Scanning electron microscopy and synchrotron x-ray diffraction studies of anatase film growth

Control over crystallite orientation in thin-films is important for improving charge carrier transport in heterojunction devices or selective catalysis in photoelectrochemical applications. 001 oriented anatase thin films were synthesized by a hydrothermal method using titanium (IV) fluoride as the titanium source and evaporated gold on silicon wafers as the substrate. The films were characterized by synchrotron X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). 2D-XRD and HR- 1D-XRD data was acquired at the Stanford Synchrotron Radiation Lightsource (SSRL) on beamlines 11-3 and 7-2 . Film microstructure was characterized by synchrotron X-ray diffraction employing an area detector and point detector. Angles of incidence were varied from 0.15 - 0.30° to detail differences between surface structure and bulk. To quantify the 001 texture, pole figures of the (004) anatase reflection were constructed from rocking curves and grazing incidence patterns after correction for background, polarization, and absorption effects. The T i0 2 films exhibit 001 texture that is strong at the surface of the film and weaker close to the substrate. However, analysis of the {101} reflection shows at least two other preferred orientations present beneath theB surface. This unexpected finding suggests that nucleation is not random and may be influenced by the substrate and solution composition. An understanding of crystal nucleation and growth under hydrothermal conditions will allow control over the film texture, thickness, and faceting, thus improving charge transport properties in opto-electric applications.