Reversible disorder-order transitions in atomic crystal nucleation

Watching early stage nucleation In classic nucleation theory, a metastable disordered dense liquid or amorphous solid cluster spontaneously and irreversibly transforms into a crystalline nucleus. Jeon et al. observed the formation of gold crystals on a graphene substrate through the reduction of a precursor using an electron beam. Rather than the classic view, they instead observed a nucleation pathway that involves dynamic and reversible fluctuations of developing nuclei between disordered and crystalline states. The lifetime in the disordered state decreases with increasing cluster size, and at sufficiently small sizes, the binding energy per atom is large enough relative to the energy required to induce melting that the heat imparted upon binding is enough to drive partial collapse of an ordered cluster into the disordered state. Science , this issue p. 498