For the sample prepared with a substrate temperature of 200 K (Fig. 4, top), the situation is markedly different. Here, only one strong peak is observed along the direction of the vertical axis at q z ≈ 1.9 Å–1. The peak also extends weakly along a Debye–Scherrer ring, again pointing to significant mosaicity in the film. However, the strength of this feature close to q xy = 0 shows that there is a strong preferred orientation, with a significant amount of lying molecules at the surface, as this peak corresponds to a d-spacing of 3.3 Å which can be related to intermolecular π–π interactions. The second significant feature is an in-plane peak at q xy ≈ 0.49 Å–1, which corresponds to a d-spacing of 12.9 Å, approximately the length of an EPI molecule. This feature confirms molecules lying with their long molecular axes parallel to substrate surface, and is in contrast to the situation observed in films prepared with a substrate temperature of 350 K, where molecules are mostly approximately upright-standing. The fact that the peak corresponding to the presence of lying molecule in the specular scan at q z = 1.9 Å–1 (Fig. 2) is not stronger when compared with the samples prepared at 300 and 350 K can be explained by the significant mosaicity of the 200 K film seen in the GIXD measurement (Fig. 4). This result shows that it is possible to tune the molecular orientation of the molecules on the surface only by changing the substrate temperature during deposition. The observed orientation of molecules in films prepared at a substrate temperature of 200 K also now clearly explains the observed poor performance of EPI transistors prepared in this manner,5 as charge transport through the film parallel to substrate is less favored due to the lying molecular orientation (i.e., perpendicular to the direction of the intermolecular π–π interactions). The absence of sharp Bragg peaks, and the presence of features resembling rods, again points to a disordered layered structure and highlights the poor order within the films, in agreement with the specular X-ray diffraction and XRR data.