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30 Jan 2012

Volume 100, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 053101 (2012); http://dx.doi.org/10.1063/1.3679127 (3 pages)

Shinya Kano, Yasuyuki Yamada, Kentaro Tanaka, and Yutaka Majima
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Correlation between superconductivity and structural properties under high pressure of iron pnictide superconductor Ce0.6Y0.4FeAsO0.8F0.2

M. Kanagaraj, S. Arumugam, Ravhi S. Kumar, N. R. Tamil Selvan, S. Esakki Muthu, J. Prakash, Gohil S. Thakur, H. Yoshino, K. Murata, K. Matsubayashi, Y. Uwatoko, S. Sinogeikin, Andrew Cornelius, A. K. Ganguli, and Yusheng Zhao

Appl. Phys. Lett. 100, 052601 (2012); http://dx.doi.org/10.1063/1.3681805 (4 pages)

Online Publication Date: 1 February 2012

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We report here the pressure dependence of the electrical resistivity and magnetic susceptibility of polycrystalline Ce0.6Y0.4FeAsO0.8F0.2 superconductor in the temperature range 4 K to 300 K up to 8 GPa. In-situ high pressure-low temperature x-ray diffraction was performed at 8 K up to 32 GPa using synchrotron x-rays with helium pressure medium. The results show that the applied pressure slightly increases the Tc up to 1 GPa and then it decreases on further pressure increase. The reduction of superconducting transition temperature occurs with a transition to a collapsed tetragonal phase and may be associated with a possible valence change of Ce.
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74.62.Fj Effects of pressure
75.30.Cr Saturation moments and magnetic susceptibilities

Long range supercurrents in ferromagnetic CrO2 using a multilayer contact structure

M. S. Anwar, M. Veldhorst, A. Brinkman, and J. Aarts

Appl. Phys. Lett. 100, 052602 (2012); http://dx.doi.org/10.1063/1.3681138 (3 pages) | Cited 6 times

Online Publication Date: 2 February 2012

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We report measurements of long ranged supercurrents through ferromagnetic and fully spin-polarized CrO2 deposited on TiO2 substrates. In earlier work, we found supercurrents in films grown on sapphire but not on TiO2. Here, we employed a special contact arrangement, consisting of a Ni/Cu sandwich between the film and the superconducting amorphous Mo70Ge30 electrodes. The distance between the contacts was almost a micrometer, and we find the critical current density to be significantly higher than found in the films deposited on sapphire. We argue this is due to spin mixing in the Ni/Cu/CrO2 layer structure, which is helpful in the generation of the odd-frequency spin triplet correlations needed to carry the supercurrent.
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74.25.Sv Critical currents
74.50.+r Tunneling phenomena; Josephson effects
74.78.Fk Multilayers, superlattices, heterostructures
74.55.+v Tunneling phenomena: single particle tunneling and STM
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Piezoelectric single crystal langatate and ferromagnetic composites: Studies on low-frequency and resonance magnetoelectric effects

G. Sreenivasulu, L. Y. Fetisov, Y. K. Fetisov, and G. Srinivasan

Appl. Phys. Lett. 100, 052901 (2012); http://dx.doi.org/10.1063/1.3679661 (4 pages) | Cited 7 times

Online Publication Date: 30 January 2012

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Mechanical strain mediated magnetoelectric (ME) effects are studied in bilayers and trilayers of piezoelectric single-crystal lanthanum gallium tantalate (LGT) and magnetostrictive permendur (P). The ME voltage coefficient ranges from 2.3 V/cm Oe at 20 Hz to 720 V/cm Oe at bending resonance and is higher by an order of magnitude than in composites with ferroelectric lead zirconate titanate or lead magnesium niobate-lead titanate. The low-frequency magnetic noise for P-LGT-P is a factor of 2-10 smaller than for ferroelectrics based composites. Langatate is free of ferroelectric hysteresis, pyroelectric effects, and phase transitions up to 1450 °C and is of interest for ultrasensitive, high temperature magnetic sensors.
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75.85.+t Magnetoelectric effects, multiferroics
75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.80.+q Magnetomechanical effects, magnetostriction
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
77.65.Fs Electromechanical resonance; quartz resonators

Magnetodielectric effects of Y3Fe5−xTixO12+x/2 ceramics

Y. J. Wu, C. Yu, X. M. Chen, and J. Li

Appl. Phys. Lett. 100, 052902 (2012); http://dx.doi.org/10.1063/1.3680090 (4 pages) | Cited 3 times

Online Publication Date: 30 January 2012

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Dielectric, magnetic, and magnetodielectric properties of Y3Fe5−xTixO12+x/2 (x = 0, 0.1, 0.2) ceramics were investigated. Ti substitution induces a low temperature dielectric relaxation which comes from the charge carrier hopping between Ti3+ and Ti4+. The Maxwell-Wagner effect related dielectric relaxation becomes weak as the content of Ti increases. The extrinsic effect and intrinsic effect play a dominant role on the magnetodielectric effects for x = 0 at f < 500 kHz and f ≥ 500 kHz, respectively. The contribution of the extrinsic effects to magnetodielectric (MD) effect decreases and the contribution of the intrinsic effects to MD effect increases with increasing Ti amount.
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77.22.Gm Dielectric loss and relaxation
75.85.+t Magnetoelectric effects, multiferroics
77.84.Cg PZT ceramics and other titanates
72.20.Ee Mobility edges; hopping transport

From mesoscopic to global polar order in the uniaxial relaxor ferroelectric Sr0.8Ba0.2Nb2O6

J. Dec, W. Kleemann, V. V. Shvartsman, D. C. Lupascu, and T. Łukasiewicz

Appl. Phys. Lett. 100, 052903 (2012); http://dx.doi.org/10.1063/1.3680599 (4 pages) | Cited 1 time

Online Publication Date: 31 January 2012

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In the relaxor ferroelectric Sr0.8Ba0.2Nb2O6 (SBN80) the relaxation of polar nanoregions (PNRs) reveals an anisotropic breathing mode when approaching the transition temperature, TC ≈ 289 K, on cooling. Two distinct dispersion steps and peaks, respectively, of the complex susceptibility components in the milli- and megahertz frequency range reflect their large length-to-width aspect ratio. Below TC power-law frequency dispersion characterizes the creep motion of the emerging ferroelectric domain walls and the fractal dimension D ≈ 2 of their contour lines. Piezoforce micrographs reveal nanometric jagged domains in accordance with the large disorder and random field magnitude in the extreme relaxor SBN80.
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77.80.Dj Domain structure; hysteresis
81.40.Lm Deformation, plasticity, and creep
82.70.-y Disperse systems; complex fluids
61.46.-w Structure of nanoscale materials
62.20.Hg Creep

Pressure-induced changes in the dielectric response of polymer relaxors

B. Hilczer, M. Szafrański, and A. Hilczer

Appl. Phys. Lett. 100, 052904 (2012); http://dx.doi.org/10.1063/1.3681372 (4 pages)

Online Publication Date: 2 February 2012

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The effect of hydrostatic pressure on the dielectric response of P(VDF/TrFE)(50/50) irradiated with fast electrons has been studied. A non-linear upward shift of the glass transition temperature Tg and the Curie temperature TC of the polymer relaxors was observed under pressure with the initial slope dTg/dp being considerably smaller than dTC/dp. Moreover, pressure was found to reduce the contribution to the low-frequency dielectric absorption originating from segmental motions in the amorphous phase whereas the contribution related to ferroelectric-paraelectric transition and that of polar nanoclusters in the crystalline phase were found to be enhanced.
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77.80.Jk Relaxor ferroelectrics
61.80.Fe Electron and positron radiation effects
72.80.Le Polymers; organic compounds (including organic semiconductors)
77.84.Jd Polymers; organic compounds
82.35.-x Polymers: properties; reactions; polymerization
64.70.pj Polymers
77.80.B- Phase transitions and Curie point
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Room-temperature single molecular memory

Shinya Kano, Yasuyuki Yamada, Kentaro Tanaka, and Yutaka Majima

Appl. Phys. Lett. 100, 053101 (2012); http://dx.doi.org/10.1063/1.3679127 (3 pages) | Cited 3 times

Online Publication Date: 30 January 2012

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Single molecular memory operation was observed on a porphyrin derivative by scanning tunneling microscopy at room temperature. A porphyrin derivative with four disulfide groups was chemically synthesized and chemisorbed on a Au(111) surface. Coulomb blockade behaviors and switching behaviors in current-voltage (I-V) characteristics were observed on a single porphyrin derivative by scanning tunneling spectroscopy. Based on the switching behaviors, the memory operation of electrical conductance in the porphyrin derivative was demonstrated by applying a programmed pulse sequence with an on/off ratio of 2.9 at room temperature.
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85.65.+h Molecular electronic devices
84.30.Sk Pulse and digital circuits
85.35.Ds Quantum interference devices
85.35.Gv Single electron devices

High‐temperature annealing of thin Au films on Si: Growth of SiO2 nanowires or Au dendritic nanostructures?

F. Ruffino, L. Romano, G. Pitruzzello, and M. G. Grimaldi

Appl. Phys. Lett. 100, 053102 (2012); http://dx.doi.org/10.1063/1.3679614 (5 pages) | Cited 3 times

Online Publication Date: 30 January 2012

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A simple and low‐cost approach for the large‐scale production of Au nanodendritic structures on Si is presented. Starting from the methodology involving deposition of a Au film on Si and heating the system to high temperatures in an inert ambient containing trace amounts of oxygen for the growth of SiO2 nanowires (NWs), we show that a suppression of the NWs growth and a promotion of the growth of Au nanodendrites occur when fast heating and cooling rates are used. We analyze the nanodendrites formation process considering the kinetics processes at the Au/Si interface in far from thermodynamic equilibrium situation.
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81.16.Rf Micro- and nanoscale pattern formation
81.40.Gh Other heat and thermomechanical treatments
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
68.35.Ct Interface structure and roughness
68.55.-a Thin film structure and morphology

Mechanisms of nanorod growth on focused-ion-beam-irradiated semiconductor surfaces: Role of redeposition

J. H. Wu and R. S. Goldman

Appl. Phys. Lett. 100, 053103 (2012); http://dx.doi.org/10.1063/1.3675641 (4 pages) | Cited 2 times

Online Publication Date: 30 January 2012

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We have examined the formation and evolution of irradiation-induced nanorod (NR) growth through a comparison of focused-ion-beam irradiation of InSb wafers and InSb/GaAs heterostructures. Above a critical ion dose, cone-shaped NRs capped with In islands form on both InSb surfaces. For InSb wafers, the NR base diameter increases with ion energy. In the case of InSb/GaAs heterostructures, as the milled depth approaches the InSb/GaAs interface, the cone-shaped NRs transition to capless NRs with a truncated cone shape. These results suggest a growth mechanism in which both the NR cap and body are supplied by redeposition of atoms sputtered from InSb.
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81.16.Mk Laser-assisted deposition
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)
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
81.05.Ea III-V semiconductors
81.07.Bc Nanocrystalline materials

Pulsed contact resonance for atomic force microscopy nanomechanical measurements

Jason P. Killgore and Donna C. Hurley

Appl. Phys. Lett. 100, 053104 (2012); http://dx.doi.org/10.1063/1.3680212 (4 pages) | Cited 2 times

Online Publication Date: 30 January 2012

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We demonstrate an improved technique for nanomechanical imaging in atomic force microscopy. By merging the sensitivity to contact stiffness inherent to contact resonance (CR) spectroscopy with the delicate nature and potential for adhesion data of pulsed-force mode, we address major shortcomings of both techniques. Fast CR data are recorded during each pulsed cycle by driving the sample at two frequencies near the CR frequency and modeling the contact as a harmonic oscillator. The technique provides nanomechanical parameters including frequency, quality factor, and adhesion force. Compared to continuous contact, the technique should reduce damage and support more complex analysis models.
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07.79.Lh Atomic force microscopes
07.10.Cm Micromechanical devices and systems

Transition-metal doping of small cadmium selenide clusters

Tejinder Singh, T. J. Mountziaris, and Dimitrios Maroudas

Appl. Phys. Lett. 100, 053105 (2012); http://dx.doi.org/10.1063/1.3680254 (3 pages) | Cited 2 times

Online Publication Date: 30 January 2012

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Using first-principles density functional theory calculations, we investigate the mechanism of Mn doping of colloidal CdSe nanocrystals. We find that Mn dopants have high binding energies for adsorption onto the sites of small CdSe clusters (with diameters d < 2 nm) as compared to those for adsorption onto the most stable surface facets of larger CdSe nanocrystals (d ≥ 5 nm) with wurtzite lattice structure. These high binding energies, in conjunction with the characteristics of Mn surface segregation on CdSe nanocrystal surface facets, explain experimental reports of high doping efficiency for small-size CdSe clusters.
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61.72.up Other materials
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.63.Bd Nanocrystalline materials
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.43.Mn Adsorption kinetics
68.35.Dv Composition, segregation; defects and impurities

Spoof-like plasmonic behavior of plasma enhanced atomic layer deposition grown Ag thin films

S. M. Prokes, O. J. Glembocki, Erin Cleveland, Josh D. Caldwell, Edward Foos, Jaakko Niinistö, and Mikko Ritala

Appl. Phys. Lett. 100, 053106 (2012); http://dx.doi.org/10.1063/1.3679106 (3 pages)

Online Publication Date: 30 January 2012

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The plasmonic behavior of Ag thin films produced by plasma enhanced atomic layer deposition (PEALD) has been investigated. We show that as-deposited flat PEALD Ag films exhibit unexpected plasmonic properties, and the plasmonic enhancement can differ markedly, depending on the microstructure of the Ag film. Electromagnetic field simulations indicate that this plasmonic behavior is due to air gaps that are an inherent property of the mosaic-like microstructure of the PEALD-grown Ag film, suggesting that this is a metamaterial with behavior very similar to what would be expected in spoof plasmonics where gaps are fabricated in films to create plasmonic-like resonances.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
81.05.Bx Metals, semimetals, and alloys
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
52.77.Dq Plasma-based ion implantation and deposition

Position-controlled [100] InP nanowire arrays

Jia Wang, Sébastien Plissard, Moïra Hocevar, Thuy T. T. Vu, Tilman Zehender, George G. W. Immink, Marcel A. Verheijen, Jos Haverkort, and Erik P. A. M. Bakkers

Appl. Phys. Lett. 100, 053107 (2012); http://dx.doi.org/10.1063/1.3679136 (3 pages) | Cited 1 time

Online Publication Date: 30 January 2012

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We investigate the growth of vertically standing [100] zincblende InP nanowire (NW) arrays on InP (100) substrates in the vapor-liquid-solid growth mode using low-pressure metal-organic vapor-phase epitaxy. Precise positioning of these NWs is demonstrated by electron beam lithography. The vertical NW yield can be controlled by different parameters. A maximum yield of 56% is obtained and the tapering caused by lateral growth can be prevented by in situ HCl etching. Scanning electron microscopy, high-resolution transmission electron microscopy, and micro-photoluminescence have been used to investigate the NW properties.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.16.-c Methods of micro- and nanofabrication and processing
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)
78.67.Uh Nanowires
78.55.Cr III-V semiconductors

Growth and photoluminescence of self-catalyzed GaP/GaNP core/shell nanowires on Si(111) by gas source molecular beam epitaxy

Y. J. Kuang (邝彦瑾), S. Sukrittanon, H. Li (李华), and C. W. Tu

Appl. Phys. Lett. 100, 053108 (2012); http://dx.doi.org/10.1063/1.3681172 (3 pages) | Cited 4 times

Online Publication Date: 30 January 2012

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We report a study on self-catalyzed GaP/GaNP core/shell nanowires (NWs) grown on Si(111) by gas-source molecular beam epitaxy. Scanning electron microscopy images show that vertical and uniform GaP NWs and GaP/GaNP core/shell NWs are grown on Si(111). The density ranges from ∼1 × 107 to ∼5 × 108 cm−2 across the substrate. Typical diameters are ∼110 nm for GaP NWs and ∼220 nm for GaP/GaNP NWs. Room temperature photoluminescence (PL) signal from the GaP/GaNP core/shell NWs confirms that N is incorporated in the shell and the average N content is ∼0.9%. The PL low-energy tail is significantly reduced, compared to bulk GaNP.
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81.07.Gf Nanowires
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.67.Uh Nanowires

Tapping-mode force spectroscopy using cantilevers with interferometric high-bandwidth force sensors

A. Fatih Sarioglu, Sergei Magonov, and Olav Solgaard

Appl. Phys. Lett. 100, 053109 (2012); http://dx.doi.org/10.1063/1.3679683 (4 pages) | Cited 4 times

Online Publication Date: 31 January 2012

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We quantitatively map the surface forces and elastic modulus in tapping-mode atomic force microscopy (AFM). To achieve this, we use custom-built cantilevers with interferometric high-bandwidth force sensors that can resolve nonlinear tip-sample interaction forces, combined with a set of algorithms to process the force sensor signals in real-time. Our technique achieves quantitative mechanical measurements, while retaining nanoscale spatial resolution and minimal loading forces in tapping-mode AFM. Moreover, conventional tapping-mode AFM images are not affected and can simultaneously be acquired. As a practical demonstration, we use our technique to quantify the mechanical properties of a polystyrene and linear low-density polyethylene blend.
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07.79.Lh Atomic force microscopes
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli

Self-driving capacitive cantilevers for high-frequency atomic force microscopy

Keith A. Brown, Benjamin H. Yang, and R. M. Westervelt

Appl. Phys. Lett. 100, 053110 (2012); http://dx.doi.org/10.1063/1.3679684 (4 pages) | Cited 3 times

Online Publication Date: 31 January 2012

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We demonstrate a simple way to actuate an atomic force microscope cantilever at high frequencies by electrically driving a thin-film capacitor on its surface. Capacitive driving directly actuates the vibrational mode of the cantilever, removing the effects of unwanted mechanical modes present in conventional driving systems and removing the need for a drive piezoelectric. Practical vibration amplitudes are attainable at drive voltages <5 V. We capacitively drive the first mechanical resonance of a tapping mode cantilever (243 kHz) and a high-frequency cantilever (1.5 MHz) with vibration amplitudes in agreement with our model of capacitive driving.
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07.79.Lh Atomic force microscopes
84.32.Tt Capacitors
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Structural phase transition of graphene caused by GaN epitaxy

Y. Gohda and S. Tsuneyuki

Appl. Phys. Lett. 100, 053111 (2012); http://dx.doi.org/10.1063/1.3680100 (4 pages) | Cited 1 time

Online Publication Date: 31 January 2012

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We report first-principles predictions, where the structure of graphene changes drastically with the epitaxial growth of GaN (which has been performed experimentally). We identify GaN-math×math/graphene-2 × 2 superstructure as the most probable interface atomic structure, where three C-C bonds are replaced with C-N-C bonds preserving the Dirac cones. As the GaN epitaxy proceeds expanding graphene gradually, the tensile strain for graphene is released suddenly by partial breaking of the C-bond network, attributable to the two-dimensionality of graphene. In contrast, graphene retains its honeycomb structure at the AlN-graphene interface. Both of GaN- and AlN-graphene interfaces exhibit spin polarization.
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.kg Semiconductors
68.35.Ct Interface structure and roughness
68.47.Fg Semiconductor surfaces

Temperature and humidity effects on superhydrophobicity of nanocomposite coatings

Yong Han Yeong, Adam Steele, Eric Loth, Ilker Bayer, Guillaume De Combarieu, and Charles Lakeman

Appl. Phys. Lett. 100, 053112 (2012); http://dx.doi.org/10.1063/1.3680567 (4 pages) | Cited 1 time

Online Publication Date: 31 January 2012

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This work investigates temperature and humidity effects on the superhydrophobicity of polyurethane/organoclay nanocomposites. Previous reports of superhydrophobic degradation at decreasing surface temperatures for both low and high humidity were generally conducted in open environments. However, the present setup allows a thermally homogeneous environment, i.e., the temperature of the nanocomposite, air and water droplet are equal with no spatial temperature gradients. In such conditions, results showed stable retention of superhydrophobicity for both low humidity (RH < 20%) cool-down and warm-up cycles (20 °C to −3 °C to 20 °C). Similar performance was also observed for a high humidity (RH > 80%) cool-down cycle, though superhydrophobicity degraded during the warm-up cycle, which was attributed to dew condensation.
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68.08.Bc Wetting

Ultrathin crystalline-silicon solar cells with embedded photonic crystals

Shrestha Basu Mallick, Mukul Agrawal, Artit Wangperawong, Edward S. Barnard, Kaushal K. Singh, Robert J. Visser, Mark L. Brongersma, and Peter Peumans

Appl. Phys. Lett. 100, 053113 (2012); http://dx.doi.org/10.1063/1.3680602 (3 pages) | Cited 5 times

Online Publication Date: 31 January 2012

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Photonic crystals (PCs) can be used to trap light in thin-film solar cells to increase optical absorption. We fabricated ultrathin c-Si solar cells whose active layer was patterned into a two-dimensional PC with a square lattice of 450 nm diameter holes spaced at a period of 750 nm. The PC couples incident light into quasiguided modes and can be engineered to increase coupling and thus optimize optical absorption. Both short-circuit current and external quantum efficiency measurements show an enhancement in optical absorption, especially at longer wavelengths. Scanning photocurrent maps confirm the improved optical absorption in the PC regions.
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88.40.H- Solar cells (photovoltaics)
42.70.Qs Photonic bandgap materials

Mapping the electronic properties of individual graphene grain boundaries

Levente Tapasztó, Péter Nemes-Incze, Gergely Dobrik, Kwon Jae Yoo, Chanyong Hwang, and László P Biró

Appl. Phys. Lett. 100, 053114 (2012); http://dx.doi.org/10.1063/1.3681375 (4 pages) | Cited 7 times

Online Publication Date: 1 February 2012

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Grain boundaries, the characteristic topological defects of chemical vapor deposition grown graphene samples, are expected to substantially alter the electronic properties of the unperturbed graphene lattice. However, there is very little experimental insight into the underlying mechanisms. Here, we systematically map the electronic properties of individual graphene grain boundaries by scanning tunneling microscopy and spatially resolved tunneling spectroscopy measurements. The tunneling spectroscopy data reveal that the conductivity inside the boundaries is markedly suppressed for both electron and hole-type charge carriers. Furthermore, graphene grain boundaries can give rise to n-type inversion channels within the p-doped graphene sheets, forming p-n junctions with sharp interfaces on the nanometer scale. These properties persist for grain boundaries of various configurations and are robust against structural disorder.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.16.-c Methods of micro- and nanofabrication and processing
61.48.Gh Structure of graphene
73.22.Pr Electronic structure of graphene
61.72.Mm Grain and twin boundaries
72.20.Fr Low-field transport and mobility; piezoresistance

Plasma enables edge-to-center-oriented graphene nanoarrays on Si nanograss

S. Kumar, I. Levchenko, Q. J. Cheng, J. Shieh, and K. Ostrikov

Appl. Phys. Lett. 100, 053115 (2012); http://dx.doi.org/10.1063/1.3681782 (4 pages) | Cited 1 time

Online Publication Date: 1 February 2012

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The formation of clearly separated vertical graphene nanosheets on silicon nanograss support is demonstrated. The plasma-enabled, two-stage mask-free process produced self-organized vertical graphenes of a few carbon layers (as confirmed by advanced microanalysis), prominently oriented in the substrate center–substrate edge direction. It is shown that the width of the alignment zone depends on the substrate conductivity, and thus the electric field in the vicinity of the growth surface is responsible for the graphene alignment. This finding is confirmed by the Monte Carlo simulations of the ion flux distribution in the silicon nanograss pattern.
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52.77.-j Plasma applications
73.25.+i Surface conductivity and carrier phenomena
72.80.Vp Electronic transport in graphene
81.05.ue Graphene

Angular distribution of field emitted electrons from vertically aligned carbon nanotube arrays

S. Iacobucci, M. Fratini, A. Rizzo, F. Scarinci, Y. Zhang, M. Mann, C. Li, W. I. Milne, M. M. El Gomati, S. Lagomarsino, and G. Stefani

Appl. Phys. Lett. 100, 053116 (2012); http://dx.doi.org/10.1063/1.3681398 (3 pages) | Cited 2 times

Online Publication Date: 2 February 2012

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Angular field emission (FE) properties of vertically aligned carbon nanotube arrays have been measured on samples grown by plasma enhanced chemical vapor deposition and characterized by scanning electron microscope and I-V measurements. These properties determine the angular divergence of electron beams, a crucial parameter in order to obtain high brilliance FE based cathodes. From angular distributions of the electron beam transmitted through extraction grids of different mesh size and by using ray-tracing simulations, the maximum emission angle from carbon nanotube tips has been determined to be about ± 30° around the tube main axis.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.07.De Nanotubes
73.63.Fg Nanotubes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Picosecond transient photoluminescence in high-density Si-nanodisk arrays fabricated using bio-nano-templates

Takayuki Kiba, Yoshiya Mizushima, Makoto Igarashi, Chi-Hsien Huang, Seiji Samukawa, and Akihiro Murayama

Appl. Phys. Lett. 100, 053117 (2012); http://dx.doi.org/10.1063/1.3681793 (4 pages) | Cited 3 times

Online Publication Date: 2 February 2012

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We study picosecond transient photoluminescence (PL) in Si-nanodisk (Si-ND) arrays fabricated using bio-nano-templates. The PL time profiles show multi-exponential decaying kinetics depending on the disk density. We attribute the fastest decaying component with a decay time of 40 ps observed only in the high-density Si-ND array to the electron transfer among the Si-NDs.
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78.47.jd Time resolved luminescence
78.47.J- Ultrafast spectroscopy (<1 psec)
61.46.-w Structure of nanoscale materials
78.55.Ap Elemental semiconductors
81.05.Cy Elemental semiconductors
81.16.-c Methods of micro- and nanofabrication and processing

Investigation of proximity effects in electron microscopy and lithography

M.-M. Walz, F. Vollnhals, F. Rietzler, M. Schirmer, H.-P. Steinrück, and H. Marbach

Appl. Phys. Lett. 100, 053118 (2012); http://dx.doi.org/10.1063/1.3681593 (4 pages) | Cited 2 times

Online Publication Date: 3 February 2012

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A fundamental challenge in lithographic and microscopic techniques employing focused electron beams are so-called proximity effects due to unintended electron emission and scattering in the sample. Herein, we apply a method that allows for visualizing electron induced surface modifications on a SiN substrate covered with a thin native oxide layer by means of iron deposits. Conventional wisdom holds that by using thin membranes proximity effects can be effectively reduced. We demonstrate that, contrary to the expectation, these can be indeed larger on a 200 nm SiN-membrane than on the respective bulk substrate due to charging effects.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Light-driven tunable dual-band plasmonic absorber using liquid-crystal-coated asymmetric nanodisk array

Yanhui Zhao, Qingzhen Hao, Yi Ma, Mengqian Lu, Bingxin Zhang, Michael Lapsley, Iam-Choon Khoo, and Tony Jun Huang

Appl. Phys. Lett. 100, 053119 (2012); http://dx.doi.org/10.1063/1.3681808 (4 pages) | Cited 3 times

Online Publication Date: 3 February 2012

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We experimentally demonstrated a light-driven reconfigurable near perfect plasmonic absorber working at dual frequencies in infrared range. By employing nanodisks with different sizes in certain arrangement, near perfect absorption of incident electromagnetic waves can be achieved for different working frequencies due to the resonance between the incident light and the nanodisk of different sizes. We showed that optically induced changes in the dielectric constant of the adjacent liquid crystal layer is an effective means to tune the absorption bands of an asymmetric gold nanodisk array. Our liquid crystal based infrared plasmonic absorber can be tuned by using visible light in real time. A tunable range of 25 nm has been confirmed by both simulation and experiment.
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42.79.-e Optical elements, devices, and systems
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