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22 Aug 2011

Volume 99, Issue 8, Articles (08xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 083104 (2011); http://dx.doi.org/10.1063/1.3625926 (3 pages)

E. Detsi, Z. G. Chen, W. P. Vellinga, P. R. Onck, and J. T. M. De Hosson
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A spin-valve device based on dumbbell-shaped graphene nanoislands

Zhaoli Ma and Weidong Sheng

Appl. Phys. Lett. 99, 083101 (2011); http://dx.doi.org/10.1063/1.3630229 (3 pages) | Cited 5 times

Online Publication Date: 22 August 2011

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Electron transport in a graphene nanoisland with mixed edge profiles is studied by using the spin-unrestricted Hubbard model. The dumbbell-shaped device consists of two hexagonal nanoislands with zigzag edges connected by a armchair nanoribbon. Including the nearest-neighbor hopping and on-site Coulomb repulsion, the self-consistent calculation shows that two distinct ferromagnetic configurations allowed for the proposed device act like ON and OFF states for spin-polarized electrons. Furthermore, the spin-valve effect is demonstrated, as a proof of concept, in the device occupied by one ferromagnetic configuration without resorting to external magnetic or electric fields.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Electrokinetic energy conversion efficiency in ion-selective nanopores

Chih-Chang Chang and Ruey-Jen Yang

Appl. Phys. Lett. 99, 083102 (2011); http://dx.doi.org/10.1063/1.3625921 (3 pages) | Cited 9 times

Online Publication Date: 22 August 2011

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Taking hydrodynamic slippage into account, we derived an exact expression for the figure of merit to evaluate the electrokinetic energy conversion efficiency and power of an ion-selective nanopore. In the absence of slip, and when the ratio of the radius and the Gouy-Chapmann length (a/λGC) is approximately 10, the highest efficiency for an electrolyte consisting of simple monovalent ions was predicted to be approximately 9.7%. While this efficiency is low, it can be greatly improved to a potentially practical efficiency (>40%) when the slip ratio (b/a) is greater than 0.7.
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82.45.Yz Nanostructured materials in electrochemistry
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
82.45.Gj Electrolytes

Pattern formation and nonlinear evolution in alloy surfaces by ion-beam sputtering

M. S. Bharathi, H. Ramanarayan, and Y. W. Zhang

Appl. Phys. Lett. 99, 083103 (2011); http://dx.doi.org/10.1063/1.3625940 (3 pages) | Cited 3 times

Online Publication Date: 22 August 2011

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Nanoscale pattern formation on surfaces by ion beam sputtering is driven by the competition between the erosion and the diffusion processes. In alloys, these processes are component-dependent. We present a kinetic Monte Carlo model for sputtering of alloy surfaces which exhibits morphological ripples and compositional patterns. The evolution of the ripple amplitude shows a crossover from an early stage exponential growth to a later stage power-law growth. We also present a nonlinear dynamic model which shows both the crossover and the surface patterns, confirming the importance of nonlinear terms in understanding the dynamics of alloy sputtering.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
68.35.Fx Diffusion; interface formation

Reversible strain by physisorption in nanoporous gold

E. Detsi, Z. G. Chen, W. P. Vellinga, P. R. Onck, and J. T. M. De Hosson

Appl. Phys. Lett. 99, 083104 (2011); http://dx.doi.org/10.1063/1.3625926 (3 pages) | Cited 7 times

Online Publication Date: 23 August 2011

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Reversible strain amplitudes up to 0.02% in response to a 15% change in relative humidity were detected in nanoporous gold. We show that the mechanism involved in dimensional changes during physisorption is associated with changes in the surface stress when molecules are adsorbed from the vapor phase onto the metal interface.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
61.43.Gt Powders, porous materials

Ultra-wide bandwidth piezoelectric energy harvesting

Arman Hajati and Sang-Gook Kim

Appl. Phys. Lett. 99, 083105 (2011); http://dx.doi.org/10.1063/1.3629551 (3 pages) | Cited 17 times

Online Publication Date: 23 August 2011

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Here, we present an ultra wide-bandwidth energy harvester by exploiting the nonlinear stiffness of a doubly clamped microelectromechanical systems (MEMSs) resonator. The stretching strain in a doubly clamped beam shows a nonlinear stiffness, which provides a passive feedback and results in amplitude-stiffened Duffing mode resonance. This design has been fabricated into a compact MEMS device, which is about the size of a US quarter coin. Based on the open circuit voltage measurement, it is expected to have more than one order of magnitude improvement in both bandwidth (more than 20% of the peak frequency) and power density (up to 2 W/cm3) in comparison to the devices previously reported.
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84.60.-h Direct energy conversion and storage
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.16.-c Methods of micro- and nanofabrication and processing

Color tunable light-emitting diodes based on copper doped semiconducting nanocrystals

Saikat Bhaumik, Batu Ghosh, and Amlan J. Pal

Appl. Phys. Lett. 99, 083106 (2011); http://dx.doi.org/10.1063/1.3626855 (3 pages) | Cited 4 times

Online Publication Date: 23 August 2011

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We have introduced copper-doped semiconducting nanocrystals in light-emitting diodes (LEDs). Characteristics of the devices show that electroluminescence (EL) emission in these LEDs is color tunable. In copper-doped ZnS nanocrystals in the core and Zn1−xCdxS host as a shell-layer, photoluminescence (PL) arises from a transition from conduction band-edge of the host to 3d-levels of copper-ions. The PL of the nanocrystals and hence the EL of LEDs based on such nanostructures become tunable by varying the Cd-content in Zn-Cd-S alloys, that is, Zn1−xCdxS with different values of x, which changes the conduction band-edge of the host.
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85.60.Jb Light-emitting devices

High magnetoresistance at room temperature in p-i-n graphene nanoribbons due to band-to-band tunneling effects

Gengchiau Liang, S. Bala Kumar, M. B. A. Jalil, and S. G. Tan

Appl. Phys. Lett. 99, 083107 (2011); http://dx.doi.org/10.1063/1.3624459 (3 pages) | Cited 2 times

Online Publication Date: 23 August 2011

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A large magnetoresistance effect is obtained at room-temperature by using p-i-n armchair-graphene-nanoribbon (GNR) heterostructures. The key advantage is the virtual elimination of thermal currents due to the presence of band gaps in the contacts. The current at B = 0 T is greatly decreased while the current at B > 0 T is relatively large due to the band-to-band tunneling effects, resulting in a high magnetoresistance ratio, even at room-temperature. Moreover, we explore the effects of edge-roughness, length, and width of GNR channels on device performance. An increase in edge-roughness and channel length enhances the magnetoresistance ratio while increased channel width can reduce the operating bias.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
81.05.ue Graphene
72.20.My Galvanomagnetic and other magnetotransport effects
75.47.-m Magnetotransport phenomena; materials for magnetotransport
85.30.Tv Field effect devices

Optimization of periodic gold nanostructures for intensity-sensitive detection

Kuang-Li Lee and Pei-Kuen Wei

Appl. Phys. Lett. 99, 083108 (2011); http://dx.doi.org/10.1063/1.3628641 (3 pages) | Cited 5 times

Online Publication Date: 23 August 2011

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We study the optimal sensing condition for periodic gold nanoslits. The intensity sensitivities for various periods, from 400 to 900 nm, were measured. The experimental results show that 500-nm-period array has a maximum bulk sensitivity, three times larger than the sensitivities of 400 and 700 nm periods. The optimal period is attributed to the coincidence of the surface plasmon resonance (SPR) wavelength and lowest imaginary dielectric constant of gold film. The structure reaches a figure of merit of 23.9 and achieves a detection limit of 2.6 × 10−5 refractive index units at 0.2% stability, better than the grating-based SPR sensors using intensity interrogation.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.22.Lp Collective excitations
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.aj Insulators
61.46.-w Structure of nanoscale materials

The role of charge traps in inducing hysteresis: Capacitance–voltage measurements on top gated bilayer graphene

Gopinadhan Kalon, Young Jun Shin, Viet Giang Truong, Alan Kalitsov, and Hyunsoo Yang

Appl. Phys. Lett. 99, 083109 (2011); http://dx.doi.org/10.1063/1.3626854 (3 pages) | Cited 5 times

Online Publication Date: 24 August 2011

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Understanding the origin of hysteresis in the channel resistance from top gated graphene transistors is important for transistor applications. Capacitance-voltage measurements across the gate oxide on top gated bilayer graphene show hysteresis with a charging and discharging time constant of ∼100 μs. However, the measured capacitance across the graphene channel does not show any hysteresis but shows an abrupt jump at a high channel voltage due to the emergence of an order, indicating that the origin of hysteresis between gate and source is due to charge traps present in the gate oxide and graphene interface.
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85.30.Tv Field effect devices

Parametric amplification in single-walled carbon nanotube nanoelectromechanical resonators

Chung-Chiang Wu and Zhaohui Zhong

Appl. Phys. Lett. 99, 083110 (2011); http://dx.doi.org/10.1063/1.3627178 (3 pages) | Cited 1 time

Online Publication Date: 24 August 2011

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The low quality factor (Q) of single-walled carbon nanotube (SWNT) resonators has limited their sensitivity in sensing application. To this end, we employ the technique of parametric amplification by modulating the spring constant of SWNT resonators at twice the resonant frequency and achieve 10 times Q enhancement. The highest Q obtained at room temperature is around ∼700, which is 3–4 times better than previous Q record reported for doubly clamped SWNT resonators. Furthermore, efficient parametric amplification is found to only occur in the catenary vibration regime. Our results open up the possibility to employ light-weight and high-Q carbon nanotube resonators in single molecule and atomic mass sensing.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.07.Oj Nanoelectromechanical systems (NEMS)
81.07.De Nanotubes

Sandwiched nanoarchitecture of reduced graphene oxide/ZnO nanorods/reduced graphene oxide on flexible PET substrate for supercapacitor

Guilve Guo, Lei Huang, Quanhong Chang, Lechun Ji, Yang Liu, Yiqun Xie, Wangzhou Shi, and Nengqin Jia

Appl. Phys. Lett. 99, 083111 (2011); http://dx.doi.org/10.1063/1.3629789 (3 pages) | Cited 5 times

Online Publication Date: 25 August 2011

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Reduced graphene oxide (rGO)/zinc oxide (ZnO) nanorods/rGO sandwich is fabricated on chemical vapor deposition graphene film/polyethylene therephthalate substrate for flexible supercapacitor electrodes. Studies show that ZnO nanorods in the electrodes prevent aggregation of rGO sheets and help forming a porous structure. Specific capacitance of 51.6 F/g at the scan rate of 10 mV/s is achieved for the rGO/ZnO nanorods/rGO sandwich, showing that such composite is promising for application in flexible supercapacitors.
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84.32.Tt Capacitors
82.47.Uv Electrochemical capacitors; supercapacitors

Electron-beam induced electric-hydraulic expansion in a silica-shelled gallium microball-nanotube structure

Y. H. Gao, M. Sun, J. Su, C. Y. Zhi, D. Golberg, Y. Bando, and X. F. Duan

Appl. Phys. Lett. 99, 083112 (2011); http://dx.doi.org/10.1063/1.3625427 (3 pages)

Online Publication Date: 25 August 2011

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Heteroshape-heteroscale structure of silica-shelled Ga microball-nanotube was fabricated. Under in situ electron-beam irradiation, an abnormally large and fast expansion of Ga was observed. Failed by a sole routine heating effect of electron-beam, the expansion was explained by an electric-hydraulic expansion effect taking into account a huge inner pressure induced by the repelling Coulomb force of positively charged Ga ions on the Ga microball surface. The ions were accumulated due to knocking-out of Ga electrons under irradiation and shielding effect of a silica shell which prevents the charge balance restoration. A circuit model is proposed to calculate the accumulation of Ga ions.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.Fg Nanotubes
61.80.Fe Electron and positron radiation effects
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.07.De Nanotubes

Magnetoresistance in epitaxial thin films of La0.85Ag0.15MnO3 produced by polymer assisted deposition

R. Cobas, S. Muñoz-Perez, J. M. Cadogan, T. Puig, and X. Obradors

Appl. Phys. Lett. 99, 083113 (2011); http://dx.doi.org/10.1063/1.3629993 (3 pages) | Cited 3 times

Online Publication Date: 26 August 2011

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We report a method of obtaining thin films of La0.85Ag0.15MnO3 using the chemical solution approach of polymer-assisted deposition. Epitaxial films with 25-30 nm thickness have been grown on single-crystal substrates of LaAlO3 (001) and SrTiO3 (001) exhibiting ferromagnetic Curie and metal-insulator transition temperatures shifted due to differences in the relaxation mechanisms of epitaxial misfit. High values of colossal magneto-resistance (−60% at 287 K and 5 T) were obtained in the case of LaAlO3 substrates which indicate that silver-doped manganite oxides have potential for room temperature applications.
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75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Crystal phase and growth orientation dependence of GaAs nanowires on NixGay seeds via vapor-solid-solid mechanism

Ning Han, Alvin T. Hui, Fengyun Wang, Jared J. Hou, Fei Xiu, TakFu Hung, and Johnny C. Ho

Appl. Phys. Lett. 99, 083114 (2011); http://dx.doi.org/10.1063/1.3630006 (3 pages) | Cited 4 times

Online Publication Date: 26 August 2011

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One of the challenges to utilize high performance III-V compound semiconductor nanowires (NWs) for large-scale technological applications is to control the crystal phase and growth orientation for homogenous nanowire properties. Here, we report the dependence of crystal structure and growth orientation of GaAs NWs on NixGay seeds via vapor-solid-solid mechanism. The crystal structure of catalytic seeds is found to direct the crystal phase of NWs with cubic NiGa seeds yielding zincblende GaAs NWs while hexagonal Ni2Ga3 seeds producing wurtzite GaAs NWs. Furthermore, the seed/nanowire interface plane relationship would dictate the epitaxial growth orientation of NWs, which is independent of the NW diameters and growth conditions. All these suggest the importance of well-controlled phase and orientation of catalysts for the synthesis of homogenous nanowires.
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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)
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation

Strain effects on the phonon thermal properties of ultra-scaled Si nanowires

Abhijeet Paul and Gerhard Klimeck

Appl. Phys. Lett. 99, 083115 (2011); http://dx.doi.org/10.1063/1.3630228 (3 pages)

Online Publication Date: 26 August 2011

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The impact of uniaxial and hydrostatic stress on the ballistic thermal conductance (κl) and the specific heat (Cν) of [100] and [110] Si nanowires are explored using a Modified Valence Force Field phonon model. An anisotropic behavior of κl and isotropic nature of Cν under strain are predicted for the two wire orientations. Compressive (tensile) strain decreases (increases) Cν. The Cv trend with strain is controlled by the high energy phonon sub-bands. Dominant contribution of the low/mid (low/high) energy bands in [100] ([110]) wire and their variation under strain governs the behavior of κl.
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63.22.Gh Nanotubes and nanowires
66.70.Df Metals, alloys, and semiconductors
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
65.40.Ba Heat capacity
71.20.Mq Elemental semiconductors
73.22.-f Electronic structure of nanoscale materials and related systems

Nanostructuring graphene on SiC by focused ion beam: Effect of the ion fluence

B. Prével, J.-M. Benoit, L. Bardotti, P. Mélinon, A. Ouerghi, D. Lucot, E. Bourhis, and J. Gierak

Appl. Phys. Lett. 99, 083116 (2011); http://dx.doi.org/10.1063/1.3628341 (3 pages) | Cited 4 times

Online Publication Date: 26 August 2011

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Epitaxial graphene on silicon carbide labeled 6H-SiC (0001) substrate has been patterned using high resolution focused ion beam. Atomic force microscopy and Raman spectroscopy measurements give evidence of the strong resilience of the graphene monolayer to ion irradiation. The morphology and electronic properties of defects versus ion doses exhibit a progressive local amorphization of graphene.
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81.05.ue Graphene
71.20.Tx Fullerenes and related materials; intercalation compounds
78.30.Na Fullerenes and related materials
61.46.Hk Nanocrystals
78.67.Wj Optical properties of graphene
81.16.Rf Micro- and nanoscale pattern formation
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