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11 Apr 2011

Volume 98, Issue 15, Articles (15xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 153103 (2011); http://dx.doi.org/10.1063/1.3555342 (3 pages)

Hsin-Yu Wu and Brian T. Cunningham
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Ultracompact, broadband slot waveguide polarization splitter

Shiyun Lin, Juejun Hu, and Kenneth B. Crozier

Appl. Phys. Lett. 98, 151101 (2011); http://dx.doi.org/10.1063/1.3579243 (3 pages) | Cited 14 times

Online Publication Date: 11 April 2011

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In this letter, we demonstrate an ultracompact polarization splitter design leveraging the giant birefringence of silicon-on-insulator slot waveguides. The fabricated splitter device has a coupling length of only 13.6 μm, and shows average polarization extinction ratios of 21 dB and 17 dB for the TE and TM polarizations, respectively, over the entire C-band.
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42.82.Et Waveguides, couplers, and arrays
42.82.Bq Design and performance testing of integrated-optical systems
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Gn Optical waveguides and couplers
42.79.Fm Reflectors, beam splitters, and deflectors
42.15.Eq Optical system design
42.79.Ci Filters, zone plates, and polarizers

Defect-reduced green GaInN/GaN light-emitting diode on nanopatterned sapphire

Yufeng Li (李虞锋), Shi You (尤适), Mingwei Zhu (朱明伟), Liang Zhao (赵亮), Wenting Hou (侯文婷), T. Detchprohm, Y. Taniguchi, N. Tamura, S. Tanaka, and C. Wetzel

Appl. Phys. Lett. 98, 151102 (2011); http://dx.doi.org/10.1063/1.3579255 (3 pages) | Cited 14 times

Online Publication Date: 11 April 2011

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Green GaInN/GaN quantum well light-emitting diode (LED) wafers were grown on nanopatterned c-plane sapphire substrate by metal-organic vapor phase epitaxy. Without roughening the chip surface, such LEDs show triple the light output over structures on planar sapphire. By quantitative analysis the enhancement was attributed to both, enhanced generation efficiency and extraction. The spectral interference and emission patterns reveal a 58% enhanced light extraction while photoluminescence reveals a doubling of the internal quantum efficiency. The latter was attributed to a 44% lower threading dislocation density as observed in transmission electron microscopy. The partial light output power measured from the sapphire side of the unencapsulated nanopatterned substrate LED die reaches 5.2 mW at 525 nm at 100 mA compared to 1.8 mW in the reference LED.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Optical interrogation system based on holographic soft matter filter

D. Donisi, L. De Sio, R. Beccherelli, M. A. Caponero, A. d’Alessandro, and C. Umeton

Appl. Phys. Lett. 98, 151103 (2011); http://dx.doi.org/10.1063/1.3579244 (3 pages) | Cited 2 times

Online Publication Date: 12 April 2011

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We present an optical interrogation system based on a holographic soft-matter filter. It provides a wavelength-dependent transmittance, with a linear relation between Bragg wavelength shift and variation in the filter output intensity. This is the demonstration of a simple and inexpensive technology to implement a, low cost, monitoring system based on a fiber Bragg grating sensor.
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42.40.Eq Holographic optical elements; holographic gratings
42.79.Ci Filters, zone plates, and polarizers
42.79.Dj Gratings
42.81.Pa Sensors, gyros

Simultaneous measurement of orthogonal components of polarization in a free-space propagating terahertz signal using electro-optic detection

M. B. Byrne, M. U. Shaukat, J. E. Cunningham, E. H. Linfield, and A. G. Davies

Appl. Phys. Lett. 98, 151104 (2011); http://dx.doi.org/10.1063/1.3579258 (3 pages) | Cited 4 times

Online Publication Date: 12 April 2011

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We report a polarization-sensitive terahertz time-domain spectroscopy system, which allows the simultaneous measurement of orthogonal components of the polarization of a free-space propagating terahertz beam using a dual electro-optic detection scheme. We demonstrate the operation of our system by measuring the birefringence of lithium niobate, simultaneously obtaining terahertz spectra from two orthogonal crystallographic directions.
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07.60.-j Optical instruments and equipment
78.20.Fm Birefringence
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques

Neodymium zirconate (Nd2Zr2O7) transparent ceramics as a solid state laser material

Tao Feng, David R. Clarke, Danyu Jiang, Jinfeng Xia, and Jianlin Shi

Appl. Phys. Lett. 98, 151105 (2011); http://dx.doi.org/10.1063/1.3579526 (3 pages) | Cited 2 times

Online Publication Date: 12 April 2011

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Transparent neodymium zirconate (Nd2Zr2O7) ceramics have been fabricated from nanoparticles prepared by combustion synthesis. Emission at 1054.5 nm has been demonstrated using a laser diode pump at 800 nm. A transmittance of 60% at wavelengths longer than ∼ 900 nm was achieved. A consequence of the very high concentration of Nd ions (1.32×1028 ions/m3) is that the absorption bands are wider than those of Nd doped Y3Al5O12 (Nd:YAG) facilitating pumping over a broader range of wavelengths. The full width at half maximum of the emission peak is also larger than that of Nd:YAG, and the decay time is 460 μs making Nd2Zr2O7 an excellent candidate for efficient high-power microchip lasers emitting at 1054 nm with diode pumping at ∼ 800 or ∼ 900 nm.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.05.Cy Elemental semiconductors
81.16.Be Chemical synthesis methods
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Square optical vortices generated by binary spiral zone plates

Nan Gao, Changqing Xie, Chun Li, Chunshui Jin, and Ming Liu

Appl. Phys. Lett. 98, 151106 (2011); http://dx.doi.org/10.1063/1.3581044 (3 pages) | Cited 1 time

Online Publication Date: 12 April 2011

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Binary phase square spiral zone plates (BPSSZPs), a special type of binary phase vortex lenses, are introduced to generate focused optical vortices showing square symmetry. The numerical solution and fabrication method, as well as the experimental results are given. Different from conventional vortex lenses, these BPSSZPs produce focused vortices with small topological charge following a modulo-4 transmutation rule. In addition, the central diffracted image rotates in the vicinity of the focal plane. These interesting properties suggest that BPSSZPs might become key components for many potential applications such as optical image processing and quantum computation.
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42.79.Bh Lenses, prisms and mirrors
42.79.Ci Filters, zone plates, and polarizers
42.86.+b Optical workshop techniques
42.82.Bq Design and performance testing of integrated-optical systems

A half wave retarder made of bilayer subwavelength metallic apertures

Z. Marcet, H. B. Chan, D. W. Carr, J. E. Bower, R. A. Cirelli, F. Klemens, W. M. Mansfield, J. F. Miner, C. S. Pai, and I. I. Kravchenko

Appl. Phys. Lett. 98, 151107 (2011); http://dx.doi.org/10.1063/1.3579245 (3 pages)

Online Publication Date: 13 April 2011

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We demonstrate a half wave plate whose principle of operation is based on the strong evanescent field coupling between two metal layers with arrays of subwavelength slits. The device is divided into two kinds of pixels in which the slits are oriented in orthogonal directions. By tuning the phase delay of the transmitted light through the lateral displacement between the top and bottom layers, the polarization of linearly polarized light at 1.55 μm can be rotated by up to 90°. The polarization extinction ratio of the transmitted light exceeds 22 dB.
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42.79.Ci Filters, zone plates, and polarizers

Selective epitaxial growth of Ge/Si0.15Ge0.85 quantum wells on Si substrate using reduced pressure chemical vapor deposition

Shen Ren (任申), Yiwen Rong (戎亦文), Theodore I. Kamins, James S. Harris, and David A. B. Miller

Appl. Phys. Lett. 98, 151108 (2011); http://dx.doi.org/10.1063/1.3574912 (3 pages) | Cited 5 times

Online Publication Date: 13 April 2011

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We investigate the selective epitaxial growth of Ge/Si0.15Ge0.85 quantum wells on prepatterned silicon substrates by reduced pressure chemical vapor deposition. A vertical p-i-n Si0.1Ge0.9 diode with Ge/Si0.15Ge0.85 quantum wells in the intrinsic region is selectively grown in holes in a SiO2 mask. We find perfect growth selectivity and very low dependence on size or arrangement of the mask holes. The fabricated p-i-n diode shows very low reverse leakage current and high breakdown voltage, suggesting good epitaxy quality. The quantum-confined Stark effect in this quantum-well system is observed for wavelengths >1.5 μm at room temperature.
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85.30.Kk Junction diodes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.07.St Quantum wells

Si nanoparticle–Er3+ coupling through contact in as-deposited nanostructured films

S. Núñez-Sánchez, P. M. Roque, R. Serna, and A. K. Petford-Long

Appl. Phys. Lett. 98, 151109 (2011); http://dx.doi.org/10.1063/1.3579523 (3 pages) | Cited 3 times

Online Publication Date: 14 April 2011

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The efficient excitation of Er3+ ions through contact with Si nanoparticles (NPs) is demonstrated. A nanostructured doping process has been developed that leads to contact between Si NPs formed in situ and optically-active Er3+ ions embedded in Al2O3. This is achieved by independent and consecutive deposition of the dopants and matrix. The Si NP–Er3+ contact regime enhances the probability of efficient interaction due to the local spatial overlap of the electronic states of the Er3+ and of the Si NP exciton, enabling energy transfer by interband exciton recombination. This leads to up to 53% of the Er3+ ions being excited in as-deposited films.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Ap Elemental semiconductors
61.72.uf Ge and Si
73.22.Lp Collective excitations
71.35.-y Excitons and related phenomena
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.20.Mq Elemental semiconductors

Plasmonic effects for light concentration in organic photovoltaic thin films induced by hexagonal periodic metallic nanospheres

Jinfeng Zhu, Mei Xue, Huajun Shen, Zhe Wu, Seongku Kim, Jyh-Jier Ho, Aram Hassani-Afshar, Baoqing Zeng, and Kang L. Wang

Appl. Phys. Lett. 98, 151110 (2011); http://dx.doi.org/10.1063/1.3577611 (3 pages) | Cited 12 times

Online Publication Date: 14 April 2011

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We present a plasmonic nanostructure design by embedding a layer of hexagonal periodic metallic nanospheres between the active layer and transparent anode for bulk heterojunction organic solar cells. The hybrid structure shows broadband optical absorption enhancement from localized surface plasmon resonance with a weak dependence on polarization of incident light. We also theoretically study the optimization of the design to enhance the absorption up to 1.90 times for a typical hybrid active layer based on a low band gap material.
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88.40.jr Organic photovoltaics
88.40.hj Efficiency and performance of solar cells

Balanced terahertz wave air-biased-coherent-detection

Xiaofei Lu and X.-C. Zhang

Appl. Phys. Lett. 98, 151111 (2011); http://dx.doi.org/10.1063/1.3574535 (3 pages) | Cited 2 times

Online Publication Date: 14 April 2011

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A balanced heterodyne air-biased-coherent-detection scheme for broadband terahertz waves is achieved using third-order nonlinear susceptibility tensor elements to produce field-induced optical second harmonic photons, which have two orthogonal polarizations. The differential signal between two orthogonally polarized second harmonic photons reduces the common noise in a balanced detection geometry and improves the signal-to-noise ratio by a factor of 2.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
42.65.An Optical susceptibility, hyperpolarizability

Critical composition of reduced pure-LiNbO3 crystals: A sudden change in optical properties

W. Yan, P. Minzioni, G. Nava, P. Galinetto, L. Shi, and V. Degiorgio

Appl. Phys. Lett. 98, 151112 (2011); http://dx.doi.org/10.1063/1.3580764 (3 pages) | Cited 1 time

Online Publication Date: 14 April 2011

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We investigated the composition dependence of photorefractivity, beam distortion, Raman lines, and birefringence in reduced pure lithium niobate. When lithium content reaches the value of 49.4 mol %, abrupt changes were observed for all these optical properties except birefringence. We suggest that such a behavior may be due to a change in the phonon spectrum occurring around the critical composition.
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78.20.Mg Photorefractive effects
78.30.Hv Other nonmetallic inorganics
78.20.Fm Birefringence
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Direct observation of photonic Fermi surfaces by plasmon tomography

C. J. Regan, A. Krishnan, R. Lopez-Boada, L. Grave de Peralta, and A. A. Bernussi

Appl. Phys. Lett. 98, 151113 (2011); http://dx.doi.org/10.1063/1.3581050 (3 pages) | Cited 7 times

Online Publication Date: 14 April 2011

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Light propagation in dielectric plasmonic crystals with different parameters and symmetries was investigated by plasmon tomography. We show that the photonic Fermi surfaces at the crystal’s reciprocal lattice space can be observed directly from the Fourier plane images. Directional gaps were observed where the isofrequency wavevectors of the propagating surface plasmon mode intersect the first Brillouin zone of the plasmonic crystal structures. We determined that the angular magnitude of the directional gaps depends strongly on the crystal symmetry and the lattice period.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Terahertz sources based on intracavity frequency mixing in mid-infrared quantum cascade lasers with passive nonlinear sections

Robert W. Adams, Augustinas Vizbaras, Min Jang, Christian Grasse, Simeon Katz, Gerhard Boehm, Markus C. Amann, and Mikhail A. Belkin

Appl. Phys. Lett. 98, 151114 (2011); http://dx.doi.org/10.1063/1.3579260 (3 pages) | Cited 2 times

Online Publication Date: 15 April 2011

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We report the design and performance of terahertz quantum cascade laser sources based on intracavity difference frequency generation in dual-wavelength mid-infrared quantum cascade lasers with a passive nonlinear section at the exit facet, designed for giant second-order nonlinear susceptibility. These devices operate in the mid-infrared at λ1 = 8.4 μm and λ2 = 9.5 μm, with terahertz output at the difference frequency, λ3 ≈ 73 μm. Terahertz output of approximately 100 nW was observed up to a heat sink temperature of 210 K.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.72.Ai Infrared sources
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Surface plasmon dispersion engineering via double-metallic Au/Ag layers for III-nitride based light-emitting diodes

Hongping Zhao, Jing Zhang, Guangyu Liu, and Nelson Tansu

Appl. Phys. Lett. 98, 151115 (2011); http://dx.doi.org/10.1063/1.3580628 (3 pages) | Cited 31 times

Online Publication Date: 15 April 2011

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Double-metallic Au/Ag layers deposited on top of InGaN/GaN quantum wells (QWs) are used to tune the Purcell peak enhancement of the radiative recombination rate for nitride light-emitting diodes. By modifying the Au/Ag thicknesses, the Purcell factor can be widely tuned between the surface plasmon frequencies of Au/GaN and Ag/GaN. Photoluminescence studies demonstrated the concept of the Purcell factor tuning by using the double-metallic Au/Ag layers.
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85.60.Jb Light-emitting devices
78.55.Cr III-V semiconductors
73.21.Fg Quantum wells

Influence of nanowires length on performance of crystalline silicon solar cell

Haofeng Li, Rui Jia, Chen Chen, Zhao Xing, Wuchang Ding, Yanlong Meng, Deqi Wu, Xinyu Liu, and Tianchun Ye

Appl. Phys. Lett. 98, 151116 (2011); http://dx.doi.org/10.1063/1.3574904 (3 pages) | Cited 13 times

Online Publication Date: 15 April 2011

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Silicon-nanowire (Si-NW) array, prepared by an electroless chemical-etching method, shows excellent optical antireflection property over a wide spectral bandwidth. The influence of the wire length on the optical antireflection property and the solar cell performance were studied for both the Si-NW array solar cells and the planar solar cells. The reflectance of NWs solar cells is almost invariable and much lower than that of the planar solar cells but the performance of planar solar cells is the best. Results show the performance of NWs solar cells is strongly affected by some other factors such as surface passivation and electrode-contact property.
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88.40.jj Silicon solar cells
88.40.H- Solar cells (photovoltaics)
81.07.Gf Nanowires
81.65.Rv Passivation
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Anisotropy induced wave birefringence in bounded supercritical plasma confined in a multicusp magnetic field

Indranuj Dey and Sudeep Bhattacharjee

Appl. Phys. Lett. 98, 151501 (2011); http://dx.doi.org/10.1063/1.3577610 (3 pages) | Cited 4 times

Online Publication Date: 11 April 2011

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Laboratory observation of rotation of the polarization axis (θc ∼ 20°–40° with respect to vacuum) of a penetrating electromagnetic wave through a bounded supercritical plasma (plasma frequency ωp>wave frequency ω), confined in a multicusp magnetic field is reported. Birefringence of the radial and polar wave electric field components (Er and Eθ) has been identified as the cause for the rotation, similar to a magneto-optic medium, however, with distinct differences owing to the presence of wave induced resonances. Numerical simulation results obtained by solving the Maxwell’s equations by incorporating the plasma and magnetostatic field inhomogeneities within a conducting boundary shows a reasonable agreement with the experimental results.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.Lf Field-reversed configurations, rotamaks, astrons, ion rings, magnetized target fusion, and cusps
52.65.-y Plasma simulation

Plasma plume propagation characteristics of pulsed radio frequency plasma jet

J. H. Liu, X. Y. Liu, K. Hu, D. W. Liu, X. P. Lu, F. Iza, and M. G. Kong

Appl. Phys. Lett. 98, 151502 (2011); http://dx.doi.org/10.1063/1.3573811 (3 pages) | Cited 3 times

Online Publication Date: 15 April 2011

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A 4 cm long helium cold atmospheric pressure plasma jet with pulsed radio frequency (rf) excitation was obtained by a copper electrode inside a quartz tube. The plasma bullet propagation characteristics common to the microseconds direct current pulse and kilohertz plasma jet is not observed in this case. The space-, time-, and wavelength-resolved optical emission profiles suggest the pulsed rf plasma channel out of the tube was strengthened by ions and metastables with longer life time than the rf period, and the plasma propagation was actually an illumination of the plasma channel caused by energetic electrons accelerated along the channel.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.75.-d Plasma devices
52.80.Pi High-frequency and RF discharges
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
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Hot wire chemical vapor deposition of germanium selenide thin films for nonvolatile random access memory applications

D. Reso, M. Silinskas, M. Lisker, A. Schubert, and E. P. Burte

Appl. Phys. Lett. 98, 151901 (2011); http://dx.doi.org/10.1063/1.3579192 (3 pages)

Online Publication Date: 11 April 2011

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Thin films of germanium selenide (GexSe100−x with 0<x<57) were deposited on different substrates by hot wire metalorganic chemical vapor deposition using tetraallylgermanium and di-tert-butylselenide. The growth kinetics of the deposition process as well as the properties of the films were investigated. The growth rate was found to decrease with increasing temperature and decreasing pressure. The conformal step coverage was demonstrated. Germanium selenide films covered and subsequently diffused by silver were used as programmable metallization cells for a verification of the electrical switching properties.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
85.40.Ls Metallization, contacts, interconnects; device isolation
68.55.A- Nucleation and growth

Mechanism for transient migration of xenon in UO2

X.-Y. Liu, B. P. Uberuaga, D. A. Andersson, C. R. Stanek, and K. E. Sickafus

Appl. Phys. Lett. 98, 151902 (2011); http://dx.doi.org/10.1063/1.3579198 (3 pages) | Cited 4 times

Online Publication Date: 11 April 2011

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In this letter, we report recent work on atomistic modeling of diffusion migration events of the fission gas product xenon in UO2 nuclear fuel. Under nonequilibrium conditions, Xe atoms can occupy the octahedral interstitial site, in contrast to the thermodynamically most stable uranium substitutional site. A transient migration mechanism involving Xe and two oxygen atoms is identified using basin constrained molecular dynamics employing a Buckingham type interatomic potential. This mechanism is then validated using density functional theory calculations using the nudged elastic band method. An overall reduction in the migration barrier of 1.6–2.7 eV is obtained compared to vacancy-mediated diffusion on the uranium sublattice.
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66.30.je Diffusion of gases
61.72.jj Interstitials
66.30.Dn Theory of diffusion and ionic conduction in solids
28.41.Bm Fuel elements, preparation, reloading, and reprocessing

Subwavelength electromagnetic diode: One-way response of cascading nonlinear meta-atoms

Yuancheng Fan, Jin Han, Zeyong Wei, Chao Wu, Yang Cao, Xing Yu, and Hongqiang Li

Appl. Phys. Lett. 98, 151903 (2011); http://dx.doi.org/10.1063/1.3579241 (3 pages) | Cited 4 times

Online Publication Date: 11 April 2011

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We propose a scheme for subwavelength electromagnetic diode by employing cascading nonlinear meta-atoms. One-way response is conceptually demonstrated on a microwave transmission line comprising of three metallic ring resonators acting as meta-atoms and a varactor as the nonlinear medium inclusion. Experiments show that our implementation can operate simultaneously as forward diode and backward diode at different frequencies. A transmission contrast of up to 14.7 dB was achieved between forward and backward transmission. Subwavelength size of our diode should be useful for miniaturization of integrated optical nanocircuits.
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84.32.Tt Capacitors
84.40.Az Waveguides, transmission lines, striplines
FREE

Mechanically and optically reliable folding structure with a hyperelastic material for seamless foldable displays

Hyuk-Jun Kwon, HongShik Shim, Sunkook Kim, Woong Choi, Youngtea Chun, InSeo Kee, and SangYoon Lee

Appl. Phys. Lett. 98, 151904 (2011); http://dx.doi.org/10.1063/1.3576906 (3 pages) | Cited 4 times

Online Publication Date: 11 April 2011

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We report a mechanically and optically robust folding structure to realize a foldable active matrix organic-light-emitting-diode (AMOLED) display without a visible crease at the junction. A nonlinear stress analysis, based on a finite element method, provided an optimized design. The folding-unfolding test on the structure exhibited negligible deterioration of the relative brightness at the junction of the individual panels up to 105 cycles at a folding radius of 1 mm, indicating highly reliable mechanical and optical tolerances. These results demonstrate the feasibility of seamless foldable AMOLED displays, with potentially important technical implications on fabricating large size flexible displays.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Jb Light-emitting devices

Emission of the terahertz electromagnetic wave from coherent longitudinal optical phonons in a GaAs buffer layer optically masked by a GaSb top epitaxial layer

Hideo Takeuchi, Syuichi Tsuruta, and Masaaki Nakayama

Appl. Phys. Lett. 98, 151905 (2011); http://dx.doi.org/10.1063/1.3574541 (3 pages)

Online Publication Date: 13 April 2011

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We demonstrate that, in a GaSb/GaAs epitaxial structure, the coherent longitudinal optical (LO) phonon in the GaAs layer optically masked by the GaSb top layer is observed utilizing terahertz- electromagnetic-wave spectroscopy. It is confirmed from a Raman scattering measurement that only the optical phonon in the GaSb layer is optically observable, where the photon energy of the excitation laser beam was almost the same as that of the femtosecond pulse pump beam for the terahertz wave measurement. In the terahertz wave measurement, the Fourier power spectrum of the terahertz waveform exhibits both the GaAs and the GaSb LO phonons; namely, the coherent LO phonon in the optically masked GaAs buffer layer is observed in the terahertz wave measurement. This fact demonstrates that the instantaneous surface potential modulation originating from the impulsive carrier excitation by the pump pulses reaches the GaAs buffer layer. Consequently, the above-mentioned surface potential modulation generates the coherent GaAs LO phonon.
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78.70.Gq Microwave and radio-frequency interactions
78.30.Hv Other nonmetallic inorganics
63.20.dd Measurements
78.66.Fd III-V semiconductors

Correlation between internal states and plasticity in bulk metallic glass

J. Tan (谭军), Y. Zhang (张岳), B. A. Sun (孙保安), M. Stoica, C. J. Li (李才巨), K. K. Song (宋凯凯), U. Kühn, F. S. Pan (潘复生), and J. Eckert

Appl. Phys. Lett. 98, 151906 (2011); http://dx.doi.org/10.1063/1.3580774 (3 pages) | Cited 6 times

Online Publication Date: 13 April 2011

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We report a close correlation between the internal states and plasticity in a bulk metallic glass (BMG) and discover that the optimization of copper-mold casting current can induce large plasticity stably in an otherwise brittle BMG. It is possible to confirm that larger plasticity corresponds to the internal states with more average free volume (FV) as revealed by lower density, higher enthalpy change, and higher Poisson’s ratio. The enhanced plastic deformation mechanism is interpreted based on the FV model of BMGs, and our results may have some implications for understanding the role of the FV during plastic deformation of BMGs.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
62.20.dj Poisson's ratio
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.43.Fs Glasses

Accurate band gaps of AlGaN, InGaN, and AlInN alloys calculations based on LDA-1/2 approach

R. R. Pelá, C. Caetano, M. Marques, L. G. Ferreira, J. Furthmüller, and L. K. Teles

Appl. Phys. Lett. 98, 151907 (2011); http://dx.doi.org/10.1063/1.3576570 (3 pages) | Cited 10 times

Online Publication Date: 14 April 2011

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We present parameter-free calculations of electronic properties of InGaN, InAlN, and AlGaN alloys. The calculations are based on a generalized quasichemical approach, to account for disorder and composition effects, and first-principles calculations within the density functional theory with the LDA-1/2 approach, to accurately determine the band gaps. We provide precise results for AlGaN, InGaN, and AlInN band gaps for the entire range of compositions, and their respective bowing parameters.
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71.20.Nr Semiconductor compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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