Adsorption behavior of cobalt phthalocyanine submonolayer coverages on B-Si(111)-$3×3R30°$

The molecular arrangement and electronic properties of submonolayer coverages of cobalt phthalocyanine (CoPc) molecules on the deactivated B-Si(111)-$3×3R30°$ surface are analyzed using scanning tunneling microscopy and spectroscopy. On the ideal surface, the dangling bonds, which typically prevent an ordered growth of molecules on semiconductors, are removed. However, the presence of single defects enables the opportunity to study the influence of their dangling bonds on the adsorption behavior in detail. Here, we focus on coverage densities below and above the Si-Si(⁠$S5$⁠) defect density. Our data demonstrate that for all submonolayer coverages, the CoPc molecules adsorb in a flat-lying geometry, with either a circular or a four-leaf cloverlike appearance. Initially, each CoPc molecule adsorbs on top of a Si-Si(⁠$S5$⁠) defect, while later, also passivated Si adatoms become occupied. For the adsorption on Si-Si(⁠$S5$⁠) defects, hybridization between its $pz$ orbital and the $dz2$ orbital of the Co atom of the molecule occurs, leading to additional hybridization states observed in the tunneling spectra.