In-situ imaging of the nucleation and growth of epitaxial anatase TiO2(001) films on SrTiO3(001)

► Initial growth of anatase TiO2(001) follows the Stranski-Krastanov mode. ► Epitaxial islands subsequently coalesce into oriented crystallites. ► The crystallites grow in units of bilayers leading to a step height of 2 monolayers. ► Each crystallite is dominated by either (1 × 4) or (4 × 1) surface reconstruction. ► A discrepancy between previous RHEED and ex-situ STM studies is resolved.