NEXAFS INVESTIGATIONS ON ORDERED ADSORBATE LAYERS OF LARGE AROMATIC-MOLECULES

It is a scientific challenge to understand and control the adsorption of large organic molecules on single crystal substrates on the same le vel as that of small molecules or atoms. This is discussed on the basi s of one of the most suitable techniques for this purpose, near edge X -ray absorption fine structure (NEXAFS). As examples we present data f or highly symmetric and flat aromates without (perylene) or with react ive groups (PTCDA, PTCDI, NDCA) on various single crystal surfaces suc h as Ag(111), Ni(111) and Si(111). Preparation parameters such as cove rage, temperature and preadsorbate have been varied to study the bondi ng and molecular orientation on the surface together with the layer gr owth behaviour. In most cases the experimental comparison between diff erent molecules and simple calculations help for the interpretation of the complicated data but ad hoc X alpha-SW calculations which have be en carried out for the largest molecule presently possible (NDCA) are required for a more detailed understanding of the rich spectral featur es.