Formation of MO+ ions from metal oxides bombarded by 10-keV Ar+ ions

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Abstract
The yields of MO+ molecular ions emitted from 26 metal oxides were measured by bombardment with argon ions accelerated at 10 kV. The yields were obtained by dividing the peak intensity of MO+ by the intensity of M+, a method which negated variations in absolute peak intensity due to surface roughness of the specimen and variations in the ion current of the primary beam. The difference in the yields of MO+ from metal oxides was investigated on the basis of their binding energies, and the following empirical expression for the yield of MO+ ions was obtained: I(MO+)/I(M+)=K(−ΔH0f×mt)n, where I(MO+) and I(M+) are the peak intensity of MO+ and M+ ions, ΔH0f the heat of formation of oxides used as a binding energy, mt the mean mass of the oxides, and K and n constants. The values of n were approximately 2, 3, and 4 for MO‐, M2O‐, and MO2‐type oxides, respectively, which was equal to the valence number of the metal atom in the oxides, calculated by assigning a valence number of −2 to oxygen.