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 char acterized by a (2 x 2) vacancy network in which CO molecules are not able t o 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 co nsistent with the observed trend that the topmost Ru layer distance increas es with O-coverage. Coadsorbing Cs atoms reside in the vacancies exposed by the (2 x 2)-3O overlayer, whereby the local structural parameters remain e ssentially unaltered. (C) 1998 Elsevier Science B.V. All rights reserved.