Surface termination, composition and reconstruction of Fe3O4(001) and gamma-Fe2O3(001)

We address a current controversy concerning the nature of the surfaces of F e3O4(001) and gamma-Fe2O3(001) grown MgO(001) by molecular beam epitaxy. De spite recent claims to the contrary, we show that gamma-Fe2O3(001) unambigu ously exhibits a (1 x 1) surface net, in contrast to Fe3O4(001), which assu mes a (root 2 x root 2)R45 reconstruction. In addition, we present high-ene rgy-resolution Fe 2p and O 1s core-level photoelectron spectra obtained at both normal and grazing emission for gamma-Fe2O3(001) and Fe3O4(001). These spectra show that the Fe3O4(001) surface has a higher Fe(III)/Fe(II) ratio than the bulk, and that the asymmetry in the O 1s line shape for Fe3O4(001 ) is due to final state effects rather than the presence of a surface oxyge n or hydroxyl species. (C) 1999 Elsevier Science B.V.