Epitaxial Growth of β‑Bi2O3 Thin Films and Particles with Mist Chemical Vapor Deposition

Metastable β-Bi2O3 (201) epitaxial thin films and particles were synthesized on α-Al2O3 (0001) single crystal substrates with mist chemical vapor deposition. With increasing synthesis temperature, the morphology of β-Bi2O3 was transformed from flat thin film with root-mean-square roughness of about 1 nm to nano- or micro-particles, in which the thin films and particles showed good crystallinity despite the large lattice mismatch between β-Bi2O3 and α-Al2O3. The key factor to stabilize the metastable β-phase was crystallization from the amorphous phase by solid phase epitaxy. Short postannealing significantly improved the crystallinity and surface flatness.