LEED investigations on Co(0001): the clean surface and the (2x2)-K overlayer

The structures of clean Co(0001) and the p(2 x 2) overlayer of potassium on Co(0001) were determined at 160 K using dynamical low-energy electron diff raction (LEED). The clean Co(0001) surface shows an oscillatory relaxation in the first two layers, with a 2.1% contraction of the first layer spacing and a 1.3% expansion of the second layer spacing compared to the bulk valu e, The potassium atoms in the p(2 x 2) overlayer adopt the top site and ind uce a buckling of 0.16 Angstrom in the top Co layer such that the Co atom b eneath the K is displaced towards the bulk. The effects of the top site and the buckling of the top Co layer on the K/Co(0001) phase diagram are discu ssed. (C) 1999 Elsevier Science B.V. All rights reserved.