30-01-2012, 02:24 PM
Carbon Nanotubes
[attachment=16834]
. Introduction
Carbon nanotubes (CNT) were discovered by Iijima [1] as elongated fullerenes in 1991. Since then research on growth, characterization and application development has exploded due to the unique electronic and extraordinary mechanical properties of CNTs. The CNT can be metallic or semiconducting and thus offers possibilities to create semiconductor–semiconductor and semiconductor–metal junctions useful in devices. The high tensile strength, Young's modulus and other mechanical properties hold promise for high strength composites for structural applications.
. Structure and Properties of Carbon Nanotubes
A single-wall carbon nanotube (SWCNT) is best described as a rolled-up tubular shell of graphene sheet [Fig.1a] which is made of benzene-type hexagonal rings of carbon atoms [2]. The body of the tubular shell is thus mainly made of hexagonal rings (in a sheet) of carbon atoms, whereas the ends are capped by half-dome shaped half-fullerene molecules. The natural curvature in the side-walls is due to the rolling of the sheet into the tubular structure, whereas the curvature in the end caps is due to the presence of topological (pentagonal rings) defects in the otherwise hexagonal structure of the underlying lattice.
Computational Modeling and Simulation
The structural, electronic, mechanical, and thermal properties of interacting, bulk condensed matter systems were studied in the earlier days with analytical approximation methods for infinite systems. Numerical simulations of the finite sample systems have become more common recently due to the availability of powerful computers. Molecular dynamics (MD) refers to an approach where the motion of atoms or molecules is treated in approximate finite difference equations of Newtonian mechanics
. Nanomechanics of Nanotubes and Composites
SWCNTs and MWCNTs have been shown to have exceptionally strong and stiff mechanical characteristics along the axis of the tube, and very flexible characteristics along normal to the axis of the tube [19-21]. For axial deformations, the Young's modulus of the SWCNTs can reach beyond 1 TPa, and the yield strength can be as large as 120 GPa. The initial investigations, using classical molecular dynamics simulations with Tersoff-Brenner potential, showed that the tubes are extremely stiff under axial compression, and that the system remains within elastic limit even for very large deformations (up to 15% strain) [9,19].
Molecular Electronics with Nanotube Junctions
The possibility of using carbon in place of silicon in the field of nanoelectronics has generated considerable enthusiasm. The metallic and semiconducting behavior as well as the electronic transport through individual single-wall nanotubes have been extensively investigated. The main thrust has been to see if the individual (or bundles of) nanotubes could be used as quantum molecular wires for interconnects in future computer systems. The ballistic electron transport through individual nanotubes has been supported by many independent studies, and considered to be one of the reason that nanotubes exhibit high current density as compared to other materials at similar nanoscale [33].
[attachment=16834]
. Introduction
Carbon nanotubes (CNT) were discovered by Iijima [1] as elongated fullerenes in 1991. Since then research on growth, characterization and application development has exploded due to the unique electronic and extraordinary mechanical properties of CNTs. The CNT can be metallic or semiconducting and thus offers possibilities to create semiconductor–semiconductor and semiconductor–metal junctions useful in devices. The high tensile strength, Young's modulus and other mechanical properties hold promise for high strength composites for structural applications.
. Structure and Properties of Carbon Nanotubes
A single-wall carbon nanotube (SWCNT) is best described as a rolled-up tubular shell of graphene sheet [Fig.1a] which is made of benzene-type hexagonal rings of carbon atoms [2]. The body of the tubular shell is thus mainly made of hexagonal rings (in a sheet) of carbon atoms, whereas the ends are capped by half-dome shaped half-fullerene molecules. The natural curvature in the side-walls is due to the rolling of the sheet into the tubular structure, whereas the curvature in the end caps is due to the presence of topological (pentagonal rings) defects in the otherwise hexagonal structure of the underlying lattice.
Computational Modeling and Simulation
The structural, electronic, mechanical, and thermal properties of interacting, bulk condensed matter systems were studied in the earlier days with analytical approximation methods for infinite systems. Numerical simulations of the finite sample systems have become more common recently due to the availability of powerful computers. Molecular dynamics (MD) refers to an approach where the motion of atoms or molecules is treated in approximate finite difference equations of Newtonian mechanics
. Nanomechanics of Nanotubes and Composites
SWCNTs and MWCNTs have been shown to have exceptionally strong and stiff mechanical characteristics along the axis of the tube, and very flexible characteristics along normal to the axis of the tube [19-21]. For axial deformations, the Young's modulus of the SWCNTs can reach beyond 1 TPa, and the yield strength can be as large as 120 GPa. The initial investigations, using classical molecular dynamics simulations with Tersoff-Brenner potential, showed that the tubes are extremely stiff under axial compression, and that the system remains within elastic limit even for very large deformations (up to 15% strain) [9,19].
Molecular Electronics with Nanotube Junctions
The possibility of using carbon in place of silicon in the field of nanoelectronics has generated considerable enthusiasm. The metallic and semiconducting behavior as well as the electronic transport through individual single-wall nanotubes have been extensively investigated. The main thrust has been to see if the individual (or bundles of) nanotubes could be used as quantum molecular wires for interconnects in future computer systems. The ballistic electron transport through individual nanotubes has been supported by many independent studies, and considered to be one of the reason that nanotubes exhibit high current density as compared to other materials at similar nanoscale [33].
