Monolayers of CF4adsorbed on graphite, studied by synchrotron x-ray diffraction

With synchrotron x-ray diffraction we have measured the phase diagram of C${\mathrm{F}}_4$ monolayers adsorbed on the graphite substrate UCAR-ZYX. We have found four two-dimensional crystalline phases including the 2×2 commensurate structure. Between this and the denser incommensurate hexagonal phase we find an axially compressed phase interpreted to be the stripe domain structure. Our data indicate that the order-disorder transition (melting) of the 2×2 commensurate phase as well as melting of the stripe and of the hexagonal incommensurate phases are continuous.