The plasmonic heating effect on the structural change of the TiO2 film should depend on the number density of the Au NPs. The crack formation, phase transition, and melting of the TiO2 were observed when samples with a low Au particle density (~75/μm 2 ) were irrigated with a 532 nm laser (Figure ). However, these changes happened at powers about 10 mW higher than those needed on the sample with higher particle density (600/μm 2 ).