On the high temperature coalescence of metallic nanocrystals

The high temperature properties of metallic particles with a size of a few nanometers are very important in modern materials science. In the present work we report in situ transmission electron microscope studies of coalescence behavior of nanoparticles at high temperatures. At T > 700 K a new mechanism for coalescence was found. This phenomenon occurs on a time scale 3 to 20 times faster than the classical liquid-like coalescence reported by Pashley [Adv. Phys. 14 (1965) 327]. Before the coalescence the particles undergo shape convulsions of the type described by Iijima and Ichihashi [Phys. Rev. Lett. 56 (1986) 616] which has been termed "quasimelting", then fast coalescence occurs. The newly formed particles also undergo convulsions until stabilized by the substrate. It is also shown that the electron beam plays a significant role on this process.