Surface modifications of TiO2 by ion implantation

Rutile is a good candidate for total water oxidation and hydrogen production due mainly to its corrosion resistance in water. In its native form, the direct band gap of 3.02eV, with the absorption edge in the visible part of the solar spectrum at 416nm, but close to the UV region, results in poor photo-catalytic efficiency of around 3%, well below the commercial threshold of around 10%. One option to enhance the photo-catalytic efficiency is band gap engineering, through the reduction of the Fermi level, which may be achieve by either changing the oxygen activity, or the incorporation of aliovalent foreign ions. The incorporation of donor and acceptor-type of ions may lead to a shift in the Fermi level close to the conduction or valence bands. Single crystals of TiO2-Rutile (SG: P4 2/mnm), with (001) orientation were implanted along <001> at 10keV and 2MeV, where the range of C in TiO2 is 21nm and 1.6μm, respectively. The ion implantation was carried out at various equivalent C concentrations, and characterised in-situ by ERDA with 82MeV Iodine, and PIXE with 2.5MeV protons. Optic band gap was assessed by ground state band structure calculations based on CASTEP code, with geometry optimisation by general gradient approximation and PBE functional, and energy optimisation by local density approximation and CA-PZ functional.