(color online) In-situ HTREM imaging of oscillatory behavior for Pt nanoparticles during CO oxidation reaction. ((a)–(e)) A series of in-situ HRTEM images of the morphology evolution of a Pt nanocrystal showing an oscillatory behavior. (f) Real-time mass spectra for probing O₂, CO₂, and CO pressures, reaction power, and shape factor. (g) Atomic-scale imaging of a single Pt particle with different shapes: the more spherical shape and the more facetted shape.^[65]