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15 Aug 2011

Volume 99, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 99, 073701 (2011); http://dx.doi.org/10.1063/1.3599706 (3 pages)

Miguel A. Santiago-Cordoba, Svetlana V. Boriskina, Frank Vollmer, and Melik C. Demirel
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Homogeneity improvement of field emission beam from metallic nano-tip arrays by noble-gas conditioning

S. Tsujino, M. Paraliev, E. Kirk, and H.-H. Braun

Appl. Phys. Lett. 99, 073101 (2011); http://dx.doi.org/10.1063/1.3624705 (3 pages) | Cited 2 times

Online Publication Date: 15 August 2011

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The authors explored control of field-emission electron beam homogeneity emitted from metallic nano-tips fabricated by molding. Improved beam homogeneity and increased maximum bunch charge were observed after DC operation of cathodes in low-pressure argon gas environment. They also observed average current per tip of 4.5 μA from a 1 × 104 emitter array device after conditioning in neon gas. Evolution of Fowler-Nordheim parameters as a result of noble-gas conditioning was discussed.
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85.45.Db Field emitters and arrays, cold electron emitters
79.70.+q Field emission, ionization, evaporation, and desorption

High charge carrier density at the NaTaO3/SrTiO3 hetero-interface

S. Nazir and U. Schwingenschlögl

Appl. Phys. Lett. 99, 073102 (2011); http://dx.doi.org/10.1063/1.3625951 (3 pages) | Cited 6 times

Online Publication Date: 15 August 2011

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The formation of a (quasi) two-dimensional electron gas between the band insulators NaTaO3 and SrTiO3 is studied by means of the full-potential linearized augmented plane-wave method of density functional theory. Optimization of the atomic positions points to only small changes in the chemical bonding at the interface. Both the p-type (NaO)−/(TiO2)0 and n-type (TaO2)+/(SrO)0 interfaces are found to be metallic with high charge carrier densities. The effects of O vacancies are discussed. Spin-polarized calculations point to the formation of isolated O 2p magnetic moments, located in the metallic region of the p-type interface.
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71.20.Ps Other inorganic compounds
61.72.jd Vacancies
71.10.Ca Electron gas, Fermi gas
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Enhanced gas-flow-induced voltage in graphene

Jun Yin, Jianxin Zhou, Xuemei Li, Yaqing Chen, Guoan Tai, and Wanlin Guo

Appl. Phys. Lett. 99, 073103 (2011); http://dx.doi.org/10.1063/1.3624590 (3 pages) | Cited 2 times

Online Publication Date: 15 August 2011

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We find experimentally that gas-flow-induced voltage in monolayer graphene is more than twenty times of that in bulk graphite. Examination over samples with sheet resistances ranging from 307 to 1600 Ω/sq shows that the induced voltage increases with the electric resistance and can be further improved by controlling the quality and doping level of graphene. The induced voltage is nearly independent of the substrate materials and can be well explained by the interplay of Bernoulli’s principle and the carrier density dependent Seebeck coefficient. The results demonstrate that graphene has great potential for flow sensors and energy conversion devices.
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73.61.Wp Fullerenes and related materials
72.20.Pa Thermoelectric and thermomagnetic effects
61.72.up Other materials
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Observation and interpretation of adjacent Moire patterns of different shapes in bilayer graphene

J. B. Jasinski, S. Dumpala, G. U. Sumanasekera, M. K. Sunkara, and P. J. Ouseph

Appl. Phys. Lett. 99, 073104 (2011); http://dx.doi.org/10.1063/1.3624703 (3 pages) | Cited 3 times

Online Publication Date: 16 August 2011

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In transmission electron micrography of few-layer thick graphene samples, two distinct regions, a region of superlattice and an adjacent region of parallel straight bands, are seen. These two features are explained as Moire patterns produced by (1) rotation of top part of one of the graphene layers and (2) a small change in the shape of the bottom part of the same layer. It is interesting to note that for the first time, Moire pattern of parallel straight bands is observed and satisfactorily explained.
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61.48.Gh Structure of graphene
68.65.Cd Superlattices

Effect of electric and stress field on structures and quantum conduction of Cu nanowires

C. He, L. Qi, W. X. Zhang, and H. Pan

Appl. Phys. Lett. 99, 073105 (2011); http://dx.doi.org/10.1063/1.3626284 (3 pages) | Cited 3 times

Online Publication Date: 16 August 2011

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The ballistic transport properties of Cu nanowires under different electric and stress fields are investigated for future application in microelectronics using first-principles density-function theory. Relative to the case with the electric field only, the stability and quantum conduction of both nonhelical and helical atomic strands are enhanced by applying a stress field F. Under V = 1 V/Å, the most excellent quantum conductivity is exhibited at F = 1.5 nN for the nonhelical atomic strands while at F = 2 nN for the helical ones, and the latter is more stable with collapse-resistant F high as 3 nN compared to the former as 2 nN.
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73.61.Cw Elemental semiconductors
73.63.Nm Quantum wires
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)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
72.20.Ht High-field and nonlinear effects
73.23.Ad Ballistic transport

Multiferroic coupling in nanoscale BiFeO3

Sudipta Goswami, Dipten Bhattacharya, P. Choudhury, B. Ouladdiaf, and T. Chatterji

Appl. Phys. Lett. 99, 073106 (2011); http://dx.doi.org/10.1063/1.3625924 (3 pages) | Cited 8 times

Online Publication Date: 16 August 2011

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Using the results of x-ray and neutron diffraction experiments, we show that the ferroelectric polarization, in ∼22 nm particles of BiFeO3, exhibits a jump by ∼30% around the magnetic transition point TN (∼635 K) and a suppression by ∼7% under 5T magnetic field at room temperature (≪TN). These results confirm the presence of strong multiferroic coupling even in nanoscale BiFeO3 and thus could prove to be quite useful for applications based on nanosized devices of BiFeO3.
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75.85.+t Magnetoelectric effects, multiferroics
77.80.B- Phase transitions and Curie point
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Gg Ferrimagnetics
75.50.Tt Fine-particle systems; nanocrystalline materials
77.22.Ej Polarization and depolarization

Charge-transfer-induced suppression of galvanic replacement and synthesis of (Au@Ag)@Au double shell nanoparticles for highly uniform, robust and sensitive bioprobes

Dao Thi Ngoc Anh, Prerna Singh, Cheshta Shankar, Derrick Mott, and Shinya Maenosono

Appl. Phys. Lett. 99, 073107 (2011); http://dx.doi.org/10.1063/1.3626031 (3 pages) | Cited 4 times

Online Publication Date: 16 August 2011

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The synthesis of double shell (Au@Ag)@Au nanoparticles is accomplished through suppression of the galvanic replacement reaction caused by an electron transfer phenomenon. The resulting nanoparticles are monodisperse with a thin and uniform second Au shell. These particles are ultimately expected to lead to sensitive probes for biomolecular sensing and diagnostics.
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82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing

Effects of GaAsSb capping layer thickness on the optical properties of InAs quantum dots

Wei-Ting Hsu, Yu-An Liao, Feng-Chang Hsu, Pei-Chin Chiu, Jen-Inn Chyi, and Wen-Hao Chang

Appl. Phys. Lett. 99, 073108 (2011); http://dx.doi.org/10.1063/1.3624464 (3 pages) | Cited 3 times

Online Publication Date: 17 August 2011

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The optical properties of GaAsSb-capped InAs quantum dots (QDs) with different capping layer thickness are investigated. Both the emission energy and the recombination lifetime are found to be correlated with the capping layer thicknesses. Theoretical calculations indicate that the quantum confinement and the wave function distribution of hole states are sensitive to the GaAsSb capping layer thickness. The Sb induced change in QD size also plays a role in the optical properties of GaAsSb-capped QDs. Controlling the GaAsSb capping layer thickness is a feasible way to tailor the InAs QDs for long-wavelength applications.
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78.67.Hc Quantum dots
81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
78.55.Cr III-V semiconductors

Nanoparticle single-electron transistor with metal-bridged top-gate and nanogap electrodes

Yasuo Azuma, Seiichi Suzuki, Kosuke Maeda, Norio Okabayashi, Daisuke Tanaka, Masanori Sakamoto, Toshiharu Teranishi, Mark R. Buitelaar, Charles G. Smith, and Yutaka Majima

Appl. Phys. Lett. 99, 073109 (2011); http://dx.doi.org/10.1063/1.3626036 (3 pages) | Cited 4 times

Online Publication Date: 17 August 2011

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Au nanoparticle single-electron transistors with metal-bridged top-gates and nanogap electrodes were fabricated using two consecutive electron beam lithography and electroless Au plating steps. The metal-bridged top-gate electrodes were suspended above electroless Au plated nanogap electrodes. Au nanoparticles (5.2 nm in diameter) were chemisorbed between the nanogap electrodes after top-gate fabrication. Clear Coulomb diamonds were observed at 9 K. The gate capacitance Cg of the top-gate electrodes was 99 zF, which is 10 times larger than that of a similar device with only side-gate electrodes.
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85.35.Gv Single electron devices
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
81.15.Pq Electrodeposition, electroplating
81.16.Nd Micro- and nanolithography

Perfect spin-filtering and giant magnetoresistance with Fe-terminated graphene nanoribbon

Chao Cao, Yan Wang, Hai-Ping Cheng, and J.-Z. Jiang

Appl. Phys. Lett. 99, 073110 (2011); http://dx.doi.org/10.1063/1.3626596 (3 pages) | Cited 2 times

Online Publication Date: 18 August 2011

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Spin-dependent electronic transport properties of Fe-terminated zig-zag graphene nanoribbons (zGNRs) have been studied using first-principles transport simulations. The spin configuration of proposed zGNRs junction can be controlled with external magnetic field, and the tunneling junction show magnetoresistance > 1000 at small bias and is a perfect spin-filter by applying uniform external magnetic filed at small bias.
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72.80.Vp Electronic transport in graphene
73.22.Pr Electronic structure of graphene
75.47.De Giant magnetoresistance
72.20.My Galvanomagnetic and other magnetotransport effects
72.25.-b Spin polarized transport
71.15.-m Methods of electronic structure calculations

Asymmetric single-particle triple-resonant metamaterial in terahertz band

Ya-Xin Zhang, Shen Qiao, Wanxia Huang, Wei Ling, Liang Li, and Sheng-gang Liu

Appl. Phys. Lett. 99, 073111 (2011); http://dx.doi.org/10.1063/1.3624828 (3 pages) | Cited 6 times

Online Publication Date: 19 August 2011

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This paper presents the design, simulation, and measurement of an asymmetric triple-band metamaterial composed of single geometry electric field coupled resonators in the terahertz region. Theoretical and experimental results show that the structure has three distinct and strong absorption frequency peaks near 0.38, 0.58, and 0.74 THz, all of which are related to the inductance-capacitance resonance of the metamaterial. Due to the well-separating of different resonances in the particle, this metamaterial shows potentially application promises in the design of multiband terahertz devices.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Role of wetting and nanoscale roughness on thermal conductance at liquid-solid interface

Y. Wang and P. Keblinski

Appl. Phys. Lett. 99, 073112 (2011); http://dx.doi.org/10.1063/1.3626850 (3 pages) | Cited 10 times

Online Publication Date: 19 August 2011

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Using non-equilibrium molecular dynamics simulations in which a temperature gradient is imposed, we determine the thermal resistance of a model liquid-solid interface with and without nanoscale roughness. Our simulations reveal that in both cases the key factor controlling interfacial thermal conductance is the strength of the bonding between liquid and solid atoms. In addition, we show that in the case of rough surfaces, the nanoscopic wetting-dewetting transition has a strong signature in the interfacial thermal conductance. Interestingly, the smooth and rough interfaces, despite distinct geometry, show quantitatively the same dependence of the interfacial conductance on the value of the interfacial adhesion.
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68.08.Bc Wetting
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.43.Bn Structural modeling: serial-addition models, computer simulation
68.35.Np Adhesion

Incorporation of a light and carrier collection management nano-element array into superstrate a-Si:H solar cells

Wook Jun Nam, Liming Ji, Travis L. Benanti, Vasundara V. Varadan, Sigurd Wagner, Qi Wang, William Nemeth, Douglas Neidich, and Stephen J. Fonash

Appl. Phys. Lett. 99, 073113 (2011); http://dx.doi.org/10.1063/1.3628460 (3 pages) | Cited 4 times

Online Publication Date: 19 August 2011

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Superstrate a-Si:H solar cells incorporating a nano-column array for light and photocarrier collection have been fabricated and evaluated. It is found that the short circuit current density (JSC) is significantly increased while the open circuit voltage and fill factor are not detrimentally affected by this architecture. Numerical analysis of JSC matches experiment and shows that the enhanced JSC observed is due to both effective absorber thickness and photonic-plasmonic effects. Further analysis shows that this nano-column architecture can lead to a 42% increase in conversion efficiency over that of the planar control for a 200 nm absorber thickness cell.
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88.40.jj Silicon solar cells
02.60.-x Numerical approximation and analysis
88.40.hj Efficiency and performance of solar cells
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