Sexithiophene films on ordered and disordered TiO2(1 1 0) surfaces: Electronic, structural and morphological properties

Growth of sexithiophene films on both ordered and disordered TiO₂(1 1 0) surfaces has been investigated by angle-resolved ultraviolet photoemission spectroscopy, atomic force microscopy, and X-ray diffraction including grazing-incidence characterization. The order (or disorder) of the TiO₂(1 1 0)-1 × 1 surface has been observed to profoundly influence the electronic, morphological, and structural properties of the 6T films: the band alignment, which determines the injection efficiency of contacts, has been considerably modified by 0.6 eV, and a morphology with either needle-like or dendritic-like islands has been obtained. The changes in the 6T film properties are associated with the orientational modifications of sexithiophene molecules within the films, either flat-lying or upright standing, 6T(0 1 0) or 6T(1 0 0) crystallites, respectively. The growth of different crystallite orientations is argued to be controlled by the kinetics mediated by the (dis)order of the TiO₂(1 1 0) surface rather than exclusively by chemical interaction between the molecule and the substrate.