Observations of the Melting Transition in Thin Lead Films

The first direct observation of the melting transition of a uniformly flat (20-{}-thick) Pb film, sandwiched between two amorphous Ge films, is reported. The transition was observed by transmission electron microscopy with dark-field imaging. The melting transition occurred over a broad temperature range, and was continuous and reversible. It is concluded that the transition proceeds by a disordering mechanism rather than the formation of a liquid-solid interface. The transition was not homogeneous but proceeded at a rate of disordering that was greater from the Pb-Pb grain boundaries than from the Pb-Ge interfacial region.