OXIDIZED SURFACES OF CU FILMS ON RU(0001)

The crystallographic aspects of O-induced structures on strained Cu fi lms grown epitaxially on Ru(0001) are studied by scanning tunneling mi croscopy and high-resolution low-energy electron diffraction. O adsorp tion at 520 R removes the thickness-dependent relaxation structures of the O-free Cu film. Instead. structures appear corresponding to a fil m thickness reduced by one monolayer, accompanied with the formation o f a O/Cu surface layer. Wave-like O-Cu-O chains along the [(1) over ba r 12] direction are formed on the pseudomorphic Cu monolayer. The O/Cu structures on uniaxially reconstructed Cu bilayers depend on both the local stacking sequence and the extension of the unit cell. On moire- like Cu films (thickness > 3 ML), an O/Cu structure of well-establishe d long-range order only occurs if O is preadsorbed on Ru(0001). The re sults obtained allow one to conclude that Cu-O segments (links) of the O-Cu-O chains should be regarded as surfactants for the O-mediated gr owth of Cu/Ru(0001). All O/Cu structures can be interpreted on the bas is of O-Cu-O strings, in close relation to Cu2O/(111). (C) 1998 Elsevi er Science B.V. All rights reserved.