Capabilities of static TOF-SIMS in the differentiation of first-row transition metal oxides

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) analyses were per formed on the first-row transition metal oxides from scandium to zinc in po sitive and negative detection modes. The nature of the numerous MwOy+/- ion ic species generated by 15 keV Ga+ primary ion bombardment allows the ident ification of a given metal-oxygen system. To identify the metal valence in the oxide under investigation, several procedures were investigated: the de tection of specific and characteristic ions, the use of ion abundance ratio s and the use of a valence model. Owing to their importance in many fields of materials science, each of these speciation methodologies was evaluated for the differentiation of vanadium, titanium, chromium, manganese, iron, c obalt and copper oxides. Trivalent-hexavalent chromium distinction was firs t intensely investigated because it really corresponds to a model system fo r inorganic speciation. For each series of metal oxides, the more pertinent speciation criteria were then systematically tested. The limitations of th e proposed methodologies are discussed. Their use is made complicated when pollutants or a superficial oxide layer, with a stoichiometry different fro m that of the bulk, are present. Finally, thermodynamic considerations rela tive to the stability of the MxOy+/- ions may also modify the relationship between the analyzed oxide and the observed positive and negative secondary ion mass spectra. Copyright (C) 2001 John Wiley & Sons, Ltd.