Surface atomic structure of the (Ö3 x Ö3)R30°-Sb reconstructions of Ag(111) and Cu(111)

We present an X-ray diffraction structure analysis of the (Ö3 × Ö3)R30° reconstructions of Ag(111)-Sb and Cu(111)-Sb surfaces. We find these structures to be very similar. Contrary to previous reports, we find that all top layer atoms reside at stacking fault positions. Each (Ö3 x Ö3)R30° surface unit cell contains one substitutional Sb atom. We determined the out-of-plane relaxations of the top layer atoms and the in-plane distortions in the second layer. For coverages below 1/3 monolayer, the Sb atoms are embedded randomly at fcc positions in the top surface layer.