Soft-x-ray investigation of Mg and Al oxides: Evidence for atomic and bandlike features.

Abstract

Soft-x-ray emission (SXE) and soft-x-ray absorption (SXA) are used to investigate the electronic structure of \ensuremath{\alpha}-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$, anodized ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$, MgO, and ${\mathrm{MgAl}}_{2}$${\mathrm{O}}_{4}$. It is found that both SXE and SXA are sensitive to the crystal phase, suggesting their use as a structural probe. Comparison of the Al ${\mathit{L}}_{2,3}$ SXE of \ensuremath{\alpha}-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ and the Mg ${\mathit{L}}_{2,3}$ SXE of MgO with local-density-approximation (LDA) density-of-states calculations shows that the agreement is good, and suggests that the final-state rule is valid for the SXE of these oxides. On the other hand, comparisons show that results of the SXA and LDA calculations are not in good agreement. A model based on atomiclike excitations explains a portion of the MgO SXA spectrum well. Evidence which suggests that the remaining features are due to band structure is given.