• epitaxy;
  • ionization potential;
  • SnO2;
  • surfaces;
  • work function

The surface potentials of SnO2 films grown epitaxially by magnetron sputtering on TiO2 and Al2O3 substrates with (110), (001), (101), and (100) SnO2 surface orientations are determined using in situ photoelectron spectroscopy. Epitaxial growth is verified using X-ray diffraction and low energy electron diffraction. The emphasis lies on the determination of work functions and ionization potentials of epitaxial SnO2 surfaces. SnO2 films prepared under chemically reducing conditions exhibit work functions φ of 4.25–4.48 eV and ionization potentials IP of 7.54–8.11 eV. It is furthermore demonstrated that a subsequent annealing in oxygen alters the surface dipole, visible through a large increase of ionization potential. This is due to a change of the surface termination from a reduced to a stoichiometric surface which exhibits Sn in the +IV oxidation state. The observed increase of IP varies from 0.48 eV for the (110) SnO2 surface to 1.05 eV for the (101) SnO2 surface.