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20 Jul 2009

Volume 95, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 95, 033502 (2009); http://dx.doi.org/10.1063/1.3178556 (3 pages)

Akihito Ikedo, Takahiro Kawashima, Takeshi Kawano, and Makoto Ishida
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High efficiency organic multilayer photodetectors based on singlet exciton fission

J. Lee, P. Jadhav, and M. A. Baldo

Appl. Phys. Lett. 95, 033301 (2009); http://dx.doi.org/10.1063/1.3182787 (3 pages) | Cited 40 times

Online Publication Date: 20 July 2009

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We employ an exciton fission process that converts one singlet exciton into two triplet excitons to increase the quantum efficiency of an organic multilayer photodetector beyond 100%. The photodetector incorporates ultrathin alternating donor-acceptor layers of pentacene and C60, respectively. By comparing the quantum efficiency after separate pentacene and C60 photoexcitation we find that singlet exciton fission in pentacene enhances the quantum efficiency by (45±7)%. In quantitative agreement with this result, we also observe that the photocurrent generated from pentacene excitons is decreased by (2.7±0.2)% under an applied magnetic field of H = 0.4 T, while the C60 photocurrent is relatively unchanged.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
72.40.+w Photoconduction and photovoltaic effects
71.35.-y Excitons and related phenomena
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CdTe nanoparticles synthesized by laser ablation

N. G. Semaltianos, S. Logothetidis, W. Perrie, S. Romani, R. J. Potter, M. Sharp, G. Dearden, and K. G. Watkins

Appl. Phys. Lett. 95, 033302 (2009); http://dx.doi.org/10.1063/1.3171941 (3 pages) | Cited 3 times

Online Publication Date: 20 July 2009

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Nanoparticle generation by laser ablation of a solid target in a liquid environment is an easy, fast, and “green” method for a large scale production of nanomaterials with tailored properties. In this letter we report the synthesis of CdTe nanoparticles by femtosecond laser [387 nm, 180 fs, 1 kHz, pulse energy = 6 μJ (fluence = 1.7 J/cm2)] ablation of the target material. Nanoparticles with diameters from ∼ 2 up to ∼ 25 nm were observed to be formed in the colloidal solution. Their size distribution follows the log-normal function with a statistical median diameter of ≈7.1 nm. Their crystal structure is the same as that of the bulk material (cubic zincblende) and they are slightly Cd-rich (Cd:Te percentage ratio ∼ 1:0.9). Photoluminescence emission from the produced nanoparticles was detected in the deep red ( ∼ 652 nm).
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena
78.55.Et II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
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Anisotropic propagation of surface plasmon polaritons caused by oriented molecular overlayer

Fadiah Adlina M. Ghazali, Minoru Fujii, and Shinji Hayashi

Appl. Phys. Lett. 95, 033303 (2009); http://dx.doi.org/10.1063/1.3184586 (3 pages) | Cited 3 times

Online Publication Date: 20 July 2009

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We performed reverse attenuated total reflection measurements on 50-nm-thick Ag thin films coated with oriented sexithiophene molecular layers. The dispersion curves obtained clearly demonstrate that the wavevectors of surface plasmon polaritons propagating parallel to the molecular orientation have larger magnitudes than those propagating perpendicular to the molecular orientation. The results provide us with an approach to generate anisotropic propagation of surface plasmon polaritons simply controlled by the molecular orientation of an overlayer.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
78.68.+m Optical properties of surfaces
78.66.Bz Metals and metallic alloys
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
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Langmuir–Blogett monolayer transistors of copper phthalocyanine

Zhongming Wei, Yang Cao, Weizhu Ma, Chengliang Wang, Wei Xu, Xuefeng Guo, Wenping Hu, and Daoben Zhu

Appl. Phys. Lett. 95, 033304 (2009); http://dx.doi.org/10.1063/1.3185151 (3 pages) | Cited 7 times

Online Publication Date: 21 July 2009

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Bottom-contact monolayer thin-film transistors (MTFTs) were fabricated using copper phthalocyanine (CuPc) Langmuir–Blodgett monolayer as the active channel. The devices with tens of micrometers long channels showed typical p-type field-effect properties and obvious saturation regimes. Mobilities of these CuPc MTFTs were channel length dependent. The best performance obtained from the molecule-scaled CuPc MTFT with a channel length of 5 μm showed mobility even higher than that of the 50 nm thick vacuum-deposited films. These MTFTs may find potential applications in sensors and organic integrated circuits.
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85.30.Tv Field effect devices
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Laser operation in nondoped thin films made of a small-molecule organic red-emitter

Hadi Rabbani-Haghighi, Sébastien Forget, Sébastien Chénais, Alain Siove, Marie-Claude Castex, and Elena Ishow

Appl. Phys. Lett. 95, 033305 (2009); http://dx.doi.org/10.1063/1.3182820 (3 pages) | Cited 11 times

Online Publication Date: 21 July 2009

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Stimulated emission in small-molecule organic films at a high dye concentration is generally hindered by fluorescence quenching, especially in the red region of the spectrum. Here we demonstrate the achievement of high net gains (up to 50 cm−1) around 640 nm in thermally evaporated nondoped films of 4-di(4′-tert-butylbiphenyl-4-yl)amino-4′-dicyanovinylbenzene, which makes this material suitable for green-light pumped single mode organic lasers with low threshold and superior stability. Lasing effect is demonstrated in a distributed Bragg resonator configuration, as well as under the form of random lasing at high pump intensities.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.70.Hj Laser materials
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
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Dye-doped polymer microring laser coupled with stimulated resonant Raman scattering

Hisao Yanagi, Rei Takeaki, Satoshi Tomita, Atsushi Ishizumi, Fumio Sasaki, Kenichi Yamashita, and Kunishige Oe

Appl. Phys. Lett. 95, 033306 (2009); http://dx.doi.org/10.1063/1.3183586 (3 pages) | Cited 4 times

Online Publication Date: 21 July 2009

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Polymer ring laser was fabricated with 1,4-bis[2-[4-[N,N-di(p-totyl)amino]phenyl]vinyl]benzene (DADSB)-doped polyvinyl-pyrrolidone (PVP) thin films coated on an inner surface of a quartz microcapillary. Ring-waveguided multimode lasing was observed under pulsed optical pumping. With increasing excitation wavelengths, an additional emission peak based on stimulated resonant Raman scattering (SRRS) appeared with a Raman shift of the stretching vibration of DADSB. When the SRRS peak just overlapped with each ring laser modes, the emission intensity was periodically enhanced. Such a wavelength-selective Raman coupling can demonstrate a tunable single-mode microring laser.
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42.55.Mv Dye lasers
42.60.By Design of specific laser systems
42.70.Hj Laser materials
42.79.Wc Optical coatings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.60.Fc Modulation, tuning, and mode locking
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Top-emission Si-based phosphor organic light emitting diode with Au doped ultrathin n-Si film anode and bottom Al mirror

Y. Z. Li, W. J. Xu, G. Z. Ran, and G. G. Qin

Appl. Phys. Lett. 95, 033307 (2009); http://dx.doi.org/10.1063/1.3186040 (3 pages) | Cited 7 times

Online Publication Date: 23 July 2009

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We report a highly efficient top-emission Si-based phosphor organic light emitting diode (PhOLED) with an ultrathin polycrystalline n-Si:Au film anode and a bottom Al mirror. This anode is formed by magnetron sputtering followed by Ni induced crystallization and then Au diffusion. By optimizing the thickness of the n-Si:Au film anode, the Au diffusion temperature, and the other parameters of the PhOLED, the highest current and power efficiencies of the n-Si:Au film anode PhOLED reached 85±9 cd/A and 80±8 lm/W, respectively, corresponding to an external quantum efficiency of 21±2% and a power conversion efficiency of 15±2%, respectively, which are about 60% and 110% higher than those of the indium tin oxide anode counterpart and 70% and 50% higher than those of the bulk n+-Si:Au anode counterpart, respectively.
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85.60.Jb Light-emitting devices
81.15.Cd Deposition by sputtering
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Highly balanced ambipolar mobilities with intense electroluminescence in field-effect transistors based on organic single crystal oligo(p-phenylenevinylene) derivatives

Hajime Nakanotani, Masatoshi Saito, Hiroaki Nakamura, and Chihaya Adachi

Appl. Phys. Lett. 95, 033308 (2009); http://dx.doi.org/10.1063/1.3184588 (3 pages) | Cited 15 times

Online Publication Date: 23 July 2009

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Single crystal organic field-effect transistors (FETs) based on highly luminescent oligo(p-phenylenevinylene) (OPV) derivatives are fabricated. Although OPV single crystal FETs show both p- and n- type FET operation, we found that an increase in the conjugation length of the OPV derivatives from three phenylene rings (P3V2) to four phenylene rings (P4V3) results in an improvement in the electron mobility by an order of magnitude, while retaining the high hole mobility. This molecular design, using P4V3, achieved an ambipolar light-emitting OFET with well-balanced high hole (0.12 cm2/V s) and electron (0.11 cm2/V s) mobilities, leading to intense electroluminescence.
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85.30.Tv Field effect devices
78.60.Fi Electroluminescence
72.20.Fr Low-field transport and mobility; piezoresistance
85.60.Jb Light-emitting devices
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In situ intercalation strategies for device-quality hybrid inorganic-organic self-assembled quantum wells

K. Pradeesh, J. J. Baumberg, and G. Vijaya Prakash

Appl. Phys. Lett. 95, 033309 (2009); http://dx.doi.org/10.1063/1.3186639 (3 pages) | Cited 9 times

Online Publication Date: 24 July 2009

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Thin films of self-organized quantum wells of inorganic-organic hybrid perovskites of (C6H9C2H4NH3)2PbI4 are formed from a simple intercalation strategy to yield well-ordered uniform films over centimeter-size scales. These films compare favorably with traditional solution-chemistry-synthesized thin films. The hybrid films show strong room-temperature exciton-related absorption and photoluminescence, which shift with fabrication protocol. We demonstrate the potential of this method for electronic and photonic device applications.
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78.66.-w Optical properties of specific thin films
71.35.-y Excitons and related phenomena
81.07.Pr Organic-inorganic hybrid nanostructures
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
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