Electron transport in deformed carbon nanotubes

Carbon nanotubes are a material system of increasing technological importance with superb mechanical and electrical properties. It is well known that depending on details of atomic structure, nanotubes may be electrically conducting, semiconducting, or insulating, so deformation is believed to have strong effects on nanotube electrical properties. In this paper, a combination of continuum, empirical atomistic, and quantum atomistic modeling methods are used to demonstrate the effect of homogeneous deformation-tension, compression, and torsion-on the electrical conductance and current versus voltage (I(V)) characteristics of a variety of single wall carbon nanotubes. The modeling methods are used in a coupled and efficient multiscale formulation that allows for computationally inexpensive analysis of a wide range of deformed nanotube configurations. Several important observations on the connection between mechanical and electrical behavior are made based on the transport-calculations. First, based on the I(V) characteristics, electron transport in the nanotubes is evidently fairly insensitive to homogeneous deformation, though in some cases there is a moderate strain effect at either relatively low or high applied voltages. In particular, the conductance, or dI/dV behavior, shows, interesting features for nanotubes deformed in torsion over small ranges of applied bias. Second, based on a survey of a range of nanotube geometries, the primary determining feature of the I(V) characteristics is simply the number of conduction electrons available per unit length of nanotube. In other words, when the current is normalized by the number of free electrons on the tube cross section per unit length, which itself is affected by extensional (but not torsional) strain, the I(V) curves of all single walled carbon nanotubes are nearly co-linear.