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7 May 2007

Volume 90, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 90, 193501 (2007); http://dx.doi.org/10.1063/1.2737344 (3 pages)

Peter Modregger, Daniel Lübbert, Peter Schäfer, and Rolf Köhler
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Two dimensional diffraction enhanced imaging algorithm

Peter Modregger, Daniel Lübbert, Peter Schäfer, and Rolf Köhler

Appl. Phys. Lett. 90, 193501 (2007); http://dx.doi.org/10.1063/1.2737344 (3 pages) | Cited 6 times

Online Publication Date: 8 May 2007

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Analyzer-based imaging provides refraction (phase) contrast due to angular filtering during reflection. By using two analyzer crystals with perpendicular diffraction planes (the so-called Bragg magnifier) the observable contrast is extended to two refraction directions. However, a nonlinear contribution of the two refraction directions to the images occurs and thus the standard diffraction-enhanced imaging algorithms are not suitable for image analysis in the case of the Bragg magnifier. Therefore, in this letter the authors introduce an algorithm (two dimensional diffraction enhanced imaging), which takes this nonlinear contribution into account and allows them to reconstruct the absorption, the horizontal, and the vertical refraction images.
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42.30.Wb Image reconstruction; tomography

Ballistic thermal conductance in a three-dimensional quantum wire modulated with stub structure

Xiao-Fang Peng, Ke-Qiu Chen, B. S. Zou, and Yan Zhang

Appl. Phys. Lett. 90, 193502 (2007); http://dx.doi.org/10.1063/1.2737363 (3 pages) | Cited 23 times

Online Publication Date: 8 May 2007

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Ballistic thermal conductance in a three-dimensional quantum wire with a stub structure is presented under both stress-free and hard wall boundary conditions at low temperatures. A comparative analysis for two-dimensional and three-dimensional models is made. The results show that when stress-free boundary conditions are applied, the universal quantum thermal conductance can be observed regardless of the geometry details in the limit T→0, and the behavior of the thermal conductance is qualitatively similar to that calculated by two-dimensional model. However, when hard wall boundary conditions are applied, the thermal conductance displays different behaviors in both two-dimensional and three-dimensional models.
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73.23.Ad Ballistic transport
73.63.Nm Quantum wires
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Demonstration of unpinned GaAs surface and surface inversion with gate dielectric made of Si3N4

W. P. Li, X. W. Wang, Y. X. Liu, S. I. Shim, and T. P. Ma

Appl. Phys. Lett. 90, 193503 (2007); http://dx.doi.org/10.1063/1.2737374 (3 pages) | Cited 8 times

Online Publication Date: 8 May 2007

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The authors have measured the electrical properties of metal insulator semiconductor capacitors of GaAs, with ex situ jet-vapor-deposited Si3N4 as a gate dielectric. Unpinning of GaAs surface was demonstrated by ac conductance and capacitance-voltage (C-V) measurement; GaAs surface inversion has been demonstrated by quasistatic C-V and hysteresis C-V measurements. Hydrogen plasma predeposition treatment at 200 °C has been shown to reduce interface-state density. The lowest interface-state density that the authors measured was 9×1011/cm2/eV at 0.57 eV above EV for p-type GaAs, and the smallest hysteresis window was 100 mV.
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85.30.Tv Field effect devices
84.32.Tt Capacitors

Liquid core photonic crystal fiber sensor based on surface enhanced Raman scattering

Yi Zhang, Chao Shi, Claire Gu, Leo Seballos, and Jin Z. Zhang

Appl. Phys. Lett. 90, 193504 (2007); http://dx.doi.org/10.1063/1.2738185 (3 pages) | Cited 28 times

Online Publication Date: 8 May 2007

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This letter reports on a hollow core photonic crystal fiber that is modified to allow for filling of only the core with a liquid and its use for detection of surface enhanced Raman scattering from molecules in solution with silver nanoparticles. Both experimental demonstration and theoretical simulation are presented and discussed. The developed sensor is tested in the detection of rhodamine 6G, human insulin, and tryptophan with good sensitivity (10−4–10−5M) due to enhanced interaction volume.
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42.81.Pa Sensors, gyros
42.81.Bm Fabrication, cladding, and splicing
42.70.Qs Photonic bandgap materials
33.20.Fb Raman and Rayleigh spectra (including optical scattering)

Effects of microvoids on the linewidth dependence of electromigration failure of dual-damascene copper interconnects

C. W. Chang, C. V. Thompson, C. L. Gan, K. L. Pey, W. K. Choi, and Y. K. Lim

Appl. Phys. Lett. 90, 193505 (2007); http://dx.doi.org/10.1063/1.2714315 (3 pages) | Cited 6 times

Online Publication Date: 9 May 2007

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The electromigration lifetime of dual-damascene Cu interconnects was found to significantly decrease with increasing linewidth, for linewidths ranging between 0.2 and 2.25 μm. Voids were also found to preexist in these lines. When void nucleation is required for failure, the electromigration reliability is generally found to be at most weakly dependent on the linewidth. In contrast, the current study suggests that growth, drift, and accumulation of existing voids lead to the observed strong linewidth dependence.
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66.30.Qa Electromigration
66.30.Lw Diffusion of other defects
61.72.Qq Microscopic defects (voids, inclusions, etc.)
85.40.Ls Metallization, contacts, interconnects; device isolation

Dual electron donor/electron acceptor character of a conjugated polymer in efficient photovoltaic diodes

Christopher R. McNeill, Agnese Abrusci, Jana Zaumseil, Richard Wilson, Mary J. McKiernan, Jeremy H. Burroughes, Jonathan J. M. Halls, Neil C. Greenham, and Richard H. Friend

Appl. Phys. Lett. 90, 193506 (2007); http://dx.doi.org/10.1063/1.2738197 (3 pages) | Cited 89 times

Online Publication Date: 9 May 2007

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The authors report efficient photovoltaic diodes which use poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2′,2″-diyl) (F8TBT) both as electron acceptor, in blends with poly(3-hexylthiophene), and as hole acceptor, in blends with (6,6)-phenyl C61-butyric acid methyl ester. In both cases external quantum efficiencies of over 25% are achieved, with a power conversion efficiency of 1.8% under simulated sunlight for optimized F8TBT/poly(3-hexylthiophene) devices. The ambipolar nature of F8TBT is also demonstrated by the operation of light-emitting F8TBT transistors. The equivalent p- and n-type operation in this conjugated polymer represent an important extension of the range of useful n-type materials which may be developed.
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85.60.-q Optoelectronic devices
85.30.-z Semiconductor devices

Current transport in short channel top-contact pentacene field-effect transistors investigated with the selective molecular doping technique

F. Fujimori, K. Shigeto, T. Hamano, T. Minari, T. Miyadera, K. Tsukagoshi, and Y. Aoyagi

Appl. Phys. Lett. 90, 193507 (2007); http://dx.doi.org/10.1063/1.2737418 (3 pages) | Cited 22 times

Online Publication Date: 9 May 2007

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The contact doping profile is controlled in the top-contact configuration to clarify a transistor operation based on a current injection process from the metal contact to the organic channel in a submicron channel pentacene field-effect transistor. The molecular doping in the pentacene film underneath the metal contact, in which a thin layer of iron (III) chloride was introduced, drastically changes transistor characteristics. The doping profile control directly revealed the resistive part for current injection. A model to explain the saturation behavior of the top-contact short channel organic transistor is presented.
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85.30.Tv Field effect devices
85.40.Ry Impurity doping, diffusion and ion implantation technology

14-pixel, multiplexed array of gamma-ray microcalorimeters with 47 eV energy resolution at 103 keV

W. B. Doriese, J. N. Ullom, J. A. Beall, W. D. Duncan, L. Ferreira, G. C. Hilton, R. D. Horansky, K. D. Irwin, J. A. B. Mates, C. D. Reintsema, L. R. Vale, Y. Xu, B. L. Zink, M. W. Rabin, A. S. Hoover, et al.

Appl. Phys. Lett. 90, 193508 (2007); http://dx.doi.org/10.1063/1.2738371 (3 pages) | Cited 20 times

Online Publication Date: 9 May 2007

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The authors present a prototype for a high-energy-resolution, high-count-rate, gamma-ray spectrometer intended for nuclear forensics and international nuclear safeguards. The prototype spectrometer is an array of 14 transition-edge-sensor microcalorimeters with an average energy resolution of 47 eV (full width at half maximum) at 103 keV. The resolution of the best pixel is 25 eV. A cryogenic, time-division multiplexer reads out the array. Several important topics related to microcalorimeter arrays are discussed, including cross-talk, the uniformity of detector bias conditions, fabrication of the arrays, and the multiplexed readout. The measurements and calculations demonstrate that a kilopixel array of high-resolution microcalorimeters is feasible.
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07.85.Nc X-ray and γ-ray spectrometers
29.30.Kv X- and γ-ray spectroscopy
29.40.Vj Calorimeters
29.40.Gx Tracking and position-sensitive detectors

(Tetrathiafulvalene)(tetracyanoquinodimethane) as a low-contact-resistance electrode for organic transistors

Koji Shibata, Hiroshi Wada, Ken Ishikawa, Hideo Takezoe, and Takehiko Mori

Appl. Phys. Lett. 90, 193509 (2007); http://dx.doi.org/10.1063/1.2738379 (3 pages) | Cited 47 times

Online Publication Date: 9 May 2007

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The authors show that source and drain electrodes made of the title metallic organic charge-transfer salt (tetrathiafulvalene)(tetracyanoquinodimethane) [(TTF)(TCNQ)] result in drastic reduction of contact resistance in organic thin-film transistors (TFTs). The contact resistance is estimated by the variable gate-length transfer-line method. Pentacene TFTs with the organic electrodes show smaller contact resistance and larger overall mobility by more than one order than those of bottom-contact Au transistors. The performance is comparable to that of top-contact Au transistors, indicating that (TTF)(TCNQ) is an excellent electrode material for bottom-contact transistors.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Surface effects on photopolymerization induced anisotropic phase separation in liquid crystal and polymer composites

Min Young Jin, Tae-Hee Lee, Jong-Wook Jung, and Jae-Hoon Kim

Appl. Phys. Lett. 90, 193510 (2007); http://dx.doi.org/10.1063/1.2734376 (3 pages) | Cited 2 times

Online Publication Date: 10 May 2007

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The surface effects on the anisotropic phase separation in photopolymerization induced phase separation of liquid crystal and polymer composites have been studied. It was found that the surface interaction between the substrate and the prepolymer and/or liquid crystal plays a crucial role in anisotropic phase separation. A theoretical model is suggested to describe the surface effects by adapting a phenomenological free energy approach. The formation of polymer layer in the presence of surface effects can be understood as competition between entropic flow and surface directed flow of polymer and liquid crystal.
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82.35.-x Polymers: properties; reactions; polymerization
82.50.-m Photochemistry
64.75.-g Phase equilibria
61.30.-v Liquid crystals

Cubic-to-monoclinic phase transition during the epitaxial growth of crystalline Gd2O3 films on Ge(001) substrates

Alessandro Molle, Claudia Wiemer, Md. Nurul Kabir Bhuiyan, Grazia Tallarida, Marco Fanciulli, and Giuseppe Pavia

Appl. Phys. Lett. 90, 193511 (2007); http://dx.doi.org/10.1063/1.2738367 (3 pages) | Cited 13 times

Online Publication Date: 11 May 2007

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Thin crystalline films of Gd2O3 are grown on an atomically flat Ge(001) surface by molecular beam epitaxy and are characterized in situ by reflection high energy electron diffraction and x-ray photoelectron spectroscopy, and ex situ by x-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy. The first stage of the growth corresponds to a cubic (110) structure, with two equiprobable, 90° rotated, in-plane domains. Increasing the thickness of the films, a phase transition from cubic (110) to monoclinic (100) oriented crystallites is observed which keeps the in-plane domain rotation, as evidenced by XRD and AFM.
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64.70.K- Solid-solid transitions
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.37.Lp Transmission electron microscopy (TEM)

Droplet evaporation-induced ferritin self-assembled monolayer as a template for nanocrystal flash memory

Moonjae Kwon, Hyejung Choi, Man Chang, Minseok Jo, Seung-Jae Jung, and Hyunsang Hwang

Appl. Phys. Lett. 90, 193512 (2007); http://dx.doi.org/10.1063/1.2737362 (3 pages) | Cited 7 times

Online Publication Date: 11 May 2007

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A nonvolatile nanocrystal (NC) memory containing a ferritin core was fabricated. A ferritin monolayer was formed through a droplet evaporation technique. High-pressure hydrogen (HP-H2) annealing effectively reduced iron oxide (Fe2O3) to form conductive iron NC. In addition, HP-H2 annealing also improved memory characteristics by passivation of the interface states at Si/HfO2. The authors observed good memory characteristics, including fast program/erase (P/E) operation, a memory window of 1.75 V under ±6 V, and a stable memory window up to 104 s at 85 °C.
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84.30.Sk Pulse and digital circuits
85.35.-p Nanoelectronic devices
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