Synchrotron x-ray study of melting in submonolayer Ar and other rare-gas films on graphite

Abstract

Synchrotron x-ray diffraction studies of the (10) peak of Ar on the (001) surface of $\mathrm{ZYX}$ graphite show a sharp but continuous broadening of the Bragg peak with increasing temperature. Below a coverage of ∼ 1 Ar atom per six surface carbon atoms ($\rho =1\mathrm{}$) the onset of this transition occurs at a coverage-independent temperature $T=47.9\mathrm{}$ K. We interpret this point as a critical end point for melting. For coverages $0.94<\mathrm{}\rho <1.2\mathrm{}$ continuous broadening is also observed, but the onset occurs at a temperature which increases approximately linearly with coverage. This behavior differs markedly from that of other rare-gas films on graphite.