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10 Aug 2009

Volume 95, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 95, 062501 (2009); http://dx.doi.org/10.1063/1.3200226 (3 pages)

O. Vávra, W. Pfaff, and Ch. Strunk
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Electrical behavior of nematic cells oriented by polypyrrole surface treatment

A. L. Alexe-Ionescu, G. Barbero, C. Dascalu, and M. Scalerandi

Appl. Phys. Lett. 95, 064101 (2009); http://dx.doi.org/10.1063/1.3196766 (3 pages) | Cited 1 time

Online Publication Date: 10 August 2009

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We have studied the electrical response of nematic liquid crystal cells with uniform planar alignment imposed by ClO4− doped polypyrrole layers. From the measured electrical current on a resistance in series with the nematic sample when applying a triangular potential with different periods and amplitudes, the diffusion of the ions from the polypyrrole layer into the liquid crystal was evidenced. The sample is described as an insulating liquid containing a distribution of ions depending on the characteristics of the applied external field and also of the polymer layers. A simple model concerning the diffusion of the ions from the aligning doped polypyrrole film inside the liquid crystal is proposed. The agreement between experimental data and numerical results is good.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
66.10.C- Diffusion and thermal diffusion

High contact angle hysteresis of superhydrophobic surfaces: Hydrophobic defects

Feng-Ming Chang, Siang-Jie Hong, Yu-Jane Sheng, and Heng-Kwong Tsao

Appl. Phys. Lett. 95, 064102 (2009); http://dx.doi.org/10.1063/1.3204006 (3 pages) | Cited 14 times

Online Publication Date: 11 August 2009

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A typical superhydrophobic surface is essentially nonadhesive and exhibits very low water contact angle (CA) hysteresis, so-called Lotus effect. However, leaves of some plants such as scallion and garlic with an advancing angle exceeding 150° show very serious CA hysteresis. Although surface roughness and epicuticular wax can explain the very high advancing CA, our analysis indicates that the unusual hydrophobic defect, diallyl disulfide, is the key element responsible for contact line pinning on allium leaves. After smearing diallyl disulfide on an extended polytetrafluoroethylene (PTFE) film, which is originally absent of CA hysteresis, the surface remains superhydrophobic but becomes highly adhesive.
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68.03.Cd Surface tension and related phenomena
68.08.Bc Wetting

Substrate Fermi level effects in photocatalysis on oxides: Properties of ultrathin TiO2/Si films

D. Kazazis, S. Guha, N. A. Bojarczuk, A. Zaslavsky, and H.-C. Kim

Appl. Phys. Lett. 95, 064103 (2009); http://dx.doi.org/10.1063/1.3196314 (3 pages) | Cited 1 time

Online Publication Date: 11 August 2009

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Photocatalysis has widespread applications from solar cells to photolithography. We studied the photocatalytic properties of TiO2 films of thicknesses down to 2 nm, grown on n-type and p-type silicon wafers, using the oxidation of isopropanol as a model system. Direct in vacuo mass spectrometry measurements were performed under irradiation above the TiO2 bandgap. We present a model consistent with our experimental results, which indicate that only near-surface electron-hole pair generation is relevant and that the reaction rate can be controlled by varying the substrate Fermi level in going from n-type to p-type silicon, by approximately a factor of 2.
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68.55.A- Nucleation and growth
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
71.20.Ps Other inorganic compounds
82.50.Hp Processes caused by visible and UV light
84.60.Jt Photoelectric conversion
61.72.jd Vacancies
68.55.jd Thickness
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
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