Films prepared at 300 K are much better ordered (seen from the increased intensity and sharpness of diffraction peaks) and several Bragg peaks are visible at 0.49, 0.57, 0.99 and 1.99 Å–1, which correspond to d-spacings of 12.66, 11.11, 6.34 and 3.15 Å, respectively. The peak at 0.49 Å–1 suggests a structure containing upright-standing molecules, similar to films prepared at 200 K, however now with a reduced tilt with respect to the surface normal; the peak at 0.99 Å–1 is the second order reflection of the same peak series. The subtle change in molecular tilt with respect to the structure observed in films prepared at 200 K suggests that there are potentially several polymorphs of EPI which differ primarily in the tilt of the long molecular axes (something previously observed for other rod-like molecules).9 The peak at 0.57 Å–1 suggests a second, more tilted polymorph of EPI is also present, with the peak having a reduced intensity compared with that of the other polymorph. The d-spacing of 11.02 Å to which it corresponds, again suggests molecules with an approximately upright-standing orientation, but now with an increased tilt away from the surface normal. This scenario is similar to the polymorphic behavior of the prototypical organic semiconductor pentacene, where several different polymorphs are known and can coexist within a thin film, each phase with a different out-of-plane d-spacing corresponding to a different molecular tilt.44 Therefore, the presence of multiple phases may suggest that a so-called surface-mediated phase9 is present in films of EPI. Finally, the comparably weak peak at 1.99 Å–1 shows that flat-lying molecules are again found to exist in the film, as this corresponds to the approximate length of a short intermolecular π–π interaction (3.15 Å).14 Overall, in EPI films prepared at 300 K, at least two (perhaps three) polymorphs are present with two distinct molecular orientations.