Sublattice Segregation of Hydrogen Adsorbates in Carbon Nanotubes

TL;DR

This study investigates sublattice segregation of hydrogen adsorbates in carbon nanotubes, revealing that asymmetries similar to those in graphene are present and more pronounced in small-diameter CNTs with dilute adsorbate concentrations.

Contribution

It demonstrates the presence and enhancement of sublattice asymmetry of hydrogen adsorbates in carbon nanotubes, extending the understanding of impurity interactions from graphene to nanotubes.

Findings

Sublattice asymmetry is observable in small-diameter CNTs.

Asymmetry diminishes with increasing nanotube diameter.

Dilute adsorbate concentrations enhance sublattice segregation.

Abstract

Recent experimental observations have reported that, rather than randomly distributed, nitrogen atoms may prefer to be located on one of the two sub-lattices of graphene. It has been suggested that such a preference may present a possible avenue to tailor the band gap of graphene whilst maintaining its excellent electronic transport properties. Among the proposed mechanisms to explain this effect is the suggestion that long-range inter-impurity interactions mediated by the conduction electrons of graphene may give rise to the asymmetry between sub-lattice occupations. Electron-mediated interactions are known to be prevalent not only between N atoms but also between impurities that are adsorbed to a specific location within the hexagonal structure, namely to the top of the carbon atom. Furthermore, this interaction is known to become more long-ranged as the dimensionality of the system is lowered. For that reason, in this paper we investigate whether a similar sub-lattice asymmetry appears in the case of metallic carbon nanotubes doped with Hydrogen adatoms. Our results indicate that similar sub-lattice asymmetries are observable and even more pronounced in small-diameter CNTs with a dilute concentration of adsorbates, diminishing with increasing diameter or impurity concentrations.