Variation in 111 d-Space and Generation of Hillocks in Platinum Thin-Film Electrodes by Heat Treatment

The variation in 111 d-space of Pt thin-film electrodes during heat treatment was precisely measured by an X-ray diffraction system with a heating stage. The 111 d-space of Pt films deposited at 200°C linearly increased as the temperature was increased to 450°C and was almost constant over the temperatures range from 450 to 600°C due to stress relaxation. The generation of hillocks was observed in the Pt films which were relaxed in this way. On the other hand, in the case of Pt films deposited at temperatures higher than 500°C, the d-space linearly increased and then linearly decreased to almost the same value in the heat treatment at a maximum temperature of 600°C, and no hillocks were observed on the surface after the heat treatment. Furthermore, Pt films prepared at room temperature (RT) at different deposition rates showed different variations in d-space and different sizes of hillocks. These results suggest that knowing the variation in 111 d-space during heat treatment is beneficial for predicting the generation of hillocks in 111-oriented Pt thin films.