On determining the presence of several polymorphs and different orientations of EPI molecules in films by analyzing the out-of-plane order within the films, grazing incidence X-ray diffraction (GIXD) measurements were performed to gain insight into the in-plane ordering, which is inaccessible to specular X-ray diffraction measurements. Reciprocal space maps generated from GIXD data for the ∼100 nm thick samples prepared at different substrate temperatures are shown in Fig. 4. The maps show the in-plane scattering vector, q xy, plotted against the out-of-plane scattering vector, q z, and reveal several clear diffraction features for each of the samples.