Unpredicted surface termination of α-Fe2O3(0001) film grown by mist chemical vapor deposition.

We analyze the surface structure of an α-Fe 2 O 3 (0001) film grown on a c-plane sapphire substrate by mist chemical vapor deposition (CVD), which has been recently developed as a simple, safe, and cost-effective film growth method. Using coaxial impact-collision ion scattering spectroscopy, we found that the atomic-layer sequence of the surface termination of an α-Fe 2 O 3 (0001) film grown by mist CVD was Fe–O 3 –Fe– from the top layer. This surface termination is predicted to form in an oxygen-poor environment by density functional theory combined with a thermodynamical approach despite that the mist CVD process is performed with atmospheric-pressure air. The surface structure markedly changes after annealing above 600 °C in ultrahigh vacuum. We found that only a couple of layers from the top layer transform into Fe 3 O 4 (111) after 650 °C annealing, which would be so-called biphase reconstruction. Complete transformation into a Fe 3 O 4 (111) film occurs at 700 °C, whose atomic-layer sequence is determined to be Fe–O 4 –Fe 3 – from the top layer. [ABSTRACT FROM AUTHOR]