Theoretical Scanning Tunneling Microscopy Images of Metal(Fe, Co, Ni, and Cu) Phthalocyanines

The scanning tunneling microscopy (STM) images of isolated iron
phthalocyanine (FePc), cobalt phthalocyanine (CoPc), nickel
phthalocyanine (NiPc) and copper phthalocyanine (CuPc) are simulated theoretically. All the simulated STM images show submolecular structures and reproduce well the features of the experimental images. The results show that there is a strong dependence of the STM images on the ion valence configuration of the metal ion. At the small tip bias voltages of less than 0.5 V, the central metal ions in NiPc and CuPc appear as holes in the molecular images, while they are the highlighted bumps in FePc and CoPc. The simulated images are interpreted by the fact that both FePc and CoPc systems have significant d_z² character near the Fermi level while the NiPc and CuPc systems do not. Moreover, we predict that the central nickel ion for NiPc appears a highlighted point when the tip bias voltage is larger than 0.7 V.