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29 Oct 2007

Volume 91, Issue 18, Articles (18xxxx)

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Appl. Phys. Lett. 91, 183501 (2007); http://dx.doi.org/10.1063/1.2801554 (3 pages)

Aurelien Du Pasquier, Daniel D. T. Mastrogiovanni, Lauren A. Klein, Tong Wang, and Eric Garfunkel
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Enhanced chemical shift of carbon nanotube from laser assisted gas incorporation

Cheng-Hao Chuang, Chia-Hao Chen, Yin-Ming Chang, Chih-Wei Peng, Sheng-Syun Wong, Shien-Der Tzeng, Shangjr Gwo, Yanwu Zhu, Chorng-Haur Sow, and Minn-Tsong Lin

Appl. Phys. Lett. 91, 183101 (2007); http://dx.doi.org/10.1063/1.2801698 (3 pages)

Online Publication Date: 29 October 2007

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We investigate the position-selected electronic structure of laser modified carbon nanotubes (CNTs) by scanning photoelectron microscopy. After laser pruning removed the top layer of CNTs in air and N2 environment, the modified region shows enhanced chemical shifts of 0.9 and 0.6 eV in carbon 1s state, respectively. The modification of electronic structure is shown to be strongly dependent on the gaseous environment. We demonstrate an effective postgrowth process to modify the electronic structure of CNTs for further applications.
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73.22.-f Electronic structure of nanoscale materials and related systems
76.60.Cq Chemical and Knight shifts
42.62.-b Laser applications
79.60.Jv Interfaces; heterostructures; nanostructures

Crisscrossed and coaligned single-wall carbon based films

S. M. Mirza and H. Grebel

Appl. Phys. Lett. 91, 183102 (2007); http://dx.doi.org/10.1063/1.2803218 (3 pages) | Cited 1 time

Online Publication Date: 29 October 2007

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We investigated p-i-n nanojunctions made between aligned and crisscrossed functionalized tubes. A network of crisscrossed diodes exhibited current-voltage staircase curves at room and liquid nitrogen temperatures unlike its randomly oriented counterpart. This was also in contrast to the I-V curves of crisscrossed and coaligned contacts between tubes of the same type. It appears that the bias values, at which current steps occur, are separated by a multiple of 0.067 V. We attributed the voltage steps to the formation of quantum dot at the point of contact.
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73.63.Fg Nanotubes
73.22.Dj Single particle states
73.63.Kv Quantum dots

Two-dimensional semiconducting nanostructures based on single graphene sheets with lines of adsorbed hydrogen atoms

Leonid A. Chernozatonskii, Pavel B. Sorokin, and Jochen W. Brüning

Appl. Phys. Lett. 91, 183103 (2007); http://dx.doi.org/10.1063/1.2800889 (3 pages) | Cited 24 times

Online Publication Date: 29 October 2007

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It is shown that lines of adsorbed hydrogen pair atoms divide the graphene sheet into strips and form hydrogen-based superlattice structures (2HG-SL). We show that the formation of 2HG-SL changes the electronic properties of graphene from semimetal to semiconductor. The electronic spectra of “zigzag” (n,0) 2HG-SL is similar to that of (n,0) carbon nanotubes and have a similar oscillation of band gap with n, but with nonzero minimal values. The composite dual-periodic (n,0)+(m,0) 2HG-SLs of zigzag strips are analyzed, with the conclusion that they may be treated as quasi-two-dimensional heterostructures.
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73.21.Cd Superlattices
71.20.Tx Fullerenes and related materials; intercalation compounds
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
68.43.Hn Structure of assemblies of adsorbates (two- and three-dimensional clustering)
68.65.Cd Superlattices
81.05.U- Carbon/carbon-based materials

Monitoring electrically driven cancellation of exciton fine structure in a semiconductor quantum dot by optical orientation

K. Kowalik, O. Krebs, A. Lemaître, B. Eble, A. Kudelski, P. Voisin, S. Seidl, and J. A. Gaj

Appl. Phys. Lett. 91, 183104 (2007); http://dx.doi.org/10.1063/1.2805025 (3 pages) | Cited 12 times

Online Publication Date: 30 October 2007

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We use optical orientation technique to monitor the degeneracy control of exciton states in a single InAs/GaAs quantum dot, achieved by applying an in-plane electric field. Under circularly polarized quasiresonant excitation, the exciton photoluminescence shows a pronounced maximum of circular polarization at electric field corresponding to zero fine structure splitting. By analyzing the width of this maximum we are able to determine the homogeneous linewidth of the excitonic transition. This experimental method is shown to be very efficient to test and possibly tune the photonic properties of an individual quantum dot for the emission of entangled photon pairs.
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71.35.-y Excitons and related phenomena
78.67.Hc Quantum dots
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.21.La Quantum dots
71.70.Gm Exchange interactions

Nanoparticle films as sensitive strain gauges

J. Herrmann, K.-H. Müller, T. Reda, G. R. Baxter, B. Raguse, G. J. J. B. de Groot, R. Chai, M. Roberts, and L. Wieczorek

Appl. Phys. Lett. 91, 183105 (2007); http://dx.doi.org/10.1063/1.2805026 (3 pages) | Cited 21 times

Online Publication Date: 30 October 2007

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We demonstrate that thin films consisting of cross-linked nanoparticle aggregates function as highly sensitive strain gauges. The sensors exploit the exponential dependence of the interparticle tunnel resistance on the particle separation. Their sensitivity (gauge factor) is two orders of magnitude higher than that of conventional metal foil gauges and rivals that of state-of-the-art semiconductor gauges. We describe the strain gauge behavior in a tunneling model that predicts the dependence of the gauge factor on several parameters, in particular, the nanoparticle size, the interparticle separation gap, and the conductance of the linker molecules.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Pz Instruments for strain, force, and torque
73.40.Gk Tunneling
73.63.Bd Nanocrystalline materials
81.07.Bc Nanocrystalline materials
85.35.-p Nanoelectronic devices

Influence of electromechanical boundary conditions on elasticity of zinc oxide nanowires

A. V. Desai and M. A. Haque

Appl. Phys. Lett. 91, 183106 (2007); http://dx.doi.org/10.1063/1.2805027 (3 pages) | Cited 5 times

Online Publication Date: 30 October 2007

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Uniaxial tensile experiments were performed on single crystal zinc oxide nanowires with a custom microfabricated tool. The measured Young’s modulus is about 30%—40% of the bulk value for specimens with 200–400 nm in diameter, which cannot be explained with classical elasticity formulations. We discuss this anomaly in light of the enhanced electromechanical coupling due to static mechanical and isolated electrical boundary conditions that can significantly contribute to the softening of the material, irrespective of the length scale.
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62.25.-g Mechanical properties of nanoscale systems
81.05.Dz II-VI semiconductors
62.20.D- Elasticity
61.46.-w Structure of nanoscale materials
81.40.Gh Other heat and thermomechanical treatments

Enhanced photoluminescence excitation in surface plasmon coupling with an InGaN/GaN quantum well

Yen-Cheng Lu, Cheng-Yen Chen, Kun-Ching Shen, Dong-Ming Yeh, Tsung-Yi Tang, and C. C. Yang

Appl. Phys. Lett. 91, 183107 (2007); http://dx.doi.org/10.1063/1.2805034 (3 pages) | Cited 6 times

Online Publication Date: 31 October 2007

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The authors report the observation of the enhancement of photoluminescence excitation through the couplings of an InGaN/GaN quantum well (QW) with localized surface plasmons (LSPs) and surface plasmon polaritons (SPPs), which are generated on a Ag nanostructure deposited on the SiN-coated QW epitaxial sample. At the wavelengths corresponding to the LSP modes, the excitation light is first absorbed by the LSPs. The LSP energy is then transferred into the QW such that the effective QW absorption is enhanced. Meanwhile, the application of the LSP local field to the QW may increase its absorption coefficient. Then, the coupling of the relaxed carriers with the SPPs enhances light emission that becomes stronger as temperature increases because of the increased carrier momentum.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.21.Fg Quantum wells
73.22.Lp Collective excitations
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Quantum dot solar cell tolerance to alpha-particle irradiation

Cory D. Cress, Seth M. Hubbard, Brian J. Landi, Ryne P. Raffaelle, and David M. Wilt

Appl. Phys. Lett. 91, 183108 (2007); http://dx.doi.org/10.1063/1.2803854 (3 pages) | Cited 13 times

Online Publication Date: 31 October 2007

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The effects of alpha-particle irradiation on an InAs quantum dot (QD) array and GaAs-based InAs QD solar cells were investigated. Using photoluminescence (PL) mapping, the PL intensity at 872 and 1120 nm, corresponding to bulk GaAs and InAs QD emissions, respectively, were measured for a five-layer InAs QD array which had a spatially varying total alpha-particle dose. The spectral response and normalized current-voltage parameters of the solar cells, measured as a function of alpha-particle fluence, were used to investigate the change in device performance between GaAs solar cells with and without InAs QDs.
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78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
84.60.Jt Photoelectric conversion
61.80.Jh Ion radiation effects

Reactive nanojets: Nanostructure-enhanced chemical reactions in a defected energetic crystal

Ken-ichi Nomura, Rajiv K. Kalia, Aiichiro Nakano, and Priya Vashishta

Appl. Phys. Lett. 91, 183109 (2007); http://dx.doi.org/10.1063/1.2804557 (3 pages) | Cited 6 times

Online Publication Date: 2 November 2007

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Nanofluidics of chemically reactive species has enormous technological potential and computational challenge arising from coupling quantum-mechanical accuracy with largescale fluid phenomena. Here, we report a million-atom reactive force field molecular dynamics simulation of shock initiation of an energetic crystal with a nanometer-scale void. The simulation reveals the formation of a nanojet which focuses into a narrow beam at the void. This, combined with the excitation of vibrational modes through enhanced intermolecular collisions by the free volume of the void, catalyzes chemical reactions that do not occur otherwise. We also observe a pinning-depinning transition of the shock wave front at the void at increased particle velocity and the resulting localization-delocalization transition of the vibrational energy.
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82.40.Fp Shock wave initiated reactions, high-pressure chemistry
81.16.Hc Catalytic methods
47.40.Nm Shock wave interactions and shock effects

Effects of molecular orientation on surface-plasmon-coupled emission patterns

Hoang Minh Hiep, Minoru Fujii, and Shinji Hayashi

Appl. Phys. Lett. 91, 183110 (2007); http://dx.doi.org/10.1063/1.2804563 (3 pages) | Cited 10 times

Online Publication Date: 2 November 2007

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We observed azimuthal distributions of surface-plasmon-coupled emission from thin layers of randomly oriented and oriented sexithiophene molecules deposited on 50-nm-thick Ag films. For the randomly oriented layer, we observed a uniform and isotropic cone of emission, showing that the surface plasmons are excited isotropically in all directions on the Ag surface. The emission pattern for the oriented layer exhibited a much stronger intensity along the direction of molecular orientation, showing that surface plasmons propagating parallel to the molecular orientation are excited most effectively. These results demonstrate that surface-plasmon-coupled emission provides a new simple approach to the determination of molecular orientation in thin films.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Qn Polymers; organic compounds

Self-organized nanostructures on atmospheric microplasma exposed surfaces

Davide Mariotti, Vladimir Švrček, and Dae-Gun Kim

Appl. Phys. Lett. 91, 183111 (2007); http://dx.doi.org/10.1063/1.2805191 (3 pages) | Cited 56 times

Online Publication Date: 2 November 2007

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We present here the observation of self-organized nanostructures on atmospheric microplasma exposed surfaces. In particular, we present the formation of self-aligned Mo-oxide nanoparticles, as well as the production of self-organized carbon-based connections between silicon nanocrystal micrograins and between Ag nanoparticles. The strong electromagnetic fields that are present at the processing surface play an important role in the self-organization process. This result represents an interesting phenomenon and suggests possible routes to promote and exploit self-organization for the production of nanostructured materials.
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81.07.Bc Nanocrystalline materials
81.05.Cy Elemental semiconductors
81.16.Dn Self-assembly
52.77.Dq Plasma-based ion implantation and deposition
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