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9 Jul 2007

Volume 91, Issue 2, Articles (02xxxx)

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Appl. Phys. Lett. 91, 023101 (2007); http://dx.doi.org/10.1063/1.2755879 (3 pages)

M. Fendrich and T. Kunstmann
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Influences of submonolayer proteins on organic light-emitting diodes

Wataru Mizutani, Kiyomi Tsukagoshi, Koichi Sakaguchi, Masayuki Chikamatsu, and Yuji Yoshida

Appl. Phys. Lett. 91, 024101 (2007); http://dx.doi.org/10.1063/1.2755920 (3 pages)

Online Publication Date: 9 July 2007

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The authors sandwiched protein molecules into the layered structure of organic light-emitting diodes (OLEDs). Light emission from the OLEDs was suppressed on the area with the protein submonolayers of 4–7 nm thick. They found that this suppression depended on the density of the proteins and light emission efficiency reflected molecular properties. A bovine serum albumin layer decreased both the current and light emission, keeping the efficiency almost unchanged. In the case of cytochrome C, the emission was suppressed while current increased, resulting in low efficiency.
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87.14.E- Proteins
87.15.M- Spectra of biomolecules
85.60.Jb Light-emitting devices

Positronium annihilation and pore surface chemistry in mesoporous silica films

Chunqing He, Toshitaka Oka, Yoshinori Kobayashi, Nagayasu Oshima, Toshiyuki Ohdaira, Atsushi Kinomura, and Ryoichi Suzuki

Appl. Phys. Lett. 91, 024102 (2007); http://dx.doi.org/10.1063/1.2756310 (3 pages) | Cited 4 times

Online Publication Date: 10 July 2007

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Lifetimes of ortho-positronium in mesoporous silica films were measured before and after surface trimethylsilylation of –OH groups. Variations of positronium lifetimes in the mesopores upon the surface modification indicate that the interaction between positronium and the pore surface is weakened in the pores, whose surface is covered with –CH3 groups, in comparison with those covered with –OH groups. This is consistent with the authors’ previous observation that positronium slowing down is less efficient in the pores covered with –CH3 groups. The present work demonstrates that in the porosimetric application of positron annihilation lifetime spectroscopy, the interaction between positronium and the pore surface has to be properly taken into consideration.
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78.70.Bj Positron annihilation
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
61.43.Gt Powders, porous materials
61.80.Fe Electron and positron radiation effects

Nonwoven electrowetting textiles

K. Bhat, J. Heikenfeld, M. Agarwal, Y. Lvov, and K. Varahramyan

Appl. Phys. Lett. 91, 024103 (2007); http://dx.doi.org/10.1063/1.2753750 (3 pages) | Cited 3 times

Online Publication Date: 11 July 2007

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Electrowetting of two nonwoven textile platforms is reported. Demonstrated nonwoven textiles include a polyethylene naphthalate film that was laser milled with ∼ 125 μm pores, and pressed paper that was made using wood microfibers of 35–50 μm diameter. Vacuum deposition provided an Al electrode on the polymer textile whereas layer-by-layer nanoassembly provided an organic PEI-PEDOT:PSS electrode on the wood microfibers. Both textiles were electrically insulated with parylene C and fluoropolymer. Irreversible electrowetting of water was achieved over contact angles of ∼ 120° to ∼ 70° by applying 0–100 V. Completely reversible electrowetting of water/oil was also demonstrated.
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68.08.Bc Wetting
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
42.62.-b Laser applications
61.46.-w Structure of nanoscale materials
68.03.Cd Surface tension and related phenomena

High friction interface with pseudoelastic NiTi

S. Chatterjee and G. P. Carman

Appl. Phys. Lett. 91, 024104 (2007); http://dx.doi.org/10.1063/1.2751608 (3 pages)

Online Publication Date: 12 July 2007

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The purpose of this letter is to introduce a mechanism that relies on a stress induced phase transformation to generate a large static friction coefficient (μf). Tribological principles were used to design a frictional interface with pseudoelastic nickel titanium (NiTi) and stainless steel with etched features. At loads large enough to form stress induced martensite increasing the applied load increased μf values. This indicates that mechanical friction instead of adhesive friction may be the dominant mechanism. Using a mechanical model combined with experimental mechanical data, the authors we estimate that μf = 0.7 is achievable without substantial plastic deformation.
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68.35.Gy Mechanical properties; surface strains
81.40.Pq Friction, lubrication, and wear
81.40.Lm Deformation, plasticity, and creep
64.70.K- Solid-solid transitions
62.20.F- Deformation and plasticity
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