Quantum Confinement and Electronic Properties of Rutile TiO2 Nanowires

The quantum confinement effect, electronic properties, and optical properties of TiO 2 nanowires in rutile structure are investigated via first-principles calculations. We calculate the size- and shape-dependent band gap of the nanowires and fit the results with the function E g = E g bulk + β/ d α . We find that the quantum confinement effect becomes significant for d < 25 Å, and a notable anisotropy exists that arises from the anisotropy of the effective masses. We also evaluate the imaginary part of the frequency-dependent dielectric function [ε 2 (ω)] within the electric-dipole approximation, for both the polarization parallel [ε 2 ∥ (ω)] and the perpendicular [ε 2 ⊥ (ω)] to the axial ( c ) direction. The band structure of the nanowires is calculated, with which the fine structure of ε 2 ∥ (ω) has been analyzed.