Transport and magnetic properties of multiwall carbon nanotubes before and after bromination

Abstract

Bulk samples of oriented carbon nanotubes were prepared by electric arc evaporation of graphite in a helium environment. The temperature dependence of the conductivity alpha(T), as well as the temperature and field dependences of the magnetic susceptibility chi(T,B) and magnetoresistance rho(B, T), was measured for both the pristine and brominated samples. The pristine samples exhibit an anisotropy in the conductivity sigma(parallel to)(T)/sigma(perpendicular to)(T)>50, which disappears in the brominated samples. The chi(T,B) data were used to estimate the carrier concentration n(0) in the samples: n(0ini) similar to 3x10(10) cm(-2) for the pristine sample, and n(0Br) similar to 10(11) cm(-2) for the brominated sample. Estimation of the total carrier concentration n=n(e)+n(p) from the data on rho(B, T) yields n(ini) = 4x10(17) cm(-3) (or 1.3x10(10) cm(-2)) and n(Br) = 2x10(18) cm(-3) (or 6.7x10(10) cm(-2)). These estimates are in good agreement with one another and indicate an approximately fourfold increase in carrier concentration in samples after bromination. (C) 2002 MAIK "Nauka/Interperiodica".