Large scale features of epitaxial films, such as terrace structure, strain distribution, and grain shape, can have a substantial effect on device properties. The diffraction spot shape captures the average large scale structure. In epitaxial SrTiO3/Si (001), the spot shows a L-dependent splitting along two axes. Analysis of this feature traces its origin to a jagged step edge formation, and determines the length scale of terrace length and step meandering. Such a structure was previously observed in dimerized Si (001) using real-space imaging. Si diffusion that occurs during the first stages of growth gives rise to this morphology. This morphology may play a key role in explaining the small critical thickness for relaxation in these films. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3420394]