On the O 1s XPS spectra of adsorbed oxygen on metallicity-sorted carbon nanotubes

Abstract

In our recent studies, looking at the C1s photoemission line, we reported a higher binding energy signal due to the formation of carbonyl groups [C=O] as reaction byproducts during adsorption on the tube defects. Making use of metallicity separated tubes, we have performed high resolution studies on the O1s region and studied its components in detail assisted by DFT calculations. This allows one to determine the specific functional groups or bonding environments measured in x-ray photoelectron spectroscopy (XPS). We have demonstrated how computed binding energies may be used to decompose a measured spectrum into its individual components. We find the XPS O 1s signal arises mostly due to the adsorption on SWCNT defects of three O-containing functional groups: ketene (C=C=O), epoxy (C2>O), and carbonyl (C2>C=O). The peak intensity for each species on the metallic SWCNT sample is almost twice that on the semiconducting SWCNT sample. This suggests a greater abundance of O-containing defect structures on the oxidized metallic SWCNT sample. For both metallic and semiconducting SWCNTs, we find O2 does not contribute to the XPS O 1s spectra.