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In this work, we synthesized high-quality InAs nanowires by a convenient chemical vapor deposition method, and developed a simple laser heating method to measure the thermal conductivity of a single InAs nanowire in air. During the measurement, a focused laser was used to heat one end of a freely suspended nanowire, with its other end embedded into a carbon conductive adhesive. In order to obtain the thermal conductivity of InAs nanowires, the heat loss in the heat transfer process was estimated, which includes the heat loss through air conduction, the heat convection, and the radiation loss. The absorption ratio of the laser power in the InAs nanowire was calculated. The result shows that the thermal conductivity of InAs nanowires monotonically increases from 6.4 W m(-1) K-1 to 10.5 W m(-1) K-1 with diameters increasing from 100 nm to 190 nm, which is ascribed to the enhanced phonon-boundary scattering.

Keyword ：

Chemical vapor deposition InAs nanowires Phonon-boundary scattering Thermal conductivity

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Peculiar vibrational modes of graphene nanoribbons (GNRs) with topological line defects were presented. We find that phonon dispersion relations of the topological defective GNRs are more similar to those of perfect armchair-edge GNR than to zigzag-edge GNR in spite of their zigzag edge. All vibrational modes at G point are assigned in detail by analyzing their eigenvectors and are presented by video. Three types of characteristic vibrational modes, namely, localized vibrational modes in defect sites, edges, and breathing modes, are observed. Five localized vibrational modes near the defect sites are found to be robust against the width of the topological line-defective GNR. The Raman D' band just originates from one localized mode, 1622 cm(-1). The vibrational mode is sensitive to symmetry. The edge modes are related with structural symmetry but not with widths. Two edge modes are asymmetrical and only one is symmetrical. The breathing modes are inversely proportional to the width for wide-defect GNRs, and inversely proportional to the square root of the width for narrow-defect GNRs. The breathing mode frequencies of defective GNRs are slightly higher than those of perfect GNRs. These vibrational modes may be useful in the manipulation of thermal conductance and implementation of single phonon storage.

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Metal doping and sensitization of photocatalyst have been jointly exploited as a novel strategy to improve photocatalytic activity under visible light irradiation. 5, 10, 15, 20-tetrakis (4-chlorophenyl) porphyrin-Cu (II) (CuPp) is chosen to sensitize La-doped TiO2 (La-TiO2) nanocrystalline. La doping results in smaller crystallite and larger specific surface area. La doping or sensitization of TiO2 exhibits higher absorption in visible-light region and photocatalytic degradation efficiency of methyl orange (MO) than pristine TiO2. Coupling effect of La doping and CuPp sensitization leads to the excellent photocatalytic activity under visible light irradiation. A tentative mechanism for the enhancment of photocatalytic activity under visible light irradiation is proposed. (C) 2013 Elsevier B.V. All rights reserved.

Keyword ：

Coupling effect Photocatalytic activity Semiconductors Sol-gel TiO2

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The Raman spectra of bilayer graphene covered with poly(methyl methacrylate) (PMMA) were investigated. Both the G and 2D peaks of PMMA-coated graphene were stiff and broad compared with those of uncovered graphene. This could be attributed to the residual strain induced by high-temperature baking during fabrication of the nanodevice. Furthermore, the two 2D peaks stiffened and broadened with increasing laser power, which is just the reverse to uncovered graphene. The stiffness is likely caused by graphene compression induced by the circular bubble of the thin PMMA film generated by laser irradiation. Our findings may contribute to the application of PMMA in the strain engineering of graphene nanodevices. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4739785]

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Through the finite element method, we study the strain-modulated heat and electronic coupling transport of armchair-edge and zigzag-edge graphene nanoribbons (GNRs) with a dimension of similar to 2 nm by 60 nm. As a direct response of heat and electronic coupling transport to strain, two types of GNRs show different evolutions on the temperature distribution and maximum temperature. Pronouncedly, the quasi-periodic change of electronic conductivity and the monotonic decrease of thermal conductivity found in our study, show a huge potential for future device applications. This tunable coupling transport provides a new avenue for the thermal management of nanoelectronic devices involving GNRs.

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Graphene Nanoribbons Heat and Electronic Coupling Transport Strain

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We studied the specific heat of graphene nanoribbons (GNRs) using an extended force constant model. We found that at low temperature, the specific heat decreases, and its variation with temperature increases with increasing GNR width. However, the specific heat increases with increasing GNR width after crossing a chaotic region. Free boundary conditions, -CHOH-terminated and armchair-edge-induced phonon nondegeneracy, shift and distortion and localized vibrational modes significantly influence GNR specific heat compared with periodic boundary conditions and bare and zigzag edges in GNRs. Finally, we found a uniform expression for specific heat vs. width at every temperature except for the chaotic region. (C) 2011 Elsevier B.V. All rights reserved.

Keyword ：

Graphene nanoribbons Specific heat

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The specific heat of uniaxially strained graphene was investigated in the present paper. A uniaxial strain can modulate specific heat depending on the amount and direction of the strain. Specific heat decreases with an increase in the amount of tension strain at a low temperature and increases with compression. Above 110 K, it varies as the amount of strain is reversed to that at a low temperature. These novel properties can be attributed to the strain-induced shift behavior of out-of-plane acoustic phonons, which is different from that of other phonons. When the strain shifts from zigzag to armchair direction, specific heat gradually decreases for a given temperature. However, the variation in specific heat with the strain direction is significantly less than that with the amount of strain. Further, the difference in specific heat between different strain directions decreases with an increase in temperature. This tunable specific heat may provide a new route for both the implementation of thermal memory and the thermal management of graphene nanoelectronic devices.

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The effect of optical phonons scattering on electronic current has been studied in metallic carbon nanotubes. The current has been calculated self-consistently by total voltage equation and the heat transport equation. The total voltage equation consists of three terms, optical phonons collision term, acoustic phonon scattering term, and contact resistance one. Including LO, A(1), and E-1(2) phonons in collision term, we can reproduce the experimental I-V curves displaying negative differential conductance. Furthermore, one conclusion is made that the more optical phonons are scattered by electron, the lower current is in metallic carbon nanotubes. By comparing the current under different conditions, we can make another conclusion that there should be nonequilibrium optical phonons under high bias in spite or whether the metallic nanotube is suspended or not. This result agrees well with the others [M. Lazzeri, F. Mauri, Phys. Rev. B 73 (2006) 165419]. Based on these results, we do not only explain the experiment, but also propose to design a heat-controlling electronic transistor with metallic carbon nanotubes as its channel, in which the electronic current can be controlled by optical phonons. (C) 2008 Elsevier B.V. All rights reserved.

Keyword ：

Carbon nanotubes Electronic current Heat transport Negative differential conductance Optical phonon scattering

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In this paper, we present a theoretical discussion about colloidal particles transporting to a meniscus deposition region for the vertical evaporation-driven colloidal deposition by the coffee-ring theory. The vertically immersed Substrate is gradually exposed with a low speed, and colloidal particles are deposited on the substrate as suspension surface descends. Due to a singular evaporation rate at the contact line. to keep a constant contact angle, a solvent flow toward the meniscus region is formed to replenish lost liquid. This solvent flow results in a particle flow to form a film on the substrate. (C) 2008 Elsevier B.V. All rights reserved.

Keyword ：

Coffee ring Colloidal particles Evaporation Film growth Self-assembly Vertical evaporation-driven colloidal deposition

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