Nitrogen-induced nanometre-scale faceting of Cu(4 1 0)

Scanning tunnelling microscopy has been used to investigate the morphological and atomic-scale structural changes to a Cu(4 1 0) surface induced by adsorbed atomic nitrogen. This (1 0 0) vicinal face is found to restructure to form ordered arrays of (1 0 0) nanofacets, separated by double-height steps of local (2 1 0) or (3 1 0) orientation, with a periodicity of approximately three times that of the step spacing of the original (4 1 0); step bunches to produce (2 1 0) and (3 1 0) nanofacets restore the correct average orientation. The (1 0 0) nanofacets show a c(2 × 2) structural phase similar to that found for N adsorption on extended Cu(1 0 0) surfaces, but do not show the novel c(2 × 2)-N 50 Å island ordering seen on Cu(1 0 0), usually attributed to the role of local compressive surface stress. However, single atomic steps occur across the (1 0 0) nanofacets at 100–200 Å intervals, and this modified morphology is attributed to the role of the narrow facets in allowing lateral strain to reduce the compressive stress. The absence of (1 1 0) facets associated with full agglomeration of surface steps is discussed in terms of the structure of the pseudo-(1 0 0) outermost layer of the (2 × 3) reconstruction which characterises the adsorption of N on extended Cu(1 1 0) surfaces.