Fig. 4: In situ TEM observation of the phase transformation.

a–f Atomic structure of the interface at different reaction time; the observation is performed at 300 kV with electron beam dosage of 4000 e⁻ Å⁻² s⁻¹ in 1 mbar of CO gas (the scale bar in panel a is 20 nm and can apply to panel b–f; g schematic drawing showing the fcc-to-4H phase transformation of the Au nanoparticles on 4H region of the rod; h–k in situ TEM observation of the phase transformation of a fcc–Au nanoparticle siting on the boundary between the 4H region and one fcc-end of the nanorod; experiments were performed at room temperature at 300 kV with electron dose of 2000 e Å⁻² s⁻¹ in 1 mbar of CO gas (the scale bar in h is 10 nm and can be applied to panel i–k).