The nanoparticle films before and after the peel test were examined by SEM. Figure 4A shows such nanoparticle film after the peel test. In the area highlighted by white square, where the peel test was applied, almost all the nanoparticles were removed from the surface, indicating a rather poor adhesion of the nanoparticles on the NH2-SAM. In order to improve the stability and to obtain a stable superhydrophobic surface, the substrates were subjected to a sintering process at high temperature. Sintering was performed under O2 at 1100 °C for 2 h.