The incommensurate adsorbed solid is found to become unstable to dislocations when the lattice period approaches that of a sufficiently low-order commensurate phase such as a 2×1 rectangular overlayer or the $(\sqrt{3}\times \sqrt{3})R30°$ hexagonal structure which occurs for krypton on graphite. In these cases, a fluid phase is expected between the commensurate and incommensurate solids.

• Received 1 December 1980

DOI:https://doi.org/10.1103/PhysRevLett.46.549