Fig. 3.

CO-induced Pt diffusion and coalescence. STM image sequence acquired during exposure to 2 × 10⁻¹⁰ mbar CO. (A) After 5 h in UHV and 10 min CO exposure: Pt adatoms coexist with a few double-lobed, bright features, identified as Pt₁–CO created by CO adsorption in Fig. 2. (B–G) Formation of a Pt tetramer: CO adsorption on Pt₁ and Pt₁*, mobility, and coalescence are observed atom by atom. (H) Partially sintered state: Only a few adatoms remain; the biggest clusters in this image contain four atoms.