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2 Aug 2004

Volume 85, Issue 5, pp. 701-848

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 807 (2004); http://dx.doi.org/10.1063/1.1777817 (3 pages)

Henry J. Liu and Kyeongjae Cho
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A molecular dynamics study of round and flattened carbon nanotube structures

Henry J. Liu and Kyeongjae Cho

Appl. Phys. Lett. 85, 807 (2004); http://dx.doi.org/10.1063/1.1777817 (3 pages) | Cited 9 times

Online Publication Date: 27 July 2004

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Large diameter single wall carbon nanotubes exist with both round right cylinder and barbell-like flattened cross sections. Using an adaptive intermolecular reactive bond order potential, we examine the characteristics of both configurations by using molecular dynamics simulations. We then continue to examine the dynamical transition from the flattened to round state by charge injection. Predictions based on these simulations provide a basis for the design of active fluid transport devices, and nanoscale mechanical systems/motors.
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61.46.-w Structure of nanoscale materials

Field emission of carbon nanotubes grown on carbon cloth

S. H. Jo, D. Z. Wang, J. Y. Huang, W. Z. Li, K. Kempa, and Z. F. Ren

Appl. Phys. Lett. 85, 810 (2004); http://dx.doi.org/10.1063/1.1776330 (3 pages) | Cited 44 times

Online Publication Date: 27 July 2004

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Field emission from carbon nanotubes grown on carbon cloth has been studied. An extremely low electric field of less than 0.4 V∕μm is required to reach an emission current density of 1 mA∕cm2. This ultralow operating electric field of carbon nanotubes grown on carbon cloth is mainly due to a very high field enhancement factor of 1.882×104, which is the result of geometrical configuration of the carbon nanotubes and the substrate. In addition to the field enhancement, the highly disordered microstructure of carbon nanotubes grown on carbon cloth plays an important role to field emission. This unexpected result indicates that the roughness of the substrates on which carbon nanotubes grow is very important. This result also brings us significantly closer to practical applications such as highly efficient lamps, field emission displays, micro vacuum electron sources, etc.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.-w Structure of nanoscale materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.07.De Nanotubes
61.43.-j Disordered solids

Chiral and quantum size effects of single-wall carbon nanotubes on field emission

Shi-Dong Liang, N. Y. Huang, S. Z. Deng, and N. S. Xu

Appl. Phys. Lett. 85, 813 (2004); http://dx.doi.org/10.1063/1.1776337 (3 pages) | Cited 21 times

Online Publication Date: 27 July 2004

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The emission current of a single-wall carbon nanotube (SWNT) in field emission is studied by the tunneling theory with the tight-binding approach. The emission current is almost independent of the chiral angle of SWNT in low fields, but increases with increase of chiral angles in very high fields. We found a room-temperature quantum size effect of SWNT on field emission. As the diameters of SWNTs increase, the current densities decrease for metallic tubes, but increase for semiconducting tubes. When the diameters of SWNTs are larger than 2 nm the current densities of metallic and semiconducting tubes are very close. These chiral and quantum size effects are originated from the energy band structure of nanotubes.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.22.-f Electronic structure of nanoscale materials and related systems
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
61.46.-w Structure of nanoscale materials
73.40.Gk Tunneling
73.20.At Surface states, band structure, electron density of states

Fabrication and properties of nanoporous GaN films

Y. D. Wang, S. J. Chua, M. S. Sander, P. Chen, S. Tripathy, and C. G. Fonstad

Appl. Phys. Lett. 85, 816 (2004); http://dx.doi.org/10.1063/1.1774273 (3 pages) | Cited 31 times

Online Publication Date: 27 July 2004

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Nanopore arrays with pore diameters of approximately 75 nm were fabricated in GaN films by inductively coupled plasma etching using anodic aluminum oxide (AAO) films as etch masks. Nanoporous AAO films were formed on the GaN surface by evaporating an Al film onto a GaN epilayer and subsequently anodizing the aluminum. To minimize plasma-induced damage, the template was exposed to CF4-based plasma conditions. Scanning electron microscopy analysis shows that the diameter and the periodicity of the nanopores in the GaN were directly transferred from the original anodic alumina template. The pore diameter in the AAO film can be easily controlled by tuning the anodization conditions. Atomic force microscopy, photoluminescence, and micro-Raman techniques were employed to assess the etched GaN nanopore surface. This cost-effective, nonlithographic method to produce nano-patterned GaN templates is expected to be useful for growth and fabrication of nitride-based nanostructures and photonic band gap materials.
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81.05.Ea III-V semiconductors
81.05.Rm Porous materials; granular materials
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
61.43.Gt Powders, porous materials
78.55.Mb Porous materials
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
68.37.Ps Atomic force microscopy (AFM)
78.30.Fs III-V and II-VI semiconductors
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Characterizing quantum-dot blinking using noise power spectra

Matthew Pelton, David G. Grier, and Philippe Guyot-Sionnest

Appl. Phys. Lett. 85, 819 (2004); http://dx.doi.org/10.1063/1.1779356 (3 pages) | Cited 48 times

Online Publication Date: 27 July 2004

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Fluctuations in the fluorescence from macroscopic ensembles of colloidal semiconductor quantum dots have the spectral form of 1∕f noise. The measured power spectral density reflects the fluorescence intermittency of individual dots with power-law distributions of “on” and “off” times, and can thus serve as a simple method for characterizing such blinking behavior.
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78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
82.70.Dd Colloids
78.55.Hx Other solid inorganic materials

Acoustic phonon mode splitting behavior of an asymmetric y-branch three terminal junction

Wen-Xia Li, Ke-Qiu Chen, Wenhui Duan, Jian Wu, and Bing-Lin Gu

Appl. Phys. Lett. 85, 822 (2004); http://dx.doi.org/10.1063/1.1779339 (3 pages) | Cited 30 times

Online Publication Date: 27 July 2004

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The acoustic phonon transport through an asymmetric y-branch semiconductor quantum structure is investigated by use of the scattering-matrix method. It is found that the quantum structure exhibits mode-splitting behavior, resonant transmission, and the noninteger quantized thermal conductance at very low temperatures. The thermal transport behavior sensitively depends on the geometric configuration of the structure. Our work suggests that such a y-branch structure with specific structural parameters could be used as a splitter of phonon modes.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
63.20.K- Phonon interactions

A phonon depletion effect in ultrathin heterostructures with acoustically mismatched layers

Evgenii P. Pokatilov, Denis L. Nika, and Alexander A. Balandin

Appl. Phys. Lett. 85, 825 (2004); http://dx.doi.org/10.1063/1.1775033 (3 pages) | Cited 18 times

Online Publication Date: 27 July 2004

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We demonstrate theoretically that modification of the acoustic phonon spectrum in semiconductor heterostructures with large acoustic impedance mismatch between the core and cladding layers may lead to strong phonon depletion in the core layer. The latter is achieved if the heterostructure parameters are properly tuned, i.e., the structure thickness is in nanometer scale to ensure phonon quantization and the cladding layers are acoustically “softer” than the core layer. Using a numerical solution of the elasticity equation, we show that one can achieve conditions when almost all acoustic phonon modes are squeezed in the cladding layers with the exception of a small fraction of phonons with very small wave vectors (q⩽0.3 nm−1). The predicted phonon depletion effect in the core layer of the acoustically mismatched heterostructures may lead to increased carrier mobility in certain regions of the heterostructure as well as improved thermal management of heterostructure-based devices.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
68.35.Ja Surface and interface dynamics and vibrations

Self-assembled three-dimensional conducting network of single-wall carbon nanotubes

Graciela B. Blanchet, Shekhar Subramoney, R. K. Bailey, G. D. Jaycox, and C. Nuckolls

Appl. Phys. Lett. 85, 828 (2004); http://dx.doi.org/10.1063/1.1776619 (3 pages) | Cited 19 times

Online Publication Date: 27 July 2004

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We described here the self-assembling of a three-dimensional array of single-wall nanotubes (SWNTs). The distinctive choice of materials allowed for the self-assembly of SWNTs with low resistance conducting polymer links into a conducting network that when embedded into an insulating host shows no disruption of the conduction path. The ability to control network formation independently of the electrical properties of the host drastically changes the design of these conducting organic networks. Thus, enabling the tailoring of their electrical properties while addressing issues of film processability relevant for their application as printable conductors in organic electronic applications. These networks provide opportunities for applications in micro- and nanoelectronics.
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61.46.-w Structure of nanoscale materials
73.61.Wp Fullerenes and related materials
68.37.Lp Transmission electron microscopy (TEM)
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