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6 Apr 2009

Volume 94, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 94, 141901 (2009); http://dx.doi.org/10.1063/1.3111813 (3 pages)

G. S. Huang (黄高山), S. Kiravittaya, V. A. Bolaños Quiñones, F. Ding (丁飞), M. Benyoucef, A. Rastelli, Y. F. Mei (梅永丰), and O. G. Schmidt
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Counting graphene layers on glass via optical reflection microscopy

P. E. Gaskell, H. S. Skulason, C. Rodenchuk, and T. Szkopek

Appl. Phys. Lett. 94, 143101 (2009); http://dx.doi.org/10.1063/1.3115026 (3 pages) | Cited 28 times

Online Publication Date: 6 April 2009

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We show that optical reflection microscopy is a reliable method to simultaneously locate and count graphene layers deposited on bulk, transparent substrates such as soda-lime glass. The visible contrast in optical reflection versus graphene layer number is resolvable on bulk substrates. A simple Fresnel theory based on the universal optical conductance of graphene layers accurately models optical reflection images taken at a wavelength of 550±5 nm. We directly count one to nine layers of graphene using reflection microscopy.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.40.Ri Fullerenes and related materials
78.68.+m Optical properties of surfaces
81.07.Bc Nanocrystalline materials

Origin of low threshold field emission from nitrogen-incorporated nanocrystalline diamond films

Tomohiro Ikeda and Kungen Teii

Appl. Phys. Lett. 94, 143102 (2009); http://dx.doi.org/10.1063/1.3115767 (3 pages) | Cited 14 times

Online Publication Date: 8 April 2009

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Highly conductive, nitrogen-incorporated nanocrystalline diamond films with quasimetallic character emit electrons at low turn-on fields ( ∼ 3 V μm−1). These films exhibit stronger delocalization of carriers, indicative of smaller energy separation between the defect bands in the band gap. We show that the emission level derived from the measured emission characteristic and electron affinity shifts upward (up to a few eV) with increasing the film conductivity, thereby decreasing the effective potential barrier height for the emission. This is attributed to higher probabilities of electron injection into upper defect levels during the transport process, originating from internal band bending and increasing band continuity.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
73.22.-f Electronic structure of nanoscale materials and related systems
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Ng Insulators
71.20.Ps Other inorganic compounds

Distribution control of 1.55 μm InAs quantum dots down to small numbers on truncated InP pyramids grown by selective area metal organic vapor phase epitaxy

Hao Wang, Jiayue Yuan, Torsten Rieger, Peter J. van Veldhoven, Peter Nouwens, Tom J. Eijkemans, Tjibbe de Vries, Barry Smalbrugge, Erik Jan Geluk, and Richard Nötzel

Appl. Phys. Lett. 94, 143103 (2009); http://dx.doi.org/10.1063/1.3116146 (3 pages) | Cited 7 times

Online Publication Date: 8 April 2009

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Distribution control of InAs quantum dots (QDs) on truncated InP pyramids by selective area growth is reported. The top surface of the pyramids is composed of a (100) facet and high-index facets aside. The arrangement of the facets is governed by the shape of the pyramid base and top surface area. The QDs preferentially nucleate on the high-index facets determining position and distribution. The QD number is reduced with shrinking top surface size. Positioning of four, three, two, and single QDs is realized depending on the top surface’s shape and size. Emission from single QDs is observed at 1.55 μm.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.47.Fg Semiconductor surfaces

Possible formation of interlayer nano-p-n junctions and quantum dot in double-walled carbon nanotube with electrode contacts to different layers

T. Shimizu, J. Haruyama, K. Nozawa, T. Sugai, and H. Shinohara

Appl. Phys. Lett. 94, 143104 (2009); http://dx.doi.org/10.1063/1.3108086 (3 pages) | Cited 2 times

Online Publication Date: 10 April 2009

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We report findings on the asymmetrical current properties on both the source-drain and back-gate voltage (VBG) dependence (unconventional ambipolar behavior) found in a double-walled carbon nanotube (DWNT) field-effect transistor, which has electrode contacts to different layers. We also find Coulomb oscillations with a large charging energy observable only in +VBG region at low temperature. As origins for these phenomena, we discuss the possible presence of outer p- and inner n-type semiconducting layers, a corresponding interlayer nano-p-n junction, and a small quantum dot region in the inner n-layer exposed from the outer layer. Annealing of the DWNT in air atmosphere after synthesis allows change in only outer layer to p-type, remaining n-type behavior in the inner layer.
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85.30.Tv Field effect devices
85.35.Kt Nanotube devices
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Effects of capping on GaN quantum dots deposited on Al0.5Ga0.5N by molecular beam epitaxy

M. Korytov, M. Benaissa, J. Brault, T. Huault, T. Neisius, and P. Vennéguès

Appl. Phys. Lett. 94, 143105 (2009); http://dx.doi.org/10.1063/1.3115027 (3 pages) | Cited 9 times

Online Publication Date: 10 April 2009

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The impact of the capping process on the structural and morphological properties of GaN quantum dots (QDs) grown on fully relaxed Al0.5Ga0.5N templates was studied by transmission electron microscopy. A morphological transition between the surface QDs, which have a pyramidal shape, and the buried ones, which have a truncated pyramid shape, is evidenced. This shape evolution is accompanied by a volume change: buried QDs are bigger than surface ones. Furthermore a phase separation into Al0.5Ga0.5N barriers was observed in the close vicinity of buried QDs. As a result, the buried QDs were found to be connected with the nearest neighbors by thin Ga-rich zones, whereas Al-rich zones are situated above the QDs.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
64.75.Qr Phase separation and segregation in semiconductors
81.07.Ta Quantum dots

Effect of gas rarefaction on the performance of submicron fins

Suresh Ramanan and Ronggui Yang

Appl. Phys. Lett. 94, 143106 (2009); http://dx.doi.org/10.1063/1.3115786 (3 pages) | Cited 2 times

Online Publication Date: 10 April 2009

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High thermal conductivity and high surface to volume ratios of nanostructures such as carbon nanotubes and metallic nanowires make them great candidates as micro/nano-fins and thus a potential solution to the ever-increasing thermal management challenges in electronics and photonics. With sizes ranging in the order of a few hundred nanometers or less, the fluid flow through these structures fall in the transition, slip, and even molecular transport regimes. The effects of the velocity and temperature slips (gas rarefaction) could not be neglected. In this study, a simple analytical model has been developed to predict the effect of gas rarefaction on the heat transfer performance of submicron fins. It is shown that the effects of gas rarefaction should be taken into account when designing micro/nano-fins since such effects can significantly reduce the heat transfer enhancement postulated for micro/nano-fins.
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44.10.+i Heat conduction

The effect of layer absorbance for complex surface enhanced Raman scattering substrates

Z.-Y. Zhang, Y.-J. Liu, Q. Zhao, and Y.-P. Zhao

Appl. Phys. Lett. 94, 143107 (2009); http://dx.doi.org/10.1063/1.3118525 (3 pages) | Cited 6 times

Online Publication Date: 10 April 2009

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The “hot spots” mechanism is a common wisdom for surface enhanced Raman scattering (SERS). We argue that this is true when the hot spots are directly exposed to the detector. For complex SERS substrates with layered structures such as nanorod arrays, the structure and the layer absorbance both play important roles, which make the effect of hot spots less significant. Using a numerical calculation of the local electric field distribution of an Ag nanorod array substrate, we demonstrate that the layer absorbance must be considered in order to obtain polarization-dependent SERS intensity that is consistent with experimental data.
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78.30.Er Solid metals and alloys
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.68.+m Optical properties of surfaces

Characteristics of 1.3 μm InAs/InGaAs/GaAs quantum dot electroabsorption modulator

C. Y. Ngo, S. F. Yoon, W. K. Loke, Q. Cao, D. R. Lim, Vincent Wong, Y. K. Sim, and S. J. Chua

Appl. Phys. Lett. 94, 143108 (2009); http://dx.doi.org/10.1063/1.3119186 (3 pages) | Cited 4 times

Online Publication Date: 10 April 2009

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We report the characteristics of 1.3 μm electroabsorption modulators (EAMs) utilizing the InAs/InGaAs/GaAs quantum dot (QD) structures. While extinction ratio of ∼ 10 dB was obtained, suppression of absorption at low reverse bias was observed. Theoretical analysis using a strained-modified, single-band, constant-potential three-dimensional model shows that this is due to the presence of In0.15Ga0.85As acting as potential barrier for the heavy hole. From the device point-of-view, this suggests that InAs/InGaAs/GaAs QD-EAMs are potentially feasible for higher optical power handling capability, which is crucial for high link gain in analog fiber links. We believe that the findings are beneficial to those working on QD-EAMs.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.79.Hp Optical processors, correlators, and modulators
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