Geometric structure of p(2×2)-S/Cu(001) determined by medium-energy ion scattering

We have determined the geometric structure of the p(2×2)-S/Cu(001) surface with medium-energy ion scattering. There are qualitative features in our data that clearly show that sulfur adsorption does not induce large atomic rearrangements of the Cu substrate. A detailed analysis based on Monte Carlo simulations shows that the sulfur atoms are located 1.30 above the copper surface. The first Cu layer moves outwards by 0.02, and the top-layer Cu atoms move laterally away from the adsorbate by 0.03. This results in a S-Cu bond length of 2.25. Our results are compared with earlier contradictory results on this controversial system. We find excellent agreement with a recent low-energy electron diffraction study.