ToF-SIMS and XPS Studies of the Adsorption Characteristics of a Zn-Porphyrin on TiO2

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) were used to study monolayers (ML) and thick films of porphyrin Zn-TFSP (C67H75N5O5SiZn) attached to titanium dioxide (TiO2) substrates via silanization. Films on ideal hydroxyl-terminated silicon (SiO2) surfaces were used for comparison. ToF-SIMS and XPS spectra show that the type of adsorption varies depending on the thickness of the organic film, the preparation temperature, and the adsorption time. We show that the intensity of a molecular peak at mass 1121.5 u in TOF-SIMS can be used as a direct measure of the ration chemisorption/physisorption of Zn-TESP. On TiO2, the amount of chemisorbed porphyrin can be increased by increasing the reaction temperature and little during the silanization process. On the SiO2 reference, only chemisorbed species were detected under all investigated preparation conditions. The present work thus not only gives information on the Zn-TESP linkage to TiO2 but provides a direct tool for generally determining the type of adsorption of monolayers.