Theoretical scanning tunnelling microscopy images of metal (Fe, Co, Ni andCu) phthalocyanines

The scanning tunnelling microscopy (STM) images of isolated iron phthalocya nine (FePc), cobalt phthalocyanine (CoPc), nickel phthalocyanine (NiPc) and copper phthalocyanine (CuPc) are simulated theoretically. All the simulate d STM images show submolecular structures and reproduce well the features o f the experimental images. The results show that there is a strong dependen ce 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 N iPc and CuPc appear as holes in the molecular images, while they are the hi ghlighted bumps in FePc and CoPc. The simulated images are interpreted by t he fact that both FePc and CoPc systems have a significant d(x2) character near the Fermi level while the NiPc and CuPc systems do not. Moreover, we p redict that the central nickel ion for NiPc appears as a highlighted point when the tip bias voltage is larger than 0.7 V.