Observations of the melting transition in thin lead films.

The first direct observation of the melting transition of a uniformly flat (20A) Pb film is reported. The transition was observed by TEM using dark field imaging. The melting transition occurred over a broad temperature range, was continuous and reversible. From these and earlier observations, it was concluded that the transition proceeded 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 interfacial region between the Pb and Ge.