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 x 3) and (1 x 2) domains, depending on the coverage. In proximity to the commensurate (1 x 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 [110BAR] 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.