Adsorption of Co-Phthalocyanine on the Rutile TiO2(110) Surface: A Scanning Tunneling Microscopy/Spectroscopy Study

We investigated the adsorption properties of Co-phthalocyanines (CoPc's) on the rutile TiO2(110) surface using scanning tunneling microscopy and spectroscopy. Analytical results showed that the adsorption properties strongly depend on the deposition conditions. Under specific deposition conditions (elevated substrate temperatures and low deposition rates), the molecules are immobilized on the surface without aggregation up to the full monolayer coverage. The substrate temperature plays a key role in determining the bonding nature between the molecules and the substrate. The immobilized molecules introduce gap states at the interface and locally decrease the surface band gap to an energy value that is lower than that of the absorption band of the CoPc thin film. Coverage dependence studies show that the adsorption structures are dominated by molecule-substrate interactions for the first monolayer growth and by a complex interaction between molecules in the first and second monolayers for the second monolayer growth.