Surface Structures of alpha-Fe2O3(0001) Phases determined by LEED Crystallography

We present a dynamical Tensor low-energy electron diffraction (LEED) study of a-Fe2O3(0001) surface structures forming in an oxygen pressure range from 10-5 to 1 mbar. Epitaxial a-Fe2O3(0001) films were prepared on Pt(111) in defined oxygen partial pressures at temperatures around 1100K. In 1 mbar O2, strongly relaxed oxygen terminated surface structures are formed while in 10-5 mbar O2 three different surface structures yield rather good Pendry R-factors. Further experimental evidence from scanning tunneling spectroscopy (STM) and ion scattering spectroscopy (ISS) in combination with a critical review of the literature is only consistent with a hydroxyl termination forming in 10-5 mbar O2. The stabilization of both structures is discussed on the basis of electrostatic arguments considering the boundary conditions at the oxide/gas as well as oxide/substrate interface (autocompensa-tion). For oxygen pressures between 10-4 to 10-1 mbar O2, both domains coexist as analyzed using a new, modified version of the symmetrized automated Tensor LEED program package. The system investigated in this study turns out to be very complex and the LEED analysis alone is not capable to identify the involved surface structures unambiguously. Only in combination with results from other surface sensitive methods it was possi-ble to deduce models for the most likely surface structures