Structural and Optical Properties of Crystal Ion Sliced BaTiO₃ Thin Films

Barium titanate (BaTiO₃) is a compelling material for integrated photonics due to its strong electro-optic and second-order nonlinear properties. Crystal Ion Slicing (CIS) presents a scalable and CMOS-compatible route for fabricating thin BaTiO₃ films; however, ion implantation during CIS introduces lattice damage that can degrade structural and optical performance. In this study, we demonstrate that post-slicing thermal annealing effectively restores the structural integrity and optical quality of CIS-processed BaTiO₃ flakes. Raman spectroscopy confirms the recovery of crystallinity, while second-harmonic generation (SHG) microscopy reveals systematic reorientation of ferroelectric domains and restoration of the associated second-order nonlinear susceptibility tensor X⁽²⁾. Notably, SHG signals persist even in regions with weak Raman signatures, indicating that long-range ferroelectric order can survive despite partial lattice disruption. Optical measurements show that the linear dispersion of annealed CIS flakes closely matches that of bulk BaTiO₃, validating their suitability for photonic integration. Together, these results qualify CIS - combined with thermal annealing - as a viable and scalable manufacturing strategy for high-quality BaTiO₃-on-insulator (BTOI) platforms, enabling advanced integrated photonic devices for modulation, frequency conversion, and quantum optics.