Controlling the density of hydrothermally grown rutile TiO2 nanorods on anatase TiO2 films

Due to their interface properties, compounds of anatase membranes and hydrothermally grown rutile TiO2 nanorods are valuable materials for (opto-) electronic applications. So far, dense nanorod arrays are typically grown on seeds such as polycrystalline rutile TiO2, fluorine-doped tin oxide (FTO) or seed particles in dispersion and the anatase modification is added subsequently. Nanorods grown on existing anatase films usually suffer from poor adhesion. In this study, we demonstrate the fabrication of anatase films that act directly as seed layers for the hydrothermal growth. The presented compounds offer a strong adhesion between the two TiO2 modifications and the substrate which resists even extensive sonication. So far, the density of nanorods is controlled with the HCl concentration, which affects also their size and shape. We control the density of nanorods with the average grain size of the anatase film without affecting their size and shape. This offers new scientific insights and applications of specific anatase/rutile compounds. The grain size of the anatase films is adjusted with the post-annealing temperature after film deposition. To satisfy the requirements of different applications, we provide suitable anatase seed layers with different deposition techniques such as sputter deposition, spray pyrolysis, and atmospheric spatial atomic layer deposition (SALD).