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4 Aug 2008

Volume 93, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 051101 (2008); http://dx.doi.org/10.1063/1.2965797 (3 pages)

Mariano A. Zimmler, Jiming Bao, Federico Capasso, Sven Müller, and Carsten Ronning
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Laser action in nanowires: Observation of the transition from amplified spontaneous emission to laser oscillation

Mariano A. Zimmler, Jiming Bao, Federico Capasso, Sven Müller, and Carsten Ronning

Appl. Phys. Lett. 93, 051101 (2008); http://dx.doi.org/10.1063/1.2965797 (3 pages) | Cited 62 times

Online Publication Date: 4 August 2008

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Direct evidence of the transition from amplified spontaneous emission to laser action in optically pumped zinc oxide (ZnO) nanowires, at room temperature, is presented. The optical power evolves from a superlinear to a linear regime as the pump power exceeds threshold, concomitant with a transition to directional emission along the nanowire and the emergence of well defined cavity Fabry–Pérot modes around a wavelength of ≈ 385 nm, the intensity of which exceeds the spontaneous emission background by orders of magnitude. The laser oscillation threshold is found to be strongly dependent on nanowire diameter, with no laser oscillation observed for diameters smaller than ∼ 150 nm. Finally, we use an alternative “head on” detection geometry to measure the output power of a single nanowire laser.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Room temperature polariton lasing in a GaN/AlGaN multiple quantum well microcavity

Gabriel Christmann, Raphaël Butté, Eric Feltin, Jean-François Carlin, and Nicolas Grandjean

Appl. Phys. Lett. 93, 051102 (2008); http://dx.doi.org/10.1063/1.2966369 (3 pages) | Cited 67 times

Online Publication Date: 4 August 2008

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The authors report room temperature polariton lasing at λ ∼ 345 nm in a hybrid AlInN/AlGaN multiple quantum well microcavity (MQW-MC) containing a GaN/AlGaN MQW active region, i.e., the achievement under nonresonant optical excitation of coherent light emission of a macroscopic population of polaritons occupying the lowest energy state of the lower polariton branch. This was made possible by taking advantage of the efficient relaxation of polaritons in a MQW-MC exhibiting a large vacuum Rabi splitting ΩVRS = 56 meV.
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78.67.De Quantum wells
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.21.Fg Quantum wells

Extreme-ultraviolet frequency comb generation by polarization-gated surface-enhanced optical fields

Jian Wu, Hongxing Qi, and Heping Zeng

Appl. Phys. Lett. 93, 051103 (2008); http://dx.doi.org/10.1063/1.2967732 (3 pages) | Cited 3 times

Online Publication Date: 4 August 2008

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We show that two synchronized counter-propagating femtosecond pulses could be controlled by adjusting their relative delay to excite surface-enhanced optical fields of time-gated linear polarization in contrast with intrinsic elliptic polarization excited by the conventional one-pulse incidence scheme. Such surface-enhanced optical fields can be used to generate efficient high harmonics and thus extreme-ultraviolet frequency combs. The energy conversion efficiency as well as the frequency span of the generated extreme-ultraviolet frequency combs can be significantly increased with controllable emission probabilities along different directions relative to the surface.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Temperature-stable operation of a quantum dot semiconductor disk laser

T. D. Germann, A. Strittmatter, J. Pohl, U. W. Pohl, D. Bimberg, J. Rautiainen, M. Guina, and O. G. Okhotnikov

Appl. Phys. Lett. 93, 051104 (2008); http://dx.doi.org/10.1063/1.2968137 (3 pages) | Cited 15 times

Online Publication Date: 5 August 2008

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We demonstrate temperature-independent output characteristics of an optically pumped semiconductor disk laser (SDL) based on quantum dots (QDs) grown in the Stranski-Krastanow regime. The gain structure consists of a stack of 7×3 QD layers, each threefold group being located at an optical antinode position. The SDL emits at 1210 nm independent of the pump power density. Threshold and differential efficiency do not dependent on heat sink temperature. Continuous-wave operation close to 300 mW output power is achieved using the ground-state transition of the InGaAs QDs.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Terahertz conductivity of thin metal films

N. Laman and D. Grischkowsky

Appl. Phys. Lett. 93, 051105 (2008); http://dx.doi.org/10.1063/1.2968308 (3 pages) | Cited 13 times

Online Publication Date: 5 August 2008

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The conductivities of thin Al, Au, and Ag films were measured via their transmission at terahertz frequencies. The conductivities of all the films, particularly the thinner films and Al films, were much smaller than their bulk dc values. This reduced conductivity can be quantitatively understood in terms of an increased scattering rate from defects. The transmission is consistent with a frequency independent conductivity, implying a very fast electron scattering time.
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73.61.At Metal and metallic alloys

Enhancement of surface plasmon-mediated radiative energy transfer through a corrugated metal cathode in organic light-emitting devices

Jing Feng, Takayuki Okamoto, Ryo Naraoka, and Satoshi Kawata

Appl. Phys. Lett. 93, 051106 (2008); http://dx.doi.org/10.1063/1.2968309 (3 pages) | Cited 15 times

Online Publication Date: 5 August 2008

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We report enhanced top emission from organic light-emitting devices by surface plasmon-mediated radiative energy transfer. A dye-doped dielectric acceptor layer was deposited onto the surface of a one-dimensionally corrugated silver cathode and was excited by the electroluminescence of a donor layer, which is located at the other side of the cathode. Ten times enhancement in emission intensity from the acceptor was observed compared to flat devices; this is due to the enhanced radiative energy transfer from the donor to the acceptor by the coupled surface plasmons on the opposite interfaces of the silver cathode.
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85.60.Jb Light-emitting devices
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
82.45.Fk Electrodes

Laser microfabrication and rotation of ship-in-a-bottle optical rotators

Shigeki Matsuo, Satoshi Kiyama, Yoshinori Shichijo, Takuro Tomita, Shuichi Hashimoto, Yoichiroh Hosokawa, and Hiroshi Masuhara

Appl. Phys. Lett. 93, 051107 (2008); http://dx.doi.org/10.1063/1.2967872 (3 pages) | Cited 8 times

Online Publication Date: 5 August 2008

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We have fabricated optical rotators inside a silica substrate and rotated them by a laser trapping technique. The fabrication method used was femtosecond laser-assisted etching, i.e., modification of the host material by irradiation with femtosecond laser pulses along a predesigned pattern, followed by selective chemical etching. The rotators, which consist of the same material as the substrate, can move inside the microcavity but cannot get out. The rotation speed was proportional to the trapping laser power, and the maximum achieved was about 100 rpm. Such rotators will be applicable to micro-total-analysis systems and microfluidics.
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81.65.Cf Surface cleaning, etching, patterning
33.55.+b Optical activity and dichroism
81.16.Ta Atom manipulation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Amplification of transition-Cherenkov terahertz radiation of femtosecond filament in air

Yi Liu, Aurélien Houard, Bernard Prade, André Mysyrowicz, Abdourahmane Diaw, and Vladimir T. Tikhonchuk

Appl. Phys. Lett. 93, 051108 (2008); http://dx.doi.org/10.1063/1.2965612 (3 pages) | Cited 5 times

Online Publication Date: 5 August 2008

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The transition-Cherenkov terahertz radiation from a femtosecond laser filament in air is enhanced by three orders of magnitude in the presence of a longitudinal static electric field, while the radiation pattern and the polarization remain the same. An amplified longitudinal electron current inside the filament is responsible for this amplified terahertz emission.
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52.38.Hb Self-focussing, channeling, and filamentation in plasmas
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Control of the gated spectra with narrow bandwidth from a supercontinuum using ultrafast optical Kerr gate of bismuth glass

Wenjiang Tan, Hui Liu, Jinhai Si, and Xun Hou

Appl. Phys. Lett. 93, 051109 (2008); http://dx.doi.org/10.1063/1.2968202 (3 pages) | Cited 7 times

Online Publication Date: 6 August 2008

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Supercontinuum generation and its application have become one of the attractive research fields in ultrafast optics. We have acquired a series of narrow bandwidth and symmetric gated spectra continuously from the chirped supercontinuum generated in a sapphire plate with a femtosecond laser, using an ultrafast optical Kerr gate (OKG) with Bi2O3–B2O3–SiO2 oxide glass as the Kerr material. Experimental results show that the gated spectra obtained using OKG of the glass have more superiorities comparing with CS2.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Ce Glasses, quartz
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

40 GHz small-signal cross-gain modulation in 1.3 μm quantum dot semiconductor optical amplifiers

C. Meuer, J. Kim, M. Laemmlin, S. Liebich, D. Bimberg, A. Capua, G. Eisenstein, R. Bonk, T. Vallaitis, J. Leuthold, A. R. Kovsh, and I. L. Krestnikov

Appl. Phys. Lett. 93, 051110 (2008); http://dx.doi.org/10.1063/1.2969060 (3 pages) | Cited 4 times

Online Publication Date: 6 August 2008

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Small-signal cross-gain modulation of quantum dot based semiconductor optical amplifiers (QD SOAs), having a dot-in-a-well structure, is presented, demonstrating superiority for ultrahigh bit rate wavelength conversion. Optimization of the QD SOA high speed characteristics via bias current and optical pump power is presented and a small-signal 3 dB bandwidth exceeding 40 GHz is demonstrated. The p-doped samples investigated here enable small-signal wavelength conversion within a range of 30 nm, limited mainly by the gain bandwidth.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes
78.67.Hc Quantum dots
42.65.-k Nonlinear optics

An experimental study of the interactions of self-trapped white light beams in a photopolymer

Kailash Kasala and Kalaichelvi Saravanamuttu

Appl. Phys. Lett. 93, 051111 (2008); http://dx.doi.org/10.1063/1.2957994 (3 pages) | Cited 3 times

Online Publication Date: 6 August 2008

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Interactions of two parallel-propagating and mutually incoherent white light beams were examined in a photopolymerizable organosiloxane. The beams fused when separated by a distance corresponding to the width of each beam but at separation distances⪢beam width, formed two self-trapped beams that repelled each other. At separation distances<beam width, they suffered filamentation but ultimately fused into a single self-trapped beam.
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42.70.Jk Polymers and organics
82.35.-x Polymers: properties; reactions; polymerization
82.50.-m Photochemistry
42.50.Wk Mechanical effects of light on material media, microstructures and particles
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Photoinduced microchannels inside silicon by femtosecond pulses

Tao Chen, Jinhai Si, Xun Hou, Shingo Kanehira, Kiyotaka Miura, and Kazuyuki Hirao

Appl. Phys. Lett. 93, 051112 (2008); http://dx.doi.org/10.1063/1.2969401 (3 pages) | Cited 9 times

Online Publication Date: 7 August 2008

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We reported on the fabrication of microchannels in the interior of silicon wafers using a femtosecond laser of 800 nm wavelength, which was in the absorption region of silicon. The scanning electron micrographs showed that microchannels were induced inside the silicon wafer when the femtosecond laser beam was focused inside the wafer. The aspect ratio of the microchannel cross section decreased with the increase in scan velocity of the laser. The formation of the photoinduced microchannels probably resulted from the microexplosions due to both the linear absorption and avalanche ionization.
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07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Migration enhanced lateral epitaxial overgrowth of AlN and AlGaN for high reliability deep ultraviolet light emitting diodes

R. Jain, W. Sun, J. Yang, M. Shatalov, X. Hu, A. Sattu, A. Lunev, J. Deng, I. Shturm, Y. Bilenko, R. Gaska, and M. S. Shur

Appl. Phys. Lett. 93, 051113 (2008); http://dx.doi.org/10.1063/1.2969402 (3 pages) | Cited 9 times

Online Publication Date: 7 August 2008

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We report on the growth of low-defect thick films of AlN and AlGaN on trenched AlGaN/sapphire templates using migration enhanced lateral epitaxial overgrowth. Incoherent coalescence-related defects were alleviated by controlling the tilt angle of growth fronts and by allowing Al adatoms sufficient residence time to incorporate at the most energetically favorable lattice sites. Deep ultraviolet light emitting diode structures (310 nm) deposited over fully coalesced thick AlN films exhibited cw output power of 1.6 mW at 50 mA current with extrapolated lifetime in excess of 5000 hours. The results demonstrate substantial improvement in the device lifetime, primarily due to the reduced density of growth defects.
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85.60.Jb Light-emitting devices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Ea III-V semiconductors

Light amplification by stimulated Raman scattering in AlGaAs-based photonic-crystal line-defect waveguides

Hisaya Oda, Kuon Inoue, Akio Yamanaka, Naoki Ikeda, Yoshimasa Sugimoto, and Kiyoshi Asakawa

Appl. Phys. Lett. 93, 051114 (2008); http://dx.doi.org/10.1063/1.2965110 (3 pages) | Cited 14 times

Online Publication Date: 7 August 2008

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The authors performed an amplification experiment of optical signal around 1550 nm by stimulated Raman scattering in a photonic-crystal slab waveguide (WG) of single-line defect. They adopted an air-bridge type AlGaAs-based WG sample to avoid two-photon absorption. Short light pulses of 5 ps in duration operated at 20 MHz and a cw laser were employed for pump (excitation) and probe (signal) lights, respectively. As a result, amplification of a net gain of ∼ 3 dB (maximum) is achieved with pulse pump energy of 22 pJ for a sample of 1.0 mm in length.
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42.65.Wi Nonlinear waveguides
42.70.Qs Photonic bandgap materials
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.82.Et Waveguides, couplers, and arrays
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Spectral optimization of phosphor-conversion light-emitting diodes for ultimate color rendering

A. Žukauskas, R. Vaicekauskas, F. Ivanauskas, H. Vaitkevičius, and M. S. Shur

Appl. Phys. Lett. 93, 051115 (2008); http://dx.doi.org/10.1063/1.2966150 (3 pages) | Cited 14 times

Online Publication Date: 8 August 2008

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We apply an optimization scheme based on rendering of all colors of the enhanced Munsell palette to phosphor-conversion (PC) light-emitting diodes (LEDs). This approach yields combinations of peak wavelengths and bandwidths for white PC LEDs with partial and complete conversion that enable lighting with better quality than that obtained using designs based on the standard color-rendering assessment procedure.
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85.60.Jb Light-emitting devices

Ultrafast spin noise spectroscopy

Sebastian Starosielec and Daniel Hägele

Appl. Phys. Lett. 93, 051116 (2008); http://dx.doi.org/10.1063/1.2969041 (3 pages) | Cited 6 times

Online Publication Date: 8 August 2008

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We propose an extension of optical spin noise spectroscopy that expands the so far accessible frequency range from a few gigahertz to several terahertz employing pairs of ultrafast femtosecond-laser pulses. The method is suitable for probing noise signals with very high bandwidths and signals centered at zero frequency. A time-resolved version of noise spectroscopy for detecting noise after a pump event follows naturally from the scheme. The analytical description of ultrafast spin noise spectroscopy along with numerical simulations proves the method a powerful spectroscopic tool.
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78.47.D- Time resolved spectroscopy (>1 psec)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Transmission measurement of the photonic band gap of GaN photonic crystal slabs

J. Caro, E. M. Roeling, B. Rong, Hoang M. Nguyen, E. W. J. M. van der Drift, S. Rogge, F. Karouta, R. W. van der Heijden, and H. W. M. Salemink

Appl. Phys. Lett. 93, 051117 (2008); http://dx.doi.org/10.1063/1.2967744 (3 pages) | Cited 1 time

Online Publication Date: 8 August 2008

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A high-contrast-ratio (30 dB) photonic band gap in the near-infrared transmission of hole-type GaN two-dimensional photonic crystals (PhCs) is reported. These crystals are deeply etched in a 650 nm thick GaN layer grown on sapphire. A comparison of the measured spectrum with finite difference time domain simulations gives quantitative agreement for the dielectric band and qualitative agreement for the air band. The particular behavior of the air band arises from the relatively low index contrast between the GaN layer and the sapphire substrate. Our results call for extension of the operation of GaN PhCs to the visible range.
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81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
42.70.Qs Photonic bandgap materials
81.65.Cf Surface cleaning, etching, patterning
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Microwave plasma torch operating in a chamber at a low pressure

Han S. Uhm, Soon C. Cho, and Yong C. Hong

Appl. Phys. Lett. 93, 051501 (2008); http://dx.doi.org/10.1063/1.2965459 (3 pages) | Cited 1 time

Online Publication Date: 5 August 2008

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A microwave plasma torch was operated in a chamber at a reduced pressure, and the properties of the torch plasma were investigated. The argon torch plasma at a reduced pressure of 150 Torr was observed to be well diffused in the discharge tube instead of the filamentary structures at the atmospheric pressure. The typical torch plasma density and electron temperature are measured to be ne = 2×1014/cm3 and Te = 1.5 eV, respectively, for argon plasmas at 150 Torr. It was also found that the microwave plasma torch at a low pressure may efficiently produce chemical radicals.
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52.75.Hn Plasma torches
52.80.-s Electric discharges
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

The multipole resonance probe: A concept for simultaneous determination of plasma density, electron temperature, and collision rate in low-pressure plasmas

M. Lapke, T. Mussenbrock, and R. P. Brinkmann

Appl. Phys. Lett. 93, 051502 (2008); http://dx.doi.org/10.1063/1.2966351 (3 pages) | Cited 9 times

Online Publication Date: 6 August 2008

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A diagnostic concept is presented which enables the simultaneous determination of plasma density, electron temperature, and collision rate in low-pressure gas discharges. The proposed method utilizes a radio-frequency driven probe of particular spherical design which is immersed in the plasma to excite a family of spatially bounded surface resonances. An analysis of the measured absorption spectrum S(ω) of the probe provides information on the distribution of the plasma in its vicinity, from which the values of the plasma parameters can be inferred. In its simplest realization, the probe consists of two dielectrically shielded, conducting hemispheres, which are symmetrically driven by an radio-frequency source, and the excited resonances can be classified as multipole fields, which allows an analytical evaluation of the measured signal. The proposed method is robust, calibration free, economical, and can be used for ideal and reactive plasmas alike.
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52.70.Gw Radio-frequency and microwave measurements
52.25.-b Plasma properties
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.20.Fs Electron collisions

Radio-frequency power assistance on a compact magnetohydrodynamic electrical power generator under high-density magnetic flux

Tomoyuki Murakami and Yoshihiro Okuno

Appl. Phys. Lett. 93, 051503 (2008); http://dx.doi.org/10.1063/1.2969044 (3 pages) | Cited 7 times

Online Publication Date: 7 August 2008

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We describe the effect of radio-frequency (rf) electromagnetic field application on a compact magnetohydrodynamic (MHD) electrical power generator under high-density magnetic flux. The rf-power assistance improves the Hall potential profile and fluid flow structure, and rectifies large-scale plasma instability. These effects are vital for the compact MHD generator. With the aid of rf power, the power generation performance is significantly improved even under the low-plasma-stability condition for high-density magnetic flux.
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84.60.Lw Magnetohydrodynamic conversion
96.25.St Plasma and MHD instabilities
94.30.C- Magnetospheric configuration and dynamics

Atmospheric pressure nitrogen plasma jet: Observation of striated multilayer discharge patterns

Yong Cheol Hong, Han Sup Uhm, and Won Ju Yi

Appl. Phys. Lett. 93, 051504 (2008); http://dx.doi.org/10.1063/1.2969287 (3 pages) | Cited 16 times

Online Publication Date: 7 August 2008

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This paper presents a nitrogen microplasma jet that operates at atmospheric pressure and provides details of an observation of the striated multilayer discharge patterns formed in the plasma jet. The plasma jet device in a microhollow electrode is a pencil-type configuration that produces a long cold plasma jet capable of reaching 3.5 cm and having various excited plasma species shown through optical emission spectrum. By introducing a gas flow rate of more than 5 l/min, striated discharge patterns in the plasma jet are produced through ionization wave propagation.
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52.75.-d Plasma devices
52.80.-s Electric discharges

Titanium dioxide nanofiber-cotton targets for efficient multi-keV x-ray generation

Minoru Tanabe, Hiroaki Nishimura, Shinsuke Fujioka, Keiji Nagai, Norimasa Yamamoto, Zhong-Ze Gu, Chao Pan, Frederic Girard, Michel Primout, Bruno Villette, Didier Brebion, Kevin B. Fournier, Akira Fujishima, and Kunioki Mima

Appl. Phys. Lett. 93, 051505 (2008); http://dx.doi.org/10.1063/1.2969300 (3 pages) | Cited 6 times

Online Publication Date: 7 August 2008

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Multi-keV x-ray generation from low-density (27±7 mg/cm3) nanofiber-cotton targets composed of titanium dioxide has been investigated. The cotton targets were heated volumetrically and supersonically to a peak electron temperature of 2.3 keV, which is optimal to yield Ti K-shell x rays. Considerable enhancement of conversion efficiency [(3.7±0.5)%] from incident laser energy into Ti K-shell x rays (4–6 keV band) was attained in comparison with that [(1.4±0.9)%] for a planar Ti-foil target.
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52.38.Ph X-ray, γ-ray, and particle generation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
52.70.La X-ray and γ-ray measurements

Femtosecond laser-induced electronic plasma at metal surface

Zhaoyang Chen and Samuel S. Mao

Appl. Phys. Lett. 93, 051506 (2008); http://dx.doi.org/10.1063/1.2966152 (3 pages) | Cited 11 times

Online Publication Date: 8 August 2008

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We develop a theoretical analysis to model plasma initiation at the early stage of femtosecond laser irradiation of metal surfaces. The calculation reveals that there is a threshold intensity for the formation of a microscale electronic plasma at the laser-irradidated metal surface. As the full width at half maximum of a laser pulse increases from 15 to 200 fs, the plasma formation threshold decreases by merely about 20%. The dependence of the threshold intensity on laser pulse width can be attributed to laser-induced surface electron emission, in particular due to the effect of photoelectric effect.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
79.20.Ds Laser-beam impact phenomena
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CdSe quantum dot-decorated double walled carbon nanotubes: The effect of chemical moieties

Yoong Ahm Kim, Hiroyuki Muramatsu, Ki Chul Park, Daisuke Shimamoto, Yong Chae Jung, Jin Hee Kim, Takuya Hayashi, Yasunori Saito, Morinobu Endo, Mauricio Terrones, and Mildred S. Dresselhaus

Appl. Phys. Lett. 93, 051901 (2008); http://dx.doi.org/10.1063/1.2966341 (3 pages) | Cited 10 times

Online Publication Date: 4 August 2008

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We report that fluorine atoms on the outer tubes of double walled carbon nanotubes (DWNTs) are more effective for nucleating and growing CdSe nanoparticles than oxygen-containing functional groups. The CdSe particles with an average size of 5–7 nm grow through infiltration into an interstitial space created by four to five thin bundled DWNTs. We envisage that DWNTs will replace single and multiwalled carbon nanotubes in a wide range of applications because chemical moieties could be introduced selectively on the outer tubes while the optical and physical properties of the inner tubes remain almost unchanged.
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81.07.De Nanotubes
81.07.Ta Quantum dots
81.16.Dn Self-assembly
61.46.Fg Nanotubes
78.30.Na Fullerenes and related materials
79.60.Jv Interfaces; heterostructures; nanostructures
78.40.-q Absorption and reflection spectra: visible and ultraviolet

Effects of transverse temperature gradient on acoustic and streaming velocity fields in a resonant cavity

Majid Nabavi, Kamran Siddiqui, and Javad Dargahi

Appl. Phys. Lett. 93, 051902 (2008); http://dx.doi.org/10.1063/1.2960576 (3 pages) | Cited 6 times

Online Publication Date: 4 August 2008

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Effects of transverse temperature gradient on acoustic and streaming velocity fields inside a gas-filled rectangular enclosure subject to acoustic standing wave are investigated experimentally. Synchronized particle image velocimetry technique has been used to measure the acoustic and streaming velocity fields. The results show that the temperature difference between the top and the bottom walls deforms the symmetric streaming vortices about the channel’s centerline to the asymmetric ones. As the temperature difference increases, the amplitude of streaming velocity increases.
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43.25.Nm Acoustic streaming
43.58.Dj Sound velocity
47.32.-y Vortex dynamics; rotating fluids
47.60.Dx Flows in ducts and channels
47.80.Cb Velocity measurements
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