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12 Jan 2009

Volume 94, Issue 2, Articles (02xxxx)

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Appl. Phys. Lett. 94, 022101 (2009); http://dx.doi.org/10.1063/1.3065067 (3 pages)

Hong Li and Qing Zhang
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Electrothermal ac electro-osmosis

Zachary R. Gagnon and Hsueh-Chia Chang

Appl. Phys. Lett. 94, 024101 (2009); http://dx.doi.org/10.1063/1.3020720 (3 pages) | Cited 5 times

Online Publication Date: 13 January 2009

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Two ac polarization mechanisms, charge accumulation due to electrode double layer charging and bulk permittivity/conductivity gradients generated by Joule heating, are combined in the double layer by introducing zwitterions to produce a new ac electrokinetic pump with the largest velocity (>1 mm/s) and flow penetration depth (100 μm) reported for low-conductivity fluids. The large fluid velocity is due to a quartic scaling with respect to voltage, as is true of electrothermal flow, but exhibits a clear maximum at a frequency corresponding to the electrode double layer inverse RC time.
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82.39.Wj Ion exchange, dialysis, osmosis, electro-osmosis, membrane processes
82.45.Fk Electrodes

Transmitting high power rf acoustic radiation via fluid couplants into superstrates for microfluidics

Ryan P. Hodgson, Ming Tan, Leslie Yeo, and James Friend

Appl. Phys. Lett. 94, 024102 (2009); http://dx.doi.org/10.1063/1.3049128 (3 pages) | Cited 12 times

Online Publication Date: 13 January 2009

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In this study, surface acoustic radiation is refracted from lithium niobate through a fluid coupling into a thin glass plate. We demonstrate and explain its propagation as an asymmetric Lamb wave along the glass plate with sufficient power to transport fluid droplets across the glass surface at 8 mm/s. Such technology enables the use of standard processing techniques to fabricate an inexpensive and disposable microfluidics device together with the power transmission capabilities of surface acoustic wave devices with an easily renewable coupling.
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77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
47.61.-k Micro- and nano- scale flow phenomena
43.25.-x Nonlinear acoustics
43.35.-c Ultrasonics, quantum acoustics, and physical effects of sound

Enhanced growth of high quality single crystal diamond by microwave plasma assisted chemical vapor deposition at high gas pressures

Qi Liang, Cheng Yi Chin, Joseph Lai, Chih-shiue Yan, Yufei Meng, Ho-kwang Mao, and Russell J. Hemley

Appl. Phys. Lett. 94, 024103 (2009); http://dx.doi.org/10.1063/1.3072352 (3 pages) | Cited 5 times

Online Publication Date: 13 January 2009

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Single crystals of diamond up to 18 mm in thickness have been grown by microwave plasma assisted chemical vapor deposition at gas pressures of up to 350 torr. Growth rates of up to 165 μm/h at 300 torr at high power density have been achieved. The processes were evaluated by optical emission spectroscopy. The high-quality single-crystal diamond grown at optimized conditions was characterized by UV-visible absorption and photoluminescence spectroscopy. The measurements reveal a direct relationship between residual absorption and nitrogen content in the gas chemistry. Fabrication of high quality single-crystal diamond at higher growth rates should be possible with improved reactor design that allows still higher gas synthesis pressures.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.40.Ha Other nonmetallic inorganics
81.05.U- Carbon/carbon-based materials
78.55.Hx Other solid inorganic materials
62.50.-p High-pressure effects in solids and liquids
52.77.Dq Plasma-based ion implantation and deposition

Microwave-induced water flows in microsystems

A. Ramos, A. Robles, P. García-Sánchez, and M. J. Freire

Appl. Phys. Lett. 94, 024104 (2009); http://dx.doi.org/10.1063/1.3070521 (3 pages) | Cited 4 times

Online Publication Date: 14 January 2009

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Alternating current electric fields are of increasing importance for the development of microfluidic pumps. We report how microwave fields can induce water flow in microsystems, irrespective of saline concentration. A drop of water is placed on two parallel coplanar microelectrodes that are energized by a microwave generator. Fluid flow is observed and the fluid velocity is about the same for two electrolytes with very different saline concentrations. Electrically induced gradients of temperature produce spatial variations in mass density and dielectric permittivity leading, respectively, to buoyancy and dielectric forces in the liquid. The observed fluid flow patterns demonstrate that both effects are taking place at different length scales: the dielectric forces dominate at lengths of the order of 100 μm or smaller, while buoyancy dominates around 1 mm.
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47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
47.55.D- Drops and bubbles
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