X-ray diffraction study of C 2F 3Cl physisorbed on graphite

Abstract

Monolayers of the planar molecule C 2F 3Cl, a polar haloethen, physisorbed on exfoliated graphite have been investigated by X-ray diffraction. At a lower coverage, the molecules lie flat on the surface, and at a higher coverage, they stand on the FCl dipod. The coverage–temperature phase diagram has been established and the structures of the three 2D crystalline phases determined. One of the two crystalline phases of the low coverage regime is commensurate 7 × 7 and orientationally disordered. The second phase of this regime is incommensurate and goes through a sequence oblique–rectangular–triangular with increasing temperature.