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13 Nov 2006

Volume 89, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 89, 202101 (2006); http://dx.doi.org/10.1063/1.2388049 (3 pages)

J. H. Lee, Zh. M. Wang, N. W. Strom, Yu. I. Mazur, and G. J. Salamo
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Electrolyte-gated charge accumulation in organic single crystals

Hidekazu Shimotani, Haruhiko Asanuma, Jun Takeya, and Yoshihiro Iwasa

Appl. Phys. Lett. 89, 203501 (2006); http://dx.doi.org/10.1063/1.2387884 (3 pages) | Cited 56 times

Online Publication Date: 13 November 2006

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Comparative studies of electrolyte-gated and SiO2-gated field-effect transistors have been carried out on rubrene single crystals by experimentally estimating their accumulated charges. The capacitance of the electrolyte gate at 1 mHz was 15 μF/cm2, which is more than two orders of magnitude larger than that of the 100-nm-thick SiO2 gate dielectric. The maximum carrier density in the electrolyte gate was 0.33 hole/molecule, which is considerably larger than that in the SiO2 gate. Furthermore, the transfer characteristics of the electrolyte-gate field-effect transistor showed reversible-peak behavior at an accumulated carrier density of 0.23 hole/molecule.
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85.30.Tv Field effect devices

Pentacene devices and logic gates fabricated by organic vapor phase deposition

Cédric Rolin, Soeren Steudel, Kris Myny, David Cheyns, Stijn Verlaak, Jan Genoe, and Paul Heremans

Appl. Phys. Lett. 89, 203502 (2006); http://dx.doi.org/10.1063/1.2388864 (3 pages) | Cited 18 times

Online Publication Date: 14 November 2006

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An organic vapor phase deposition (OVPD) tool has been developed and optimized for the deposition of pentacene thin films. Pentacene is grown with a good thickness uniformity, a good material consumption efficiency, and deposition rates up to 9.5 Å/s. Top-contact transistors based on OVPD-grown pentacene show high mobilities (up to 1.35 cm2/V s) and excellent characteristics, even at high deposition rates. Elementary circuit blocks have also been produced using an OVPD-deposited pentacene film. A five-stage ring oscillator features a stage delay of 2.7 μs at a supply voltage of 22 V.
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85.30.Tv Field effect devices
84.30.Sk Pulse and digital circuits
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Trapping mechanism on oxygen-terminated diamond surfaces

Yutaka Itoh, Yu Sumikawa, Hitoshi Umezawa, and Hiroshi Kawarada

Appl. Phys. Lett. 89, 203503 (2006); http://dx.doi.org/10.1063/1.2387983 (3 pages) | Cited 4 times

Online Publication Date: 14 November 2006

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Mechanisms of the hole trap and detrap on the oxygen-terminated diamond surfaces measured by diamond in-plane-gated field-effect transistors (FETs) have been investigated. Reproducible hysteresis characteristics are observed in the IDS-VGS characteristics of the diamond in-plane-gated FETs. They are caused by carrier trapping in the oxidized diamond surface and detrapping under a light irradiation, the wavelength of which affects the hysteresis width. Carriers are trapped by continuous surface states deeper than 2.0 eV from the valence band maximum in the oxidized diamond surface, where the position of the highest occupied level (Fermi level) is located between 2.0 and 2.4 eV.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.20.At Surface states, band structure, electron density of states
85.30.Tv Field effect devices

Wavelength tunable device for neutron radiography and tomography

W. Treimer, M. Strobl, N. Kardjilov, A. Hilger, and I. Manke

Appl. Phys. Lett. 89, 203504 (2006); http://dx.doi.org/10.1063/1.2384801 (3 pages) | Cited 34 times

Online Publication Date: 14 November 2006

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A special double monochromator system was tested for a conventional operating tomography setup in order to use a broad wavelength band of monochromatic neutrons for radiography and tomography. Scanning through the wavelength region of Bragg edges, it is possible to make series of radiographs and tomographs at different wavelengths from 2.0 until 6.5 Å. So no beam hardening influences the measurements and is not to be corrected. With this instrument for cold neutron radiography and tomography, energy selecting quantitative radiography, stress and strain mapping, and phase radiography were performed.
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81.70.-q Methods of materials testing and analysis
41.85.Si Particle beam collimators, monochromators
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations

Improvements in the device characteristics of random-network single-walled carbon nanotube transistors by using high-κ gate insulators

Megumi Ohishi, Masashi Shiraishi, Kenji Ochi, Yoshihiro Kubozono, and Hiromichi Kataura

Appl. Phys. Lett. 89, 203505 (2006); http://dx.doi.org/10.1063/1.2388150 (3 pages) | Cited 6 times

Online Publication Date: 15 November 2006

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The authors fabricated random-network single-walled carbon nanotube field-effect transistors (FETs) with high-κ gate insulators. The gate insulator in the FETs was changed from SiO2 to Ba0.4Sr0.6Ti0.96O3 (BST, εs = 100), which was fabricated by a sol-gel method. The gate-switching voltage of a FET with a BST insulator is about one-tenth of that of a FET with a SiO2 insulator, and the values of the transconductance and the on/off ratio are 0.18 μS and 105, respectively. In addition, hysteresis in the operation of the FETs was dramatically decreased, probably because of improvements in the surface condition of the insulator.
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85.35.Kt Nanotube devices
85.30.Tv Field effect devices

Organic tandem solar cells comprising polymer and small-molecule subcells

Alexander Colsmann, Johannes Junge, Christian Kayser, and Uli Lemmer

Appl. Phys. Lett. 89, 203506 (2006); http://dx.doi.org/10.1063/1.2388938 (3 pages) | Cited 35 times

Online Publication Date: 15 November 2006

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In this work the authors report monolithic organic tandem solar cells. The front cell is fabricated from a blend of poly(3-hexylthiophene-2,5-diyl) and [6,6]-phenyl C61-butyric acid methyl ester while a copper phthalocyanine/fullerene (CuPc/C60) bilayer is used for the back cell. An intermediate recombination zone is realized using two doped organic semiconductor layers and a thin noble metal interlayer. The active polymer layer thickness is optimized to ensure matching of the subcell currents. The open circuit voltage Voc = 1 V nearly reaches the sum of the open circuit voltages of each contributing cell.
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84.60.Jt Photoelectric conversion
FREE

Polarization-independent liquid crystal grating on azo-dye film fabricated through intensity holography

Xuemin Lu, Qinghua Lu, Fuk Kay Lee, and Ophelia K. C. Tsui

Appl. Phys. Lett. 89, 203507 (2006); http://dx.doi.org/10.1063/1.2388940 (3 pages) | Cited 1 time

Online Publication Date: 15 November 2006

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Diffraction phase gratings have found applications in many fields. In this letter the authors described how intensity holography was used to fabricate liquid crystal diffraction phase gratings on azo-dye films. The diffraction efficiency of this liquid crystal phase grating was determined to be independent of the polarization direction of incident light.
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42.79.Kr Display devices, liquid-crystal devices
42.79.Dj Gratings
42.70.Df Liquid crystals
42.70.Jk Polymers and organics
42.79.Wc Optical coatings
42.40.Kw Holographic interferometry; other holographic techniques

Hot carrier type exchange in inorganic electroluminescent thin films

Katsu Tanaka and Shinji Okamoto

Appl. Phys. Lett. 89, 203508 (2006); http://dx.doi.org/10.1063/1.2388942 (3 pages) | Cited 3 times

Online Publication Date: 15 November 2006

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The authors have observed the hot carrier type (holes or electrons) exchange in rare-earth-ion-activated strontium thiogallate (SrGa2S4) thin films by measuring the transient electroluminescent wave forms of the devices having a single insulating thin film. Measured wave forms revealed that the green electroluminescence of europium activated SrGa2S4 thin film occurs due to hot hole excitation. In contrast, the blue electroluminescence of cerium activated SrGa2S4 thin film occurs due to hot electron excitation. Hence, the hot carrier type is exchanged by the different rare-earth-ion doping.
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73.61.Ng Insulators
78.66.Nk Insulators
73.50.Fq High-field and nonlinear effects
78.60.Fi Electroluminescence
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals

Influence of contact effect on the performance of microcrystalline silicon thin-film transistors

Kah-Yoong Chan, Eerke Bunte, Helmut Stiebig, and Dietmar Knipp

Appl. Phys. Lett. 89, 203509 (2006); http://dx.doi.org/10.1063/1.2390634 (3 pages) | Cited 15 times

Online Publication Date: 15 November 2006

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Microcrystalline silicon thin-film transistors were prepared by plasma-enhanced chemical vapor deposition at substrate temperatures below 200 °C. The transistors exhibit electron mobilities of 38 cm2/V s, threshold voltages in the range of 2 V, and subthreshold slopes of 0.3 V/decade. Despite the realization of transistors with high carrier mobility, contact effects limit the performance of the transistors. The influence of the drain and source contacts on device parameters including the mobility, the threshold voltage, and the subthreshold slope will be discussed in detail.
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85.30.Tv Field effect devices

Metal electrode effects on spin-orbital coupling and magnetoresistance in organic semiconductor devices

Yue Wu and Bin Hu

Appl. Phys. Lett. 89, 203510 (2006); http://dx.doi.org/10.1063/1.2387118 (3 pages) | Cited 21 times

Online Publication Date: 16 November 2006

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This letter reports the modifications of spin-orbital coupling and magnetoresistance of conjugated polymer upon deposition of metal electrode based on organic light-emitting diodes of poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene]. We find that the reverse bias yields a largely increased magnetoresistance when the electron-hole capture zone is away from the metal electrode as compared to the forward bias with the electron-hole capture zone close to the metal electrode. The electroluminescence suggests that the deposited metal atoms enhance the spin-orbital coupling at the polymer/metal interface and consequently lead to electron-hole capture zone dependent magnetic field effects in organic semiconductor devices.
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85.60.Jb Light-emitting devices

Increasing the Q factor in the constant-excitation mode of frequency-modulation atomic force microscopy in liquid

D. Ebeling, H. Hölscher, and B. Anczykowski

Appl. Phys. Lett. 89, 203511 (2006); http://dx.doi.org/10.1063/1.2387122 (3 pages) | Cited 10 times

Online Publication Date: 16 November 2006

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By adding a Q-control electronics to the setup of the constant-excitation mode of the frequency-modulation atomic force microscope, the authors are able to increase the effective Q factor of a self-oscillated cantilever in liquid to values comparable to ambient conditions. During imaging of soft biological samples adsorbed on a mica substrate, the authors observed an increased corrugation of the topography with increased Q factors. This effect is caused by the reduction of tip-sample indentation forces as demonstrated by numerical simulations and an analytical approach.
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07.79.Lh Atomic force microscopes
87.64.Dz Scanning tunneling and atomic force microscopy

Thermally actuated untethered impact-driven locomotive microdevices

O. J. Sul, M. R. Falvo, R. M. Taylor, S. Washburn, and R. Superfine

Appl. Phys. Lett. 89, 203512 (2006); http://dx.doi.org/10.1063/1.2388135 (3 pages) | Cited 9 times

Online Publication Date: 17 November 2006

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The authors have developed steerable locomotive devices as small as 30 μm using the inertial impact drive as the thrust method. The devices consist of three-legged, thin-metal-film bimorphs designed to rest on three sharp tips with the device body curved up off the surface. Rapid, thermally induced curvature of one leg leads to stepwise translation on a low friction surface. A focused laser was used to supply energy and its parameters controlled the velocity and direction of motion of the device.
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07.07.Tw Servo and control equipment; robots
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
46.55.+d Tribology and mechanical contacts

Cryogenic sapphire oscillator with exceptionally high long-term frequency stability

J. G. Hartnett, C. R. Locke, E. N. Ivanov, M. E. Tobar, and P. L. Stanwix

Appl. Phys. Lett. 89, 203513 (2006); http://dx.doi.org/10.1063/1.2387969 (3 pages) | Cited 20 times

Online Publication Date: 17 November 2006

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The authors report on the development of a sapphire cryogenic microwave resonator oscillator with long-term fractional frequency stability of 2×10−17√τ for integration times τ>103 s and a negative drift of about 2.2×10−15/day. The short-term frequency instability of the oscillator is highly reproducible and also state of the art: 5.6×10−16 for an integration time of τ ≈ 20 s.
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84.40.Az Waveguides, transmission lines, striplines
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
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