Termination and Verwey transition of the (111) surface of magnetite studied by scanning tunneling microscopy and first-principles calculations

Scanning tunneling microscopy and scanning tunneling spectroscopy combined with first-principles calculations have been applied to investigate the (111) surface of a naturally grown Fe₃O₄ single crystal. The commonly observed surface is determined as a layer of Fe cations at tetrahedral sites, known as the Feₜₑₜ₁ termination. A surface terminated with Fe cations at octahedral sites, another proposed termination in previous studies, is found only when the surface was prepared under oxygen-poor conditions. Scanning tunneling spectra at room temperature and at 77 K indicate that the (111) surface undergoes a metal-insulator transition.