Characterization of nitrogen-doped carbon nanotubes by atomic force microscopy, X-ray photoelectron spectroscopy and X-ray absorption near edge spectroscopy.

In this work, we perform a comparative study on single-walled carbon nanotubes (CNT) before and after low energy nitrogen ion bombardment (70 eV and 25 x 10-6 A/cm2) at room temperature. The morphology and the mechanical properties were studied by Atomic Force Microscopy (AFM). The bonding configuration of the N-doped CNTs was established by X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Near Edge Spectroscopy (XANES). Single-walled carbon nanotubes were prepared using non-intrusive methods and deposited onto silicon substrates. For the spectroscopic studies, samples with a high concentration of CNTs were analyzed. XPS reveals different chemical states for carbon related to the incorporation of nitrogen. XANES confirms the hexagonal structure of the CNTs, resembling the bonding structure of hexagonal carbon nitrides. AFM images confirm that the CNTs were not destroyed after low energy N2+. The morphology of the original nanotubes maintains after nitrogen ion bombardment except for the incorporation of some pearl-shaped decoration, probably due to the adsorption of some contaminants or to deposition of re-sputtered material. Whereas CNTs improve their adherence to the substrate, this extra granularity on the CNT is easily removed even with the AFM tip. In conclusion, spectroscopic measurements and mechanical properties made clear information on the changes produced on CNT after nitrogen incorporation.