Influence of structural defects, functional groups and dopant impurities on the electronic structure of multiwalled carbon nanotubes
The complex of X-ray photoelectron analysis methods (XPS and NEXAFS) were used to investigate the structure, composition, number and type of functional groups, the density of electron states near the Fermi level of multi-walled carbon nanotubes (MWCNTs), which were nitrogen doped and modified with ionic and thermal treatments. On the basis of experimental data on the density of electronic states near the Fermi level, a band structure model for MWCNTs containing various types of defects was made. It is shown that doping of MWCNTs with nitrogen (N-MWCNTs) leads to an increase in the density of occupied states near the Fermi level, which indicates an increase in the number of free n-type charge carriers in the N-MWCNTs surface layer. It was found that annealing of N-MWCNTs in vacuum leads to a more significant overlap of the bands, which is due to annealing of structural defects and an increase in the amount of electrically active nitrogen. It was determined that irradiation of N-MWCNTs by a continuous beam of argon ions with an energy of 5 keV and a dose of ~ 1016 ion / cm2 leads to the formation of a band gap (~ 1.2 eV) due to the destruction of the π-subsystem of sp2-hybridized carbon and strong oxidation of the surface of carbon nanotubes. An increase in the fluence of the ions to 5x1016 ion / cm2 leads only to an increase in the number of oxygen-containing groups on the surface of carbon nanotubes without changing the width of the bandgap. The obtained results showed that the application of nitrogen doping, ion beam and thermal treatment allows directional influence on the electronic properties and chemical activity of the MWCNTs surface.
The work is supported by the RFBR (Russian Foundation for Basic Research, Russia), research project no. 18-32-00233 mol_a.