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

We have investigated temperature σ(T) and magnetic field σ(B) dependences of the conductivity of multiwalled carbon nanotubes (MWNTs) with different average outer diameter d̄ 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 σ(T) and σ(H) we have found that quantum corrections to the conductivity for interaction electrons is dominated in MWNTs with average outer diameters d̄ ∼ 23 nm and MWNT/PMMA composite materials. We determined the constant of electron–electron interaction λ from quantum correction to σ(T) and σ(H). In the result we have found that λ 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 λ in MWNTs. For MWNTs with average outer diameters d̄ ≤ 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(EF) and demonstrated that N(EF) is decreasing in composite materials.