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9 Jul 2012

Volume 101, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 023101 (2012); http://dx.doi.org/10.1063/1.4731792 (4 pages)

Feng Wang, Ayan Chakrabarty, Fred Minkowski, Kai Sun, and Qi-Huo Wei
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Polarization conversion with elliptical patch nanoantennas

Feng Wang, Ayan Chakrabarty, Fred Minkowski, Kai Sun, and Qi-Huo Wei

Appl. Phys. Lett. 101, 023101 (2012); http://dx.doi.org/10.1063/1.4731792 (4 pages) | Cited 8 times

Online Publication Date: 9 July 2012

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In this paper, we demonstrate arrays of optical patch nanoantennas can convert light polarization through reflection. By breaking the azimuthal symmetry, elliptical plasmonic patch nanoantennas exhibit both even and odd cavity modes, which can be expressed by Mathieu functions. It is shown that by properly orienting the incident polarization, a linearly polarized light in resonance with one cavity mode can be converted into an elliptical or circular polarization after reflection. Since the major cavity modes can be excited at all incident angles, the polarization conversion by these elliptical patch nanoantennas can be realized with wide range of incident angles.
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84.40.Ba Antennas: theory, components and accessories

Towards spin injection from silicon into topological insulators: Schottky barrier between Si and Bi2Se3

C. Ojeda-Aristizabal, M. S. Fuhrer, N. P. Butch, J. Paglione, and I. Appelbaum

Appl. Phys. Lett. 101, 023102 (2012); http://dx.doi.org/10.1063/1.4733388 (4 pages) | Cited 2 times

Online Publication Date: 9 July 2012

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A scheme is proposed to electrically measure the spin-momentum coupling in the topological insulator surface state by injection of spin polarized electrons from silicon. As an initial approach, devices were fabricated consisting of thin (<100 nm) exfoliated crystals of Bi2Se3 on n-type silicon with independent electrical contacts to silicon and Bi2Se3. Analysis of the temperature dependence of thermionic emission in reverse bias indicates a barrier height of 0.34 eV at the Si-Bi2Se3 interface. This robust Schottky barrier opens the possibility of original device designs based on sub-band gap internal photoemission from Bi2Se3 into Si.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
79.40.+z Thermionic emission
79.60.-i Photoemission and photoelectron spectra
72.25.-b Spin polarized transport

Photoinduced conductance switching in a dye-doped gold nanoparticle transistor

Makoto Yamamoto, Toshifumi Terui, Rieko Ueda, Keisuke Imazu, Kaoru Tamada, Takeshi Sakano, Kenji Matsuda, Hisao Ishii, and Yutaka Noguchi

Appl. Phys. Lett. 101, 023103 (2012); http://dx.doi.org/10.1063/1.4733612 (4 pages)

Online Publication Date: 9 July 2012

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Photoinduced conductance switching was demonstrated in a copper phthalocyanine (CuPc)-doped gold nanoparticle (GNP) transistor formed in a nanogap electrode with a back gate structure. Two specific states were reversibly induced in conductance of the CuPc-doped devices by light irradiation and applied voltages. The probability of occurrence of conductance switching decreased with a reduction in the number of incident photons. In addition, conductance switching was not observed in the devices before CuPc doping. Conductance switching originates from change in the local potential of GNPs, possibly induced by a charge-state bistability of an individual CuPc molecule worked as a floating gate.
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85.35.Gv Single electron devices

Altering regularities of electronic transport properties in twisted graphene nanoribbons

G. P. Tang, J. C. Zhou, Z. H. Zhang, X. Q. Deng, and Z. Q. Fan

Appl. Phys. Lett. 101, 023104 (2012); http://dx.doi.org/10.1063/1.4733618 (5 pages) | Cited 1 time

Online Publication Date: 9 July 2012

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Based on density-function theory combined with nonequilibrium Green’s function method, the electronic transport properties of twisted armchair- and zigzag-edge graphene nanoribbons (AGNRs and ZGNRs) are investigated. Results show that electronic transport properties are sensitive to twisting deformations for semiconductor-type AGNRs, but are robust against twisting deformations for quasi-metallic AGNRs and ZGNRs. The electronic conduction becomes weaker gradually for moderate-gap semiconductor-type AGNRs, but gets stronger for wide-gap semiconductor-type AGNRs when the twisted angle increases to 120°. While for quasi-metallic AGNRs and ZGNRs, the electronic conduction is strong and obeys Ohm’s law of resistance strictly. Mechanisms for such results are suggested.
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72.80.Vp Electronic transport in graphene

Confinement of vacancies during annealing of H implanted GaN sandwiched between two {InGaN/GaN} superlattices

N. Cherkashin, A. Claverie, D. Sotta, J.-M. Bethoux, L. Capello, and O. Kononchuk

Appl. Phys. Lett. 101, 023105 (2012); http://dx.doi.org/10.1063/1.4733619 (5 pages)

Online Publication Date: 9 July 2012

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Using transmission electron microscopy techniques, we identify the extended defects of interstitial and vacancy types found after H implantation and annealing in GaN. We statistically analyze the effect of boarding or sandwiching GaN between strained superlattices on these populations of defects. We finally demonstrate the possibility to use compressively strained layers to localize and favour the precipitation of vacancy type defects in GaN. The source of excess vacancies, the mechanism responsible for the cavity localization, and the drastic increase of their volume fraction are discussed.
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61.72.jd Vacancies
61.72.Cc Kinetics of defect formation and annealing
61.72.U- Doping and impurity implantation
81.30.Mh Solid-phase precipitation

Growth and photoluminescence of InxGa1−xAs quantum dots on the surface of GaAs nanowires by metal organic chemical vapor deposition

Xin Yan, Xia Zhang, Xiaomin Ren, Junshuai Li, Xiaolong Lv, Qi Wang, and Yongqing Huang

Appl. Phys. Lett. 101, 023106 (2012); http://dx.doi.org/10.1063/1.4734391 (4 pages) | Cited 1 time

Online Publication Date: 10 July 2012

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InxGa1−xAs (x = 0.6-1) quantum dots are grown on the {112} side facets of GaAs nanowires by metal organic chemical vapor deposition. The emission spectrum of quantum dots exhibits a multi-peak structure due to size and composition fluctuations. The emission wavelength of quantum dots ranges from 857 nm to 930 nm at 77 K, which is distinctly blueshifted relative to that on traditional GaAs (100) planar substrate. The emission linewidth of an ensemble of quantum dots increases from 29.5 meV to 40.5 meV with increasing the In content, indicating a broader composition distribution of quantum dots.
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81.07.Ta Quantum dots
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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)
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
81.05.Ea III-V semiconductors

Ternary eutectic growth of nanostructured thermoelectric Ag-Pb-Te materials

Hsin-jay Wu, Wei-jian Foo, Sinn-wen Chen, and G. Jeffrey Snyder

Appl. Phys. Lett. 101, 023107 (2012); http://dx.doi.org/10.1063/1.4733661 (4 pages) | Cited 1 time

Online Publication Date: 10 July 2012

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Nanostructured Ag-Pb-Te thermoelectric materials were fabricated by unidirectionally solidifying the ternary Ag-Pb-Te eutectic and near-eutectic alloys using the Bridgeman method. Specially, the Bridgman-grown eutectic alloy exhibited a partially aligned lamellar microstructure, which consisted of Ag5Te3 and Te phases, with additional 200-600 nm size particles of PbTe. The self-assembled interfaces altered the thermal and electronic transport properties in the bulk Ag-Pb-Te eutectic alloy. Presumably due to phonon scattering from the nanoscale microstructure, a low thermal conductivity (κ = 0.3 W/mK) was achieved of the eutectic alloy, leading to a zT peak of 0.41 at 400 K.
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81.16.Dn Self-assembly
81.30.Fb Solidification
72.15.Jf Thermoelectric and thermomagnetic effects
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
63.22.Kn Clusters and nanocrystals
81.05.Bx Metals, semimetals, and alloys

Thickness dependence oscillations of transport properties in thin films of a topological insulator Bi91Sb9

E. I. Rogacheva, D. S. Orlova, O. N. Nashchekina, M. S. Dresselhaus, and S. Tang

Appl. Phys. Lett. 101, 023108 (2012); http://dx.doi.org/10.1063/1.4730950 (4 pages)

Online Publication Date: 11 July 2012

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The dependences of the electrical conductivity, Hall coefficient, magnetoresistance, and Seebeck coefficient on the thickness d (d = 15–400 nm) of the topological insulator Bi91Sb9 thin films grown on mica substrates were obtained at room temperature. In addition to the oscillations with a period Δd = (105 ± 5) nm in the thickness range d = 100–400 nm which are attributed to the quantization of the semiconductor electron energy spectrum, oscillations with a period Δd = (8 ± 2) nm in the range d = 15–60 nm were also revealed. It is suggested that the existence of the high-frequency oscillations in the thin films may be connected with the quantization of the metallic surface states energy spectrum.
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73.61.At Metal and metallic alloys
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Pa Thermoelectric and thermomagnetic effects
73.43.Qt Magnetoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Lw Thermoelectric effects

Emission aperture size limited the guided mode extraction characteristics of GaN-based ultrathin-film photonic crystal micro-light-emitting diodes

Chun-Feng Lai

Appl. Phys. Lett. 101, 023109 (2012); http://dx.doi.org/10.1063/1.4734509 (4 pages)

Online Publication Date: 11 July 2012

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This study experimentally and theoretically investigated individual GaN-based ultrathin-film micro-light-emitting diodes (μ-uTFLEDs) with photonic crystal (PhC) nanostructures of varying emission aperture sizes from 5 to 100 μm. High-resolution angular-spectra-resolved electroluminescence measurements revealed the guided mode extraction characteristics that dependence on the emission aperture size. Experimental results indicate that the different diffraction vectors of guided modes have varying extraction lengths; therefore, the emission aperture size acts as a gradual guided mode filter. This effect also limits the suitability of GaN PhC μ-uTFLEDs for the optical engine in pico-projectors.
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85.60.Jb Light-emitting devices

Structural characterization of CdSe/ZnS quantum dots using medium energy ion scattering

M. A. Sortica, P. L. Grande, C. Radtke, L. G. Almeida, R. Debastiani, J. F. Dias, and A. Hentz

Appl. Phys. Lett. 101, 023110 (2012); http://dx.doi.org/10.1063/1.4734686 (4 pages)

Online Publication Date: 11 July 2012

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In the present work, we have analyzed CdSe/ZnS core-shell quantum dots by medium energy ion scattering (MEIS), which is a powerful technique to explore the synthesis, formation, stability, and elemental distribution of such core-shell structures, along with other auxiliary analytical techniques. By comparing different quantum-dot structural models spectra with the experimental MEIS data, we were able to obtain some sample structural information. We found that, despite the well known non stoichiometric Cd:Se ratio, the core is stoichiometric, and there is an excess of cadmium distributed in the shell.
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68.65.Hb Quantum dots (patterned in quantum wells)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.07.Ta Quantum dots

Long minority carrier lifetime in Au-catalyzed GaAs/AlxGa1−xAs core-shell nanowires

N. Jiang, P. Parkinson, Q. Gao, S. Breuer, H. H. Tan, J. Wong-Leung, and C. Jagadish

Appl. Phys. Lett. 101, 023111 (2012); http://dx.doi.org/10.1063/1.4735002 (4 pages) | Cited 3 times

Online Publication Date: 11 July 2012

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GaAs/AlxGa1−xAs core-shell nanowires were grown by metal organic chemical vapor deposition with optimized AlxGa1−xAs shell and twin-free Au-catalyzed GaAs cores. Time-resolved photoluminescence measurements were carried out on single nanowires at room temperature, revealing minority carrier lifetimes of 1.02 ± 0.43 ns, comparable to self-assisted nanowires grown by molecular beam epitaxy. The long minority carrier lifetimes are mainly attributed to improvement of the GaAs/AlxGa1−xAs interface quality. The upper limit of surface recombination velocity of the structure is calculated to be 1300 cm/s with the AlxGa1−xAs shell grown at 750 °C, which is comparable with planar double heterostructures.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Surface enhanced Raman scattering and localized surface plasmon resonance of nanoscale ultrathin films prepared by atomic layer deposition

Ming Chih Lin, Li-Wei Nien, Ching-Hsiang Chen, Chia-Wei Lee, and Miin-Jang Chen

Appl. Phys. Lett. 101, 023112 (2012); http://dx.doi.org/10.1063/1.4729411 (5 pages) | Cited 1 time

Online Publication Date: 11 July 2012

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An approach was proposed to characterize nanoscale ultrathin films using surface enhanced Raman scattering (SERS). Raman spectroscopy of the TiO2 film as thin as ∼2 nm, which was prepared by atomic layer deposition, was obtained by depositing a nanostructured Au layer on the film surface. Red-shift in the extinction spectrum of the nanostructured Au layer was observed with increasing TiO2 film thickness, ascribed to the increase in effective refractive index of the substrate slab and coupled plasmon resonance. This SERS technique can be applied to investigate a variety of solid-state ultrathin films in nanosclae materials and devices in future studies.
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78.30.Hv Other nonmetallic inorganics
81.07.Bc Nanocrystalline materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.-c Methods of micro- and nanofabrication and processing
68.55.A- Nucleation and growth
73.22.Lp Collective excitations

Acoustic and breathing phonon modes in bilayer graphene with Moiré patterns

Jin-Wu Jiang, Bing-Shen Wang, and Timon Rabczuk

Appl. Phys. Lett. 101, 023113 (2012); http://dx.doi.org/10.1063/1.4735246 (4 pages) | Cited 2 times

Online Publication Date: 12 July 2012

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The lattice dynamics properties are investigated for twisting bilayer graphene. There are big jumps for the inter-layer potential at twisting angle θ = 0° and 60°, implying the stability of Bernal-stacking and the instability of AA-stacking structures, while a long platform in [8,55]° indicates the ease of twisting bilayer graphene in this wide angle range. Significant frequency shifts are observed for the z breathing mode around θ = 0° and 60°, while the frequency is a constant in a wide range [8,55]°. Using the z breathing mode, a mechanical nanoresonator is proposed to operate on a robust resonant frequency in terahertz range.
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63.20.-e Phonons in crystal lattices
61.48.Gh Structure of graphene

Enhanced electrical and dielectric properties of polymer covered silicon nanowire arrays

Kamran Rasool, M. A. Rafiq, C. B. Li, E. Krali, Z. A. K. Durrani, and M. M. Hasan

Appl. Phys. Lett. 101, 023114 (2012); http://dx.doi.org/10.1063/1.4735278 (4 pages) | Cited 5 times

Online Publication Date: 12 July 2012

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We investigate DC and AC electrical characteristics of ∼40 μm long p-type silicon nanowire (SiNW) arrays, prepared by metal assisted chemical etching and filled with polyacrylic acid (PAA). PAA diluted to different concentrations with deionized (DI) water is incorporated into the arrays in three steps, yielding polymer filling to the bottom of the arrays. DC and AC electrical measurements show that PAA reduces the array resistance. The AC conductivity increases up to ∼1000 times, and the real part of the overall dielectric constant (ɛ′) by ∼100. We attribute these effects to the formation of acceptor-like states at nanowire/polymer interface.
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77.22.Ch Permittivity (dielectric function)
81.65.Cf Surface cleaning, etching, patterning
73.63.Bd Nanocrystalline materials

Piezoelectrically actuated time-averaged atomic microtraps

A. D. West, C. G. Wade, K. J. Weatherill, and I. G. Hughes

Appl. Phys. Lett. 101, 023115 (2012); http://dx.doi.org/10.1063/1.4736580 (4 pages) | Cited 3 times

Online Publication Date: 12 July 2012

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We present a scheme for creating tight and adiabatic time-averaged atom-traps through the piezoelectric actuation of nanomagnetic structures. We show that potentials formed by the circular translation of magnetic structures have several advantages over conventional rotating-field techniques, particularly for high trap frequencies. As the magnitude of the actuation is changed, the trapping potential can be changed adiabatically between harmonic 3D confinement and a toroidal trap.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Two-dimensional magnetotransport in Bi2Te2Se nanoplatelets

Pascal Gehring, Bo Gao, Marko Burghard, and Klaus Kern

Appl. Phys. Lett. 101, 023116 (2012); http://dx.doi.org/10.1063/1.4736404 (4 pages) | Cited 5 times

Online Publication Date: 13 July 2012

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Single-crystalline Bi2Te2Se nanoplates with thicknesses between 8 and 30 nm and lateral sizes of several micrometers were synthesized by a vapour-solid growth method. Angle-dependent magnetoconductance measurements on individual nanoplates revealed the presence of a two-dimensional weak anti-localization effect. In conjunction with gate-dependent charge transport studies performed at different temperatures, evidence was gained that this effect originates from the topologically protected surface states of the nanoplates.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.20.Fz Weak or Anderson localization
73.61.Ng Insulators
81.07.Bc Nanocrystalline materials

Aerosol fabrication of thermosensitive nanogels and in situ hybridization with iron nanoparticles

Jeong Hoon Byeon and Jang-Woo Kim

Appl. Phys. Lett. 101, 023117 (2012); http://dx.doi.org/10.1063/1.4736574 (4 pages) | Cited 1 time

Online Publication Date: 13 July 2012

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Collison atomized n-isopropylacrylamide (NIPAM) droplets were thermally treated with different furnace wall temperatures to form nanogels in an aerosol state. The size of the aerosol nanogels decreased from 40.3 nm to 32.8 nm by increasing the temperature from 40 °C to 90 °C due to the coil-to-globule transition of the NIPAM. A serial reactor consisting of a spark generator coupled to a collison atomizer was further employed to efficiently (>90% in production yield) fabricate biocompatible (78.8% in cell viability)-magnetic (30.3 emu g−1 in saturation magnetization) hybrid nanogels of NIPAM and iron nanoparticles.
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81.20.Rg Aerosols in materials synthesis and processing
82.70.Gg Gels and sols
82.70.Rr Aerosols and foams
81.07.Bc Nanocrystalline materials

Lifetime imaging of radiative and non-radiative fluorescence decays on nanoplasmonic surface

Manas Ranjan Gartia, John P. Eichorst, Robert M. Clegg, and G. Logan Liu

Appl. Phys. Lett. 101, 023118 (2012); http://dx.doi.org/10.1063/1.4736575 (5 pages)

Online Publication Date: 13 July 2012

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We report the fluorescence lifetime imaging and quantum yield measurement of five different fluorescence dyes spanning different quantum yield and excitation wavelength ranges in solution as well as on irregular nanoplasmonic substrate surface. Due to a distribution of dye molecules at random distances and orientation to the metal nanoplasmonic structure, the dyes showed multi-component lifetime decays on the surface. We have simulated the distribution of lifetime on the surface based on fractional intensity relative to steady-state value and derived an average lifetime with species fraction. From the quantum yield and fluorescence lifetime measurements we calculated the modified radiative and non-radiative decay rates for the dyes due to energy coupling on the substrate. We measured up to 100 fold fluorescence enhancement on nanoplasmonic substrate, and all molecule fluorescence showed not only considerably higher radiative decay rate but also higher non-radiative decay rate.
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73.22.Lp Collective excitations
78.55.Kz Solid organic materials
71.35.-y Excitons and related phenomena

Ultrafast room temperature wiping-rubbing fabrication of graphene nanosheets as flexible transparent conductive films with high surface stability

Yan Yu, Shenglin Jiang, Wenli Zhou, Xiangshui Miao, Yike Zeng, Guangzu Zhang, Yangyang Zhang, Qingfeng Zhang, and Han Zhao

Appl. Phys. Lett. 101, 023119 (2012); http://dx.doi.org/10.1063/1.4736576 (5 pages) | Cited 3 times

Online Publication Date: 13 July 2012

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In this letter, we developed an original innovative wiping-rubbing method to fabricate flexible transparent conductive films (TCFs) based on graphene nanosheets. We achieved this by using only commercial graphite block and polycarbonate film as raw materials, through a cost effective and ultrafast room temperature wiping-rubbing process (within 2 min). The properties of our flexible TCFs were competitive when comparing with literature reported graphene TCFs. Our flexible TCFs showed enough surface stability under a series of surface destructive treatments. The physical mechanism aspects of wiping-rubbing processes and surface stability were discussed.
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81.05.ue Graphene
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.16.-c Methods of micro- and nanofabrication and processing

Magnetovoltaic effect in a quantum dot undergoing Jahn-Teller transition

Shyamalendu M. Bose, Didier Ndengeyintwali, Surjyo N. Behera, and Peter Entel

Appl. Phys. Lett. 101, 023120 (2012); http://dx.doi.org/10.1063/1.4737009 (4 pages)

Online Publication Date: 13 July 2012

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A model is proposed to study the electrical transport properties of a quantum dot capable of undergoing a structural phase transition driven by the Jahn-Teller mechanism. The dot attached to two metallic leads is described by the single impurity Anderson model Hamiltonian to which a term describing the Jahn-Teller distortion and another term to include the possibility of the presence of a magnetic field are added. Calculation of the electrical conductance and Jahn-Teller order parameter reveals several interesting features the most striking of which is the new phenomenon of “magnetovoltaic effect.”
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73.63.Kv Quantum dots
75.85.+t Magnetoelectric effects, multiferroics
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
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