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30 Jun 2008

Volume 92, Issue 26, Articles (26xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 264101 (2008); http://dx.doi.org/10.1063/1.2951485 (3 pages)

Wei Xiang Jiang, Tie Jun Cui, Qiang Cheng, Jessie Yao Chin, Xin Mi Yang, Ruopeng Liu, and David R. Smith
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Tunable generation of Bessel beams with a fluidic axicon

Graham Milne, Gavin D. M. Jeffries, and Daniel T. Chiu

Appl. Phys. Lett. 92, 261101 (2008); http://dx.doi.org/10.1063/1.2952833 (3 pages) | Cited 12 times

Online Publication Date: 30 June 2008

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This paper describes a tunable fluidic conical lens, or axicon, for the generation and dynamic reconfiguration of Bessel beams. When illuminated with a Gaussian laser beam, our fluidic axicon generates a diverging beam with an annular cross section. By varying the refractive index of the solution that fills our device, we can vary easily the spatial properties of the resulting Bessel beam.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.79.Bh Lenses, prisms and mirrors

Viewing-angle controllable liquid crystal display using a fringe- and vertical-field driven hybrid aligned nematic liquid crystal

Eun Jeong, Young Jin Lim, Mi Hyung Chin, Jin Ho Kim, Seung Hee Lee, Seung Hoon Ji, Gi-Dong Lee, Kyoung Ho Park, Hyun Chul Choi, and Byung Chul Ahn

Appl. Phys. Lett. 92, 261102 (2008); http://dx.doi.org/10.1063/1.2953456 (3 pages) | Cited 7 times

Online Publication Date: 1 July 2008

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Viewing-angle controllable liquid crystal display (LCD) without using an additional panel or pixel division is proposed. In the device, hybrid aligned nematic liquid crystal using a liquid crystal with negative dielectric anisotropy is used. The device shows narrow viewing angle when it is driven only by fringe-electric field, however, it exhibits wide viewing angle if driven by vertical- as well as fringe-electric field. With the approach, the viewing angle of the LCD can be controlled from 120° to 20° in horizontal direction.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems

On the importance of radiative and Auger losses in GaN-based quantum wells

J. Hader, J. V. Moloney, B. Pasenow, S. W. Koch, M. Sabathil, N. Linder, and S. Lutgen

Appl. Phys. Lett. 92, 261103 (2008); http://dx.doi.org/10.1063/1.2953543 (3 pages) | Cited 67 times

Online Publication Date: 1 July 2008

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Fully microscopic many-body models are used to study the importance of radiative and Auger carrier losses in InGaN/GaN quantum wells. Auger losses are found to be negligible in contrast to recent speculations on their importance for the experimentally observed efficiency droop. Good agreement with experimentally measured threshold losses is demonstrated. The results show no significant dependence on details of the well alloy profile.
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68.65.Fg Quantum wells
81.05.Ea III-V semiconductors

Midinfrared intersubband absorption in wide band gap II-VI ZnxCd1−xSe multiple quantum wells with metastable zincblende MgSe barriers

B. S. Li, A. Shen, W. O. Charles, Q. Zhang, and M. C. Tamargo

Appl. Phys. Lett. 92, 261104 (2008); http://dx.doi.org/10.1063/1.2943660 (3 pages) | Cited 5 times

Online Publication Date: 1 July 2008

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The authors report the observation of midinfrared intersubband (ISB) absorption in MgSe/ZnxCd1−xSe multiple quantum wells (MQWs) grown on (001) InP substrates by molecular beam epitaxy. The in situ reflection high energy electron diffraction shows that zincblende MgSe/ZnxCd1−xSe MQWs can be grown with the introduction of ZnxCd1−xSe spacer layers. For quantum wells with the nominal well width of 11–15 ML (3.2–4.4 nm) ISB absorption in the wavelength range of 3.3–4.9 μm is observed. The conduction band offset (CBO) of the MgSe/ZnxCd1−xSe heterostructure is estimated to be 1.2 eV. Using the estimated CBO, the theoretically calculated interband and ISB transition energies agree well with photoluminescence and Fourier-transform infrared spectroscopy measurements. With such a large CBO, ISB transitions in this material system could be extended to the near infrared region.
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78.30.Fs III-V and II-VI semiconductors
78.55.Et II-VI semiconductors
68.65.Fg Quantum wells

Enhanced characteristics of blue InGaN/GaN light-emitting diodes by using selective activation to modulate the lateral current spreading length

Ray-Ming Lin, Yuan-Chieh Lu, Yi-Lun Chou, Guo-Hsing Chen, Yung-Hsiang Lin, and Meng-Chyi Wu

Appl. Phys. Lett. 92, 261105 (2008); http://dx.doi.org/10.1063/1.2953700 (3 pages)

Online Publication Date: 1 July 2008

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We have studied the characteristics of blue InGaN/GaN multiquantum-well light-emitting diodes (LEDs) after reducing the length of the lateral current path through the transparent layer through formation of a peripheral high-resistance current-blocking region in the Mg-doped GaN layer. To study the mechanism of selective activation in the Mg-doped GaN layer, we deposited titanium (Ti), gold (Au), Ti/Au, silver, and copper individually onto the Mg-doped GaN layer and investigated their effects on the hole concentration in the p-GaN layer. The Mg-doped GaN layer capped with Ti effectively depressed the hole concentration in the p-GaN layer by over one order of magnitude relative to that of the as-grown layer. This may suggest that high resistive regions are formed by diffusion of Ti and depth of high resistive region from the p-GaN surface depends on the capped Ti film thickness. Selective activation of the Mg-doped GaN layer could be used to modulate the length of the lateral current path. Furthermore, the external quantum efficiency of the LEDs was improved significantly after reducing the lateral current spreading length. In our best result, the external quantum efficiency was 52.3% higher (at 100 mA) than that of the as-grown blue LEDs.
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85.60.Jb Light-emitting devices
73.63.Hs Quantum wells
72.20.-i Conductivity phenomena in semiconductors and insulators

A three-dimensional isotropic transmission-line metamaterial topology for free-space excitation

Ashwin K. Iyer and George V. Eleftheriades

Appl. Phys. Lett. 92, 261106 (2008); http://dx.doi.org/10.1063/1.2953709 (3 pages) | Cited 9 times

Online Publication Date: 1 July 2008

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This work proposes a three-dimensional isotropic transmission-line metamaterial topology for free-space excitation whose negative-refractive-index properties are validated by full-wave simulation. The topology is based on a physical realization of the symmetrical condensed node of transmission-line matrix modeling, but reverses the positions of the inductive and capacitive lumped elements in order to yield an isotropic negative refractive index and good matching to free space.
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42.70.-a Optical materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
84.40.Az Waveguides, transmission lines, striplines

Electroluminescence from monolayer ZnO nanoparticles using dry coating technique

Chun-Yu Lee, Yuen-Yung Hui, Wei-Fang Su, and Ching-Fuh Lin

Appl. Phys. Lett. 92, 261107 (2008); http://dx.doi.org/10.1063/1.2952283 (3 pages) | Cited 8 times

Online Publication Date: 1 July 2008

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We report ultraviolet electroluminescence from ZnO nanoparticle-based devices prepared by the dry-coating technique. With dry-coating process, the structure of the ZnO nanoparticle monolayer (90 nm) in the device can be easily achieved. The method reduces the density of pinhole defects in the ZnO nanoparticles. The confirmation for dry coating is investigated using field-emission scanning electron microscopy. The devices show the ZnO band-gap emission peak at 380 nm and the background emission from the interface between the host matrix and Aluminum tris-8-hydroxyquinoline. The origins of the ZnO band-gap emission and background emission are also discussed.
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81.05.Dz II-VI semiconductors
81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
78.60.Fi Electroluminescence
81.65.-b Surface treatments

Monocrystalline AlxGa1−xAs heterostructures for high-reflectivity high-Q micromechanical resonators in the megahertz regime

Garrett D. Cole, Simon Gröblacher, Katharina Gugler, Sylvain Gigan, and Markus Aspelmeyer

Appl. Phys. Lett. 92, 261108 (2008); http://dx.doi.org/10.1063/1.2952512 (3 pages) | Cited 10 times

Online Publication Date: 1 July 2008

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We present high-performance megahertz micromechanical oscillators based on freestanding epitaxial AlxGa1−xAs distributed Bragg reflectors. Compared with dielectric reflectors, the low mechanical loss of the monocrystalline heterostructure gives rise to significant improvements in the achievable mechanical quality factor Q while simultaneously exhibiting near unity reflectivity. Experimental characterization yields an optical reflectivity exceeding 99.98% and mechanical quality factors up to 20 000 at 4 K. This materials system is not only an interesting candidate for optical coatings with ultralow thermal noise, but also provides a promising path toward quantum optical control of massive micromechanical mirrors.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
42.82.-m Integrated optics

Longitudinal coherence in thermal ghost imaging

F. Ferri, D. Magatti, V. G. Sala, and A. Gatti

Appl. Phys. Lett. 92, 261109 (2008); http://dx.doi.org/10.1063/1.2945642 (3 pages) | Cited 9 times

Online Publication Date: 1 July 2008

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We show theoretically and experimentally that lensless ghost imaging with thermal light is fully interpretable in terms of classical statistical optics. The disappearance of the ghost image when the object and the reference planes are located at different distances from the source is due to the fading out of the intensity-intensity cross correlation between the two planes. Thus the visibility and the resolution of the ghost image are determined by the longitudinal coherence of the speckle beam, and no quantum explanation is necessary.
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42.79.Pw Imaging detectors and sensors
42.50.Ar Photon statistics and coherence theory
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Enhanced photoluminescence from embedded PbSe colloidal quantum dots in silicon-based random photonic crystal microcavities

Jun Yang, Junseok Heo, Ting Zhu, Jian Xu, Juraj Topolancik, Frank Vollmer, Rob Ilic, and Pallab Bhattacharya

Appl. Phys. Lett. 92, 261110 (2008); http://dx.doi.org/10.1063/1.2954007 (3 pages) | Cited 8 times

Online Publication Date: 2 July 2008

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The experimental observation of enhanced photoluminescence from high-Q silicon-based random photonic crystal microcavities embedded with PbSe colloidal quantum dots is being reported. The emission is optically excited at room temperature by a continuous-wave Ti-sapphire laser and exhibits randomly distributed localized modes with a minimum spectral linewidth of 4 nm at 1.5 μm wavelength.
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78.55.Hx Other solid inorganic materials
78.67.Hc Quantum dots
42.70.Qs Photonic bandgap materials
82.70.Dd Colloids
42.82.-m Integrated optics

Photonic nanojet-induced modes in chains of size-disordered microspheres with an attenuation of only 0.08 dB per sphere

Seungmoo Yang and Vasily N. Astratov

Appl. Phys. Lett. 92, 261111 (2008); http://dx.doi.org/10.1063/1.2954013 (3 pages) | Cited 13 times

Online Publication Date: 2 July 2008

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By using spatially resolved spectroscopy the authors demonstrate that the periodical focusing of light in straight chains of touching 5 μm polystyrene microspheres is characterized with the periodicity of photonic nanojets corresponding to the size of two spheres. In transmission spectra of long (>20 spheres) chains they observe Fabry–Pérot fringes with propagation losses of only 0.08 dB per sphere in the maxima of transmission peaks. Due to mechanical robustness, tight focusing of the beam, high optical throughput, and broad spectral transmission properties such chains can be used in a variety of biomedical applications as optical microprobes with subwavelength spatial resolution.
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87.64.M- Optical microscopy
87.50.wf Biophysical mechanisms of interaction
42.79.-e Optical elements, devices, and systems

Photonic crystal cavity based gas sensor

T. Sünner, T. Stichel, S.-H. Kwon, T. W. Schlereth, S. Höfling, M. Kamp, and A. Forchel

Appl. Phys. Lett. 92, 261112 (2008); http://dx.doi.org/10.1063/1.2955523 (3 pages) | Cited 18 times

Online Publication Date: 2 July 2008

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We have studied the response of a photonic crystal cavity to changes of the ambient refractive index. Transmission measurements of the cavity under different gaseous environments and pressures showed a linear dependence of the resonance wavelength on the refractive index of the ambient gas. A change of the refractive index by 10−4 leads to a shift of the resonance by 8 pm, which is readily detectable due to the high quality factor of the cavity. The observed wavelength shifts agree well with finite-difference time domain simulations of the cavity.
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82.80.-d Chemical analysis and related physical methods of analysis

Quantum dot nanocolumn photodetectors for light detection in the infrared

M. Böberl, M. V. Kovalenko, G. Pillwein, G. Brunthaler, and W. Heiss

Appl. Phys. Lett. 92, 261113 (2008); http://dx.doi.org/10.1063/1.2949084 (3 pages) | Cited 5 times

Online Publication Date: 2 July 2008

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Colloidal quantum dots absorbing in the infrared are filled into nanoporous alumina membranes to form narrow columns with aspect ratios of 300:1. The columns define the charge carrier path vertical through the ordered pore structure of the membrane. Electrical transport and photocurrent of various quantum dot column photodetectors based on two different nanomaterials, namely, HgTe and PbS quantum dots, with different quantum dot sizes are investigated. Photocurrents up to long wavelengths of 3 μm are demonstrated.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
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Effect of gas pressure on ion flux in 2 MHz capacitive discharge

I. V. Schweigert

Appl. Phys. Lett. 92, 261501 (2008); http://dx.doi.org/10.1063/1.2955526 (3 pages) | Cited 2 times

Online Publication Date: 2 July 2008

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We have studied the ion energy and angular distribution functions in a 2 MHz capacitive discharge using combined particle in cell Monte Carlo collision simulations. We found that secondary electrons produced by ion bombardment from the electrodes make important contribution to the ionization at higher gas pressure. Calculations showed that the ion flux on the electrode is very sensitive to the plasma parameters. However, the ion angular distribution function weakly responds to a change of the gas pressure.
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52.77.Dq Plasma-based ion implantation and deposition
52.80.Pi High-frequency and RF discharges
52.65.Pp Monte Carlo methods
52.65.Rr Particle-in-cell method

Label free biosensor incorporating a replica-molded, vertically emitting distributed feedback laser

M. Lu, S. S. Choi, C. J. Wagner, J. G. Eden, and B. T. Cunningham

Appl. Phys. Lett. 92, 261502 (2008); http://dx.doi.org/10.1063/1.2913007 (3 pages) | Cited 12 times

Online Publication Date: 3 July 2008

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A label free biosensor based upon a vertically emitting distributed feedback (DFB) laser has been demonstrated. The DFB laser comprises a replica-molded, one-dimensional dielectric grating coated with laser dye-doped polymer as the gain medium. Adsorption of biomolecules onto the laser surface alters the DFB laser emission wavelength, thereby permitting the kinetic adsorption of a protein polymer monolayer or the specific binding of small molecules to be quantified. A bulk sensitivity of 16.6 nm per refractive index unit and the detection of a monolayer of the protein polymer poly(Lys, Phe) have been observed with this biosensor. The sensor represents a departure from conventional passive resonant optical sensors from the standpoint that the device actively generates its own narrowband high intensity output without stringent requirements on the coupling alignments, resulting in a simple, robust illumination and detection configuration.
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87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)
87.14.E- Proteins
42.55.Px Semiconductor lasers; laser diodes
42.79.Pw Imaging detectors and sensors
42.70.Jk Polymers and organics
87.15.N- Properties of solutions of macromolecules
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Shear-strain-induced low symmetry phase and domain ordering in epitaxial La0.7Sr0.3MnO3 thin films

S. W. Jin, G. Y. Gao, Z. Huang, Z. Z. Yin, X. Zheng, and Wenbin Wu

Appl. Phys. Lett. 92, 261901 (2008); http://dx.doi.org/10.1063/1.2952764 (3 pages) | Cited 2 times

Online Publication Date: 30 June 2008

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The domain structure in epitaxial La0.7Sr0.3MnO3 films grown on (LaAlO3)0.3(Sr2AlTaO6)0.7(001) substrates has been investigated by x-ray reciprocal space maps on (003), (103), (math03), (013), and (0math3) reflections in the high-resolution scattering zone containing the c* axis, and the transmission electron microscopy. We revealed that at above 20 nm, the films show clearly a low symmetry monoclinic phase, and the shear strain relaxation can induce a patterned domain structure and in-plane superlattice in the films. The domain width versus the film thickness and the shear strain effect on the Curie temperature of the films were also discussed.
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75.70.Ak Magnetic properties of monolayers and thin films
75.47.Lx Magnetic oxides
75.47.Gk Colossal magnetoresistance
75.60.Ch Domain walls and domain structure
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
68.55.-a Thin film structure and morphology

Poisson’s Ratio and Intrinsic Plasticity of Metallic Glasses

S. J. Poon, Aiwu Zhu, and G. J. Shiflet

Appl. Phys. Lett. 92, 261902 (2008); http://dx.doi.org/10.1063/1.2952827 (3 pages) | Cited 19 times

Online Publication Date: 30 June 2008

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Through a comparison of the activation barrier densities for plastic deformation and brittle fracture at the yield point, a condition for intrinsic plasticity versus brittleness of metallic glasses under shear loading is derived. The quantitative role of Poisson’s ratio ν on fracture is revealed and additional effects due to local shear modulus (G) fluctuations are pointed out. The findings account for the onset of plasticity near reported ν values, as well as the brittleness of some high-ν alloys. Structural relaxation increases G and reduces fluctuations, incurring dual adverse effects on ductility. Implications for designing ductile metallic glasses are discussed.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dj Poisson's ratio
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mj Brittleness
62.20.fk Ductility, malleability

Cylindrical-to-plane-wave conversion via embedded optical transformation

Wei Xiang Jiang, Tie Jun Cui, Hui Feng Ma, Xiao Yang Zhou, and Qiang Cheng

Appl. Phys. Lett. 92, 261903 (2008); http://dx.doi.org/10.1063/1.2953447 (3 pages) | Cited 27 times

Online Publication Date: 1 July 2008

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We investigate the conversion from cylindrical waves to plane waves in a short range through a metamaterial layer which has a circular shape in the inner outline and a square shape in the outer outline. Based on an embedded optical transformation, analytical formulas of the permittivity and permeability tensors are presented for the metamaterial layer which converts the cylindrical waves to plane waves. The designed conversion materials are validated by full-wave simulations using the finite-element method. The proposed structure can be used either as a four-beam antenna or a compact range for near-field measurement of plane waves.
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42.70.-a Optical materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Correlation between hardness and elastic moduli of the ultraincompressible transition metal diborides RuB2, OsB2, and ReB2

Hsiu-Ying Chung, Michelle B. Weinberger, Jenn-Ming Yang, Sarah H. Tolbert, and Richard B. Kaner

Appl. Phys. Lett. 92, 261904 (2008); http://dx.doi.org/10.1063/1.2946665 (3 pages) | Cited 36 times

Online Publication Date: 1 July 2008

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The ultraincompressible transition metal diborides RuB2, OsB2, and ReB2 were synthesized by arc melting the elemental metals and boron under an argon atmosphere at ambient pressure. The hardness and Young’s modulus were measured using nanoindentation with a Berkovich diamond indenter. The bulk modulus and shear modulus were derived based on an isotropic model and then plotted as a function of hardness. A strong correlation is observed between the hardness and shear modulus for these transition metal diborides.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.Qp Friction, tribology, and hardness
62.20.de Elastic moduli
62.20.M- Structural failure of materials

Anisotropic medium with parabolic dispersion

Linfang Shen, Jin-Jei Wu, and Tzong-Jer Yang

Appl. Phys. Lett. 92, 261905 (2008); http://dx.doi.org/10.1063/1.2953546 (3 pages) | Cited 1 time

Online Publication Date: 1 July 2008

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A layered metamaterial which is predicted by the effective medium theory to be an anisotropic medium with partial zero permittivities is analyzed carefully. It is shown that such a material has a dispersion relation in parabolic form, which is quite different from the known ones. This material may be viewed as a homogeneous medium but is spatially dispersive strongly. The structured medium may support either forward wave or backward wave, depending on the magnitude of the wave vector. Moreover, it is demonstrated that this medium with parabolic dispersion is especially suitable for the transmission of Gaussian beam with subwavelength width.
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42.70.-a Optical materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Anisotropic crystallographic properties, strain, and their effects on band structure of m-plane GaN on LiAlO2(100)

B. Liu, R. Zhang, Z. L. Xie, J. Y. Kong, J. Yao, Q. J. Liu, Z. Zhang, D. Y. Fu, X. Q. Xiu, P. Chen, P. Han, Y. Shi, Y. D. Zheng, S. M. Zhou, and G. Edwards

Appl. Phys. Lett. 92, 261906 (2008); http://dx.doi.org/10.1063/1.2951618 (3 pages) | Cited 9 times

Online Publication Date: 1 July 2008

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The m-plane GaN films grown on LiAlO2(100) by metal-organic chemical vapor deposition exhibit anisotropic crystallographic properties. The Williamson–Hall plots point out they are due to the different tilts and lateral correlation lengths of mosaic blocks parallel and perpendicular to GaN[0001] in the growth plane. The symmetric and asymmetric reciprocal space maps reveal the strain of m-plane GaN to be biaxial in-plane compress εxx = −0.79% and εzz = −0.14% with an out-of-plane dilatation εyy = 0.38%. This anisotropic strain further separates the energy levels of top valence band at Γ point. The energy splitting as 37 meV as well as in-plane polarization anisotropy for transitions are found by the polarized photoluminescence spectra at room temperature.
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68.55.-a Thin film structure and morphology
71.20.Nr Semiconductor compounds
68.60.Bs Mechanical and acoustical properties
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Quantitative determination of the dopant distribution in Si ultrashallow junctions by tilted sample annular dark field scanning transmission electron microscopy

A. Parisini, V. Morandi, S. Solmi, P. G. Merli, D. Giubertoni, M. Bersani, and J. A. van den Berg

Appl. Phys. Lett. 92, 261907 (2008); http://dx.doi.org/10.1063/1.2951896 (3 pages) | Cited 8 times

Online Publication Date: 1 July 2008

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In this letter, it is shown how the application of a Z-contrast scanning transmission electron microscopy technique to the study of the dopant signal in ultrashallow junctions in Si can lead, in the case of As in Si, to a quantitative determination of the dopant depth profile at subnanometer resolution. The quantitative results thus obtained demonstrate that As accumulates on the Si side of the SiO2/Si interface with a negligible loss of dopant into the oxide. Modeling of the effect indicates that segregation occurring during the recrystallization of the implanted layer is the dominant cause of this dopant pileup.
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61.72.sh Impurity distribution
61.72.uf Ge and Si
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
68.35.Dv Composition, segregation; defects and impurities
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Size dependence of twin formation energy in cubic SiC at the nanoscale

Yongfeng Zhang, Hyun Woo Shim, and Hanchen Huang

Appl. Phys. Lett. 92, 261908 (2008); http://dx.doi.org/10.1063/1.2953976 (3 pages) | Cited 3 times

Online Publication Date: 1 July 2008

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This letter reports the size dependence of twin formation energy in cubic SiC at the nanoscale, while the bulk value is nearly zero. Atomic edges surround the twin boundary of SiC nanowires, and they are responsible for the finite twin formation energy and its size dependence. Based on classical molecular statics calculations, the average formation energy of convex and concave edges is 73 meV/nm. Effectively, the twin formation energy is inversely proportional to the length of edges surrounding the twin boundary. Results of this letter make it possible to understand large separations of twin boundaries in SiC nanowires.
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68.65.La Quantum wires (patterned in quantum wells)
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
61.72.Mm Grain and twin boundaries

Cool white III-nitride light emitting diodes based on phosphor-free indium-rich InGaN nanostructures

C. B. Soh, W. Liu, J. H. Teng, S. Y. Chow, S. S. Ang, and S. J. Chua

Appl. Phys. Lett. 92, 261909 (2008); http://dx.doi.org/10.1063/1.2952459 (3 pages) | Cited 17 times

Online Publication Date: 1 July 2008

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Phosphor-free cool white emitting light emitting diodes (LEDs) have been fabricated using a dual stacked InGaN/GaN multiple quantum wells (MQWs) comprising of a lower set of MQWs emitting yellow and an upper set of MQWs emitting blue. The lower set of MQWs incorporates indium-rich InGaN connected-dot nanostructures with a height of ∼ 1.0 nm in the well. The well is first grown with an InGaN layer serving as the wetting layer, then treated with trimethylindium (TMIn) to initiate nanostructure growth of another InGaN layer to complete the well layer. This gives a broadened yellow emission peak. With the combination of emission from the upper blue emitting InGaN/GaN MQWs subsequently grown, cool white light emission is achieved. The In-rich nanostructures formed during TMIn treatment enhance indium incorporation in InGaN well and also act as effective radiative recombination sites for carriers at the lower set of MQWs.
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85.60.Jb Light-emitting devices
73.21.Fg Quantum wells
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.60.Fi Electroluminescence

Optical detection of deoxyribonucleic acid hybridization with InGaN/GaN multiple quantum wells

H. Y. Shih, T. T. Chen, C. H. Wang, K. Y. Chen, and Y. F. Chen

Appl. Phys. Lett. 92, 261910 (2008); http://dx.doi.org/10.1063/1.2948907 (3 pages) | Cited 1 time

Online Publication Date: 1 July 2008

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Based on the high surface sensitivity of piezoelectric polarization of strained nitride semiconductors, surface functionalized nitride light emitting devices (LEDs) provide an excellent opportunity for the development of biological sensors. To demonstrate our working principle, a probe chip based on In0.22Ga0.78N/GaN multiple quantum wells has been constructed and exposed to target DNA solutions, matched and/or mismatched, with different concentrations. The pronounced changes of photoluminescence spectra as well as Raman scattering A1(LO) spectra in matched target DNA clearly illustrate the feasibility of our proposed mechanism. The results shown here open up a new possibility for the application of nitride LEDs in biosensor engineering.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Gz Photodetectors (including infrared and CCD detectors)
78.67.Hc Quantum dots
87.14.gk DNA
87.85.Rs Nanotechnologies-applications
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  1. Focal length modulation based on a metallic slit surrounded with grooves in curved depths
  2. Initial stages of chain formation in a single layer of (In,Ga)As quantum dots grown on GaAs (100)
  3. Magnetoacoustic tomographic imaging of electrical impedance with magnetic induction
  4. High density single molecule surface patterning with colloidal epitaxy
  5. Generation of nanoparticle colloids by picosecond and femtosecond laser ablations in liquid flow
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