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12 Mar 2007

Volume 90, Issue 11, Articles (11xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 113108 (2007); http://dx.doi.org/10.1063/1.2714186 (3 pages)

Samuel L. Mensah, Vijaya K. Kayastha, Ilia N. Ivanov, David B. Geohegan, and Yoke Khin Yap
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Prospects for electron imaging with ultrafast time resolution

Michael R. Armstrong, Bryan W. Reed, Ben R. Torralva, and Nigel D. Browning

Appl. Phys. Lett. 90, 114101 (2007); http://dx.doi.org/10.1063/1.2712838 (3 pages) | Cited 13 times

Online Publication Date: 13 March 2007

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Many pivotal aspects of material science, biomechanics, and chemistry would benefit from nanometer imaging with ultrafast time resolution. Here the authors demonstrate the feasibility of short-pulse electron imaging with 10 nm/10 ps spatiotemporal resolution, sufficient to characterize phenomena that propagate at the speed of sound in materials (1–10 km/s) without smearing. The authors outline resolution-degrading effects that occur at high current density followed by strategies to mitigate these effects. Finally, the authors present a model electron imaging system that achieves 10 nm/10 ps spatiotemporal resolution.
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61.05.jd Theories of electron diffraction and scattering

Three-image diffraction enhanced imaging algorithm to extract absorption, refraction, and ultrasmall-angle scattering

Luigi Rigon, Fulvia Arfelli, and Ralf-Hendrik Menk

Appl. Phys. Lett. 90, 114102 (2007); http://dx.doi.org/10.1063/1.2713147 (3 pages) | Cited 20 times

Online Publication Date: 13 March 2007

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As different methods to improve diffraction enhanced imaging are proposed, the authors introduce a simple algorithm that follows the original idea of Chapman et al. [Phys. Med. Biol. 42, 2015 (1997)] , but extend it to a general object featuring absorption, refraction, and ultrasmall-angle scattering. The information relative to the three effects is decoupled, requiring only three images in input. Simulation and experiment give accurate results, provided the refraction and scattering angles are small compared to the rocking curve width. The proposed algorithm can be readily and fruitfully implemented in several applications, particularly when time and dose constraints are relevant.
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07.60.-j Optical instruments and equipment
42.25.Fx Diffraction and scattering

Changes in microbubble dynamics near a boundary revealed by combined optical micromanipulation and high-speed imaging

V. Garbin, D. Cojoc, E. Ferrari, E. Di Fabrizio, M. L. J. Overvelde, S. M. van der Meer, N. de Jong, D. Lohse, and M. Versluis

Appl. Phys. Lett. 90, 114103 (2007); http://dx.doi.org/10.1063/1.2713164 (3 pages) | Cited 38 times

Online Publication Date: 13 March 2007

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The authors report optical observations of the change in the dynamics of one and the same ultrasound contrast agent microbubble due to the influence of interfaces and neighboring bubbles. The bubble is excited by a 2.25 MHz ultrasound burst and its oscillations are recorded with an ultrahigh-speed camera at 15 million frames per second. The position of an individual bubble relative to a rigid wall or second bubble is precisely controlled using optical tweezers based on Laguerre-Gaussian laser beams [ P. Prentice et al., Opt. Express 12, 593 (2004) ; V. Garbin et al., Jpn. J. Appl. Phys. 44, 5773 (2005) ]. This allows for repeated experiments on the very same bubble and for a quantitative comparison of the effect of boundaries on bubble behavior.
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42.50.-p Quantum optics
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
47.55.dd Bubble dynamics
47.80.Jk Flow visualization and imaging

Influence of crystallite size on the thermal conductivity in BaTiO3 nanoceramics

A. Jeżowski, J. Mucha, R. Pazik, and W. Strek

Appl. Phys. Lett. 90, 114104 (2007); http://dx.doi.org/10.1063/1.2711195 (3 pages) | Cited 6 times

Online Publication Date: 14 March 2007

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The grain size effect on the thermal conductivity in BaTiO3 nanoceramics was investigated. The nanoceramics were produced by the low temperature high pressure technique. The averaged sizes of grain varied from 30 to 100 nm. It was found that the thermal conductivity of BaTiO3 nanoceramics decreased with decreasing the grain sizes. For the smallest grains the thermal conductivity was similar to the glasslike materials, whereas for larger grains it behaved as in crystalline dielectrics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
61.46.-w Structure of nanoscale materials
77.80.-e Ferroelectricity and antiferroelectricity

Automatic navigation of an untethered device in the artery of a living animal using a conventional clinical magnetic resonance imaging system

Sylvain Martel, Jean-Baptiste Mathieu, Ouajdi Felfoul, Arnaud Chanu, Eric Aboussouan, Samer Tamaz, Pierre Pouponneau, L’Hocine Yahia, Gilles Beaudoin, Gilles Soulez, and Martin Mankiewicz

Appl. Phys. Lett. 90, 114105 (2007); http://dx.doi.org/10.1063/1.2713229 (3 pages) | Cited 37 times

Online Publication Date: 14 March 2007

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The feasibility for in vivo navigation of untethered devices or robots is demonstrated with the control and tracking of a 1.5 mm diameter ferromagnetic bead in the carotid artery of a living swine using a clinical magnetic resonance imaging (MRI) platform. Navigation is achieved by inducing displacement forces from the three orthogonal slice selection and signal encoding gradient coils of a standard MRI system. The proposed method performs automatic tracking, propulsion, and computer control sequences at a sufficient rate to allow navigation along preplanned paths in the blood circulatory system. This technique expands the range of applications in MRI-based interventions.
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87.61.Ff Instrumentation
87.80.-y Biophysical techniques (research methods)
87.19.U- Hemodynamics
87.19.Wx Pneumodyamics, respiration
07.07.Tw Servo and control equipment; robots

Wafer-level filling of microfabricated atomic vapor cells based on thin-film deposition and photolysis of cesium azide

Li-Anne Liew, John Moreland, and Vladislav Gerginov

Appl. Phys. Lett. 90, 114106 (2007); http://dx.doi.org/10.1063/1.2712501 (3 pages) | Cited 9 times

Online Publication Date: 15 March 2007

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The thin-film deposition and photodecomposition of cesium azide are demonstrated and used to fill arrays of miniaturized atomic resonance cells with cesium and nitrogen buffer gas for chip-scale atomic-based instruments. Arrays of silicon cells are batch fabricated on wafers into which cesium azide is deposited by vacuum thermal evaporation. After vacuum sealing, the cells are irradiated with ultraviolet radiation, causing the azide to photodissociate into pure cesium and nitrogen in situ. This technology integrates the vapor-cell fabrication and filling procedures into one continuous and wafer-level parallel process, and results in cells that are optically transparent and chemically pure.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
85.40.Sz Deposition technology
82.50.Hp Processes caused by visible and UV light
37.20.+j Atomic and molecular beam sources and techniques

Design of a crystalline undulator based on patterning by tensile Si3N4 strips on a Si crystal

V. Guidi, L. Lanzoni, A. Mazzolari, G. Martinelli, and A. Tralli

Appl. Phys. Lett. 90, 114107 (2007); http://dx.doi.org/10.1063/1.2712510 (3 pages) | Cited 3 times

Online Publication Date: 15 March 2007

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A crystalline undulator consists of a crystal with a periodic deformation in which channeled particles undergo oscillations and emit coherent undulator radiation. Patterning by an alternate series of tensile Si3N4 strips on a Si crystal is shown to be a tractable method to construct a crystalline undulator. The method allows periodic deformation of the crystal with the parameters suitable for implementation of a crystalline undulator. The resulting periodic deformation is present in the bulk of the Si crystal with an essentially uniform amplitude, making the entire volume of the crystal available for channeling and in turn for emission of undulator radiation.
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61.85.+p Channeling phenomena (blocking, energy loss, etc.)
78.70.-g Interactions of particles and radiation with matter
68.60.Bs Mechanical and acoustical properties
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Prototype dispenser photocathode: Demonstration and comparison to theory

N. A. Moody, K. L. Jensen, D. W. Feldman, P. G. O’Shea, and E. J. Montgomery

Appl. Phys. Lett. 90, 114108 (2007); http://dx.doi.org/10.1063/1.2713341 (3 pages) | Cited 12 times

Online Publication Date: 15 March 2007

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A method to significantly extend the operational lifetime of alkali-based photocathodes by diffusing cesium to the surface at moderate temperature is presented and shown to restore the quantum efficiency (QE) of cesiated tungsten. Experimental measurements of QE as a function of surface cesium coverage compare exceptionally well with a recent theoretical photoemission model, notably without the use of adjustable parameters. A prototype cesium dispenser cell is demonstrated and validates the concept upon which long-life dispenser photocathodes can be based.
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85.60.Ha Photomultipliers; phototubes and photocathodes

Scaling of interface displacement in a microfluidic comparator

S. A. Vanapalli, D. van den Ende, M. H. G. Duits, and F. Mugele

Appl. Phys. Lett. 90, 114109 (2007); http://dx.doi.org/10.1063/1.2713800 (3 pages) | Cited 5 times

Online Publication Date: 15 March 2007

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The authors quantify both experimentally and theoretically the scaling behavior between interface displacement and excess pressure drop in a microfluidic comparator. Unlike previous studies, the authors measure the interface displacement in the outlet channel of the comparator that yields a unique power-law scaling. For an outlet channel width to depth ratio r = 3, the authors experimentally determine the scaling exponent to be 0.60±0.01, which is in excellent agreement with theory. In general, the authors find the scaling exponent to increase from 0.51 for square channels (r = 1) to 0.93 for very wide channels (r>100). This geometry dependent scaling exponent offers greater sensitivity and flexibility in measurement of hydrodynamic resistance of soft objects.
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47.85.Np Fluidics
47.85.Dh Hydrodynamics, hydraulics, hydrostatics
47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)
47.60.-i Flow phenomena in quasi-one-dimensional systems
07.10.Cm Micromechanical devices and systems

Microcantilever mechanics in flowing viscous fluids

Anirban Jana, Arvind Raman, Babita Dhayal, Steven L. Tripp, and Ronald G. Reifenberger

Appl. Phys. Lett. 90, 114110 (2007); http://dx.doi.org/10.1063/1.2713238 (3 pages) | Cited 6 times

Online Publication Date: 16 March 2007

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Microcantilevers are often deployed in flowing fluids to measure local flow velocities or to detect rapidly the nanomechanical binding of trace quantities of target analytes. The authors investigate the flow-induced mechanics of microcantilevers by deriving a semianalytical theoretical model for the nanoscale deflections of an elastic microcantilever due to a laminar viscous flow incident upon it. Conversely, the model allows for the estimation of the local flow velocities based on measured microcantilever deflection. Careful experiments performed on silicon microcantilevers in flowing nitrogen confirm the theoretical predictions up to a critical flow rate, beyond which unsteady flow-induced vibrations are seen to occur.
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47.85.Np Fluidics
47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)
47.15.Rq Laminar flows in cavities, channels, ducts, and conduits
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.15.Fe Stability of laminar flows
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