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19 May 2008

Volume 92, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 92, 202101 (2008); http://dx.doi.org/10.1063/1.2927379 (3 pages)

Jasmin Aghassi, Matthias H. Hettler, and Gerd Schön
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Collapse of the Förster energy transfer in doped p-hexaphenylene thin films undergoing crystallization

G. Bardizza, R. Caniello, P. Milani, N. Casati, and V. I. Srdanov

Appl. Phys. Lett. 92, 203301 (2008); http://dx.doi.org/10.1063/1.2927355 (3 pages) | Cited 1 time

Online Publication Date: 19 May 2008

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A fluorescence resonant energy transfer study is presented, which uses composition-spread libraries of para-hexaphenylene doped with tris-(8-hydroxyquinolinato)aluminum(III) (p6P:Alq3), prepared by a combinatorial physical vapor deposition technique. The p6P:Alq3 libraries deposited at room temperature are polycrystalline and exhibit an inefficient energy transfer. The energy transfer efficiency increases significantly in amorphous p6P:Alq3 libraries deposited at −78 °C, yielding the Förster transfer radius of 22 Å, in good agreement with the theory. The amorphous p6P:Alq3 libraries undergo slow spontaneous crystallization at room temperature accompanied by a gradual collapse of the energy transfer.
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78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials
64.70.kg Semiconductors
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Near-resonance electro-optic activity enhancement and improved modulation performance for polymer based Fabry–Pérot interferometers

Haiyong Gan, Charles Greenlee, Chuanxiang Sheng, Robert A. Norwood, Mahmoud Fallahi, Shuangxi Wang, Weiping Lin, Michiharu Yamamoto, Kathaperumal Mohanalingam, and Nasser Peyghambarian

Appl. Phys. Lett. 92, 203302 (2008); http://dx.doi.org/10.1063/1.2931086 (3 pages) | Cited 3 times

Online Publication Date: 20 May 2008

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Fabry–Pérot interferometers (FPIs) are designed to work near and off the absorption resonance of an electro-optic (EO) polymer. The near-resonance EO activity (EO coefficient r13 ∼ 25.4 pm/V at ∼ 1086 nm) is enhanced over that off resonance (r13 ∼ 9.0 pm/V at ∼ 1526 nm). The full width at half maximum of the FPI transmission band is ∼ 16 nm near resonance compared to ∼ 22 nm off resonance. The modulation performance can, therefore, be improved with a modulation ratio increased to ∼ 78% near resonance (at 1064 nm) from ∼ 19% off resonance (at 1520 nm). The modulation speed is approximately megahertz and can be increased to greater than gigahertz with improved circuit design.
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07.60.Ly Interferometers
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Insights into the characterization of polymer-based organic thin-film transistors using capacitance-voltage analysis

B. H. Hamadani, C. A. Richter, J. S. Suehle, and D. J. Gundlach

Appl. Phys. Lett. 92, 203303 (2008); http://dx.doi.org/10.1063/1.2917523 (3 pages) | Cited 9 times

Online Publication Date: 21 May 2008

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Frequency dependent capacitance-voltage characteristics of organic thin-film transistors based on poly(3-hexylthiophene) as the active polymer layer are investigated. The frequency response of the channel capacitance in accumulation is examined through an analytical transmission line model, with the effect of contact resistances included in the model to account for deviations from ideal behavior. The model provides an excellent fit to the data. Furthermore, we show that the technique can be used to extract device parameters such as the mobility and the contact resistance and quantitative information on the influence of charge trapping on transport.
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85.30.Tv Field effect devices
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Observation of light-induced reorientational effects in periodic structures with planar nematic-liquid-crystal defects

Urszula A. Laudyn, Andrey E. Miroshnichenko, Wieslaw Krolikowski, Deng Feng Chen, Yuri S. Kivshar, and Miroslaw A. Karpierz

Appl. Phys. Lett. 92, 203304 (2008); http://dx.doi.org/10.1063/1.2936085 (3 pages) | Cited 9 times

Online Publication Date: 22 May 2008

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We report on the experimental studies of the light-induced reorientational effects in a one-dimensional periodic photonic structure with an embedded planar nematic-liquid-crystal defect. We demonstrate that in the presence of a periodic structure, the self-action of light in a liquid-crystal layer demonstrates sharp power-dependent characteristics for the intensity-dependent optical transmission. Robustness of the effect suggests its applications for all-optical tunable photonic devices.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
61.30.Jf Defects in liquid crystals
42.70.Df Liquid crystals
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Effects of interlayers on phosphorescent blue organic light-emitting diodes

Jonghee Lee, Jeong-Ik Lee, Ki-Im Song, Su Jin Lee, and Hye Yong Chu

Appl. Phys. Lett. 92, 203305 (2008); http://dx.doi.org/10.1063/1.2936837 (3 pages) | Cited 31 times

Online Publication Date: 22 May 2008

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We demonstrate that the electroluminescence efficiencies of blue organic light-emitting diodes can be significantly enhanced by the incorporation of interlayers at the hole transporting layer (HTL)/emitting layer (EML) and/or EML/electron transporting layer (ETL) interfaces. Blue light-emitting iridium(III)bis(4,6-difluorophenyl)-pyridinato-N,C2′) picolinate was doped in an m-bis-(triphenylsilyl)benzene (UGH3) host and hole transporting wide band gap materials were introduced between the HTL and the EML as interlayers in order to block triplet exciton quenching and reduce electron overflow. The effects of adding a second undoped UGH3 interlayer at the EML/ETL interface were also studied. When the appropriate interlayers were added, the device performances were found to be dramatically enhanced, with peak external quantum and power efficiencies of 20.1% and 29.2 lm/W.
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85.60.Jb Light-emitting devices
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Threshold voltage shift and formation of charge traps induced by light irradiation during the fabrication of organic light-emitting diodes

Yutaka Noguchi, Naoki Sato, Yuya Tanaka, Yasuo Nakayama, and Hisao Ishii

Appl. Phys. Lett. 92, 203306 (2008); http://dx.doi.org/10.1063/1.2936084 (3 pages) | Cited 20 times

Online Publication Date: 23 May 2008

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We examined the effects of ambient light on the device properties of an organic light-emitting diode, indium tin oxide/4,4′-bis[N-(1-naphthyl)-N-phenylamino]-biphenyl (α-NPD)/tris-(8-hydroxyquinolate) aluminum (Alq3)/Al, during fabrication using displacement current measurement. Light irradiation induces a shift in the threshold voltage for hole injection and results in the formation of charge traps in the Alq3 layer. The voltage shift implies a reduction in charge density at the α-NPD/Alq3 interface. The origin of the interfacial charge can be attributed to dipole moment ordering in the Alq3 layer.
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85.60.Jb Light-emitting devices
85.30.De Semiconductor-device characterization, design, and modeling
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
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