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23 Dec 2002

Volume 81, Issue 26, pp. 4895-5074

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Microstructure and field emission properties of coral-like carbon nanotubes

N. G. Shang, C. P. Li, W. K. Wong, C. S. Lee, I. Bello, and S. T. Lee

Appl. Phys. Lett. 81, 5024 (2002); http://dx.doi.org/10.1063/1.1527992 (3 pages) | Cited 14 times

Online Publication Date: 17 December 2002

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Coral-like carbon nanotubes (CNTs) have been synthesized by using chemical vapor deposition. Unlike conventional CNTs, the as-deposited CNT consisted of a high density of interlaced graphitic nanoflakes of about 5 nm in thickness. The CNTs had a bamboo-like internal structure with their outer walls consisting of many open graphite layers, and the nanoflakes stemming from the “bamboo knots.” The growth mechanism of CNTs was discussed. The field emission characteristics of CNT films showed a turn-on field as low as 4 V/μm. This special CNT might extend mechanical and electronic properties and applications of the CNTs. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.De Nanotubes
79.70.+q Field emission, ionization, evaporation, and desorption
68.37.Lp Transmission electron microscopy (TEM)

Electron-stimulated hydrogen desorption from diamond surfaces and its influence on the low-pressure synthesis of diamond

C. Goeden and G. Dollinger

Appl. Phys. Lett. 81, 5027 (2002); http://dx.doi.org/10.1063/1.1526460 (3 pages) | Cited 4 times

Online Publication Date: 17 December 2002

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A total cross section σD = (5±2.6)×10−18 cm2 is measured for electron-stimulated desorption (ESD) of deuterium from a boron-doped, deuterated diamond(100) surface at 5 eV incident electron energy. This large ESD cross section means a significant contribution of ESD to hydrogen abstraction reactions in microwave-driven chemical vapor deposition of diamond. The ESD cross section decreases when changing to a nitrogen-doped diamond. This change is suggested to be the reason for the reported influence of small concentrations of nitrogen or boron added to the process gas on diamond growth. © 2002 American Institute of Physics.
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68.43.Rs Electron stimulated desorption
81.05.U- Carbon/carbon-based materials
79.20.La Photon- and electron-stimulated desorption

Enhancing the resolution of scanning near-field optical microscopy by a metal tip grown on an aperture probe

Heinrich G. Frey, Fritz Keilmann, Armin Kriele, and Reinhard Guckenberger

Appl. Phys. Lett. 81, 5030 (2002); http://dx.doi.org/10.1063/1.1530736 (3 pages) | Cited 66 times

Online Publication Date: 17 December 2002

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We show improvement of the optical and topographical resolution of scanning near-field optical microscopy by introducing a “tip-on-aperture” probe, a metallic tip formed on the aperture of a conventional fiber probe. The tip concentrates the light passing through the aperture. Thus the advantages of aperture and apertureless scanning near-field optical microscopy are combined. Tips are grown by electron beam deposition and then covered with metal. Fluorescent beads are imaged with a resolution down to 25 nm (full width at half maximum) in the optical signal. The near-field appears strongly localized within 5 nm in z direction, thus promising even higher resolution with sharper tips. © 2002 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
68.37.Uv Near-field scanning microscopy and spectroscopy

Vacancy clustering model for Ti non-steady-state radiation-enhanced diffusion in MgO(100)

M. Lu, C. Lupu, and J. W. Rabalais

Appl. Phys. Lett. 81, 5033 (2002); http://dx.doi.org/10.1063/1.1531829 (3 pages) | Cited 4 times

Online Publication Date: 17 December 2002

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Ti diffusion in MgO(100) prebombarded by Ar+, Cl+, and Cr+ has been studied by secondary ion mass spectroscopy under conditions for non-steady-state radiation-enhanced diffusion. The Ti diffusion behaviors of these samples are different, although the ballistic behaviors of the implanting ions are similar. For short annealing periods, the Ti diffusion enhancements follow the order Cr+>Ar+>Cl+, while for long annealing periods the order is Cl+>Ar+>Cr+. A model based on a vacancy clustering mechanism during thermal relaxation of the energetic cascade is proposed to explain these trends. © 2002 American Institute of Physics.
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66.30.J- Diffusion of impurities
61.72.J- Point defects and defect clusters
61.80.Jh Ion radiation effects
61.82.Ms Insulators
61.72.S- Impurities in crystals
61.72.up Other materials

Self-organized ZnO quantum dots on SiO2/Si substrates by metalorganic chemical vapor deposition

Sang-Woo Kim, Shizuo Fujita, and Shigeo Fujita

Appl. Phys. Lett. 81, 5036 (2002); http://dx.doi.org/10.1063/1.1527690 (3 pages) | Cited 65 times

Online Publication Date: 17 December 2002

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ZnO quantum dots (QDs) were fabricated on SiO2/Si substrates by metalorganic chemical vapor deposition. The densities and sizes of dots were investigated by atomic force microscopy. Photoluminescence at 10 K showed the broad spectra with band tails up to about 3.55 and 3.65 eV for the as-grown and the annealed ZnO QDs, respectively, which were located at the higher energy with respect to the free exciton emission of the ZnO thin film located at about 3.377 eV. These results indicate that the broad emission band results from the quantum size effect, reflecting the dot size inhomogeneity. © 2002 American Institute of Physics.
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81.07.Ta Quantum dots
78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
78.55.Et II-VI semiconductors
68.37.Ps Atomic force microscopy (AFM)
71.35.Lk Collective effects (Bose effects, phase space filling, and excitonic phase transitions)

Colloidal particle foams: Templates for Au nanowire networks?

J. N. O’Shea, M. A. Phillips, M. D. R. Taylor, P. Moriarty, M. Brust, and V. R. Dhanak

Appl. Phys. Lett. 81, 5039 (2002); http://dx.doi.org/10.1063/1.1526924 (3 pages) | Cited 9 times

Online Publication Date: 17 December 2002

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Spin coating a dilute solution of thiol-passivated Au nanoparticles onto silicon produces nanostructured cellular networks. Photoemission measurements, coupled with atomic force microscopy imaging and a statistical crystallography analysis, show that although annealing in the 500–600 K range removes the thiol surfactants surrounding the nanoparticles, the cellular morphology of the nanocrystal foam is preserved following annealing. Thus, self-assembled nanocrystal arrays may be exploited as templates for (bare) Au nanostructures on Si. Although appreciable particle diffusion during annealing does not occur, significant sintering of Au nanocrystals within the cellular network branches is observed. © 2002 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
81.07.Vb Quantum wires
81.05.Bx Metals, semimetals, and alloys
81.16.Dn Self-assembly
61.46.-w Structure of nanoscale materials
82.70.Dd Colloids
61.72.Cc Kinetics of defect formation and annealing
82.70.Rr Aerosols and foams

Charge imaging and manipulation using carbon nanotube probes

S.-D. Tzeng, C.-L. Wu, Y.-C. You, T. T. Chen, S. Gwo, and H. Tokumoto

Appl. Phys. Lett. 81, 5042 (2002); http://dx.doi.org/10.1063/1.1530377 (3 pages) | Cited 14 times

Online Publication Date: 17 December 2002

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Due to their high aspect ratio, well-defined cylindrical structure, and good electrical conductivity, carbon nanotubes (CNTs) are ideal probes for “true” local imaging of electric domain structures at the nanoscale. By performing force–distance measurements and tip-shape profiling with a uniformly charged oxide square, we clearly demonstrate the local nature of the CNT tip for electrostatic force microscopy. We show that CNTs can be used to probe long-range electrostatic forces with a lateral resolution better than 5 nm. © 2002 American Institute of Physics.
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07.79.Lh Atomic force microscopes
85.35.Kt Nanotube devices
68.37.Ps Atomic force microscopy (AFM)

Reversible adsorption-enhanced quantum confinement in semiconductor quantum dots

Shaibal K. Sarkar, Nirmala Chandrasekharan, Sasha Gorer, and Gary Hodes

Appl. Phys. Lett. 81, 5045 (2002); http://dx.doi.org/10.1063/1.1532109 (3 pages) | Cited 17 times

Online Publication Date: 17 December 2002

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See Also: Publisher's Note

Show Abstract
Semiconductor quantum dots possess two important properties: Size-dependent increase in band gap (size quantization) and a very high surface-to-volume ratio. We show that cyanide adsorption on this high surface further increases the size quantization in films of CdSe and CdS quantum dots and that removal of the cyanide reverses this effect. This effect is explained by increased localization due to compression of the electron wave function in the dots by the strongly adsorbed [on both Cd and Se(S)] negatively charged cyanide. © 2002 American Institute of Physics.
Show PACS
73.21.La Quantum dots
81.07.Ta Quantum dots
73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
78.67.Hc Quantum dots

Field emission from MoO3 nanobelts

Y. B. Li, Y. Bando, D. Golberg, and K. Kurashima

Appl. Phys. Lett. 81, 5048 (2002); http://dx.doi.org/10.1063/1.1532104 (3 pages) | Cited 102 times

Online Publication Date: 17 December 2002

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Single-crystalline MoO3 nanobelts having an orthorhombic structure were prepared on a Si wafer via heating a Mo foil in air. The nanobelts were 50–300 nm wide and tens of nanometers thick. The nanobelt lengths lie in the [001] direction. Field-emission measurements showed that the threshold field decreased with the anode–sample separation increasing. Typically, a threshold field of 12.9 V/μm was determined at a spacing of 80 μm. The nanobelts exhibited a sharp increase in emission current density near the threshold field and, thus, reached a high current density at a relatively low field. Emission from both sharp corners and edges of the nanobelts is assumed to contribute to the high emission current. The high-current emission paired with high stability indicates that the prepared MoO3 nanobelt films are excellent field emitters. © 2002 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.16.-c Methods of micro- and nanofabrication and processing
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.A- Nucleation and growth

GaN nanorods coated with pure BN

Wei-Qiang Han and A. Zettl

Appl. Phys. Lett. 81, 5051 (2002); http://dx.doi.org/10.1063/1.1531836 (3 pages) | Cited 29 times

Online Publication Date: 17 December 2002

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We report a method to efficiently synthesize gallium nitride (GaN) nanorods coated with insulating boron nitride (BN) layers. The GaN core is crystalline (with either a cubic zincblende or hexagonal wurtzite structure) and has diameters ranging from 10 to 85 nm and lengths up to 60 μm. The outer encapsulating BN shells with typical thicknesses less than 5 nm extend fully over, and adhere well to, the entire nanorod surface. © 2002 American Institute of Physics.
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81.07.De Nanotubes
61.46.-w Structure of nanoscale materials
81.16.Be Chemical synthesis methods
81.16.Hc Catalytic methods

Charge injection in individual silicon nanoparticles deposited on a conductive substrate

T. Mélin, D. Deresmes, and D. Stiévenard

Appl. Phys. Lett. 81, 5054 (2002); http://dx.doi.org/10.1063/1.1532110 (3 pages) | Cited 27 times

Online Publication Date: 17 December 2002

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We report on charge injection in individual silicon nanoparticles deposited on conductive substrates. Charges are injected using a metal-plated atomic force microscope tip, and detected by electric force microscopy (EFM). Due to the screening efficiency of the conductive substrate, up to ∼200 positive or negative charges can be stored at moderate (<10 V) tip–substrate injection voltage in ∼40 nm high nanoparticles, with discharging time constants of a few minutes. We propose an analytical model in the plane-capacitor approximation to estimate the nanoparticle charge from EFM data. It falls in quantitative agreement with numerical calculations using realistic tip/nanoparticle/substrate geometries. © 2002 American Institute of Physics.
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73.40.-c Electronic transport in interface structures
85.35.-p Nanoelectronic devices
73.63.Bd Nanocrystalline materials
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