J. Phys. IV France 04 (1994) C9-183-C9-186
Oxygen 2s spectroscopy of tin oxides with synchrotron radiation-induced photoemissionJ.-M. Themlin1, J.-M. Gilles2 and R.L. Johnson3
1 Groupe de Physique des Etats Condensés, URA 783 du CNRS, Faculté des Sciences de Luminy, Case 901, 13288 Marseille cedex 9, France
2 LASMOS, Facultés Universitaires Notre-Dame de la Paix, 61 rue de Bruxelles, 5000 Namur, Belgium
3 II Institute for Experimental Physics, Uni. Hamburg, 149 Luruper Chaussee, 2000 Hamburg 52, Germany
Oxygen 2s spectroscopy can be especially useful in studies using synchrotron radiation (SR) where the deeper O 1s level frequently can not be excited. For tin oxides (SnO and SnO2), the weak emission from the O 2s levels has been previously found degenerate with the intense photoemission peak from Sn 4d levels around a binding energy (BE) of 26 eV. By working at the Cooper minimum of the interfering tin signal, a distinct peak near BE ≈22.5 eV could be unambiguously attributed to emission from O 2s levels in tin oxides considering photoionization cross-section arguments. The O 2s intensity could now be used for the quantitative evaluation of the near-surface oxygen-species concentration. We have used the O 2s in combination with the Sn 4d areas to study the variations of the [Sn]/[O] ratio as a function of the preparation of a SnO2 single crystal. Although the dominant formal valence state for tin determined from a Sn 4d lineshape analysis remains essentially Sn4+, we show that this [Sn]/[O] ratio can vary from simple to double. This can be explained by oxygen interstitials buried in a sub-surface region during ion bombardment, which segregate at the surface upon annealing.
© EDP Sciences 1994