Application of anomalous oxygen Kα 532 eV peak for the determination of metal oxide thickness

Oxygen Kα spectra emitted from oxides formed on several metals were analysed with a potassium acid phthalate (KAP) crystal, which showed a strong anomalous peak due to the reflectivity spike of KAP at the particular energy region ～532 eV. The relative intensity of the 532 eV peak to the main peak decreased rapidly with the increase of the oxide thickness, while absolute intensities of both peaks increased. The relative intensity also changed depending upon an incident energy of electrons (E₀) to excite X-rays: for thick oxide it decreased relative to E₀, and for thin oxide it had a minimum value at E₀ ～5 ke V. These experimental features were well explained theoretically by taking into account a contribution both of characteristic and continuous X-rays to the 532 eV peak. As an application of this experiment, we propose a convenient, nondestructive determination of the oxide thickness.