(a–e,k–n) Sequential snapshots of HRTEM imaging showing the microscopic structural details of melting process. (f–j) The enlarged images corresponding to the regions as marked by the yellow squares in a–e. The lattice fringes in f,g are highlighted by red lines. The dashed blue circle in h indicates a vacancy. The blue arrow in g indicates the atomic column before transforming to the vacancy in h. The area marked in dashed blue line in i indicates the gap formed by the coalescence of the defects. The areas marked in dashed blue lines in j indicate the domains in liquid-like structure with an irregular shape. The insets of a–e and k–n show the corresponding FFT patterns of the nanoparticle. The scale bar in a is 5 nm, which applies to a–e and k–n. The scale bar in f is 1 nm, which applies to f–j.