Coverage dependence of LEED arced streak intensities for Li adsorption on Cu(001) surface

The coverage dependence of arced streak intensities observed in LEED pattern, for Li on Cu(001) surface at low coverage, (0 - 0.50), is studied theoretically. The streaks essentially originate from the deviation of numbers of adatoms on sublattice sites. In a lattice gas adsorption model, we can see two sublattices in terms of a phase on a wave number k_y = 2π=2a, which corresponds to the streaks. Then we calculate an expectation value for the deviation of numbers of adatoms on the two sublattice sites, for a given coverage. This deviation brings an atomic density wave and also gives an intensity of the streak. The calculated coverage dependence of the intensity is similar to the experiment. In the real experimental system, the streaks are expanded and deformed in diffraction space. It means inclined or incommensurate atomic density wave. Even in such a case, we show that the above two sublattice model is essentially sufficient.