Initial stage of YBa₂Cu₃O_7-x film growth on SrTiO₃

We observed the epitaxy onset of YBa₂Cu₃O_7-x on SrTiO₃ (001) substrates by recording the reflection high-energy electron diffraction pattern in-situ as a function of time. The first "anomalous" patterns were indentified to be due to epitaxial Cu islands which then oxidize to form an average monolayer of epitaxial Cu₂O before the first YBa₂Cu₃O_7-x monolayer nucleates and spreads rapidly incorporating the Cu₂O. The growth of further layers leads to regular oscillations of the specular beam intensity. The maxima of these oscillations occur prior to layer completion. We argue that this is due to the formation of small islands on the terraces which act as strong scattering centers and thus diminish the specularity before the terraces can coalesce to complete the layer.