X-Ray Scattering Study of the Commensurate-Incommensurate Transition of Monolayer Krypton on Graphite

We describe an x-ray scattering study of the commensurate-incommensurate transition in monolayer Kr films physisorbed onto basal planes of $z-y-x$ exfoliated graphite. At temperatures of 80.0 and 89.3 K there appears to be a single hexagonal-commensurate-to-hexagonal-incommensurate transition which is at least nearly second order with mean exponent $\beta =0.30\mathrm{}\pm 0.06$. In the incommensurate phase we directly observe domainwall superlattice effects.