Mechanism for bias-assisted indium mass transport on carbon nanotube surfaces

In this paper, results of ab initio pseudopotential density-functional calculations of indium adsorption on graphitelike surfaces are presented. The adsorption energy was calculated as a function of In coverage, and it is shown that, for low surface densities, In becomes positively charged by donating about one electron to the underlying nanotube surface. This is consistent with experimental observations of bias-assisted In flux in the direction opposite to that of electron flow. The effects of nanotube surface curvature on In adsorption are shown to be small. Based on the calculated energy barrier between two neighboring energy minima and the calculated vibrational frequencies, the hopping rate for In adsorbed on graphene is estimated. It is also shown that In adsorption is stronger on and around a Stone-Wales defect on a graphene sheet, which suggests that defects can work as nucleation centers for crystal growth. Adsorption of In on BN sheets and of Au on graphene is also discussed. No significant charge transfer is present in these two alternative systems and the adsorption energies are weaker.