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3 Mar 2008

Volume 92, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 093101 (2008); http://dx.doi.org/10.1063/1.2888164 (3 pages)

C. K. Lee, S. J. Kim, S. J. Shin, J. B. Choi, and Y. Takahashi
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Application of frustrated total internal reflection of millimeter waves for detection and evaluation of disbonds in dielectric joints

Sergey Kharkovsky, Emilio Nanni, and Reza Zoughi

Appl. Phys. Lett. 92, 094101 (2008); http://dx.doi.org/10.1063/1.2890054 (3 pages) | Cited 3 times

Online Publication Date: 4 March 2008

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Millimeter waves penetrate inside of low loss dielectric materials and they are sensitive to the presence of internal interfaces and nonuniformities. This allows millimeter wave nondestructive inspection techniques to be utilized for inspecting dielectric composite structures. A disbond (a thin and extended airgap) in structures possessing adhesively bonded joints with complex geometries is commonly difficult to inspect. In this letter, we demonstrate the operational principle and the useful features of a millimeter wave technique, employing a frustrated total internal reflection of signals transmitted and received by dielectric waveguide probes for detecting and evaluating disbonds in such joints.
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81.70.-q Methods of materials testing and analysis
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.40.-x Radiowave and microwave (including millimeter wave) technology

Femtosecond carrier dynamics in electron-beam-irradiated C60 film

Y. Toda, S. Ryuzaki, and J. Onoe

Appl. Phys. Lett. 92, 094102 (2008); http://dx.doi.org/10.1063/1.2838347 (3 pages) | Cited 12 times

Online Publication Date: 5 March 2008

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Time-resolved temperature-dependent transmission changes were measured for both pristine C60 and electron-beam-irradiated C60 polymer films using an optical pump-probe technique. Only the signals obtained for the C60 polymer show a temperature-dependent slow decay, which appears in the low temperature region below ∼ 60 K. This slow decay component exhibits a monotonic increase in both relaxation time and amplitude with decreasing temperature, providing evidence of gap formation associated with ordering fluctuations.
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78.66.Tr Fullerenes and related materials
78.66.Qn Polymers; organic compounds
78.47.D- Time resolved spectroscopy (>1 psec)
61.80.Fe Electron and positron radiation effects
61.48.-c Structure of fullerenes and related hollow and planar molecular structures

Multifunctional carbon nanotube networks for fuel cells

M. Kaempgen, M. Lebert, N. Nicoloso, and S. Roth

Appl. Phys. Lett. 92, 094103 (2008); http://dx.doi.org/10.1063/1.2891095 (3 pages) | Cited 11 times

Online Publication Date: 5 March 2008

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A single walled carbon nanotube (SWCNT) network is functionalized in different ways to achieve a multifunctional electrode. This electrode material is used as light and thin gas diffusion electrodes in fuel cells. In contrast to any previous work, no other carbon material is part of the electrode. We demonstrate that the performance of such all-SWCNT gas diffusion electrodes is comparable to that of regular electrodes which are based on amorphous carbon. This allows the entire replacement of these regular carbon electrodes by such multifunctionalized SWCNT networks. This way, extremely thin and light gas diffusion electrodes are realized, potentially fulfilling the demands of light-weight power supplies.
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82.47.-a Applied electrochemistry
66.30.-h Diffusion in solids

Subwavelength focusing of surface acoustic waves generated by an annular interdigital transducer

Vincent Laude, Davy Gérard, Naima Khelfaoui, Carlos F. Jerez-Hanckes, Sarah Benchabane, and Abdelkrim Khelif

Appl. Phys. Lett. 92, 094104 (2008); http://dx.doi.org/10.1063/1.2891055 (3 pages) | Cited 5 times

Online Publication Date: 5 March 2008

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We propose and demonstrate experimentally the concept of the annular interdigital transducer that focuses acoustic waves on the surface of a piezoelectric material to a single, diffraction-limited spot. The shape of the transducing fingers follows the wave surface. Experiments conducted on lithium niobate substrates evidence that the generated surface waves converge to the center of the transducer, producing a spot that shows a large concentration of acoustic energy. This concept is of practical significance to design new intense microacoustic sources, for instance for enhanced acousto-optical interactions.
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77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
68.35.Iv Acoustical properties
43.38.-p Transduction; acoustical devices for the generation and reproduction of sound

Fully developed thermocreep-driven gas microflow

Huei Chu Weng and Cha’o-Kuang Chen

Appl. Phys. Lett. 92, 094105 (2008); http://dx.doi.org/10.1063/1.2884697 (3 pages) | Cited 4 times

Online Publication Date: 6 March 2008

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In this study, we develop the mathematical model of thermocreep-driven gas flow in an unheated parallel-plate microchannel with discrepant temperatures at both ends. The fully developed solutions for flow and thermal fields as well as the corresponding characteristics are derived analytically and presented for air. Results reveal that the velocity and temperature distributions are uniform. This means that the local flow drag and the local heat transfer rate are zero and that the influence of fluid-wall interaction is negligible. In addition, the velocity slip induced by gas rarefaction is shown to increase the flow rate and the average heat transfer rate. Such effect can be magnified by the decreases of the channel width and the channel length.
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47.60.Dx Flows in ducts and channels
44.15.+a Channel and internal heat flow

An x-ray probe of laser-aligned molecules

E. R. Peterson, C. Buth, D. A. Arms, R. W. Dunford, E. P. Kanter, B. Krässig, E. C. Landahl, S. T. Pratt, R. Santra, S. H. Southworth, and L. Young

Appl. Phys. Lett. 92, 094106 (2008); http://dx.doi.org/10.1063/1.2890846 (3 pages) | Cited 18 times

Online Publication Date: 6 March 2008

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We demonstrate a hard x-ray probe of laser-aligned small molecules. To align small molecules with optical lasers, high intensities at nonresonant wavelengths are necessary. We use 95 ps pulses focused to 40 μm from an 800 nm Ti:sapphire laser at a peak intensity of 1012 W/cm2 to create an ensemble of aligned bromotrifluoromethane (CF3Br) molecules. Linearly polarized, 120 ps x-ray pulses, focused to 10 μm, tuned to the Br 1s→σ* preedge resonance at 13.476 keV, probe the ensemble of laser-aligned molecules. The demonstrated methodology has a variety of applications and can enable ultrafast imaging of laser-controlled molecular motions with Ångstrom-level resolution.
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07.85.-m X- and γ-ray instruments
06.60.Jn High-speed techniques (microsecond to femtosecond)
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