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4 Jul 2011

Volume 99, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 99, 011107 (2011); http://dx.doi.org/10.1063/1.3606505 (3 pages)

Kosei Ueno, Satoaki Takabatake, Ko Onishi, Hiroko Itoh, Yoshiaki Nishijima, and Hiroaki Misawa
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Identifying catalyst in Li-N-H system by x-ray absorption spectroscopy

Shigehito Isobe, Satoshi Hino, Takayuki Ichikawa, and Yoshitsugu Kojima

Appl. Phys. Lett. 99, 013101 (2011); http://dx.doi.org/10.1063/1.3606534 (3 pages) | Cited 3 times

Online Publication Date: 5 July 2011

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Chemical bonding states of titanium compounds in LiH and LiNH2 mixture, which have been a candidate for a hydrogen storage material, have been examined by x-ray absorption spectroscopy measurement as the characterization of the catalysts. The results of x-ray absorption near-edge structure indicated that the Ti atoms in the Ti compounds, which had the catalytic effect on the kinetics of the hydrogen desorption properties, had a common electronic (chemical bonding) state. Additionally, this common electronic state of the Ti catalysts agrees with that of TiCl3·5NH3. These results indicated that TiCl3·5NH3 could act as the catalyst.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
78.70.Dm X-ray absorption spectra
88.30.R- Hydrogen storage
64.75.Ef Mixing
68.43.Nr Desorption kinetics

Electronic properties of twisted armchair graphene nanoribbons

Arta Sadrzadeh, Ming Hua, and Boris I. Yakobson

Appl. Phys. Lett. 99, 013102 (2011); http://dx.doi.org/10.1063/1.3606553 (3 pages) | Cited 6 times

Online Publication Date: 5 July 2011

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We study the effect of twist on the electronic structure of H-terminated armchair graphene nanoribbons, for both relaxed and unrelaxed unit cell size. We investigate the band gap change as a function of the twist angle for different ribbon widths. In the case of unrelaxed unit cell size, the band gap closes for smaller twist angles as opposed to relaxed unit cell size. We calculate strain energy as a function of twist angle and show its direct correlation with the reduction of the band gap. Furthermore, the conductance is calculated at arbitrary degree of torsion.
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73.22.Pr Electronic structure of graphene
73.20.At Surface states, band structure, electron density of states
61.48.Gh Structure of graphene

Top-gate dielectric induced doping and scattering of charge carriers in epitaxial graphene

Conor P. Puls, Neal E. Staley, Jeong-Sun Moon, Joshua A. Robinson, Paul M. Campbell, Joseph L. Tedesco, Rachael L. Myers-Ward, Charles R. Eddy, Jr., D. Kurt Gaskill, and Ying Liu

Appl. Phys. Lett. 99, 013103 (2011); http://dx.doi.org/10.1063/1.3607284 (3 pages) | Cited 2 times

Online Publication Date: 5 July 2011

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We show that an e-gun deposited dielectric impose severe limits on epitaxial graphene-based device performance based on Raman spectroscopy and low-temperature transport measurements. Specifically, we show from studies of epitaxial graphene Hall bars covered by SiO2 that the measured carrier density is strongly inhomogenous and predominantly induced by charged impurities at the grapheme/dielectric interface that limit mobility via Coulomb interactions. Our work emphasizes that material integration of epitaxial graphene and a gate dielectric is the next major road block towards the realization of graphene-based electronics.
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85.30.Tv Field effect devices

Investigation of structural and electronic properties of graphene oxide

Sumit Saxena, Trevor A. Tyson, Shobha Shukla, Ezana Negusse, Haiyan Chen, and Jianming Bai

Appl. Phys. Lett. 99, 013104 (2011); http://dx.doi.org/10.1063/1.3607305 (3 pages) | Cited 13 times

Online Publication Date: 5 July 2011

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The local atomic structure of graphene oxide has been probed using synchrotron radiations. Detailed investigations of recently proposed simplistic model of graphene oxide using x-ray absorption near edge spectroscopy have been performed. X-ray diffraction measurements and calculations indicate loss of coherence between graphene-like layers. However, larger in-plane structural coherence is understood to be present. Selected area electron diffraction measurements indicate the presence of graphitic regions in graphene oxide which is expected to produce interesting confinement effects in graphene oxide which could be important for the development of tunable electronic and photonic devices.
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61.48.Gh Structure of graphene
73.22.Pr Electronic structure of graphene
81.05.ue Graphene
71.20.Tx Fullerenes and related materials; intercalation compounds
78.70.Dm X-ray absorption spectra

Electromechanics of twisted graphene nanoribbons

Pekka Koskinen

Appl. Phys. Lett. 99, 013105 (2011); http://dx.doi.org/10.1063/1.3607956 (3 pages) | Cited 8 times

Online Publication Date: 5 July 2011

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Graphene nanoribbons are the flimsiest material systems in the world, and they get readily distorted. Distortion by twisting, for one, is important because it couples to ribbon’s electronic properties. In this letter, using simulations with density-functional tight-binding and revised periodic boundary conditions, I show that twisting appears almost equivalent to stretching; electronic structures in a given nanoribbon either upon twisting or upon certain stretching are quantitatively similar. This simple equivalence will provide a valuable guideline for interpreting and designing experiments with these flimsy ribbons.
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73.22.Pr Electronic structure of graphene
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
77.65.-j Piezoelectricity and electromechanical effects
62.25.-g Mechanical properties of nanoscale systems
61.48.Gh Structure of graphene

NiSi crystal structure, site preference, and partitioning behavior of palladium in NiSi(Pd)/Si(100) thin films: Experiments and calculations

Zugang Mao, Yeong-Cheol Kim, Hi-Deok Lee, Praneet Adusumilli, and David N. Seidman

Appl. Phys. Lett. 99, 013106 (2011); http://dx.doi.org/10.1063/1.3606536 (3 pages) | Cited 4 times

Online Publication Date: 6 July 2011

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The crystal structure of a NiSi thin-film on a Si substrate and Pd site-substitution in NiSi and the partitioning behavior of Pd for NiSi(Pd)/Si(100) are investigated by x-ray diffraction (XRD), first-principles calculations, and atom-probe tomography (APT). The NiSi layer is a distorted orthorhombic structure from XRD patterns via experiments and calculations. We find that Pd has a strong driving force, 0.72 eV atom−1, for partitioning from Si into the orthorhombic NiSi layer. The calculated substitutional energies of Pd in NiSi indicate that Pd has a strong preference for Ni sublattice-sites, which is in agreement with concentration profiles determined by APT.
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61.66.Dk Alloys
68.55.aj Insulators

Thermoelectric power factor of In2O3:Pd nanocomposite films

Otto J. Gregory, Matin Amani, and Gustave C. Fralick

Appl. Phys. Lett. 99, 013107 (2011); http://dx.doi.org/10.1063/1.3607289 (3 pages)

Online Publication Date: 6 July 2011

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A nanocomposite exhibiting large thermoelectric powers and capable of operating at temperatures as high as 1100 °C in air was fabricated by embedding palladium nanoparticles into an indium oxide matrix via co-sputtering from metal and ceramic targets. Combinatorial chemistry techniques were used to systematically investigate the effect of palladium content in these nanocomposite films on thermoelectric response. Based on these rapid screening experiments, the thermoelectric properties of the most promising nanocomposites were evaluated as a function of post-deposition heat treatment at high temperatures. An n-type nanocomposite film was developed exhibiting a power factor of 4.5 × 10−4 W/m·K2 at 1000 °C in air.
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81.05.Hd Other semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
61.72.up Other materials
72.20.Pa Thermoelectric and thermomagnetic effects
73.63.-b Electronic transport in nanoscale materials and structures

Comparative study on size dependence of melting temperatures of pure metal and alloy nanoparticles

C. L. Chen, J.-G. Lee, K. Arakawa, and H. Mori

Appl. Phys. Lett. 99, 013108 (2011); http://dx.doi.org/10.1063/1.3607957 (3 pages) | Cited 5 times

Online Publication Date: 6 July 2011

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A comparative study on the size dependence of the melting temperatures of pure metal and alloy nanoparticles has been carried out. It was found that the melting temperatures of Bi-Sn, In-Sn, and Pb-Sn alloy nanoparticles decreased more rapidly with decreasing particle size than those of the constituent metal nanoparticles (Bi, In, Pb, Sn). Namely, the size dependence of the melting temperature was stronger for the alloy nanoparticles than that for the constituent metal nanoparticles. Results calculated with a thermodynamic model were in good agreement with the experimental observations.
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81.05.Bx Metals, semimetals, and alloys
64.70.dj Melting of specific substances
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Fermi level shifting of TiO2 nanostructures during dense electronic excitation

Avesh Kumar, M. K. Jaiswal, D. Kanjilal, Rakesh K. Joshi, and T. Mohanty

Appl. Phys. Lett. 99, 013109 (2011); http://dx.doi.org/10.1063/1.3608140 (3 pages) | Cited 2 times

Online Publication Date: 6 July 2011

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Scanning Kelvin probe microscopy has been used to understand the modification of work function of TiO2 with swift heavy ion irradiation. The observed increase in contact potential difference (CPD) indicates a shift in Fermi level towards the valence band, which is due to the development of defects during the bombardment of high energy heavy ions. The change in CPD values on ion irradiation is attributed to electronic excitation induced defect concentration and surface roughness.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Cg Contact resistance, contact potential
61.80.Jh Ion radiation effects

Probing nanoscale conductance of monolayer graphene under pressure

Sangku Kwon, Sunghyun Choi, H. J. Chung, Heejun Yang, Sunae Seo, Seung-Hoon Jhi, and Jeong Young Park

Appl. Phys. Lett. 99, 013110 (2011); http://dx.doi.org/10.1063/1.3609317 (3 pages) | Cited 8 times

Online Publication Date: 7 July 2011

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The correlation between charge transport and mechanical deformation of the single layer graphene layer was studied with conductive probe atomic force microscopy/friction force microscopy in ultra-high vacuum. By measuring the current and friction on a graphene layer that is under mechanical stress, we identify crossover of two regimes in the current density that depend on the applied pressure. We suggest that the difference in work function under mechanical deformation as well as a change in the density of state and formation of a dipole field are responsible for this crossover behavior.
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72.80.Vp Electronic transport in graphene
81.05.ue Graphene
73.30.+y Surface double layers, Schottky barriers, and work functions
81.40.Lm Deformation, plasticity, and creep
81.40.Pq Friction, lubrication, and wear
62.20.F- Deformation and plasticity

Molecular beam epitaxy and characterization of thin Bi2Se3 films on Al2O3 (110)

Phillip Tabor, Cameron Keenan, Sergei Urazdhin, and David Lederman

Appl. Phys. Lett. 99, 013111 (2011); http://dx.doi.org/10.1063/1.3609326 (3 pages) | Cited 8 times

Online Publication Date: 7 July 2011

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The structural and electronic properties of thin Bi2Se3 films grown on Al2O3 (110) by molecular beam epitaxy are investigated. The epitaxial films grow in the Frank-van der Merwe mode and are c-axis oriented. They exhibit the highest crystallinity, the lowest carrier concentration, and optimal stoichiometry at a substrate temperature of 200 °C determined by the balance between surface kinetics and desorption of Se. The crystallinity of the films improves with increasing Se/Bi flux ratio. Our results enable studies of thin topological insulator films on inert, non-conducting substrates that allow optical access to both film surfaces.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.43.Nr Desorption kinetics
68.55.aj Insulators
73.61.Ng Insulators

Klein tunnelling model of low energy electron field emission from single-layer graphene sheet

S. Sun, L. K. Ang, D. Shiffler, and J. W. Luginsland

Appl. Phys. Lett. 99, 013112 (2011); http://dx.doi.org/10.1063/1.3609781 (3 pages) | Cited 8 times

Online Publication Date: 7 July 2011

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By considering the effect of Klein tunneling for low energy electrons with linear energy dispersion, a model has been constructed to calculate the amount of emitted line current density from a single-layer graphene sheet, which is vertically aligned inside a dc gap. It is found that the current-voltage scaling obtained from the constructed Klein tunneling model is very different from the traditional field emission model based on the Fowler-Nordheim (FN) law. Under the same geometrical field enhancement factor, our model predicts a much higher emitted current as compared to the FN law at low voltages.
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79.70.+q Field emission, ionization, evaporation, and desorption
72.80.Vp Electronic transport in graphene
73.40.Gk Tunneling

Discrete-time quadrature feedback cooling of a radio-frequency mechanical resonator

M. Poot, S. Etaki, H. Yamaguchi, and H. S. J. van der Zant

Appl. Phys. Lett. 99, 013113 (2011); http://dx.doi.org/10.1063/1.3608148 (3 pages) | Cited 5 times

Online Publication Date: 7 July 2011

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We have employed a feedback cooling scheme, which combines high-frequency mixing with digital signal processing. The frequency and damping rate of a 2 MHz micromechanical resonator embedded in a dc SQUID are adjusted with the feedback, and active cooling to a temperature of 14.3 mK is demonstrated. This technique can be applied to GHz resonators and allows for flexible control strategies.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems

Multiply resonant high quality photonic crystal nanocavities

Kelley Rivoire, Sonia Buckley, and Jelena Vučković

Appl. Phys. Lett. 99, 013114 (2011); http://dx.doi.org/10.1063/1.3607281 (3 pages) | Cited 3 times

Online Publication Date: 8 July 2011

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We propose and experimentally demonstrate a photonic crystal nanocavity with multiple resonances that can be tuned nearly independently. The design is composed of two orthogonal intersecting nanobeam cavities. Experimentally, we measure cavity quality factors of 6600 and 1000 for resonances separated by 382 nm; we measure a maximum separation between resonances of 506 nm. These structures are promising for enhancing efficiency in nonlinear optical processes such as sum/difference frequency and stimulated Raman scattering.
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42.70.Qs Photonic bandgap materials
42.15.Eq Optical system design
42.79.-e Optical elements, devices, and systems

Thermoelectric power of graphene as surface charge doping indicator

Anton N. Sidorov, Andriy Sherehiy, Ruwantha Jayasinghe, Robert Stallard, Daniel K. Benjamin, Qingkai Yu, Zhihong Liu, Wei Wu, Helin Cao, Yong P. Chen, Zhigang Jiang, and Gamini U. Sumanasekera

Appl. Phys. Lett. 99, 013115 (2011); http://dx.doi.org/10.1063/1.3609858 (3 pages) | Cited 4 times

Online Publication Date: 8 July 2011

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We report on simultaneous thermoelectric power and four-probe resistance measurements of chemical vapor deposition grown graphene during a degas process, as well as in exposure to various gases. For all investigated samples, a dramatic change in thermoelectric power was observed and found to be sensitive to the gas molecule charge doping on the surface of graphene. The observed p-type behavior under ambient conditions supports an electrochemical charge transfer mechanism between the graphene and oxygen redox couple, while the n-type behavior under degassed conditions is ascribed to the electron doping caused by the surface states of the SiO2/Si substrate.
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72.20.Pa Thermoelectric and thermomagnetic effects
73.20.At Surface states, band structure, electron density of states
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.up Other materials
81.05.ue Graphene

Heat conduction across a solid-solid interface: Understanding nanoscale interfacial effects on thermal resistance

Ganesh Balasubramanian and Ishwar K. Puri

Appl. Phys. Lett. 99, 013116 (2011); http://dx.doi.org/10.1063/1.3607477 (3 pages) | Cited 8 times

Online Publication Date: 8 July 2011

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Phonons scatter and travel ballistically in systems smaller than the phonon mean free path. At larger lengths, the transport is instead predominantly diffusive. We employ molecular dynamics simulations to describe the length dependence of the thermal conductivity. The simulations show that the interfacial thermal resistance Rk for a Si-Ge superlattice is inversely proportional to its length, but reaches a constant value as the system dimension becomes larger than the phonon mean free path. This nanoscale effect is incorporated into an accurate continuum model by treating the interface as a distinct material with an effective thermal resistance equal to Rk.
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66.70.Df Metals, alloys, and semiconductors
68.35.Ja Surface and interface dynamics and vibrations
63.22.Np Layered systems
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