TEMPERATURE-DEPENDENCE OF ELECTRIC-RESISTANCE AND MAGNETORESISTANCE OF PRESSED NANOCOMPOSITES OF MULTILAYER NANOTUBES WITH THE STRUCTURE OFNESTED CONES

Bulk samples of carbon multilayer nanotubes with the structure of nest ed cones (fishbone structure) suitable for transport measurements, wer e prepared by compressing under high pressure (similar to 25 kbar) a n anotube precursor synthesized through thermal decomposition of polyeth ylene catalyzed by nickel. The structure of the initial nanotube mater ial was studied using high-resolution transmission electron microscopy . In the low-temperature range (4.2-100 K) the electric resistance of the samples changes according to the law ln R-proportional to(T-0/T)(1 /3), where T-o similar to 7 K. The measured magnetoresistance is quadr atic in the magnetic field and linear in the reciprocal temperature. T he measurements have been interpreted in terms of two-dimensional vari able-range hopping conductivity. It is suggested that the space betwee n the inside and outside walls of nanotubes acts as a two-dimensional conducting medium. Estimates suggest a high value of the density of el ectron states at the Fermi level of about 5 x 10(21) eV(-1)cm(-3). (C) 1998 American Institute of Physics.