Positive and negative ion emissions induced by low-energy ion single scattering from a single crystalline Fe3O4(001) surface

We investigated the energy spectra of positive and negative ions emitted from the (0 0 1) surface of a single crystalline magnetite, Fe3O4, under low-energy He+, Ne+ and Ar+ ion bombardments (4-8 keV). Under He+ ion bombardments, two distinct peaks in the LEIS spectra were observed at the energies where the single binary elastic scattering respectively from oxygen (He+-O) and from iron (He+-Fe) ions are expected. A large enhancement of the He+-O scattering peak was observed at 90 K. Under Ne+ ion bombardments, two observed peaks were assigned to the O+-recoil peak and to the Ne+-Fe scattering peak. Under Ar+ ion bombardments, the Fe-recoil peak and the Ar+-Fe scattering peak were revealed. The intensity and the characteristic of the Fe-recoil peak are found to depend strongly on the azimuthal angle. In all cases the large peak-width and the very high background indicated a large contribution of ion trajectories from the quasi-single scattering and multiple scattering processes. A very large O-1-recoil peak was observed under the Ne+ and Ar+ ion bombardments. The LEIS results suggest that the octahedral-Fe ions and a large amount of negative-charge oxygen ions were present on the surface and that the neutralization related to the change in the electronic state of magnetite played a dominant role in a final yield of ions. (C) 2003 Elsevier Science B.V. All rights reserved.