Optical and structural investigations on titanium oxynitride films for visible-UV photocatalytic applications

摘要

We report on the epitaxial growth of titanium oxynitride (TiO_xN_y) films on α-Al_2O_3 (0001) substrates by using a pulsed-laser deposition technique and their optical properties. Using TiN as a solid source, N content (y) in the films was tuned by changing the partial pressure of O_2 gas. The crystalline phase was found to evolve up to y ≈ 0.4 either from rock-salt type or from rutile-type structures. The optical absorption spectra of the films had two distinct components in regions of 0.44-2.4 eV and 2.4-6 eV, which arise from d-d and charge-transfer transitions, respectively. The former transition decreased with decreasing y and vanished at y ≈ 0.26, where a fundamental absorption edge due to the latter transition was found to be 2.4 eV. The results demonstrate a range of anion compositions in the TiO_xN_y being suitable for visible-light harvesting applications.