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4 Aug 2008

Volume 93, Issue 5, Articles (05xxxx)

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Appl. Phys. Lett. 93, 051101 (2008); http://dx.doi.org/10.1063/1.2965797 (3 pages)

Mariano A. Zimmler, Jiming Bao, Federico Capasso, Sven Müller, and Carsten Ronning
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Zr-metal adhesion on graphenic nanostructures

Y. Sanchez-Paisal, D. Sanchez-Portal, N. Garmendia, R. Muñoz, I. Obieta, J. Arbiol, L. Calvo-Barrio, and A. Ayuela

Appl. Phys. Lett. 93, 053101 (2008); http://dx.doi.org/10.1063/1.2966373 (3 pages) | Cited 7 times

Online Publication Date: 4 August 2008

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Our high resolution transmission electronic microscopy studies of multiwall carbon nanotubes show, after the growth of zirconia nanoparticles by a hydrothermal route, the presence of surface Zr, forming an atomically thin layer. Using first-principles calculations we investigate the nature of the Zr–C interaction, which is neither ionic nor covalent, and the optimal coverage for the Zr metal in a graphene flake. This preferred coverage is in agreement with that deduced from electron energy loss spectra experiments. We show also that the amount of charge transferred to the C layer saturates as the Zr coverage increases and the Zr–C bond becomes weaker.
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68.35.Np Adhesion
61.46.Fg Nanotubes
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
79.20.Uv Electron energy loss spectroscopy

Carrier relaxation through two-electron process during photoconduction in highly UV sensitive quasi-one-dimensional ZnO nanowires

A. Bera and D. Basak

Appl. Phys. Lett. 93, 053102 (2008); http://dx.doi.org/10.1063/1.2968131 (3 pages) | Cited 28 times

Online Publication Date: 5 August 2008

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We have investigated the carrier relaxation process during photoconduction in quasi-one-dimensional (Q1D) ZnO nanowires (NWs) of diameters 29–36 nm on different substrates using photocurrent transient measurements. Ultraviolet (UV) sensitive NWs show around three to four orders of change in the photo-to-dark current ratio. Under steady UV illumination, the photocarrier relaxation occurs through two-electron process—carrier loss due to the trapping by the surface states and recombination at the deep defect states. The results demonstrate that the carrier relaxation during photoconduction in Q1D NWs of diameter comparable to the Debye length is also dominated by the surface states.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
71.55.Gs II-VI semiconductors
73.20.At Surface states, band structure, electron density of states

A nuclear magnetic resonance study on rubrene-cobalt nanocomposites

Masashi Shiraishi, Haruka Kusai, Ryo Nouchi, Takayuki Nozaki, Teruya Shinjo, Yoshishige Suzuki, Makoto Yoshida, and Masashi Takigawa

Appl. Phys. Lett. 93, 053103 (2008); http://dx.doi.org/10.1063/1.2966149 (3 pages) | Cited 4 times

Online Publication Date: 6 August 2008

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We implemented a nuclear magnetic resonance (NMR) study on rubrene (C42H28)−Co nanocomposites that exhibit an enhanced magnetoresistance (MR) ratio of 80%. The 59Co NMR spin echo experiment enabled clarification of the hyperfine field of Co at the interface between the ferromagnet and the molecules, which has not been investigated for molecular spintronics. An enhanced hyperfine field of the Co was observed in the rubrene-Co nanocomposites, which may be related to the enhancement of the MR ratio. This study demonstrates the importance of microscopic investigation of the interface between molecules and ferromagnets that governs spin-dependent transport in molecular spin devices.
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76.60.Lz Spin echoes
72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Xx Molecular magnets
75.50.Dd Nonmetallic ferromagnetic materials

Atomic resolution study of the interfacial bonding at Si3N4/CeO2−δ grain boundaries

W. Walkosz, R. F. Klie, S. Öğüt, A. Borisevich, P. F. Becher, S. J. Pennycook, and J. C. Idrobo

Appl. Phys. Lett. 93, 053104 (2008); http://dx.doi.org/10.1063/1.2968683 (3 pages) | Cited 5 times

Online Publication Date: 6 August 2008

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Using a combination of atomic-resolution Z-contrast imaging and electron energy-loss spectroscopy (EELS) in the scanning transmission electron microscope, we examine the atomic and electronic structures at the interface between Si3N4 (10math0) and CeO2−d intergranular film (IGF). Ce atoms are observed to segregate to the interface in a two-layer periodic arrangement, which is significantly different from the structure observed in a previous study. Our EELS experiments show (i) oxygen in direct contact with the terminating Si3N4 open-ring structures, (ii) a change in the Ce valence from a nominal oxidation state of +3 to almost +4 moving from the interface into the IGF, and (iii) a uniform concentration of Si in the film.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
61.72.Mm Grain and twin boundaries
71.20.Ps Other inorganic compounds
64.75.-g Phase equilibria

High-performance nanowire complementary metal-semiconductor inverters

R. M. Ma, L. Dai, C. Liu, W. J. Xu, and G. G. Qin

Appl. Phys. Lett. 93, 053105 (2008); http://dx.doi.org/10.1063/1.2967725 (3 pages) | Cited 3 times

Online Publication Date: 6 August 2008

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We demonstrated the construction of complementary metal-semiconductor (CMES) inverters with single n- and p-type nanowires (NWs) on the same chip. A single p-type NW was assembled by the side of an n-type NW via the electric field assembly method. n- and p-channel metal-semiconductor field-effect transistors were fabricated with n- and p-type NWs, respectively. Based on this, high-performance NW CMES NOT logic gate (inverter) was built. The NW CMES inverters have low operating voltage ( ≤ 2 V), high voltage gain ( ≥ 7), and low static power dissipation ( ≤ 0.3 nW).
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84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices

Excitation enhancement of CdSe quantum dots by single metal nanoparticles

Yeechi Chen, Keiko Munechika, Ilan Jen-La Plante, Andrea M. Munro, Sara E. Skrabalak, Younan Xia, and David S. Ginger

Appl. Phys. Lett. 93, 053106 (2008); http://dx.doi.org/10.1063/1.2956391 (3 pages) | Cited 36 times

Online Publication Date: 6 August 2008

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We study plasmon-enhanced fluorescence from CdSe/CdS/CdZnS/ZnS core/shell quantum dots near a variety of Ag and Au nanoparticles. The photoluminescence excitation (PLE) spectrum of quantum dots closely follows the localized surface plasmon resonance (LSPR) scattering spectrum of the nanoparticles. We measure excitation enhancement factors of ∼ 3 to 10 for different shapes of single metal nanoparticles.
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78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
78.68.+m Optical properties of surfaces
73.22.Lp Collective excitations
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Carbon nanotubes on carbon fabrics for flexible field emitter arrays

Kenichi Suzuki, Hidetoshi Matsumoto, Mie Minagawa, Akihiko Tanioka, Yasuhiko Hayashi, Kazuyuki Fukuzono, and Gehan A. J. Amaratunga

Appl. Phys. Lett. 93, 053107 (2008); http://dx.doi.org/10.1063/1.2967868 (3 pages) | Cited 3 times

Online Publication Date: 6 August 2008

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Flexible carbon fabrics (CFs) prepared by electrospray deposition were used for the substrate of carbon nanotube (CNT) field emitter arrays. CNTs were grown on the CFs by chemical vapor deposition. The CNT field emitter arrays on CFs produced a higher current density at a lower turn-on voltage compared to ones on a Si substrate.
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81.07.De Nanotubes
85.45.Db Field emitters and arrays, cold electron emitters
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Two-dimensional growth of lattice matched Nd-doped (Gd,Lu)2O3 films on Y2O3 by pulsed laser deposition

Teoman Gün, Andreas Kahn, Bilge İleri, Klaus Petermann, and Günter Huber

Appl. Phys. Lett. 93, 053108 (2008); http://dx.doi.org/10.1063/1.2967870 (3 pages) | Cited 7 times

Online Publication Date: 6 August 2008

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This letter focuses on epitaxial growth of a 1-μm-thick lattice matched Nd-doped monocrystalline (Gd,Lu)2O3 film deposited on a {100} oriented Y2O3 substrate by pulsed laser deposition. Layer-by-layer growth indicated by in situ reflection high energy electron diffraction was observed up to film thicknesses of 100 nm. The subsequent growth behavior could be explained by a multilevel growth mode. Thus, the growth mode was two-dimensional and epitaxial. Lattice matching of up to 99.3% was achieved. The evolution of the structural and topographical properties of the films was verified by ex situ x-ray diffraction analysis and atomic force microscopy, respectively.
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81.15.Fg Pulsed laser ablation deposition
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.A- Nucleation and growth
68.55.jd Thickness
68.37.Ps Atomic force microscopy (AFM)
42.70.Hj Laser materials

Synthesis of horizontally aligned ZnO nanowires localized at terrace edges and application for high sensitivity gas sensor

J. Y. Son, S. J. Lim, J. H. Cho, W. K. Seong, and Hyungjun Kim

Appl. Phys. Lett. 93, 053109 (2008); http://dx.doi.org/10.1063/1.2967871 (3 pages) | Cited 29 times

Online Publication Date: 6 August 2008

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We developed step edge decoration method for the fabrication of semiconductor ZnO nanodots and nanowires using pulsed laser deposition. We synthesized high quality ZnO nanowires with the small diameter of about 20 nm and the uniform interval of about 80 nm between each nanowire, which has a simple structure for the formation of contact electrodes. The ZnO nanowire-based sensor was prepared only with the simple process of a gold electrode formation. The ZnO nanowire-based sensor exhibited the high surface-to-volume ratio of 58.6 μm−1 and the significantly high sensitivity of about 10 even for the low ethanol concentration of 0.2 ppm.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition

Nearly intrinsic exciton lifetimes in single twin-free GaAs/AlGaAs core-shell nanowire heterostructures

S. Perera, M. A. Fickenscher, H. E. Jackson, L. M. Smith, J. M. Yarrison-Rice, H. J. Joyce, Q. Gao, H. H. Tan, C. Jagadish, X. Zhang, and J. Zou

Appl. Phys. Lett. 93, 053110 (2008); http://dx.doi.org/10.1063/1.2967877 (3 pages) | Cited 18 times

Online Publication Date: 6 August 2008

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CW and time-resolved photoluminescence measurements are used to investigate exciton recombination dynamics in GaAs/AlGaAs heterostructure nanowires grown with a recently developed technique which minimizes twinning. A thin capping layer is deposited to eliminate the possibility of oxidation of the AlGaAs shell as a source of oxygen defects in the GaAs core. We observe exciton lifetimes of ∼ 1 ns, comparable to high quality two-dimensional double heterostructures. These GaAs nanowires allow one to observe state filling and many-body effects resulting from the increased carrier densities accessible with pulsed laser excitation.
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71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors
61.72.Mm Grain and twin boundaries
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Nano-optical microlens with ultrashort focal length using negative refraction

B. D. F. Casse, W. T. Lu, Y. J. Huang, and S. Sridhar

Appl. Phys. Lett. 93, 053111 (2008); http://dx.doi.org/10.1063/1.2968873 (3 pages) | Cited 12 times

Online Publication Date: 7 August 2008

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We have experimentally realized an ultrashort focal length planoconcave microlens in an InP/InGaAsP semiconductor two-dimensional (2D) photonic crystal with negative index of refraction (−0.7). At λ = 1.5 μm, the lens exhibits ultrashort focal lengths of 12 μm ( ∼ 8λ) and numerical aperture close to unity. The focused beam has a near diffraction-limited spot size of 1.05 μm ( ∼ 0.68λ) at full width at half maximum. The negative refractive index and focusing properties of the microlens are confirmed by 2D finite-difference time-domain simulations. Such ultrarefractive negative-index nano-optical microlenses can be integrated into existing semiconductor heterostructure platforms for next-generation optoelectronic applications.
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42.79.Bh Lenses, prisms and mirrors
42.82.Gw Other integrated-optical elements and systems

High-density horizontally aligned growth of carbon nanotubes with Co nanoparticles deposited by arc-discharge plasma method

D. Phokharatkul, Y. Ohno, H. Nakano, S. Kishimoto, and T. Mizutani

Appl. Phys. Lett. 93, 053112 (2008); http://dx.doi.org/10.1063/1.2969290 (3 pages) | Cited 15 times

Online Publication Date: 7 August 2008

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High-density horizontally aligned single-walled carbon nanotubes are grown on a quartz substrate using Co nanoparticles deposited by arc-discharge plasma method. The Co nanoparticles with a density as high as 6.0×1010 cm−2 are formed by a single pulse of arc discharge at room temperature. The density of the aligned nanotubes is ∼ 8 μm−1 in average. Multichannel nanotube field-effect transistors with a high-k top-gate structure are fabricated with aligned nanotubes. The devices show high-performance, normally on, and n-type conduction property without any doping process. A high on current of 1.3 mA and a large transconductance of 0.23 mS for a channel width of 100 μm are obtained. The normally on and n-type property is attributed to fixed positive charges in the HfO2 gate insulator and at the interfaces.
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81.07.De Nanotubes
85.35.Kt Nanotube devices
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
85.30.Tv Field effect devices
81.05.Cy Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Current-voltage characteristics and transport mechanism of solar cells based on ZnO nanorods/In2S3/CuSCN

T. Dittrich, D. Kieven, M. Rusu, A. Belaidi, J. Tornow, K. Schwarzburg, and M. Lux-Steiner

Appl. Phys. Lett. 93, 053113 (2008); http://dx.doi.org/10.1063/1.2969291 (3 pages) | Cited 17 times

Online Publication Date: 8 August 2008

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Temperature dependent current-voltage characteristics in the dark and under illumination have been analyzed on up to 3.2% efficient solar cells with extremely thin absorber based on ZnO nanorods/In2S3/CuSCN structures. The diode ideality factor and the open circuit voltage are strongly influenced on a thermal activation process. Significant enhancement of the devices efficiency by annealing at moderate temperatures has been demonstrated. After this annealing, the activation energy of the saturation current increased from 1.00 to 1.46 eV (in the dark). Transport mechanisms at the In2S3/CuSCN interface region are discussed.
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84.60.Jt Photoelectric conversion
61.72.Cc Kinetics of defect formation and annealing

Microwave absorption properties of conducting polymer composite with barium ferrite nanoparticles in 12.4–18 GHz

Anil Ohlan, Kuldeep Singh, Amita Chandra, and S. K. Dhawan

Appl. Phys. Lett. 93, 053114 (2008); http://dx.doi.org/10.1063/1.2969400 (3 pages) | Cited 29 times

Online Publication Date: 8 August 2008

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Conducting polymer nanocomposites of polyphenyl amine with barium ferrite nanoparticles (50–70 nm) have been synthesized via emulsion polymerization. The complex permittivity, permeability, and microwave absorption properties of the composite were studied in the 12.4–18 GHz (Ku band) frequency range. The composite has shown high shielding effectiveness due to absorption (SEA) of 28.9 dB ( ∼ 99.9%), which strongly depends on dielectric loss, magnetic permeability, and volume fraction of barium ferrite nanoparticles. The high value of SEA suggests that these composites can be used as a promising radar absorbing materials.
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78.70.Gq Microwave and radio-frequency interactions
72.80.Tm Composite materials
84.40.-x Radiowave and microwave (including millimeter wave) technology
77.22.Ch Permittivity (dielectric function)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.22.Gm Dielectric loss and relaxation
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