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27 Dec 2010

Volume 97, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 97, 263701 (2010); http://dx.doi.org/10.1063/1.3530124 (3 pages)

Shu-Hsien Liao, Kai-Wen Huang, Hong-Chang Yang, Chang-Te Yen, M. J. Chen, Hsin-Hsien Chen, Herng-Er Horng, and Shieh Yueh Yang
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Ion and electron beam nanofabrication of the which-way double-slit experiment in a transmission electron microscope

Stefano Frabboni, Gian Carlo Gazzadi, and Giulio Pozzi

Appl. Phys. Lett. 97, 263101 (2010); http://dx.doi.org/10.1063/1.3529947 (3 pages) | Cited 1 time

Online Publication Date: 28 December 2010

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We have realized a which-way experiment closely resembling the original Feynman’s proposal exploiting focused ion beam milling to prepare two nanoslits and electron beam induced deposition to grow, selectively over one of them, electron transparent layers of low atomic number amorphous material to realize a which-way detector for high energy electrons. By carrying out the experiment in an electron microscope equipped with an energy filter, we show that the inelastic scattering of electron transmitted through amorphous layers of different thicknesses provides the control of the dissipative interaction process responsible for the localization phenomena which cancels out the interference effects.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.15.Dj E-beam and hot filament evaporation deposition
81.16.-c Methods of micro- and nanofabrication and processing
79.20.Uv Electron energy loss spectroscopy

Nonradiative energy transfer between vertically coupled indirect and direct bandgap InAs quantum dots

Timur S. Shamirzaev, Demid S. Abramkin, Dmitry V. Dmitriev, and Anton K. Gutakovskii

Appl. Phys. Lett. 97, 263102 (2010); http://dx.doi.org/10.1063/1.3532102 (3 pages)

Online Publication Date: 28 December 2010

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Nonradiative energy transfer from indirect bandgap InAs/AlAs quantum dots (QDs) to direct bandgap InAs/AlGaAs QDs was studied by steady-state and transient photoluminescence. We demonstrate that long excitonic lifetime in donor InAs/AlAs QDs allows one to extend the efficient exciton energy transfer between coupled QDs to distances up to 9 nm.
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73.21.La Quantum dots
73.63.Kv Quantum dots
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots

The effect of Ti and ITO adhesion layers on gold split-ring resonators

Claus Jeppesen, Niels Asger Mortensen, and Anders Kristensen

Appl. Phys. Lett. 97, 263103 (2010); http://dx.doi.org/10.1063/1.3532096 (3 pages)

Online Publication Date: 28 December 2010

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Ultrathin adhesion layers serve a well-documented fabrication purpose while its influence on the optical properties of gold nanostructures is often neglected. Gold split-ring resonators are fabricated with two commonly used adhesion layers: titanium and indium tin oxide. When compared to all-gold reference samples, a spectral shift of the ground mode resonance is observed. For the titanium sample the spectral shift is accompanied by a resonance broadening, which is less profound for indium tin oxide. The mutual correlation between the shift and the broadening is shown to be qualitatively consistent with perturbative considerations.
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42.79.-e Optical elements, devices, and systems
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.86.+b Optical workshop techniques

Different longitudinal optical—transverse optical mode amplification in tip enhanced Raman spectroscopy of GaAs(001)

Pietro Giuseppe Gucciardi and Jean-Christophe Valmalette

Appl. Phys. Lett. 97, 263104 (2010); http://dx.doi.org/10.1063/1.3532841 (3 pages)

Online Publication Date: 28 December 2010

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We report on tip enhanced Raman spectroscopy of GaAs(100) crystals taking advantage of the fields polarization to maximize the near-field contrast. Excitation parallel to either the [100] or the [110] crystallographic axis provide minimum far-field background provided that cross- or parallel-component of the Raman field are detected. Experiments highlight a tip-induced selective enhancement of the one-phonon longitudinal optical mode with respect to the transverse optical mode. We interpret this effect in terms of depolarization of the excitation field and beam deflection which breaks the polarization-based selection rules of the Raman scattering.
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63.20.dd Measurements
78.30.Fs III-V and II-VI semiconductors

Work function of single-wall silicon carbide nanotube

Fawei Zheng, Yu Yang, and Ping Zhang

Appl. Phys. Lett. 97, 263105 (2010); http://dx.doi.org/10.1063/1.3532842 (3 pages)

Online Publication Date: 28 December 2010

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Using first-principles calculations, we study the work function of single-wall silicon carbide nanotube (SiCNT). The work function is found to be highly dependent on the tube chirality and diameter. It increases by decreasing the tube diameter. The work function of zigzag SiCNT is always larger than that of armchair SiCNT. We reveal that the difference between the work function of zigzag and armchair SiCNT comes from their different intrinsic electronic structures, for which the singly degenerate energy band above the Fermi level of zigzag SiCNT is specifically responsible. Our finding offers potential usages of SiCNT in field-emission devices.
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73.30.+y Surface double layers, Schottky barriers, and work functions
71.15.-m Methods of electronic structure calculations
73.22.-f Electronic structure of nanoscale materials and related systems

Observation of efficient transfer from Mott–Wannier to Frenkel excitons in a hybrid semiconductor quantum dot/polymer composite at room temperature

Sedat Nizamoglu, Xiao Wei Sun, and Hilmi Volkan Demir

Appl. Phys. Lett. 97, 263106 (2010); http://dx.doi.org/10.1063/1.3529450 (3 pages)

Online Publication Date: 29 December 2010

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Efficient conversion from Mott–Wannier to Frenkel excitons is observed at room temperature. The time-resolved photoluminescence shows that the energy transfer rate and efficiency reach 0.262 ns−1 and 80.9%, respectively. The energy transfer is enabled by strong dipole-dipole coupling in a hybrid inorganic/organic system of CdSe/ZnS core/shell heteronanocrystal and poly[2-methoxy-5-(3,7-dimethyl-octyloxy)-1,4-phenylenevinylene] homopolymer composite, and the measured energy transfer efficiencies are consistent with the analytical model.
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73.22.Lp Collective excitations
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.55.-m Photoluminescence, properties and materials
78.47.jd Time resolved luminescence

Thermal conductivity of GaAs nanowires studied by micro-Raman spectroscopy combined with laser heating

Martin Soini, Ilaria Zardo, Emanuele Uccelli, Stefan Funk, Gregor Koblmüller, Anna Fontcuberta i Morral, and Gerhard Abstreiter

Appl. Phys. Lett. 97, 263107 (2010); http://dx.doi.org/10.1063/1.3532848 (3 pages) | Cited 1 time

Online Publication Date: 29 December 2010

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The thermal properties of freely suspended GaAs nanowires are investigated by applying a method which relies on laser heating and the determination of the local temperature by Raman spectroscopy. In order to determine the values for the thermal conductivity κ, the fraction of the laser power absorbed inside the GaAs nanowire is estimated by numerical simulations. The thermal conductivity of nanowires with homogeneous diameter is found to lie in the range of 8–36 W m−1 K−1. The change of the temperature profile in the presence of a tapering was investigated. Furthermore, we discuss the influence of laser heating in ambient conditions on the value of κ.
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66.70.Df Metals, alloys, and semiconductors
78.67.Lt Quantum wires
42.62.-b Laser applications
78.30.Fs III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing

Enhanced photorefractivity in a polymer/nanocrystal composite photorefractive device at telecommunication wavelength

Jing Zhu (朱菁), Won Jin Kim, Guang S. He, Jangwon Seo, Ken-Tye Yong, Dongho Lee, Alexander N. Cartwright, Yiping Cui (崔一平), and Paras N. Prasad

Appl. Phys. Lett. 97, 263108 (2010); http://dx.doi.org/10.1063/1.3531650 (3 pages)

Online Publication Date: 29 December 2010

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Enhanced photorefractive (PR) response in nanocrystal-polymer nanocomposite PR devices at the telecommunication wavelength of 1.3 μm is achieved using facile surface treatment of PbS nanocrystals functionalized with thermally cleavable ligands. The cleavage of the ligands, by heat treatment, results in significant improvement in both photocharge generation and PR response, as demonstrated by photoconductivity and two-beam coupling (TBC) experiments, respectively. The TBC experiment shows that the optical gain coefficient is improved drastically (about 63%) at an applied electric field of 84 V/μm.
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85.60.-q Optoelectronic devices
85.30.-z Semiconductor devices

Electron-hole duality during band-to-band tunneling process in graphene-nanoribbon tunnel-field-effect-transistors

Deblina Sarkar, Michael Krall, and Kaustav Banerjee

Appl. Phys. Lett. 97, 263109 (2010); http://dx.doi.org/10.1063/1.3528338 (3 pages) | Cited 6 times

Online Publication Date: 29 December 2010

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This letter provides clear insight into the interplay between electron and hole characteristics of carriers within the forbidden gap during the band-to-band tunneling process, taking graphene-nanoribbons as an example. Accurate numerical models are presented and analytical formulas for tunneling probabilities are derived for both source/drain to channel and direct source-drain tunneling based on the Wentzel–Kramers–Brillouin (WKB) method. It is shown that not considering the electron-hole duality can lead to significant errors in numerical calculations, and more importantly, lack of proper understanding of the phenomenon gives rise to seriously misleading conclusions. Furthermore, the regime of validity of the WKB approximation for graphene-nanoribbon tunnel-field-effect-transistors is discussed in light of the electron-hole duality concept.
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73.40.Gk Tunneling
73.63.-b Electronic transport in nanoscale materials and structures
72.80.Vp Electronic transport in graphene
85.30.Tv Field effect devices

Comparative study of field enhancement between isolated and coupled metal nanoparticles: An analytical approach

G. Sun and J. B. Khurgin

Appl. Phys. Lett. 97, 263110 (2010); http://dx.doi.org/10.1063/1.3532101 (3 pages) | Cited 3 times

Online Publication Date: 29 December 2010

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We present an analytical model that takes into account the coupling between the surface plasmon modes in complex metal nanostructures. We apply this model to evaluate the field enhancement in the gap of two coupled Au metal spheres embedded in GaN dielectric and compare the result with that obtained by the single sphere. The results show additional improvement can be obtained in the gap depending on the width of the gap. This approach offers a clear physical insight for the enhancement and a straightforward method for optimization.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Electrical signatures of ferromagnetism in epitaxial FeSi2 nanowires

T. Kim and J. P. Bird

Appl. Phys. Lett. 97, 263111 (2010); http://dx.doi.org/10.1063/1.3533400 (3 pages) | Cited 1 time

Online Publication Date: 30 December 2010

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We perform electrical characterization of epitaxial FeSi2 nanowires (NWs) realized by reactive epitaxy. Typical resistance values exceed 100 kΩ, a high value that is attributed to the combined influence of interfacial scattering and process-related damage. Negative magnetoresistance due to weak localization, as well as hysteresis and anisotropic magnetoresistance, are also observed at low temperatures, confirming the ferromagnetic nature of these NWs.
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75.47.Np Metals and alloys
73.20.Fz Weak or Anderson localization
75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films
73.61.Le Other inorganic semiconductors

Electrical study of trapped charges in nanoscale Ge islands by Kelvin probe force microscopy for nonvolatile memory applications

Z. Lin, P. Brunkov, F. Bassani, and G. Bremond

Appl. Phys. Lett. 97, 263112 (2010); http://dx.doi.org/10.1063/1.3533259 (3 pages)

Online Publication Date: 30 December 2010

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Isolated Germanium nanoisland on top of silicon dioxide (SiO2) layer has been studied by Kelvin probe force microscopy (KPFM) at room temperature. Different surface potentials between Ge island and SiO2 dielectric layer were directly visualized from the KPFM image. The image contrast greatly increased after electron injection by applying a negative bias of −7 V. The dissipation of injected electrons was evaluated by measuring the surface potential variation due to the leakage of these injected charges. The long retention time of local charges in Ge dot is promising for applications in nonvolatile memories.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.63.Bd Nanocrystalline materials

Separation of ultrafast photoexcited electron and hole dynamics in CdSe quantum dots adsorbed onto nanostructured TiO2 films

Qing Shen, Yasumasa Ayuzawa, Kenji Katayama, Tsuguo Sawada, and Taro Toyoda

Appl. Phys. Lett. 97, 263113 (2010); http://dx.doi.org/10.1063/1.3533374 (3 pages)

Online Publication Date: 30 December 2010

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The ultrafast photoexcited electron and hole dynamics of CdSe quantum dots (QDs) deposited onto nanostructured TiO2 films were studied using an improved transient grating (TG) technique. By comparing the TG responses measured in air and in a Na2S solution (hole acceptor), we succeeded in separating the dynamic characteristics of photoexcited electrons and holes in the CdSe QDs. We found that charge separation in the CdSe QDs occurred over a very fast time scale from a few hundreds of femtoseconds in the Na2S solution via hole transfer to S2− ions to a few picoseconds in air via hole trapping.
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73.63.Kv Quantum dots
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Spin-polarized energy-gap opening in asymmetric bilayer graphene nanoribbons

Gyubong Kim and Seung-Hoon Jhi

Appl. Phys. Lett. 97, 263114 (2010); http://dx.doi.org/10.1063/1.3533643 (3 pages)

Online Publication Date: 30 December 2010

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Electronic and magnetic properties of bilayer zigzag graphene nanoribbon (bZGNR) are studied using pseudopotential density functional method. The edge atoms in the top and bottom layers of bZGNR make a weak hybridization, which leads to electronic structures different from monolayer ZGNR. For asymmetric bZGNR, where the top and bottom layers have different widths, one edge is pinched by the interlayer bonding and the other sustains antiferromagnetic ordering. A small amount of charge transfer occurs from narrower to wider layer, producing spin-polarized electron and hole pockets. External electric field produces asymmetric energy-gap opening for each spin component, inducing half-metallicity in bZGNR.
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73.22.Pr Electronic structure of graphene
75.50.Ee Antiferromagnetics
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.-c Magnetic properties of nanostructures
71.20.Tx Fullerenes and related materials; intercalation compounds

Carbon-based nanomaterials as contacts to graphene nanoribbons

Yijian Ouyang and Jing Guo

Appl. Phys. Lett. 97, 263115 (2010); http://dx.doi.org/10.1063/1.3533803 (3 pages) | Cited 1 time

Online Publication Date: 30 December 2010

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Making good electrical contacts to nanodevice channels is crucial for device performance. Carbon-based nanomaterials are studied and compared to each other as the contact materials for graphene nanoribbons (GNRs) by atomistic quantum transport simulations. A monolayer graphene that has an AB stacking structure on the GNR offers the best electrical contact. Rotation of the graphene layer with regard to the GNR leads to a considerable increase in the contact resistance and contact transfer length. Importance of wave vector matching and interfacial defects is examined for improving electrical contacts to GNRs. This paper could be useful for designing all-carbon-based circuits.
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73.63.Rt Nanoscale contacts
73.40.Cg Contact resistance, contact potential
61.48.Gh Structure of graphene
61.46.-w Structure of nanoscale materials

Formation of nickel germanide contacts to Ge nanowires

N. S. Dellas, S. Minassian, J. M. Redwing, and S. E. Mohney

Appl. Phys. Lett. 97, 263116 (2010); http://dx.doi.org/10.1063/1.3533808 (3 pages) | Cited 2 times

Online Publication Date: 30 December 2010

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Nickel germanide contacts are expected to play an important role in Ge-based electronics similar to that of their nickel silicide counterparts in Si devices. Here we have studied the solid state reaction between Ni contact pads and Ge nanowires. We observe the formation of axial nickel germanide segments after annealing at temperatures as low as 300 °C for 2 min. The nickel germanide segments are polycrystalline, without an epitaxial relationship to the Ge nanowire, in contrast to observations of epitaxial nickel silicide formation from Si nanowires. The crystal structure of the nickel germanide phase is consistent with the Ni2In prototype structure. Annealing above 400 °C results in fracture in the nickel germanide segment; however, nickel germanide segments as long as 1.7 μm can be formed by annealing at 400 °C for 5 min.
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73.40.Cg Contact resistance, contact potential
61.66.Fn Inorganic compounds
81.40.Gh Other heat and thermomechanical treatments

Morphology-dependent field emission characteristics of SiC nanowires

Z. J. Li, W. P. Ren, and A. L. Meng

Appl. Phys. Lett. 97, 263117 (2010); http://dx.doi.org/10.1063/1.3533813 (3 pages)

Online Publication Date: 30 December 2010

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Felted, curly, and straight β-SiC nanowires (SiCNWs) had been synthesized by chemical vapor reaction, and morphology-dependent field emission (FE) characteristics were chiefly investigated. The turn-on and threshold fields were 2.0 and 5.3 V/μm for felted nanowires, 1.5 and 3.25 V/μm for curly nanowires, and 1.0 and 2.05 V/μm for straight nanowires, respectively, suggesting that morphology played an important role in FE properties of the SiCNWs. Magnetic field shielding effect is proposed to explain the morphology-dependent FE characteristics, and it may stand as a nice referential work for researching FE properties of other wirelike materials.
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79.70.+q Field emission, ionization, evaporation, and desorption
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
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
81.16.-c Methods of micro- and nanofabrication and processing

Room temperature negative differential resistance based on a single ZnO nanowire/CuPc nanofilm hybrid heterojunction

Wen Guo, Ya Yang, Junjie Qi, and Yue Zhang

Appl. Phys. Lett. 97, 263118 (2010); http://dx.doi.org/10.1063/1.3532104 (3 pages) | Cited 2 times

Online Publication Date: 30 December 2010

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We report a room temperature negative differential resistance (RT-NDR) phenomenon in the ZnO nanowire/CuPc nanofilm hybrid heterojunction by using conductive atomic force microscope (C-AFM). The NDR behavior is observed only in the positive sample bias range with the peak-to-valley current ratio as high as 4.7 in the dark. Under light illumination (centered at 716 nm), the NDR peak current increases from 2.1 to 7.53 nA and the peak voltage decreases from 4.2 to 3.1 V with increasing the light intensity. The origin and the modulation of the NDR are discussed in terms of energy band diagram of the heterojunction.
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73.61.Ga II-VI semiconductors
73.22.-f Electronic structure of nanoscale materials and related systems
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