Analysis of Defect-Free Graphene Blocks in Nitrogen-Doped Bamboo-Like Carbon Nanotubes

The structure and electronic properties of the N-doped bamboo-like carbon nanotubes with different nitrogen content (N-CNTs) are studied by the use of transmission electron microscopy, electron energy loss spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy supplemented by measurements of the temperature dependence of conductivity. XPS data are used to estimate the content of nitrogen represented by pyridinic, pyrrolic, graphitic, and oxidized N species and encapsulated molecular nitrogen. The graphene blocks surrounded by borders containing hole defects and N-species are considered as building blocks of N-CNT walls. The intensity ratio of D, G, and 2D bands in Raman spectra and XPS data on the concentration of N-species are used to analyze the size of defect-free graphene blocks in N-CNTs. The size of such blocks depends on the N-defect content and is estimated to be 1-2 nm. The increase of N-species content resulting in a decrease of graphene block size correlates with the decrease of current carrier concentration (n(ES)) estimated within the Efros-Shklovskii model.