TEMPERATURE-DEPENDENCE OF THE RESISTIVITY AND STRUCTURE OF CARBON NANOTUBE FILMS CONTAINING VARIOUS KINDS OF TUBULES

The temperature dependence of the resistivity is measured over a range of 4.2 to 300 K on carbon films containing multilayer nanotubes (MLTs) or single-layer nanotubes (SLTs) oriented perpendicular to the substrate. The structure of these films is examined by high-resolution electron microscopy. At low temperatures, the planar resistivity of all the films is well fit by the expression In rho proportional to [T-0/T](1/n), with n = 4 and T-0 similar to 10(6) K for the MLT films but with n = 2 and T-0 similar to 20 K for the films containing bundles of SLTs 0.71 nm in diameter. The data obtained are considered in terms of the variable-range hopping conductivity. The estimations made show a fairly high density of states at the Fermi level (similar to 10(21) eV(-1)cm(-3)) for the films containing SLTs. (C) 1995 American Institute of Physics.