STM OBSERVATIONS OF CU(100)-C(2X2)N SURFACES - EVIDENCE FOR ATTRACTIVE INTERACTIONS AND AN INCOMMENSURATE C(2X2) STRUCTURE

STM studies of N on Cu(100), adsorbed via activated ion bombardment, reveal behaviour consistent with attractive interactions and an incommensurate c(2 x 2)N structure. For extremely low N doses, images of the resultant surface show roughly square shaped islands with island edges running along the [001] directions. The island have an internal c(2 x 2) periodicity and while tending to group together do not coalesce. For higher N doses, island coalescence occurs simultaneously with the appearance of trench-like defect structures running in the [011] directions and small one-atomic layer high islands. Lack of island coalescence at low coverages and the appearance of trench-like defects at higher coverages are interpreted as strain-relief mechanisms for an incommensurate c(2 x 2)N structure. To derive the N adsorption site, S has also been coadsorbed along with the c(2 x 2)N islands to form coexisting p(2 x 2)S domains. The spatial relationships between features in both domains show that the protrusions observed in the c(2 x 2)N areas are located above four-fold hollow sites. Finally, in order to compare our work with previous studies, we have obtained detailed LEED I-V data from the various Cu(100)-c(2 x 2)N surfaces studied with STM.