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7 Nov 2011

Volume 99, Issue 19, Articles (19xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 193101 (2011); http://dx.doi.org/10.1063/1.3657777 (3 pages)

Sungwook Chung, Jonathan R. Felts, Debin Wang, William P. King, and James J. De Yoreo
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Fast-response signal upconversion by the use of a “time-space conversion” method

Mitsunori Saito, Shingo Nakamura, and Teppei Kita

Appl. Phys. Lett. 99, 191101 (2011); http://dx.doi.org/10.1063/1.3660262 (3 pages)

Online Publication Date: 7 November 2011

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Lanthanide-doped phosphors achieve signal wavelength conversion between visible and infrared communication systems. A long lifetime of their excited states is advantageous for inducing two-photon absorption that realizes upconversion. The long lifetime, however, restricts the conversion rate to ∼500 bit/s because of the afterglow. This contradiction was solved by embedding a phosphor (YbEr:Gd2O2S) in a rotating disk. When an infrared (940 nm) pulse train of 1 Mbit/s (time domain) was focused on the disk, a fluorescent dot array (space domain) was created and moved with the disk rotation. Consequently, a visible (∼550 nm) pulse train was detected on the dot trajectory.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Optical fiber tips functionalized with semiconductor photonic crystal cavities

Gary Shambat, J Provine, Kelley Rivoire, Tomas Sarmiento, James Harris, and Jelena Vučković

Appl. Phys. Lett. 99, 191102 (2011); http://dx.doi.org/10.1063/1.3660278 (3 pages) | Cited 5 times

Online Publication Date: 7 November 2011

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We demonstrate a simple and rapid epoxy-based method for transferring photonic crystal (PC) cavities to the facets of optical fibers. Passive Si cavities were measured via fiber taper coupling as well as direct transmission from the fiber facet. Active quantum dot containing GaAs cavities showed photoluminescence that was collected both in free space and back through the original fiber. Cavities maintain a high quality factor (2000-4000) in both material systems. This design architecture provides a practical mechanically stable platform for the integration of photonic crystal cavities with macroscale optics and opens the door for innovative research on fiber-coupled cavity devices.
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42.70.Qs Photonic bandgap materials
42.15.Eq Optical system design
42.82.Bq Design and performance testing of integrated-optical systems
42.81.Wg Other fiber-optical devices

Biomimetic broadband antireflection gratings on solar-grade multicrystalline silicon wafers

Blayne M. Phillips, Peng Jiang, and Bin Jiang

Appl. Phys. Lett. 99, 191103 (2011); http://dx.doi.org/10.1063/1.3660263 (3 pages) | Cited 4 times

Online Publication Date: 9 November 2011

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We report a simple and scalable bottom-up technique for fabricating broadband antireflection gratings on solar-grade multicrystalline silicon (mc-Si) wafers. A Langmuir-Blodgett process is developed to assemble close-packed silica microspheres on rough mc-Si substrates. Subwavelength moth-eye pillars can then be patterned on mc-Si by using the silica microspheres as structural template. Hemispherical reflectance measurements show that the resulting mc-Si gratings exhibit near zero reflection for a wide range of wavelengths. Both experimental results and theoretical prediction using a rigorous coupled-wave analysis model show that close-packed moth-eye arrays exhibit better antireflection performance than non-close-packed arrays due to a smoother refractive index gradient.
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88.40.jj Silicon solar cells
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Ultra-broadband heterogeneous quantum cascade laser emitting from 2.2 to 3.2 THz

Dana Turčinková, Giacomo Scalari, Fabrizio Castellano, Maria I. Amanti, Mattias Beck, and Jérôme Faist

Appl. Phys. Lett. 99, 191104 (2011); http://dx.doi.org/10.1063/1.3658874 (3 pages) | Cited 8 times

Online Publication Date: 9 November 2011

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We present a heterogeneous terahertz quantum cascade laser that emits continuously between 2.2 and 3.2 THz, covering an emission range of over 40% around the central frequency. Devices were realized by stacking different active region designs into a double-metal waveguide. They operate up to 125 K with 15 mW peak power at 10 K in pulsed mode. Smaller devices show broadband emission also in continuous wave. Time-resolved measurements of the emission spectra were realized, confirming the broadband emission within a 5 ns time window.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Ultra-high four wave mixing efficiency in slot waveguides with silicon nanocrystals

A. Trita, C. Lacava, P. Minzioni, J.-P. Colonna, P. Gautier, J.-M. Fedeli, and I. Cristiani

Appl. Phys. Lett. 99, 191105 (2011); http://dx.doi.org/10.1063/1.3659694 (3 pages) | Cited 1 time

Online Publication Date: 9 November 2011

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We report on wavelength conversion through four-wave-mixing in silicon slot-waveguides with embedded silicon nanocrystals. The combination of strong optical confinement and Si:nc nonlinearity provides a huge waveguide nonlinear coefficient γ = 1100 W−1m−1. Moreover, the improvement in the fabrication procedure allowed a loss reduction with respect to previous reported structures, enabling the achievement of an extreme value for the conversion efficiency which represents the best result ever reported in the scientific literature.
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42.79.Gn Optical waveguides and couplers
61.46.-w Structure of nanoscale materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Wavelength-dependent frustrated internal reflection via photonic interface states

G. H. Cross and S. Brand

Appl. Phys. Lett. 99, 191106 (2011); http://dx.doi.org/10.1063/1.3660266 (3 pages)

Online Publication Date: 10 November 2011

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Conventional frustrated internal reflection in which light is able to tunnel across a small air gap between two prisms is a well known phenomenon. In this work, an experimental proof-of-concept demonstration of a polarization and highly wavelength selective version of a similar effect via photonic interface states is given. The photonic interface states are designed to exist within the photonic band gap of Bragg reflectors on the surfaces of the two prisms.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.79.Bh Lenses, prisms and mirrors
42.70.Qs Photonic bandgap materials

Tailoring the Faraday effect by birefringence of two dimensional plasmonic nanorod array

G. X. Du, S. Saito, and M. Takahashi

Appl. Phys. Lett. 99, 191107 (2011); http://dx.doi.org/10.1063/1.3660318 (3 pages) | Cited 1 time

Online Publication Date: 10 November 2011

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The ability to rotate the polarization of light propagating through a material by applying a magnetic field was discovered by Faraday. It is critically important for applications involving light modulation and sensors. Shaped plasmonic crystals function as miniature polarizers. This study investigates a gold nanorod array that can be used to significantly vary the Faraday effect originating from a dielectric material. The dependence of the Faraday effect on the polarizer angle exhibited well-defined characteristics. The birefringence of the nanorod array was characterized using a simplified setup for optical polarization tomography. The enhanced Faraday effect due to the plasmonic nanorods is promising for applications involving plasmonic circuits and refractometry.
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78.20.Ls Magneto-optical effects
78.67.Qa Nanorods
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
61.46.-w Structure of nanoscale materials

Adaptive beam tracking and steering via electrowetting-controlled liquid prism

Jiangtao Cheng and Chung-Lung Chen

Appl. Phys. Lett. 99, 191108 (2011); http://dx.doi.org/10.1063/1.3660578 (3 pages) | Cited 3 times

Online Publication Date: 10 November 2011

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We report an electrowetting-controlled optofluidic system for adaptive beam tracking and agile steering. With two immiscible fluids in a transparent cell, we can actively control the contact angle along the fluid-fluid-solid tri-junction line and hence the orientation of the fluid-fluid interface via electrowetting. The naturally formed meniscus between the two liquids can function as an optical prism. We have fabricated a liquid prism module with an aperture size of 10 mm × 10mm. With 1 wt. % KCl and 1 wt. % Sodium Dodecyl Sulfate added into deionized water, the orientation of the water-silicone oil interface has been modulated between −26° and 26° that can deflect and steer beam within the incidence angle of 0°–15°. The wide-range beam tracking and steering enables the liquid prism work as an electrowetting solar cell.
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88.40.H- Solar cells (photovoltaics)
68.08.Bc Wetting
68.03.Cd Surface tension and related phenomena
42.79.Bh Lenses, prisms and mirrors

Enhanced photorefractive effect in liquid crystal structures co-doped with semiconductor quantum dots and metallic nanoparticles

A. Anczykowska, S. Bartkiewicz, M. Nyk, and J. Myśliwiec

Appl. Phys. Lett. 99, 191109 (2011); http://dx.doi.org/10.1063/1.3659485 (3 pages) | Cited 3 times

Online Publication Date: 10 November 2011

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In this paper, we present strong enhancement of optical properties of hybrid liquid crystal structures functionalized with metallic and semiconductor nanoparticles. Several experiments done in two wave mixing experimental set-up have reported that diffraction efficiency can be improved by up to 14 times by introducing nanoparticles of cadmium selenide or gold into the photoconducting polymer adjacent to the liquid crystal layer. Our research may open up a possible route for the development of faster and more efficient holographic materials which can be used in dynamic data processing systems.
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78.15.+e Optical properties of fluid materials, supercritical fluids and liquid crystals
78.20.Mg Photorefractive effects
42.40.Eq Holographic optical elements; holographic gratings
42.70.Df Liquid crystals
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
61.30.Vx Polymer liquid crystals

Confinement enhancing barriers for high performance quantum dots-in-a-well infrared detectors

A. V. Barve, S. Sengupta, J. O. Kim, Y. D. Sharma, S. Adhikary, T. J. Rotter, S. J. Lee, Y. H. Kim, and S. Krishna

Appl. Phys. Lett. 99, 191110 (2011); http://dx.doi.org/10.1063/1.3660317 (3 pages) | Cited 5 times

Online Publication Date: 11 November 2011

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We demonstrate the use of thin AlGaAs barrier layers in the quantum dots in a well heterostructure to enhance the quantum confinement of carriers in the excited energy level, while maintaining high escape probability. This is achieved by controlling the excited state energy between the confinement enhancing (CE) barriers and the continuum level. Responsivity of ∼0.1 A/W, detectivity of 6.5 × 1010 cmHz1/2 W−1 (77 K, 0.6 V, 7.5 µm, f/2), and a factor of 10 improvement over a control sample without the CE barriers have been measured. The effect of changing the quantum well thickness and quantum dot size is also reported.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Photodiode with nanocrystalline Si/amorphous Si absorber bilayer

Y. Vygranenko, A. Sazonov, M. Fernandes, and M. Vieira

Appl. Phys. Lett. 99, 191111 (2011); http://dx.doi.org/10.1063/1.3660725 (3 pages)

Online Publication Date: 11 November 2011

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This letter reports a near-ultraviolet/visible/near-infrared n+-n-i-δi-p photodiode with an absorber comprising a nanocrystalline silicon n layer and a hydrogenated amorphous silicon i layer. Device modeling reveals that the dominant source of reverse dark current is deep defect states in the n layer, and its magnitude is controlled by the i layer thickness. The photodiode with the 900/400 nm thick n-i layers exhibits a reverse dark current density of 3nA/cm2 at −1 V. Donor concentration and diffusion length of holes in the n layer are estimated from the capacitance-voltage characteristics and from the bias dependence of long-wavelength response, respectively.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.De Semiconductor-device characterization, design, and modeling
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Negative ions: The overlooked species in thin film growth by pulsed laser deposition

M. Esposito, M. Bator, M. Döbeli, T. Lippert, C. W. Schneider, and A. Wokaun

Appl. Phys. Lett. 99, 191501 (2011); http://dx.doi.org/10.1063/1.3660399 (3 pages) | Cited 4 times

Online Publication Date: 8 November 2011

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Plasma plume species from a ceramic La0.4Ca0.6MnO3 target were studied by plasma mass spectrometry as a function of laser fluence, background gas, and deposition pressure to understand the interplay between plasma composition and oxide thin film growth by pulsed laser deposition. The plume composition reveals a significant contribution of up to 24% of negative ions, most notably using a N2O background. The significance of negative ions for thin film growth is shown for La0.4Ca0.6MnO3 films grown in different background conditions where the best structural properties coincide with the largest amount of negative plasma species.
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81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
52.77.Dq Plasma-based ion implantation and deposition
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Extreme ultraviolet source at 6.7 nm based on a low-density plasma

Takeshi Higashiguchi, Takamitsu Otsuka, Noboru Yugami, Weihua Jiang, Akira Endo, Bowen Li, Deirdre Kilbane, Padraig Dunne, and Gerry O’Sullivan

Appl. Phys. Lett. 99, 191502 (2011); http://dx.doi.org/10.1063/1.3660275 (3 pages) | Cited 11 times

Online Publication Date: 9 November 2011

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We demonstrate an efficient extreme ultraviolet (EUV) source for operation at λ = 6.7 nm by optimizing the optical thickness of gadolinium (Gd) plasmas. Using low initial density Gd targets and dual laser pulse irradiation, we observed a maximum EUV conversion efficiency (CE) of 0.54% for 0.6% bandwidth (BW) (1.8% for 2% BW), which is 1.6 times larger than the 0.33% (0.6% BW) CE produced from a solid density target. Enhancement of the EUV CE by use of a low-density plasma is attributed to the reduction of self-absorption effects.
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52.77.-j Plasma applications
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
42.72.Bj Visible and ultraviolet sources

Oscillatory quantum screening effects on the positronium (Ps) formation in quantum plasmas

Chang-Geun Kim and Young-Dae Jung

Appl. Phys. Lett. 99, 191503 (2011); http://dx.doi.org/10.1063/1.3660741 (3 pages)

Online Publication Date: 9 November 2011

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The oscillatory quantum screening effects on the positronium formation by the positron are investigated in quantum plasmas. It is found that the oscillatory screening effects suppress the positronium formation radius as well as the positronium formation cross section. It is also found that the positronium formation radius decreases with increasing quantum wave number. It is found that the peak position of the differential cross section is receded from the projectile with decreasing quantum wave number. In addition, the oscillatory screening effects on the positronium formation cross section are found to be decreased with an increase of the collision energy.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.20.Fs Electron collisions

Single-molecule measurement of strand breaks on large DNA induced by atmospheric pressure plasma jet

Hirofumi Kurita, Tomoko Nakajima, Hachiro Yasuda, Kazunori Takashima, Akira Mizuno, John I. B. Wilson, and Samia Cunningham

Appl. Phys. Lett. 99, 191504 (2011); http://dx.doi.org/10.1063/1.3660581 (3 pages) | Cited 1 time

Online Publication Date: 10 November 2011

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We report a single-molecule-based analysis of strand breakages on large DNA molecules induced by an atmospheric pressure plasma jet. We exposed DNA solution to an argon plasma jet; single-molecule observation that involved molecular combing was then used to measure the length of individual DNA molecules. The measured DNA length showed that plasma exposure caused a marked change in length of DNA molecules. The rate of plasma-induced strand breakage on large random-coiled DNA molecules was determined using a simple mathematical model. For strand breaks on large DNA molecules the rate was estimated.
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87.14.gk DNA
87.15.B- Structure of biomolecules
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Identification of boron clusters in silicon crystal by B1s core-level X-ray photoelectron spectroscopy: A first-principles study

Jun Yamauchi, Yoshihide Yoshimoto, and Yuji Suwa

Appl. Phys. Lett. 99, 191901 (2011); http://dx.doi.org/10.1063/1.3658030 (3 pages) | Cited 1 time

Online Publication Date: 7 November 2011

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We carried out a comprehensive study on the B1s core-level X-ray photoelectron spectroscopy (XPS) binding energies for B clusters in crystalline Si using a first-principles calculation with careful evaluation of the local potential boundary condition for the model system, where convergence within 0.1 eV was confirmed for the supercell size. For ion-implanted samples, we identified experimental peaks due to B clusters and threefold B as icosahedral B12 and 〈001〉B-Si defects, respectively. For as-doped samples prepared by plasma doping, it was found that the calculated XPS binding energies for complexes of vacancies and B atoms were consistent with the experimental spectra.
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81.05.Cy Elemental semiconductors
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
61.72.jd Vacancies
61.72.uf Ge and Si
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Surface rippling on bulk metallic glass under nanosecond pulse laser ablation

Y. Liu, M. Q. Jiang, G. W. Yang, Y. J. Guan, and L. H. Dai

Appl. Phys. Lett. 99, 191902 (2011); http://dx.doi.org/10.1063/1.3656700 (3 pages) | Cited 3 times

Online Publication Date: 8 November 2011

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We report an interesting surface ripple patterns in the irradiated area of a Zr-based bulk metallic glass by nanosecond pulse laser with single shot. Such surface rippling phenomenon can be ascribed to the Kelvin-Helmholtz instability at the interface between the molten layer and the expanding plasma plume. The analytical instability criterion is obtained via a perturbation analysis. Furthermore, the model demonstrates that the characteristic spacing of the ripples is dominated by the density, transverse velocity of the plasma wind, and the surface tension of the molten layer. The predicted spacing agrees well with the experimentally observed values. The results are fundamentally useful for laser-processing bulk metallic glasses (BMGs) and even for understanding the nature of flow in BMGs.
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61.43.Fs Glasses
81.15.Fg Pulsed laser ablation deposition
47.15.Fe Stability of laminar flows
68.03.Cd Surface tension and related phenomena
81.05.Kf Glasses (including metallic glasses)
47.20.-k Flow instabilities

Electronic structure and optical properties of Ag3PO4 photocatalyst calculated by hybrid density functional method

J. J. Liu, X. L. Fu, S. F. Chen, and Y. F. Zhu

Appl. Phys. Lett. 99, 191903 (2011); http://dx.doi.org/10.1063/1.3660319 (3 pages) | Cited 5 times

Online Publication Date: 8 November 2011

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The electronic structure and optical properties of Ag3PO4 were studied by hybrid density functional theory. The results indicated that the band gap is 2.43 eV, which agrees well with the experimental value of 2.45 eV. The conduction bands of Ag3PO4 are mainly attributable to Ag 5s and 5p states, while the valence bands are dominated by O 2p and Ag 4d states. The highest valence band edge potential was 2.67 V (vs. normal hydrogen electrode), which has enough driving force for photocatalytic water oxidation and pollutants degradation. The optical absorption spectrum showed that Ag3PO4 is a visible light response photocatalyst.
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71.20.Nr Semiconductor compounds
78.40.Fy Semiconductors
82.50.Hp Processes caused by visible and UV light
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Designing shape-memory Heusler alloys from first-principles

M. Siewert, M. E. Gruner, A. Dannenberg, A. Chakrabarti, H. C. Herper, M. Wuttig, S. R. Barman, S. Singh, A. Al-Zubi, T. Hickel, J. Neugebauer, M. Gillessen, R. Dronskowski, and P. Entel

Appl. Phys. Lett. 99, 191904 (2011); http://dx.doi.org/10.1063/1.3655905 (3 pages) | Cited 10 times

Online Publication Date: 8 November 2011

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The phase diagrams of magnetic shape-memory Heusler alloys, in particular, ternary Ni-Mn-Z and quarternary (Pt, Ni)-Mn-Z alloys with Z = Ga, Sn, have been addressed by density functional theory and Monte Carlo simulations. Finite temperature free energy calculations show that the phonon contribution stabilizes the high-temperature austenite structure while at low temperatures magnetism and the band Jahn-Teller effect favor the modulated monoclinic 14M or the nonmodulated tetragonal structure. The substitution of Ni by Pt leads to a series of magnetic shape-memory alloys with very similar properties to Ni-Mn-Ga but with a maximal eigenstrain of 14%.
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81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity
64.60.De Statistical mechanics of model systems (Ising model, Potts model, field-theory models, Monte Carlo techniques, etc.)
64.70.kd Metals and alloys
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
81.30.Kf Martensitic transformations

Enhanced transmission in rolled-up hyperlenses utilizing Fabry-Pérot resonances

Jochen Kerbst, Stephan Schwaiger, Andreas Rottler, Aune Koitmäe, Markus Bröll, Jens Ehlermann, Andrea Stemmann, Christian Heyn, Detlef Heitmann, and Stefan Mendach

Appl. Phys. Lett. 99, 191905 (2011); http://dx.doi.org/10.1063/1.3659287 (3 pages) | Cited 4 times

Online Publication Date: 8 November 2011

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We experimentally demonstrate that the transmission through rolled-up metal/semiconductor hyperlenses can be enhanced at desired frequencies utilizing Fabry-Pérot resonances. By means of finite difference time domain simulations, we prove that hyperlensing occurs at frequencies of high transmission.
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42.79.Bh Lenses, prisms and mirrors
02.70.Bf Finite-difference methods
42.25.Bs Wave propagation, transmission and absorption

Ab initio study of acoustic velocities in molybdenum under high pressure and high temperature

Zhao-Yi Zeng, Cui-E Hu, Xun Liu, Ling-Cang Cai, and Fu-Qian Jing

Appl. Phys. Lett. 99, 191906 (2011); http://dx.doi.org/10.1063/1.3659696 (3 pages) | Cited 2 times

Online Publication Date: 8 November 2011

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Acoustic velocities of Molybdenum (Mo) under high pressure and high temperature are calculated by using the generalized gradient approximation within density functional theory. The break in acoustic velocities of bcc Mo along Hugoniot occurs around 175–275 GPa, which agrees with shock-wave experimental results in which the phase transition was found at 210 GPa, 4100 K [R. S. Hixson, Phys. Rev. Lett. 62, 637 (1989)]. By comparing the acoustic velocities, we confirmed the phase transition from bcc to fcc Mo.
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62.65.+k Acoustical properties of solids
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mm Fracture
64.70.kd Metals and alloys
61.50.Ks Crystallographic aspects of phase transformations; pressure effects

Transmission electron microscopy study of GaInNAs(Sb) thin films grown by atomic hydrogen-assisted molecular beam epitaxy

R. Oshima, J. Y. Huang, N. Miyashita, K. Matsubara, Y. Okada, and F. A. Ponce

Appl. Phys. Lett. 99, 191907 (2011); http://dx.doi.org/10.1063/1.3660232 (3 pages) | Cited 2 times

Online Publication Date: 9 November 2011

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The quaternary GaInNAs is a promising material system for use in next generation multijunction photovoltaic devices. We have investigated the effect of introducing antimony on the growth by using transmission electron microscopy and energy dispersive x-ray (EDX) spectroscopy. Two-dimensional growth was observed in GaInNAs films with striation features associated with compositional fluctuation and nanometer scale elemental segregation on the growth front. On the contrary, GaInNAsSb films exhibit uniform contrast throughout. EDX profile indicates uniform compositional distribution, as antimony atoms suppress the surface mobilites of adatoms resulting in a lower probability to generate the favored bonds, such as Ga-N and In-As.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Terahertz coherent acoustic experiments with semiconductor superlattices

A. Huynh, B. Perrin, B. Jusserand, and A. Lemaître

Appl. Phys. Lett. 99, 191908 (2011); http://dx.doi.org/10.1063/1.3658458 (3 pages) | Cited 5 times

Online Publication Date: 9 November 2011

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We demonstrate the generation, propagation, and detection of coherent acoustic waves at 1 THz. We performed picosecond ultrasonics experiments in an acoustic transmission geometry, which allows a total decoupling of the phonon generation and detection processes, occurring in two different superlattices grown on opposite sides of a substrate, respectively. We show that a 1 ns burst of monochromatic terahertz coherent acoustic waves could be generated on one side of a substrate, propagated over a large distance and detected on the opposite side. We also measured the lattice dispersion owing to the time delay between the terahertz burst and much lower frequency acoustic waves.
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62.65.+k Acoustical properties of solids
78.70.Gq Microwave and radio-frequency interactions
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

An ultrabroad terahertz bandpass filter based on multiple-resonance excitation of a composite metamaterial

Yi-Ju Chiang, Chan-Shan Yang, Yu-Hang Yang, Ci-Ling Pan, and Ta-Jen Yen

Appl. Phys. Lett. 99, 191909 (2011); http://dx.doi.org/10.1063/1.3660273 (3 pages) | Cited 4 times

Online Publication Date: 9 November 2011

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We experimentally present an ultrabroad terahertz (THz) bandpass filter based on a composite metamaterial (CMM) by exciting its multiple resonances. This metamaterial-based filter, consisting of a metal-dielectric-metal sandwiched structure, possesses a notable spectral-filtering capability with a 0.5-THz-broad bandwidth and excellent band-edge transitions of 140% THz and 182% THz in the THz-gap region. Furthermore, we manifest the mechanism for each of the resonances and the coupling within the composite metamaterial. This realization enables the capacity for engineering the electromagnetic properties to develop other complex optical functionalities. An example of a high-profile dualband THz bandpass filter is also proposed theoretically in this work.
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84.30.Vn Filters
84.40.-x Radiowave and microwave (including millimeter wave) technology

A variable constraint tube model for size effects of polymer nano-structures

Shan Tang, M. Steven Greene, and Wing Kam Liu

Appl. Phys. Lett. 99, 191910 (2011); http://dx.doi.org/10.1063/1.3660585 (3 pages) | Cited 1 time

Online Publication Date: 9 November 2011

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We develop a molecular-based hyperelastic model to simulate the size dependent mechanical properties of polymer nano-structures. We assume that polymer chains are confined to a different “tube” size in a boundary layer than that in the core, which alters the free energy and produces the size effect. Simulations also explore anisotropic orientations of polymer chains and surface tension. The axial modulus of nanofibers is studied in detail, although the model is applicable to other systems like thin films and nano-biological systems.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
65.40.G- Other thermodynamical quantities
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