The electronic structures of epitaxially grown films of Ti3AlC2, Ti3SiC2 and Ti3GeC2 have been investigated by bulk-sensitive soft X-ray emission spectroscopy. The measured high-resolution Ti L, C K, Al L, Si L and Ge M emission spectra are compared
with ab initio density-functional theory including core-to-valence dipole matrix elements. A qualitative agreement between experiment and theory is obtained. A weak covalent Ti-Al bond is manifested by a pronounced shoulder in the Ti L-emission of Ti3AlC2. As Al is replaced with Si or Ge, the shoulder disappears. For the buried Al and Si-layers, strongly hybridized spectral shapes are detected in Ti3AlC2 and Ti3SiC2, respectively. As a result of relaxation of the crystal structure and the increased charge-transfer from Ti to C, the Ti-C bonding is strengthened. The differences between the electronic structures are discussed in relation to the bonding in the nanolaminates and the corresponding change of materials properties.
The electronic structure in the new transition metal carbide Ti4SiC3 has been investigated by bulk-sensitive soft x-ray emission spectroscopy and compared to the well-studied Ti3SiC2 and TiC systems. The measured high-resolution Ti L, C K and Si L x-
ray emission spectra are discussed with ab initio calculations based on density-functional theory including core-to-valence dipole matrix elements. The detailed investigations of the Ti-C and Ti-Si chemical bonds provide increased understanding of the physical properties of these nanolaminates. A strongly modified spectral shape is detected for the buried Si monolayers due to Si 3p hybridization with the Ti 3d orbitals. As a result of relaxation of the crystal structure and the charge-transfer from Ti (and Si) to C, the strength of the Ti-C covalent bond is increased. The differences between the electronic and crystal structures of Ti4SiC3 and Ti3SiC2 are discussed in relation to the number of Si layers per Ti layer in the two systems and the corresponding change of materials properties.
The electronic structure of nanolaminate Ti2AlN and TiN thin films has been investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured Ti L, N K, Al L1 and Al L2,3 emission spectra are compared with calculated spectra using ab init
io density-functional theory including dipole transition matrix elements. Three different types of bond regions are identified; a relatively weak Ti 3d - Al 3p bonding between -1 and -2 eV below the Fermi level, and Ti 3d - N 2p and Ti 3d - N 2s bonding which are deeper in energy observed at -4.8 eV and -15 eV below the Fermi level, respectively. A strongly modified spectral shape of 3s states of Al L2,3 emission from Ti2AlN in comparison to pure Al metal is found, which reflects the Ti 3d - Al 3p hybridization observed in the Al L1 emission. The differences between the electronic and crystal structures of Ti2AlN and TiN are discussed in relation to the intercalated Al layers of the former compound and the change of the materials properties in comparison to the isostructural carbides.
