Deformation and transfer doping of a single-walled carbon nanotube adsorbed on metallic substrates

We have examined the effects of radial deformation and transfer doping on the electronic properties of an armchair single-walled carbon nanotube (SWNT) adsorbed on the gold (Au) and silver (Ag) surfaces. Using a semiempirical method developed on the basis of the continuum elastic shell model, it is found that the radial deformation of SWNTs with D < 21 A degrees, where D is nanotube diameter, is reversible in the whole range of radial deformation. Whereas, large deformations of SWNTs with D > 21 A degrees tend to be irreversible and a collapsed nanotube can be stabilized. We have chosen the metallic armchair (21,21) SWNT with D approximate to 28.5 A degrees and confirmed by ab initio calculations that large deformation of this nanotube can actually be stabilized and the collapsed tube is a semiconductor with small band gap of similar to 60 meV. The charge transfers of this nanotube, both circular and collapsed, adsorbed on the Au(100) and Ag(100) were investigated by large-scale ab initio calculations and a phenomenological model, which was developed on the basis of the rigid-band model. The model yields the Fermi-level shift of the nanotube adsorbed on the Au(100) surface in good agreement with the experiments and provides a useful insight into the transfer doping. On the other hand, the transfer doping virtually does not occur for the nanotube adsorbed on the Ag surface, not in agreement with the experiments with large uncertainty. The phenomenological model is also applied to the graphene adsorption on the metallic surfaces and is found to yield reasonable results for the transfer doping and to be useful in understanding the previous results, both experimental and theoretical.