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18 Jul 2011

Volume 99, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 032501 (2011); http://dx.doi.org/10.1063/1.3610947 (3 pages)

G. X. Miao, M. D. Mascaro, C. H. Nam, C. A. Ross, and J. S. Moodera
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Effect of microstructure on the thermal conductivity of disordered carbon

I. Suarez-Martinez and N. A. Marks

Appl. Phys. Lett. 99, 033101 (2011); http://dx.doi.org/10.1063/1.3607872 (3 pages) | Cited 1 time

Online Publication Date: 18 July 2011

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Computational methods are used to control the degree of structural order in a variety of carbon materials containing primarily sp2 bonding. Room-temperature thermal conductivities are computed using non-equilibrium molecular dynamics. Our results reproduce experimental data for amorphous and glassy carbons and confirm previously proposed structural models for vitreous carbons. An atomistic model is developed for highly oriented thin films seen experimentally, with a maximum computed thermal conductivity of 35 W m−1 K−1. This value is much higher than that of the amorphous and glassy structures, demonstrating that the microstructure influences the thermal conductivity more strongly than the density.
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61.43.Bn Structural modeling: serial-addition models, computer simulation
61.72.-y Defects and impurities in crystals; microstructure
68.55.-a Thin film structure and morphology
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Physical origin of the incubation time of self-induced GaN nanowires

V. Consonni, A. Trampert, L. Geelhaar, and H. Riechert

Appl. Phys. Lett. 99, 033102 (2011); http://dx.doi.org/10.1063/1.3610964 (3 pages) | Cited 10 times

Online Publication Date: 19 July 2011

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The nucleation process of self-induced GaN nanowires grown by molecular beam epitaxy has been investigated by reflection high-energy electron diffraction measurements. It is found that stable nuclei in the form of spherical cap-shaped islands develop only after an incubation time that is strongly dependent upon the growth conditions. Its evolution with the growth temperature and gallium rate has been described within standard island nucleation theory, revealing a nucleation energy of 4.9 ± 0.1 eV and a very small nucleus critical size. The consideration of the incubation time is critical for the control of the nanowire morphology.
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68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)

Room temperature detection of NO2 using InSb nanowire

Rajat Kanti Paul, Sushmee Badhulika, and Ashok Mulchandani

Appl. Phys. Lett. 99, 033103 (2011); http://dx.doi.org/10.1063/1.3614544 (3 pages) | Cited 4 times

Online Publication Date: 20 July 2011

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Room temperature detection of NO2 down to one part-per-million (ppm) using single crystalline n-type InSb nanowires (NWs) chemiresistive gas sensor is presented. These sensors were synthesized and fabricated by the combination of chemical vapor deposition and dielectrophoresis alignment techniques. The sensor devices showed an increase in resistance upon exposure to successive increments of NO2 concentration up to 10 ppm. The reduction in conductance of n-type InSb NWs when exposed to NO2 is made possible due to the charge transfer from the InSb NW surface to the adsorbed electron acceptor NO2 molecules. The demonstrated results suggest InSb NW as a promising candidate in sensing applications as well as being environmental friendly over existing arsenic and/or phosphorous-based III-V NW sensors.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Site selective surface enhanced Raman on nanostructured cavities

Frances Lordan, James H. Rice, Bincy Jose, Robert J. Forster, and Tia E. Keyes

Appl. Phys. Lett. 99, 033104 (2011); http://dx.doi.org/10.1063/1.3615282 (3 pages) | Cited 11 times

Online Publication Date: 20 July 2011

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Presented here are angle dependence studies on the surface enhanced Raman (SER) signal obtained from dye placed on plasmon active nanocavity arrays. A comparative study was carried out between two modified array supports. One array had dye placed only on the interior walls of the cavities in the array. The other array had dye placed only on its top flat surface. Results show that Raman intensities as a function of angle depend on the location of the dye on the array; this was interpreted to arise from the presence of different plasmon polariton modes in these sites.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.30.-j Infrared and Raman spectra
61.46.-w Structure of nanoscale materials
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Annular aperture array based color filter

Guangyuan Si, Yanhui Zhao, Hong Liu, Siewlang Teo, Mingsheng Zhang, Tony Jun Huang, Aaron J. Danner, and Jinghua Teng

Appl. Phys. Lett. 99, 033105 (2011); http://dx.doi.org/10.1063/1.3608147 (3 pages) | Cited 8 times

Online Publication Date: 20 July 2011

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In this letter, we propose and experimentally demonstrate a color filter based on an annular aperture geometry working in the visible range. The device is built by configuring an array of annular apertures in a gold film suitable for transmission measurement. We show effective fine tuning of resonance peaks through precise geometric control of the aperture dimensions. Selective transmission through annular apertures of various sizes leads to continuous color tuning of transmitted electromagnetic waves. This may find potential for application in high-definition displays, optical filters, ultrafast switching, and bio-sensing.
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42.79.Ci Filters, zone plates, and polarizers

Assessing the delay of plastic relaxation onset in SiGe islands grown on pit-patterned Si(001) substrates

F. Boioli, R. Gatti, M. Grydlik, M. Brehm, F. Montalenti, and Leo Miglio

Appl. Phys. Lett. 99, 033106 (2011); http://dx.doi.org/10.1063/1.3615285 (3 pages) | Cited 4 times

Online Publication Date: 21 July 2011

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The onset of plastic relaxation in SiGe islands grown on pit-patterned Si(001) substrates is investigated using elasticity theory solved by finite element methods. Larger critical island volumes with respect to the unpatterned case are predicted. A justification based on the qualitatively different stressors acting on the substrate in the presence of pits is provided. Experimental results in terms of critical SiGe-island volumes as a function of the Ge content are nicely reproduced by the model.
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81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
62.20.fq Plasticity and superplasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations

Optical absorption in c-Si/a-Si:H core/shell nanowire arrays for photovoltaic applications

W. Q. Xie, W. F. Liu, J. I. Oh, and W. Z. Shen

Appl. Phys. Lett. 99, 033107 (2011); http://dx.doi.org/10.1063/1.3615297 (3 pages) | Cited 3 times

Online Publication Date: 21 July 2011

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The optical properties have been numerically investigated in crystalline Si (c-Si)/hydrogenated amorphous Si (a-Si:H) core/shell nanowire (CSNW) arrays for various structural parameters. We have demonstrated that the light absorption can be greatly enhanced in c-Si/a-Si:H CSNW arrays especially for the weak absorption solar band (1.5–2.5 eV) of crystalline silicon nanowire (c-SiNW) arrays. We have also obtained the optimal parameters for photovoltaic applications, at which the photocurrent enhancement factors have been achieved to be 14% and 345% per volume material compared to in c-SiNW arrays and c-Si films, respectively. Furthermore, the underlying mechanism of the absorption enhancement in CSNW arrays has been discussed.
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78.67.Lt Quantum wires
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
72.40.+w Photoconduction and photovoltaic effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Post-complementary metal-oxide-semiconductor vertical and molecular transistors: A platform for molecular electronics

Elad D. Mentovich and Shachar Richter

Appl. Phys. Lett. 99, 033108 (2011); http://dx.doi.org/10.1063/1.3612913 (3 pages) | Cited 1 time

Online Publication Date: 21 July 2011

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We demonstrate two types of post-complementary vertical-metal-insulator tunneling transistor in which a self-assembled monolayer is coupled to the channel of one of them. It is found that the properties of the molecular device are better than those of similar transistors in which these molecules are absent. The molecular transistor exhibits higher currents than the non-molecular device and shows negligible leakage currents, with clear features which are attributed to the properties of the molecules.
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85.30.Tv Field effect devices
85.65.+h Molecular electronic devices

Modifying electronic transport properties of graphene by electron beam irradiation

Y. H. He, L. Wang, X. L. Chen, Z. F. Wu, W. Li, Y. Cai, and N. Wang

Appl. Phys. Lett. 99, 033109 (2011); http://dx.doi.org/10.1063/1.3615294 (3 pages) | Cited 7 times

Online Publication Date: 22 July 2011

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We demonstrate that electron beam irradiation with precise dosage control under clean vacuum conditions can induce bond disorder and inter-valley scattering but not necessarily lattice damage in high quality single-layer graphene, as evidenced by the changes of temperature-dependent transport properties, quantum Hall effects, and large negative magnetoresistance effects observed at cryogenic temperatures. The bond disorder significantly modified the Raman scattering and electronic transport properties of graphene, which is consistent with that observed in hydrogenated graphene. In situ transport measurements at different sample treatment stages revealed an interesting activation process of graphene through electron beam irradiation. The activated graphene samples are very sensitive to oxygen and water vapors.
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81.05.ue Graphene
73.43.Qt Magnetoresistance
73.63.Bd Nanocrystalline materials
78.30.Na Fullerenes and related materials
81.07.Bc Nanocrystalline materials
78.67.Wj Optical properties of graphene

Strontium vacancy clustering in Ti-excess SrTiO3 thin film

Y. Tokuda, S. Kobayashi, T. Ohnishi, T. Mizoguchi, N. Shibata, Y. Ikuhara, and T. Yamamoto

Appl. Phys. Lett. 99, 033110 (2011); http://dx.doi.org/10.1063/1.3616136 (3 pages) | Cited 3 times

Online Publication Date: 22 July 2011

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The defect structure of a homoepitaxial thin film of SrTiO3 containing excess Ti grown by pulsed laser deposition is investigated. The Sr/Ti ratio of the film is controlled to possess a slight excess of Ti by tuning the laser fluence. High-resolution transmission electron microscopy and electron energy loss spectroscopy studies reveal that the film contains Sr vacancies because of the presence of excess Ti. These vacancies tend to cluster as platelets several nanometers in diameter on (001) planes in the films. The SrO planes that contain the vacancy clusters exhibit lattice expansion due to Coulomb repulsion.
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61.72.jd Vacancies
79.20.Uv Electron energy loss spectroscopy
81.15.Fg Pulsed laser ablation deposition

Capacitive carbon nanotube networks in polymer composites

Ji-Jia Ding, Chieh-Lien Lu, and Wen-Kuang Hsu

Appl. Phys. Lett. 99, 033111 (2011); http://dx.doi.org/10.1063/1.3615052 (3 pages)

Online Publication Date: 22 July 2011

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Carbon nanotube networks behave as capacitive elements in polymers and carrier transport across tube junctions resembles charging a capacitive tube/polymer/tube structure. Spin localization at interface is verified by electron paramagnetic resonance and a transport mechanism based on temperature controlled free volume of polymer is proposed.
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73.63.Fg Nanotubes
76.30.-v Electron paramagnetic resonance and relaxation
81.07.De Nanotubes

Coplanar waveguide on graphene in the range 40 MHz–110 GHz

M. Dragoman, D. Neculoiu, A. Cismaru, A. A. Muller, G. Deligeorgis, G. Konstantinidis, D. Dragoman, and R. Plana

Appl. Phys. Lett. 99, 033112 (2011); http://dx.doi.org/10.1063/1.3615289 (3 pages) | Cited 8 times

Online Publication Date: 22 July 2011

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We present the modeling and measurements of microwave propagation in a coplanar waveguide over graphene in the range of frequencies 40 MHz-110 GHz, which suggest that graphene could work well in a very large bandwidth. Graphene is acting as a natural matching device because its equivalent resistance at these frequencies is able to vary more than 75% when DC biases are applied in the range −4 V to 4 V on the graphene waveguide.
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81.05.ue Graphene
41.20.Jb Electromagnetic wave propagation; radiowave propagation
84.40.Az Waveguides, transmission lines, striplines
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