On the theory of adsorption on graphene-like compounds

Based on a previously proposed model of the electronic spectrum of binary A$_{N}$B$_{8-N}$ graphene-like compounds (GLC), adsorption theory is constructed, which allows determination of the role of the adatom level position, the adatom–substrate coupling constant, and the gap inherent to GLC in the free state with heteropolar bonds in the formation of the adatom electronic structure. The cases of free-standing and epitaxial GLCs on a metal surface are considered. In the case of free-standing GLCs, analysis shows local states mainly contribute to the adatom occupation number $n_{a}$ at large and intermediate adatom–GLC coupling constants; as the coupling constants decrease, the contribution of the GLC valence band increases. The main feature of an epitaxial GLC on metal is the absence of a gap, hence, the contribution of adatom local states to $n_{a}$. Estimations show that changes in the adatom–substrate and GLC–metal coupling constants affect $n_{a}$ in almost the same way. In this case, the dependence of $n_{a}$ on the GLC gap is not critical from the qualitative viewpoint. Adsorption on the GLC–semiconductor structure is briefly discussed.