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4 Jul 2011

Volume 99, Issue 1, Articles (01xxxx)

Issue Cover Spotlight Figure

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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Polarity-dependent kinetics of ferroelectric switching in epitaxial BiFeO3(111) capacitors

T. H. Kim, S. H. Baek, S. M. Yang, Y. S. Kim, B. C. Jeon, D. Lee, J.-S. Chung, C. B. Eom, J.-G. Yoon, and T. W. Noh

Appl. Phys. Lett. 99, 012905 (2011); http://dx.doi.org/10.1063/1.3609235 (3 pages) | Cited 3 times

Online Publication Date: 8 July 2011

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We report on the intriguing polarity-dependent kinetics of polarization switching in epitaxial BiFeO3(111) capacitors. Two seemingly incompatible switching kinetics were observed depending on the polarity of the applied switching bias. Under a negative switching bias, the polarization switching process occurs mainly through sideways domain wall motion, but under a positive switching bias, domain nucleation governs the polarization reversal. The modified piezoresponse force microscopy reveals these polarity-dependent ferroelectric domain evolutions. This polarity dependence of ferroelectric switching kinetics is attributed to defect-related local fields that have different distributions near film/electrode interfaces, probably due to structural relaxation in the BiFeO3(111) film.
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84.32.Tt Capacitors
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
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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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Tetracene thin film transistors with polymer gate dielectrics

Simone Bertolazzi, Julia Wünsche, Fabio Cicoira, and Clara Santato

Appl. Phys. Lett. 99, 013301 (2011); http://dx.doi.org/10.1063/1.3606535 (3 pages) | Cited 3 times

Online Publication Date: 6 July 2011

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The use of polymer dielectrics is an important step towards large-area, flexible, and low-cost electronics. In this letter, we study the effect of the polymer dielectrics polystyrene and parylene C on the charge transport properties of tetracene thin films in transistor configuration. By using polymer dielectrics, the tetracene hole mobility increased by more than one order of magnitude, up to 0.2 cm2 V−1 s−1, as compared to bare silicon dioxide. We correlate this result to a favorable morphology of the tetracene films during the early stages of growth.
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85.30.Tv Field effect devices
FREE

On the efficiency of exciton dissociation at the interface between a conjugated polymer and an electron acceptor

M. Wiemer, A. V. Nenashev, F. Jansson, and S. D. Baranovskii

Appl. Phys. Lett. 99, 013302 (2011); http://dx.doi.org/10.1063/1.3607481 (3 pages) | Cited 5 times

Online Publication Date: 6 July 2011

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It is a matter of controversy why excitons can efficiently dissociate into free carriers at an intrinsic polymer/fullerene interface, despite the strong Coulomb interaction between the charges provided by the very low dielectric constant in organic materials. The effect has been ascribed to the presence of intrinsic dipoles on the polymer/fullerene interface, though assuming an unrealistically small carrier effective mass necessary for exciton dissociation. We improve the model showing that it allows realistic carrier effective masses. The dissociation probability is calculated as a function of electric field acting on the dissociating electron-hole pairs.
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71.35.Pq Charged excitons (trions)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.-r Conductivity of specific materials
77.22.Ch Permittivity (dielectric function)
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
FREE

Extending the voltage window in the characterization of electrical transport of large-area molecular junctions

Ilias Katsouras, Auke J. Kronemeijer, Edsger C. P. Smits, Paul A. van Hal, Tom C. T. Geuns, Paul W. M. Blom, and Dago M. de Leeuw

Appl. Phys. Lett. 99, 013303 (2011); http://dx.doi.org/10.1063/1.3608154 (3 pages) | Cited 4 times

Online Publication Date: 6 July 2011

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A large bias window is required to discriminate between different transport models in large-area molecular junctions. Under continuous DC bias, the junctions irreversibly break down at fields over 9 MV/cm. We show that, by using pulse measurements, we can reach electrical fields of 35 MV/cm before degradation. The breakdown voltage is shown to depend logarithmically on both duty cycle and pulse width. A tentative interpretation is presented based on electrolysis in the polymeric top electrode. Expanding the bias window using pulse measurements unambiguously shows that the electrical transport exhibits not an exponential but a power-law dependence on bias.
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85.65.+h Molecular electronic devices
FREE

Utilizing n-type vanadium oxide films as hole-extracting layers for small molecule organic photovoltaics

I. Hancox, L. A. Rochford, D. Clare, P. Sullivan, and T. S. Jones

Appl. Phys. Lett. 99, 013304 (2011); http://dx.doi.org/10.1063/1.3607478 (3 pages) | Cited 17 times

Online Publication Date: 7 July 2011

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We report increased cell performance for boron subphthalocyanine chloride (SubPc)/fullerene (C60) organic photovoltaic (OPV) cells when thermally evaporated vanadium oxide (V2OX) thin films are incorporated as a hole-extracting layer at the indium-tin oxide (ITO)/SubPc interface. Ultra-violet photoemission spectroscopy (UPS) studies of the V2OX films reveal highly n-type character, with a large work function of 6.8 eV. This correlates well with recently reported data for other metal oxide hole-extracting layers, such as molybdenum oxide and tungsten oxide, in contrast to the p-type character previously reported for V2OX films. There is significant improvement in energy level alignment for hole-extraction when cells utilise the V2OX layer at the ITO/SubPc interface, resulting in substantial increases in open circuit voltage (VOC) and power conversion efficiency (ηp).
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88.40.hj Efficiency and performance of solar cells
88.40.jr Organic photovoltaics
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A frequency shifting liquid metal antenna with pressure responsiveness

Mohammad Rashed Khan, Gerard J. Hayes, Ju-Hee So, Gianluca Lazzi, and Michael D. Dickey

Appl. Phys. Lett. 99, 013501 (2011); http://dx.doi.org/10.1063/1.3603961 (3 pages) | Cited 8 times

Online Publication Date: 5 July 2011

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This letter describes the fabrication and characterization of a shape shifting antenna that changes electrical length and therefore, frequency, in a controlled and rapid response to pressure. The antenna is composed of a liquid metal alloy (eutectic gallium indium) injected into microfluidic channels that feature rows of posts that separate adjacent segments of the metal. The initial shape of the antenna is stabilized mechanically by a thin oxide skin that forms on the liquid metal. Rupturing the skin merges distinct segments of the metal, which rapidly changes the length, and therefore frequency, of the antenna. A high speed camera elucidates the mechanism of merging and simulations model accurately the spectral properties of the antennas.
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84.40.Ba Antennas: theory, components and accessories

Characterization of a junctionless diode

Ran Yu, Isabelle Ferain, Nima Dehdashti Akhavan, Pedram Razavi, Ray Duffy, and Jean-Pierre Colinge

Appl. Phys. Lett. 99, 013502 (2011); http://dx.doi.org/10.1063/1.3608150 (3 pages)

Online Publication Date: 5 July 2011

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A diode has been realised using a silicon junctionless (JL) transistor. The device contains neither PN junction nor Schottky junction. The device is measured at different temperatures. The characteristics of the JL diode are essentially identical to those of a regular PN junction diode. The JL diode has an on/off current ratio of 108, an ideality factor of 1.09, and a reverse leakage current of 1 × 10−14 A at room temperature. The mechanism of the leakage current is discussed using the activation energy (EA). The turn-on voltage of the device can be tuned by JL transistor threshold voltage.
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85.30.Tv Field effect devices

Temperature performance of the edge emitting transistor laser

Song Liang, Hongliang Zhu, Duanhua Kong, Bin Niu, Lingjuan Zhao, and Wei Wang

Appl. Phys. Lett. 99, 013503 (2011); http://dx.doi.org/10.1063/1.3608384 (3 pages)

Online Publication Date: 6 July 2011

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The characteristic temperature (T0) of the edge emitting transistor laser (TL) is studied numerically. For the deep-ridge TL, the common base (CB) mode characteristic temperature (T0,CB) is a lot lower than the common emitter (CE) mode characteristic temperature (T0,CE), which is comparable to a conventional laser. This is resulted from the increase of the emitter to base current gain with the base current, which amplifies the increase of the CB threshold current with temperature. For the shallow-ridge TL, the T0,CE is found to be also rather low and is only slightly higher than the T0,CB. This can be attributed to the large fraction of electron current in the total base current, which is related to the large thickness of base layer and the insertion of quantum wells in the TL.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.30.Pq Bipolar transistors

Graphene-based quantum Hall effect infrared photodetector operating at liquid Nitrogen temperatures

Nikolai G. Kalugin, Lei Jing, Wenzhong Bao, Lee Wickey, Christopher Del Barga, Mekan Ovezmyradov, Eric A. Shaner, and Chun Ning Lau

Appl. Phys. Lett. 99, 013504 (2011); http://dx.doi.org/10.1063/1.3609320 (3 pages) | Cited 2 times

Online Publication Date: 8 July 2011

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We demonstrate a quantum Hall effect (QHE) graphene-based infrared photodetector that functions at 70K—a temperature achievable using liquid Nitrogen in vapor evacuation regime. This result opens up the possibility of wider use of QHE photodetectors if graphene is utilized instead of “classical” materials with two-dimensional electron gas. The potential advantages to this approach are increased operating temperature, reduced magnetic field, and wider range of operating frequency compared to previous implementations of QHE detectors.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
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