The Si 2p spectrum is commonly measured in XPS studies of the SiO2/Si interface. However, the core-level binding energy shift ΔE2p of Si 2p on formation of SiO2 films largely depends on some extrinsic effects [1], which makes it difficult to obtain ΔE2p values intrinsic to the local environment. In order to eliminate the extrinsic contributions, we focused on the difference between the core-level binding energy shift ΔE1s for Si 1s on formation of SiO2 and ΔE2p, or the relative chemical shift ΔE1s - ΔE2p [2].
Recently we found that the ΔE1s - ΔE2p values determined for the Si compounds (Si, SiC, Si3N4, SiO2) have a reasonably good linear relationship with the (ε - 1) / (ε + 2) values for these compounds (ε: the optical dielectric constant) [3]. We tentatively suppose that the ΔE1s - ΔE2p values determined by the valence charges of Si atoms in the Si compounds have a good correlation with the polarizability of Si bonds in the Si compounds and that the ΔE1s - ΔE2p values thus can give a good estimation of the dielectric constant through the Clausius-Mossoti equation, which describes a relation between the polarizability and the dielectric constant.
In this study, we examine a correlation between the optical dielectric constant ε and ΔE1s - ΔE2p values for other dielectric compounds, namely Al compounds. The Al 1s and 2p photoemission spectra from the samples are measured using high-resolution high-energy x-ray radiation at SPring-8. The ΔE1s values and ΔE2p values on formation of the Al2O3 and AlN are determined with respect to Al.
We find a good linear relationship between the ΔE1s - ΔE2p values and the (ε - 1) / (ε + 2) values for the Al compounds as like for the Si compounds. This shows that the ΔE1s - ΔE2p values give a very good estimation of the optical dielectric constants for the Al compounds as well as the Si compounds. First-principles calculation is performed to reveal the mechanism behind the observed relationship.
[1] K. Hirose, et al., Prog. Surf. Sci. 82, 3 (2007). [2] K. Hirose, et al., J. Phys. IV 132, 83 (2006). [3] K. Hirose, et al., Appl. Phys. Lett. 89, 154103 (2006).
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