As different structures and domains are observed in relatively thick (∼100 nm) films, EPI films with an approximate thickness of 7 nm were investigated using X-ray reflectivity (XRR) measurements to observe if the structure is different in thinner films where the growth is not allowed to proceed. Such studies are of particular interest for the films prepared at 300 K, as it may allow the observation of which phase forms first and if there may be a thickness dependence for the different phases. The XRR data were fitted using a model-independent fitting routine20 to obtain an electron density profile of the film perpendicular to the substrate surface. Details on the morphology of ∼7 nm thick films by AFM are given in Fig. S1 of the ESI.†