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31 Jan 2011

Volume 98, Issue 5, Articles (05xxxx)

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Appl. Phys. Lett. 98, 053101 (2011); http://dx.doi.org/10.1063/1.3549154 (3 pages)

Minggang Zeng, Lei Shen, Ming Yang, Chun Zhang, and Yuanping Feng
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Charge and spin transport in graphene-based heterostructure

Minggang Zeng, Lei Shen, Ming Yang, Chun Zhang, and Yuanping Feng

Appl. Phys. Lett. 98, 053101 (2011); http://dx.doi.org/10.1063/1.3549154 (3 pages) | Cited 16 times

Online Publication Date: 31 January 2011

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We investigate electron transport properties of a heterostructure based on zigzag graphene nanoribbon (ZGNR) by first-principles calculations. This heterostructure consists of hydrogen-terminated ZGNR (ZGNR-H) and oxygen-terminated ZGNR (ZGNR-O). We find that both charge and spin transport can be well controlled with the ZGNR-H/ZGNR-O heterostructure. A large charge transmission gap appears near the Fermi energy, and rectification behavior is observed. Moreover, the ZGNR-H/ZGNR-O heterostructure can act as a perfect bipolar spin filter or magnetoresistance device. Our results show that the ZGNR-H/ZGNR-O heterostructure hold promise for combining magnetoelectronics and conventional charge-based electronics.
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73.63.-b Electronic transport in nanoscale materials and structures
73.40.Ei Rectification
73.22.Pr Electronic structure of graphene
72.20.My Galvanomagnetic and other magnetotransport effects

Tailoring band gap in GaN sheet by chemical modification and electric field: Ab initio calculations

Qian Chen, Hong Hu, Xiaojie Chen, and Jinlan Wang

Appl. Phys. Lett. 98, 053102 (2011); http://dx.doi.org/10.1063/1.3549299 (3 pages) | Cited 7 times

Online Publication Date: 31 January 2011

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Ab initio calculations show that the GaN monolayer (GaN-ML) in (0001) face is a planar semiconductor with an indirect band gap of 1.95 eV. The gap converts into a direct one and is enlarged by 0.81 eV when the GaN-ML is modified by H and F atoms. Furthermore, the gap can be efficiently manipulated in a range of 1.8 to 3.5 eV by applying an external electric field. Moreover, because of the spontaneous polarization, the gap is remarkably broadened by a positive electric field while it is rapidly decreased under a negative field. The chemical modification also significantly improves the stability of GaN-ML.
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71.20.Nr Semiconductor compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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Contacting graphene

Joshua A. Robinson, Michael LaBella, Mike Zhu, Matt Hollander, Richard Kasarda, Zachary Hughes, Kathleen Trumbull, Randal Cavalero, and David Snyder

Appl. Phys. Lett. 98, 053103 (2011); http://dx.doi.org/10.1063/1.3549183 (3 pages) | Cited 31 times

Online Publication Date: 1 February 2011

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We present a robust method for forming high quality ohmic contacts to graphene, which improves the contact resistance by nearly 6000 times compared to untreated metal/graphene interfaces. The optimal specific contact resistance for treated Ti/Au contacts is found to average <10−7 Ω cm2. Additionally, we examine Al/Au, Ti/Au, Ni/Au, Cu/Au, Pt/Au, and Pd/Au contact metallizations and find that most metallizations result in similar specific contact resistances in this work regardless of the work function difference between graphene and the metal overlayer. The results presented in this work serve as a foundation for achieving ultralow resistance ohmic contacts to graphene for high speed electronic and optoelectronic applications.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
85.40.Ls Metallization, contacts, interconnects; device isolation

Epitaxial integration of ferromagnetic correlated oxide LaCoO3 with Si (100)

A. Posadas, M. Berg, H. Seo, A. de Lozanne, A. A. Demkov, D. J. Smith, A. P. Kirk, D. Zhernokletov, and R. M. Wallace

Appl. Phys. Lett. 98, 053104 (2011); http://dx.doi.org/10.1063/1.3549301 (3 pages) | Cited 7 times

Online Publication Date: 1 February 2011

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We have grown epitaxial strained LaCoO3 on (100)-oriented silicon by molecular beam epitaxy using a relaxed epitaxial SrTiO3 buffer layer. Superconducting quantum interference device magnetization measurements show that, unlike the bulk material, the ground state of the strained LaCoO3 on silicon is ferromagnetic with a TC of 85 K. First principles calculations suggest that a ferromagnetic ground state can be stabilized in LaCoO3 by a sufficiently large biaxial tensile strain with the transition accompanied by a partial untilting of the CoO6 octahedra.
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68.55.A- Nucleation and growth
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.05.Cy Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.78.-n Magnetization dynamics
71.15.-m Methods of electronic structure calculations

Bandgap tailoring of rutile TiO2(110) via surface patterning with electron cyclotron resonance sputtering

Subrata Majumder, D. Paramanik, V. Solanki, B. P. Bag, and Shikha Varma

Appl. Phys. Lett. 98, 053105 (2011); http://dx.doi.org/10.1063/1.3549768 (3 pages) | Cited 5 times

Online Publication Date: 1 February 2011

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Crystalline TiO2 nanodots have been formed on single crystal rutile TiO2(110) surfaces via ion beam sputtering method by utilizing Ar ion beams from electron cyclotron resonance source. Nearly five times enhancement in absorbance of visible light, ∼ 5 times increase in luminescence, and ∼ 0.1 eV narrowing of bandgap are observed for nanodot-patterned surfaces, in the absence of any dopant material. Formation of crystalline rutile TiO2 nanodots and development of Ti interstitials on the TiO2(110) surface, after ion beam sputtering, are responsible for these observations. Results suggest that these nanodot-patterned rutile TiO2 surfaces can become effective photocatalysts.
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81.16.Rf Micro- and nanoscale pattern formation
81.07.Bc Nanocrystalline materials
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.15.Cd Deposition by sputtering
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Electrically controlled hydrophobicity in a surface modified nanoporous carbon

Taewan Kim, Weiyi Lu, Hyuck Lim, Aijie Han, and Yu Qiao

Appl. Phys. Lett. 98, 053106 (2011); http://dx.doi.org/10.1063/1.3549295 (3 pages) | Cited 2 times

Online Publication Date: 2 February 2011

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Conventional surface treatments lead to constant surface morphologies and properties. Here we show that as the inner surfaces of a nanoporous carbon are modified by 16-mercaptohexadecanoic acid through a two-step grafting process, due to the flexibility of the surface chains, the end groups can be repelled by negative surface charges and attracted by positive surface charges. Thus, the surface wettability is controlled electrically. The effective solid-liquid interfacial tension in the nanopores is analyzed in a pressure induced infiltration experiment.
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68.03.Cd Surface tension and related phenomena
68.08.Bc Wetting
81.65.-b Surface treatments

Dopant homogeneity and transport properties of impurity-doped oxide nanowires

Annop Klamchuen, Takeshi Yanagida, Masaki Kanai, Kazuki Nagashima, Keisuke Oka, Shu Seki, Masaru Suzuki, Yoshiki Hidaka, Shoichi Kai, and Tomoji Kawai

Appl. Phys. Lett. 98, 053107 (2011); http://dx.doi.org/10.1063/1.3549703 (3 pages) | Cited 4 times

Online Publication Date: 3 February 2011

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Controlling and understanding an impurity doping on semiconductor oxide nanowires grown by the vapor-liquid-solid (VLS) method remains an important challenge. Homogeneous dopant distribution within oxide nanowires has been assumed without the direct evaluations to interpret the transport properties. Here we report the direct measurements of dopant distributions for Ta-doped SnO2 nanowires. We find that differences in dopant incorporations between VLS and vapor-solid growth processes give rise to a heavily doped shell surrounding an underdoped core. Thus, understanding the dopant incorporation pathways is essential to designing and controlling impurity doping on VLS grown oxide nanowires.
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61.72.up Other materials
68.65.La Quantum wires (patterned in quantum wells)
81.16.-c Methods of micro- and nanofabrication and processing
81.07.Gf Nanowires
81.07.Vb Quantum wires
73.63.Nm Quantum wires

Anomalous optical selection rule of an organic molecule controlled by extremely localized light field

Takuya Iida, Yuta Aiba, and Hajime Ishihara

Appl. Phys. Lett. 98, 053108 (2011); http://dx.doi.org/10.1063/1.3551710 (3 pages) | Cited 7 times

Online Publication Date: 4 February 2011

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We have theoretically demonstrated the drastic enhancement of light-induced electric polarization in molecular nondipole type dark states. Its magnitude can exceed that of bright states, even in a nanoscale molecule, due to the spatial correlation between the wave function of the excited states and the localized light field. Moreover, it was clarified that the direct observation of such an anomalous enhancement of dark states in a metal nanogap is possible through near field spectroscopy under one-photon excitation. The results obtained will open the way to single molecule detection methods to reveal the molecular level scheme including parity-forbidden states.
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42.50.-p Quantum optics
33.57.+c Magneto-optical and electro-optical spectra and effects
31.15.vj Electron correlation calculations for atoms and ions: excited states

Adiabatic charge control in a single donor atom transistor

Enrico Prati, Matteo Belli, Simone Cocco, Guido Petretto, and Marco Fanciulli

Appl. Phys. Lett. 98, 053109 (2011); http://dx.doi.org/10.1063/1.3551735 (3 pages) | Cited 4 times

Online Publication Date: 4 February 2011

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We charge an individual donor quantum dot with an electron originally stored in another quantum dot in its proximity. The single arsenic donor quantum dot and the electrostatic quantum dot in parallel are contained in a silicon nanometric field effect transistor. Their different coupling capacitances with the control and back gates determine a honeycomb pattern at high control gate voltage. It is therefore possible to control the exchange coupling of an electron of the quantum dot with the electrons bound to the donor quantum dot toward the realization of a physical qubit for quantum information processing applications.
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85.30.Tv Field effect devices
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.07.Ta Quantum dots
81.07.Oj Nanoelectromechanical systems (NEMS)
81.05.Cy Elemental semiconductors
71.70.Gm Exchange interactions

Magnetoresistance of single molecular junctions measured by a mechanically controllable break junction method

Ryo Yamada, Motoki Noguchi, and Hirokazu Tada

Appl. Phys. Lett. 98, 053110 (2011); http://dx.doi.org/10.1063/1.3549190 (3 pages) | Cited 6 times

Online Publication Date: 4 February 2011

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The magnetoresistance of Ni/single benzene-1,4-dithiol/Ni molecular junctions was measured by a mechanically controllable break junction method under a magnetic field. The negative magnetoresistance of the molecular junction as large as 30% and the anisotropic magnetoresistance of atomic contacts and tunnel junctions of Ni as large as 30% were observed.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.30.Gw Magnetic anisotropy

Large room temperature magnetoresistance in ion beam synthesized surface Fe nanoclusters on SiO2

J. Leveneur, J. Kennedy, G. V. M. Williams, J. Metson, and A. Markwitz

Appl. Phys. Lett. 98, 053111 (2011); http://dx.doi.org/10.1063/1.3553274 (3 pages) | Cited 3 times

Online Publication Date: 4 February 2011

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A large room temperature magnetoresistance ratio of up ∼ 40% at 8 T is observed in ion beam synthesized surface Fe nanoclusters on SiO2 where there is negligible hysteresis, and quasilinear behavior occurs for fields above 2 T. The negligible hysteresis can be attributed to the small dimensions of the Fe nanoparticles that are superparamagnetic with blocking temperatures ranging from 170 to 250 K. The large magnetoresistance is likely to be due to a combination of geometric and extraordinary magnetoresistances as well as spin-dependent scattering. The observed properties have great potential for magnetic sensing in the high field regime.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.Cd Fabrication of magnetic nanostructures
75.20.En Metals and alloys

Size effect on the coalescence-induced self-propelled droplet

Feng-Chao Wang, Fuqian Yang, and Ya-Pu Zhao

Appl. Phys. Lett. 98, 053112 (2011); http://dx.doi.org/10.1063/1.3553782 (3 pages) | Cited 11 times

Online Publication Date: 4 February 2011

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An analysis based on the energy conservation is presented for the self-propelled droplet during coalescence of two droplets of the same size over a superhydrophobic rough surface. The self-propelled behavior occurs only for the coalescence of droplets with a certain range of radius. An analytical relation is established among the coalescence-induced velocity, surface energy, viscous dissipation, and droplet size if gravity is negligible. The coalescence-induced velocity increases with increasing droplet size to a maximum and then decreases with the size, which is in good accord with the experimental observation reported in the literature.
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61.20.-p Structure of liquids
66.20.Ej Studies of viscosity and rheological properties of specific liquids
68.03.Cd Surface tension and related phenomena
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