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13 Dec 2010

Volume 97, Issue 24, Articles (24xxxx)

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Appl. Phys. Lett. 97, 241101 (2010); http://dx.doi.org/10.1063/1.3525583 (3 pages)

Kanghee Lee and Jaewook Ahn
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Enhancement and suppression effect of molecules on nanocavity plasmon emissions excited by tunneling electrons

Y. Zhang, F. Geng, H. Y. Gao, Y. Liao, Z. C. Dong, and J. G. Hou

Appl. Phys. Lett. 97, 243101 (2010); http://dx.doi.org/10.1063/1.3525603 (3 pages)

Online Publication Date: 14 December 2010

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We use tunneling electron induced luminescence techniques to investigate the role of adsorbed molecules in nanocavity plasmon (NCP) mediated emissions. Porphyrin molecules directly adsorbed on metals are found to suppress NCP emissions, while molecules on top of an inserted ultrathin oxide layer on the metal substrate yield enhanced NCP emissions. We attribute such difference in enhancement versus suppression to a competing mechanism of two major roles of molecules on the local field enhancement: geometrical spacer and dynamic dipole oscillator. The latter could become dominant when molecules are sufficiently decoupled from the substrate, leading to the overall enhancement of NCP emissions.
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81.07.Bc Nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials
78.55.Kz Solid organic materials
68.43.Mn Adsorption kinetics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

InGaAs heterostructure formation in catalyst-free GaAs nanopillars by selective-area metal-organic vapor phase epitaxy

J. N. Shapiro, A. Lin, P. S. Wong, A. C. Scofield, C. Tu, P. N. Senanayake, G. Mariani, B. L. Liang, and D. L. Huffaker

Appl. Phys. Lett. 97, 243102 (2010); http://dx.doi.org/10.1063/1.3526734 (3 pages) | Cited 5 times

Online Publication Date: 14 December 2010

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We investigate axial GaAs/InGaAs/GaAs heterostructures embedded in GaAs nanopillars via catalyst-free selective-area metal-organic chemical vapor deposition. Structural characterization by transmission electron microscopy with energy dispersive x-ray spectroscopy (EDS) indicates formation of axial InxGa1−xAs (x ∼ 0.20) inserts with thicknesses from 36 to 220 nm with ±10% variation and graded Ga:In transitions controlled by In segregation. Using the heterointerfaces as markers, the vertical growth rate is determined to increase linearly during growth. Photoluminescence from 77 to 290 K and EDS suggest the presence of strain in the shortest inserts. This capability to control the formation of axial nanopillar heterostructures is crucial for optimized device integration.
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68.35.Fx Diffusion; interface formation
68.35.Ct Interface structure and roughness
78.70.-g Interactions of particles and radiation with matter
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Optimization of branched resonant nanostructures illuminated by a strongly focused beam

Juan Elezgaray, Lotfi Berguiga, and Françoise Argoul

Appl. Phys. Lett. 97, 243103 (2010); http://dx.doi.org/10.1063/1.3526753 (3 pages)

Online Publication Date: 14 December 2010

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In the design of nanostructures to perform single molecule surface enhanced Raman spectroscopy (SM-SERS), metallic structures with very narrow gaps (<1 nm) have been shown to contain regions with electric fields compatible with SM-SERS. However, this geometrical condition does not allow many biomolecules to reach the hot-spot regions. Here, we show that optimized branched structures formed by appropriate arrangements of gold nanoparticles with gaps ≥ 2 nm display field enhancements >102, compatible with SM-SERS.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.30.Er Solid metals and alloys
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Carbon-coated Magnéli-phase TinO2n−1 nanobelts as anodes for Li-ion batteries and hybrid electrochemical cells

Wei-Qiang Han and Xiao-Liang Wang

Appl. Phys. Lett. 97, 243104 (2010); http://dx.doi.org/10.1063/1.3525369 (3 pages)

Online Publication Date: 15 December 2010

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We describe a method for preparing carbon-coated Ti9O17 nanowires using H2Ti3O7 nanobelts as precursors to react with ethane and hydrogen at high-temperature. The carbon-coating layers play a key role in restraining the sintering growth of the core during the phase transformation from H2Ti3O7 to Magnéli-phase TinO2n−1, and in retaining the morphology of nanobelts. We demonstrated that the initial reversible capacity of these Ti9O17 nanobelts attained 182 mA h g−1, a value even higher than the theoretical value of a-TiO2 (167 mA h g−1). Cyclic-voltammetry measurement supports the pseudocapacitive lithium-storage behavior of these Magnéli-phase Ti9O17 nanobelts. Furthermore, the nanobelts exhibit high power density along with excellent cycling stability in their application as hybrid electrochemical cells.
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
73.61.Le Other inorganic semiconductors
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.55.-a Thin film structure and morphology
82.47.Aa Lithium-ion batteries
81.16.-c Methods of micro- and nanofabrication and processing

Quantitative analysis of CO-humidity gas mixtures with self-heated nanowires operated in pulsed mode

J. D. Prades, F. Hernández-Ramírez, T. Fischer, M. Hoffmann, R. Müller, N. López, S. Mathur, and J. R. Morante

Appl. Phys. Lett. 97, 243105 (2010); http://dx.doi.org/10.1063/1.3515918 (3 pages)

Online Publication Date: 15 December 2010

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Self-heating effect in individual metal oxide nanowires can be used to activate their response to gases with power consumptions below tenths of microwatts. The thermal response time of these devices is extremely fast (a few milliseconds) and it makes it possible to observe the kinetics of the interactions between the gas molecules and the metal oxide. In this work we demonstrate that such effects enable an experimental methodology to improve the selectivity of metal oxide-based sensors based on the analysis of their fast response dynamics. Specifically, this work jointly analyzes the magnitude and response time of SnO2 nanowire-based sensors to carbon monoxide (CO) and humidity (H2O) mixtures, proving that a quantitative analysis of CO–H2O gas blends can be achieved by modulating their work temperature through the self-heating effect.
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82.80.-d Chemical analysis and related physical methods of analysis
78.47.D- Time resolved spectroscopy (>1 psec)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
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)

Graphene quantum dots formed by a spatial modulation of the Dirac gap

G. Giavaras and Franco Nori

Appl. Phys. Lett. 97, 243106 (2010); http://dx.doi.org/10.1063/1.3525858 (3 pages)

Online Publication Date: 15 December 2010

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An electrostatic quantum dot cannot be formed in monolayer graphene because of the Klein tunneling. However, a dot can be formed with the help of a uniform magnetic field. As shown here, a spatial modulation of the Dirac gap leads to confined states with discrete energy levels, thus defining a dot, without applying external electric and magnetic fields. Gap-induced dot states can coexist and couple with states introduced by an electrostatic potential. This property allows the region in which the resulting states are localized to be tuned with the potential.
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81.05.ue Graphene
81.07.Ta Quantum dots
73.63.Kv Quantum dots
73.40.Gk Tunneling
73.22.Pr Electronic structure of graphene
73.21.La Quantum dots

Controlled B-site ordering in Sr2CrReO6 double perovskite films by using pulsed laser interval deposition

S. Chakraverty, A. Ohtomo, and M. Kawasaki

Appl. Phys. Lett. 97, 243107 (2010); http://dx.doi.org/10.1063/1.3525578 (3 pages) | Cited 2 times

Online Publication Date: 15 December 2010

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We have investigated the effects of growth interval in pulsed laser deposition on structural, magnetic, and electrical transport properties of (111)-oriented Sr2CrReO6 double perovskite films. It was found that the degree of B-site ordering varied in a wide range by just changing the growth interval. Magnetization under 1 T and metallicity (the ratio of room-temperature resistivity to minimum resistivity at low temperatures) monotonically increased with increasing degree of ordering and reached values nearly identical to bulk. This technique, called pulsed laser interval deposition, may provide more efficient way to study relations between structural and physical properties in double perovskites than controlling growth parameters, such as temperature and oxygen partial pressure.
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81.15.Fg Pulsed laser ablation deposition
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.A- Nucleation and growth

Effect of current on Coulomb oscillation in a Ni–Nb–Zr–H glassy alloy with multiple junctions

Mikio Fukuhara and Akihisa Inoue

Appl. Phys. Lett. 97, 243108 (2010); http://dx.doi.org/10.1063/1.3527084 (3 pages) | Cited 1 time

Online Publication Date: 16 December 2010

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The effect of current on Coulomb oscillation in a (Ni0.36Nb0.24Zr0.40)90H10 glassy alloy was carried out under currents of 1 nA, 10 nA, 100 nA, 1 μA, 10 μA, 100 μA, 1 mA, 10 mA, and 100 mA in the temperature range of 300–6 K. The amplitude of the Coulomb oscillation showed maximum values at around 1 μA. The discrete variation of the oscillation can be described as E = 2×10−4 exp(2.34 N) (r2 = 0.993), showing clear quantization of Coulomb oscillation, where E and N are the units of h/2e2 and step number, respectively. We suggested that this would be associated with nanometer-sized RC circuits in the alloy.
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73.23.Hk Coulomb blockade; single-electron tunneling

Millimeter-wave on-chip solenoid inductor by on-demand three-dimensional printing of colloidal nanoparticles

Niklas C. Schirmer, Jan Hesselbarth, Stefan Ströhle, Brian R. Burg, Manish K. Tiwari, and Dimos Poulikakos

Appl. Phys. Lett. 97, 243109 (2010); http://dx.doi.org/10.1063/1.3527923 (3 pages)

Online Publication Date: 16 December 2010

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Millimeter-wave on-chip solenoid inductor structures with wire diameters of O(1 μm) are investigated. The wires are formed by on-demand three-dimensional printing of nanoparticle laden droplets with known droplet size, deposition frequency, and evaporation time. After thermal annealing and morphological characterization, the solenoids are evaluated using two-port S parameter based electrical transmission measurements. The measurements over 0.1–110 GHz, combined with finite-element based electromagnetic field modeling, reveal a quality factor of 0.8 at 110 GHz for an 80 pH coil resulting in an inductance-per-area value of 80 nH/mm2, which is the highest reported value at these scales.
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84.32.Hh Inductors and coils; wiring
84.40.-x Radiowave and microwave (including millimeter wave) technology

Nonlinear optical spectrum of bilayer graphene in the terahertz regime

Yee Sin Ang, Shareef Sultan, and C. Zhang

Appl. Phys. Lett. 97, 243110 (2010); http://dx.doi.org/10.1063/1.3527934 (3 pages)

Online Publication Date: 17 December 2010

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We demonstrate that the nonlinear optical response in bilayer graphene is among the strongest, especially in the important frequency regime of terahertz to far-infrared. Furthermore, we show that both the single frequency and frequency tripled nonlinear response become comparable to the linear response at very moderate electric field. The field strength for the onset of nonlinear effect in bilayer graphene is well within the experimental achievable range in laboratories. Our result suggests that bilayers are preferred structures for developing graphene-based nonlinear photonics and optoelectronics devices.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.-k Nonlinear optics
78.30.Na Fullerenes and related materials
78.67.Wj Optical properties of graphene
78.70.Gq Microwave and radio-frequency interactions

Radio frequency electrical transduction of graphene mechanical resonators

Yuehang Xu, Changyao Chen, Vikram V. Deshpande, Frank A. DiRenno, Alexander Gondarenko, David B. Heinz, Shuaimin Liu, Philip Kim, and James Hone

Appl. Phys. Lett. 97, 243111 (2010); http://dx.doi.org/10.1063/1.3528341 (3 pages) | Cited 8 times

Online Publication Date: 17 December 2010

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We report radio frequency (rf) electrical readout of graphene mechanical resonators. The mechanical motion is actuated and detected directly by using a vector network analyzer, employing a local gate to minimize parasitic capacitance. A resist-free doubly clamped sample with resonant frequency ∼ 34 MHz, quality factor ∼ 10 000 at 77 K, and signal-to-background ratio of over 20 dB is demonstrated. In addition to being over two orders of magnitude faster than the electrical rf mixing method, this technique paves the way for use of graphene in rf devices such as filters and oscillators.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems

Quantum pumping in graphene with a perpendicular magnetic field

Rakesh P. Tiwari and M. Blaauboer

Appl. Phys. Lett. 97, 243112 (2010); http://dx.doi.org/10.1063/1.3528457 (3 pages) | Cited 3 times

Online Publication Date: 17 December 2010

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We consider quantum pumping of Dirac fermions in a monolayer of graphene in the presence of a perpendicular magnetic field in the central pumping region. The two external pump parameters are electrical voltages applied to the graphene sheet on either side of the pumping region. We analyze this pump within scattering matrix formalism and calculate both pumped charge and spin currents. The predicted charge currents are of the order of 1000 nA, which is readily observable using current technology.
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72.80.Vp Electronic transport in graphene
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