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23 Jun 2008

Volume 92, Issue 25, Articles (25xxxx)

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Appl. Phys. Lett. 92, 254102 (2008); http://dx.doi.org/10.1063/1.2945893 (3 pages)

M. Trinker, S. Groth, S. Haslinger, S. Manz, T. Betz, S. Schneider, I. Bar-Joseph, T. Schumm, and J. Schmiedmayer
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Air-stable inverted flexible polymer solar cells using zinc oxide nanoparticles as an electron selective layer

Steven K. Hau, Hin-Lap Yip, Nam Seob Baek, Jingyu Zou, Kevin O’Malley, and Alex K.-Y. Jen

Appl. Phys. Lett. 92, 253301 (2008); http://dx.doi.org/10.1063/1.2945281 (3 pages) | Cited 194 times

Online Publication Date: 23 June 2008

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The performance and stability of unencapsulated inverted bulk-heterojunction solar cells with zinc oxide (ZnO) made by different processes as the electron selective contact are compared to conventional bulk-heterojunction solar cells. The low temperature processed inverted devices using ZnO nanoparticles on indium tin oxide plastic substrates showed high power conversion efficiency of ∼ 3.3%. This inverted device structure possessed much better stability under ambient conditions retaining over 80% of its original conversion efficiency after 40 days while the conventional one showed negligible photovoltaic activity after 4 days. This is due to the improved stability at the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/Ag interface.
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84.60.Jt Photoelectric conversion
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A three-dimensional polymeric optical circuit fabrication using a femtosecond laser-assisted self-written waveguide technique

Bin Cai, Kyoji Komatsu, Okihiro Sugihara, Manabu Kagami, Masaaki Tsuchimori, Takayuki Matsui, and Toshikuni Kaino

Appl. Phys. Lett. 92, 253302 (2008); http://dx.doi.org/10.1063/1.2951598 (3 pages) | Cited 3 times

Online Publication Date: 25 June 2008

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We demonstrated a femtosecond pulse laser-assisted self-written waveguide technique that can fabricate three-dimensional (3D) optical waveguides in a photopolymerizing resin. A 488 nm Ar+ laser and an 800 nm pulse laser were used in this technique. Using the femtosecond laser scanning technique, two optical fibers were connected three dimensionally by a waveguide. The alignment-free aspect of the light-induced self-written waveguide-fabrication technique and the possibilities of 3D waveguide creation inherent in the femtosecond laser polymerization technique were combined to yield a highly versatile technique for the fabrication of 3D waveguides.
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42.79.Gn Optical waveguides and couplers
42.70.Jk Polymers and organics
42.82.Cr Fabrication techniques; lithography, pattern transfer
82.35.-x Polymers: properties; reactions; polymerization
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Enhanced electromechanical response of nonpercolating polymer-nanoparticle composite films

David Mainwaring, Pandiyan Murugaraj, Nelson Mora-Huertas, and Kanikrishnan Sethupathi

Appl. Phys. Lett. 92, 253303 (2008); http://dx.doi.org/10.1063/1.2937093 (3 pages) | Cited 7 times

Online Publication Date: 25 June 2008

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We have prepared semiconducting carbon nanoparticle polyimide composite thin film with spatially distributed localized energy states exhibiting three-dimensional variable range hopping electron transport. Applied strain (compression or extensional) introduces proportional variations in the spacing between these energy states, as demonstrated in the linear variation of measured electrical resistance. The electromechanical sensitivity is the same in both deformation modes due to this underlying operating mechanism, enabling quantitative measurement of torsional deformations also. Electrical responses across all deformation modes remained in phase with applied strain indicating negligible hysteresis and an ability to operate over a wide strain ranges up to 40 000 microstrains.
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68.60.Bs Mechanical and acoustical properties
77.65.-j Piezoelectricity and electromechanical effects
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
73.61.-r Electrical properties of specific thin films
72.20.Ee Mobility edges; hopping transport
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Real time monitoring of pentacene growth on SiO2 from a supersonic source

S. Hong, A. Amassian, A. R. Woll, S. Bhargava, J. D. Ferguson, G. G. Malliaras, J. D. Brock, and J. R. Engstrom

Appl. Phys. Lett. 92, 253304 (2008); http://dx.doi.org/10.1063/1.2946497 (3 pages) | Cited 13 times

Online Publication Date: 25 June 2008

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Thin film growth of pentacene on SiO2 using a supersonic source has been investigated with in situ real time synchrotron x-ray scattering and ex situ atomic force microscopy, focusing on the effects of incident kinetic energy Ei and growth rate GR on the evolution of surface roughness and the crystalline structure of the thin films. For the conditions examined here, Ei = 2.5–7.2 eV and GR = 0.0015–0.2 ML s−1, the thin film phase is always observed. We find that while the effect of Ei on interlayer transport is minimal, at high growth rates, slightly smoother films are observed.
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81.05.Hd Other semiconductors
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.70.Ck X-ray scattering
68.35.bg Semiconductors
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Three gratings coupling during the holographic grating recording process in azobenzene-functionalized polymer

Anna Sobolewska and Stanislaw Bartkiewicz

Appl. Phys. Lett. 92, 253305 (2008); http://dx.doi.org/10.1063/1.2948858 (3 pages) | Cited 9 times

Online Publication Date: 26 June 2008

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The authors present a mechanism explaining complex diffraction efficiency dynamics of the holographic grating recording process in azobenzene-functionalized polymer. The mechanism assumes simultaneous formation of three coupling phase gratings with different recording time constants and constant, equal to 0 or π, phase shifts between them. Two of gratings originate from the refractive index changes in the bulk of material and the third one from the surface relief modulation. Diffraction efficiency dynamics curves calculated using the proposed model are in a very good agreement with the experimental results.
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42.40.Eq Holographic optical elements; holographic gratings
42.40.Ht Hologram recording and readout methods
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All-optical switching and multistability in photonic structures with liquid crystal defects

Andrey E. Miroshnichenko, Etienne Brasselet, and Yuri S. Kivshar

Appl. Phys. Lett. 92, 253306 (2008); http://dx.doi.org/10.1063/1.2949076 (3 pages) | Cited 21 times

Online Publication Date: 26 June 2008

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We demonstrate that one-dimensional photonic crystals with pure nematic liquid-crystal defects can operate as all-optical switching devices based on optical orientational nonlinearities of liquid crystals. We show that such a periodic structure is responsible for a modulated threshold of the optical Fréedericksz transition in the spectral domain, and this leads to all-optical switching and light-induced multistability. This effect has no quasistatics electric field analog, and it results from nonlinear coupling between light and a defect mode.
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61.30.Jf Defects in liquid crystals
42.70.Df Liquid crystals
42.65.-k Nonlinear optics
42.70.Qs Photonic bandgap materials
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Balancing the ambipolar conduction for pentacene thin film transistors through bifunctional electrodes

Chuan-Yi Yang, Dhananjay, Shiau-Shin Cheng, Chun-Wei Ou, You-Che Chuang, Meng-Chyi Wu, and Chih-Wei Chu

Appl. Phys. Lett. 92, 253307 (2008); http://dx.doi.org/10.1063/1.2939553 (3 pages) | Cited 7 times

Online Publication Date: 27 June 2008

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We report an effective way to equilibrate hole and electron transport in ambipolar pentacene thin film transistors (TFTs). It was achieved by inserting an ultra thin lithium fluoride (LiF) layer at the electrode/organic interface to form a bifunctional source/drain electrode. It can be observed that the presence of ultrathin LiF layer will facilitate the injection of electrons from source/drain electrodes to organic semiconductor, resulting in a significant enhancement of the n-channel conduction, without sacrificing p-channel conduction for ambipolar pentacene TFTs. These factors make them potential candidates for the organic complementary circuits and inverter circuits of these ambipolar TFTs are also demonstrated.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.61.Ph Polymers; organic compounds
85.30.De Semiconductor-device characterization, design, and modeling
72.20.Ee Mobility edges; hopping transport
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Reversible switching characteristics of polyfluorene-derivative single layer film for nonvolatile memory devices

Tae-Wook Kim, Seung-Hwan Oh, Hyejung Choi, Gunuk Wang, Hyunsang Hwang, Dong-Yu Kim, and Takhee Lee

Appl. Phys. Lett. 92, 253308 (2008); http://dx.doi.org/10.1063/1.2952825 (3 pages) | Cited 22 times

Online Publication Date: 27 June 2008

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This letter reports on reversible switching behavior of metal-insulator-metal type nonvolatile organic memory devices using polyfluorene-derivative (WPF-oxy-F) single layer film. The current-voltage (I-V) characteristics showed that the WPF-oxy-F single layer film has two distinguished resistance states, low resistance state and high resistance state, with four orders of on/off ratio (Ion/Ioff ∼ 104). From the analysis of I-V curves, area dependent I-V characteristics, and current images obtained by conducting atomic force microscopy we propose that the space charge limited current with filamentary conduction is a potential mechanism for the reversible switching behavior of WPF-Oxy-F memory devices.
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84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices
77.22.Jp Dielectric breakdown and space-charge effects
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High efficiency electrophosphorescence device using a thin cleaving layer in an Ir-complex doped emitter layer

Dongfang Yang, Wenlian Li, Bei Chu, Dongyu Zhang, Jianzhuo Zhu, Zisheng Su, Wenming Su, Liangliang Han, Defeng Bi, Yiren Chen, Fei Yan, Huihui Liu, and Dan Wang

Appl. Phys. Lett. 92, 253309 (2008); http://dx.doi.org/10.1063/1.2952954 (3 pages) | Cited 6 times

Online Publication Date: 27 June 2008

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The authors demonstrate a considerable increase in current efficiency of fac-tris(2-phenylpyridine) iridium doped phosphorescent organic green-light emitting diode in which a thin 4,7 dipheny-1,10-phenanthroline (Bphen) layer acts as a cleaving layer. As 4 nm Bphen layer divides the emitting layer (EML) into two sub-EMLs, a maximum current efficiency of 53 cd/A (corresponding to external efficiency quantum of 15%) is obtained, which is higher for 2.3 folds than that of the device without it, especially the current efficiency increases 64% over the reference device at a luminance of 40 000 cd/m2. The increases are demonstrated to the high electron mobility and special energy level alignment of Bphen with 4,4′-N,N′-dicarbazole-biphenyl host. The efficiency improvement attributes to a higher exciton formation probability in the recombination zone and better balance of the carrier injection. The detail enhancement mechanism of the efficiency is also discussed.
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85.60.Jb Light-emitting devices
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Thermal tunability of monolithic polymer microcavities

P. Regoliosi, M. Guehl, G. Scarpa, P. Lugli, L. Persano, P. Del Carro, A. Camposeo, R. Cingolani, D. Pisignano, S. Bietti, E. Grilli, and M. Guzzi

Appl. Phys. Lett. 92, 253310 (2008); http://dx.doi.org/10.1063/1.2953069 (3 pages) | Cited 3 times

Online Publication Date: 27 June 2008

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We demonstrate the thermal tunability of the emission of polymer embedded in microcavities. The large thermo-optic coefficients of a conjugated polymer is combined with the possibility to tailor the emission properties by means of cavities acting as optical filters. Both the transmission and the photoluminescence spectra of the polymer in cavities can be finely tuned with slopes up to about −0.2 nm/°C. Such an effect could be exploited to realize thermally tunable organic light-emitting devices for optical communication or sensing applications.
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42.70.Jk Polymers and organics
42.79.Ci Filters, zone plates, and polarizers
78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
42.65.-k Nonlinear optics
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Effects of gate dielectrics and metal electrodes on air-stable n-channel perylene tetracarboxylic dianhydride single-crystal field-effect transistors

Koichi Yamada, J. Takeya, T. Takenobu, and Y. Iwasa

Appl. Phys. Lett. 92, 253311 (2008); http://dx.doi.org/10.1063/1.2953079 (3 pages) | Cited 9 times

Online Publication Date: 27 June 2008

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The effects of gate dielectric materials and metal electrodes are studied systematically for air-stable n-type single-crystal field-effect transistors based on perylene tetracarboxylic dianhydride. It is demonstrated that neither the use of high-work-function electrodes nor exposure to air is fatal to the n-type operations for the single crystals with sufficiently large electron affinity. Mobility values are ∼ 5×10−3 cm2 V−1 s−1, which is one order of magnitude higher than those reported for thin-film transistors in vacuum. The most crucial among the common suspects for the generally poorer performance of n-type organic transistors was the effect of acidic hydroxyl groups in gate dielectrics.
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85.30.Tv Field effect devices
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
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