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

Abstract 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 d 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 d ∼ 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 d ≤ 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.