Melting of Pb as it approaches a two-dimensional solid

The melting behavior of modulated Pb-Ge foils has been investigated by differential scanning calorimetry and x-ray diffraction. As the Pb layer thickness decreases, the melting temperature is depressed and broadened. For a 20-{}-thick Pb film, the start of the transition is 45^∘{}C below the bulk melting temperature and the transition breadth is on the order of 40^∘{}C. The transition has the characteristics of being second order. The normal thermodynamic variables and macroscopic interfacial energy considerations have been eliminated as mechanisms for broadening the transition by a series of first-order transitions.