(color online) In-situ characterization of Pt_0.5Co_0.5 nanocrystals during oxidation and reduction reactions. HRTEM images showing the CoO-island forming behavior in a Pt_0.5Co_0.5 nanocrystal under 0.1 mbar O₂ and 250 °C at 2 s (a), 6 s (b), and 12 s (c), and the corresponding lattice spacing as measured from the HRTEM images ((d)–(f)). (g) STEM-LAADF images for the in-situ reduction of oxidized PtCo nanoparticles under H₂ at 400 °C (CoO in blue and the metallic core in yellow).^[64]