Dynamic behavior of ultrafine particles of gold around 20 Å in size was examined at the level of the atomic resolution by an electron microscope equipped with a real-time video recording system. In real time, it was observed that the shape of the particles changed continually through an internal transformation from a single crystal to a twinned crystal, and vice versa. The transformations were induced to some extent by the irradiation of the electron beam. They took place abruptly in less than 0.1 sec.

• Received 25 September 1985

DOI:https://doi.org/10.1103/PhysRevLett.56.616