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30 Jul 2012

Volume 101, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 051103 (2012); http://dx.doi.org/10.1063/1.4738774 (4 pages)

Alec Rose, Da Huang, and David R. Smith
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Orbital symmetry induced conductance switching in a graphene nanoribbon heterojunction with different edge hydrogenations

X. H. Zheng, J. Lan, X. L. Wang, L. F. Huang, H. Hao, and Z. Zeng

Appl. Phys. Lett. 101, 053101 (2012); http://dx.doi.org/10.1063/1.4739938 (4 pages) | Cited 2 times

Online Publication Date: 30 July 2012

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First principles calculations are performed to investigate the electron transport through a zigzag-edged graphene nanoribbon (ZGNR) heterojunction constructed by connecting a monohydrogenated ZGNR and a dihydrogenated ZGNR and its response to external magnetic fields. It is found that the heterojunction can be switched between a conducting state and an insulating state by tuning the magnetic fields. It arises from the matching or mismatching between the π or π* states of the two ribbons under different magnetic fields. This mechanism of conductance switching by tuning the orbital symmetry can be considered in the future design of graphene based electronic devices.
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72.60.+g Mixed conductivity and conductivity transitions
61.46.-w Structure of nanoscale materials
71.15.-m Methods of electronic structure calculations

Phononic dispersion of a two-dimensional chessboard-patterned bicomponent array on a substrate

V. L. Zhang, C. G. Hou, H. H. Pan, F. S. Ma, M. H. Kuok, H. S. Lim, S. C. Ng, M. G. Cottam, M. Jamali, and H. Yang

Appl. Phys. Lett. 101, 053102 (2012); http://dx.doi.org/10.1063/1.4739950 (4 pages) | Cited 1 time

Online Publication Date: 30 July 2012

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Brillouin measurements of the dispersion relations of surface acoustic- and optical-like waves along Γ-M and Γ-X symmetry directions in a two-dimensional bicomponent nanostructured crystal are reported. The sample, in the form of a periodic chessboard array of alternating Permalloy and cobalt square dots on a SiO2/Si substrate, was fabricated using high-resolution electron-beam lithographic, sputtering, etching, and lift-off techniques. The measured phononic band structures exhibit diverse features, such as a partial hybridization bandgap and unusual surface optical-like phonon branches, where there are out-of-phase vibrational characteristics between nearest-neighbor dots. Numerical simulations, based on the finite element analysis, reproduced the experimental dispersion relations.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
68.35.Ja Surface and interface dynamics and vibrations
78.35.+c Brillouin and Rayleigh scattering; other light scattering
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Diameter dependent optical emission properties of InAs nanowires grown on Si

G. Koblmüller, K. Vizbaras, S. Hertenberger, S. Bolte, D. Rudolph, J. Becker, M. Döblinger, M.-C. Amann, J. J. Finley, and G. Abstreiter

Appl. Phys. Lett. 101, 053103 (2012); http://dx.doi.org/10.1063/1.4739001 (5 pages) | Cited 2 times

Online Publication Date: 30 July 2012

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We report on the optical emission properties of catalyst-free, molecular beam epitaxy grown InAs nanowires (NW) on Si (111) using photoluminescence spectroscopy. InAs NW ensembles with similar density, length, and crystal structure (wurtzite-phase with stacking faults) but substantially different NW diameter (40–135 nm) are investigated, and the role of diameter on band-edge emission elucidated. Thick (>100 nm) as-grown NWs show relatively strong emission efficiency with emission up to >130 K, red-shift with temperature (T) and low-T band‐edge energy of ∼0.41 eV similar to bulk zincblende InAs. Reduction in NW diameter yields a characteristic blue‐shift (∼0.435 eV for 40-nm thin NWs), which is related to quantum confinement effects and confirmed by simulations.
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78.67.Lt Quantum wires
81.07.Vb Quantum wires
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)
81.07.Gf Nanowires
61.72.Nn Stacking faults and other planar or extended defects
78.55.Cr III-V semiconductors

Behavior of Au-Si droplets in Si(001) at high temperatures

Y. M. Shao, T. X. Nie, Z. M. Jiang, and J. Zou

Appl. Phys. Lett. 101, 053104 (2012); http://dx.doi.org/10.1063/1.4739413 (3 pages) | Cited 2 times

Online Publication Date: 30 July 2012

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The transport behavior of Au-Si droplets near the Si(001) surface at elevated temperatures is investigated using transmission electron microscopy. It has been found that Au-Si droplets move differently under different temperatures, which lead to the formation of SiOx surface islands on top of droplets, and result in the lateral movements of smaller droplets away from their corresponding surface islands. Since Au droplets have been widely used as catalysts to induce semiconductor nanowires, this study provides insight behavior of Au containing droplets on semiconductor surfaces, which is critical for understanding the formation mechanisms of semiconductor nanowires.
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68.35.bg Semiconductors
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Competing elastic and adhesive interactions govern deformation behaviors of aligned carbon nanotube arrays

Xiaodong Yang, Pengfei He, and Huajian Gao

Appl. Phys. Lett. 101, 053105 (2012); http://dx.doi.org/10.1063/1.4739414 (5 pages) | Cited 4 times

Online Publication Date: 30 July 2012

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Recent experiments have revealed diverse and sometimes conflicting deformation behaviors of vertically aligned carbon nanotube arrays under compression, but a thorough understanding of this phenomenon is still elusive. Here, we employ a mesoscale bead-spring model to demonstrate that the seemingly complex deformation behaviors of carbon nanotube arrays can be understood from competing elastic and adhesive interactions at the micro scale.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
62.20.F- Deformation and plasticity

Internal resonance based sensing in non-contact atomic force microscopy

E. Hacker and O. Gottlieb

Appl. Phys. Lett. 101, 053106 (2012); http://dx.doi.org/10.1063/1.4739416 (5 pages) | Cited 1 time

Online Publication Date: 30 July 2012

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In this letter, the nonlinear dynamics of a non-uniform micro-cantilever for atomic force microscopy is investigated numerically for a non-contact mode of operation. A step-like heterogeneity in the cantilever longitudinal direction yields conditions for both 3:1 and 2:1 internal resonances that govern quasiperiodic energy transfer between the first and second structural bending modes. Thus, quasiperiodic micro-cantilever response can enable multiple function sensing, and possible increased accuracy of time-varying forces via single frequency base excitation.
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07.79.Lh Atomic force microscopes
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Cm Micromechanical devices and systems

Photoinduced molecular desorption from graphene films

Pengzhan Sun, Miao Zhu, Kunlin Wang, Minlin Zhong, Jinquan Wei, Dehai Wu, Yao Cheng, and Hongwei Zhu

Appl. Phys. Lett. 101, 053107 (2012); http://dx.doi.org/10.1063/1.4742147 (4 pages) | Cited 1 time

Online Publication Date: 30 July 2012

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Photoinduced molecular desorption from solid surfaces will modify the electrical transporting properties of matter and result in significant change in resistance. The UV induced resistive response of graphene films prepared by chemical vapor deposition was investigated. The resistance of graphene increased exponentially upon UV irradiation and decreased also in an exponential form when the UV light was turned off. Both processes exhibited large time constants of hundreds of seconds. UV-induced molecular desorption mechanisms for graphene, carbon nanotubes, and reduced graphene oxides were compared and discussed.
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68.43.Tj Photon stimulated desorption
73.61.Wp Fullerenes and related materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.22.Pr Electronic structure of graphene
81.05.ue Graphene
68.43.Mn Adsorption kinetics

Realization of gigahertz-frequency impedance matching circuits for nano-scale devices

Gabriel Puebla-Hellmann and Andreas Wallraff

Appl. Phys. Lett. 101, 053108 (2012); http://dx.doi.org/10.1063/1.4739451 (4 pages) | Cited 2 times

Online Publication Date: 30 July 2012

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Integrating nano-scale objects, such as single molecules or carbon nanotubes, into impedance transformers and performing radio-frequency measurements allows for high time-resolution transport measurements with improved signal-to-noise ratios. The realization of such transformers implemented with superconducting transmission lines for the 2–10 GHz frequency range is presented here. Controlled electromigration of an integrated gold break junction is used to characterize a 6 GHz impedance matching device. The real part of the radio frequency impedance of the break junction extracted from microwave reflectometry at a maximum bandwidth of 45 MHz of the matching circuit is in good agreement with the measured direct current resistance.
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84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

Ultrathin organic bulk heterojunction solar cells: Plasmon enhanced performance using Au nanoparticles

Shiva Shahin, Palash Gangopadhyay, and Robert A. Norwood

Appl. Phys. Lett. 101, 053109 (2012); http://dx.doi.org/10.1063/1.4739519 (4 pages) | Cited 2 times

Online Publication Date: 30 July 2012

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The plasmonic effect of gold nanoparticles (AuNPs) enhances light absorption and, thus, the efficiency of organic bulk heterojunction solar cells with poly (3-hexylthiophene) (P3HT): [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as active layer. We report optimization of this enhancement by varying the attachment density of the self-assembled AuNPs on silanized ITO using N1-(3-trimethoxysilylpropyl)diethylenetriamine. Using finite difference time domain simulations, the thicknesses of poly (3,4-ethylenedioxythiophene) (PEDOT): poly (styrenesulfonate) (PSS) and P3HT:PCBM layers were suitably varied to ensure broadband optical absorption enhancement and minimal exciton quenching within the active layer. Our experimental results demonstrate that for solar cell structures with 20% surface coverage, absorption is increased by 65% as predicted by simulations. Further, we show that AuNPs increase the efficiency by 30% and that silanization of ITO positively impacts device performance.
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88.40.H- Solar cells (photovoltaics)

Microwave transmission properties of chemical vapor deposition graphene

Yunqiu Wu, Yuehang Xu, Zegao Wang, Cao Xu, Zongxi Tang, Yuanfu Chen, and Ruimin Xu

Appl. Phys. Lett. 101, 053110 (2012); http://dx.doi.org/10.1063/1.4737424 (3 pages)

Online Publication Date: 31 July 2012

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In this letter, the microwave transmission properties of graphene grown by the chemical vapor deposition are studied by using a multiple-layer coplanar-waveguide transmission-line based measurement method. Remarkable energy loss and phase shift have been observed in graphene from the measured scattering parameters through vector network analyzer. The effective permittivity is deduced by partial-capacitance technique, and the complex permittivity of graphene are extracted in the frequency range of 500 MHz to 6 GHz. Different from conventional dielectric material, the permittivity of graphene shows frequency-dependent below 4 GHz and has an magnitude larger than 104 for both real and imaginary parts.
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78.70.Gq Microwave and radio-frequency interactions
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.48.Gh Structure of graphene
77.22.Ch Permittivity (dielectric function)

Composite axial/core-shell nanopillar light-emitting diodes at 1.3 μm

A. C. Scofield, A. Lin, J. N. Shapiro, P. N. Senanayake, G. Mariani, M. Haddad, B. L. Liang, and D. L. Huffaker

Appl. Phys. Lett. 101, 053111 (2012); http://dx.doi.org/10.1063/1.4738997 (4 pages)

Online Publication Date: 31 July 2012

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Selective-area growth of III-V nanopillars (NPs) is used to demonstrate near-infrared emitters that employ a composite axial/core-shell heterostructure. The axial p-i-n heterostructure allows growth of strain relaxed InGaAs inserts emitting at 1.3 μm. Radial growth of an InGaP shell provides in-situ surface passivation to reduce non-radiative recombination and space-charge limited transport due to mid-gap surface states. The resulting light-emitting diode is comparable to bulk devices with an ideality factor of η = 1.67 and reverse bias leakage of 12 nA at −5 V. This device performance makes the combination of axial current injection with in-situ passivation a promising approach to NP based emitters.
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42.79.-e Optical elements, devices, and systems
81.65.Rv Passivation
85.60.Jb Light-emitting devices

Tilting of carbon encapsulated metallic nanocolumns in carbon-nickel nanocomposite films by ion beam assisted deposition

Matthias Krause, Arndt Mücklich, Thomas W. H. Oates, Matthias Zschornak, Sebastian Wintz, Jose Luis Endrino, Carsten Baehtz, Artem Shalimov, Sibylle Gemming, and Gintautas Abrasonis

Appl. Phys. Lett. 101, 053112 (2012); http://dx.doi.org/10.1063/1.4739417 (5 pages)

Online Publication Date: 31 July 2012

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The influence of assisting low-energy (∼50-100 eV) ion irradiation effects on the morphology of C:Ni (∼15 at. %) nanocomposite films during ion beam assisted deposition (IBAD) is investigated. It is shown that IBAD promotes the columnar growth of carbon encapsulated metallic nanoparticles. The momentum transfer from assisting ions results in tilting of the columns in relation to the growing film surface. Complex secondary structures are obtained, in which a significant part of the columns grows under local epitaxy via the junction of sequentially deposited thin film fractions. The influence of such anisotropic film morphology on the optical properties is highlighted.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.Jj Ion and electron beam-assisted deposition; ion plating
78.67.Sc Nanoaggregates; nanocomposites
61.46.-w Structure of nanoscale materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.82.Rx Nanocrystalline materials

Observation of room-temperature negative differential resistance in Gd-doped Si nanowires on Si(110) surface

Ie-Hong Hong, Tsung-Ming Chen, and Yung-Feng Tsai

Appl. Phys. Lett. 101, 053113 (2012); http://dx.doi.org/10.1063/1.4739947 (4 pages) | Cited 1 time

Online Publication Date: 1 August 2012

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The massively parallel arrays of highly periodic Gd-doped Si nanowires (SiNWs) self-organized on Si(110)-16 × 2 surface were investigated by scanning tunneling microscopy and spectroscopy. These periodic Gd-doped SiNWs are atomically precise and show equal size, periodic positions, and high-integration densities. Surprisingly, the scanning tunneling spectroscopy results show that each metallic-like, Gd-doped SiNW exhibits room-temperature negative differential resistance (RT-NDR) behavior, which can be reproducible with various Gd dopings and is independent of the tips. Such massively parallel arrays of highly ordered and atomically identical Gd-doped SiNWs with one-dimensional laterally confined RT-NDR can be exploited in Si-based RT-NDR nanodevices.
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73.63.Nm Quantum wires

Mechanical properties of the nanoscale molecular cluster of water meniscus by high-precision frequency modulation atomic force spectroscopy

Sangmin An, Jongwoo Kim, Kunyoung Lee, Bongsu Kim, Manhee Lee, and Wonho Jhe

Appl. Phys. Lett. 101, 053114 (2012); http://dx.doi.org/10.1063/1.4740083 (4 pages)

Online Publication Date: 1 August 2012

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The mechanical properties (viscoelasticity) of the nanoscale molecular cluster of water meniscus, spontaneously formed between a quartz tip ( ∼ 100 nm curvature) and a mica substrate were quantitatively studied. The theoretical and experimental investigation was performed on the basis of the quartz tuning fork-based frequency modulation-atomic force microscope system with a high vertical resolution ( ∼ 0.5 Å). The proposed system is suitable apparatus for the dynamic force spectroscopy of nanoscopic materials with several advantages including high sensitivity, short response time, immunity to the electrical noise, and simple and intuitive interpretation of the results using the frequency shift.
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62.10.+s Mechanical properties of liquids
68.47.Jn Clusters on oxide surfaces
62.25.Jk Mechanical modes of vibration
63.22.Kn Clusters and nanocrystals
61.25.Em Molecular liquids

Tuning thermal conductivity of bilayer graphene by inter-layer sp3 bonding: A molecular dynamics study

A. Rajabpour and S. M. Vaez Allaei

Appl. Phys. Lett. 101, 053115 (2012); http://dx.doi.org/10.1063/1.4740259 (4 pages) | Cited 1 time

Online Publication Date: 1 August 2012

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Using nonequilibrium molecular dynamics simulations, the effect of inter-layer sp3 bonding on the thermal conductivity of bilayer graphene were investigated. Up to 5% fractions of randomly distributed inter-layer sp3 bonds, lead to considerable decreases in the thermal conductivity of bilayer graphene, up to 70%. Phonon power spectrum calculations revealed the strong influence of sp3 inter-layer bonds—compared to weak effect of inter-layer Lennard-Jones interactions—on the thermal transport of the system. These measurements propose the application of the inter-layer sp3 bonding in designing nanoscale devices with tunable thermal conductivities.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
63.22.Rc Phonons in graphene
72.80.Vp Electronic transport in graphene
65.80.Ck Thermal properties of graphene
61.50.Lt Crystal binding; cohesive energy

Unaltered electrical conductance in single-walled carbon nanotubes functionalized with divalent adducts

Delphine Bouilly, Janie Cabana, and Richard Martel

Appl. Phys. Lett. 101, 053116 (2012); http://dx.doi.org/10.1063/1.4739495 (4 pages)

Online Publication Date: 1 August 2012

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Covalent functionalization offers promising avenues to manipulate and add new functions to carbon nanotubes. However, monovalent grafts are known to alter the nanotube electronic properties. Here, divalent functionalization using different carbene reactions is shown to preserve the electrical conductance of single-walled carbon nanotubes (SWNTs) for both metallic and semiconducting species. Devices functionalized with methylene or dichloromethylene groups show electrical characteristics identical to pristine SWNT devices, whereas monovalent 4-bromophenyl groups cause a current loss of more than an order of magnitude. Divalent functionalization can thus be used to derive functional SWNT-based electronic devices without compromising their electrical transport properties.
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85.35.Kt Nanotube devices
73.63.Fg Nanotubes
85.30.Tv Field effect devices

Application of well-defined indium tin oxide nanorods as Raman active platforms

Songqing Zhao, Yi Guo, Sheng Song, Daniel Choi, and Jong-in Hahm

Appl. Phys. Lett. 101, 053117 (2012); http://dx.doi.org/10.1063/1.4740273 (4 pages)

Online Publication Date: 2 August 2012

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We determine the surface enhanced Raman (SER) capability of indium tin oxide nanorods (ITO NRs) whose physical, chemical, and optical properties are precisely and uniformly controlled during synthesis. We demonstrate that the Raman intensities observed from varying concentrations of the pure and mixed molecules of rhodamine 6G and 4′,6-diamidino-2-phenylindole are much larger on ITO NRs relative to those measured on commercially available ITO-coated glass or Si. Our efforts signify the first attempt to assess the SER capability of precisely controlled metal oxide NRs and will be highly beneficial to many basic and applied Raman applications requiring exceptional detection sensitivity.
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78.30.Hv Other nonmetallic inorganics
81.07.Bc Nanocrystalline materials
78.67.Qa Nanorods

Gold nanorod-induced localized surface plasmon for microparticle aggregation

Ying Li, Linlin Xu, and Baojun Li

Appl. Phys. Lett. 101, 053118 (2012); http://dx.doi.org/10.1063/1.4742259 (3 pages)

Online Publication Date: 2 August 2012

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We investigate a technique for microparticle aggregation via optical fiber-excited localized surface plasmon resonance of gold nanorods, which were deposited on the designated surface of a tapered optical fiber (TOF). Through the enhanced photothermal effect, a microbubble forms on the TOF at an input optical power of 14 mW. Marangoni convection transports the microparticles dispersed in water to the bubble, where they accumulate on the gold nanorod surface because of strong optical gradient force.
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73.22.Lp Collective excitations
78.68.+m Optical properties of surfaces
81.16.-c Methods of micro- and nanofabrication and processing
78.67.Qa Nanorods
78.20.nb Photothermal effects
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
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Sub-ppt gas detection with pristine graphene

Gugang Chen, Tereza M. Paronyan, and Avetik R. Harutyunyan

Appl. Phys. Lett. 101, 053119 (2012); http://dx.doi.org/10.1063/1.4742327 (4 pages) | Cited 2 times

Online Publication Date: 2 August 2012

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Graphene is widely regarded as one of the most promising materials for sensor applications. Here, we demonstrate that a pristine graphene can detect gas molecules at extremely low concentrations with detection limits as low as 158 parts-per-quadrillion (ppq) for a range of gas molecules at room temperature. The unprecedented sensitivity was achieved by applying our recently developed concept of continuous in situ cleaning of the sensing material with ultraviolet light. The simplicity of the concept, together with graphene’s flexibility to be used on various platforms, is expected to intrigue more investigations to develop ever more sensitive sensors.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Exciton mediated self-organization in glass driven by ultrashort light pulses

Martynas Beresna, Mindaugas Gecevičius, Peter G. Kazansky, Thomas Taylor, and Alexey V. Kavokin

Appl. Phys. Lett. 101, 053120 (2012); http://dx.doi.org/10.1063/1.4742899 (4 pages) | Cited 2 times

Online Publication Date: 3 August 2012

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We propose an exciton-polariton-mediated self-organization effect in transparent SiO2 glass under intense femtosecond light irradiation. Interference and dipole-dipole interaction of polaritons causes formation of gratings of dielectric polarization. Due to an ultrafast exciton self-localization into a quasicrystal structure, the polariton gratings remain frozen in glass and a permanent three-dimensional image of exciton-polariton gas is created. We show that coherent effects in propagation of exciton-polaritons can serve as a tool for nanostructuring and fabrication of 5-dimensional optical memories in glass, opening new horizons for polaritronics.
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71.35.-y Excitons and related phenomena
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
77.22.Ej Polarization and depolarization
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.47.J- Ultrafast spectroscopy (<1 psec)
61.44.Br Quasicrystals

Rocking chair defect generation in nanowire growth

Shadi A. Dayeh, Xiao Hua Liu, Xing Dai, Jian Yu Huang, S. T. Picraux, and Cesare Soci

Appl. Phys. Lett. 101, 053121 (2012); http://dx.doi.org/10.1063/1.4739948 (3 pages)

Online Publication Date: 3 August 2012

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We report the observation of a different defect generation phenomenon in layer-by-layer crystal growth. Steps at a nanowire liquid-solid growth interface, resulting from edge nucleated defects, are found to cause a gradual multiplication of stacking faults in the regions bounded by two edge defects. In the presence of a twin boundary, these generated defects continue to propagate along the entire nanowire length. This rocking chair generation mechanism is a unique feature of nanoscale layer-by-layer growth and is significantly different from well-known defect multiplication mechanisms in bulk materials.
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81.07.Gf Nanowires
61.72.Mm Grain and twin boundaries
61.72.Nn Stacking faults and other planar or extended defects
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)

External electric field dependence of the structure of the electric double layer at an ionic liquid/Au interface

Ryosuke Yamamoto, Hazuki Morisaki, Osami Sakata, Hidekazu Shimotani, Hongtao Yuan, Yoshihiro Iwasa, Tsuyoshi Kimura, and Yusuke Wakabayashi

Appl. Phys. Lett. 101, 053122 (2012); http://dx.doi.org/10.1063/1.4742920 (4 pages)

Online Publication Date: 3 August 2012

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In order to clarify its electric double layer (EDL) structure under external voltage, an interface between the ionic liquid N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide and a Au (111) surface was studied by x-ray reflectometry. A clear change in reflectivity was observed as a function of applied voltage. The electron density profile of the ionic liquid around the interface was calculated using liquid structure models. Switching of the external electric field reversed the polarity of the EDL, and the magnitude of the applied voltage controlled the magnitude of the layering structure as well as molecular position fluctuation.
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68.08.-p Liquid-solid interfaces
82.45.-h Electrochemistry and electrophoresis

High-frequency performance of scaled carbon nanotube array field-effect transistors

Mathias Steiner, Michael Engel, Yu-Ming Lin, Yanqing Wu, Keith Jenkins, Damon B. Farmer, Jefford J. Humes, Nathan L. Yoder, Jung-Woo T. Seo, Alexander A. Green, Mark C. Hersam, Ralph Krupke, and Phaedon Avouris

Appl. Phys. Lett. 101, 053123 (2012); http://dx.doi.org/10.1063/1.4742325 (4 pages) | Cited 1 time

Online Publication Date: 3 August 2012

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We report the radio-frequency performance of carbon nanotube array transistors that have been realized through the aligned assembly of highly separated, semiconducting carbon nanotubes on a fully scalable device platform. At a gate length of 100 nm, we observe output current saturation and obtain as-measured, extrinsic current gain and power gain cut-off frequencies, respectively, of 7 GHz and 15 GHz. While the extrinsic current gain is comparable to the state-of-the-art, the extrinsic power gain is improved. The de-embedded, intrinsic current gain and power gain cut-off frequencies of 153 GHz and 30 GHz are the highest values experimentally achieved to date. We analyze the consistency of DC and AC performance parameters and discuss the requirements for future applications of carbon nanotube array transistors in high-frequency electronics.
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85.30.Tv Field effect devices
85.35.Kt Nanotube devices
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