Tracking ferroelectric domain formation during epitaxial growth of PbTiO3 films

The arrangement of domains and domain walls is a crucial factor in determining the functional properties of ferroelectric materials. Here, we track the ferroelectric domain formation mechanism in ultrathin PbTiO3 films in real time during epitaxial growth using in situ optical second harmonic generation. In combination with complementary ex situ piezoresponse force microscopy and second harmonic generation imaging, we unambiguously identify the tensile-epitaxial-strain-induced partial conversion of out-of-plane-polarized c-domains into in-plane-polarized a-domains. We further show that, in the strongly compressive epitaxial regime, the c-to-a conversion can be shifted to the early stage of the growth to favor a remarkable randomization in the distribution of a- and c-domains. This unprecedented access to the domain-formation dynamics constitutes an important step toward deterministic domain architectures in technologically relevant ultrathin ferroelectrics which, in turn, is valuable for the development of functional ferroelectric and piezoelectric structures.