Fig. 5: Direct observation of Pt oxidation by in situ STEM.

a–c, STEM images of Pt nanoparticles under NO2 at 300 K (a), 620 K (b) and 1,000 K (c). The right panel in c is a magnified image of the grey-box area (c, left) together with a superimposed PtO3–Pt model. d–f, Intensity profiles of the arrow-marked regions in a (d), b (e) and c (f).