skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Small Si clusters on surfaces of carbon nanotubes

Abstract

Structures of small Si clusters, Sin, on surfaces of carbon nanotubes have been studied by molecular dynamics simulation. We show that the lowest-energy structures of Sin are three-dimensional clusters rather than thin Si sheets covering the surface of a nanotube. As n increases from 10 to 30, Sin undergoes structural transitions from a tent-like structure (with nanotube surface as its base) to a cage-like structure (without interior atoms) and further to a spherical compact structure (with interior atoms). Our results are different from the structures of small Si clusters found in a free space without Si-nanotube interaction.

Authors:
 [1];  [2];  [3];  [3]
  1. unknown
  2. Xiangtan University, Xiangtan Hunan, China
  3. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Laboratory Directed Research and Development (LDRD) Program
OSTI Identifier:
931711
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 100; Journal Issue: 12
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 77 NANOSCIENCE AND NANOTECHNOLOGY; CARBON; NANOTUBES; SILICON; MOLECULAR CLUSTERS; SURFACE PROPERTIES; MOLECULAR DYNAMICS METHOD; MORPHOLOGICAL CHANGES; silicon; nanoparticle; carbon nanotube

Citation Formats

Meng, Lijun, Zhang, Kaiwang, Stocks, George Malcolm, and Zhong, Jianxin. Small Si clusters on surfaces of carbon nanotubes. United States: N. p., 2006. Web. doi:10.1063/1.2405133.
Meng, Lijun, Zhang, Kaiwang, Stocks, George Malcolm, & Zhong, Jianxin. Small Si clusters on surfaces of carbon nanotubes. United States. doi:10.1063/1.2405133.
Meng, Lijun, Zhang, Kaiwang, Stocks, George Malcolm, and Zhong, Jianxin. Sun . "Small Si clusters on surfaces of carbon nanotubes". United States. doi:10.1063/1.2405133.
@article{osti_931711,
title = {Small Si clusters on surfaces of carbon nanotubes},
author = {Meng, Lijun and Zhang, Kaiwang and Stocks, George Malcolm and Zhong, Jianxin},
abstractNote = {Structures of small Si clusters, Sin, on surfaces of carbon nanotubes have been studied by molecular dynamics simulation. We show that the lowest-energy structures of Sin are three-dimensional clusters rather than thin Si sheets covering the surface of a nanotube. As n increases from 10 to 30, Sin undergoes structural transitions from a tent-like structure (with nanotube surface as its base) to a cage-like structure (without interior atoms) and further to a spherical compact structure (with interior atoms). Our results are different from the structures of small Si clusters found in a free space without Si-nanotube interaction.},
doi = {10.1063/1.2405133},
journal = {Journal of Applied Physics},
number = 12,
volume = 100,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • The electrostrictive response of small carbon clusters, hydrocarbon molecules, and carbon nanotubes is investigated using the density functional theory. For ringlike carbon clusters, one can get insight on the deformations induced by an electric field from a simple two-dimensional model in which the positive charge of the carbon ions is smeared out in a circular homogeneous line of charge and the electronic density is calculated for a constant applied electric field within a two-dimensional Thomas-Fermi method. According to the Hellmann-Feynman theorem, this model predicts, for fields of about 1 V/A ring , only a small elongation of the ring clustersmore » in the direction of the electric field. Full three-dimensional density functional calculations with an external electric field show similar small deformations in the ring carbon clusters compared to the simple model. The saturated benzene and phenanthrene hydrocarbon molecules do not experience any deformation, even under the action of relatively intense (1 V/A ring ) electric fields. In contrast, finite carbon nanotubes experience larger elongations ({approx}2.9%) induced by relatively weak (0.1 V/A ring ) applied electric fields. Both C-C bond length elongation and the deformation of the honeycomb structure contribute equally to the nanotube elongation. The effect of the electric field in hydrogen terminated nanotubes is reduced with respect to the nanotubes with dangling bonds in the edges.« less
  • We report total-energy electronic-structure calculations based on the density-functional theory that provide stable adsorption sites, structural characteristics, and energy bands of carbon nanotubes (CNTs) adsorbed on the Si(001) stepped surfaces. We choose (5,5), (9,9), and (13,13) armchair CNTs with the diameters of 6.8 Å, 12.2 Å, and 17.6 Å, respectively, as representatives of CNTs and explore all the possible adsorption sites either on the terrace or at step edges. We find that the (9,9) CNT is most favorably adsorbed at the edge of the double-layer step D{sub B} along the 〈110〉 direction, whereas the (5,5) and (13,13) CNTs favor the terrace site wheremore » the CNTs are perpendicular to the Si dimer rows. This finding is indicative of the diameter-selective self-organized alignment of CNTs by exploiting the Si surface steps along the particular direction. We also find that the electronic structure of each CNT is modified upon adsorption depending on the adsorption site and the diameter of the CNTs. In particular, the (9,9) CNT at the most stable step edge site becomes semiconducting and the resultant valence and conduction bands exhibit nearly linear dispersion with the effective mass of 0.085 m{sub 0} (m{sub 0}: bare electron mass), preserving the characteristics of the Dirac electrons. We also find that the flat bands appear near the Fermi level (E{sub F}) when the (13,13) CNT is adsorbed at the metastable D{sub B} step edge, inferring that spin polarization is possible for the CNT on the Si(001) stepped surface.« less
  • Reactions of silicon atoms and small clusters with carbon monoxide molecules in solid argon have been studied using matrix isolation infrared absorption spectroscopy. In addition to the previously reported SiCO monocarbonyl, Si{sub 2}(CO){sub 2} and Si{sub n}CO (n=2-5) carbonyl molecules were formed spontaneously on annealing and were characterized on the basis of isotopic substitution and theoretical calculations. It was found that Si{sub 2}CO, Si{sub 3}CO, and Si{sub 5}CO are bridge-bonded carbonyl compounds, whereas Si{sub 4}CO is a terminal-bonded carbonyl molecule. The Si{sub 2}(CO){sub 2} and Si{sub 3}CO molecules photochemically rearranged to the more stable c-Si{sub 2}({mu}-O)({mu}-CCO) and c-Si{sub 2}({mu}-O) ({mu}-CSi)more » isomers where Si{sub 2} is inserted into the CO triple bond.« less
  • Thermal and diffusion properties of hot gas around a dc arc discharge under a gravity-free condition are investigated using a jet plane in order to improve the arc production of carbon clusters. Spherically symmetric temperature distribution of He gas around the arc plasma and monotonic slow expansion of the high-temperature region are observed. By means of the passive-type Mie scattering method, random slow diffusion of carbon clusters around the arc plasma is clearly observed under the gravity-free condition. This indicates that carbon clusters including single-walled carbon nanotubes are synthesized around the arc plasma where the He temperature is higher thanmore » 1000 K. It is confirmed that large bundles of fatter single-walled carbon nanotubes are produced under the gravity-free condition.« less
  • Direct growth of carbon nanotubes (CNTs) on silicon is of great importance for their potential exploitation in the semiconductor industry. In this article we investigate the chemical vapor deposition growth of CNTs on Si substrates from ethylene precursor using an iron catalyst. We observe that CNTs are produced only at temperatures between 830 and 980 deg. C, and within this narrow temperature window CNT yield initially increases with temperature to reach a maximum around 900 deg. C and then declines. While the requirement of a minimum temperature to initiate CNT growth can be understood by considering the minimum energy necessarymore » to activate the catalyst particles, characterization of the as-grown CNTs by atomic force microscopy and x-ray photoelectron spectroscopy reveals that a loss of catalyst is responsible for the observed decline in CNT yield above 900 deg. C. However, unlike some previous reports suggesting surface silicide formation as the mechanism for catalyst loss, we find that either subsurface diffusion or evaporation is the mechanism for the loss of catalyst material in the current study.« less