CLEAN AND OXYGEN-COVERED CU3AU(110) - A SURFACE-STRUCTURE INVESTIGATION WITH STM AND NICISS

Cu3Au(110) has been investigated by scanning tunneling microscopy (STM ) and 180 degrees low energy ion scattering and detection of neutrals (NICISS). Two different terminations would be possible on the basis of a bulk-truncated surface, a gold-rich or a pure copper surface layer. From the NICISS investigation the gold-rich termination has been foun d. Two surface modifications could be prepared. Rapid cool-down after annealing at 800 K results in a 2 x 1 LEED superstructure, but careful preparation and prolonged cooling below 600 K gives a LEED 4 x 1 supe rstructure. A new pairing row model has been proposed. Upon oxygen exp osure at 330 K on the quenched 2 x 1 surface and subsequent annealing at 800 K, a 2 x 1 LEED superstructure presents itself with considerabl y sharper half order reflexes. NICISS data propose a segregation of Cu atoms to the surface layer forming -Cu-O- rows just above the Cu rows in the Au-rich layer. The 2 x 1 superstructure formed is in part simi lar to the well-known added row structure at Cu(110)-(2 x 1)-O. The st ructure model has been verified by direct imaging of the added rows wi th STM.