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31 May 2010

Volume 96, Issue 22, Articles (22xxxx)

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Appl. Phys. Lett. 96, 223101 (2010); http://dx.doi.org/10.1063/1.3439728 (3 pages)

Seokho Yun, Jeremy A. Bossard, Theresa S. Mayer, and Douglas H. Werner
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Angle and polarization tolerant midinfrared dielectric filter designed by genetic algorithm optimization

Seokho Yun, Jeremy A. Bossard, Theresa S. Mayer, and Douglas H. Werner

Appl. Phys. Lett. 96, 223101 (2010); http://dx.doi.org/10.1063/1.3439728 (3 pages) | Cited 4 times

Online Publication Date: 1 June 2010

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We report a dielectric frequency selective surface filter with an angularly tolerant, polarization independent stop band designed at a midinfrared wavelength of 3.0 μm. The structure, consisting of a doubly-periodic amorphous silicon grating supported by a polyimide membrane, was optimized using a genetic algorithm to have a transmission stop band with a 3.33% 10 dB bandwidth for incidence angles as large as 10° from normal. The measured properties of the fabricated filter were within 1% of theoretical predictions. This strategy provides a practical and efficient approach to creating advanced dielectric filters for highly customized infrared optical device and coating applications.
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42.79.Ci Filters, zone plates, and polarizers
42.25.Ja Polarization

Spin-orbit interaction effects on magnetoresistance in graphene-based ferromagnetic double junctions

Chunxu Bai, Juntao Wang, Shuanwen Jia, and Yanling Yang

Appl. Phys. Lett. 96, 223102 (2010); http://dx.doi.org/10.1063/1.3432438 (3 pages) | Cited 11 times

Online Publication Date: 1 June 2010

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Based on the transfer-matrix method, the spin polarized transport properties through a ballistic graphene-based quantum tunneling junctions with the spin-orbit interaction have been investigated. It is found that the magnetoresistance (MR) oscillates with the Rashba spin-orbit interaction (RSOI) and the intrinsic spin-orbit interaction (ISOI). In addition, when the RSOI is present, the negative MR can be observed due to the spin-flip effect, whereas for the ISOI alone no such negative MR can be found. It is anticipated to apply such a phenomenon to design the electron devices based on the graphene.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Tj Spin-orbit effects
75.76.+j Spin transport effects
75.47.Pq Other materials
73.23.Ad Ballistic transport
72.25.Mk Spin transport through interfaces

Negative differential resistance and resistive switching behaviors in Cu2S nanowire devices

Xiaohua Liu, Matthew T. Mayer, and Dunwei Wang

Appl. Phys. Lett. 96, 223103 (2010); http://dx.doi.org/10.1063/1.3442919 (3 pages) | Cited 7 times

Online Publication Date: 1 June 2010

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Two-terminal devices of Cu2S/ZnO core/shell nanowires were fabricated and measured. Forward bias sweeping produced a rectified I-V characteristic of a diode, with turn-on voltages varying from 150 to 300 mV. The turn-on voltages depended on the rate at which the bias was varied. When the bias scan was reversed, a resistive switching (RS) behavior was observed. A low-resistance state was measured, and the diode characteristic diminished. At −50 to −150 mV, negative differential resistance (NDR) was observed, after which the diode behavior was restored. This phenomenon was explained using the diffusion of Cu+ within Cu2S. ZnO acted to limit RS to the positive bias range and NDR to the negative bias range.
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73.61.Ga II-VI semiconductors
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)
72.20.Ht High-field and nonlinear effects
85.30.Tv Field effect devices
81.16.-c Methods of micro- and nanofabrication and processing

Bubble generation in a nanoconfined liquid film between dielectric-coated electrodes under alternating current electric fields

Guoxin Xie, Jianbin Luo, Shuhai Liu, Dan Guo, and Chenhui Zhang

Appl. Phys. Lett. 96, 223104 (2010); http://dx.doi.org/10.1063/1.3443633 (3 pages) | Cited 3 times

Online Publication Date: 2 June 2010

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In this letter, the bubble generation behavior in a nanoconfined liquid film under external alternating current (ac) electric fields (EEFs) has been investigated with the relative optical interference intensity technique. A counterintuitive phenomenon has been found that bubbles generate more easily and intensively when the electrode is coated with a dielectric coating while the total electrical power in the system is significantly lower than the case without the coating. The bubble generation under ac EEFs has been found to be highly ac frequency dependent. The variations in the threshold external voltage and current beyond which bubbles begin to generate with the frequency become more significant in the system with a dielectric-coated electrode. Mechanisms of these experimental phenomena have been discussed.
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68.15.+e Liquid thin films
77.55.-g Dielectric thin films
82.45.Fk Electrodes

Tailoring the luminescence emission of ZnO nanostructures by hydrothermal post-treatment in water

Baodian Yao, Lin Feng, Chun Cheng, Michael M. T. Loy, and Ning Wang

Appl. Phys. Lett. 96, 223105 (2010); http://dx.doi.org/10.1063/1.3443636 (3 pages) | Cited 17 times

Online Publication Date: 2 June 2010

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ZnO nanorods and nanowires fabricated from solution methods exhibit poor optical properties. Using hydrothermal post-treatment in pure water, the green emission can be significantly suppressed at 250 °C and completely eliminated at 350 °C. Meanwhile, the near-band-edge UV radiative recombination efficiency is greatly improved and the UV emission intensity is increased up to 50 times. The morphology and structure of the ZnO nanostructures remain intact after the treatment. As evidenced by the electron paramagnetic resonance investigation, this simple treatment can completely remove or passivate the point defects responsible for the green emission of as-grown ZnO.
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78.67.Uh Nanowires
78.55.Et II-VI semiconductors
78.67.Qa Nanorods
61.72.J- Point defects and defect clusters
76.30.-v Electron paramagnetic resonance and relaxation

A three-dimensional model of electrical percolation thresholds in carbon nanotube-based composites

Weibang Lu, Tsu-Wei Chou, and Erik T. Thostenson

Appl. Phys. Lett. 96, 223106 (2010); http://dx.doi.org/10.1063/1.3443731 (3 pages) | Cited 5 times

Online Publication Date: 2 June 2010

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A three-dimensional modeling approach is developed to simulate the electrical percolation thresholds in carbon nanotube-based composites, wherein the effects of intertube Van der Waals interactions and electrical tunneling are taken into consideration. Numerical studies using the Monte Carlo method show that these two factors play significant roles when the aspect ratio of the constituent carbon nanotubes is low. For high aspect ratios, the effects of these two factors are negligible. The influence of carbon nanotube waviness on electrical percolation thresholds has also been studied.
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73.40.Gk Tunneling

On direct-writing methods for electrically contacting GaAs and Ge nanowire devices

Guannan Chen, Eric M. Gallo, Joan Burger, Bahram Nabet, Adriano Cola, Paola Prete, Nico Lovergine, and Jonathan E. Spanier

Appl. Phys. Lett. 96, 223107 (2010); http://dx.doi.org/10.1063/1.3441404 (3 pages) | Cited 7 times

Online Publication Date: 2 June 2010

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The electronic transport and gating characteristics in GaAs and Ge nanowires (NWs) are altered significantly following either indirect or direct exposure to a focused Ga+ ion beam (FIB), such as that used to produce Pt electrical contacts to NWs. While these results challenge the assumptions made in some previously reported work relating to the electronic properties of semiconductor NWs using FIB-assisted production of contacts and/or their leads, local electron beam induced deposition is shown to be a reliable and facile route for producing robust electrical contacts to individual vapor phase-grown NWs in a manner that enables study of their actual carrier transport properties.
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73.61.Ey III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Three-dimensional imaging of pore structures inside low-κ dielectrics

Huolin L. Xin, Peter Ercius, Kevin J. Hughes, James R. Engstrom, and David A. Muller

Appl. Phys. Lett. 96, 223108 (2010); http://dx.doi.org/10.1063/1.3442496 (3 pages) | Cited 2 times

Online Publication Date: 2 June 2010

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The three-dimensional reconstruction of a porous low-dielectric constant film (κ = 2.5), resolving pores as small as 1 nm, was achieved using annular dark-field scanning transmission electron tomography, enabling quantitative measurements of the pore morphologies and size distribution. Most large pores were elliptical. Together with log-normal pore-size distribution, this suggests pore coalescence during the material’s growth. Ellipsometric porosimetry indicates a high degree of interconnectivity between pores. Tomography shows the material exhibits little large-scale pore connectivity, thus placing an upper limit on the size of the interconnections at below 1 nm. Systematic errors in the tomographic and ellipsometric size distributions appear to be largely complementary.
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77.55.Bh Low-permittivity dielectric films
61.46.-w Structure of nanoscale materials
61.43.Gt Powders, porous materials

Study on reaction mechanism of dehydrogenation of magnesium hydride by in situ transmission electron microscopy

Shigehito Isobe, Akifumi Ono, Hao Yao, Yongming Wang, Naoyuki Hashimoto, and Somei Ohnuki

Appl. Phys. Lett. 96, 223109 (2010); http://dx.doi.org/10.1063/1.3442910 (3 pages) | Cited 6 times

Online Publication Date: 2 June 2010

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In situ observation on dehydrogenation of MgH2 was performed by using transmission electron microscope (TEM). The dehydrogenation of MgH2 with 1 mol % Nb2O5 and formation of nanosized Mg particles were observed at 150 °C. Nb2O5 was not confirmed in diffraction patterns and TEM images probably due to wide dispersion. On MgH2 with 10 mol % Nb2O5, the high resolution TEM could recognize the dehydrogenation at the interface between MgH2 and Nb2O5, proceeding with increasing temperature. This suggests that hydrogen atoms could diffuse from MgH2 phase to the interface between Mg and Nb2O5, resulting in formation of hydrogen molecules at the interface.
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68.43.Vx Thermal desorption
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
88.30.R- Hydrogen storage
82.80.-d Chemical analysis and related physical methods of analysis
68.35.Fx Diffusion; interface formation
68.37.Lp Transmission electron microscopy (TEM)

Characterization of electronic structure of silicon nanocrystals in silicon nitride by capacitance spectroscopy

Chang-Hee Cho, Baek-Hyun Kim, Sang-Kyun Kim, and Seong-Ju Park

Appl. Phys. Lett. 96, 223110 (2010); http://dx.doi.org/10.1063/1.3431572 (3 pages) | Cited 4 times

Online Publication Date: 2 June 2010

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The electronic structure of silicon nanocrystals embedded in a silicon nitride insulating film is identified by using a capacitance spectroscopy. The tunneling capacitor device, which is used in this study, consists of a tunneling silicon nitride, an array of silicon nanocrystals embedded in a silicon nitride film, and a blocking silicon nitride deposited on p-type (100) Si substrate. The absolute position of the lowest conduction and the highest valence levels of the silicon nanocrystal is revealed and the band-gap energy of silicon nanocrystals estimated by the capacitance spectroscopy agrees well with that measured by photoluminescence spectroscopy.
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71.20.Ps Other inorganic compounds
73.61.Ng Insulators
73.40.-c Electronic transport in interface structures
78.55.Hx Other solid inorganic materials

Multidielectric polarizations in the core/shell Co/graphite nanoparticles

X. F. Zhang, P. F. Guan, and X. L. Dong

Appl. Phys. Lett. 96, 223111 (2010); http://dx.doi.org/10.1063/1.3446868 (3 pages) | Cited 11 times

Online Publication Date: 3 June 2010

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Hybrid core/shell Co/graphite nanoparticles synthesized by an arc-discharge method exhibit an enhanced dielectric loss property in the frequency range of 2–18 GHz. Complex permittivity expressed by Debye dipolar polarization approximate show that three kinds of dielectric polarizations coexist in this hybrid system. Combined with theoretical simulation, we further clarified that the dielectric polarizations are ascribed to the high defective graphite shells, and additional interfacial polarizations arising from the special core/shell architecture.
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77.22.Ej Polarization and depolarization
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
77.22.Gm Dielectric loss and relaxation

Approaching ideal weak link behavior with three dimensional aluminum nanobridges

R. Vijay, E. M. Levenson-Falk, D. H. Slichter, and I. Siddiqi

Appl. Phys. Lett. 96, 223112 (2010); http://dx.doi.org/10.1063/1.3443716 (3 pages) | Cited 9 times

Online Publication Date: 4 June 2010

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We investigate unshunted dc superconducting quantum interference devices (SQUIDs) consisting of aluminum nanobridges of varying length L contacted with (two dimensional, or 2D) and (three dimensional, or 3D) banks. 3D nanobridge SQUIDs with L ≤ 150 nm (approximately four times the superconducting coherence length) exhibit ≈70% critical current modulation with applied magnetic field, approaching the theoretical limit for an ideal short metallic weak link. In contrast, 2D nanobridge SQUIDs exhibit significantly lower critical current modulation. This enhanced nonlinearity makes 3D nanobridge Josephson junctions well suited to optimize sensitivity in weak link SQUID magnetometers as well as realize ultralow-noise amplifiers and qubits.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
85.25.Cp Josephson devices
85.25.-j Superconducting devices
74.25.Sv Critical currents
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements

Surface-passivation-induced metallic and magnetic properties of ZnO graphitic sheet

Yang Zhang, Shun-Qing Wu, Yu-Hua Wen, and Zi-Zhong Zhu

Appl. Phys. Lett. 96, 223113 (2010); http://dx.doi.org/10.1063/1.3442507 (3 pages) | Cited 6 times

Online Publication Date: 4 June 2010

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First-principles calculations were used to investigate the electronic and magnetic properties of surface-passivated ZnO graphitic sheets. The results show that ZnO graphitic sheet with hydrogenation on both O and Zn atoms exhibits indirect band gap, while ZnO graphitic sheet is found to be metallic for hydrogenation on only O atoms and magnetic semiconducting for surface passivation by H or NH2 on only Zn atoms. The relative stability of ZnO graphitic sheet passivated by H or NH2 has also been discussed.
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71.20.Nr Semiconductor compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
75.50.Pp Magnetic semiconductors
68.35.bg Semiconductors
75.30.Cr Saturation moments and magnetic susceptibilities
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