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10 Mar 2008

Volume 92, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 92, 102101 (2008); http://dx.doi.org/10.1063/1.2890735 (3 pages)

Qing Wan, Jin Huang, Zhong Xie, Taihong Wang, Eric N. Dattoli, and Wei Lu
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Stable freestanding thin films of pure water

B. M. Weon, J. H. Je, Y. Hwu, and G. Margaritondo

Appl. Phys. Lett. 92, 104101 (2008); http://dx.doi.org/10.1063/1.2892078 (2 pages) | Cited 5 times

Online Publication Date: 10 March 2008

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Obtaining water microstructures is very difficult because of low viscosity and high surface tension. We produced stable freestanding thin films of pure water by x-ray bombardment of small liquid volumes in capillary tubes. A detailed characterization with phase-contrast radiology demonstrated a lifetime beyond 1 h with no chemical stabilizer for micron-thickness films with half-millimeter-level diameter. This can be attributed to the interplay of two x-ray effects: water evaporation and surface charging.
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68.15.+e Liquid thin films
68.03.Fg Evaporation and condensation of liquids
64.70.fm Thermodynamics studies of evaporation and condensation
61.25.Em Molecular liquids
61.80.Cb X-ray effects

Probing epitaxial growth of graphene on silicon carbide by metal decoration

Siew Wai Poon, Wei Chen, Eng Soon Tok, and Andrew T. S. Wee

Appl. Phys. Lett. 92, 104102 (2008); http://dx.doi.org/10.1063/1.2883941 (3 pages) | Cited 19 times

Online Publication Date: 10 March 2008

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Using Co-decoration technique coupled with in situ scanning tunneling microscope (STM), the evolution of epitaxial graphene was found to preferentially begin at step edges of the silicon carbide surface and occurs with loss of Si and breakdown of C-rich (6math×6math)R30° template, which provides the C source for graphene growth. Interestingly, a new C-rich phase is also formed at the interface and it acts as a buffer layer for graphene from underlying bulk. STM reveals that graphene lies 2.3±0.3 Å above the buffer layer, larger than sp3 C–C bond length (1.54 Å) but shorter than graphite interlayer separation (3.37 Å), suggesting a pseudo-van der Waals interfacial interaction.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.55.A- Nucleation and growth
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Acoustic-counterflow microfluidics by surface acoustic waves

Marco Cecchini, Salvatore Girardo, Dario Pisignano, Roberto Cingolani, and Fabio Beltram

Appl. Phys. Lett. 92, 104103 (2008); http://dx.doi.org/10.1063/1.2889951 (3 pages) | Cited 18 times

Online Publication Date: 10 March 2008

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In this letter, we demonstrate an unexpected surface-acoustic-wave (SAW)-driven pumping effect in hydrophobic polydimethilsiloxane (PDMS)-lithium niobate (LiNbO3) microchannels. Atomization within the fluidic channel followed by SAW-assisted coalescence leads to liquid counterflow with respect to the SAW propagation direction. This physical mechanism is contrasted with the acoustic-streaming process driving isolated drop displacement on piezoelectric substrates. This principle is shown not to be readily applicable to the present microchannel case. The proposed device geometry can be exploited to integrate micropumps into complex microfluidic chips, improving the portability of micro-total-analysis systems.
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47.60.Dx Flows in ducts and channels
68.35.Iv Acoustical properties
77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

A scanning near-field middle-infrared microscope for the study of objects submerged in water

Max Platkov, Alexander Tsun, Lev Nagli, and Abraham Katzir

Appl. Phys. Lett. 92, 104104 (2008); http://dx.doi.org/10.1063/1.2891060 (3 pages) | Cited 2 times

Online Publication Date: 11 March 2008

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We had developed a scanning near-field middle-infrared microscope, based on AgClBr probes, which has a subwavelength resolution in air. We adapted this microscope for imaging of samples submerged in water. Toward this goal, we had to develop a theoretical model for the mechanical vibration of the probes in water and use it for the construction of an improved microscope. Using this system, we obtained infrared and topographic images of polymer beads of subwavelength diameters. This microscope will be particularly useful for high resolution spectral imaging of living biological cells in the middle infrared.
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07.79.Fc Near-field scanning optical microscopes
61.41.+e Polymers, elastomers, and plastics

Electrohydrodynamic size stratification and flow separation of giant vesicles

S. Lecuyer, W. D. Ristenpart, O. Vincent, and H. A. Stone

Appl. Phys. Lett. 92, 104105 (2008); http://dx.doi.org/10.1063/1.2894182 (3 pages) | Cited 6 times

Online Publication Date: 11 March 2008

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We demonstrate an electrohydrodynamic (EHD) technique for separating giant unilamellar vesicles by size in polydisperse suspensions. An oscillatory electric field ( ∼ 30 Hz) generates EHD flow around each vesicle close to an electrode. Nearby vesicles are entrained in the flow and the vesicles move toward one another. Upon aggregation, smaller vesicles are pulled underneath the larger vesicles, which ultimately lifts them off of the electrode. A brief spike in the electric field then serves to irreversibly adhere the bottom layer of smaller vesicles to the electrode, and the large vesicles are subsequently removed by flow. We demonstrate that a single application of this technique can remove more than 90% of the smallest vesicles (diameter <20 μm) from a suspension of electroformed giant lipid vesicles.
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47.65.-d Magnetohydrodynamics and electrohydrodynamics
47.55.Hd Stratified flows
47.57.eb Diffusion and aggregation
82.70.Kj Emulsions and suspensions

A study of electrostatic force nonlinearities in resonant microstructures

Manu Agarwal, Saurabh A. Chandorkar, Harsh Mehta, Robert N. Candler, Bongsang Kim, Matthew A. Hopcroft, Renata Melamud, Chandra M. Jha, Gaurav Bahl, Gary Yama, Thomas W. Kenny, and Boris Murmann

Appl. Phys. Lett. 92, 104106 (2008); http://dx.doi.org/10.1063/1.2834707 (3 pages) | Cited 4 times

Online Publication Date: 14 March 2008

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This letter investigates the nature of amplitude frequency (A-f) dependence caused by nonlinearities in the parallel plate electrostatic transduced in resonant microstructures. We present analytical and experimental evidences that the A-f nonlinearities are practically always dominated by third order nonlinear terms. For an electrostatically unbalanced system, we show that the bias voltage at which second and third order nonlinearities have equal impact on A-f dependence corresponds to ∼ 90% of the dc pull-in voltage.
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07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Dopant dependent band gap tailoring of hydrothermally prepared cubic SrTixM1−xO3 (M = Ru,Rh,Ir,Pt,Pd) nanoparticles as visible light photocatalysts

Sang Won Bae, Pramod H. Borse, and Jae Sung Lee

Appl. Phys. Lett. 92, 104107 (2008); http://dx.doi.org/10.1063/1.2897300 (3 pages) | Cited 10 times

Online Publication Date: 14 March 2008

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Nanostructured cubic SrTiO3 particles were hydrothermally synthesized and studied experimentally/theoretically for photoreduction of water. The particles were doped with metal atoms (M = Ru,Rh,Ir,Pt,Pd), which acquired high cyrstallinity after thermal treatment. SrTiO3:Rh showed the highest rate of H2  evolution under λ>420 nm photons. The density functional theory calculations of SrTixM1−xO3 (M = Ru,Rh,Ir,Pt) implied that the photocatalytic activity of SrTixRh1−xO3 was due to its suitable band energetics, and the induced hybridized Ti/Rh orbitals in the bandgap of SrTiO3.
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73.22.-f Electronic structure of nanoscale materials and related systems
61.72.up Other materials
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.50.-m Photochemistry
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Mechanical characterization of individual Ni/Au coated microsize polymer particles

Guangbin Dou, David C. Whalley, and Changqing Liu

Appl. Phys. Lett. 92, 104108 (2008); http://dx.doi.org/10.1063/1.2898219 (3 pages) | Cited 3 times

Online Publication Date: 14 March 2008

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We report on a mechanical characterization technique for individual Ni/Au coated microsize polymer particles. This technique allows a clearer understanding of the effects of load force and rate on the particle deformation. This has been achieved through measurements of the deformation against force using a specially configured nanoindenter machine, where the “indenters,” instead of being pointed, had a flat tip of 20 μm in diameter. The results show that the particle deformation process is nonlinear and that the force/deformation at which particle crushing occurs is affected by the load rate. The technique could be used to design/manufacture more effective conductive particles.
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62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
68.35.Gy Mechanical properties; surface strains
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
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