Comparative study of air and vacuum annealing atmosphere towards Pt/Ti–W/SiO2 stability

• Platinum thin films were deposited on silica substrates with a Ti–W adhesive layer
• The film interface and surface chemistry were studied upon annealing
• Above 600 °C, under vacuum, there is tungsten diffusion through Pt layer
• Under air, we report the oxidation of Ti–W layer and diffusion of WO3 through Pt

The thermal stability of Pt/Ti–W/SiO2 system was studied after annealing under air or vacuum in the present work. A Ti–W adhesive film (30 at. % Ti) was deposited on a SiO2 substrate followed by a thicker Pt layer. Depositions were performed using DC magnetron sputtering. The whole as-deposited films are metallic with a columnar growth of platinum deposit which totally wets the substrate. Whatever the atmosphere is, annealing at 500 °C for 12 h does not change the platinum state but modifies the morphology of platinum particles, the lateral average size of which increasing from less than 10 nm up to ca. 75 nm. Besides, a noticeable diffusion of metallic tungsten through Pt film is revealed for annealing carried out under vacuum. When annealing under air, oxygen diffusion through the Pt layer causes an oxidation of the whole Ti–W interlayer, inducing an important volume increase and degraded interfaces. Such an oxidation process comes with the migration of WO3 species through Pt-grain boundaries, up to the Pt surface. As the width of Ti–W interlayer is increased, a higher amount of WO3 reaches the surface, ultimately leading to discontinuities of the Pt layer.