Arrangement and electronic properties of cobalt phthalocyanine molecules on B-Si(111)- 3×3 R30∘

The molecular arrangement and the interfacial electronic properties of cobalt phthalocyanine (CoPc) on the deactivated B-Si(111)-$\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\phantom{\rule{0.16em}{0ex}}R{30}^{\ensuremath{\circ}}$ surface are analyzed using scanning tunneling microscopy and spectroscopy as well as photoemission studies. Our data demonstrate that for low coverages of CoPc the molecules lie flat with the ${p}_z$ orbital of the Si surface atom forming a hybrid state with the ${d}_{{z}²}$ orbital of the transition metal. This hybridization is observed in a broadening of the corresponding Si $2p$ core level photoemission spectra and in an additional contribution to the valence band spectra. Furthermore, this additional hybridization state is detected in the tunneling spectra. For higher CoPc coverages, the CoPc molecules are tilted with respect to the Si surface forming highly ordered organic molecular films. The spectroscopic data of the thick film demonstrates that the electronic properties resemble those of pure CoPc.