The Liquid-Solid Transition of Xenon on Graphite: a Vapor Pressure Isotherm Study of Two-Dimensional Melting.

We have performed a high precision vapor-pressure isotherm study of the melting transition of near monolayer xenon adsorbed on Union Carbide's ZYX exfoliated graphite. The data are analyzed in terms of the film isothermal compressibility, K(,T). We identify a sharp peak in K(,T), which occurs in the low temperature data, as a first order melting transition. As the temperature is increased, the amplitude of the peak decreases, reaching zero at a tricritical temperature, T(,trc) = 152 (+OR-) 6 K. On the basis of our results and the results of other studies, we conclude that the melting is continuous above this temperature. A temperature independent, weak and relatively broad contribution to K(,T) underlies the sharp peak at all temperatures studied; we discuss possible origins of this component.