Positive and negative ion emissions induced by low-energy ion single scattering from a single crystalline Fe 3O 4(0 0 1) surface

Abstract

We investigated the energy spectra of positive and negative ions emitted from the (0 0 1) surface of a single crystalline magnetite, Fe 3O 4, 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.