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The electronic structures of epitaxially grown films of so-called MAX-phases were investigated by soft X-ray emission spectroscopy. These nanolaminated carbide and nitide compounds represent a class of layered materials with a combination of properties from both metals and ceramics. The bulk-sensitive soft X-ray emission technique is shown to be particularly useful for detecting detailed electronic structure information about internal monolayers and interfaces. A weak covalent Ti-Al bond is manifested by a pronounced shoulder in the Ti L-emission of Ti3AlC2, Ti2AlC and Ti2AlN. When Al is replaced by Si or Ge, the shoulder disappears. Furthermore, the spectral shapes of Al, Si and Ge in the MAX-phases are strongly modified in comparison to the corresponding pure elements. The measured X-ray emission spectra are compared and interpreted with ab initio density-functional theory including core-to-valence dipole matrix elements. The calculated results are found to yield consistent spectral functions to the experimental data. By varying the constituting elements, a change of the electron population is achieved, causing a change of covalent bonding between the laminated layers, which enables control of the macroscopic properties of the materials. |