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13 Feb 2012

Volume 100, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 073501 (2012); http://dx.doi.org/10.1063/1.3682479 (3 pages)

S. Tongay, M. Lemaitre, J. Fridmann, A. F. Hebard, B. P. Gila, and B. R. Appleton
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Stretch-induced plasmonic anisotropy of self-assembled gold nanoparticle mats

Matthew G. Millyard, Fu Min Huang, Richard White, Elisabetta Spigone, Jani Kivioja, and Jeremy J. Baumberg

Appl. Phys. Lett. 100, 073101 (2012); http://dx.doi.org/10.1063/1.3683535 (3 pages) | Cited 3 times

Online Publication Date: 13 February 2012

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Close-packed monolayers of 20 nm Au nanoparticles are self-assembled at hexane/water interfaces and transferred to elastic substrates. Stretching the resulting nanoparticle mats provides active and reversible tuning of their plasmonic properties, with a clear polarization dependance. Both uniaxial and biaxial strains induce strong blue shifts in the plasmonic resonances. This matches theoretical simulations and indicates that plasmonic coupling at nanometer scale distances is responsible for the observed spectral tuning. Such stretch-tunable metal nanoparticle mats can be exploited for the development of optical devices, such as flexible colour filters and molecular sensors.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.07.Wx Nanopowders
81.16.Dn Self-assembly

Conduction band structure in wurtzite GaAs nanowires: A resonant Raman scattering study

Wang Peng, F. Jabeen, B. Jusserand, J. C. Harmand, and M. Bernard

Appl. Phys. Lett. 100, 073102 (2012); http://dx.doi.org/10.1063/1.3684837 (3 pages) | Cited 5 times

Online Publication Date: 13 February 2012

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We report on a room temperature Raman resonance at 1.56 eV in GaAs wurtzite nanowires together with the emergence of a strong forbidden longitudinal optical phonon line. We attribute this resonance, absent in zinc blende wires with similar diameters, to an additional excitonic transition due to conduction band folding in agreement with recent theoretical predictions.
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71.20.Nr Semiconductor compounds
73.22.-f Electronic structure of nanoscale materials and related systems
63.22.Gh Nanotubes and nanowires
78.67.Uh Nanowires
78.30.Fs III-V and II-VI semiconductors

Top-gated germanium nanowire quantum dots in a few-electron regime

Sung-Kwon Shin, Shaoyun Huang, Naoki Fukata, and Koji Ishibashi

Appl. Phys. Lett. 100, 073103 (2012); http://dx.doi.org/10.1063/1.3684941 (4 pages) | Cited 1 time

Online Publication Date: 13 February 2012

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Top gated quantum dots (QDs) have been fabricated from n-type chemically synthesized germanium nanowires (GeNWs) by constricting its length with metal electrode contacts. With an intermediate HfO2 thin film, the constricted GeNW was fully covered by an Omega-shaped top-gate. The QD was probed and characterized by single-electron transport measurements at liquid helium temperature and has been found to reach a few-electron regime, in which the number of confined electrons was tunable from zero. The absolute zero-electron was confirmed with a charge stability diagram, and it was revealed that the extremely small QD arose from potential fluctuations due to phosphorus donors.
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81.16.Be Chemical synthesis methods
73.63.Nm Quantum wires
73.63.Kv Quantum dots
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Nanofluid based optical sensor for rapid visual inspection of defects in ferromagnetic materials

V. Mahendran and John Philip

Appl. Phys. Lett. 100, 073104 (2012); http://dx.doi.org/10.1063/1.3684969 (3 pages) | Cited 8 times

Online Publication Date: 13 February 2012

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We have developed a simple sensor for imaging internal defects in materials using a magnetically polarizable nanoemulsion. The gradient in the magnetic flux lines around the defective region leads to the formation of one-dimensional nanodroplet arrays along the field direction, which incredibly diffract the incident white light to produce bright colors. As the diffracted wavelength has a direct correlation with the defect features, this approach enable visual inspection of ferromagnetic components and has several advantages over existing flux leakage sensors in terms of cost, re-usability and complexity.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Enhancement of thermoelectric properties in graphene nanoribbons modulated with stub structures

Zhong-Xiang Xie, Li-Ming Tang, Chang-Ning Pan, Ke-Min Li, Ke-Qiu Chen, and Wenhui Duan

Appl. Phys. Lett. 100, 073105 (2012); http://dx.doi.org/10.1063/1.3685694 (4 pages) | Cited 6 times

Online Publication Date: 14 February 2012

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The thermoelectric properties in graphene nanoribbons modulated with stub structures are studied using atomistic simulation of electron and phonon transport. The results show that the phonon transport is dramatically suppressed by the elastic scattering of the stub structure; while the thermopower S can be enhanced by a few times of magnitude. This leads to a strong enhancement of the figure of merit (ZT). Moreover, it is found that the enhancement of ZT can be effectively tuned by modulating geometric parameters of the stub and edge shapes, which offers an effective way to improve the thermoelectric performance of graphene nanoribbons.
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72.20.Pa Thermoelectric and thermomagnetic effects
81.07.Bc Nanocrystalline materials
72.80.Vp Electronic transport in graphene

Loss tangent imaging: Theory and simulations of repulsive-mode tapping atomic force microscopy

Roger Proksch and Dalia G. Yablon

Appl. Phys. Lett. 100, 073106 (2012); http://dx.doi.org/10.1063/1.3675836 (3 pages) | Cited 5 times

Online Publication Date: 14 February 2012

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An expression for loss tangent measurement of a surface in amplitude modulation atomic force microscopy is derived using only the cantilever phase and the normalized cantilever amplitude. This provides a direct measurement of substrate compositional information that only requires tuning of the cantilever resonance to provide quantitative information. Furthermore, the loss tangent expression incorporates both the lost and stored energy into one term that represents a fundamental interpretation of the phase signal in amplitude modulation imaging. Numerical solutions of a cantilever tip interacting with a simple Voigt modeled surface agree with the derived loss tangent to within a few percent.
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06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
68.37.Ps Atomic force microscopy (AFM)

The effect of crystallite size on thermoelectric properties of bulk nanostructured magnesium silicide (Mg2Si) compounds

Nikhil Satyala and Daryoosh Vashaee

Appl. Phys. Lett. 100, 073107 (2012); http://dx.doi.org/10.1063/1.3684615 (4 pages) | Cited 7 times

Online Publication Date: 14 February 2012

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In nanostructured bulk materials, the additional interfaces in the material enhance phonon scattering and reduce the thermal conductivity. However, interfaces also scatter electrons and deteriorate charge carrier transport. In order to benefit from the interfacial effects, the crystallite size in the material must be small compared with phonon mean free path (PMFP) and large compared with the charge carrier mean free path (CMFP). In this paper, we solve the Boltzmann transport equation for charge carriers and phonons. We show that bulk nanostructuring of Mg2Si is not an efficient method to enhance the figure-of-merit as the PMFP and CMFP are in the same range.
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72.20.Pa Thermoelectric and thermomagnetic effects
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.07.Bc Nanocrystalline materials
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.

Layer dependent mechanical responses of graphene composites to near-infrared light

James Loomis, Ben King, and Balaji Panchapakesan

Appl. Phys. Lett. 100, 073108 (2012); http://dx.doi.org/10.1063/1.3685479 (4 pages) | Cited 6 times

Online Publication Date: 15 February 2012

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The authors report layer dependent physical responses of graphene-based polymer composites to near-infrared (NIR) light. Thin film polymer composites were fabricated and compared utilizing both single layer graphene and few layer graphene (∼5 layers). NIR-induced axial stress and kinetics were measured and found to exhibit three distinct pre-strain dependent response states. Composite stress responses, elastic moduli, and efficiencies were observed to depend on the number of graphene layers in the two-dimensional crystal.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.05.Qk Reinforced polymers and polymer-based composites
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
68.60.Bs Mechanical and acoustical properties

Atomic structure of a Σ3 [110]/(111) grain boundary in CeO2

B. Feng, H. Hojo, T. Mizoguchi, H. Ohta, S. D. Findlay, Y. Sato, N. Shibata, T. Yamamoto, and Y. Ikuhara

Appl. Phys. Lett. 100, 073109 (2012); http://dx.doi.org/10.1063/1.3682310 (3 pages)

Online Publication Date: 15 February 2012

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The atomic structure of a Σ3 [110]/(111) grain boundary in CeO2 was studied by scanning transmission electron microscopy, electron energy loss spectroscopy, and the first-principles calculations. It was revealed that this grain boundary does not promote the formation of oxygen vacancies and keeps oxygen stoichiometry, which is different from that of Σ5 CeO2 grain boundary studied previously [H. Hojo, T. Mizoguchi, H. Ohta, S. D. Findlay, N. Shibata, T. Yamamoto, and Y. Ikuhara, Nano Lett. 10, 4668 (2010)]. It was found that the difference in grain boundary oxygen stoichiometry is correlated with the grain boundary atomic structure.
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61.72.Mm Grain and twin boundaries
79.20.Uv Electron energy loss spectroscopy
61.66.Bi Elemental solids
61.66.Dk Alloys
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Mechanical cleaning of graphene

A. M. Goossens, V. E. Calado, A. Barreiro, K. Watanabe, T. Taniguchi, and L. M. K. Vandersypen

Appl. Phys. Lett. 100, 073110 (2012); http://dx.doi.org/10.1063/1.3685504 (3 pages) | Cited 8 times

Online Publication Date: 16 February 2012

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Contamination of graphene due to residues from nanofabrication often introduces background doping and reduces electron mobility. For samples of high electronic quality, post-lithography cleaning treatments are therefore needed. We report that mechanical cleaning based on contact mode atomic force microscopy removes residues and significantly improves the electronic properties. A mechanically cleaned dual-gated bilayer graphene transistor with hexagonal boron nitride dielectrics exhibited a mobility of ∼36 000 cm2/Vs at low temperature.
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81.65.Cf Surface cleaning, etching, patterning
72.80.Vp Electronic transport in graphene
68.35.bp Fullerenes
85.65.+h Molecular electronic devices
72.20.Fr Low-field transport and mobility; piezoresistance

Tip-plasmon mediated molecular electroluminescence on the highly oriented pyrolytic graphite substrate

C. Zhang, R. Zhang, S. Jiang, L. Zhang, H. Y. Gao, X. L. Zhang, L. G. Chen, Y. Liao, and Z. C. Dong

Appl. Phys. Lett. 100, 073111 (2012); http://dx.doi.org/10.1063/1.3687178 (4 pages) | Cited 3 times

Online Publication Date: 16 February 2012

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Well-defined molecular fluorescence is realized by tunneling electron excitations from porphyrins on highly oriented pyrolytic graphite that is non-plasmonic in the visible spectral range. The occurrence of molecular electroluminescence is found to rely critically on the plasmonic emitting state of scanning tunneling microscope tip that is pre-examined on silver. These observations, together with the selective enhancement of molecular emission bands by energy-matching tip plasmons, suggest that the plasmonic field is indispensable for the generation of molecular electroluminescence, and the tip plasmon alone is sufficient in achieving this. Excitation of molecules directly by electrons is inefficient to produce light.
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78.60.Fi Electroluminescence
78.55.Kz Solid organic materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.40.Me Organic compounds and polymers

Sub-hertz relaxation process in chiral smectic mixtures doped with silver nanoparticles

Pradip Kr. Mandal, Artsiom Lapanik, Robert Wipf, Bernd Stuehn, and Wolfgang Haase

Appl. Phys. Lett. 100, 073112 (2012); http://dx.doi.org/10.1063/1.3685700 (3 pages) | Cited 4 times

Online Publication Date: 17 February 2012

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A thermal activated sub-hertz frequency dielectric absorption process in both SmC* and SmA* phases along with characteristic Goldstone mode have been observed in both pure and silver nano particle doped liquid crystal mixtures. This process is well resolved, in particular, in the composites probably due to capturing of ions/charges inside the thiol group layer around the silver particles surface, thereby increasing the resistivity of the composites. The process is interpreted as space charge accumulation of ions/charges at the interface between liquid crystals and the cell polymer layer close to the electrodes. Improved switching characteristics and reduced spontaneous polarization have been detected.
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61.30.-v Liquid crystals
82.45.-h Electrochemistry and electrophoresis
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
82.70.Rr Aerosols and foams
64.75.Bc Solubility

Thermal properties of the hybrid graphene-metal nano-micro-composites: Applications in thermal interface materials

Vivek Goyal and Alexander A. Balandin

Appl. Phys. Lett. 100, 073113 (2012); http://dx.doi.org/10.1063/1.3687173 (4 pages) | Cited 18 times

Online Publication Date: 17 February 2012

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The authors report on synthesis and thermal properties of the electrically conductive thermal interface materials with the hybrid graphene-metal particle fillers. The thermal conductivity of resulting composites was increased by ∼500% in a temperature range from 300 K to 400 K at a small graphene loading fraction of 5-vol.-%. The unusually strong enhancement of thermal properties was attributed to the high intrinsic thermal conductivity of graphene, strong graphene coupling to matrix materials, and the large range of the length-scale—from nanometers to micrometers—of the graphene and silver particle fillers. The obtained results are important for the thermal management of advanced electronics and optoelectronics.
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81.16.-c Methods of micro- and nanofabrication and processing
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
65.80.Ck Thermal properties of graphene
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
61.48.Gh Structure of graphene

Realization of a mesoscopic reprogrammable magnetic logic based on a nanoscale reconfigurable magnonic crystal

J. Ding, M. Kostylev, and A. O. Adeyeye

Appl. Phys. Lett. 100, 073114 (2012); http://dx.doi.org/10.1063/1.3687177 (5 pages) | Cited 4 times

Online Publication Date: 17 February 2012

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We demonstrate functionality of magnetic logic based on a reconfigurable magnonic crystal in the form of a meander-type ferromagnetic nanowire. A ferromagnetic resonance method employing a microscopic coplanar waveguide has been used to detect the logic state of the structure coded in its magnetic ground state. Ferromagnetic resonance responses of anti-ferromagnetic and multi-cluster (mix of anti-ferromagnetic and ferromagnetic) ground states can be switched by applying a DC current in the signal line of the coplanar waveguide. Experimental demonstrations of device functionality as XOR and NOT logic gates are supported by the magnetic force microscopy images and micromagnetic simulations.
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85.75.Ff Reprogrammable magnetic logic
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