Order-disorder transition of the c (2x2) phase in the Pb/Cu(110) system: Significance of surface defects

The tight-binding method has been combined with Monte Carlo simulations to study the structure and order-disorder transition of a Pb half-monolayer on a Cu(110) surface. Using coverage dependent lateral interactions a low-temperature c(2 x 2) structure and its transition to a disordered state was obtained. The general behavior of the two-dimensional (2D) order-disorder transition was found to be in very close agreement with experimental findings. Equilibrium surface Pb-Cu alloying was also observed during the disordering transition. The critical behavior of the system is shown to depend crucially on the initial order in the 2D overlayer: a continuous Ising type with initially perfect c(2 x 2) ordering, and first-order when in the initial configuration of the adlayer, has "frozen-in" distortions. [S0163-1829(98)03740-0].