Structural Phase Transition in Epitaxial Solid Krypton Monolayers on Graphite

Lattice-constant measurements of epitaxial solid krypton monolayers adsorbed on the basal plane of graphite reveal an apparently second- (or higher-) order structural phase transition from an in-registry (√3×√3)30^∘ structure to an out-of-registry compressed structure. Measurements as a function of equilibrium vapor pressure were made with a high-resolution, low-energy-electron diffraction apparatus for three temperatures near 57 K. Indirect evidence for spatial modulation of the compressed structure by the substrate potential is presented.