Inter-step-edge correlations on crystalline surfaces measured with helium-atom scattering

For close-packed metal surfaces the large-angle scattering of helium atoms is dominated by short-range interactions with surface defects. Along certain azimuths, monatomic step edges are the major contributors to diffuse scattering. The broad intensity oscillations provide information on the local step shape, and the finer structure is an indication of interstep correlation, which becomes more prevalent at higher step densities. Differently oriented step edges scatter along different final azimuths and thus the correlations between like step edges are only observed. The energy dependence of angular scans has been used to investigate the correlation between step edges on a sputtered Cu(111) surface. Comparison with structure-factor calculations indicates the presence of (331) and (211) microfacets.