Adhesive Mechanism between Pt Thin Film and SiO2 Substrate after Annealing Pt/Ti/SiO2 in Air

A transmission electron microscopic study equipped with a field emission gun together with an electron energy loss spectroscopic study were carried out to investigate the adhesive mechanism between SiO2 substrate and platinum layer prepared by magnetron sputtering technique, particularly focused on its deterioration after annealing at 1000 degrees C for 4h in ambient condition. This study describes the details of contact mechanism of Pt (450 nm) /Ti (50 nm) /SiO2 substrate. It is revealed, after annealing, that well crystallized rutile type TiO2 particles were segregated from the original Ti metal thin film introduced as a contact layer between Pt and the substrate, spread across the Pt layer or diffused along its grain boundaries, and some of them even reached the surface. This brought about depletion of the contact layer and eventually made most of the Pt film facing the substrate directly, resulting in the weakening of the adhesion of the film. Movement of a sub-nanometer sized beam from inside of a TiO2 particle formed between Pt and SiO2 substrate to the Pt side, as well as disappearance of shoulders were observed as oxygen content decreased, somewhat shift of Ti L-2,L-3 peaks to lower energy side. This suggests that Ti4+ in TiO2 reduces towards the TiO2/Pt boundary and may imply metallic state to form a Pt Ti alloy in the vicinity of the boundary, which plays a crucial role to sustain adhesion of the film.