Scanning Tunneling Microscopy and Spectroscopy of Phthalocyanine Molecules on Metal Surfaces

We studied the electronic structure of cobalt-phthalocyanine (CoPc) molecules on Au(111) and Cu(100) surfaces by scanning tunneling microscopy and spectroscopy at 5 K. In the differential conductance (dI/dV) spectra, there were some peaks related to the highest occupied molecular orbital (HOMO), the lowest unoccupied MO (LUMO) and the d-orbitals of the Co atom. CoPc molecules on the Cu(100) surface had new electronic states between the peaks related to HOMO and LUMO, while those on the Au(111) surface did not show additional peaks. A dI/dV image indicated that the new states were generated by the hybridization between the LUMO of molecules and the electronic states of the Cu(100) surface.