Surface relaxation in Cu(4Â 1Â 0)-O: A medium energy ion scattering study

Medium energy ion scattering (MEIS), using 100 keV H+ ions, has been applied to investigate the surface relaxations involved in the Cu(4 1 0)-O phase through the measurement and simulation of a series of blocking curves. Measurements were made in six different scattering geometries that exploit the intrinsic asymmetry of the stepped surface by using the scattering plane that is perpendicular to the surface and to the [0 0 1] steps (i.e. in the [14¯0] azimuth). Specifically, incidence in 'up-step' and 'down-step' directions were used that are equivalent relative to the (1 0 0) terraces, but not relative to the (4 1 0) surface. A range of relaxation models were tested, investigating the influence of 16 distinct structural parameters that define surface-induced displacements perpendicular and parallel to the surface, but optimising only the eight parameters associated with movements of the outermost four Cu atom rows that lie directly at the solid/vacuum interface. Relaxations broadly similar to those found in a previous study based on X-ray diffraction and density functional theory calculations are found, although there are some significant quantitative differences. The results are also compared with relaxations previously measured on the related Cu(1 0 0)(√2 × 2√2)R45°-O 'missing row' structure.