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3 Dec 2001

Volume 79, Issue 23, pp. 3749-3889

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Temperature-induced change from p to n conduction in metallofullerene nanotube peapods

P. W. Chiu, G. Gu, G. T. Kim, G. Philipp, S. Roth, S. F. Yang, and S. Yang

Appl. Phys. Lett. 79, 3845 (2001); http://dx.doi.org/10.1063/1.1415770 (3 pages) | Cited 22 times

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Metallofullerene nanotube peapods were prepared by introducing DyC82 into the interior space of single-walled carbon nanotubes. Transport measurements show that the DyC82 molecules function as electron donors and transfer charge to the carbon nanotube host. The amount of charge transferred varies with the temperature. At room temperature, the doped nanotube shows p-type behavior as seen from the response to a back gate. As the temperature decreases, the conductance becomes n type and at T<215 K metallic behavior is observed, indicating the degenerate state by doping. Below about 75 K, single-electron charging phenomena dominate the transport and show irregular Coulomb blockade oscillation, implying that the insertion of DyC82 splits the tube into a series of several quantum dots. © 2001 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
72.80.Rj Fullerenes and related materials
72.60.+g Mixed conductivity and conductivity transitions
73.22.-f Electronic structure of nanoscale materials and related systems

Alignment of self-assembled magnetic nanostructures: Co dot chains and stripes on grooved Ru(0001)

Chengtao Yu, Dongqi Li, J. Pearson, and S. D. Bader

Appl. Phys. Lett. 79, 3848 (2001); http://dx.doi.org/10.1063/1.1421624 (3 pages) | Cited 21 times

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We have deposited 0–60 nm Co with a wedge-shaped thickness gradient onto a grooved Ru(0001) substrate by means of molecular-beam epitaxy at 350 °C. The resultant epitaxial Co island (dot) structure was characterized ex situ using atomic- and magnetic-force microscopy and the magneto-optic Kerr effect. The dots self-assemble with ∼ 70–500 nm diameter, ∼ 1–7 nm height, and align into linear chains along the grooves with spacings in the chains to decrease from ∼ 1 μm until they form continuous stripes, depending on dosage and groove structure. The dots have magnetic single domains with in-plane easy axes. © 2001 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys
81.07.Ta Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.70.Ak Magnetic properties of monolayers and thin films

Tunneling current through a quantum dot array

David M.-T. Kuo, G. Y. Guo, and Yia-Chung Chang

Appl. Phys. Lett. 79, 3851 (2001); http://dx.doi.org/10.1063/1.1420775 (3 pages) | Cited 12 times

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The tunneling current through a quantum dot array (QDA) is studied theoretically. Strong electron correlation effect is taken into account in the QDA in which the quantum dots provide a strong three-dimensional confinement effect. A mixed Hubbard and Anderson model is used to simulate the system. It is found that Coulomb charging splits the band resulting from interdot coupling into two subbands. The tunneling current is thus influenced significantly by both Coulomb charging and interdot coupling. © 2001 American Institute of Physics.
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73.21.La Quantum dots
73.63.Kv Quantum dots
73.23.Hk Coulomb blockade; single-electron tunneling

Faceting evolution during self-assembling of InAs/InP quantum wires

H. R. Gutiérrez, M. A. Cotta, and M. M. G. de Carvalho

Appl. Phys. Lett. 79, 3854 (2001); http://dx.doi.org/10.1063/1.1424476 (3 pages) | Cited 26 times

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The self-assembling of InAs quantum wires on (001) InP substrates during chemical beam epitaxy has been studied. The samples were characterized by reflection high-energy electron diffraction (RHEED), atomic force microscopy, and high-resolution transmission electron microscopy (HRTEM). By monitoring the RHEED chevron structures along the [1math0] direction, we studied the facets formation during the initial states of InAs growth. The facets angles measured by HRTEM are in perfect agreement with the angles between chevron streaks. A time dependence of the chevron streaks angles is reported and correlated to the wire formation. These results can be interpreted using nonequilibrium models existing in literature. © 2001 American Institute of Physics.
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68.65.La Quantum wires (patterned in quantum wells)
81.07.Vb Quantum wires
81.16.Dn Self-assembly
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Rh Phase transitions and critical phenomena
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Lp Transmission electron microscopy (TEM)
68.37.Ps Atomic force microscopy (AFM)
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Controlled striped phase formation on ultraflat Si(001) surfaces during diborane exposure

J.-F. Nielsen, J. P. Pelz, H. Hibino, C.-W. Hu, I. S. T. Tsong, and J. Kouvetakis

Appl. Phys. Lett. 79, 3857 (2001); http://dx.doi.org/10.1063/1.1421084 (3 pages) | Cited 2 times

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We have used low-energy electron microscopy to study spontaneous step formation in “striped” domains on ultraflat Si(001)-(2×1) surfaces during B2H6 exposure at elevated temperatures. We show that the size and arrangement of striped domains are kinetically limited, and propose that the limiting factor is the supply of diffusing Si surface adatoms. By adding controlled amounts of extra Si to ultraflat terraces, it is possible to foster the formation of very large (>5 μm) single-domain striped regions with adjustable stripe widths. © 2001 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Nq Low energy electron microscopy (LEEM)
68.35.Md Surface thermodynamics, surface energies
68.35.Fx Diffusion; interface formation

Dipole-assisted self-assembly of light-emitting p-nP needles on mica

F. Balzer and H.-G. Rubahn

Appl. Phys. Lett. 79, 3860 (2001); http://dx.doi.org/10.1063/1.1424071 (3 pages) | Cited 74 times

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We report on dipole-assisted, self-assembled formation of p-6P and p-5P needles on cleaved and heated mica (0001) surfaces. Low-energy electron diffraction (LEED) reveals that the needles are single crystalline with the (1mathmath) face parallel to the surface, consisting of parallel stacks of laying molecules oriented along the direction of microscopic dipoles on the mica surface. They have submicrometer cross-sectional dimensions and lengths as large as millimeters. Moreover, due to the strong dipole confinement of individual molecules, the needles form large domains with parallel oriented entities. A pronounced optical dichroism agrees with the findings from LEED. © 2001 American Institute of Physics.
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68.43.Hn Structure of assemblies of adsorbates (two- and three-dimensional clustering)

Adsorption of NH3 and NO2 molecules on carbon nanotubes

Hyunju Chang, Jae Do Lee, Seung Mi Lee, and Young Hee Lee

Appl. Phys. Lett. 79, 3863 (2001); http://dx.doi.org/10.1063/1.1424069 (3 pages) | Cited 123 times

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Adsorption of NH3 and NO2 molecules on semiconducting single-walled carbon nanotubes is investigated using density functional theory. Both NH3 and NO2 molecules are found to bind to carbon nanotubes via physisorption. Electron charge transfer is found to be a major mechanism determining the conductivity change in carbon nanotubes upon exposure to NH3 and NO2 molecules. The calculated density of states is also considered to elucidate the differences in the NO2 and NH3 gas detection mechanism of carbon nanotubes. © 2001 American Institute of Physics.
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68.43.Fg Adsorbate structure (binding sites, geometry)
68.43.Mn Adsorption kinetics
73.20.Hb Impurity and defect levels; energy states of adsorbed species
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Creation of nanodiamonds by single impacts of highly charged ions upon graphite

T. Meguro, A. Hida, M. Suzuki, Y. Koguchi, H. Takai, Y. Yamamoto, K. Maeda, and Y. Aoyagi

Appl. Phys. Lett. 79, 3866 (2001); http://dx.doi.org/10.1063/1.1424047 (3 pages) | Cited 26 times

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The local modification of the electronic states of highly oriented pyrolytic graphite (HOPG) surfaces using highly charged ion (HCI) irradiation has been demonstrated as a promising technique in the design of nanoscale materials. The high potential energy of HCI and subsequent surface treatment by either electron injection from a scanning tunneling microscopy (STM) tip or by He–Cd laser irradiation provide a localized transition from sp2 to sp3 hybridization in HOPG, resulting in the formation of nanoscale diamond-like structures (nanodiamond). It is of interest that a single impact of HCI creates one nanodiamond structure without inducing any defects in the area surrounding the impact region, suggesting potential applications of HCI in nanoscale material processing. © 2001 American Institute of Physics.
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81.05.U- Carbon/carbon-based materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
73.20.At Surface states, band structure, electron density of states
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