We have studied epitaxial lateral overgrowth from the liquid phase in the system Si/SiO_x/Si using a dedicated, synchrotron-based x-ray diffraction setup (topomicroscopy) and transmission electron microscopy. A combination of high angular resolution in reciprocal space with a high spatial resolution in real space may probe lattice tilts in the microradian range on a micrometer scale. We attribute the observed curvature of the silicon lamella to an oxygen loss within the SiO_x layer. Finite-element calculations on the elastic strain distribution and a numerical description of the x-ray scattering process strongly support this scenario.