Strain effects on the electronic and transport properties of TiO2 nanotubes

Abstract

TiO₂ nanotubes are promising materials for photocatalysis, solar cells and lithium ion batteries. Using first-principles calculations, we found that strain is an efficient way to improve the electronic properties and transport properties of TiO₂ nanotubes. For our modeled nanotubes, the armchair (12,12) nanotube shows a higher Young's modulus and Poisson ratio than its zigzag counterpart (12,0) nanotube due to the different orientations of Ti–O bond topologies. An increase in axial compressive strain leads to a progressive decrease in the band gap for the armchair nanotube. Moreover, there is an indirect-to-direct band gap transition at a compressive strain of about 6% in the (12,12) nanotube. For both armchair and zigzag nanotubes, holes uniformly have a larger effective mass than electrons, in addition to the (12,0) TiO₂ nanotube with compressive strain. It is found that the hole mobility is higher than its electron counterpart for the (12,12) nanotube, whereas the electron mobility is higher than its hole counterpart for the (12,0) nanotube with compressive strain. Our results highlight the tunable electron transport properties of TiO₂ nanotubes that are promising for interesting applications in optoelectronic applications.