
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72.80.Tm Composite materials
72.20.Fr Low-field transport and mobility; piezoresistance
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
72.10.-d Theory of electronic transport; scattering mechanisms

LuAG:Ce fibers for high energy calorimetry

C. Dujardin, C. Mancini, D. Amans, G. Ledoux, D. Abler, E. Auffray, P. Lecoq, D. Perrodin, A. Petrosyan, and K. L. Ovanesyan

J. Appl. Phys. 108, 013510 (2010); http://dx.doi.org/10.1063/1.3452358 (7 pages) | Cited 6 times

Online Publication Date: 6 July 2010

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The main objective of this contribution is to point out the potentialities of cerium doped LuAG single crystal as pixels and fibers. We first show that after optimization of growth conditions using Bridgman technology, this composition exhibits very good performances for scintillating applications (up to 26 000 photons/MeV). When grown with the micropulling down technology, fiber shapes can be obtained while the intrinsic performances are preserved. For the future high energy experiments requiring new detector concepts capable of delivering much richer informations about x- or gamma-ray energy deposition, unusual fiber shaped dense materials need to be developed. We demonstrate in this frame that cerium doped LuAG is a serious candidate for the next generation of ionizing radiation calorimeters.
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07.20.Fw Calorimeters
81.10.Fq Growth from melts; zone melting and refining
29.40.Mc Scintillation detectors

Annealing induced extended defects in as-grown and ion-implanted 4H–SiC epitaxial layers

M. Nagano, H. Tsuchida, T. Suzuki, T. Hatakeyama, J. Senzaki, and K. Fukuda

J. Appl. Phys. 108, 013511 (2010); http://dx.doi.org/10.1063/1.3457840 (8 pages) | Cited 2 times

Online Publication Date: 6 July 2010

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The formation of extended defects in the 4H–SiC epilayer induced by the implantation/annealing process was investigated using synchrotron reflection x-ray topography, KOH etching analysis, and transmission electron microscopy. High temperature annealing was performed for the 4H–SiC epilayer with or without the implantation of nitrogen or aluminum ions. Other than the formation of platelet extrinsic Frank-type faults in the implanted region as reported previously, we find the formation modes of extended defects in following three categories: (i) dislocation formation near the epilayer/substrate interface, (ii) dislocation formation near the implanted region, and (iii) the formation of Shockley-type defects near the surface. The defect morphology and process dependence of each type are also discussed.
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68.55.ag Semiconductors
61.72.up Other materials
61.72.Cc Kinetics of defect formation and annealing
81.65.Cf Surface cleaning, etching, patterning
61.72.Nn Stacking faults and other planar or extended defects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Shape profile of acoustic radiation-induced static displacement pulses in solids

John H. Cantrell and William T. Yost

J. Appl. Phys. 108, 013512 (2010); http://dx.doi.org/10.1063/1.3457850 (4 pages) | Cited 1 time

Online Publication Date: 7 July 2010

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In a recent article Narasimha et al. [J. Appl. Phys. 105, 073506 (2009)] claim to show that the shape of static displacement pulses generated by ultrasonic tone-bursts in nondispersive solids is that of a growing trapezoid in the spatial domain that leads to a flat-topped pulse shape in the time domain for a fixed spatial position. Flaws in their theoretical arguments are corrected to show that their model actually predicts a right-triangular pulse shape for nondispersive monocrystals in both the spatial and time domains as originally reported by Yost and Cantrell [Phys. Rev. B 30, 3221 (1984)] and Cantrell et al. [Phys. Rev. B 35, 9780 (1987)] .
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62.65.+k Acoustical properties of solids
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