Scanning tunnelling microscopy investigation of the oxygen-induced faceting and ''nano-faceting'' of a vicinal copper surface

Scanning tunnelling microscopy (STM) has been applied to investigate the well-known tendency of Cu(100) vicinals to facet to Cu(410) in the presence of chemisorbed oxygen. Room-temperature imaging was performed on a nominally (610) face of Cu following different oxygen exposures and annealing treatments. The well-annealed oxygen-exposed surface shows large (410) facets but a rather small tendency to produce comparably sized (100) facets; these only occur in conjunction with (401) facets which arise due to a miscut of the crystal surface by a few degrees out of the [001] zone relative to a pure (n10) face. Instead, the additional (100) surface needed to make up the average surface orientation occurs in the form of regions of wider (100) terraces between groups of terraces of (410) width, leading to nanofacet regions with modulated step-edge spacings. Oxygen dosing around room temperature produces small (410) facets elongated in the [001] direction, with pile-up of the kinks resulting from the azimuthal twist leading to (100) step-edge facets as a precursor to the formation of (100) and (401) two-dimensional facets which form on annealing. Explicit evidence is found for significant adatom diffusion at room temperature, even over the oxygen-induced (410) facets. Atomic-scale images of nanofacets, which can be regarded (4n10) regions with n an integer, provide some further information on specific atomic models of oxygen-covered Cu(100) vicinals in this zone. (C) 1997 Elsevier Science B.V.