Phase transitions and domain-wall structures in the K/Cu(110) system: Scanning-tunneling-microscopy observations and Monte Carlo simulations

The surface structures formed by adsorption of K atoms up to 0.3 monolayers at room temperature on a Cu(110) surface were analyzed by means of scanning tunneling microscopy (STM). Surface reconstruction proceeds via formation of local nuclei, which arrange to stable (1×{}3) and (1×{}2) domains, depending on the coverage. In proximity to the commensurate (1×{}3) phase, the misfit of the coverage causes the formation of domain-wall structures, which reflect the transition into an incommensurate phase. Dislocations disorder these domain-wall structures only at larger misfit of the coverage. A simple lattice-gas model is developed, based on the dipole repulsion between neighboring adsorbates and the net attractive interfacial energy of adjacent nuclei in the [11{}0] direction. Monte Carlo simulations of this model agree qualitatively well with the corresponding STM images, and the findings are discussed in the framework of the closely related axial-next-nearest-neighbor Ising model.