Ion-Sliced BaTiO3 Thin Films: Structural and Optical Properties for Photonic Integration

Barium titanate (BaTiO3) is a promising material for integrated photonics due to its large electro-optic and second-order nonlinear coefficients. Crystal ion slicing (CIS) enables the fabrication of thin BaTiO3 films, but ion implantation introduces crystal damage and strain that can degrade their structural and optical quality. We investigate bulk BaTiO3 subjected to low- and high-dose implantation as well as exfoliated CIS-processed flakes following thermal annealing. In bulk, ion implantation reorients ferroelectric domains from partially out-of-plane to fully in-plane polarization. Low doses relax the initial surface strain but do not enable exfoliation, whereas higher doses allow BaTiO3 thin film release at the cost of increased crystalline disorder. Raman spectroscopy reveals that phonon coherence and crystallinity, key to electro-optic performance, are restored only after thermal recovery, while second-harmonic generation microscopy shows that CIS-exfoliated flakes retain ferroelectric order and χ2 activity even before annealing. Thermal annealing further reorganizes the ferroelectric domain structure underlying the χ2 nonlinear response and returns the optical dispersion into close agreement with that of bulk BaTiO3. The results suggest that optimized CIS processing can yield optically nonlinear and electro-optically active films suitable for integrated photonics, with an accessible thickness range that surpasses what is achievable with epitaxial growth methods.