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2 Mar 2009

Volume 94, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 092101 (2009); http://dx.doi.org/10.1063/1.3089231 (3 pages)

Serguei I. Maximenko, Jaime A. Freitas, Jr., Paul B. Klein, Amitesh Shrivastava, and Tangali S. Sudarshan
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Role of interface roughness in the transport and lasing characteristics of quantum-cascade lasers

Jacob B. Khurgin, Yamac Dikmelik, Peter Q. Liu, Anthony J. Hoffman, Matthew D. Escarra, Kale J. Franz, and Claire F. Gmachl

Appl. Phys. Lett. 94, 091101 (2009); http://dx.doi.org/10.1063/1.3093819 (3 pages) | Cited 21 times

Online Publication Date: 3 March 2009

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A density-matrix based theory of transport and lasing in quantum-cascade lasers reveals that large disparity between luminescent linewidth and broadening of the tunneling transition changes the design guidelines to favor strong coupling between injector and upper laser level. This conclusion is supported by the experimental evidence.
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42.55.Px Semiconductor lasers; laser diodes

Ultrahigh spontaneous emission extraction efficiency induced by evanescent wave coupling

X.-L. Wang, S. Furue, M. Ogura, V. Voliotis, M. Ravaro, A. Enderlin, and R. Grousson

Appl. Phys. Lett. 94, 091102 (2009); http://dx.doi.org/10.1063/1.3086887 (3 pages) | Cited 4 times

Online Publication Date: 3 March 2009

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A spontaneous emission extraction efficiency greater than 50% is observed in a GaAs/AlGaAs quantum well structure grown on the subwavelength-sized ridge top facet of a V-grooved substrate by means of photoluminescence study. This is an extraction efficiency about 20 times higher than that of a similar structure grown on a flat substrate. It is demonstrated both experimentally and theoretically that the high extraction efficiency is the result of the efficient conversion of evanescent waves into propagating waves in air through constructive coupling of evanescent waves generated on the two sidewall facets of the V-grooved substrate by total internal reflection.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors

Self-mixing interferometry in vertical-cavity surface-emitting lasers for nanomechanical cantilever sensing

David Larsson, Anders Greve, Jørn M. Hvam, Anja Boisen, and Kresten Yvind

Appl. Phys. Lett. 94, 091103 (2009); http://dx.doi.org/10.1063/1.3086893 (3 pages) | Cited 5 times

Online Publication Date: 3 March 2009

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We have experimentally investigated self-mixing interference produced by the feedback of light from a polymer micrometer-sized cantilever into a vertical-cavity surface-emitting laser for sensing applications. In particular we have investigated how the visibility of the optical output power and the junction voltage depends on the laser injection current and the distance to the cantilever. The highest power visibility obtained from cantilevers without reflective coatings was ∼ 60%, resulting in a very high sensitivity of 45 mV/nm with a noise floor below 1.2 mV. Different detection schemes are discussed.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.60.Mi Dynamical laser instabilities; noisy laser behavior
42.70.Jk Polymers and organics
42.79.Wc Optical coatings
07.60.Ly Interferometers
42.55.Px Semiconductor lasers; laser diodes
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Intervalley separation in the conduction band of InGaAs measured by terahertz excitation spectroscopy

G. Molis, A. Krotkus, and V. Vaičaitis

Appl. Phys. Lett. 94, 091104 (2009); http://dx.doi.org/10.1063/1.3092483 (3 pages) | Cited 6 times

Online Publication Date: 3 March 2009

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Spectral dependencies of terahertz radiation from the femtosecond laser-illuminated surfaces of GaxIn1−xAs (x = 1, 0.8, and 0.47) have been investigated experimentally at high optical fluencies and laser wavelengths ranging from 600 to 800 nm. The terahertz pulse amplitude increased with the increasing laser photon energy due to larger excess energies of photoexcited electrons and more efficient spatial separation of electrons and holes at the illuminated surface. This increase was stopped with the onset of electron transitions to subsidiary conduction band valleys. Analysis of these experiments was used for evaluating the energy positions of the X and L conduction band valleys in GaxIn1−xAs alloys as a function of their composition.
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71.20.Nr Semiconductor compounds
78.70.Gq Microwave and radio-frequency interactions
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena

Enhancement of carrier focusing GaN based vertical cavity surface emitting lasers and polariton lasers

E. Petrolati and A. Di Carlo

Appl. Phys. Lett. 94, 091105 (2009); http://dx.doi.org/10.1063/1.3080220 (3 pages)

Online Publication Date: 3 March 2009

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We have studied the electron and hole focusing problem observed in gallium nitride (GaN) based microcavity lasers. We outlined the relation between the focusing efficiency and the unbalance between electron and hole mobilities. A new device structure is proposed where the n-layer is on the top of the p-layer, which overcomes the focusing limitation of conventional GaN based vertical cavity surface emitting lasers and polariton lasers.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.55.Sa Microcavity and microdisk lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Voltage-driven in-plane steering of nematicons

Armando Piccardi, Marco Peccianti, Gaetano Assanto, Andriy Dyadyusha, and Malgosia Kaczmarek

Appl. Phys. Lett. 94, 091106 (2009); http://dx.doi.org/10.1063/1.3093529 (3 pages) | Cited 5 times

Online Publication Date: 3 March 2009

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Using an external voltage and interdigitated electrodes in a liquid crystalline cell, we demonstrate tunable steering of light beams and spatial solitons without the detrimental walk-off out of the plane of propagation. The results agree well with a simple model describing birefringence and reorientation in uniaxial nematic liquid crystals.
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42.70.Df Liquid crystals
42.65.Tg Optical solitons; nonlinear guided waves

Experimental demonstration of phase resonances in metallic compound gratings with subwavelength slits in the millimeter wave regime

Miguel Navarro-Cía, Diana C. Skigin, Miguel Beruete, and Mario Sorolla

Appl. Phys. Lett. 94, 091107 (2009); http://dx.doi.org/10.1063/1.3086892 (3 pages) | Cited 16 times

Online Publication Date: 4 March 2009

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We provide experimental evidence of phase resonances in metallic periodic structures in which each period comprises several subwavelength slits of the same width. We have analyzed and measured the response of these structures in the millimeter wave regime and show that phase resonances are characterized by a remarkable minimum in the transmission response, as predicted by numerical calculations. We compare experimental with numerical results, obtaining a very good agreement between them. This experimental confirmation encourages research in compound structures and their multiple potential applications, such as frequency selective surfaces.
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42.79.Dj Gratings
84.40.-x Radiowave and microwave (including millimeter wave) technology
84.40.Ba Antennas: theory, components and accessories

All-optical polarization switch in a quadratic nonlinear photonic quasicrystal

Ayelet Ganany-Padowicz, Irit Juwiler, Ofer Gayer, Alon Bahabad, and Ady Arie

Appl. Phys. Lett. 94, 091108 (2009); http://dx.doi.org/10.1063/1.3090488 (3 pages) | Cited 8 times

Online Publication Date: 4 March 2009

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We present an all-optical intensity-dependent polarization switch based on cascaded three-wave-mixing interactions in a quasiperiodic quadratic nonlinear photonic crystal. The polarization switching is realized by simultaneous quasiphase matching of upconversion and downconversion processes in LiNbO3 and achieves three orders of magnitude better efficiency than previous devices based on cascaded cubic nonlinearities. The switch allows extending mode-cleaning and mode-locking techniques to considerably lower input power. We demonstrate experimentally that a single linearly polarized 1550 nm fundamental wave generates a new fundamental wave of orthogonal polarization.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Qs Photonic bandgap materials

Wavelength selection for quantum cascade lasers by cavity length

Christina Young, Richard Cendejas, Scott S. Howard, Wendy Sanchez-Vaynshteyn, Anthony J. Hoffman, Kale J. Franz, Yu Yao, Boris Mizaikoff, Xiaojun Wang, Jenyu Fan, and Claire F. Gmachl

Appl. Phys. Lett. 94, 091109 (2009); http://dx.doi.org/10.1063/1.3093422 (3 pages) | Cited 2 times

Online Publication Date: 4 March 2009

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A systematic shift in spectral emission wavenumbers in quantum cascade lasers (QCLs) is observed over a variation in cavity lengths from 0.5 to 3 mm resulting in a gain peak shift ranging from 2404 to 2286 cm−1. Thereby, a wavelength selection range of 118 cm−1 is provided, which is sufficiently broad for selecting the laser emission across the entire CO2 absorption band at 2326 cm−1 (4.3 μm). In contrast to current QCL wavelength selection techniques, modifying the cavity length is a straightforward postprocessing procedure. Experimental evidence confirms that this frequency shift is due to a change in threshold voltage and applied electric field as a function of cavity length which is in agreement with the theory.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Nematicons in chiral nematic liquid crystals

Urszula A. Laudyn, Michal Kwasny, and Miroslaw A. Karpierz

Appl. Phys. Lett. 94, 091110 (2009); http://dx.doi.org/10.1063/1.3093498 (3 pages) | Cited 6 times

Online Publication Date: 4 March 2009

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We report on the experimental studies of the existence of spatial solitons called nematicons in chiral nematic liquid crystal cells. The low absorption allows us to observe soliton propagation at a distance of over a few millimeters in range. The results of our experiment also show that it is possible to create independent nematicons in different layers formed by a helical structure of the liquid crystals.
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42.70.Df Liquid crystals
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
42.65.Tg Optical solitons; nonlinear guided waves
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Midinfrared GaInSb/AlGaInSb quantum well laser diodes operating above 200 K

G. R. Nash, S. J. B. Przeslak, S. J. Smith, G. de Valicourt, A. D. Andreev, P. J. Carrington, M. Yin, A. Krier, S. D. Coomber, L. Buckle, M. T. Emeny, and T. Ashley

Appl. Phys. Lett. 94, 091111 (2009); http://dx.doi.org/10.1063/1.3094879 (3 pages) | Cited 5 times

Online Publication Date: 5 March 2009

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Electroluminescence from GaInSb/AlGaInSb type I quantum well diode lasers, grown on GaAs, has been investigated as a function of strain in the quantum wells. Lasing was observed, in pulsed operation, up to temperatures of 161, 208, 219, and 202 K for structures containing 0.55%, 0.62%, 0.78%, and 1.1% strain, respectively, with lasing occurring at ∼ 3.3 μm at 200 K for the 1.1% structure.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
78.60.Fi Electroluminescence

Positron generation through laser Compton scattering gamma ray

D. Li, K. Imasaki, S. Miyamoto, K. Horikawa, S. Amano, and T. Mochizuki

Appl. Phys. Lett. 94, 091112 (2009); http://dx.doi.org/10.1063/1.3094882 (3 pages) | Cited 1 time

Online Publication Date: 5 March 2009

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The positron source is developed through a high brightness gamma-ray beam, which is produced from a laser light scattering off a high-energy electron beam circulating in a storage ring. A thin Pb target is irradiated by the gamma ray to generate positrons via pair creation. By using imaging plate, we measured the generation rate and worked out the energy spectrum of generated positrons and electrons. The experimental results are close to that from Monte Carlo simulation. About 3618 positrons/s at several MeV can be generated by the present experimental setup, and this value can be improved by optimizing experimental conditions.
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29.25.Bx Electron sources
41.75.Fr Electron and positron beams
29.20.db Storage rings and colliders
61.80.Ed γ-ray effects

Tailoring the electronic properties of GaxIn1−xP beyond simply varying alloy composition

Yong Zhang, C.-S. Jiang, D. J. Friedman, J. F. Geisz, and A. Mascarenhas

Appl. Phys. Lett. 94, 091113 (2009); http://dx.doi.org/10.1063/1.3094918 (3 pages) | Cited 2 times

Online Publication Date: 5 March 2009

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Spontaneous ordering in GaxIn1−xP provides the possibility of tuning electronic structure and improving transport properties. A quasiperiodic twinning structure of two ordered variants offers additional flexibilities in designing the material properties. The superstructure is shown to have distinctively different electronic and electrical properties from the single-variant ordered structure, as revealed in polarized elecroreflectance and cross-sectional scanning Kelvin probe force microscopy measurements. The entire potentially accessible range of the “direct” bandgap is defined for this alloy system, and thus the optimal bandgap for any intended application can be achieved through the interplay of the effects of alloying, ordering, and domain structure engineering.
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71.20.Nr Semiconductor compounds
78.20.Jq Electro-optical effects
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors

Broadside excitation of surface plasmon waveguides on Cytop

Richard Daviau, Ewa Lisicka-Skrzek, R. Niall Tait, and Pierre Berini

Appl. Phys. Lett. 94, 091114 (2009); http://dx.doi.org/10.1063/1.3093500 (3 pages) | Cited 10 times

Online Publication Date: 5 March 2009

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Long-range surface plasmon waveguides consisting of a Au stripe on Cytop, covered with an index-matched aqueous solution, are described and characterized. The waveguides are tested using a broadside coupling technique, whereby tapered single-mode fibers are positioned in direct contact with the stripe such that the slow mode of the fiber couples through partial modal overlap to the long-range surface plasmon. Attenuation measurements obtained at λ0 = 1310 nm agree well with theory, thus validating the waveguide fabrication and experimental techniques. The waveguides are useful for (bio)chemical sensing and the broadside coupling technique is useful for on-wafer optical probing.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.82.Et Waveguides, couplers, and arrays

All-inorganic light emitting device based on ZnO nanoparticles

E. Neshataeva, T. Kümmell, G. Bacher, and A. Ebbers

Appl. Phys. Lett. 94, 091115 (2009); http://dx.doi.org/10.1063/1.3093675 (3 pages) | Cited 7 times

Online Publication Date: 5 March 2009

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We report on room-temperature electroluminescence from an all-inorganic light emitting device based on spin-coated ZnO nanoparticles. A tight submicron thick layer was fabricated on a fluorine doped tin oxide glass as a substrate using commercially available ZnO nanoparticles from the gas phase. After the evaporation of the top Al electrode, a diodelike I-V characteristic was obtained. An emission peak at around 390 nm and a broad defect-related electroluminescence in the visible range were observed at voltages below 10 V and ambient air conditions.
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85.60.Jb Light-emitting devices
85.35.-p Nanoelectronic devices
81.16.-c Methods of micro- and nanofabrication and processing

Periodically poled silicon

Nick K. Hon, Kevin K. Tsia, Daniel R. Solli, and Bahram Jalali

Appl. Phys. Lett. 94, 091116 (2009); http://dx.doi.org/10.1063/1.3094750 (3 pages) | Cited 11 times

Online Publication Date: 6 March 2009

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We propose a new class of photonic devices based on periodic stress fields in silicon that enable second-order nonlinearity as well as quasi-phase matching. Periodically poled silicon (PePSi) adds the periodic poling capability to silicon photonics and allows the excellent crystal quality and advanced manufacturing capabilities of silicon to be harnessed for devices based on second-order nonlinear effects. As an example of the utility of the PePSi technology, we present simulations showing that midwave infrared radiation can be efficiently generated through difference frequency generation from near-infrared with a conversion efficiency of 50%.
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42.70.Qs Photonic bandgap materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Hybrid waveguides for optically pumped amplifiers

S. Saini, C.-Y. Hong, S. Bernardis, N. Pfaff, L. C. Kimerling, and J. Michel

Appl. Phys. Lett. 94, 091117 (2009); http://dx.doi.org/10.1063/1.3094752 (3 pages) | Cited 2 times

Online Publication Date: 6 March 2009

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A hybrid waveguide based on simultaneous propagation of photonic crystal (PC) and total internal reflection confined optical modes is introduced for a scheme to uniformly pump waveguide optical amplifiers (WOAs). Planar one-dimensional PC structures were deposited by plasma enhanced chemical vapor deposition and characterized by reflectivity as a function of angle, confirming the existence of PC defect states. Two design trade-offs, angular acceptance and critical coupling, are modeled to demonstrate optimization of optically pumped gain within the PC defect state. The advantage of uniform pumping on the WOA gain profile is briefly discussed.
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42.82.-m Integrated optics
42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials

High-Q terahertz Bragg resonances within a metal parallel plate waveguide

S. Sree Harsha, N. Laman, and D. Grischkowsky

Appl. Phys. Lett. 94, 091118 (2009); http://dx.doi.org/10.1063/1.3094919 (3 pages) | Cited 19 times

Online Publication Date: 6 March 2009

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One-dimensional (1D) Bragg waveguides are demonstrated at terahertz (THz) frequencies. Lithographically made 1D symmetric and asymmetric dielectric gratings on metallized high conductivity Si chips are incorporated within metal parallel plate waveguides to form Bragg waveguides. These waveguides have high throughput and have Bragg resonances with linewidths approaching 6 GHz and Q as high as 430. These high-Q resonant Bragg waveguides are excellent structures for applications in THz sensing.
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42.82.Et Waveguides, couplers, and arrays
84.40.Az Waveguides, transmission lines, striplines
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
42.79.Dj Gratings
85.60.-q Optoelectronic devices
42.82.Cr Fabrication techniques; lithography, pattern transfer

Two-dimensional electro-optic sampling of terahertz radiation using high-speed complementary metal-oxide semiconductor camera combined with arrayed polarizer

Hideaki Kitahara, Masahiko Tani, and Masanori Hangyo

Appl. Phys. Lett. 94, 091119 (2009); http://dx.doi.org/10.1063/1.3095668 (3 pages) | Cited 4 times

Online Publication Date: 6 March 2009

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We developed a terahertz imaging system based on two-dimensional electro-optic (EO) sampling using a high speed complementary metal-oxide semiconductor (CMOS) camera and an arrayed polarizer matched to the camera. By operating the CMOS camera in a normalized differential mode on a single-shot basis, two-dimensional EO sampling is demonstrated.
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07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
42.79.Pw Imaging detectors and sensors
42.79.Ci Filters, zone plates, and polarizers

Doppler frequency up conversion of electromagnetic waves in a slotline on an optically excited silicon substrate

Jongsuck Bae, Yuan Jun Xian, Sho Yamada, and Ryo Ishikawa

Appl. Phys. Lett. 94, 091120 (2009); http://dx.doi.org/10.1063/1.3095846 (3 pages)

Online Publication Date: 6 March 2009

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The Doppler frequency up conversion of microwaves in a slotline on an optically excited silicon substrate was experimentally observed. An array of 24 optical fibers with different lengths was used to effectively tilt the wave front of a 532 nm neodymium-doped yttrium aluminum garnet laser beam with a pulse duration of 33 ps. The tilted laser beam produced electron-hole surface plasma whose boundary moved at a relativistic velocity of about c/3.4 (c is the speed of light) along the slotline. The experiments showed that microwaves reflected at the moving boundary of the plasma in the slotline are converted to millimeter waves with a frequency up conversion ratio of 3.82.
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84.40.Az Waveguides, transmission lines, striplines
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.27.Ny Relativistic plasmas
52.40.Hf Plasma-material interactions; boundary layer effects
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A lighting mechanism for flat electron emission lamp

Jung-Yu Li, Shih-Pu Chen, Chia-Hung Li, Yi-Ping Lin, Yen-I Chou, Ming-Chung Liu, Po-Hung Wang, Hui-Kai Zeng, Tai-Chiung Hsieh, and Jenh-Yih Juang

Appl. Phys. Lett. 94, 091501 (2009); http://dx.doi.org/10.1063/1.3093802 (3 pages) | Cited 2 times

Online Publication Date: 4 March 2009

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We propose a lighting mechanism for generating uniform planar light. The device integrates electron beams induced by gas discharge with cathodoluminescence at the anode, where the spectra of the emitted light depend entirely on the phosphor materials coated on the anode. Consequently, ultraviolet is not required and the usage of mercury can be avoided. In addition, the features of double-side lighting, transparency, and gray-scale images indicate that the flat electron emission lamp might become potential candidate for the next generation green lighting source.
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42.72.-g Optical sources and standards
78.60.Hk Cathodoluminescence, ionoluminescence
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

A simple dielectric barrier discharge device for generating slot homogeneous plasma in atmospheric pressure air

Lifang Dong, Yanzhao Zhang, Weiyuan Liu, Li Yang, and Junying Chen

Appl. Phys. Lett. 94, 091502 (2009); http://dx.doi.org/10.1063/1.3095921 (3 pages) | Cited 4 times

Online Publication Date: 6 March 2009

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We report a simple dielectric barrier discharge device for generating slot homogeneous plasma in atmospheric pressure air. It consists of two parallel water electrodes with a distance adjusting micrometer. With increasing the applied voltage, the discharge becomes homogeneous. The electron temperature, vibrational temperature (TV) of N2, and rotational temperature (TR) of N2+ are estimated by optical emission spectroscopy. Both TV and TR remain unchanged along the slot in the homogeneous discharge regime. The trend of the TV with respect to the applied voltage is opposite from that of TR, while the electron temperature keeps constant with the increasing applied voltage.
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52.50.-b Plasma production and heating
52.80.-s Electric discharges
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.75.-d Plasma devices
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Surface adsorption phase diagram of O/Ni(110) system: An ab initio atomistic thermodynamics investigation

Wei-Bing Zhang and Bi-Yu Tang

Appl. Phys. Lett. 94, 091901 (2009); http://dx.doi.org/10.1063/1.3088860 (3 pages) | Cited 1 time

Online Publication Date: 3 March 2009

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Based on ab initio atomistic thermodynamics model, the surface adsorption diagram of O/Ni(110) system over a wide range of temperature and pressure conditions has been determined. Different surface phases including oxygen adsorption on reconstructed and unreconstructed substrates are considered. Clean nickel surface, p(2×1)-O and p(3×1)f-O, and bulk oxide phase are found to be the most stable phases under different oxygen chemical potential regions. Our calculations suggest that the unreconstructed (n×1)(n = 2,3)-O overlayer and p(3×1)i-O phases are just metastable at the equilibrium condition. These results could effectively solve the debate in different experiments and give a consistent description for the reproducibility of overlayer and p(3×1)i-O reconstructed phases.
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68.43.Mn Adsorption kinetics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.35.bd Metals and alloys
68.43.Bc Ab initio calculations of adsorbate structure and reactions
68.35.Md Surface thermodynamics, surface energies
81.30.Bx Phase diagrams of metals, alloys, and oxides

Sr3Al2O5Cl2:Ce3+,Eu2+: A potential tunable yellow-to-white-emitting phosphor for ultraviolet light emitting diodes

Yanhua Song, Guang Jia, Mei Yang, Yeju Huang, Hongpeng You, and Hongjie Zhang

Appl. Phys. Lett. 94, 091902 (2009); http://dx.doi.org/10.1063/1.3094753 (3 pages) | Cited 29 times

Online Publication Date: 4 March 2009

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The Sr3Al2O5Cl2:Ce3+,Eu2+ phosphors were prepared by solid state reaction. The obtained phosphors exhibit a strong absorption in the UV-visible region and have two intense emission bands at 444 and 609 nm. The energy transfer from the Ce3+ to Eu2+ ions was observed, and the critical distance has been estimated to be about 24.5 Å by spectral overlap method. Furthermore, the developed phosphors can generate lights from yellow-to-white region under the excitation of UV radiation by appropriately tuning the activator content, indicating that they have potential applications as an UV-convertible phosphor for white light emitting diodes.
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85.60.Jb Light-emitting devices
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.55.Hx Other solid inorganic materials

Photoluminescence studies of impurity transitions in Mg-doped AlGaN alloys

M. L. Nakarmi, N. Nepal, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 94, 091903 (2009); http://dx.doi.org/10.1063/1.3094754 (3 pages) | Cited 5 times

Online Publication Date: 4 March 2009

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Deep ultraviolet photoluminescence spectroscopy was employed to study the impurity transitions in Mg-doped AlGaN alloys. A group of deep level impurity transitions was observed in Mg-doped AlxGa1−xN alloys, which was identified to have the same origin as the previously reported blue line at 2.8 eV in Mg-doped GaN and was assigned to the recombination of electrons bound to the nitrogen vacancy with three positive charges (VN3+) and neutral Mg acceptors. Based on the measured activation energies of the Mg acceptors in AlGaN and the observed impurity emission peaks, the VN3+ energy levels in AlxGa1−xN have been deduced for the entire alloy range. It is demonstrated that the presence of high density of VN3+ deep donors translates to the reduced p-type conductivity in AlGaN alloys due to their ability for capturing free holes.
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78.55.Cr III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.jd Vacancies
72.80.Ey III-V and II-VI semiconductors
78.40.Fy Semiconductors
71.55.Eq III-V semiconductors
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