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

Bulk samples of oriented carbon nanotubes were prepared by electric arc evaporation of graphite in a helium environment. The temperature dependence of the conductivity σ( T ), as well as the temperature and field dependences of the magnetic susceptibility χ( T , B ) and magnetoresistance ρ( B , T ), was measured for both the pristine and brominated samples. The pristine samples exhibit an anisotropy in the conductivity σ ∥ ( T )/σ ⊥ >50, which disappears in the brominated samples. The χ( T , B ) data were used to estimate the carrier concentration n 0 in the samples: n 0 ini ∼3×10 10 cm −2 for the pristine sample, and n 0Br ∼10 11 cm —2 for the brominated sample. Estimation of the total carrier concentration n = n e + n p from the data on ρ( B , T ) yields n ini =4×10 17 cm −3 (or 1.3×10 10 cm −2 ) and n Br =2×10 18 cm −3 (or 6.7×10 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.