Structural analyses of the pure and cesiated Ru(0001)-(2x2)-3O phase

The structures of the (2 x 2)-3O and the (2 x 2)-3O-Cs overlayers on the Ru(0001) surface were analyzed by LEED. The Ru(0001)-(2 x 2)-3O phase is characterized by a (2 x 2) vacancy network in which CO molecules are not able to adsorb whereas Ca atoms are. The averaged topmost Ru layer distance (2.21 Angstrom) is slightly expanded with respect to the bulk value, which is consistent with the observed trend that the topmost Ru layer distance increases with O-coverage. Coadsorbing Cs atoms reside in the vacancies exposed by the (2 x 2)-3O overlayer, whereby the local structural parameters remain essentially unaltered. (C) 1998 Elsevier Science B.V. All rights reserved.