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3 Aug 2009

Volume 95, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 052901 (2009); http://dx.doi.org/10.1063/1.3190518 (3 pages)

Didit Yudistira, Sarah Benchabane, Davide Janner, and Valerio Pruneri
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Ultrafast pulse characterization using cross phase modulation in silicon

En-Kuang Tien, Xing-Zhu Sang, Feng Qing, Qi Song, and Ozdal Boyraz

Appl. Phys. Lett. 95, 051101 (2009); http://dx.doi.org/10.1063/1.3193538 (3 pages) | Cited 7 times

Online Publication Date: 3 August 2009

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Based on the high nonlinearity of the chip-scale silicon waveguide with small dispersion, a compact frequency-resolved optical gating system has been demonstrated using cross phase modulation for ultrafast pulse characterization. The principal component generalized projections algorithm is used to retrieve the amplitude and phase from the spectrogram. Amplitude and phase of a 540 fs pulse have been measured. The measured amplitude result is confirmed by the autocorrelation measurement.
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42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.79.Hp Optical processors, correlators, and modulators

Strain-induced nitrogen incorporation in atomic layer epitaxy growth of InAsN/GaAs quantum wells using metal organic chemical vapor deposition

Asaf Albo, Catherine Cytermann, Gad Bahir, and Dan Fekete

Appl. Phys. Lett. 95, 051102 (2009); http://dx.doi.org/10.1063/1.3193663 (3 pages) | Cited 3 times

Online Publication Date: 4 August 2009

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We report on the growth of high-quality high-indium-content (Ga)InAsN/GaAs quantum wells grown using low-pressure metal organic chemical vapor deposition. The growth was performed employing a strain-controlled atomic layer epitaxy technique. We verified experimentally that the strain enables the incorporation of nitrogen atoms during the atomic layer epitaxy growth of InAsN monolayers on GaAs. Photoluminescence and secondary ion mass spectroscopy measurements indicate that about 2.5% of the nitrogen was incorporated in the grown layers. Utilizing this strain-controlled atomic layer epitaxy technique, we designed and demonstrated highly strained InAsN/GaAs short-period superlattice structure suitable for applications in optical communication.
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68.55.ag Semiconductors
68.65.Fg Quantum wells
78.67.De Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Cr III-V semiconductors
68.65.Cd Superlattices
81.07.St Quantum wells

Micrometric spatial control of rare earth ion emission in LiNbO3: A two-dimensional multicolor array

P. Molina, M. O. Ramírez, J. V. García-Santizo, S. Álvarez-García, R. Pazik, W. Strek, P. J. Dereń, and L. E. Bausá

Appl. Phys. Lett. 95, 051103 (2009); http://dx.doi.org/10.1063/1.3190502 (3 pages) | Cited 2 times

Online Publication Date: 4 August 2009

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We report on the preparation and optical characterization of a two-dimensional multicolor emission arrangement obtained by embedding high refractive-index Er3+ doped CaTiO3 nanoparticles into a Nd3+ doped LiNbO3 crystal substrate prepatterned with an array of microvoids. By controlling the spatial location of the rare earth ions at the micrometer scale, we show the possibility of simultaneous spatial and spectral control of the spontaneous emission in a two-dimensional rare earth optically activated array. The results can be useful for the development of microcomposite rare earth based photonic devices, such as multicolor emission displays or pixelated color structures.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.up Other materials
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials

Burn-in mechanism of 450 nm InGaN ridge laser test structures

Jens Müller, Georg Brüderl, Marc Schillgalies, Sönke Tautz, Dimitri Dini, Andreas Breidenassel, Bastian Galler, and Stephan Lutgen

Appl. Phys. Lett. 95, 051104 (2009); http://dx.doi.org/10.1063/1.3194139 (3 pages) | Cited 9 times

Online Publication Date: 5 August 2009

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We investigated the short term stability of the optical output power of 450 nm InGaN test lasers. The short term degradation strongly depended on ridge width. It was mainly caused by an increase in threshold current. From measurements of subthreshold wave-length blueshift, carrier lifetime, and output power, we found a decrease in carrier density after 15 h of aging. We show a direct correlation of the short term aging with current spreading effects.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Gn Optical waveguides and couplers

Fabry–Pérot nanocavities in multilayered plasmonic crystals for enhanced biosensing

Alp Artar, Ahmet Ali Yanik, and Hatice Altug

Appl. Phys. Lett. 95, 051105 (2009); http://dx.doi.org/10.1063/1.3202391 (3 pages) | Cited 18 times

Online Publication Date: 6 August 2009

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We have demonstrated extraordinary light transmission effect through Fabry–Pérot cavities in multilayered plasmonic crystals formed by coupling two physically separated metallic nanohole and nanodisk array layers. Superior field-medium overlap is observed with Fabry–Pérot resonances as a result of stronger electromagnetic field confinement in the dielectric region far from the metallic surfaces. We show that these cavity resonances are highly sensitive to refractive index changes. The large field-material overlap combined with simple fabrication scheme used here makes these structures an ideal candidate for biosensing applications.
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07.60.-j Optical instruments and equipment
87.80.-y Biophysical techniques (research methods)

Effect of defect saturation on terahertz emission and detection properties of low temperature GaAs photoconductive switches

Samir Rihani, Richard Faulks, Harvey Beere, Hideaki Page, Ian Gregory, Michael Evans, David A. Ritchie, and Michael Pepper

Appl. Phys. Lett. 95, 051106 (2009); http://dx.doi.org/10.1063/1.3193680 (3 pages) | Cited 4 times

Online Publication Date: 6 August 2009

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We present a study into the properties of terahertz (THz) emission and detection using low temperature grown GaAs photoconductive switches over a range of ex situ anneal temperatures. Our analysis focuses on the effect of defect saturation, which has been confirmed in many experiments. However its effect on the THz emission and detection has so far not been fully investigated. In this letter, we examine the dependence of the radiated THz pulse width (full width at half maximum) upon optical power, and show that the differences in the characteristics with annealing can be theoretically accounted for when defect saturation is taken into account. Defect saturation was found to substantially increase the trapping time of photoexcited electrons, which in turn can cause THz pulse broadening at high optical powers. This effect was found to increase with anneal temperature due to the decrease in defect density. The radiated peak THz amplitude from emitters increases monotonically with increasing optical power across the range of anneal temperatures investigated. In the detector configuration, however, the detected peak THz amplitude reaches a maximum before starting to decrease with increasing optical power. The latter trend was observed for devices annealed at temperatures higher than 300 °C and is attributed to the onset of defect saturation.
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85.60.-q Optoelectronic devices
61.72.Cc Kinetics of defect formation and annealing

Dynamics of microbubble generation and trapping by self-focused femtosecond laser pulses

Kun Yang, Yun Zhou, Qiushi Ren, Jing Yong Ye, and Cheri X. Deng

Appl. Phys. Lett. 95, 051107 (2009); http://dx.doi.org/10.1063/1.3187535 (3 pages) | Cited 4 times

Online Publication Date: 6 August 2009

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Different from conventional optical tweezers used for trapping high refractive index micron-sized particles, bubble generation and trapping by femtosecond laser offer a unique strategy to manipulate microbubbles. Using high frequency ultrasound imaging and fast-frame optical video microscopy, we obtained results revealing the spatiotemporal characteristics of bubble generation and trapping by self-focused femtosecond laser pulses at multiple locations along the laser beam. We detected distinct acoustic signals associated with the laser focus and measured the trapping force by using acoustic radiation force to detrap the bubble from the laser beam.
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47.55.db Drop and bubble formation
47.55.dd Bubble dynamics
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.50.Wk Mechanical effects of light on material media, microstructures and particles
47.80.Jk Flow visualization and imaging

Spontaneous formation of a polariton condensate in a planar GaAs microcavity

Esther Wertz, Lydie Ferrier, Dmitry D. Solnyshkov, Pascale Senellart, Daniele Bajoni, Audrey Miard, Aristide Lemaître, Guillaume Malpuech, and Jacqueline Bloch

Appl. Phys. Lett. 95, 051108 (2009); http://dx.doi.org/10.1063/1.3192408 (3 pages) | Cited 24 times

Online Publication Date: 7 August 2009

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We report on polariton condensation in a planar GaAs microcavity under nonresonant optical excitation. Angularly resolved photoluminescence measurements demonstrate polariton condensation for temperature up to 40 K. Numerical simulations using Boltzmann equations give an overall description of the observed condensation for various detunings and temperatures. This model highlights the importance of the polariton relaxation rate as compared to the polariton decay for condensation to occur on the lowest energy polariton states.
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81.05.Ea III-V semiconductors
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
78.55.Cr III-V semiconductors
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Observation and quantification of OH radicals in the far downstream part of an atmospheric microwave plasma jet using cavity ringdown spectroscopy

Chuji Wang, Nimisha Srivastava, and Theodore S. Dibble

Appl. Phys. Lett. 95, 051501 (2009); http://dx.doi.org/10.1063/1.3177314 (3 pages) | Cited 5 times

Online Publication Date: 3 August 2009

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An atmospheric argon microwave plasma jet with a plasma column 8 mm long and 1–2 mm wide is studied. Existence of hydroxyl (OH) radicals down to 28 mm away from the plasma orifice is evidenced by UV cavity ringdown spectroscopy. The measured OH (v″ = 0, J″ = 3.5) number density at 28 mm is 7.2×1012 molecule/cm3. The plasma gas flow velocity, along with the known OH lifetimes, suggests that OH radicals observed in the downstream are not the OH radicals formed in the plasma column but were formed in the downstream.
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52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.75.-d Plasma devices
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

Current scaling in an atmospheric pressure capillary dielectric barrier discharge

Brian L. Sands, Shih K. Huang, and Biswa N. Ganguly

Appl. Phys. Lett. 95, 051502 (2009); http://dx.doi.org/10.1063/1.3187939 (3 pages) | Cited 3 times

Online Publication Date: 4 August 2009

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Current scaling in an atmospheric pressure capillary dielectric barrier discharge, comprising a structured rare gas flow that extends into ambient air, is characterized by electrical and optical measurements. In the transient glow mode, two current scaling regimes were identified that are separated by the static free shear flow boundary. The peak current was sensitive to cathode placement relative to this flow structure and could be scaled from ∼ 300 mA to over 5 A. Applying a Boltzmann equation solver, it was found that ∼ 1% air entrainment into the flow and an E/N≲5×10−16 V cm−2 could account for the observed trends.
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52.80.Hc Glow; corona
52.30.-q Plasma dynamics and flow

Surface-plasmon-enhanced photoluminescence from metal-capped Alq3 thin Films

Man Chun Tam, Huimin Su, Kam Sing Wong, Xiuling Zhu, and Hoi Sing Kwok

Appl. Phys. Lett. 95, 051503 (2009); http://dx.doi.org/10.1063/1.3190501 (3 pages) | Cited 6 times

Online Publication Date: 6 August 2009

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Absolute quantum efficiencies of surface-plasmon-enhanced photoluminescence from Au capped Alq3 films were measured using an integrating sphere. The metal “mirror” and directional enhancement effects due to surface roughness which usually occur in forward/backward collection measurements were eliminated using this integrating sphere technique. Up to 40% of the enhanced photoluminescence observed using the forward/backward collection method was shown to have come from mirror and/or enhanced directional scattering effects. Purcell factors obtained from the integrating sphere data and from time-resolved photoluminescence measurements were consistent, confirming surface-plasmon coupling. Incorporating a thin spacer layer enhanced the quantum efficiency and also eliminated nonradiative recombination due to the metal layer. The results clearly show the importance of using an integrating sphere when measuring overall surface-plasmon quantum efficiencies to eliminate directional scattering effects.
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78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
68.35.bg Semiconductors

Temporal evolution of double layers in pulsed helicon plasmas

Ioana A. Biloiu and Earl E. Scime

Appl. Phys. Lett. 95, 051504 (2009); http://dx.doi.org/10.1063/1.3204014 (3 pages) | Cited 4 times

Online Publication Date: 7 August 2009

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Delays of the order of tens of milliseconds in the appearance of the fast argon ion population in the expansion region of a pulsed helicon plasma are observed in time-resolved, laser induced fluorescence measurements. The fast ion population is a proxy for the presence of a double layer. The magnitude of the time delay depends strongly on the length of the interval between plasma pulses; the shorter the time between pulses, the shorter the time delay. The time delay approaches zero for inter-pulse intervals smaller than 30 ms. The double layer strength is not affected by plasma source modulation frequency.
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52.40.Kh Plasma sheaths
72.30.+q High-frequency effects; plasma effects
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Anomalies in the thermomechanical behavior of Ba0.5Sr0.5Co0.8Fe0.2O3−δ ceramic oxygen conductive membranes at intermediate temperatures

B. X. Huang, J. Malzbender, R. W. Steinbrech, P. Grychtol, C. M. Schneider, and L. Singheiser

Appl. Phys. Lett. 95, 051901 (2009); http://dx.doi.org/10.1063/1.3193657 (3 pages) | Cited 10 times

Online Publication Date: 3 August 2009

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The thermomechanical properties of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) were measured using ring-on-ring tests and depth-sensitive microindentation. The cubic BSCF material exhibits an anomaly in mechanical properties between 200 and 400 °C. The observed anomaly is attributed to the transition of Co3+ spin states which is experimentally confirmed by susceptibility measurements. Furthermore, slip lines were observed around the impression when indentation tests were carried out above 260 °C.
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81.40.Gh Other heat and thermomechanical treatments
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mm Fracture
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dq Other elastic constants

Rapid laminating mixer using a contraction-expansion array microchannel

Myung Gwon Lee, Sungyoung Choi, and Je-Kyun Park

Appl. Phys. Lett. 95, 051902 (2009); http://dx.doi.org/10.1063/1.3194137 (3 pages) | Cited 7 times

Online Publication Date: 3 August 2009

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Three-dimensional lamination mixing is demonstrated in a simple and easily fabricated contraction-expansion array microchannel. The abrupt change of the cross-sectional area of the channel curves fluid streams and accelerates the flow velocity especially at the entrance of the contraction region. Centrifugal effects at that region result in Dean vortices that continuously split and redirect fluid streams, thereby enabling appreciable mixing. The presented mixer provides a level of 90% mixing in the relatively large range of Reynolds number from 4.3 to 28.6 by employing the channel with 30 contraction-expansion units.
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47.85.Np Fluidics
47.51.+a Mixing
47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)
47.60.Dx Flows in ducts and channels
47.32.cb Vortex interactions
47.15.Rq Laminar flows in cavities, channels, ducts, and conduits

Blue-emitting LaSi3N5:Ce3+ fine powder phosphor for UV-converting white light-emitting diodes

Takayuki Suehiro, Naoto Hirosaki, Rong-Jun Xie, and Tsugio Sato

Appl. Phys. Lett. 95, 051903 (2009); http://dx.doi.org/10.1063/1.3193549 (3 pages) | Cited 25 times

Online Publication Date: 4 August 2009

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We have synthesized the pure ternary nitride phosphor, LaSi3N5:Ce3+ from the multicomponent oxide system La2O3–CeO2–SiO2, by using the gas-reduction-nitridation method. Highly pure, single-phase LaSi3N5:Ce3+ powders possessing particle sizes of ∼ 0.4–0.6 μm were obtained with the processing temperature ≤ 1500 °C. The synthesized LaSi3N5:Ce3+ exhibits tunable blue broadband emission with the dominant wavelength of 464–475 nm and the external quantum efficiency of ∼ 34%–67% under excitation of 355–380 nm. A high thermal stability of LaSi3N5:Ce3+ compared to the existing La–Si–O–N hosts was demonstrated, indicating the promising applicability as a blue-emitting phosphor for UV-converting white light-emitting diodes.
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81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
61.43.Gt Powders, porous materials

Combined polarized Raman and atomic force microscopy: In situ study of point defects and mechanical properties in individual ZnO nanobelts

Marcel Lucas, Zhong Lin Wang, and Elisa Riedo

Appl. Phys. Lett. 95, 051904 (2009); http://dx.doi.org/10.1063/1.3177065 (3 pages) | Cited 13 times

Online Publication Date: 4 August 2009

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We present a method, polarized Raman (PR) spectroscopy combined with atomic force microscopy (AFM), to characterize in situ and nondestructively the structure and the physical properties of individual nanostructures. PR-AFM applied to individual ZnO nanobelts reveals the interplay between growth direction, point defects, morphology, and mechanical properties of these nanostructures. In particular, we find that the presence of point defects can decrease the elastic modulus of the nanobelts by one order of magnitude. More generally, PR-AFM can be extended to different types of nanostructures, which can be in as-fabricated devices.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.30.Fs III-V and II-VI semiconductors
61.72.J- Point defects and defect clusters
62.25.-g Mechanical properties of nanoscale systems
62.20.de Elastic moduli
81.40.Jj Elasticity and anelasticity, stress-strain relations

Freestanding high quality GaN substrate by associated GaN nanorods self-separated hydride vapor-phase epitaxy

C. L. Chao, C. H. Chiu, Y. J. Lee, H. C. Kuo, Po-Chun Liu, Jeng Dar Tsay, and S. J. Cheng

Appl. Phys. Lett. 95, 051905 (2009); http://dx.doi.org/10.1063/1.3195684 (3 pages) | Cited 12 times

Online Publication Date: 4 August 2009

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This work proposes a method for fabricating 2 in. freestanding GaN substrates of high crystallographic quality and low residual strain. Arrays of GaN nanorods with sidewalls coated with silicon dioxide (SiO2) were randomly arranged on the sapphire substrate as a growth template for subsequent hydride vapor-phase epitaxy (HVPE). The passivation of the sidewalls coated with SiO2 prevents the coalescence of GaN grains in spaces between the rods, causing them to grow preferentially on the top of individual rods. The proposed method significantly improves GaN crystal quality and results in self-separation from the underlying host sapphire substrate due to the relaxation of thermal strains in the HVPE cooling-down process.
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81.16.-c Methods of micro- and nanofabrication and processing
81.65.Rv Passivation
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Ea III-V semiconductors
68.55.ag Semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures

Influence of lattice symmetry on ultrasound transmission through plates with subwavelength aperture arrays

Héctor Estrada, Pilar Candelas, Antonio Uris, Francisco Belmar, F. Javier García de Abajo, and Francisco Meseguer

Appl. Phys. Lett. 95, 051906 (2009); http://dx.doi.org/10.1063/1.3196330 (3 pages) | Cited 10 times

Online Publication Date: 4 August 2009

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We study the transmission of sound waves through aluminum plates perforated with square and triangular hole arrays. We demonstrate both theoretically and experimentally that lattice symmetry affects the position of the Wood anomalies and the width of the transmission peaks. The angle and frequency dependence of sound transmission through perforated plates are thoroughly discussed. Finally, we observe unexpected anisotropic behavior in the long-wavelength Lamb-mode bands of perforated plates.
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43.35.-c Ultrasonics, quantum acoustics, and physical effects of sound

Thermal transport through superlattice solid-solid interfaces

Sohail Murad and Ishwar K. Puri

Appl. Phys. Lett. 95, 051907 (2009); http://dx.doi.org/10.1063/1.3197012 (3 pages) | Cited 4 times

Online Publication Date: 4 August 2009

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Using molecular dynamics, we consider the thermal resistances of superlattices consisting of varying numbers of distinct nanolayers of two different materials. These are placed between two water reservoirs at uniform hot and cold temperatures. The interfacial resistances produced between different solid layers can lead to significantly lower heat transfer for a specified temperature difference. Such a large reduction in thermal transport cannot be explained by the interfacial resistance alone. In addition to the interfacial resistance between two adjacent superlattice layers, the relatively wide thermal boundary layers that are produced adjacent to the interfaces introduces a supplementary resistance.
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73.40.Cg Contact resistance, contact potential
61.43.Bn Structural modeling: serial-addition models, computer simulation
73.63.Bd Nanocrystalline materials
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics

The origin of stretched exponential function in dynamic response of photodarkening in amorphous chalcogenides

K. Shimakawa, N. Nakagawa, and T. Itoh

Appl. Phys. Lett. 95, 051908 (2009); http://dx.doi.org/10.1063/1.3197631 (3 pages) | Cited 8 times

Online Publication Date: 5 August 2009

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An increase in the optical absorption coefficient during illumination [photodarkening (PD)] is known to be described by a stretched exponential function (SEF) 1−exp[−(t/τ)β], where τ and β, respectively, are the effective response time and the dispersion parameter. τ and β deduced experimentally depend on the thickness of films. A model calculation, assuming a series sequence of PD along the thickness direction from the illuminated surface to the back surface, produces the SEF and replicates well the experimental results.
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78.66.Jg Amorphous semiconductors; glasses
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.jd Thickness

Pull-in control due to Casimir forces using external magnetic fields

R. Esquivel-Sirvent, M. A. Palomino-Ovando, and G. H. Cocoletzi

Appl. Phys. Lett. 95, 051909 (2009); http://dx.doi.org/10.1063/1.3193666 (3 pages) | Cited 3 times

Online Publication Date: 5 August 2009

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We present a theoretical calculation of the pull-in control in capacitive microswitches actuated by Casimir forces using external magnetic fields. The external magnetic fields induce an optical anisotropy due to the excitation of magnetoplasmons that reduces the Casimir force. The calculations are performed in the Voigt configuration and the results show that as the magnetic field increases the system becomes more stable. The detachment length for a cantilever is also calculated for a cantilever, showing that it increases with increasing magnetic field. At the pull-in separation, the stiffness of the system decreases with the increasing magnetic field.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
84.32.Dd Connectors, relays, and switches
07.10.Cm Micromechanical devices and systems

The role of stress in the time-dependent optical response of silicon photonic band gap crystals

H. Wei, D. F. Underwood, S. E. Han, D. A. Blank, and D. J. Norris

Appl. Phys. Lett. 95, 051910 (2009); http://dx.doi.org/10.1063/1.3194140 (3 pages) | Cited 1 time

Online Publication Date: 5 August 2009

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Amorphous silicon inverse opals with a complete photonic band gap have been studied with optical pump-probe spectroscopy. The pump-generated free carriers cause the reflection near the band gap to be lowered for the first few picoseconds due to induced absorption. After ∼ 5 ps, this effect disappears and an unexpected blue spectral shift is seen in the photonic band gap. The shift appears consistent with photoinduced stress caused by the thermal expansion mismatch between the silicon and its native oxide. However, simple mechanical models fail to quantify this behavior.
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78.47.D- Time resolved spectroscopy (>1 psec)
65.40.De Thermal expansion; thermomechanical effects
42.70.Qs Photonic bandgap materials

Polarized micro-Raman study of the field-induced phase transition in the relaxor 0.67PbMg1/3Nb2/3O3–0.33PbTiO3 single crystal

Y. Yang, Y. L. Liu, S. Y. Ma, K. Zhu, L. Y. Zhang, J. Cheng, G. G. Siu, Z. K. Xu, and H. S. Luo

Appl. Phys. Lett. 95, 051911 (2009); http://dx.doi.org/10.1063/1.3194149 (3 pages) | Cited 3 times

Online Publication Date: 5 August 2009

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Polarized Raman spectroscopy has been performed to investigate the effects of the electric field on 0.67PbMg1/3Nb2/3O3–0.33PbTiO3 (PMN–33%PT) single crystal. The electric-field-evolution of Raman spectra differed from one microarea to another. In the crossed polarization geometry, the abrupt changes in the intensities of the Raman bands at around 570 and 780 cm−1 indicated the occurrence of the field induced phase transition from the MC-type to the MA-type monoclinic structure. On the other hand, the Raman spectra for the microarea that was initially in the MA phase exhibited no obvious changes. All these results revealed the microheterogeneity in PMN–33%PT single crystal, which is useful for understanding the field-induced superior electromechanical properties.
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78.30.Hv Other nonmetallic inorganics
77.80.B- Phase transitions and Curie point
61.66.Fn Inorganic compounds
77.65.-j Piezoelectricity and electromechanical effects

Emission of terahertz radiation from SiC

Jared H. Strait, Paul A. George, Jahan Dawlaty, Shriram Shivaraman, Mvs Chandrashekhar, Farhan Rana, and Michael G. Spencer

Appl. Phys. Lett. 95, 051912 (2009); http://dx.doi.org/10.1063/1.3194152 (3 pages) | Cited 4 times

Online Publication Date: 5 August 2009

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We report the emission of strong coherent broadband terahertz radiation from 6H-silicon-carbide (SiC) excited with optical pulses. The measured terahertz spectral signal-to-noise ratio is better than one thousand. We determine that the terahertz radiation is generated via second order optical nonlinearity (optical rectification). We present a measurement of the ratio of nonlinear susceptibility tensor elements χzzz(2)/χzxx(2) and the complex index of refraction of silicon carbide at terahertz frequencies.
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78.70.Gq Microwave and radio-frequency interactions
42.65.An Optical susceptibility, hyperpolarizability

Tailoring of inclined crystal orientation in layered cobaltite thin films for the development of off-diagonal thermoelectric effect

Kouhei Takahashi, Akihiro Sakai, Tsutomu Kanno, and Hideaki Adachi

Appl. Phys. Lett. 95, 051913 (2009); http://dx.doi.org/10.1063/1.3194796 (3 pages) | Cited 7 times

Online Publication Date: 5 August 2009

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A highly inclined CoO2 plane orientation was realized in CaxCoO2 thin films grown on sapphire single crystal substrates. The inclination angle of the CoO2 plane orientation was controlled by changing the inclination angle of the sapphire(0001) plane with respect to the substrate surface and additionally by introducing an epitaxial buffer layer of hematite. We demonstrate that the highly inclined crystal orientation results in a unique off-diagonal thermoelectric effect with a potential to produce a voltage signal of up to 600 mV along the film in-plane direction by a unit temperature difference along the film out-of-plane direction.
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68.55.at Other materials
61.50.-f Structure of bulk crystals
72.20.Pa Thermoelectric and thermomagnetic effects
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