Diffraction from domain-wall systems

We present kinematical calculations of the diffraction patterns from domain-wall systems on a hexagonal substrate lattice. Diffraction-peak positions and intensities are calculated for the ({}3×{}{}3)R30^∘{} commensurate-to-incommensurate phase transition, assuming all possible domain-wall systems: heavy, superheavy, light, and superlight walls for both the hexagonal and the striped symmetry. In addition, we allow for wall relaxation and determine its effect on the diffraction-peak intensities. As an example, the ({}3 ×{} {}3 )R30^∘{} commensurate-to-incommensurate phase transition of Xe/Pt(111) is explained as a continuous transition involving striped superheavy walls with increasing relaxation followed by a first-order transition into a hexagonal incommensurate phase.