IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Wednesday Sessions
       Session SS2-WeA

Paper SS2-WeA7
The Dynamics of CO and H co-adsorption on Ru(0001)

Wednesday, October 31, 2001, 4:00 pm, Room 121

Session: Adsorption on Metal Surfaces
Presenter: A.W. Kleyn, Leiden University, The Netherlands
Authors: B. Riedmüller, FOM Institute for Atomic and Molecular Physics, The Netherlands
I.M. Ciobica, Eindhoven University of Technology, The Netherlands
R.A. van Santen, Eindhoven University of Technology, The Netherlands
A.W. Kleyn, Leiden University, The Netherlands
Correspondent: Click to Email
Chemical reactions at surfaces form an exciting example of co-adsorbate systems on surfaces. The dynamics of such systems is still poorly understood. In this paper we will consider the dynamics of CO and H co-adsorption on Ru(0001). In earlier experiments we have demonstrated that H-adsorption turns the Ru surface in an almost perfect inert mirror for CO molecules. However, the sticking probability does not go to zero. There are adsorbing spots on the mirror. We carried out DFT calculations that demonstrate the nature of the activated adsorption of CO on H-Ru(0001). There is one specific site (atop) exclusively binding CO. In contrast, at the clean surface the entire unit cell strongly binds CO, and the molecule will reside at the most strongly bound site. This means that the reactivity of the H-covered surface strongly varies over distances of much less than an Angstrom. The nature of the bonding will be elucidated. Although we have computed a stable CO-H-Ru(0001) configuration this does not mean that this is the most stable. In fact the system shows phase separation. We studied its formation by Thermal Energy Atom Scattering. We find that on adsorption of CO on a H-Ru(0001) surface the CO nucleates in islands. The island size depends on the CO flux. In contrast to what has been seen for epitaxy of metals on metals at low CO flux small 'magic' CO-7 clusters are formed, at high flux large islands nucleate.