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13 Oct 2008

Volume 93, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 93, 151101 (2008); http://dx.doi.org/10.1063/1.2996271 (3 pages)

Xuefeng Zeng and Hongrui Jiang
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Interface engineering for molecular alignment and device performance of quaterrylene thin films

Ryoma Hayakawa, Matthieu Petit, Toyohiro Chikyow, and Yutaka Wakayama

Appl. Phys. Lett. 93, 153301 (2008); http://dx.doi.org/10.1063/1.2998404 (3 pages) | Cited 4 times

Online Publication Date: 13 October 2008

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We investigated the impact of interface modification by an octadecyltrichlorosilane self-assembled monolayer (OTS-SAM) on growth mode and transistor performance of quaterrylene thin films. Interface modification by OTS-SAM contributed effectively to stress-free film growth and highly molecular ordering, particularly in the initial layers, dramatically improving transistor performance. We found that the structural features in a few layers were key factors for determining the overall thin film growth mode and ameliorating carrier transport in organic field-effect transistors (OFETs). These results clearly demonstrated the effectiveness of interface engineering in the OFETs.
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85.30.Tv Field effect devices
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Organic single-crystal transistors with secondary gates on source and drain electrodes

K. Nakayama, K. Hara, Y. Tominari, M. Yamagishi, and J. Takeya

Appl. Phys. Lett. 93, 153302 (2008); http://dx.doi.org/10.1063/1.2996587 (3 pages) | Cited 2 times

Online Publication Date: 14 October 2008

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Rubrene and tetracyanoquinodimethane single-crystal transistors are fabricated incorporating secondary gates (split gates) on source and drain electrodes to reduce the interfacial barriers at the metal/semiconductor contacts. Separating the effect of the injection barriers, the intrinsic carrier transport in the semiconductor channels is extracted for the p-type rubrene crystal transistors and the n-type tetracyanoquinodimethane crystal transistors. The transconductance of the tetracyanoquinodimethane devices is drastically improved by activating the split-gate electrodes, indicating significant injection barriers in the n-type transistors. The result demonstrates that the technique is useful to improve transistor performance when it is restricted by the injection barriers.
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85.30.Tv Field effect devices
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The reduced triplet-triplet annihilation of electrophosphorescent device doped by an iridium complex with active hydrogen

Liangliang Han, Dongfang Yang, Wenlian Li, Bei Chu, Yiren Chen, Zisheng Su, Dongyu Zhang, Fei Yan, Zhizhi Hu, and Zhiqiang Zhang

Appl. Phys. Lett. 93, 153303 (2008); http://dx.doi.org/10.1063/1.2998571 (3 pages) | Cited 6 times

Online Publication Date: 14 October 2008

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We demonstrate high efficiency electrophosphorescent devices doped by bis(2-phenyl-benzoimidazole) iridium (III) acetylacetonate [Ir(ppi)2acac] with active hydrogen. At 100 mA/cm2 2 wt % Ir(ppi)2acac doped device offers an external quantum efficiency (ηext) of 5.1% and an efficiency roll-off of 28.2%, which decreases for 33.5% and 39.1% compared with that of 2 and 6 wt % fac-tris(2-phenylpyridine) iridium (III) [fac-Ir(ppy)3] doped reference devices, respectively. 7 wt % Ir(ppi)2acac doped device behaves a maximum ηext of 13.4% and a ηext of 8.0% at a luminance of 10 000 cd/m2. Both the ηext are higher than that of the reference device. The improvement in electroluminescent performance was assumed to be the very short triplet lifetime (3.74 ns) induced by the active hydrogen atom.
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85.60.-q Optoelectronic devices
78.55.Kz Solid organic materials
61.72.up Other materials
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Stochastic model for photoinduced surface relief grating formation through molecular transport in polymer films

M. L. Juan, J. Plain, R. Bachelot, P. Royer, S. K. Gray, and G. P. Wiederrecht

Appl. Phys. Lett. 93, 153304 (2008); http://dx.doi.org/10.1063/1.2999625 (3 pages) | Cited 1 time

Online Publication Date: 14 October 2008

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We use a stochastic model to study photoinduced surface relief grating (SRG) formation due to molecular transport in azobenzene polymer films. The model is shown to reproduce the essential experimental features of SRG formation. In particular, it predicts SRG formation under both p and s polarizations, and the double peaked topographies that can occur at early times of the process. The evolving molecular positions and orientations during exposure are also followed, providing a useful mechanistic picture of SRG dynamics.
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68.35.bm Polymers, organics
78.66.Qn Polymers; organic compounds
82.50.-m Photochemistry
82.30.Qt Isomerization and rearrangement
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Electrical bistability and charge transport behavior in Au nanoparticle/poly(N-vinylcarbazole) hybrid memory devices

Pei Ying Lai and J. S. Chen

Appl. Phys. Lett. 93, 153305 (2008); http://dx.doi.org/10.1063/1.3002281 (3 pages) | Cited 5 times

Online Publication Date: 16 October 2008

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Polymer memory devices using poly(N-vinylcarbazole) (PVK) as the active layer, incorporated with various weight ratios (0, 0.083, and 0.2) of dodecanethiol capped gold nanoparticles (Au NPs), are investigated. Electrical bistability is demonstrated for all three PVK-based devices, regardless of Au-NP ratios. However, current fluctuation is observed during stress test for both zero (PVK-only) and Au NPs:PVK = 0.2:1 devices, while good current stability is obtained for the Au NPs:PVK = 0.083:1 device. Capacitance-frequency (C-f) curves present the comparable negative capacitance feature for all three devices in both high-conductivity (“on”) state and low-conductivity (“off”) state, indicating that the carrier transport is dominated by the PVK matrix. However, minor differences in the C-f curves are dependent on the weight ratios of Au NPs, and the connection is discussed.
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42.79.Vb Optical storage systems, optical disks
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Thin films of pentacene formed by transferring crystals dispersed in liquid media

Takashi Minakata and Yutaka Natsume

Appl. Phys. Lett. 93, 153306 (2008); http://dx.doi.org/10.1063/1.3001931 (3 pages)

Online Publication Date: 17 October 2008

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We fabricate thin films of pentacene by coating flake crystals dispersed in a liquid media. The films are structured with oriented crystals and have a well-defined grain structure obtained from the source crystals. The films assembled with large or small crystals show the carrier mobility of 1 cm2/V s and above 0.01 cm2/V s, respectively. Small electrode contact resistance of the films and transport barrier heights below 56 meV were confirmed from the temperature dependence of the mobility.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.ag Semiconductors
73.61.Ph Polymers; organic compounds
73.50.Dn Low-field transport and mobility; piezoresistance
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Direct evidence of Al diffusion into tris-(8-hydroquinoline) aluminum layer: medium energy ion scattering analysis

Jung Han Lee, Yeonjin Yi, and Dae Won Moon

Appl. Phys. Lett. 93, 153307 (2008); http://dx.doi.org/10.1063/1.3002290 (3 pages) | Cited 4 times

Online Publication Date: 17 October 2008

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The diffusion of Al into tris-(8-hydroquinoline) aluminum (Alq3) was studied using in situ medium energy ion scattering (MEIS) spectroscopy. Al was thermally deposited on an Alq3 thin film in a stepwise manner, with MEIS performed after each deposition step. At the initial stage of interface formation, Al diffuses deep into the Alq3 layer and reaches the bottom of the Alq3 layer of thickness 20 nm. Some Al is stacked at the surface of Alq3 and starts to form an Al layer. The deep diffusion of Al is diminished when sufficient Al aggregates at the surface. After this stage, Al is stacked only at the surface, but does not diffuse into the Alq3 film.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
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Multilayer polymer light-emitting diodes by blade coating method

Shin-Rong Tseng, Hsin-Fei Meng, Kuan-Chen Lee, and Sheng-Fu Horng

Appl. Phys. Lett. 93, 153308 (2008); http://dx.doi.org/10.1063/1.2999541 (3 pages) | Cited 24 times

Online Publication Date: 17 October 2008

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Multilayer polymer light-emitting diodes fabricated by blade coating are presented. Multilayer of polymers can be easily deposited by blade coating on a hot plate. The multilayer structure is confirmed by the total thickness and the cross section view in the scanning electron microscope. The film thickness variation is only 3.3% in 10 cm scale and the film roughness is about 0.3 nm in the micron scale. The efficiency of single layer poly(para-phenylene vinylene) copolymer Super Yellow and poly(9,9-dioctylfluorene) (PFO, deep blue) devices are 9 and 1.7 cd/A, respectively, by blade coating. The efficiency of the PFO device is raised to 2.9 cd/A with a 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD) hole-blocking layer and to 2.3 cd/A with a poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl))diphenylamine)] elec-tron-blocking layer added by blade coating.
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85.60.Jb Light-emitting devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.am Polymers and organics
68.65.Ac Multilayers
61.41.+e Polymers, elastomers, and plastics
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ZnO/poly(9,9-dihexylfluorene) based inorganic/organic hybrid ultraviolet photodetector

Hai-Guo Li, Gang Wu, Min-Min Shi, Li-Gong Yang, Hong-Zheng Chen, and Mang Wang

Appl. Phys. Lett. 93, 153309 (2008); http://dx.doi.org/10.1063/1.3003881 (3 pages) | Cited 12 times

Online Publication Date: 17 October 2008

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Solution processed inorganic/organic hybrid films of ZnO nanoparticles and poly(9,9-dihexylfluorene) (PFH) are sandwiched between two electrodes to form bulk heterojunction in this letter. The devices obtained show high ultraviolet photo-to-dark current ratio of about three orders of magnitude for −1 V bias with a relatively fast response speed of less than 200 ms after aging in air for enough time. The spectral response covers 300–420 nm, with its peak locating around 335 nm. Those results indicate that the ZnO/PFH hybrid devices might be used as low-cost UV optical switches or photodetectors.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
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