DETERMINATION OF THE ADSORPTION SITE OF SULFUR ON RU(0001) BY STM

STM not only provides information about lateral and vertical distances and the atomic structure in the layer of the adsorbate, it can also b e used for site determinations of an adsorbate under favourable condit ions, even on a closed packed metal surface without atomic resolution of the bare surface. Using the lateral shifts between the inequivalent terraces A and B of the Ru(0001) surface we show that sulphur, ordere d in p(2 x 2) and (square-root 3 x square-root 3)R30-degrees structure s, exclusively occupies the hcp threefold site up to a coverage of the ta = 1/3.