In this work, we investigated the effect of bismuth incorporation on the growth and stabilisation of r-GeO2 films deposited on rutile TiO2 (001) substrates by mist chemical vapour deposition (Mist-CVD). The addition of only 1% Bi acted as an effective surfactant, facilitating the growth of the rutile GeO2 phase. The grown films were homogeneous, flat and resistant to water degradation. High-Resolution XRD (HRXRD) measurements suggested the formation of a diffusion zone in the upper side of the r-TiO2 substrate, which reduced the mismatch and enhanced the crystallinity of the r-GeO2. Further examinations using Secondary Ion Mass Spectrometry (SIMS) and High-Resolution TEM (HRTEM) confirmed the presence of this diffusion zone. Cross-sectional TEM revealed a single-crystal rutile structure in the main body of the film. This study demonstrates the effectiveness of Bi-assisted growth to obtain r-GeO2 thin films while providing insight into the effects occurring at the interphase that govern structural formation and chemical stability.
