Surface modification of titanium dioxide thin films via manganese doping

Abstract

Mn-doped TiO2 thin films were produced by spin coating on FTO glass substrates to investigate the effects of Mn concentration on the structural, morphological, and optical properties of the films. Titanium isopropoxide and manganese chloride tetrahydrate were used as titanium and manganese sources respectively, in the precursor solution with isopropanol. The solution was added drop-wise on the substrate which was spun at 2000 rpm; annealing was done in air at 500 °C for 5 h. Films with very low dopant concentrations (≤ 1 wt%) were composed of anatase; those with moderate concentrations (3-5 wt%) showed the presence of anatase and rutile; while those with high Mn concentrations (≤ 7 wt% Mn) showed rutile formation. Increasing the dopant concentrations resulted in a slight increase in the surface roughness, except for the sample with 15 wt% Mn, that showed surface dimple formation. The films containing ≤ 10 wt% Mn showed similarity in grain sizes (̃ 10 nm) and thickness (̃ 300 nm). All the films showed relatively high transparencies, with the absorption edges shifting to longer wavelengths with increasing Mn levels. The optical indirect band gaps of the films decreased from 3.32 eV to 2.86 eV, and this data suggests that the formation of shallow trapping sites and reduced rate of electron-hole recombination are the result of the variable valence of Mn. © 2012 The Surface Science Society of Japan.