Fig. 9. (a–d) SEM images of (a) Au–Ag/ and (b–d) various Au/TiO₂ nanocavity arrays structures formed by (b, d) dewetting–dealloying and only (c) dealloying. (a) Arrays of single Au–Ag alloyed NPs per cavity after thermal dewetting in Ar (400 °C) of sequentially sputter-coated Au and Ag films and (b) arrays of single porous Au NPs after dealloying in HNO₃ (insets in (a) and (b): high magnification SEM and TEM images of (a) Au–Ag alloyed NP and (b) porous Au NP after dealloying). (c, d) Non ideal dewetting–dealloying conditions: TiO₂ nanocavities decorated by dealloying of Au 10 nm to Ag 20 nm film (c) without dewetting process and (d) after dewetting in air. (e, f) XPS spectra of the (e) Au and (f) Ag regions of: (i) as-formed TiO₂ NTs, (ii) Au (1 nm)/TiO₂ NTs, (iii) dewetted Au (1 nm)–Ag (2 nm)/TiO₂ NTs and (iv) dewetted–dealloyed Au (1 nm)–Ag (2 nm)/TiO₂ NTs. (g) SEM image of TiO₂ compact layer decorated by dewetting and dealloying (in HNO₃) a Au 10 nm–Ag 20 nm film. Fig. (a–c and e–g) are reproduced with permission from ref. 120.