Coverage temperature phase diagram of LEED spot and arced streak intensities for Li on Cu(0 0 1) surface using lattice gas model

It has been established that the arced streaks connecting four spots observed in LEED for a Li system adsorbed on a Cu(0 0 1) surface originate from the Bragg reflection from parallel adatomic lines on a c(2 × 2) lattice site. For example, one streak at about k_y = π/a originates from the parallel atomic lines including two atoms separated at a distance of d_y = 2a, which is the second-neighbor distance in a c(2 × 2) lattice.The c(2 × 2) structure sites consist of two sublattices with y = 2na and y = (2n + 1)a. Here, the difference in the number of adatoms on the two sublattices is the cause of the intensity of the midpoint of the streak, where the differences depend on the coverage of adatoms, Θ.In this study, using a lattice gas model on the substrate lattice with Monte Carlo simulation, we obtain the coverage and temperature dependence of intensities of the spots for the c(2 × 2) structure and the streaks.We found that the intensity of the streaks increase and decrease within the coverage range 0 < Θ < 0.5. That of the spots increases monotonically in this coverage range. These theoretical findings are similar to the experimental results.On the other hand, as temperature is increased, the intensity of the streaks increases and becomes saturated. We found a similar phenomenon using analytical calculation by statistical mechanics. In addition, the intensity of the spots decreased with the second-order transition.