Monolayers of CF4 Adsorbed on Graphite, Studied by Synchrotron X-Ray Diffraction

With synchrotron x-ray diffraction we have measured the phase diagram of CF4 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.