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13 Jun 2011

Volume 98, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 243101 (2011); http://dx.doi.org/10.1063/1.3598468 (3 pages)

M. Beleggia, T. Kasama, R. E. Dunin-Borkowski, S. Hofmann, and G. Pozzi
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Si-interdiffusion in heavily doped AlN-GaN-based quantum well intersubband photodetectors

Daniel Hofstetter, Joab Di Francesco, Denis Martin, Nicolas Grandjean, Yulia Kotsar, and Eva Monroy

Appl. Phys. Lett. 98, 241101 (2011); http://dx.doi.org/10.1063/1.3599846 (3 pages)

Online Publication Date: 13 June 2011

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We demonstrate the effect of rapid thermal annealing on heavily Si-doped AlN/GaN quantum wells. After 1000 °C annealing during 5, 10, and 20 min, the dominant effect was interdiffusion of Si rather than intermixing between the Al and Ga atoms. Both their original value and the magnitude of the changes after annealing reveal that intersubband absorption and photovoltage are related to two different optical transitions as follows: absorption occurs in the 1 to 2 intersubband transition, whereas photovoltage is due to a subsequent process from the 1 to 2 and the manifold of 2 to higher order transitions.
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85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)

Design and fabrication of high efficiency power coupler between different photonic crystal waveguides

Wei Jia, Jun Deng, Ajeesh M. Sahadevan, Hong Wu, Liyong Jiang, Xiangyin Li, Charanjit S. Bhatia, Hyunsoo Yang, and Aaron J. Danner

Appl. Phys. Lett. 98, 241102 (2011); http://dx.doi.org/10.1063/1.3599841 (3 pages) | Cited 4 times

Online Publication Date: 14 June 2011

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Based on inspiration from an inverse optimization strategy and theoretical finite-difference time-domain method simulations, an ultralow loss power coupler between two different photonic crystal waveguides was designed, fabricated and characterized. The experimental results showed that the loss was less than 1 dB for transverse electric polarized light at a wavelength of 1550 nm, which is consistent with expectations from numerical modeling. High efficiency optical couplers are critical for development of integrated optical circuit functionality.
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42.79.Gn Optical waveguides and couplers
42.86.+b Optical workshop techniques
42.70.Qs Photonic bandgap materials

Subwavelength plasmonic lens patterned on a composite optical fiber facet for quasi-one-dimensional Bessel beam generation

Sehun Kang, Hang-Eun Joe, Jongki Kim, Yoonseob Jeong, Byung-Kwon Min, and Kyunghwan Oh

Appl. Phys. Lett. 98, 241103 (2011); http://dx.doi.org/10.1063/1.3596442 (3 pages) | Cited 1 time

Online Publication Date: 14 June 2011

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We demonstrate a beam shaping method by engraving plasmonic lens consisted of subwavelength slit-metallic groove structure on the cleaved end facet of a composite optical fiber. The fiber consisted of a single mode optical fiber serially concatenated with a coreless silica fiber segment to expand the beam diameter. The subwavelength slit-groove structure on a gold film was fabricated using focused ion beam milling process. Plasmonic interaction in the film generated a quasi-one-dimensional Bessel-like beam with a beam width of 0.8 μm at the focal length of 2 μm. Detailed two- and three-dimensional finite-difference time-domain analyses showed beam characteristics consistent with experimental observations.
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42.81.Bm Fabrication, cladding, and splicing
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Bh Lenses, prisms and mirrors

Nonvolatile bistable all-optical switch from mechanical buckling

Varat Intaraprasonk and Shanhui Fan

Appl. Phys. Lett. 98, 241104 (2011); http://dx.doi.org/10.1063/1.3600335 (3 pages)

Online Publication Date: 14 June 2011

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We propose a nonvolatile all-optical bistable optomechanical switch comprising two parallel buckling waveguides. The bistability comes from mechanical buckling so the operation of the switch does not require maintenance power. The switching and reading of the states are all optical; they involve relatively strong and relatively weak optical pulses, respectively, similar to conventional bistable optical switches.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Gn Optical waveguides and couplers

Strong absorption and selective thermal emission from a midinfrared metamaterial

J. A. Mason, S. Smith, and D. Wasserman

Appl. Phys. Lett. 98, 241105 (2011); http://dx.doi.org/10.1063/1.3600779 (3 pages) | Cited 16 times

Online Publication Date: 15 June 2011

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We demonstrate thin-film metamaterials with resonances in the midinfrared (mid-IR) wavelength range. Our structures are numerically modeled and experimentally characterized by reflection and angularly resolved thermal emission spectroscopy. We demonstrate strong and controllable absorption resonances across the mid-IR wavelength range. In addition, the polarized thermal emission from these samples is shown to be highly selective and largely independent of emission angles from normal to 45°. Experimental results are compared to numerical models with excellent agreement. Such structures hold promise for large-area, low-cost metamaterial coatings for control of gray- or black-body thermal signatures, as well as for possible mid-IR sensing applications.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.20.N- Thermo-optic effects
42.70.-a Optical materials
78.66.-w Optical properties of specific thin films

Efficient electro-optic switching in a photonic liquid crystal fiber

Alexander Lorenz and Heinz-S. Kitzerow

Appl. Phys. Lett. 98, 241106 (2011); http://dx.doi.org/10.1063/1.3599848 (3 pages) | Cited 2 times

Online Publication Date: 15 June 2011

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Results on the attenuation properties of a band gap guiding microstructured fiber filled with a nematic liquid crystal are presented. The fiber shows broad transmission bands and moderate attenuation in the visible wavelength range. By electric addressing, the fiber can be utilized either as switchable linear polarizer or as a polarization-independent shutter. In the former case, the plane of polarization can be controlled by adjusting the electric field utilizing a four-electrode setup.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.81.Wg Other fiber-optical devices
42.70.Qs Photonic bandgap materials
42.70.Df Liquid crystals

Lasing in localized modes of a slow light photonic crystal waveguide

Jin-Kyu Yang, Heeso Noh, Michael J. Rooks, Glenn S. Solomon, Frank Vollmer, and Hui Cao

Appl. Phys. Lett. 98, 241107 (2011); http://dx.doi.org/10.1063/1.3600344 (3 pages) | Cited 7 times

Online Publication Date: 15 June 2011

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We demonstrate lasing in GaAs photonic crystal waveguides with InAs quantum dots as gain medium. Structural disorder is present due to fabrication imperfection and causes multiple scattering of light and localization of light. Lasing modes with varying spatial extend are observed at random locations along the guide. Lasing frequencies are determined by the local structure and occur within a narrow frequency band which coincides with the slow light regime of the waveguide mode. The three-dimensional numerical simulation reveals that the main loss channel for lasing modes located away from the waveguide end is out-of-plane scattering by structural disorder.
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42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer
02.60.-x Numerical approximation and analysis
42.25.Fx Diffraction and scattering
42.70.Qs Photonic bandgap materials

The impact of temperature and strain-induced band gap variations on current competition and emitter power in laser bars

C. K. Amuzuvi, S. Bull, J. W. Tomm, J. Nagle, B. Sumpf, G. Erbert, N. Michel, M. Krakowski, and E. C. Larkins

Appl. Phys. Lett. 98, 241108 (2011); http://dx.doi.org/10.1063/1.3600644 (3 pages) | Cited 1 time

Online Publication Date: 15 June 2011

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We report on current competition and emitter power distributions of unaged 650 nm red-emitting and 980 nm infrared tapered high-power laser bars. We observe a correlation between temperature and packaging-induced strain with respect to the emitter output power. A frown-shaped profile of the output power distribution is seen when the temperatures of the emitters near the center of the bar increase compared to those at the edges of the bar. The effect of temperature is found to dominate that of strain and therefore determine the output power distribution across the bar.
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42.55.-f Lasers
42.70.Qs Photonic bandgap materials

Light scattering assisted surface plasmon resonance at electrospun nanofiber-coated gold surfaces

Kazuma Tsuboi, Hidetoshi Matsumoto, Mie Minagawa, and Akihiko Tanioka

Appl. Phys. Lett. 98, 241109 (2011); http://dx.doi.org/10.1063/1.3601465 (3 pages) | Cited 1 time

Online Publication Date: 16 June 2011

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This letter reports the polarized optical response of nanofiber-coated gold surfaces that originated from surface plasmon resonance (SPR). The reflection spectra of the poly(vinylpyrrolidone) nanofiber-coated gold surfaces prepared by electrospinning showed a clear polarization dependence. This indicates that the SPR at the air/gold interface was assisted by light scattering of the nanofibers. In addition, the optical response of the gold surface depends on the density of the coated nanofibers. This can be explained by the scattering and the interference of the surface plasmons in the pores between the nanofibers.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
78.68.+m Optical properties of surfaces
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

Directional and low-divergence emission in a rounded half-moon shaped microcavity

Myung-Woon Kim, Kyu-Won Park, Chang-Hwan Yi, and Chil-Min Kim

Appl. Phys. Lett. 98, 241110 (2011); http://dx.doi.org/10.1063/1.3598406 (3 pages) | Cited 1 time

Online Publication Date: 16 June 2011

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Emission characteristics of a rounded half-moon shaped InGaAsP semiconductor microcavity laser are studied. When excited by pulse current, the laser generates whispering gallery type modes (WGTMs) with equidistant mode spacing in two directions with a narrow divergence angle of 4°. It is confirmed from the mode spacing that the lasing modes are WGTMs. A numerical analysis by the boundary element method shows that the emission direction of resonances well coincides with the experimental result.
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42.55.Sa Microcavity and microdisk lasers
42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Improvement of efficiency of GaN-based polarization-doped light-emitting diodes grown by metalorganic chemical vapor deposition

L. Zhang, X. C. Wei, N. X. Liu, H. X. Lu, J. P. Zeng, J. X. Wang, Y. P. Zeng, and J. M. Li

Appl. Phys. Lett. 98, 241111 (2011); http://dx.doi.org/10.1063/1.3601469 (3 pages) | Cited 4 times

Online Publication Date: 17 June 2011

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Our simulated results [ Appl. Phys. Lett. 98, 101110 (2011)] reveal that polarization-doped light-emitting diodes (LEDs) have improved internal quantum efficiency due to the enhanced hole injection caused by the improved hole concentration and smooth valence band. In this letter, in order to verify these calculated results, polarization-doped LEDs grown by metalorganic chemical vapor deposition are investigated. The results show that the polarization-doped LED has the improved electroluminescence intensity and external quantum efficiency (EQE) compared with the conventional LED. The influence of the degree of AlGaN gradation on polarization-doped LEDs is also studied. It is found that the polarization-doped LED has the highest EQE when the Al composition of the graded AlGaN is linearly decreased from 0.2 to 0.
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85.60.Jb Light-emitting devices

Plasmon-enhanced low-intensity laser switching of gold::vanadium dioxide nanocomposites

D. W. Ferrara, E. R. MacQuarrie, J. Nag, A. B. Kaye, and R. F. Haglund, Jr.

Appl. Phys. Lett. 98, 241112 (2011); http://dx.doi.org/10.1063/1.3593388 (3 pages) | Cited 3 times

Online Publication Date: 17 June 2011

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Transient absorption of gold nanoparticle (NP) arrays covered by a 60 nm thick film of VO2 was measured using a mechanically shuttered 785 nm pump laser and a 1550 nm cw probe. Even though the Au NPs constitute only 4% by volume of the nanocomposite, they increase the effective absorption coefficient by a factor of 1.5 and reduce the threshold laser power required to induce the semiconductor-to-metal transition (SMT) by as much as 37%. It is argued that the NPs function as thermal initiators for the SMT and as “nanoradiators” to increase the scattering and absorption of light into interband transitions of the VO2.
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71.30.+h Metal-insulator transitions and other electronic transitions
78.67.Sc Nanoaggregates; nanocomposites
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.22.Lp Collective excitations
72.60.+g Mixed conductivity and conductivity transitions

Picosecond response times in GaAs/AlGaAs core/shell nanowire-based photodetectors

Eric M. Gallo, Guannan Chen, Marc Currie, Terrence McGuckin, Paola Prete, Nico Lovergine, Bahram Nabet, and Jonathan E. Spanier

Appl. Phys. Lett. 98, 241113 (2011); http://dx.doi.org/10.1063/1.3600061 (3 pages) | Cited 9 times

Online Publication Date: 17 June 2011

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High-speed metal-semiconductor-metal (MSM) photodetectors based on Schottky-contacted core/shell GaAs/AlGaAs and bare GaAs nanowires were fabricated and characterized. The measured core/shell temporal response has a ∼ 10 ps full-width at half-maximum and an estimated corrected value less than 5 ps. The bare GaAs devices exhibit a slower response ( ∼ 35 ps) along with a slow decaying persistent photocurrent ( ∼ 80 s). The core/shell devices exhibit significantly improved dc and high-speed performance over bare nanowires and comparable performance to planar MSM photodetectors. The picosecond temporal response, coupled with picoampere dark current, demonstrate the potential for core/shell nanowires in high-speed imaging arrays and on-chip optical interconnects.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Čerenkov third-harmonic generation in χ(2) nonlinear photonic crystal

Yan Sheng, Wenjie Wang, Roy Shiloh, Vito Roppo, Yongfa Kong, Ady Arie, and Wieslaw Krolikowski

Appl. Phys. Lett. 98, 241114 (2011); http://dx.doi.org/10.1063/1.3602312 (3 pages) | Cited 10 times

Online Publication Date: 17 June 2011

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We report on the observation of Čerenkov emission of a third-harmonic frequency in a two-dimensional nonlinear photonic crystal, where the second-order nonlinearity χ(2) is spatially modulated by the reversal of ferroelectric domains. We analyze both spatial and polarization properties of the emitted radiation and find the results in agreement with our theoretical predictions.
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42.70.Qs Photonic bandgap materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Mp Nonlinear optical crystals

Secondary ions mass spectroscopy measurements of dopant impurities in highly stressed InGaN laser diodes

L. Marona, P. Perlin, R. Czernecki, M. Leszczyński, M. Boćkowski, R. Jakiela, T. Suski, and S. P. Najda

Appl. Phys. Lett. 98, 241115 (2011); http://dx.doi.org/10.1063/1.3600338 (3 pages)

Online Publication Date: 17 June 2011

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We performed a systematic secondary ions mass spectroscopy (SIMS) study of dopant impurities in life-time stressed InGaN laser devices in order to investigate the main degradation mechanism that is observed in nitride laser diodes. A continuous wave (cw) current density of 3 kA/cm2 was applied to InGaN laser diodes over an extended period of time and we observed the characteristic square root degradation of optical power. We compared the SIMS profiles of Mg, H, and Si impurities in the aged devices and observe that the impurities are remarkably stable over 10 000 h of cw operation. Nor is there any SIMS evidence of p-contact metals penetrating into the semiconductor material. Thus our SIMS results are contrary to what one would expect for impurity diffusion causing the observed square root degradation characteristic.
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42.55.Px Semiconductor lasers; laser diodes
61.72.sd Impurity concentration
61.72.sh Impurity distribution
61.72.uj III-V and II-VI semiconductors
07.75.+h Mass spectrometers

Optical group-velocity control in a phase-shifted narrowband filter

Wolfgang Horn, Sebastian Kroesen, and Cornelia Denz

Appl. Phys. Lett. 98, 241116 (2011); http://dx.doi.org/10.1063/1.3600646 (3 pages) | Cited 1 time

Online Publication Date: 17 June 2011

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We demonstrate group-velocity control with an optically reconfigurable narrow-band filter at 1550 nm based on a volume-holographic Bragg grating. The filter is dynamically addressed to obtain different tunable magnitude and phase function by modification of the length, coupling strength, apodization, and phase discontinuities. We characterize the switching behavior, group-delay, electro-optical tuning, and Gaussian pulse propagation.
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42.79.Ci Filters, zone plates, and polarizers
42.79.Dj Gratings
42.81.-i Fiber optics
42.40.Eq Holographic optical elements; holographic gratings
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An atmospheric pressure quasiuniform planar plasma jet generated by using a dielectric barrier configuration

Qing Li, Hidemasa Takana, Yi-Kang Pu, and Hideya Nishiyama

Appl. Phys. Lett. 98, 241501 (2011); http://dx.doi.org/10.1063/1.3599845 (3 pages) | Cited 6 times

Online Publication Date: 13 June 2011

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A stable nonthermal quasiuniform planar plasma jet, originating from a planar dielectric duct with a rectangular exit and issuing into ambient air at atmospheric pressure, is reported in the present work. Current-voltage characteristics, one discharge current pulse per sinusoidal half voltage cycle, show that the discharge is not filamentary. Its spatial uniformity in the transverse direction is shown to be excellent by monitoring optical emission spectra in the jet core region except jet boundaries. This is possibly resulted from high preionization in the upstream region, and it is a challenge to the traditional single streamer explanation for nonthermal plasma jets.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.25.Fi Transport properties
52.75.-d Plasma devices
52.50.Dg Plasma sources
52.80.-s Electric discharges
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Origin of the low thermal conductivity of the thermoelectric material β-Zn4Sb3: An ab initio theoretical study

Weibing Chen and Jingbo Li

Appl. Phys. Lett. 98, 241901 (2011); http://dx.doi.org/10.1063/1.3599483 (3 pages) | Cited 2 times

Online Publication Date: 13 June 2011

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By modeling β-Zn4Sb3 material as a Zn36Sb30 crystal with defects, the crystal structure and thermal properties of β-Zn4Sb3 are studied by ab initio method to explain its extremely low thermal conductivity at moderate temperature. The formation and migration energies of defects are calculated and used to explain the partial occupation of Zn at the lattice sites, the disordered local structures and the origin of the low thermal conductivity of β-Zn4Sb3. Our study also unravels the puzzling dependence of thermal conductivity on doping in β-Zn4Sb3. A doping strategy is proposed to improve the thermoelectric performance of β-Zn4Sb3.
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72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
61.72.jj Interstitials
61.72.jd Vacancies
72.15.Jf Thermoelectric and thermomagnetic effects
61.66.Dk Alloys
61.72.up Other materials

Role of electronic correlations in Ga

Zhiyong Zhu, Xuhui Wang, and Udo Schwingenschlögl

Appl. Phys. Lett. 98, 241902 (2011); http://dx.doi.org/10.1063/1.3599532 (3 pages) | Cited 1 time

Online Publication Date: 13 June 2011

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An extended around mean field (AMF) functional for less localized p electrons is developed to quantify the influence of electronic correlations in α-Ga. Both the local density approximation (LDA) and generalized gradient approximation are known to mispredict the Ga positional parameters. The extended AMF functional together with an onsite Coulomb interaction of Ueff = 1.1 eV, as obtained from constraint LDA calculations, reduces the deviations by about 20%. The symmetry lowering coming along with the electronic correlations turns out to be in line with the Ga phase diagram.
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71.20.Be Transition metals and alloys
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
81.30.Bx Phase diagrams of metals, alloys, and oxides
73.23.Hk Coulomb blockade; single-electron tunneling

SmNiO3/NdNiO3 thin film multilayers

C. Girardot, S. Pignard, F. Weiss, and J. Kreisel

Appl. Phys. Lett. 98, 241903 (2011); http://dx.doi.org/10.1063/1.3599580 (3 pages) | Cited 2 times

Online Publication Date: 13 June 2011

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Rare earth nickelates RENiO3 (RE = rare earth), which attract interest due to their sharp metal-insulator phase transition, are instable in bulk form due to the necessity of an important oxygen pressure to stabilize Ni in its 3+ state of oxidation. Here, we report the stabilization of RE nickelates in [(SmNiO3)t/(NdNiO3)t]n thin film multilayers, t being the thickness of layers alternated n times. Both bilayers and multilayers have been deposited by metal-organic chemical vapor deposition. The multilayer structure and the presence of the metastable phases SmNiO3 and NdNiO3 are evidenced from by x-ray and Raman scattering. Electric measurements of a bilayer structure further support the structural quality of the embedded RE nickelate layers.
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68.65.Ac Multilayers
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
71.30.+h Metal-insulator transitions and other electronic transitions
78.66.Li Other semiconductors
78.30.Hv Other nonmetallic inorganics

Surface plasmon enhanced broadband spectrophotometry on black silver substrates

Zhida Xu, Yi Chen, Manas R. Gartia, Jing Jiang, and Gang Logan Liu

Appl. Phys. Lett. 98, 241904 (2011); http://dx.doi.org/10.1063/1.3599551 (3 pages) | Cited 4 times

Online Publication Date: 14 June 2011

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We demonstrate surface plasmon-induced enhancements in optical imaging and spectroscopy on silver coated silicon nanocones which we call black silver. The black silver with dense and homogeneous nanocone forest structure is fabricated with a mass-producible nanomanufacturing method. It can efficiently trap and convert incident photons into localized plasmons in broad wavelength range, permitting the enhancement in optical absorption from ultraviolet to near infrared range by 12 times, the visible fluorescence enhancement of ∼ 30 times and the Raman scattering enhancement factor up to ∼ 108. We show the potential of the black silver in high sensitivity and broadband optical sensing of molecules.
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82.80.Dx Analytical methods involving electronic spectroscopy
73.22.Lp Collective excitations
78.40.-q Absorption and reflection spectra: visible and ultraviolet
74.25.nd Raman and optical spectroscopy

Band gap bowing in quaternary nitride semiconducting alloys

I. Gorczyca, T. Suski, N. E. Christensen, and A. Svane

Appl. Phys. Lett. 98, 241905 (2011); http://dx.doi.org/10.1063/1.3597795 (3 pages) | Cited 2 times

Online Publication Date: 14 June 2011

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Structural properties of InxGayAl1−x−yN alloys are derived from total-energy minimization within the local-density approximation (LDA). The electronic properties are studied by band structure calculations including a semiempirical correction for the “LDA gap error.” The effects of varying the composition and atomic arrangements are examined using a supercell geometry. An analytical expression for the band gap is derived for the entire range of compositions. The range of (x, y) values for which InxGayAl1−x−yN is lattice matched to GaN, and the ensuing energy gaps, are given. This range of available gaps becomes smaller when In atoms form clusters. Comparison to experimental data is made.
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71.20.Nr Semiconductor compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Nc Total energy and cohesive energy calculations

Coupled shear and shuffle modes during twin growth in B2-NiTi

T. Ezaz and H. Sehitoglu

Appl. Phys. Lett. 98, 241906 (2011); http://dx.doi.org/10.1063/1.3596458 (3 pages) | Cited 4 times

Online Publication Date: 14 June 2011

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Deformation twinning of B2 austenitic phase in NiTi has not been understood despite its significance. A number of experimental observations have been made, but these alone cannot explain the complex shears and shuffles that produce the twin. We propose that twinning can occur via (math11)[mathmathmath] shear and the proposed shuffle differs from previous work and is parallel to the twinning shear. We established a twin energy barrier which is lower compared the previously proposed twinning modes, and has a magnitude of 79 mJ/m2. Hydrostatic pressure is found to alter this energy barrier and the coupling of shear and shuffle mechanism.
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81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity
61.72.Mm Grain and twin boundaries
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In situ observation of the formation of hollow zinc oxide shells

J. W. Tringe, H. W. Levie, B. S. El-Dasher, R. Swift, and M. A. Wall

Appl. Phys. Lett. 98, 241907 (2011); http://dx.doi.org/10.1063/1.3598436 (3 pages)

Online Publication Date: 14 June 2011

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Single crystal zinc particles, 1–2 μm in diameter, were observed in situ with transmission electron microscopy during sublimation. The rate of sublimation is strongly dependent on the presence of a surface oxide layer. Near 375 °C, minimally oxidized Zn surfaces sublime in tens of seconds, consistent with a model in which the particle behaves similarly to an isolated microscale effusion cell. By contrast, zinc particles fully enclosed by oxide sublime less than one-tenth as quickly. These results provide new insight into the synthesis mechanisms of hollow ZnO microspheres and related structures formed from metallic zinc at elevated temperatures.
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64.70.Hz Solid-vapor transitions
68.37.Lp Transmission electron microscopy (TEM)
81.05.Ea III-V semiconductors

Driving intervalley scattering and impact ionization in InAs with intense terahertz pulses

I-Chen Ho and X.-C. Zhang

Appl. Phys. Lett. 98, 241908 (2011); http://dx.doi.org/10.1063/1.3600791 (3 pages) | Cited 2 times

Online Publication Date: 15 June 2011

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We report intense terahertz (THz) pulses inducing intervalley scattering and impact ionization mechanisms in doped InAs crystals by THz pump-THz probe measurements. Two competing mechanisms are observed by varying the impurity doping type of the semiconductors and the strength of the THz field. For p-doped InAs, a cascaded carrier generation dominates while for n-doped InAs, both mechanisms have to be considered. Electron fractional occupancy between the Γ and L valleys is estimated at different field strengths.
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72.20.Ht High-field and nonlinear effects
72.80.Ey III-V and II-VI semiconductors
78.70.Gq Microwave and radio-frequency interactions
61.72.uj III-V and II-VI semiconductors
78.47.J- Ultrafast spectroscopy (<1 psec)
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