Finite-concentration gas molecule adsorption on carbon nanotubes investigated by a tight-binding approach

Abstract

A theoretical approach based on tight-binding model is developed to study the effects of finite concentrations of adsorption of diatomic gas molecules (in the general form denoted by ${X}_{2}$) and also triatomic gas molecules (in the general form denoted by $Y{X}_{2}$) on the single-walled carbon nanotube (SWCNT) electronic properties. To obtain proper hopping integrals and random on-site energies, for the case of one molecule adsorption, the local density of states for various hopping integrals and random on-site energies are calculated. We found, for some specified values of hopping integrals and random on-site energies, adsorbed molecule bound states located inside the (10,0) SWCNT energy gap, where it is consistent with the reported experimental results for ${\mathrm{O}}_{2}$ and $\mathrm{N}{\mathrm{O}}_{2}$ adsorption, while for other values, there are no bound states inside of energy gap. The last case is similar to the ${\mathrm{N}}_{2}$ and $\mathrm{C}{\mathrm{O}}_{2}$ adsorption on semiconductor SWCNTs. Then, by using these obtained parameters and coherent potential approximation, we investigate the effects of finite gas molecule adsorption on the average density of states. Our results could be used to make a $p$-type or $n$-type semiconductors by finite-concentration adsorption of gas molecules.