METAL D-ORBITAL OCCUPATION-DEPENDENT IMAGES IN THE SCANNING - TUNNELING MICROSCOPY OF METAL PHTHALOCYANINES

A strong d-orbital dependence in the scanning tunneling microscopy ima ge of metal phthalocyanines is demonstrated. Unlike copper phthalocyan ine (CuPc) wherein the central metal appears as a hole in the molecula r image, the cobalt atom in CoPc is the highest point (about 0.3 nm) i n the molecular image. On the other hand, the benzene ring regions of CoPc and CuPc appear to have the same height. These data are consisten t with theoretical calculations that predict a large contribution of c obalt d-orbitals near the Fermi energy. An intriguing aspect of this w ork is that it may be possible to chemically identify the different me tal phthalocyanines simply by their appearance. This is demonstrated f or the case of a mixed monolayer of CuPc and CoPc on Au(111).