SURFACE STRUCTURES OF α-Fe2O3(0001) PHASES DETERMINED BY LEED CRYSTALLOGRAPHY

Abstract

We present a dynamical tensor low energy electron diffraction (LEED) study of α- Fe 2 O 3(0001) surface structures that form in an oxygen pressure range from 10-5 to 1 mbar. Epitaxial α- Fe 2 O 3(0001) films were prepared on Pt(111) in defined oxygen partial pressures at temperatures of around 1100 K. In 1 mbar O 2 strongly relaxed oxygen-terminated surface structures are formed, while in 10-5 mbar O 2 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 O 2. The stabilization of both structures is discussed on the basis of electrostatic arguments considering the boundary conditions at the oxide–gas as well as the oxide–substrate interface (autocompensation). For oxygen pressures between 10-4 and 10-1 mbar O 2, the two 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 of identifying the involved surface structures unambiguously. Only in combination with results from other surface-sensitive methods was it possible to deduce models for the most likely surface structures.