By extending the growth time to 20 and 30 minutes, films with thicknesses of ~6.6 nm and ~10.2 nm, respectively, could be synthesized (Fig. and Supplementary Fig. ). Increasing growth time beyond 30 min resulted in the deposition of randomly oriented crystals without further increase in the film thickness (Supplementary Fig. ). This indicates the onset of homogeneous nucleation and its competition with the growth of the film at the late stage of film growth.