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7 Jan 2008

Volume 92, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 92, 011101 (2008); http://dx.doi.org/10.1063/1.2828458 (3 pages)

F. Pedaci, S. Barland, E. Caboche, P. Genevet, M. Giudici, J. R. Tredicce, T. Ackemann, A. J. Scroggie, W. J. Firth, G.-L. Oppo, G. Tissoni, and R. Jäger
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Nonrelativistic electron bunch train for coherently enhanced terahertz radiation sources

Yuelin Li and Kwang-Je Kim

Appl. Phys. Lett. 92, 014101 (2008); http://dx.doi.org/10.1063/1.2828337 (3 pages) | Cited 10 times

Online Publication Date: 2 January 2008

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We propose to generate a train of prebunched electron beams for producing coherently enhanced Smith-Purcell radiation [ S. J. Smith and E. M. Purcell, Phys. Rev. 92, 1069 (1953) ] in the terahertz wavelength range. In this scheme, a train of picosecond laser pulses is produced to drive a photoemission gun to generate a train of 50 keV electron pulses. The parameters are chosen so that the space-charge effect does not destroy the pulse time structure. Smith-Purcell radiation from the electron pulse train is enhanced due both to the short length of the individual electron bunch and to the repetitive structure of the beam. Example systems producing coherent terahertz power at about 1 mW are described.
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07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
41.75.Fr Electron and positron beams

Femtosecond laser heat affected zones profiled in Co/Si multilayer thin films

Yoosuf N. Picard and Steven M. Yalisove

Appl. Phys. Lett. 92, 014102 (2008); http://dx.doi.org/10.1063/1.2832640 (3 pages) | Cited 1 time

Online Publication Date: 8 January 2008

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In this letter, we describe an approach for assessing collateral thermal damage resulting from high intensity, femtosecond laser irradiation. Polycrystalline Co thin films deposited on Si (100) substrates and buried under an amorphous Si film were prepared for plan-view transmission electron microscopy (TEM) prior to laser irradiation by femtosecond laser pulses. A heat affected zone (HAZ) resulting from single pulse irradiation at a fluence of 0.9 J/cm2 was determined by TEM imaging and point-wise selected area diffraction. The spatially Gaussian laser pulse generated a HAZ extending up to 3 μm radially from the femtosecond laser irradiated region.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Bg Metals and alloys
68.65.Ac Multilayers
78.47.J- Ultrafast spectroscopy (<1 psec)

General analytical solution for photoacoustic effect with multilayers

Hanping Hu, Wei Zhang, Jun Xu, and Yi Dong

Appl. Phys. Lett. 92, 014103 (2008); http://dx.doi.org/10.1063/1.2828695 (3 pages) | Cited 1 time

Online Publication Date: 8 January 2008

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A general solution of the photoacoustic (PA) effect with multilayers is derived by using a fully thermally-mechanically coupled PA model. This expression takes thermal, mechanical, optical, and geometry properties of multilayers, as well as the thermal contact resistances between layers into consideration. The PA frequency is extended to the ultrasonic region. Therefore, the PA effect at high frequency and laser induced ultrasonic wave in multilayers can also be studied.
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78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
68.65.Ac Multilayers
73.40.Cg Contact resistance, contact potential
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
62.65.+k Acoustical properties of solids

Electrical conductivity of thermoresponsive shape-memory polymer with embedded micron sized Ni powder chains

J. S. Leng, X. Lan, Y. J. Liu, S. Y. Du, W. M. Huang, N. Liu, S. J. Phee, and Q. Yuan

Appl. Phys. Lett. 92, 014104 (2008); http://dx.doi.org/10.1063/1.2829388 (3 pages) | Cited 32 times

Online Publication Date: 8 January 2008

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The electrical resistivity of a thermoresponsive polyurethane shape-memory polymer (SMP) filled with micron sized Ni powders is investigated in this letter. We show that, by forming conductive Ni chains under a weak static magnetic field (0.03 T), the electrical conductivity of the SMP composite in the chain direction can be improved significantly, which makes it more suitable for Joule heat induced shape recovery. In addition, Ni chains reinforce the SMP significantly but their influence on the glass transition temperature is about the same as that of the randomly distributed Ni powders.
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81.05.Qk Reinforced polymers and polymer-based composites
72.80.Tm Composite materials
81.40.Lm Deformation, plasticity, and creep
64.70.pj Polymers
64.70.km Polymers
62.20.fg Shape-memory effect; yield stress; superelasticity

Optical manipulation of paramagnetic particles with on-chip detection using spin valve sensors

L. W. Y. Lui, K. B. Li, S. J. O’Shea, and C. H. Sow

Appl. Phys. Lett. 92, 014105 (2008); http://dx.doi.org/10.1063/1.2829797 (3 pages)

Online Publication Date: 9 January 2008

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In this work, we present a combinatory approach where optical tweezers were used to trap and position a single superparamagnetic particle over a spin valve sensor, with the particle then detected by the sensor. This approach is demonstrated using superparamagnetic particles of 2 μm together with a spin valve sensor with dimensions of 2×4 μm2, whereby a single magnetic particle was positioned over the sensor and a corresponding drop in the voltage across the sensor was detected. The results are explained using a simple model where the particle is treated as a pure magnetic dipole.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
75.47.De Giant magnetoresistance
75.30.Cr Saturation moments and magnetic susceptibilities

Optical switching based on high-speed phased array optical beam steering

Mona Jarrahi, R. Fabian W. Pease, David A. B. Miller, and Thomas H. Lee

Appl. Phys. Lett. 92, 014106 (2008); http://dx.doi.org/10.1063/1.2831005 (3 pages) | Cited 8 times

Online Publication Date: 10 January 2008

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We present a high-speed optical switching scheme based on phased array optical beam steering, and analyze the trade-off between the switch power efficiency, signal-to-noise-ratio, number of output channels, and switching speed. For the proof of concept, a two-channel optical switch has been fabricated, using a high-speed GaAs/AlGaAs multiple quantum well phase modulator. We demonstrate a beam deflection angle of 100 mrad at the fastest ever reported speed of 18 GHz, consuming 1.8 mW. A signal-to-noise ratio of 8 dB is measured at each output channel. The relatively low signal-to-noise ratio can be further improved by increasing the number of phased arrays.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Piezoelectric ultrasonic bidirectional linear actuator for micropositioning fulfilling Feynman’s criteria

James Friend, Leslie Yeo, and Matt Hogg

Appl. Phys. Lett. 92, 014107 (2008); http://dx.doi.org/10.1063/1.2814044 (3 pages) | Cited 11 times

Online Publication Date: 11 January 2008

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A bidirectional linear microactuator with a stator less than 400 μm3, fulfilling Feynman’s original criteria for a motor less than 1/64th of an inch on a side [ R. Feynman, Engineering and Science Magazine (Caltech) 4, 23 (1960) ], is shown to generate forces over 30 mN in either direction at speeds of up to 40 mm/s using a large 28 g polished alumina slider. Using the thickness mode of a stepped piezoelectric block in conjunction with a pair of fundamental flexural modes of a pair of slanted beams—each slightly differs in configuration—gives the ability to generate silent bidirectional motion at an excitation frequency of about 1.7 MHz. In addition to offering forces at least one order of magnitude larger than those of the other methods, the system also serves as a platform for studying nonlinear frictional phenomena on the nanoscale and its manipulation through acoustic irradiation of the contact interface for propulsion.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
06.60.Sx Positioning and alignment; manipulating, remote handling

Tuning of the electrical parameters of a twisted-nematic display material by using electron beam irradiation

R. Dhar, Rohit Verma, M. C. Rath, S. K. Sarkar, V. K. Wadhawan, R. Dabrowski, and M. Tykarska

Appl. Phys. Lett. 92, 014108 (2008); http://dx.doi.org/10.1063/1.2829882 (3 pages) | Cited 7 times

Online Publication Date: 11 January 2008

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Electron beam irradiation studies on 4′-pentyl-4-cyanobiphenyl (5CB) have been carried out. Dielectric measurements demonstrate that even a low level of irradiation (beyond a critical dose of ∼ 6 kGy) results in a dramatic increase in the transverse component of the dielectric permittivity, and a corresponding decrease in the dielectric anisotropy. It is shown that the changes in dielectric parameters due to the irradiation can be fruitfully utilized to control the display performance of the device to a certain extent. The observed change in the dielectric parameters is attributed to the formation of a donor-acceptor type charge-transfer complex due to the irradiation.
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42.79.Kr Display devices, liquid-crystal devices
61.80.Fe Electron and positron radiation effects
77.22.Ch Permittivity (dielectric function)
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