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5 Mar 2012

Volume 100, Issue 10, Articles (10xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 101903 (2012); http://dx.doi.org/10.1063/1.3673327 (3 pages)

Michael Ian Lapsley, Anaram Shahravan, Qingzhen Hao, Bala Krishna Juluri, Stephen Giardinelli, Mengqian Lu, Yanhui Zhao, I-Kao Chiang, Themis Matsoukas, and Tony Jun Huang
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The enhanced optical conductivity for zigzag-edge graphene nanoribbons with applied gate voltage

Wen-Huan Zhu, Guo-Hui Ding, and Bing Dong

Appl. Phys. Lett. 100, 103101 (2012); http://dx.doi.org/10.1063/1.3692171 (3 pages) | Cited 1 time

Online Publication Date: 5 March 2012

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We study the optical absorption properties of zigzag-edge graphene nanoribbons (ZGNRs) taking into account the Coulomb interaction effect in the Hartree-Fock approximation. The optical selection rules for the incident light polarized along the longitudinal and transverse directions are investigated. We demonstrate that the excitations from the edge states are essential for the optical properties of ZGNRs in the neutral case. With the chemical potential shifting away from the Dirac point, the optical conductivity is drastically enhanced in the low frequency region for the transverse polarized incident light.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.48.Gh Structure of graphene
78.67.Wj Optical properties of graphene
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Site-selective photoluminescence in thiol-capped gold nanoclusters

T. N. Lin, C. H. Liu, G. W. Shu, J. L. Shen, C. A. J. Lin, W. H. Chang, H. H. Wang, H. I. Yeh, and W. H. Chan

Appl. Phys. Lett. 100, 103102 (2012); http://dx.doi.org/10.1063/1.3692575 (4 pages)

Online Publication Date: 5 March 2012

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Photoluminescence (PL) from the thiol-capped Au nonoclusters (NCs) has been investigated under site-selective excitation. Upon scanning the excitation light with energy below 2.1 eV down to 1.6 eV, the PL narrows and begins shifting linearly with excitation energy. The time-resolved PL was studied and the PL decay traces of Au NCs were found to depend on the excitation and emission energies. The slow carrier relaxation in the localized states is suggested to be responsible for the line narrowing and peak-shift in the site-selective PL.
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78.55.-m Photoluminescence, properties and materials
78.47.jd Time resolved luminescence

Contacting nanowires and nanotubes with atomic precision for electronic transport

Shengyong Qin, Sondra Hellstrom, Zhenan Bao, Boyan Boyanov, and An-Ping Li

Appl. Phys. Lett. 100, 103103 (2012); http://dx.doi.org/10.1063/1.3692585 (3 pages) | Cited 1 time

Online Publication Date: 5 March 2012

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Making contacts to nanostructures with atomic precision is an important process in the bottom-up fabrication and characterization of electronic nanodevices. Existing contacting techniques use top-down lithography and chemical etching, but lack atomic precision and introduce the possibility of contamination. Here, we report that a field-induced emission process can be used to make local contacts onto individual nanowires and nanotubes with atomic spatial precision. The gold nano-islands are deposited onto nanostructures precisely by using a scanning tunneling microscope tip, which provides a clean and controllable method to ensure both electrically conductive and mechanically reliable contacts. To demonstrate the wide applicability of the technique, nano-contacts are fabricated on silicide atomic wires, carbon nanotubes, and copper nanowires. The electrical transport measurements are performed in situ by utilizing the nanocontacts to bridge the nanostructures to the transport probes.
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73.63.Rt Nanoscale contacts
81.07.Lk Nanocontacts
73.40.Ns Metal-nonmetal contacts
73.40.Jn Metal-to-metal contacts
81.16.-c Methods of micro- and nanofabrication and processing

Effects of nanowire texturing on the performance of Si/organic hybrid solar cells fabricated with a 2.2 μm thin-film Si absorber

Lining He, Changyun Jiang, Hao Wang, Donny Lai, Yew Heng Tan, Chuan Seng Tan, and Rusli

Appl. Phys. Lett. 100, 103104 (2012); http://dx.doi.org/10.1063/1.3692590 (4 pages) | Cited 6 times

Online Publication Date: 6 March 2012

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Hybrid solar cells are fabricated by spin coating poly(3,4-ethylene-dioxythiophene):polystyrenesulfonate (PEDOT:PSS) on planar Si and Si-nanowires (SiNWs) arrays prepared by electroless chemical etching. With only a 2.2 μm thick Si absorber thin film, the short-circuit current density and power conversion efficiency (PCE) of SiNWs/PEDOT cell increase from 12.5 to 13.6 mA/cm2 and from 5.4% to 5.6%, respectively, as compared to planar Si/PEDOT cell. A maximum external quantum efficiency of 56.6% is obtained for the SiNWs/PEDOT cell. The promising PCE obtained demonstrates the potential of realizing Si/PEDOT and SiNWs/PEDOT hybrid cells using low-cost Si thin films instead of bulk Si substrate.
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88.40.jr Organic photovoltaics
88.40.hj Efficiency and performance of solar cells

Interface engineering of epitaxial graphene on SiC(000math) via fluorine intercalation: A first principles study

Chen Si, Gang Zhou, Yuanchang Li, Jian Wu, and Wenhui Duan

Appl. Phys. Lett. 100, 103105 (2012); http://dx.doi.org/10.1063/1.3692586 (4 pages) | Cited 2 times

Online Publication Date: 7 March 2012

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Our first-principles calculations show that a change of carrier type from electron to hole can be achieved in monolayer epitaxial graphene on SiC(000math) by fluorine (F) intercalation. The p-doping level in graphene, however, is not monotonously enhanced as the F coverage increases, and an interesting interface magnetism is observed at the partially passivated interface. Because intercalated F atoms prefer to bond to the substrate than to the graphene, F-intercalation provides a promising way of “interface modulation doping” to tailor the electronic properties of epitaxial graphene on SiC(000math) without appreciably degrading its intrinsic high mobility.
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71.20.Tx Fullerenes and related materials; intercalation compounds
75.70.Ak Magnetic properties of monolayers and thin films
72.20.Fr Low-field transport and mobility; piezoresistance
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
61.72.sm Impurity gradients

Patterning graphene nanoribbons using copper oxide nanowires

Alexander Sinitskii and James M. Tour

Appl. Phys. Lett. 100, 103106 (2012); http://dx.doi.org/10.1063/1.3692744 (3 pages) | Cited 1 time

Online Publication Date: 7 March 2012

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We present a fabrication technique for graphene nanoribbons (GNRs) that employs copper oxide nanowires as the etch masks. We demonstrate that these etch masks have numerous advantages: they can be synthesized simply by heating a copper foil in air, deposited on graphene from a solution, they are inert to oxygen plasma, and can be removed from the substrate by dissolution in mild acids. We fabricated GNRs in the device configuration and tested their electrical properties. Depending on the duration of the plasma etching, GNR devices exhibiting either standard ambipolar electric field effects or p-type transistor behaviors with ON-OFF ratios > 50 can be fabricated. The resulting devices based on narrow GNRs are demonstrated to exhibit promising electronic properties, which can be exploited in studies where GNR devices are required.
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81.16.Rf Micro- and nanoscale pattern formation
72.80.Vp Electronic transport in graphene
73.63.Bd Nanocrystalline materials
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning

Intrinsic half-metallicity in hydrogenated boron-nitride nanoribbons

Duminda K. Samarakoon and Xiao-Qian Wang

Appl. Phys. Lett. 100, 103107 (2012); http://dx.doi.org/10.1063/1.3693174 (4 pages) | Cited 4 times

Online Publication Date: 7 March 2012

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We have investigated the structural and electronic characteristics of fully hydrogenated boron-nitride (BN) layer and zigzag-edged nanoribbons using dispersion-corrected density-functional calculations. In the fully hydrogenated BN structure, the hydrogen atoms adsorb on top of the B and N sites, alternating on both sides of the hexagonal BN-plane in a specific periodic manner. Among various low-energy hydrogenated membranes referred to as chair, boat, twist-boat, and stirrup, the stirrup conformation is the most energetically favorable one. The zigzag-edged BN nanoribbon, prominently fabricated in experiments, possesses intrinsic half-metallicity with full hydrogenation. The half-metallicity can be tuned by applying a transverse electric bias, thereby providing a promising route for spintronics device applications.
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61.46.-w Structure of nanoscale materials
73.22.-f Electronic structure of nanoscale materials and related systems
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Nc Total energy and cohesive energy calculations

Detection of electromagnetic waves using charged cantilevers

P. G. Datskos, N. V. Lavrik, J. D. Tobin, and L. T. Bowland

Appl. Phys. Lett. 100, 103108 (2012); http://dx.doi.org/10.1063/1.3689017 (4 pages)

Online Publication Date: 7 March 2012

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We describe micromechanical structures that are capable of sensing both electrostatic fields and electromagnetic fields over a wide frequency range. Typically, sensing of electromagnetic waves is achieved with electrically conducting antennas, which despite the many advantages do not exhibit high sensitivity over a broad frequency range. An important aspect of our present work is that, in contrast to traditional antennas, the dimensions of micromechanical oscillators sensitive to electromagnetic waves can be much smaller than the wavelength. We characterized the micromechanical oscillators and measured responses to electric fields and estimated the performance limits by evaluating the signal-to-noise ratio theoretically and experimentally.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
84.30.Ng Oscillators, pulse generators, and function generators
84.40.Ba Antennas: theory, components and accessories
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Transport properties of hybrid graphene/graphane nanoribbons

Wei Zou, Zhizhou Yu, C. X. Zhang, J. X. Zhong, and L. Z. Sun

Appl. Phys. Lett. 100, 103109 (2012); http://dx.doi.org/10.1063/1.3692725 (4 pages)

Online Publication Date: 9 March 2012

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The transport properties of hybrid nanoribbons constructed by substituting zigzag graphane nanoribbons into zigzag graphene nanoribbons are investigated using the first-principles calculations and non-equilibrium Green’s function. The transport properties of the hybrid systems are improved due to the appearance of transport platform with nontrivial conductance around the Fermi level. This enhancement attributes to the extra bands induced by the substituted graphane nanoribbons. Moreover, this enhancement is sensitive to the position and concentration of the substituted graphane nanoribbons in the system. Our results indicate that such hybrid system is an effective approach to modulate the transport properties of zigzag graphene nanoribbons.
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73.22.Pr Electronic structure of graphene
72.80.Vp Electronic transport in graphene
73.63.Bd Nanocrystalline materials
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Bias-dependent oscillatory electron transport of monatomic sulfur chains

Jing-Xin Yu, Yan Cheng, Stefano Sanvito, and Xiang-Rong Chen

Appl. Phys. Lett. 100, 103110 (2012); http://dx.doi.org/10.1063/1.3693380 (4 pages)

Online Publication Date: 9 March 2012

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The bias-dependent oscillatory electron transport of monatomic sulfur chains sandwiched between gold electrodes is investigated with density functional theory and non-equilibrium Green’s function method. At zero bias, in contrast to the typical odd-even oscillations observed in most metallic chains, we find that the conductance oscillates with a period of four atoms. However, as the bias voltage is increased the current displays a two-atom periodicity. This emerges gradually, first for the longer chains and then, at voltages larger than 0.7 V, for lengths. The oscillatory behaviors are analyzed by the density of states and the energy-dependent and bias-dependent transmission coefficients.
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73.20.At Surface states, band structure, electron density of states
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.46.-w Structure of nanoscale materials
73.40.-c Electronic transport in interface structures

Ultra-long, free-standing, single-crystalline vanadium dioxide micro/nanowires grown by simple thermal evaporation

Chun Cheng, Kai Liu, Bin Xiang, Joonki Suh, and Junqiao Wu

Appl. Phys. Lett. 100, 103111 (2012); http://dx.doi.org/10.1063/1.3693381 (4 pages) | Cited 1 time

Online Publication Date: 9 March 2012

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Recently, it was discovered that single-crystalline VO2 nanostructures exhibit unique, single-domain metal-insulator phase transition. They enable a wide range of device applications as well as discoveries of oxide physics beyond those can be achieved with VO2 bulk or thin films. Previous syntheses of these nanostructures are limited in density, aspect ratio, single-crystallinity, or by substrate clamping. Here we break these limitations and synthesize ultra-long, ultra-dense, and free-standing VO2 micro/nanowires using a simple vapor transport method. These are achieved by enhancing the VO2 nucleation and growth rates using rough-surface quartz as the substrate and V2O5 powder as the evaporation source.
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81.16.-c Methods of micro- and nanofabrication and processing
71.30.+h Metal-insulator transitions and other electronic transitions
64.60.Q- Nucleation
68.55.-a Thin film structure and morphology
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)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Influence of Si Co-doping on electrical transport properties of magnesium-doped boron nanoswords

Yuan Tian, Hongliang Lu, Jifa Tian, Chen Li, Chao Hui, Xuezhao Shi, Yuan Huang, Chengmin Shen, and Hong-jun Gao

Appl. Phys. Lett. 100, 103112 (2012); http://dx.doi.org/10.1063/1.3693383 (5 pages)

Online Publication Date: 9 March 2012

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Magnesium-doped boron nanoswords were synthesized via a thermoreduction method. The as-prepared nanoswords are single crystalline and β-rhombohedral (β-rh) phase. Electrical transport measurements show that variable range hopping conductivity increases with temperature, and carrier mobility has a greater influence than carrier concentration. These results are consistent with the three dimensional Mott’s model (M. Cutler and N. F. Mott, Phys. Rev. 181, 1336 (1969)) besides a high density of localized states at the Fermi level compared with bulk β-rh boron. Conductivity of Mg-doped boron nanoswords is significantly lower than that of “pure” (free of magnesium) boron nanoswords. Electron energy loss spectroscopy studies confirm that the poorer conductivity arises from silicon against magnesium doping.
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81.05.Bx Metals, semimetals, and alloys
79.20.Uv Electron energy loss spectroscopy
73.22.-f Electronic structure of nanoscale materials and related systems
73.63.Bd Nanocrystalline materials
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
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