Influence of surface layer conditions of multiwall carbon nanotubes on their electrophysical properties

We have investigated temperature sigma(T) and magnetic field sigma(B) dependences of the conductivity of multiwalled carbon nanotubes (MWNTs) with different average outer diameter (d) over bar and composite materials on the bases of these MWNTs in dielectric polymethyl methacrylate matrix (PMMA). It was shown that the percolation threshold of the electrical conductance for MWNT/PMMA composites lies in the range of concentration of MWNTs lower than 0.5 wt.%. From the joint analysis of sigma(T) and sigma(H) we have found that quantum corrections to the conductivity for interaction electrons is dominated in MWNTs with average outer diameters (d) over bar similar to 23 nm and MWNT/PMMA composite materials. We determined the constant of electron-electron interaction lambda from quantum correction to sigma(T) and sigma(H). In the result we have found that lambda depends on the concentration of MWNTs in MWNT/PMMA materials. This fact demonstrates that the interaction of the dielectric material of PMMA with surface atoms of MWNTs leads to the change of the lambda in MWNTs. For MWNTs with average outer diameters (d) over bar <= 13 nm and for composite on the base of these MWNTs we have observed the domination of one dimensional variable range hopping conductivity (VRHC) at a temperature below 20 K. From the data of VRHC we estimated the density of localized states at the Fermi level N(E(F)) and demonstrated that N(E(F)) is decreasing in composite materials. (C) 2010 Elsevier B.V. All rights reserved.