Localized surface plasmon resonance and structural characteristics of Ti nanodot arrays covered with an amorphous TiO2 native oxide layer

Localized surface plasmon resonance (LSPR) of Ti nanodot arrays (NDA) has not been studied much due to the surface oxide layer. In this study, we report the LSPR of titania on titanium (TOT) NDA fabricated on an indium tin oxide (ITO) glass using an anodic aluminum oxide layer with through-holes as a shadow mask. After depositing a 50 nm thick Ti layer, the TOT NDA was revealed on the ITO glass by dissolving the mask. The surface of TOT NDA was identified as TiO2 due to surface oxidation. Using XPS depth profiling, a chemical shift from the surface to interior showed a change of 4.6 eV, which corresponded to the difference in the binding energy between the TiO2 and Ti metal at the Ti 2p core level. Thus, the TOT NDA indicated that the Ti metal core was covered with a TiO2 layer. The LSPR of the TOT NDA with an 80 nm diameter was clearly observed at ~420 nm in the visible range, demonstrating the potential application of TOT NDA as a visible light-responsive photocatalyst.