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6 Dec 2010

Volume 97, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 97, 233101 (2010); http://dx.doi.org/10.1063/1.3523252 (3 pages)

Hoonkyung Lee, Marvin L. Cohen, and Steven G. Louie
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Selective functionalization of halogens on zigzag graphene nanoribbons: A route to the separation of zigzag graphene nanoribbons

Hoonkyung Lee, Marvin L. Cohen, and Steven G. Louie

Appl. Phys. Lett. 97, 233101 (2010); http://dx.doi.org/10.1063/1.3523252 (3 pages) | Cited 1 time

Online Publication Date: 6 December 2010

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Using the ab initio pseudopotential density functional method, we investigate the functionalization of halogen molecules into graphene-based nanostructures with zigzag and armchair edges. We find that halogen molecules adsorb through chemisorption on the zigzag edge carbon atoms with a binding energy of ∼ 1–5 eV, in sharp contrast to physisorption on the armchair edge and elsewhere where they adsorb with a binding energy of ∼ 0.07 eV. Our findings would be utilized for an approach to the separation of zigzag graphene nanoribbons with regular edges with the change of the solubility of the functionalized nanoribbons.
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68.43.Mn Adsorption kinetics
64.75.Bc Solubility

Magnetic imaging of the pinning mechanism of asymmetric transverse domain walls in ferromagnetic nanowires

Dorothée Petit, Huang T. Zeng, Joao Sampaio, Emma Lewis, Liam O’Brien, Ana-Vanessa Jausovec, Dan Read, Russell P. Cowburn, Kerry J. O’Shea, Stephen McVitie, and John N. Chapman

Appl. Phys. Lett. 97, 233102 (2010); http://dx.doi.org/10.1063/1.3523351 (3 pages) | Cited 2 times

Online Publication Date: 6 December 2010

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The pinning of asymmetric transverse magnetic domain walls by constrictions and protrusions in thin permalloy nanowires is directly observed using the Fresnel mode of magnetic imaging. Different domain wall (DW)/trap configurations are initialized using in situ applied magnetic fields, and the resulting configurations are imaged both at remanence and under applied fields. The nature of the chirality dependent pinning potentials created by the traps is clearly observed. The effect of the asymmetry of the DW is discussed. Micromagnetic simulations are also presented, which are in excellent agreement with the experiments.
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75.78.Fg Dynamics of domain structures
75.60.Ch Domain walls and domain structure
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.-c Magnetic properties of nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.78.Cd Micromagnetic simulations

Nanoscale investigations of shift of individual interfaces in temperature induced processes of Ni–Si system by secondary neutral mass spectrometry

A. Lakatos, G. A. Langer, A. Csik, C. Cserhati, M. Kis-Varga, L. Daroczi, G. L. Katona, Z. Erdélyi, G. Erdelyi, K. Vad, and D. L. Beke

Appl. Phys. Lett. 97, 233103 (2010); http://dx.doi.org/10.1063/1.3524491 (3 pages)

Online Publication Date: 6 December 2010

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We describe a method for measurement of nanoscale shift of interfaces in layered systems by a combination of secondary neutral mass spectrometry and profilometer. We demonstrate it by the example of the investigation of interface shifts during the solid state reaction in Ni/amorphous-Si system. The kinetics of the shrinkage of the initial nanocrystalline Ni film and the amorphous Si layer as well as the average growth kinetics of the product phases were determined at 503 K. The results show that nanoscale resolution can be reached and the method is promising for following solid state reactions in different thin film systems.
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64.70.Nd Structural transitions in nanoscale materials
64.70.kt Molecular crystals
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

On the mechanism for plasma hydrogenation of graphene

J. D. Jones, W. D. Hoffmann, A. V. Jesseph, C. J. Morris, G. F. Verbeck, and J. M. Perez

Appl. Phys. Lett. 97, 233104 (2010); http://dx.doi.org/10.1063/1.3524517 (3 pages) | Cited 3 times

Online Publication Date: 6 December 2010

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We report that hydrogenation of mono-, bi-, and trilayer graphene samples via exposure to H2 plasma occurs as a result of electron irradiation of H2O adsorbates on the samples, rather than H species in the plasma as reported by [ Elias et al., Science 323, 610 (2009)] . We propose that the hydrogenation mechanism is electron-impact fragmentation of H2O adsorbates into H+ ions. At incident electron energies >60 eV, we observe hydrogenation that is significantly more stable at temperatures >200 °C than previously reported.
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82.30.-b Specific chemical reactions; reaction mechanisms

Electronic properties of metal-semiconductor and metal-oxide-semiconductor structures composed of carbon nanotube film on silicon

Ashkan Behnam, Nischal Arkali Radhakrishna, Zhuangchun Wu, and Ant Ural

Appl. Phys. Lett. 97, 233105 (2010); http://dx.doi.org/10.1063/1.3524194 (3 pages) | Cited 3 times

Online Publication Date: 7 December 2010

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We fabricate and experimentally characterize the electrical properties of metal-semiconductor (MS) and metal-oxide-semiconductor (MOS) structures where the metal is single-walled carbon nanotube (CNT) film and the semiconductor is a Si substrate. Our results suggest that for the MS devices thermionic emission is the main high-temperature current transport mechanism, while tunneling becomes the dominant mechanism for MOS devices with thermally grown thin oxide layers between the CNT film and Si. In addition, the CNT film workfunction, a key parameter for the performance of CNT film-based devices, is obtained from the capacitance-voltage measurements on the MOS structures.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
79.40.+z Thermionic emission
73.40.Gk Tunneling
73.40.Ns Metal-nonmetal contacts
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
73.30.+y Surface double layers, Schottky barriers, and work functions

Diameter-modulated nanowires as candidates for high thermoelectric energy conversion efficiency

Xanthippi Zianni

Appl. Phys. Lett. 97, 233106 (2010); http://dx.doi.org/10.1063/1.3523360 (3 pages) | Cited 2 times

Online Publication Date: 8 December 2010

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High optimal thermoelectric efficiencies are theoretically demonstrated in ballistic nanowires with diameter modulation. The physics underlying the good thermoelectric performance of diameter-modulated nanowires is the strong energy dependence of their transmission coefficients. It is shown that the thermoelectric efficiency is directly related to the geometry of the diameter modulation. It becomes evident that geometry optimization can lead to efficient thermoelectric devices based on modulated nanowires.
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73.63.Nm Quantum wires
72.20.Pa Thermoelectric and thermomagnetic effects
73.23.Ad Ballistic transport
72.20.Ht High-field and nonlinear effects

Closed-air induced composite wetting on hydrophilic ordered nanoporous anodic alumina

Zhirong Li, Jingxia Wang, Youzhuan Zhang, Jianjun Wang, Lei Jiang, and Yanlin Song

Appl. Phys. Lett. 97, 233107 (2010); http://dx.doi.org/10.1063/1.3527076 (3 pages)

Online Publication Date: 9 December 2010

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We investigate wetting behaviors of two kinds of hydrophilic ordered nanoporous anodic alumina (PAA). The water contact angle (CA) increases at first and subsequently decreases with increasing pore diameter of PAA with closed-pore structure, while the water CA decreases monotonously on PAA with open-pore structure. These interesting wetting behaviors are mainly due to the presence/absence of closed-air in the PAA. The closed-air could prevent water from entering into the nanopores. This work offers insight to control wetting by tailoring the surface nanostructure and will be significant for applications in printing, coating, etc.
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61.46.-w Structure of nanoscale materials
61.43.Gt Powders, porous materials
68.35.bt Other materials

Rational computational design of optimal catalytic surfaces

Sujata Paul and Marco Buongiorno Nardelli

Appl. Phys. Lett. 97, 233108 (2010); http://dx.doi.org/10.1063/1.3525372 (3 pages)

Online Publication Date: 9 December 2010

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Using calculations from first-principles based on density functional theory, we introduce an innovative concept for the design of catalysts based on the tuning of the surface properties by progressive layering of thin metal films on an oxide support, where the substrate is substantially exploited as an active design element for the tuning of the reactivity of the metallic surface. We demonstrate this idea by studying the adsorption and activation properties of CO2 on Pd and oxide-supported Pd thin films.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.43.Mn Adsorption kinetics

Enhanced stability of hydrogen atoms at the graphene/graphane interface of nanoribbons

Z. M. Ao, A. D. Hernández-Nieves, F. M. Peeters, and S. Li

Appl. Phys. Lett. 97, 233109 (2010); http://dx.doi.org/10.1063/1.3525377 (3 pages) | Cited 4 times

Online Publication Date: 9 December 2010

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The thermal stability of graphene/graphane nanoribbons (GGNRs) is investigated using density functional theory. It is found that the energy barriers for the diffusion of hydrogen atoms on the zigzag and armchair interfaces of GGNRs are 2.86 and 3.17 eV, respectively, while the diffusion barrier of an isolated H atom on pristine graphene was only ∼ 0.3 eV. These results unambiguously demonstrate that the thermal stability of GGNRs can be enhanced significantly by increasing the hydrogen diffusion barriers through graphene/graphane interface engineering. This may provide new insights for viable applications of GGNRs.
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81.05.uj Diamond/nanocarbon composites
81.05.ub Fullerenes and related materials
68.35.Fx Diffusion; interface formation
68.35.Ct Interface structure and roughness
68.35.Md Surface thermodynamics, surface energies
73.20.At Surface states, band structure, electron density of states

Impact of strain on radio frequency characteristics of flexible microwave single-crystalline silicon nanomembrane p-intrinsic-n diodes on plastic substrates

Guoxuan Qin, Hao-Chih Yuan, George K. Celler, Jianguo Ma, and Zhenqiang Ma

Appl. Phys. Lett. 97, 233110 (2010); http://dx.doi.org/10.1063/1.3521409 (3 pages) | Cited 2 times

Online Publication Date: 9 December 2010

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This letter presents radio frequency (rf) characterization of flexible microwave single-crystalline silicon nanomembrane (SiNM) p-intrinsic-n (PIN) diodes on plastic substrate under various uniaxial mechanical tensile bending strains. The flexible single-crystalline SiNM PIN diode shows significant/negligible performance enhancement on strains under forward/reverse operation modes from dc to 20 GHz. An rf strain equivalent circuit model is developed to analyze the underlying mechanism and reveals unproportional device parameters change with bending strains ( ∼ 0.4% tensile strain induces ∼ 10% change for diode internal and parasitic inductance/resistance). The study provides guidelines of properly designing and using single-crystalline SiNMs diodes for flexible monolithic microwave integrated circuits.
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85.30.Kk Junction diodes
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
84.30.Bv Circuit theory

Modulating the electronic structures of graphene by controllable hydrogenation

Zhiqiang Luo, Jingzhi Shang, Sanhua Lim, Dehui Li, Qihua Xiong, Zexiang Shen, Jianyi Lin, and Ting Yu

Appl. Phys. Lett. 97, 233111 (2010); http://dx.doi.org/10.1063/1.3524217 (3 pages) | Cited 6 times

Online Publication Date: 10 December 2010

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The evolution of electronic structures of hydrogenated graphene with different amount of hydrogen (H) coverage was investigated by ultraviolet photoemission spectroscopy and optical absorption spectroscopy. Raman spectroscopy and x-ray photoelectron spectroscopy were used to monitor and evaluate the H coverage. At low H coverage, the sp3 C–H bonds embedded within a sp2 C matrix behave as defects in graphene and depress the delocalized π electron system. At high H coverage, two localized π electron states originating from the sp2 C clusters encircled by the sp3 C–H matrix appear in the electronic band structures, and an opening of a band gap has been observed.
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73.22.Pr Electronic structure of graphene
78.67.Wj Optical properties of graphene
78.40.Ri Fullerenes and related materials
78.30.Na Fullerenes and related materials
79.60.-i Photoemission and photoelectron spectra
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