Interaction of atomic species with surface adsorbates

A number of modern technologies are based on the interaction of atomic species rather than molecules with surfaces. In particular, atomic hydrogen is involved in chemical processes like silicon etching and growth or synthetic diamond production. Nuclear fusion and hydrogen storage are other examples for processes involving atomic hydrogensurface interactions. In the proposed project the interaction of atomic hydrogen with coadsorbates on metal surfaces will be investigated. We will focus on the kinetics and the dynamics of this process. Hydrogen atoms impinging on a surface can react immediately with already adsorbed hydrogen or coadsorbates to form volatile products. This type of interaction is called an Eley-Rideal reaction, in contrast to the Langmuir-Hinshelwood reaction, which takes place between accommodated surface species. Only little experimental work has been done so far on the kinetics and dynamics of Eley-RideAl reactions. The potential energy of the impinging hydrogen atoms may be released fully or partially to the nascent product yielding highly excited molecules. The angular distribution of these molecules will be studied, as well as the dependence of the reaction rate on the incident angle of the impinging atoms. The interaction of atomic hydrogen with electronegative coadsorbates, like oxygen, sulfur, carbon, and electropositive coadsorbates, like potassium, will be investigated in this context. The question is, will these coadsorbates react with hydrogen or will they just poison or promote the hydrogen-hydrogen interaction. From the experimental results we hope to get a better understanding of the individual reaction steps involved in the interaction of atomic species with surfaces. The results should be of technological relevance since they may allow to improve the procedures applied in surface etching, surface cleaning and surface modification by atomic species.