COMPARATIVE SNMS AND SIMS STUDIES OF OXIDIZED CE AND GD

Polycrystalline Ce and Gd surfaces of various oxidation states have been investigated in situ and alternately by Sputtered Neutral Mass Spectrometry SNMS and by SIMS. For the bombardment with 4 keV Ar+ ions the dominating peaks in the mass spectra of postionized sputtered neutrals and positive secondary ions refer to metal atoms Me and monoxide molecules MeO. At oxygen concentrations of several atomic percent the sensitivity of SNMS and SIMS are of the same order. Characteristic differences are found between the behaviour of corresponding SNMS and SIMS signals: For SNMS the intensitiesI(MeO0) and I(Me0) in general vary complementarily when the oxygen is removed from the surface. The intensity ratios I(MeO0) I(Me0) decrease monotonously by 1 to 2 orders of magnitude. With SIMS both I(MeO+) and I(Me+) are found to decrease with the oxygen content. The SIMS ratios I(MeO+ I(Me+) display an oscillatory behaviour with only little variation of their absolute values. As an example, quantitative results for the behaviour of the ionisation probability α+Me for the secondary ions Ce+ and Gd+ are derived for low oxygen concentrations. © 1979.