Theoretical study of atomic chemisorption on single-walled carbon nanotubes. Application of Anderson–Newns model

Abstract

A theory of chemisorption relevant to individual atoms on the outer surface of zig–zag single-walled carbon nanotubes (SWCNTs) and based on an Anderson–Newns-type model is presented with specific reference to the adsorption of hydrogen atoms. It is shown that the chemisorption energy Δ E displays a nontrivial dependence on the nanotube radius R, oscillating jump-like with increasing R. We also found that the dependence Δ E on R for semiconducting SWCNTs is significantly different from that for metallic ones: an increase in R leads to a reduction in Δ E for the former and to an enhancement in Δ E for the latter. Such a sharply contrasting behaviour in the chemisorption energy trends is attributed to an additional contribution to Δ E arising from the occupied localized states, which occur in the band gap of semiconducting SWCNTs. The results obtained can provide deeper insight into the mechanism of single-atom chemisorption on SWCNTs and suggest a simple way to improve atomic hydrogen storage cells fabricated on SWCNTs by selecting preferably metallic ones with the smallest radius.