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14 Jan 2008

Volume 92, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 022509 (2008); http://dx.doi.org/10.1063/1.2807274 (3 pages)

Sang-Koog Kim, Ki-Suk Lee, Young-Sang Yu, and Youn-Seok Choi
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Cluster related hole traps with enhanced-field-emission—the source for long term annealing in hadron irradiated Si diodes

I. Pintilie, E. Fretwurst, and G. Lindström

Appl. Phys. Lett. 92, 024101 (2008); http://dx.doi.org/10.1063/1.2832646 (3 pages) | Cited 4 times

Online Publication Date: 14 January 2008

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Cluster related defects were investigated by the thermally stimulated current (TSC) method in neutron irradiated n-type Si diodes during 80 °C annealing. Three hole traps labeled H (116 K), H (140 K), and H (152 K) proved to have an electric-field-enhanced emission characteristic of Coulombic wells. Their zero field emission rates were deduced describing the TSC peaks with the three-dimensional Poole-Frenkel formalism when accounting for the electric field distribution. As acceptors in the lower half of the gap, these centers have a direct impact on the effective doping of the n-type diodes. They are revealed as causing the long term annealing effects.
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85.30.Kk Junction diodes
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
79.70.+q Field emission, ionization, evaporation, and desorption
81.40.Gh Other heat and thermomechanical treatments
61.80.Hg Neutron radiation effects
61.82.Fk Semiconductors

Temperature measurement in microfluidic chips using photobleaching of a fluorescent thin film

Lin Gui and Carolyn L. Ren

Appl. Phys. Lett. 92, 024102 (2008); http://dx.doi.org/10.1063/1.2828717 (3 pages) | Cited 8 times

Online Publication Date: 14 January 2008

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A method for the whole chip temperature measurement is developed and presented here. This method includes two major contributions: (i) a specially developed measurement model illustrating the relationship between the photobleaching speed of a fluorescent dye and its temperature and (ii) an introduction of a thin polydimethylsiloxane film with rhodamine B homogeneously saturated aiming for significantly reducing fluorescent dyes’ absorption to and diffusion into polymer-made channel walls. The developed method is validated by comparing the experimentally measured temperature distribution in a microfluidic chip with the numerically predicted results.
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07.20.Dt Thermometers
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

High-speed x-ray reflectometory in multiwavelength-dispersive mode

Tadashi Matsushita, Yasuhiro Niwa, Yasuhiro Inada, Masaharu Nomura, Masashi Ishii, Kenji Sakurai, and Etsuo Arakawa

Appl. Phys. Lett. 92, 024103 (2008); http://dx.doi.org/10.1063/1.2833690 (3 pages) | Cited 7 times

Online Publication Date: 14 January 2008

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The potential of a high speed x-ray reflectometer for time-resolved studies on the subsecond to millisecond timescales is demonstrated by recording x-ray reflection curves from a small area (1 mm×10 mm) of a 14.3 nm thick gold film on a silicon substrate with data collection times of 0.05–1 s. A horizontally convergent x-ray beam having a one-to-one correlation between ray direction and energy is produced by a curved crystal polychromator, and the beam is incident on and vertically reflected by a specimen placed at the focus. The x-ray reflectivity is measured as a function of the x-ray energy downstream of the focus using a one dimensional detector with no need for angle scan of the specimen and detector.
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07.85.-m X- and γ-ray instruments
61.05.cm X-ray reflectometry (surfaces, interfaces, films)

Self-organized twinning of actuated particles for microfluidic pumping

Roy J. S. Derks, Arjan J. H. Frijns, Menno W. J. Prins, and Andreas H. Dietzel

Appl. Phys. Lett. 92, 024104 (2008); http://dx.doi.org/10.1063/1.2834851 (3 pages) | Cited 4 times

Online Publication Date: 14 January 2008

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The motion of monodisperse particle ensembles in fluidic channels actuated by axial magnetic or gravitation forces is studied. Interactions between particles, fluid, and nearby walls induce unforeseen self-organization phenomena. Superparamagnetic microparticles aligned on a channel axis successively organize toward a stable polytwin system under constant force conditions. In the absence of repelling particle interactions, full contact twinning is observed for particles driven by gravity. The mechanisms of successive twinning and spacing regulation are explained by a one-dimensional model based on the axis flow profile. Related performance enhancements for particle based microfluidic pumping are discussed.
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47.60.-i Flow phenomena in quasi-one-dimensional systems
47.85.Np Fluidics
75.50.Tt Fine-particle systems; nanocrystalline materials

Optoacoustic tomography utilizing focused transducers: The resolution study

T. D. Khokhlova, I. M. Pelivanov, and A. A. Karabutov

Appl. Phys. Lett. 92, 024105 (2008); http://dx.doi.org/10.1063/1.2834855 (3 pages) | Cited 8 times

Online Publication Date: 14 January 2008

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The goal of this work was to investigate numerically the dependence of the resolution and the imaging window size, provided by a cylindrically focused wideband piezoelectric detector in optoacoustic tomography, on the detector dimensions and frequency bandwidth. Analytical expressions found by O’Neil for a continuous spherically focused ultrasonic radiator were found to fit the numerical data accurately to within a constant factor. The range of application and limitations of these expressions were investigated.
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07.64.+z Acoustic instruments and equipment
43.58.+z Acoustical measurements and instrumentation
43.38.+n Transduction; acoustical devices for the generation and reproduction of sound

Diffraction microscopy using 20 kV electron beam for multiwall carbon nanotubes

Osamu Kamimura, Kota Kawahara, Takahisa Doi, Takashi Dobashi, Takashi Abe, and Kazutoshi Gohara

Appl. Phys. Lett. 92, 024106 (2008); http://dx.doi.org/10.1063/1.2834372 (3 pages) | Cited 13 times

Online Publication Date: 15 January 2008

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Diffraction microscopy with iterative phase retrieval using a 20 kV electron beam was carried out to explore the possibility of high-resolution imaging for radiation-sensitive materials. Fine, homogeneous, and isolated multiwall carbon nanotubes (MWCNTs) were used as specimens. To avoid lens aberrations, the diffraction patterns were recorded without a postspecimen lens. One- and two-dimensional iterative phase retrievals were executed. Images reconstructed from the diffraction pattern alone showed a characteristic structure of MWCNTs with the finest feature corresponding to a carbon wall spacing of 0.34 nm.
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61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
42.30.Wb Image reconstruction; tomography
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
61.05.J- Electron diffraction and scattering

Ultrathin films of homeotropically aligned columnar liquid crystals on indium tin oxide electrodes

E. Charlet, E. Grelet, P. Brettes, H. Bock, H. Saadaoui, L. Cisse, P. Destruel, N. Gherardi, and I. Seguy

Appl. Phys. Lett. 92, 024107 (2008); http://dx.doi.org/10.1063/1.2831009 (3 pages) | Cited 16 times

Online Publication Date: 15 January 2008

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We report the achievement of very thin films (thickness of about 50 nm) of thermotropic columnar liquid crystal in homeotropic (columns normal to the interface) orientation on indium tin oxide (ITO) electrodes. The face-on alignment of the discotic compound has been obtained by thermal annealing without any intermediate coating between the mesophase and the ITO substrate. Such a columnar mesophase alignment is thus shown on a substrate of technological interest in open supported thin film reaching the thickness range suitable for organic photovoltaic devices.
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84.60.Jt Photoelectric conversion
42.79.Kr Display devices, liquid-crystal devices
85.60.-q Optoelectronic devices

Reduction of nonspecific surface-particle interactions in optoelectronic tweezers

Hyundoo Hwang, Youngjae Oh, Jae-Jun Kim, Wonjae Choi, Je-Kyun Park, Se-Hwan Kim, and Jin Jang

Appl. Phys. Lett. 92, 024108 (2008); http://dx.doi.org/10.1063/1.2834901 (3 pages) | Cited 11 times

Online Publication Date: 16 January 2008

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We demonstrate three-dimensional optoelectronic tweezers (3D OET) for the adsorption-free manipulation of microparticles. In typical OET, nonspecific interactions between the manipulated particles and the device surfaces, such as hydrophobic, Van der Waals, and electrostatic interactions, interfere with the effective microparticle manipulation. Here, by using the 3D OET device, which is composed of two photoconductive layers, we succeeded in three-dimensional focusing and manipulating polystyrene microbeads in a channel-less microenvironment without the particle adsorption. The 3D OET with the light-induced negative dielectrophoresis also shows a higher particle trapping efficiency and less particle adsorption rate than typical OET.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles
82.45.Wx Polymers and organic materials in electrochemistry

Sound controlled rotation of a cluster of small particles on an ultrasonically vibrating metal strip

Xueyi Zhang, Yun Zheng, and Junhui Hu

Appl. Phys. Lett. 92, 024109 (2008); http://dx.doi.org/10.1063/1.2831660 (3 pages) | Cited 5 times

Online Publication Date: 18 January 2008

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We show that a vibrating metal strip, mechanically driven by an ultrasonic transducer, can rotate a cluster of small particles around a fixed point, and the diameter of the cluster of small particles can reach a stable value (steady diameter) for a given driving condition. The rotation is very stable when the vibration of the metal strip is appropriate. The revolution speed, its direction, and steady diameter of the particle cluster can be controlled by the operating frequency of the ultrasonic transducer. For shrimp eggs, a revolution speed up to 360 rpm can be obtained.
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43.40.Ng Effects of vibration and shock on biological systems, including man
46.40.-f Vibrations and mechanical waves
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