Electronic structure investigation of Ti3AlC2, Ti3SiC2, and Ti3GeC2 by soft-X-ray emission spectroscopy

摘要

The electronic structures of epitaxially grown films of Ti3AlC2, Ti3SiC2 andTi3GeC2 have been investigated by bulk-sensitive soft X-ray emissionspectroscopy. The measured high-resolution Ti L, C K, Al L, Si L and Ge Memission spectra are compared with ab initio density-functional theoryincluding core-to-valence dipole matrix elements. A qualitative agreementbetween experiment and theory is obtained. A weak covalent Ti-Al bond ismanifested by a pronounced shoulder in the Ti L-emission of Ti3AlC2. As Al isreplaced with Si or Ge, the shoulder disappears. For the buried Al andSi-layers, strongly hybridized spectral shapes are detected in Ti3AlC2 andTi3SiC2, respectively. As a result of relaxation of the crystal structure andthe increased charge-transfer from Ti to C, the Ti-C bonding is strengthened.The differences between the electronic structures are discussed in relation tothe bonding in the nanolaminates and the corresponding change of materialsproperties.