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1 Oct 2007

Volume 91, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 143101 (2007); http://dx.doi.org/10.1063/1.2789812 (3 pages)

Hyun S. Kim, Hua Qin, and Robert H. Blick
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Auger recombination in InGaN measured by photoluminescence

Y. C. Shen, G. O. Mueller, S. Watanabe, N. F. Gardner, A. Munkholm, and M. R. Krames

Appl. Phys. Lett. 91, 141101 (2007); http://dx.doi.org/10.1063/1.2785135 (3 pages) | Cited 247 times

Online Publication Date: 1 October 2007

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The Auger recombination coefficient in quasi-bulk InxGa1−xN (x ∼ 9%–15%) layers grown on GaN (0001) is measured by a photoluminescence technique. The samples vary in InN composition, thickness, and threading dislocation density. Throughout this sample set, the measured Auger coefficient ranges from 1.4×10−30 to 2.0×10−30 cm6 s−1. The authors argue that an Auger coefficient of this magnitude, combined with the high carrier densities reached in blue and green InGaN/GaN (0001) quantum well light-emitting diodes (LEDs), is the reason why the maximum external quantum efficiency in these devices is observed at very low current densities. Thus, Auger recombination is the primary nonradiative path for carriers at typical LED operating currents and is the reason behind the drop in efficiency with increasing current even under room-temperature (short-pulsed, low-duty-factor) injection conditions.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Jb Light-emitting devices

Room-temperature lasing at 1.82 μm of GaInSb/AlGaSb quantum wells grown on GaAs substrates using an interfacial misfit array

J. Tatebayashi, A. Jallipalli, M. N. Kutty, S. H. Huang, G. Balakrishnan, L. R. Dawson, and D. L. Huffaker

Appl. Phys. Lett. 91, 141102 (2007); http://dx.doi.org/10.1063/1.2793186 (3 pages) | Cited 12 times

Online Publication Date: 1 October 2007

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The authors report the device characteristics of GaInSb/AlGaSb quantum well (QW) lasers monolithically grown on GaAs substrates. The 7.8% lattice mismatch between GaAs substrates and GaSb buffer layers can be completely accommodated by using an interfacial misfit (IMF) array. Room-temperature lasing operation is obtained from a 1.25-mm-long device containing six-layer Ga0.9In0.1Sb/Al0.35Ga0.65Sb QWs at 1.816 μm with a threshold current density of 1.265 kA/cm2. The observed characteristic temperature and temperature coefficient are 110 K and 9.7 Å/K, respectively. This IMF technique will enable a wide range of lasing wavelengths from near-infrared to midwavelength-infrared regimes on a GaAs platform.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
78.67.De Quantum wells

Application of nanoparticle-induced vertical alignment in hybrid-aligned nematic liquid crystal cell

Chia-Wei Kuo, Shie-Chang Jeng, Hsing-Lung Wang, and Chi-Chang Liao

Appl. Phys. Lett. 91, 141103 (2007); http://dx.doi.org/10.1063/1.2794007 (3 pages) | Cited 18 times

Online Publication Date: 1 October 2007

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The spontaneous vertical alignment of the mixtures consisting of nematic liquid crystals (LCs) and nanoparticles and its application to hybrid-aligned nematic (HAN) modes were investigated. The LC directors were aligned perpendicular to the nontreated indium-tin-oxide surface by adding the nanoparticles. Therefore, we fabricated a nanoparticle-filled HAN LC cell without using the vertical alignment layer. The electro-optical properties of nanoparticle-filled HAN cells are very similar to those of conventional HAN cells containing vertical alignment layers. The method of nanoparticle-induced vertical alignment is suitable for fabricating a flexible display due to the reduction of high temperature process of alignment layers.
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61.30.-v Liquid crystals
64.70.M- Transitions in liquid crystals
78.20.Jq Electro-optical effects

Intersubband absorption in AlN/GaN/AlGaN coupled quantum wells

Kristina Driscoll, Anirban Bhattacharyya, Theodore D. Moustakas, Roberto Paiella, Lin Zhou, and David J. Smith

Appl. Phys. Lett. 91, 141104 (2007); http://dx.doi.org/10.1063/1.2794013 (3 pages) | Cited 14 times

Online Publication Date: 1 October 2007

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AlN/GaN/AlGaN coupled quantum wells grown by molecular beam epitaxy have been developed and characterized via intersubband absorption spectroscopy. In these structures, an AlGaN layer of sufficiently low Al content is used to achieve strong interwell coupling without the need for ultrathin inner barriers. At the same time, AlN is used in the outer barriers to provide the large quantum confinement required for near-infrared intersubband transitions. The composition of the inner barriers also provides a continuously tunable parameter to control the coupling strength. Double intersubband absorption peaks are measured in each sample, at photon energies in good agreement with theoretical expectations.
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81.07.St Quantum wells
78.67.De Quantum wells
68.65.Fg Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.30.Fs III-V and II-VI semiconductors

Experimental characterization of the frequency modulation behavior of vertical cavity surface emitting lasers

Jia Chen, Andreas Hangauer, Rainer Strzoda, and Markus-Christian Amann

Appl. Phys. Lett. 91, 141105 (2007); http://dx.doi.org/10.1063/1.2794406 (3 pages) | Cited 1 time

Online Publication Date: 1 October 2007

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The frequency response of the current-to-wavelength tuning rate (FM response) was measured for two different vertical cavity surface emitting lasers (VCSELs) up to frequencies of 1 MHz: GaAs-based VCSEL (763 nm) and InP-based VCSEL (1853 nm). Both of them show the same qualitative FM response behavior, which can be described by a square root law and therefore cannot be modeled by a first order low pass. The square root law behavior is a significant advantage for laser spectroscopy applications with VCSELs because the decrease of the current-to-wavelength tuning coefficient is less severe as in the case of the first order low pass.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking

High temperature operation of λ ≈ 3.3 μm quantum cascade lasers

J. Devenson, O. Cathabard, R. Teissier, and A. N. Baranov

Appl. Phys. Lett. 91, 141106 (2007); http://dx.doi.org/10.1063/1.2794414 (3 pages) | Cited 28 times

Online Publication Date: 1 October 2007

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We report quantum cascade lasers emitting at a wavelength near 3.3 μm up to a temperature of 400 K in pulsed mode. A fine tuning of the InAs/AlSb active region design allowed to maintain efficient electron injection and to reduce thermal backfilling at high temperatures. The threshold current density is 3 kA/cm2 at 300 K with characteristic temperature T0 of 175 K. The lasers emitted up to 1 W peak power in a single lateral mode at room temperature.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Optical coherence computed tomography

Li Li and Lihong V. Wang

Appl. Phys. Lett. 91, 141107 (2007); http://dx.doi.org/10.1063/1.2793625 (3 pages)

Online Publication Date: 2 October 2007

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A time-resolved optical tomography, optical coherence computed tomography, is proposed to bridge the gap between diffuse optical tomography and optical coherence tomography. Both ballistic and multiple-scattered photons are measured at multiple source-detection positions by low-coherence interferometry providing a temporal resolution smaller than 100 fs. A light-tissue interaction model was established using the time-resolved Monte Carlo method. The optical properties were then reconstructed by solving the inverse transient radiative transport problem under the first Born approximation. Absorbing inclusions of 100 μm diameter were imaged through a 2.6-mm-thick ( ∼ 30 scattering mean-free-paths) scattering medium.
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87.63.L- Visual imaging
02.50.Ng Distribution theory and Monte Carlo studies
87.50.W- Optical/infrared radiation effects

Two-layered metallic film induced surface plasmons for enhanced optical propulsion of microparticles

Y. Y. Tan, X.-C. Yuan, B. H. Ong, J. Bu, and Q. Y. Lin

Appl. Phys. Lett. 91, 141108 (2007); http://dx.doi.org/10.1063/1.2794409 (3 pages) | Cited 5 times

Online Publication Date: 2 October 2007

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We demonstrate the use of surface plasmons (SPs) excited on a two-layered metallic film for enhanced particle propulsion. The extended SP field is predominantly attributed to propel particles with increased speed along metal-deposited regions. Various silver-gold combinations were used to quantify for the SP field enhancement. The underlying silver yields better SP evanescent field enhancement, while the overlying gold ensures that the stability of the sensing surface is not compromised. In comparison to the conventional single gold film SP resonance configuration for particle manipulation, the two-layered metallic structure enhances the propulsive force, as verified experimentally by ∼ 2.0 times increase in particle velocities.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Bz Metals and metallic alloys

A simple technique of enhancement of efficiency in optical frequency conversion

S. Das, C. Ghosh, and S. Gangopadhyay

Appl. Phys. Lett. 91, 141109 (2007); http://dx.doi.org/10.1063/1.2794427 (3 pages) | Cited 1 time

Online Publication Date: 2 October 2007

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A simple technique for enhancement of conversion efficiency focusing by cylindrical lens of the interacting beams in three wave nonlinear interaction has been reported by generating second and third harmonics of 1064 nm radiation in a Li2B4O7 crystal and compared the generated beam energy focusing by spherical lens. An increase in conversion efficiency of about 5.2 times has been realized in focusing by cylindrical lens than that in focusing by spherical lens.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Bh Lenses, prisms and mirrors

Self-controlled signal branch by the use of a nonlinear liquid crystal cell

Mitsunori Saito, Ryosuke Takeda, Kazuhiro Yoshimura, Ryota Okamoto, and Itsunari Yamada

Appl. Phys. Lett. 91, 141110 (2007); http://dx.doi.org/10.1063/1.2783269 (3 pages) | Cited 4 times

Online Publication Date: 3 October 2007

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A nonlinear input-output characteristic was observed when neodymium doped yttrium aluminum garnet laser passed through a silicon cell containing a twisted-nematic liquid crystal. The laser beam excited free carriers in the silicon plate, which triggered electrical reorientation of the liquid crystal. Consequently, the polarization direction of the laser beam changed, and the output beam passing through a polarizer became weaker as the input power increased. This function was utilized for self-branching of an optical pulse train.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.70.Df Liquid crystals
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.20.Jq Electro-optical effects
42.79.Ci Filters, zone plates, and polarizers

Nanochannels fabricated by high-intensity femtosecond laser pulses on dielectric surfaces

Sergey I. Kudryashov, Gerard Mourou, Ajit Joglekar, Jeffrey F. Herbstman, and Alan J. Hunt

Appl. Phys. Lett. 91, 141111 (2007); http://dx.doi.org/10.1063/1.2790741 (3 pages) | Cited 10 times

Online Publication Date: 3 October 2007

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Direct scanning electron microscopy examination reveals a complex structure of narrow, micron-deep, internal nanochannels within shallow, nanoscale, external craters fabricated on glass and sapphire surfaces by single high-intensity femtosecond laser pulses, with nearly the same intensity thresholds for both features. Formation of the channels is accompanied by extensive expulsion of molten material produced via surface spallation and phase explosion mechanisms, and redeposited around the corresponding external craters. Potential mechanisms underlying fabrication of the unexpectedly deep channels in dielectrics are considered.
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81.16.Mk Laser-assisted deposition
61.82.Ms Insulators
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Holographic inscription of helical wavefronts in a liquid crystal polarization grating

Hyunhee Choi, J. H. Woo, J. W. Wu, Dong-Wook Kim, Tong-Kun Lim, and Seok Ho Song

Appl. Phys. Lett. 91, 141112 (2007); http://dx.doi.org/10.1063/1.2793173 (3 pages) | Cited 4 times

Online Publication Date: 3 October 2007

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A space-varying polarization hologram (PH) grating is fabricated in a nematic liquid crystal (LC) cell with azo-side-chain polymer alignment layers. The polarization-sensitive photoisomerization property of azo-side-chain polymer is utilized to inscribe the PH in a LC cell. Both transmission and reflection holographic configurations are adopted in fabrication. The transmission PH made by the circular orthogonal polarizations exhibits the polarization-controlled Laguerre-Gaussian beam generation, while the reflection PH made by the linear orthogonal polarizations generates a variety of Laguerre-Gaussian beam, though not polarization controlled.
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42.40.Eq Holographic optical elements; holographic gratings
42.70.Df Liquid crystals

InGaN/GaN multi-quantum-well ultraviolet photosensors by capping an unactivated Mg-doped GaN layer

P. C. Chang and C. L. Yu

Appl. Phys. Lett. 91, 141113 (2007); http://dx.doi.org/10.1063/1.2793504 (3 pages) | Cited 4 times

Online Publication Date: 3 October 2007

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InGaN/GaN multi-quantum-well (MQW) metal-semiconductor-metal (MSM) photosensors with an unactivated Mg-doped GaN cap layer were fabricated and characterized. The experimental results showed that dark pits of threading dislocation termination was hardly observed after capping a thin Mg-doped GaN layer. It was also found that we could significantly suppress the dark leakage current by inserting an additional Mg-doped GaN layer due to a thicker and higher potential barrier and effective surface passivation. For InGaN/GaN MQW MSM photosensors with the unactivated Mg-doped GaN cap layer, the responsivity at 380 nm and UV to visible rejection ratio were found to be 0.366 A/W and 1.99×103 under 4 V applied bias.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Phototunable photonic crystals with reversible wavelength choice

Guo-Zhi Han, Zhuo-Ying Xie, Da Zheng, Li-Guo Sun, and Zhong-Ze Gu

Appl. Phys. Lett. 91, 141114 (2007); http://dx.doi.org/10.1063/1.2793624 (3 pages) | Cited 10 times

Online Publication Date: 3 October 2007

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We report a phototunable photonic crystal device whose reflection at the stop band position can be switched between valley and peak. The device is comprised of a colloidal crystal film, a photoresponsible polymer-dispersed liquid crystal film, and a holophote. The reflection spectrum of the device can be reversibly switched by ultraviolet and visible light irradiations. It was demonstrated that this device is not only used for the application of wavelength selection but is also useful for applications such as display.
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42.70.Qs Photonic bandgap materials
42.79.Kr Display devices, liquid-crystal devices

Diffusion study in tailored gratings recorded in photopolymer glass with high refractive index species

Óscar Martínez-Matos, María L. Calvo, José A. Rodrigo, Pavel Cheben, and Francisco del Monte

Appl. Phys. Lett. 91, 141115 (2007); http://dx.doi.org/10.1063/1.2794792 (3 pages) | Cited 14 times

Online Publication Date: 3 October 2007

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We report results on the temporal evolution of the diffraction efficiency of volume holographic gratings recorded in a photopolymer glass incorporating Zr-based high refractive index species (HRIS) at molecular level. We record high spatial frequency gratings in this material with diffraction efficiencies near 100%. A two-component diffusion model is introduced for the evolution of refractive index modulation in darkness. Diffusion parameters for the Zr-based HRIS and monomer components have been determined. Codirectional diffusion of both components is demonstrated. The results show the feasibility for tailoring in this photomaterial holographic gratings with high diffraction efficiency over a wide range of spatial frequencies.
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42.70.Ce Glasses, quartz
42.70.Jk Polymers and organics
42.40.Ht Hologram recording and readout methods
42.40.Eq Holographic optical elements; holographic gratings

High Q optical resonances of polystyrene microspheres in water controlled by optical tweezers

Julie Lutti, Wolfgang Langbein, and Paola Borri

Appl. Phys. Lett. 91, 141116 (2007); http://dx.doi.org/10.1063/1.2795332 (3 pages) | Cited 8 times

Online Publication Date: 3 October 2007

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Using evanescent field coupling via frustrated total internal reflection, we measured whispering-gallery optical resonances of polystyrene microspheres held in aqueous buffer by optical tweezers, as a function of the distance from the planar coupling substrate. An intrinsic Q factor of 4×106 was found for a microsphere of 30 μm diameter, indicating the potential of such microresonators for highly sensitive biomolecular detection. These measurements provide an upper limit of 2×10−7 for the imaginary part of the complex refractive index of polystyrene at 770 nm wavelength.
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42.79.-e Optical elements, devices, and systems
07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Optoelectronic properties in quantum-confined germanium dots

M. Scarselli, S. Masala, P. Castrucci, M. De Crescenzi, E. Gatto, M. Venanzi, A. Karmous, P. D. Szkutnik, A. Ronda, and I. Berbezier

Appl. Phys. Lett. 91, 141117 (2007); http://dx.doi.org/10.1063/1.2793179 (3 pages) | Cited 3 times

Online Publication Date: 4 October 2007

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Photocurrent generation of nanometric Ge dots has been investigated by using electrochemical measurements. Photocurrent features have been ascribed, for large Ge dots, to Ge bulk direct electronic transitions at L and X points as evidenced by their close correspondence with the optical absorption coefficient. A blueshift of the photocurrent features has been detected by reducing the Ge dot size. These changes have been interpreted as due to quantum confinement effect. This result suggests that Ge dots could be applied in photovoltaic nanodevices and quantum dot based lasers.
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73.63.Kv Quantum dots
78.67.Hc Quantum dots
72.40.+w Photoconduction and photovoltaic effects
68.65.Hb Quantum dots (patterned in quantum wells)
82.45.-h Electrochemistry and electrophoresis
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Passive all-optical diode using asymmetric nonlinear absorption

Reji Philip, M. Anija, Chandra S. Yelleswarapu, and D. V. G. L. N. Rao

Appl. Phys. Lett. 91, 141118 (2007); http://dx.doi.org/10.1063/1.2794015 (3 pages) | Cited 12 times

Online Publication Date: 4 October 2007

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Saturable and reverse saturable absorptions are well-known phenomena, originating from the imaginary component of the third order nonlinear optical susceptibility. We note that structures with an axially asymmetric nonlinear absorption can be easily realized from saturable and reverse saturable absorption materials arranged in tandem. In this paper, the basic transmission behavior of such a structure is worked out. Detailed numerical simulations demonstrate passive all-optical diode behavior, and the results are verified experimentally. The principle will work for all light polarizations, has no phase-matching restrictions, and can be extended to a large number of available nonlinear media for possible applications.
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42.65.An Optical susceptibility, hyperpolarizability
42.82.Bq Design and performance testing of integrated-optical systems

Liquid crystal polymer composite films for reconfigurable photomasking applications

Anna E. Fox and Adam K. Fontecchio

Appl. Phys. Lett. 91, 141119 (2007); http://dx.doi.org/10.1063/1.2794735 (3 pages) | Cited 4 times

Online Publication Date: 4 October 2007

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We show proof of concept of a real-time reconfigurable photomask fabricated from holographically formed polymer-dispersed liquid crystal (H-PDLC) reflection gratings on etched indium tin oxide patterned electrodes. H-PDLC films were formed using a thiolene based polymer to have a reflection wavelength that modulates 440 nm, the peak sensitivity wavelength of Shipley 1800 series positive photoresist. A working prototype of this adaptable photomask device is shown by comparing patterns formed using the H-PDLC mask and similar patterns formed using a static contact photomask showing that H-PDLC films have the ability to modulate 440 nm light and control the exposure dose of photoresist.
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61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems
68.15.+e Liquid thin films
42.70.Df Liquid crystals
42.70.Jk Polymers and organics
42.40.Eq Holographic optical elements; holographic gratings

A silicon-based spot-size converter between single-mode fibers and Si-wire waveguides using cascaded tapers

Kazuo Shiraishi, Hidehiko Yoda, Akihiko Ohshima, Hideki Ikedo, and Chen S. Tsai

Appl. Phys. Lett. 91, 141120 (2007); http://dx.doi.org/10.1063/1.2795337 (3 pages) | Cited 19 times

Online Publication Date: 4 October 2007

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Theoretical and experimental performances of a robust Si-based spot-size converter (SSC) for efficient coupling between a single-mode fiber and a photonic Si-wire waveguide are reported. The SSC is comprised of cascaded horizontal linear and vertical nonlinear up tapers measured 2.0 mm and 86 μm in length, respectively, in a silicon-on-insulator substrate. The fine modal field of a Si-wire waveguide, 0.54×0.38 μm2 in diameters, was expanded to diameters of 5.1×9.2 μm2 with measured net transmission loss of 0.5 dB at the wavelength of 1.55 μm by the miniature SSC.
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42.79.Gn Optical waveguides and couplers

Room temperature, continuous-wave operation of quantum cascade lasers with single phonon resonance-continuum depopulation structures grown by metal organic vapor-phase epitaxy

K. Fujita, S. Furuta, A. Sugiyama, T. Ochiai, T. Edamura, N. Akikusa, M. Yamanishi, and H. Kan

Appl. Phys. Lett. 91, 141121 (2007); http://dx.doi.org/10.1063/1.2795793 (3 pages) | Cited 17 times

Online Publication Date: 4 October 2007

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We propose a new quantum-cascade laser structure with single phonon resonance-continuum depopulation and demonstrate room temperature, continuous-wave operation of the proposed 7.9 μm quantum-cascade laser. The laser grown by metal organic vapor-phase epitaxy emits a cw output power of 36 mW at 30 °C, exhibiting a threshold current density of 2.23 kA/cm2. The cw operation is reported for higher temperatures up to slightly above 60 °C. The proposed structure may lead to a successful commercial mass production of the lasers.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Extraordinary optical gain from silicon implanted with erbium

M. A. Lourenço, R. M. Gwilliam, and K. P. Homewood

Appl. Phys. Lett. 91, 141122 (2007); http://dx.doi.org/10.1063/1.2797975 (3 pages) | Cited 7 times

Online Publication Date: 5 October 2007

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Here we report on measurements of optical gain at 1.5 μm in crystalline silicon. Gain is achieved by the incorporation of the rare earth erbium in silicon. A method was developed to enable the gain measurement in short silicon waveguides. Crucially, gain values obtained are significantly greater than previously supposed. We have measured a lower limit for the optical cross section for Er3+ of 5×10−19 cm2, 30 times higher than previously anticipated. Given these higher values, this system now offers a realistic route to the production of electrically pumped silicon optical amplifier and laser devices using standard silicon process technology.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.uf Ge and Si
61.72.S- Impurities in crystals
71.55.Cn Elemental semiconductors
61.80.Jh Ion radiation effects

Electrically pumped photonic crystal distributed feedback quantum cascade lasers

Y. Bai, S. R. Darvish, S. Slivken, P. Sung, J. Nguyen, A. Evans, W. Zhang, and M. Razeghi

Appl. Phys. Lett. 91, 141123 (2007); http://dx.doi.org/10.1063/1.2798062 (3 pages) | Cited 24 times

Online Publication Date: 5 October 2007

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We demonstrate electrically pumped, room temperature, single mode operation of photonic crystal distributed feedback (PCDFB) quantum cascade lasers emitting at λ ∼ 4.75 μm. Ridge waveguides of 100 μm width were fabricated with both PCDFB and Fabry-Pérot feedback mechanisms. The Fabry-Pérot device has a broad emitting spectrum and a double lobed far-field character. The PCDFB device, as expected, has primarily a single spectral mode and a diffraction limited far field characteristic with a full angular width at half maximum of 2.4°. This accomplishment represents the first step in power scaling of single mode, midinfrared laser diodes operating at room temperature.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Tv Photonic crystal lasers and coherent effects
42.60.By Design of specific laser systems
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Effects of the medium on synthesis of nanopowders by wire explosion process

C. Cho, Y. W. Choi, C. Kang, and G. W. Lee

Appl. Phys. Lett. 91, 141501 (2007); http://dx.doi.org/10.1063/1.2794724 (3 pages) | Cited 17 times

Online Publication Date: 2 October 2007

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Silver nanopowder was produced in air and water media by wire explosion process. Size of the particles formed in water was smaller than that in air. In water medium, compared with air, the delay of plasma formation resulted in a higher energy deposition in the wire. As a consequence, there were no micrometer size particles in the powder, which is attributed to the complete vaporization of the wire. It is considered that the wire explosion in liquid medium meets three conditions to form smaller particles, namely, higher energy deposition in the wire, sufficient expansion volume, and quick cooling of the particles.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.07.Wx Nanopowders

Observation of atmospheric pressure arc on a cold cathode

Lakshminarayana Rao, Richard J. Munz, and Sylvain Coulombe

Appl. Phys. Lett. 91, 141502 (2007); http://dx.doi.org/10.1063/1.2783179 (3 pages)

Online Publication Date: 4 October 2007

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Pictures of an atmospheric pressure arc between two concentric copper electrodes at different external magnetic fields (B field) were taken using a charge-coupled device camera and a complementary metal-oxide-semiconductor camera. The pictures reveal splitting of the arc column into a column with multiple arc roots (i.e., cathode spots), repulsion of cathode spots due to their self-induced B fields, and grouping of cathode spots under the influence of B field. Power frequency spectra analysis of the voltage fluctuations was also performed.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Vp Discharge in vacuum
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