Quantitative X-Ray Photoelectron Spectroscopy Characterization of Magnesium Oxidized in Air

Abstract

The ratio of the photoionization cross section of the Mg 2+ KL 2,3 L 2,3 transition to that of the O 1s electrons σ(Mg 2+ KL 2,3 L 2,3 )/σ(O 1s) is determined as 2.16 ± 0.02 for the Al Kα X-ray excitation. Application of this value is limited to oxidic Mg. Based on the above ratio, the photoionization cross section ratio of the Mg 2p electrons to the O 1s electrons, σ(Mg 2p)/σ(O 1s) was determined to be 0.147 ± 0.005, which can be used for quantitative X-ray photoelectron spectroscopy analysis of both oxidic and metallic states of Mg. Using the σ(Mg 2p)/σ(O 1s) thus determined, the surface compositions and film thicknesses were quantitatively determined of (i) a pure magnesium specimen immediately after scratching in laboratory air at room temperature, (ii) a specimen scratched and then aged in air for a month, and (iii) a specimen immediately after scratching in cyclohexane. A clear correlation between the composition and the thickness of surface film is observed, i.e., thickness t/nm = 4.63 - 2.73 × ([O 2- ] + 0.037 × [H 2 O])/[Mg 2+ ] or = 1.91 + 1.36 × ([OH - ] - 0.074 × [H 2 O])/[Mg 2+ ], where [E] denotes molar composition of E.