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13 Aug 2007

Volume 91, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 91, 071906 (2007); http://dx.doi.org/10.1063/1.2753092 (3 pages)

Cheng Zhang, Rajiv K. Kalia, Aiichiro Nakano, and Priya Vashishta
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High resolution microresonator-based digital temperature sensor

C. M. Jha, G. Bahl, R. Melamud, S. A. Chandorkar, M. A. Hopcroft, B. Kim, M. Agarwal, J. Salvia, H. Mehta, and T. W. Kenny

Appl. Phys. Lett. 91, 074101 (2007); http://dx.doi.org/10.1063/1.2768629 (3 pages) | Cited 11 times

Online Publication Date: 13 August 2007

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A digital temperature sensing technique using a complementary metal oxide semiconductor (CMOS) compatible encapsulated microresonator is presented. This technique leverages our ability to select the temperature dependence of the resonant frequency for micromechanical silicon resonators by adjusting the relative thickness of a SiO2 compensating layer. A dual-resonator design is described that includes a pair of resonators with differential temperature compensations so that the difference between the two resonant frequencies is a sensitive function of temperature. The authors demonstrate a temperature resolution of approximately 0.008 °C for 1 s averaging time, which is better than that of the best CMOS temperature sensors available today.
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07.10.Cm Micromechanical devices and systems
07.20.Dt Thermometers
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Liquid crystal surface alignments by using ion beam sputtered magnetic thin films

Hsin-Ying Wu and Ru-Pin Pan

Appl. Phys. Lett. 91, 074102 (2007); http://dx.doi.org/10.1063/1.2770763 (3 pages) | Cited 8 times

Online Publication Date: 13 August 2007

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A method for liquid crystal surface alignment by using a one-step, ion beam bombardment of the glass substrates is demonstrated. Precoating by polyimide is not necessary. The authors show that the homeotropic alignment is achieved due to orientation of the diamagnetic nematogenic molecules by the magnetic field from the γ-Fe2O3 ferrimagnetic thin films created on the substrates by ion beam bombardment. The film exhibits a high Curie temperature well above 300 K and a compensation temperature which is the typical feature of ferrimagnetism. This is a simple, noncontact, and reliable alignment method for liquid crystal devices.
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61.30.Cz Molecular and microscopic models and theories of liquid crystal structure
81.15.Cd Deposition by sputtering

Optically actuated thermocapillary movement of gas bubbles on an absorbing substrate

Aaron T. Ohta, Arash Jamshidi, Justin K. Valley, Hsan-Yin Hsu, and Ming C. Wu

Appl. Phys. Lett. 91, 074103 (2007); http://dx.doi.org/10.1063/1.2771091 (3 pages) | Cited 21 times

Online Publication Date: 14 August 2007

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The authors demonstrate an optical manipulation mechanism of gas bubbles for microfluidic applications. Air bubbles in a silicone oil medium are manipulated via thermocapillary forces generated by the absorption of a laser in an amorphous silicon thin film. In contrast to previous demonstrations of optically controlled thermally driven bubble movement, transparent liquids can be used, as the thermal gradient is formed from laser absorption in the amorphous silicon substrate, and not in the liquid. A variety of bubbles with volumes ranging from 19 pl to 23 nl was transported at measured velocities of up to 1.5 mm/s.
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47.55.dm Thermocapillary effects
47.55.nb Capillary and thermocapillary flows
47.55.dr Interactions with surfaces
47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)
47.55.pb Thermal convection
47.85.Np Fluidics

Phase-contrast x-ray imaging with a liquid-metal-jet-anode microfocus source

T. Tuohimaa, M. Otendal, and H. M. Hertz

Appl. Phys. Lett. 91, 074104 (2007); http://dx.doi.org/10.1063/1.2769760 (3 pages) | Cited 14 times

Online Publication Date: 14 August 2007

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Phase-contrast methods increase contrast, detail, and selectivity in x-ray imaging. Present compact x-ray sources do not provide the necessary spatial coherence with sufficient power to allow the laboratory-scale high-resolution phase-contrast imaging with adequate exposure times. In this letter, the authors demonstrate phase-contrast imaging with few-micron detail employing a compact ∼ 6.5 μm spot liquid-metal-jet-anode high-brightness microfocus source. The 40 W source is operated at more than ten times higher electron-beam power density than present microfocus sources and is shown to provide sufficient spatial coherence as well as scalability to high power, thereby enabling the application of phase-contrast x-ray imaging with short exposure times in clinics and laboratories.
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87.59.B- Radiography

Electric field distribution on knife-edge field emitters

Ryan Miller, Y. Y. Lau, and John H. Booske

Appl. Phys. Lett. 91, 074105 (2007); http://dx.doi.org/10.1063/1.2771375 (3 pages) | Cited 27 times

Online Publication Date: 15 August 2007

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Conformal mapping is used to calculate the electric field on a knife-edge cathode, modeled as a rectangular ridge on a flat surface. It is found that the field enhancement factor scales approximately as the square root of the height-to-width ratio of the knife edge. A simple analytic approximation for the divergent electric field in the immediate vicinity of the sharp edge is derived. When a smaller knife edge is placed on top of a larger one, both assumed to have large height-to-width ratios, the composite field enhancement factor is shown to be approximately equal to the product of the field enhancement factor of the individual knife edges, thereby proving the conjecture on multiplication of field enhancement factors for one special case.
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79.70.+q Field emission, ionization, evaporation, and desorption

A coded-aperture technique allowing x-ray phase contrast imaging with conventional sources

Alessandro Olivo and Robert Speller

Appl. Phys. Lett. 91, 074106 (2007); http://dx.doi.org/10.1063/1.2772193 (3 pages) | Cited 31 times

Online Publication Date: 16 August 2007

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Phase contrast imaging (PCI) solves the basic limitation of x-ray imaging, i.e., poor image contrast resulting from small absorption differences. Up to now, it has been mostly limited to synchrotron radiation facilities, due to the stringent requirements on the x-ray source and detectors, and only one technique was shown to provide PCI images with conventional sources but with limits in practical implementation. The authors propose a different approach, based on coded apertures, which provides high PCI signals with conventional sources and detectors and imposes practically no applicability limits. They expect this method to cast the basis of a widespread diffusion of PCI.
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87.59.-e X-ray imaging

Flux locking a superfluid interferometer

Yuki Sato, Aditya Joshi, and Richard Packard

Appl. Phys. Lett. 91, 074107 (2007); http://dx.doi.org/10.1063/1.2772659 (3 pages) | Cited 5 times

Online Publication Date: 16 August 2007

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The authors demonstrate a flux locking technique using injected heat current to linearize the output of a superfluid helium-4 interferometer. A rotation flux through the interferometer loop produces a shift in the phase of the superfluid order parameter. This shift is nullified via negative feedback by a phase shift caused by the injected heat current. The feedback signal is then a linear function of rotation flux.
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07.60.Ly Interferometers
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