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9 Nov 2009

Volume 95, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 95, 193101 (2009); http://dx.doi.org/10.1063/1.3258663 (3 pages)

L. Gaudreau, A. Kam, G. Granger, S. A. Studenikin, P. Zawadzki, and A. S. Sachrajda
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A tunable few electron triple quantum dot

L. Gaudreau, A. Kam, G. Granger, S. A. Studenikin, P. Zawadzki, and A. S. Sachrajda

Appl. Phys. Lett. 95, 193101 (2009); http://dx.doi.org/10.1063/1.3258663 (3 pages) | Cited 14 times

Online Publication Date: 9 November 2009

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In this paper, we report on a tunable few electron lateral triple quantum dot design. The quantum dot potentials are arranged in series. The device is aimed at studies of triple quantum dot properties where knowing the exact number of electrons is important as well as quantum information applications involving electron spin qubits. We demonstrate tuning strategies for achieving required resonant conditions such as quadruple points where all three quantum dots are on resonance. We find that in such a device resonant conditions at specific configurations are accompanied by complex charge transfer behavior.
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73.63.Kv Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)

Gold adsorption induced surface alloying on Si(111)-√3×√3-Pb surface

Lin Tang, Ze-Lei Guan, Dan Hao, Jin-Feng Jia, Xu-Cun Ma, and Qi-Kun Xue

Appl. Phys. Lett. 95, 193102 (2009); http://dx.doi.org/10.1063/1.3262950 (3 pages) | Cited 2 times

Online Publication Date: 10 November 2009

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The formation of surface Au/Pb alloys on a Pb-induced Si(111)-√3×√3 surface is investigated using scanning tunneling microscopy (STM). Two types of alloy islands, compact and loose islands, have been observed. The former shows a long-range ordered 3×3-Au/Pb reconstruction corresponding to an Au0.57Pb0.43 alloy, while the latter is not totally disordered with a short-range ordered structure. Based on the atomic structure of the substrate around the compact islands, Si atoms are excluded in the formation process of the Au/Pb surface alloys.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.65.-b Surface treatments
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.43.Fg Adsorbate structure (binding sites, geometry)

Nanowire-quantum-dot solar cells and the influence of nanowire length on the charge collection efficiency

Kurtis S. Leschkies, Alan G. Jacobs, David J. Norris, and Eray S. Aydil

Appl. Phys. Lett. 95, 193103 (2009); http://dx.doi.org/10.1063/1.3258490 (3 pages) | Cited 32 times

Online Publication Date: 10 November 2009

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External quantum efficiency in solar cells based on junctions between PbSe quantum dots (QDs) and thin ZnO films is increased by replacing the ZnO films with a vertically oriented array of single-crystalline ZnO nanowires, and infiltrating this array with colloidal QDs. When illuminated with 100 mW/cm2 of simulated solar light, QD-nanowire solar cells exhibited power conversion efficiencies approaching 2%, approximately three times higher than that achieved with thin-film ZnO devices constructed with the same amount of QDs. Significant photocurrent and power conversion improvement with increasing nanowire length is consistent with higher exciton and charge collection efficiencies.
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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)
73.50.Pz Photoconduction and photovoltaic effects
68.55.-a Thin film structure and morphology
82.70.Dd Colloids

ZnO/TiO2 nanonetwork as efficient photoanode in excitonic solar cells

A. Vomiero, I. Concina, M. M. Natile, E. Comini, G. Faglia, M. Ferroni, I. Kholmanov, and G. Sberveglieri

Appl. Phys. Lett. 95, 193104 (2009); http://dx.doi.org/10.1063/1.3257370 (3 pages) | Cited 5 times

Online Publication Date: 11 November 2009

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An innovative nanonetwork composed of TiO2 nanoparticles and single-crystalline ZnO nanowires is demonstrated as efficient photoanode in excitonic solar cells. Such architecture benefits of the capability of high sensitizer loading offered by the nanoparticles and of the direct conduction path for electrons guaranteed by the nanowires. The combination of these features leads to improved light absorption, electron photogeneration, and charge collection. The nanonetwork was implemented in a dye-sensitized solar-cell architecture demonstrating threefold enhancement of the efficiency with respect to a nanowire photoanode of the same thickness. Cell efficiency of 1.6% was obtained in 1.5 μm thick nanonetwork.
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88.40.hj Efficiency and performance of solar cells
88.40.jm Thin film III-V and II-VI based solar cells

Prediction of surface passivation doping of silicon nanowires with phosphorus

X. B. Yang, C. S. Guo, and R. Q. Zhang

Appl. Phys. Lett. 95, 193105 (2009); http://dx.doi.org/10.1063/1.3250162 (3 pages) | Cited 7 times

Online Publication Date: 11 November 2009

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We report a prediction of enhanced surface passivation doping effect in silicon nanowires (SiNWs) by phosphorus adsorption based on first-principles calculations. Recent theoretical and experimental studies all showed that hydrogen-passivated SiNWs present typical p-type characteristic due to charge transfer between the surface passivant and the SiNW core. Here, we show that a phosphorus-passivated SiNW with a moderate diameter facilitates improved hole generation in the core and efficient separation of electron and hole, which may provide a practical avenue for fabricating low cost solar cells with high efficiency.
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81.65.Rv Passivation
71.70.-d Level splitting and interactions
84.60.Jt Photoelectric conversion
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.-b Nanoscale materials and structures: fabrication and characterization
68.43.Mn Adsorption kinetics

Photon statistics in enhanced fluorescence from a single CdSe/ZnS quantum dot in the vicinity of silver nanoparticles

Sadahiro Masuo, Hiroyuki Naiki, Shinjiro Machida, and Akira Itaya

Appl. Phys. Lett. 95, 193106 (2009); http://dx.doi.org/10.1063/1.3259792 (3 pages) | Cited 8 times

Online Publication Date: 11 November 2009

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Single-photon emission behavior in the enhanced fluorescence from single colloidal quantum dots (QDs) near silver nanoparticles (AgNPs) was investigated using a single molecule fluorescence spectroscopy technique. It was found that the degree of fluorescence enhancement from single QDs with AgNPs increased with decrease in the lifetime and the probability of single-photon emission, that is, highly enhanced fluorescence with a shortened lifetime exhibited a low probability of single-photon emission. The present results yield new insights into fundamentals of QD-metal nanostructure interactions, and are also important to understand the mechanism of the fluorescence enhancement by localized surface plasmon of metal nanostructures.
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81.05.Dz II-VI semiconductors
73.22.Lp Collective excitations
73.21.La Quantum dots
82.70.Dd Colloids
78.55.Et II-VI semiconductors
78.67.Hc Quantum dots
81.07.Ta Quantum dots

Direct imaging of doped fluorine in LaFeAsO1−xFx superconductor by atomic scale spectroscopy

Tetsuya Tohei, Teruyasu Mizoguchi, Hidenori Hiramatsu, Yoichi Kamihara, Hideo Hosono, and Yuichi Ikuhara

Appl. Phys. Lett. 95, 193107 (2009); http://dx.doi.org/10.1063/1.3263148 (3 pages) | Cited 5 times

Online Publication Date: 11 November 2009

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We report direct observation of fluorine ion dopants in the recently discovered LaFeAsO1−xFx superconductor, where the doping is critical for the superconductivity. Employing spectroscopic imaging based on scanning transmission electron microscopy, the spatial distribution of the doped fluorine ions, which are invisible in Z-contrast imaging, is clearly visualized with atomic-scale resolution. The observation directly proves that fluorine substitutes into the oxygen site in the superconducting LaFeAsO1−xFx compound. Our results demonstrate the potential of the present method for revealing dopants undetectable by conventional microscopy imaging.
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74.62.Dh Effects of crystal defects, doping and substitution
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
74.70.-b Superconducting materials other than cuprates
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Capacitance tuning of nanoscale split-ring resonators

Claus Jeppesen, Niels Asger Mortensen, and Anders Kristensen

Appl. Phys. Lett. 95, 193108 (2009); http://dx.doi.org/10.1063/1.3263191 (3 pages) | Cited 4 times

Online Publication Date: 12 November 2009

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We investigate the capacitance tuning of nanoscale split-ring resonators. Based on a simple inductor-capacitor circuit model, we derive an expression, where the inductance is proportional to the area while the capacitance reflects the aspect ratio of the slit. The resonance frequency may thus be tuned by the slit aspect ratio leaving the area, the lattice constant Λ, and nearest-neighbor coupling in periodic structures invariant. Experimental data follow the predictions of the simple LC-model.
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84.40.Az Waveguides, transmission lines, striplines

Radio frequency operation of clocked quantum-dot cellular automata latch

Yong Tang, Alexei O. Orlov, Gregory L. Snider, and Patrick J. Fay

Appl. Phys. Lett. 95, 193109 (2009); http://dx.doi.org/10.1063/1.3265919 (3 pages) | Cited 1 time

Online Publication Date: 12 November 2009

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The radio frequency operation of a single-electron latch based on Al–AlOx–Al tunnel junctions is presented. By capacitively coupling the latch to a radio frequency single electron transistor, charge switching on the microsecond timescale is demonstrated. The fast switching and high repeatability of the latch response indicates that high speed operation of pipelines, signal fan-outs, and more complex logic devices are possible with this technology. The experimental technique developed is also promising for enabling the investigation of the intrinsic switching speed in electronic quantum-dot cellular automata-based circuits.
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85.35.Gv Single electron devices
81.07.Ta Quantum dots
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Silver half-shell arrays with controlled plasmonic response for fluorescence enhancement optimization

Cosmin Farcău and Simion Aştilean

Appl. Phys. Lett. 95, 193110 (2009); http://dx.doi.org/10.1063/1.3263193 (3 pages) | Cited 12 times

Online Publication Date: 13 November 2009

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Regular arrays of interconnected silver half-shells (HSs) deposited on self-organized polystyrene microspheres are proposed as plasmonic substrates for metal-enhanced fluorescence. An emission enhancement of 28 times was demonstrated for Rose Bengal fluorophore placed at about 1 nm above HSs. The enhancement correlates with the spectral overlap between the fluorophore emission and the plasmonic resonance of the HSs, indicating a surface plasmon-coupled emission mechanism for the amplification. As the overlap can be easily tuned by controlling the diameter of underlying microspheres, such plasmonic structures could be relevant for building fluorescence-based sensing devices with optimized efficiency for any given fluorophore.
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78.66.Bz Metals and metallic alloys
78.68.+m Optical properties of surfaces
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Anharmonic phonon coupling in vapor-liquid-solid grown ZnO nanowires

A. Soudi, R. Lopez, Jr., R. D. Dawson, and Y. Gu

Appl. Phys. Lett. 95, 193111 (2009); http://dx.doi.org/10.1063/1.3263709 (3 pages) | Cited 2 times

Online Publication Date: 13 November 2009

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We have determined quantitatively third-order anharmonic phonon coupling matrix elements in vapor-liquid-solid (VLS) grown ZnO nanowires, via an analysis of the Raman line shape of the E2high phonon mode. The results suggest that the decay of the E2high phonon into the sum of two acoustic phonons is suppressed in VLS-grown ZnO nanowires compared to bulk ZnO. While further studies are needed to elucidate the origin of this phenomenon, we suggest that isotope effects on Zn vapor transport and diffusion through metal nanocatalysts, processes during the VLS growth, can be contributing mechanisms.
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63.22.Gh Nanotubes and nanowires
63.20.kg Phonon-phonon interactions
63.20.Ry Anharmonic lattice modes
78.67.Uh Nanowires
78.30.Fs III-V and II-VI semiconductors
66.30.Pa Diffusion in nanoscale solids

Strategies for nanoplasmonic core-satellite biomolecular sensors: Theory-based Design

Benjamin M. Ross, John R. Waldeisen, Tim Wang, and Luke P. Lee

Appl. Phys. Lett. 95, 193112 (2009); http://dx.doi.org/10.1063/1.3254756 (3 pages) | Cited 4 times

Online Publication Date: 13 November 2009

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We present a systematic theoretical study of core-satellite gold nanoparticle assemblies using the Generalized Multiparticle Mie formalism. We consider the importance of satellite number, satellite radius, the core radius, and the satellite distance, and we present approaches to optimize spectral shift due to satellite attachment or release. This provides clear strategies for improving the sensitivity and signal-to-noise ratio for molecular detection, enabling simple colorimetric assays. We quantify the performance of these strategies by introducing a figure of merit. In addition, we provide an improved understanding of the nanoplasmonic interactions that govern the optical response of core-satellite nanoassemblies.
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87.85.Rs Nanotechnologies-applications
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.60.Dq Photometers, radiometers, and colorimeters
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
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