A Photoelectron Spectroscopy Study on the Interfacial Chemistry and Electronic Structure of Terephthalic Acid Adsorption on TiO2(110)-(1x1) Surface

The chemical bonding mechanism, electronic structure, and the energy level alignment at the terephthalic acid (TPA)/TiO2 (110)- (1x1) interface were investigated in situ by means of X-ray photoelectron spectroscopy (XPS) and synchrotron radiation photoetnission spectroscopy (SRPES). It has been found that the adsorption of TPA on TiO2(110)-(1x1) at room temperature leads to the formation of dicarboxylate species at lower coverage (similar to 0.2 ML) followed by the formation of monocarboxylate species below 1 ML, indicating a geometry variation from flat-lying to upright adsorption. Further deposition of TPA onto the first monolayer results in a multilayer growth without deprotonation. The energy level alignment at the TPA/TiO2 (110) interface demonstrates a straddling lineup of the organic frontier molecular levels with respect to the oxide bands at the interface. A large energy difference with a value of similar to 1.1 eV is present between the lowest unoccupied molecular orbital (LUMO) of TPA and the conduction band (CB) of TiO2, suggesting an energetically favorable electron transfer from TPA into TiO2. Fundamental understanding of the chemical interactions and electronic properties at the TPA/TiO2 interface could facilitate unravelling the microscopic mechanism for interfacial charge transfer dynamics, which is desirable for exploring a new generation of hybrid energy devices.