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1 Jan 2010

Volume 107, Issue 1, Articles (01xxxx)

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back to top Lasers, Optics, and Optoelectronics

Surface plasmon-enhanced emission from Ag-coated Ce doped Y3Al5O12 thin films phosphor capped with a dielectric layer of SiO2

Wen-Hsuan Chao, Ren-Jye Wu, Chih-Song Tsai, and Tai-Bor Wu

J. Appl. Phys. 107, 013101 (2010); http://dx.doi.org/10.1063/1.3277015 (5 pages) | Cited 8 times

Online Publication Date: 4 January 2010

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The effect of a surface plasmon (SP) on the yellow emission of Ce doped Y3Al5O12 (YAG:Ce) phosphor thin films was studied. The coating of YAG:Ce thin films with silver nanoislands on a 3-nm-thick SiO2 spacer significantly enhanced their photoluminescence (PL). The PL enhancement is caused by the resonant coupling of photoemission in YAG:Ce into SP and the electric field of incident light at the metal interfaces. Varying the mass thickness and the annealing condition of the Ag layer indicated that the PL intensity was highest at an Ag mass thickness of 20 nm. Therefore, yellow emission was enhanced by tuning the matching conditions of thin film phosphor-SP coupling by controlling the structure of silver nanoislands. The PL intensity can be further and remarkably enhanced by capping Ag islands with a 10-nm-thick SiO2 layer as a dielectric medium.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.55.Hx Other solid inorganic materials
81.40.Gh Other heat and thermomechanical treatments
79.60.Dp Adsorbed layers and thin films
68.55.-a Thin film structure and morphology
78.68.+m Optical properties of surfaces

Temperature-dependent modulation characteristics for 1.3 μm InAs/GaAs quantum dot lasers

Peng-Fei Xu (徐鹏飞), Tao Yang (杨涛), Hai-Ming Ji (季海铭), Yu-Lian Cao (曹玉莲), Yong-Xian Gu (谷永先), Yu Liu (刘宇), Wen-Quan Ma (马文全), and Zhan-Guo Wang (王占国)

J. Appl. Phys. 107, 013102 (2010); http://dx.doi.org/10.1063/1.3277042 (5 pages) | Cited 4 times

Online Publication Date: 4 January 2010

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Temperature-dependent modulation characteristics of 1.3 μm InAs/GaAs quantum dot (QD) lasers under small signals have been carefully studied at various bias currents. Based on experimental observations, it is found that the modulation bandwidth significantly increases when excited state (ES) lasing emerges at high temperature. This is attributed to additional photons emitted by ES lasing which contribute to the modulation response. A rate equation model including two discrete electron energy levels and the level of wetting layer has been used to investigate the temperature-dependent dynamic behavior of the QD lasers. Numerical investigations confirm that the significant jump for the small signal modulation response is indeed caused by ES photons. Furthermore, we identify how the electron occupation probabilities of the two discrete energy levels can influence the photon density of different states and finally the modulation rate. Both experiments and numerical analysis show that the modulation bandwidth of QD lasers at high temperature can be increased by injecting more carriers into the ES that has larger electron state degeneracy and faster carrier’s relaxation time than the ground state.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking

Size-dependent light output, spectral shift, and self-heating of 400 nm InGaN light-emitting diodes

Zheng Gong, Shirong Jin, Yujie Chen, Jonathan McKendry, David Massoubre, Ian. M. Watson, Erdan Gu, and Martin D. Dawson

J. Appl. Phys. 107, 013103 (2010); http://dx.doi.org/10.1063/1.3276156 (6 pages) | Cited 9 times

Online Publication Date: 6 January 2010

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We have systematically investigated the impact of device size scaling on the light output, spectral shift, and self-heating of 400 nm InGaN light-emitting diodes (LEDs). Devices with diameters in the range 20–300 μm have been studied. It is shown that smaller LED pixels can deliver higher power densities (despite the lower absolute output powers) and sustain higher current densities. Investigations of the electroluminescence characteristics of differently sized pixels against current density reveal that the spectral shift is dominated by blueshift at the low current density level and then by redshift at the high current density level, owing to the competition between the bandgap shrinkage caused by self-heating and band-filling effects. The redshift of the emission wavelength with increasing current density is much faster and larger for the bigger pixels, suggesting that the self-heating effect is also size dependent. This is further confirmed by the junction-temperature rise measured by the established spectral shift method. It is shown that the junction-temperature rise in smaller pixels is slower, which in turn explains why the smaller redshift of the emission wavelength with current density is present in smaller pixels. The measured size-dependent junction temperature is in reasonable agreement with finite element method simulation results.
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85.60.Jb Light-emitting devices
02.70.Dh Finite-element and Galerkin methods

Modeling bound-to-continuum terahertz quantum cascade lasers: The role of Coulomb interactions

Christian Jirauschek, Alpar Matyas, and Paolo Lugli

J. Appl. Phys. 107, 013104 (2010); http://dx.doi.org/10.1063/1.3276160 (6 pages) | Cited 7 times

Online Publication Date: 7 January 2010

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Based on an ensemble Monte Carlo analysis, we show that Coulomb interactions play a dominant role in bound-to-continuum terahertz quantum cascade lasers and thus require careful modeling. Coulomb interactions enter our simulation in the form of space charge effects as well as Coulomb scattering events. By comparison to a full many-subband Coulomb screening model, we show that simplified approaches produce considerable deviations for such structures. Also the spin dependence of electron-electron scattering has to be adequately considered. Moreover, we demonstrate that iterative Schrödinger–Poisson and carrier transport simulations are necessary to correctly account for space charge effects.
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42.55.Px Semiconductor lasers; laser diodes
02.50.Ng Distribution theory and Monte Carlo studies

Electromechanical tuning of cholesteric liquid crystals

C. A. Bailey, V. P. Tondiglia, L. V. Natarajan, M. M. Duning, R. L. Bricker, R. L. Sutherland, T. J. White, M. F. Durstock, and T. J. Bunning

J. Appl. Phys. 107, 013105 (2010); http://dx.doi.org/10.1063/1.3270410 (8 pages) | Cited 10 times

Online Publication Date: 12 January 2010

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The electrical tuning of negative dielectric anisotropy (−Δε) cholesteric liquid crystals (CLCs) under the influence of ac and dc electric fields was studied. Unlike (+Δε) CLCs, these materials align their helical axis along the applied electric field, allowing the preservation of the optical band gap. Our results show band gap shifts greater than 20% of the original notch position with little change in the quality of the band gap, including the bandwidth and notch depth. These results can be understood by using an electromechanical model, which shows that the Maxwell’s stresses are sufficiently strong to distort the ITO glass substrates. Simple beam and plate elasticity theory is shown to adequately describe the observed behavior. The electromechanical effect is then used to create CLC cells, which can both red and blue tune. This mechanism may have interesting applications in tunable optical filters, optical pressure/stress sensors, and tunable laser technologies.
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62.10.+s Mechanical properties of liquids
78.15.+e Optical properties of fluid materials, supercritical fluids and liquid crystals
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
77.65.-j Piezoelectricity and electromechanical effects

Performance of a CsBr coated Nb photocathode at room temperature

Juan R. Maldonado, Piero Pianetta, David H. Dowell, John Smedley, and Peter Kneisel

J. Appl. Phys. 107, 013106 (2010); http://dx.doi.org/10.1063/1.3276222 (3 pages) | Cited 3 times

Online Publication Date: 12 January 2010

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Experiments performed on Nb substrates coated with thin films of CsBr indicate a substantial enhancement of 150 to 800 times of the photoyield at 257 nm relative to the uncoated substrates. Results are presented for several power density illuminations and sample thickness. Further enhancement of photoyield was observed when the laser illumination was interrupted for a short time in samples with 5–10 nm thick CsBr coatings.
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85.60.Ha Photomultipliers; phototubes and photocathodes
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
41.60.Cr Free-electron lasers
81.65.Ps Polishing, grinding, surface finishing
79.60.-i Photoemission and photoelectron spectra

The optical gain and radiative current density of GaInNAs/GaAs/AlGaAs separate confinement heterostructure quantum well lasers

Shudong Wu, Yongge Cao, Stanko Tomić, and Fumitaro Ishikawa

J. Appl. Phys. 107, 013107 (2010); http://dx.doi.org/10.1063/1.3277019 (6 pages) | Cited 4 times

Online Publication Date: 12 January 2010

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The optical gain and radiative current density of GaInNAs/GaAs/AlGaAs separate confinement heterostructure quantum well (QW) lasers with an emission wavelength of 1.3 μm have been theoretically investigated. The effect of carrier leakage from the GaInNAs QW to the GaAs waveguide layer is studied, and its influence on the optical gain and radiative current density is identified. The hole filling caused by an injected carrier has a strong impact on the optical gain and radiative current density, while the effect of electron filling is negligible, reflecting the smaller band-gap discontinuity in the valence band than in the conduction band. Hole occupation in the waveguide layer decreases the optical gain, and increases the radiative and threshold current densities of the laser. Our calculated threshold current density (659.6 A/cm2) at T = 300 K is in good agreement with the experimental value (650.9 A/cm2) reported in literature [ R. Fehse et al., IEEE J. Sel. Top. Quantum Electron. 8, 801 (2002) ].
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42.55.Px Semiconductor lasers; laser diodes
71.20.Nr Semiconductor compounds
73.21.Fg Quantum wells
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
42.60.By Design of specific laser systems

Photonic band-gap maps for different two dimensionally periodic photonic crystal structures

A. V. Dyogtyev, I. A. Sukhoivanov, and R. M. De La Rue

J. Appl. Phys. 107, 013108 (2010); http://dx.doi.org/10.1063/1.3247544 (7 pages) | Cited 2 times

Online Publication Date: 12 January 2010

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In this paper, the photonic band-gap (PBG) maps of fundamental photonic crystal (PhC) lattices are presented, and discussed. Two fundamental types of lattice: square and hexagonal (triangular, graphite or honeycomb and kagome) with circular, square, and hexagonal hole shapes are considered. Because they show the largest area gap map and because of the relative ease of fabrication of circular holes, it can be asserted that square and triangular lattices of circular holes offer the best choice of two dimensionally periodic photonic crystal (PhC) structure. Graphite and kagome lattices of circular holes in GaAs also show large area gap maps (and the largest gap map is for the second or third higher PBG region). So graphite and kagome lattices are also relevant for exploitation in PhC devices. At the scale required, fabrication process limitations are a significant problem for the realization of hole shapes other than circular.
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42.70.Qs Photonic bandgap materials

Propagation length of surface plasmon polaritons determined by emission from introduced surface discontinuities

Richard A. Flynn, Konrad Bussmann, B. S. Simpkins, Igor Vurgaftman, Chul Soo Kim, and James P. Long

J. Appl. Phys. 107, 013109 (2010); http://dx.doi.org/10.1063/1.3273480 (6 pages) | Cited 4 times

Online Publication Date: 12 January 2010

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Flexible far-field microscopy methods suitable for directly measuring surface plasmon polariton propagation along optically thick or buried waveguides are introduced. The methods monitor the local intensity of surface plasmon polaritons by imaging the light scattered when the plasmons encounter discontinuities in the form of (i) the terminal end of the guide, (ii) randomly dispersed nanoparticles, and (iii) nanoholes drilled through the guide. Measurements by these three methods give consistent values to within ∼ 15% of 39 μm for the propagation length along 5-μm-wide Au-stripe waveguides deposited on an oxidized silicon wafer and excited at a wavelength of 860 nm. This range is due to varying losses associated with the introduction of the nanoholes and nanoparticles. These losses are quantified and could be reduced with realistic experimental improvements. Finite-element computations find that propagation in these optically thick (107 nm) guides is intrinsically limited not only by Ohmic losses, but also by radiation emitted into the substrate from the stripe edges. The radiative loss depends on the slope of the edge sidewall and on the wafer oxide thickness, both of which must be considered when reconciling experiment with theory.
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42.79.Gn Optical waveguides and couplers
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Terahertz waveguide emitter with subwavelength confinement

Michael Martl, Juraj Darmo, Daniel Dietze, Karl Unterrainer, and Erich Gornik

J. Appl. Phys. 107, 013110 (2010); http://dx.doi.org/10.1063/1.3280038 (5 pages) | Cited 3 times

Online Publication Date: 15 January 2010

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The generation of broadband terahertz pulses on the facet of waveguides is presented as an alternative to widely used coupling techniques. Dielectric loaded subwavelength waveguide structures with lateral confinement are investigated with respect to propagating modes and waveguide losses. The results show the terahertz waveguide emitter to be a promising tool for terahertz spectroscopy in the near field and for the probing of microstructured devices such as quantum cascade lasers.
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07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
84.40.Az Waveguides, transmission lines, striplines
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
back to top Plasmas and Electrical Discharges

Characterization of ion emission of an extreme ultraviolet generating discharge produced Sn plasma

K. Gielissen, Y. Sidelnikov, D. Glushkov, W. A. Soer, V. Banine, and J. J. A. M. v. d. Mullen

J. Appl. Phys. 107, 013301 (2010); http://dx.doi.org/10.1063/1.3268462 (7 pages) | Cited 2 times

Online Publication Date: 4 January 2010

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The ion emission of a Sn-based discharge produced extreme ultraviolet producing plasma is characterized with the combined use of different time-of-flight techniques. An electrostatic ion spectrometer is employed to measure the average charge distribution of the emitted Sn ions. A dedicated Faraday cup configuration is used to measure the total ion flux from the source for different discharge energies. High-energy Sn ions emitted by the plasma with energies up to 100 keV have been identified. The number of high-energy ions increases for higher electrical input energy into the plasma while the signal associated with the expanding plasma ions does not show such dependence. The ion energy distribution for a bulk of detected ions is calculated based on the Faraday cup measurements and compared with theoretical plasma expansion dynamics.
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52.50.Dg Plasma sources
52.80.Yr Discharges for spectral sources (including inductively coupled plasma)
52.25.Tx Emission, absorption, and scattering of particles
52.70.Nc Particle measurements

Input impedance of a powerful single-core ferromagnetic inductively coupled plasma source

Y. P. Bliokh, Yu. L. Brodsky, Kh. B. Chashka, J. Felsteiner, and Ya. Z. Slutsker

J. Appl. Phys. 107, 013302 (2010); http://dx.doi.org/10.1063/1.3273499 (6 pages) | Cited 4 times

Online Publication Date: 4 January 2010

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An experimental study of the recently developed version of the ferromagnetic inductively coupled plasma source has shown that under certain circumstances its input impedance becomes almost independent of the delivered rf driving power and (therefore) of the produced plasma density. This plasma source consists of a large ferromagnetic core, which is fully immersed in plasma. This core is surrounded by a primary winding and plasma appears due to gas discharge driven by an rf voltage applied to this primary winding. We have found values of parameters which determine the input impedance in such an “independent” regime and derived a quantitative theory which is in good agreement with the measured impedance values.
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52.50.Dg Plasma sources
52.25.Fi Transport properties
52.80.-s Electric discharges

Wall charge evolution models and emission of exoelectrons from MgO thin film of ac-PDPs

Yong-Seog Kim, Sang-Hoon Yoon, and Heesun Yang

J. Appl. Phys. 107, 013303 (2010); http://dx.doi.org/10.1063/1.3275869 (11 pages) | Cited 5 times

Online Publication Date: 7 January 2010

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Two different wall charge evolution models, i.e., reversion and accumulation models, were proposed incorporating the phenomenon of secondary electron emission during the glow discharges of alternating current-PDPs. Based on the wall charge evolution models, theoretical analyses on exoelectron emission kinetics were conducted, and the effects of initial electron concentration trapped and temperature on the exoelectron currents were predicted. The theoretical prediction was compared with the currents measured experimentally. The theoretical analyses and experimental observations suggest that wall charge evolution model and the first- and second-order reaction kinetics may represent the wall charge formation and exoelectron emission from MgO layer of ac-PDPs.
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68.55.aj Insulators
79.20.Hx Electron impact: secondary emission
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
52.80.Hc Glow; corona

Molecular dynamics simulation of hyperthermal neutrals generated by energetic ion impact on a metal plate

Seung-hoon Park, Suk Jae Yoo, and Choong-Seock Chang

J. Appl. Phys. 107, 013304 (2010); http://dx.doi.org/10.1063/1.3276097 (5 pages)

Online Publication Date: 12 January 2010

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A hyperthermal neutral beam (HNB) source is one of candidate methods to reduce plasma-induced damage problems. The HNB is generated by vertical collisions between energetic ions and a reflector composed of a tungsten plate. We perform a HNB generation simulation using a molecular dynamics algorithm. The roughness of the reflector surface is experimentally measured and the surface structure is taken into consideration in the simulation. The energy and angular distributions of the HNB are obtained by the simulation and the energy yield of the reflected neutral particles is found to be in good agreement with experimental data.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.43.Bn Structural modeling: serial-addition models, computer simulation
68.35.B- Structure of clean surfaces (and surface reconstruction)

Hard graphitelike hydrogenated amorphous carbon grown at high rates by a remote plasma

S. V. Singh, T. Zaharia, M. Creatore, R. Groenen, K. Van Hege, and M. C. M. van de Sanden

J. Appl. Phys. 107, 013305 (2010); http://dx.doi.org/10.1063/1.3273412 (10 pages) | Cited 15 times

Online Publication Date: 15 January 2010

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Hydrogenated amorphous carbon (a-C:H) deposited from an Ar-C2H2 expanding thermal plasma chemical vapor deposition (ETP-CVD) is reported. The downstream plasma region of an ETP is characterized by a low electron temperature ( ∼ 0.3 eV), which leads to an ion driven chemistry and negligible physical effects, such as ion bombardment (ion energy <2 eV) on the depositing surface. The material properties in ETP-CVD can be controlled by varying the plasma chemistry. In this article we investigate the change in a-C:H material properties by varying the Ar/C2H2 gas flow ratio over a wide range (1.33–150), with emphasis on low gas flow ratios (1.33–5). By changing the Ar/C2H2 gas flow ratio, the gas residence time in the ETP expansion can be tuned, which in turn defines the chemistry of the ETP-CVD. Soft polymerlike a-C:H to moderately hard a-C:H films have been deposited by lowering the Ar/C2H2 gas flow ratio. Recently, under very low Ar/C2H2 gas flow ratios, a hard graphitelike a-C:H material has been deposited. The striking feature of this material is the infrared absorption spectrum in the CHx stretching region (2800–3100 cm−1), which is a distinct narrow bimodal spectrum evolving from a broad spectrum for the moderately hard a-C:H. This transition was attributed to the absence of end groups (sp2 CH2 and sp3 CH3), which favors an enhanced cross-linking in the film in a similar effect to elevated ion bombardment or annealing. Moreover, the hard graphitelike film has an increased refractive index (n) as high as 2.5 at 633 nm with a corresponding mass density of ∼ 2.0 g/cm3.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.35.+c Brillouin and Rayleigh scattering; other light scattering
52.77.Dq Plasma-based ion implantation and deposition
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
61.43.-j Disordered solids
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Correlating the structural, chemical, and optical properties at nanometer resolution

L. Gu, V. B. Özdöl, W. Sigle, C. T. Koch, V. Srot, and P. A. van Aken

J. Appl. Phys. 107, 013501 (2010); http://dx.doi.org/10.1063/1.3275048 (4 pages) | Cited 1 time

Online Publication Date: 4 January 2010

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Valence electron spectroscopic imaging (VESI) techniques, taking advantages of the energy-losses suffered by inelastic scattering of the fast electrons in the transmission electron microscope, offer an inherently high spatial resolution to characterize the electronic structure of materials close to the Fermi level. Here we demonstrate that the combination of an electron monochromator and a highly dispersive imaging energy filter, which has become available only recently, allows reliable measurements of local bandgaps on the nanometer scale. In addition, the correlations of structural, chemical, and optical properties can be revealed via VESI using monochromated electrons with a high spatial resolution.
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07.81.+a Electron and ion spectrometers

Improved quality of nonpolar m-plane GaN [10math0] on LiAlO2 substrate using a modified chemical vapor deposition

Mitch M. C. Chou, Da-Ren Hang, Liuwen Chang, Chenlong Chen, Wen-Fu Yang, Chu-An Li, and Jih-Jen Wu

J. Appl. Phys. 107, 013502 (2010); http://dx.doi.org/10.1063/1.3273493 (5 pages) | Cited 3 times

Online Publication Date: 4 January 2010

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Nonpolar GaN crystal on lattice-matched [100] γ-LiAlO2 substrate was grown by a newly designed chemical vapor deposition (CVD) reactor. Following the CVD growth, x-ray diffraction indicated that the GaN film was oriented in the nonpolar m-plane with [10math0] orientation. Further structural characterizations and defect analysis of nonpolar GaN material was performed using transmission electron microscope. Low-temperature photoluminescence was dominated by neutral donor bound excitons and the yellow luminescence was negligible. Raman spectroscopy showed that the as-grown GaN {10math0} epilayer on [100] γ-LiAlO2 substrate were indeed of good quality. Compared to the previous report, nonpolar GaN with an improved quality was demonstrated by modifying the inner structure of the CVD reactor.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
68.55.ag Semiconductors

Influence of the interfacial chemical environment on the luminescence of 3CSiC nanoparticles

Yu. Zakharko, J. Botsoa, S. Alekseev, V. Lysenko, J.-M. Bluet, O. Marty, V. A. Skryshevsky, and G. Guillot

J. Appl. Phys. 107, 013503 (2010); http://dx.doi.org/10.1063/1.3273498 (7 pages) | Cited 12 times

Online Publication Date: 4 January 2010

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Surface chemistry of as-prepared 3CSiC nanoparticles obtained by electrochemical etching of bulk 3CSiC substrates was studied. Chemical environment was found to influence strongly the photoinduced electronic transitions in the 3CSiC nanoparticles. The influence of different interfacial chemical environments of the 3CSiC nanoparticles, such as surface chemistry, solvent nature, and surface charges on the photoinduced absorption and luminescence of the nanoparticles at room temperature, is described and discussed in detail. For example, oxidation induced passivation of the radiative band gap states allows visualization of the transitions between energy levels in the nanoparticles in which photogenerated charge carriers are quantumly confined. Electrostatic screening of the radiative band gap states by highly polar solvent media leads to a blueshift and a decrease in the width at half maximum of the photoluminescence spectra of the nanoparticles. As for the surface charges, they govern band bending slope and thus influence strongly the radiative transitions via energy states in the band gap.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials
81.65.Cf Surface cleaning, etching, patterning
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.65.Rv Passivation
73.22.-f Electronic structure of nanoscale materials and related systems

Acoustic losses in a thick quartz plate at low temperatures

A. Grib, D. Heinert, R. Nawrodt, C. Schwarz, V. Große, P. Seidel, I. Martin, S. Rowan, and J. Hough

J. Appl. Phys. 107, 013504 (2010); http://dx.doi.org/10.1063/1.3275425 (5 pages) | Cited 2 times

Online Publication Date: 5 January 2010

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We have shown that thermoelastic losses give the significant contribution to the total mechanical damping in the low loss quartz even for the bulk samples if the thickness of the sample is smaller than other dimensions. We have developed a model that describes experimental data of mechanical losses in a round quartz plate with the diameter 7.48 cm and the thickness 1.2 cm at temperatures 5–25 K in the range of eigenfrequencies 11–300 kHz. The model takes into account both the contribution of thermoelastic losses and the contribution due to the interaction of the acoustic wave with thermal phonons (Akhieser damping). Thermoelastic processes determine losses below 120 kHz. At larger eigenfrequencies, the Akhieser damping dominates.
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62.65.+k Acoustical properties of solids
62.20.D- Elasticity
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
63.20.-e Phonons in crystal lattices

Elastic anomalies due to structural phase transitions in mechanoluminescent SrAl2O4:Eu

M. A. Carpenter, C. J. Howard, M. J. Andrew, R. E. A. McKnight, Y. Liu, and R. L. Withers

J. Appl. Phys. 107, 013505 (2010); http://dx.doi.org/10.1063/1.3269723 (10 pages) | Cited 3 times

Online Publication Date: 5 January 2010

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Elastic and anelastic properties of a ceramic sample of elasticoluminescent SrAl2O4:Eu have been characterized as a function of temperature by resonant ultrasound spectroscopy. Both the bulk (K) and shear (G) moduli show changes attributable to the influence of the P6322→P63 (mathA)→P21 sequence of structural phase transitions. Softening of K and stiffening of G at the P6322→P63 (mathA) transition (Tc ≈ 1135 K) is consistent with weak strain/order parameter coupling and tricritical character. In marked contrast, the first order P63 (mathA)→P21 transition near 930 K is accompanied by stiffening such that G is ∼ 50% larger at room temperature than the value for a P6322 structure extrapolated directly from high temperatures and K is ∼ 15% larger. Softening of G at high temperatures is consistent with the existence of a soft acoustic mode. Both the P63 (mathA) and P6322 phases show an increasing acoustic dissipation with increasing temperature and there is an additional peak in the dissipation behavior below ∼ 650 K. Landau theory has been used to analyze the overall strain and elastic behavior of SrAl2O4:Eu. The stability of the P21 structure is considered in terms of coupling between order parameters with Γ6 and M2 symmetry, though it could also be stabilized by pairwise coupling of order parameters corresponding to irreps Γ4+M2, Γ4+M3, Γ6+M3, and M2+M3. Twin walls in this material should have interesting properties, which are quite distinct from those of the bulk material and could contribute differently to the elasticoluminescent properties.
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78.60.Mq Sonoluminescence, triboluminescence
62.65.+k Acoustical properties of solids
62.20.de Elastic moduli
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions

Structured shock waves and the fourth-power law

Dennis E. Grady

J. Appl. Phys. 107, 013506 (2010); http://dx.doi.org/10.1063/1.3269720 (13 pages) | Cited 9 times

Online Publication Date: 6 January 2010

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A fourth-power law relating the stress jump through a steady structured shock wave and the maximum strain rate within the shock wave has received recognition as a unifying relation over a sensibly wide range of materials and shock compression amplitudes. Less widely recognized is the complementary applicability of the invariance of the product of the energy dissipated and the time over which this energy is dissipated through a structure shock wave—a property with the dimensions of action. While the latter invariance implies the fourth-power behavior for steady shock waves, this invariance also has an apparent application to unsteady structured waves under certain conditions. A brief history of the origin of the fourth-power law is provided. Some commentary is offered on the physical principles of solid viscosity in the shock wave and the underlying invariance of the energy-time product in the shock wave event. The results for steady structured waves in porous and composite solids, which do not in general exhibit fourth-power behavior, are examined. Observations of systematic behaviors with component cell size and impedance disparities suggest acoustic scattering may contribute to wave structuring in selected materials.
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62.50.Ef Shock wave effects in solids and liquids
62.20.F- Deformation and plasticity
61.43.Gt Powders, porous materials
62.65.+k Acoustical properties of solids
81.40.Lm Deformation, plasticity, and creep

Ferromagnetic metamaterial with tunable negative index of refraction

Da-yong Zou, Ai-min Jiang, and Rui-xin Wu

J. Appl. Phys. 107, 013507 (2010); http://dx.doi.org/10.1063/1.3275857 (4 pages) | Cited 2 times

Online Publication Date: 6 January 2010

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We investigate the index of refraction of the ferromagnetic metamaterial, which consists of periodic layered ferrite and semiconductor or metallic mesh. We find that the metamaterial has the negative index; the frequency range and magnitude of the negative index are tunable in applied magnetic fields. The frequency range of the negative index shifts to higher frequencies as the applied magnetic fields increase. The permeability and permittivity of the ferrite and other component materials, as well as their thickness ratios, influence the tunable range of the negative index. It is demonstrated that ferrite-mesh structure has a much lower loss than that of a ferrite-semiconductor structure.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
72.30.+q High-frequency effects; plasma effects
77.22.Ch Permittivity (dielectric function)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Gg Ferrimagnetics
42.70.-a Optical materials
75.50.Dd Nonmetallic ferromagnetic materials

Refractive error correction for in situ curvature measurement using laser beam deflection method

Xinran Xiao and Daniel Schleh

J. Appl. Phys. 107, 013508 (2010); http://dx.doi.org/10.1063/1.3276190 (5 pages) | Cited 3 times

Online Publication Date: 6 January 2010

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Stoney’s equation allows one to calculate the internal stress in a thin film deposited on a thick substrate from the curvature of the bilayer beam. The curvature measurement is thus critical in the bending beam method, which is based on this equation. When an optical technique is used in curvature measurement, the refraction at optical boundaries needs to be corrected. An approximate correction to Stoney’s equation accounting for refractive error in the bending beam method in electrochemical applications was reported previously. This paper revisits the derivation. A set of diagrams for optical paths in in situ curvature measurement using the laser beam deflection method are presented. These diagrams allow us to establish the triangular relationships among the incident angles of the light beam and the deflection angle of the cantilever beam. Correction solutions are derived for three possible optical arrangements with the consideration of the travel distance of the light beam in liquid and in the container wall. In its approximated form, the correction derived in this paper differs from the previous formula by a factor of 2. It was discovered that an incorrect relationship for curvature was used in the previous derivation.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
68.60.-p Physical properties of thin films, nonelectronic
68.55.-a Thin film structure and morphology

Wave propagation in prestretched polymer nanofibers

Xiang-Fa Wu

J. Appl. Phys. 107, 013509 (2010); http://dx.doi.org/10.1063/1.3275870 (8 pages) | Cited 4 times

Online Publication Date: 7 January 2010

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Wave propagation in prestretched ultrathin polymer fibers (e.g., those as-electrospun polymer nanofibers) are under the influence of prestretch, surface energy, and nonlinear elasticity. A one-dimensional nonlinear elastic model is proposed to take into account such combined influence in the wave propagation phenomenon. In the model, the polymer nanofibers are considered to behave as hyperelastic Mooney–Rivlin solid. For small dynamic disturbance, linearized wave equation is established by superimposing the dynamic displacement as linear disturbance on the prestretched equilibrium state. Explicit wave dispersion relations are obtained and relevant numerical examples are demonstrated in examining the dependency of wave phase speed upon the wave number at varying surface properties, fiber radius, and prestretch. In the limiting case of neglecting the dynamic effect, the present wave equation can yield the governing equation of surface rippling in compliant nanofibers. This governing equation is capable of predicting the initiation condition of surface rippling and the critical fiber radius, below which compliant nanofibers cannot be produced due to surface instability. Results obtained in this study are applicable as the theoretical basis of dynamic characterization of compliant nanowires/nanofibers, nanofiber device design, and nanostructural analysis.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.25.-g Mechanical properties of nanoscale systems
62.20.F- Deformation and plasticity
65.40.gp Surface energy
68.35.Md Surface thermodynamics, surface energies

Optical and electrical properties of gallium-doped MgxZn1−xO

Wei Wei, Chunming Jin, Jagdish Narayan, and Roger J. Narayan

J. Appl. Phys. 107, 013510 (2010); http://dx.doi.org/10.1063/1.3271415 (5 pages) | Cited 6 times

Online Publication Date: 7 January 2010

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In this study, the optical and electrical properties of epitaxial single crystal gallium-doped MgxZn1−xO thin films grown on c-plane sapphire substrates by pulsed laser deposition were investigated. In these films, the Ga content was varied from 0.05 to 7 at. % and the Mg content was varied from 5 to 15 at. %. X-ray diffraction showed that the solid solubility limit of Ga in MgxZn1−xO is less than 3 at. %. The absorption spectra were fitted to examine Ga doping effects on bandgap and band tail characteristics. Distinctive trends in fitted bandgap and band tail characteristics were determined in films with Ga content below 3 at. % and Ga content above 3 at. %. The effects of bandgap engineering on optical transparency were evaluated using transmission spectra. Carrier concentration and Hall mobility data were obtained as functions of Ga content and Mg content. The electrical properties were significantly degraded when the Ga content exceeded 3 at. %. Correlations between conduction mechanisms and gallium doping of MgxZn1−xO thin films were described. In addition, the effect of bandgap engineering on the electrical properties of epitaxial single crystal gallium-doped MgxZn1−xO thin films was discussed.
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68.55.ag Semiconductors
73.61.Ey III-V semiconductors
81.15.Fg Pulsed laser ablation deposition
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
72.20.My Galvanomagnetic and other magnetotransport effects
71.20.Nr Semiconductor compounds
78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Fs III-V and II-VI semiconductors
78.40.Fy Semiconductors
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