Optical emissions of products sputtered from Fe, Fe sub(2)O sub(3) and Fe sub(3)O sub(4) powders

Powder iron has been bombarded by a 5 keV Kr super(+) ions in a vacuum better than 10 super(-7) torr and under few 10 super(-6) torr ultra pure oxygen partial pressure. The optical spectra of the sputtered particles were recorded between 340.0 nm and 410.0 nm. These spectra exhibit discrete lines, which are attributed to neutral excited atoms of iron. Two iron oxides, namely hematite (Fe sub(2)O$_{3})$ and magnetite (Fe sub(3)O$_{4})$, in powder form, were studied under the same experimental conditions and identical lines were observed in the obtained spectra. The absolute intensities of the spectral lines in all spectra were measured and the differences in the recorded yield photons were discussed in term of electron-transfer processes between the excited sputtered atom and the bombarded surface. In accordance with the proposed interpretation, we suggest values for the energy gaps and electronic affinities for the studied oxides and for the oxide layer that might be formed by the adsorption of oxygen atoms.