Anisotropy in the electronic structure of V2GeC investigated by soft x-ray emission spectroscopy and first-principles theory

The anisotropy of the electronic structure of ternary nanolaminate V(2)GeC is investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured polarization-dependent emission spectra of V L(2,3), C K, Ge M(1), and Ge M(2,3) in V(2)GeC are compared with those from monocarbide VC and pure Ge. The experimental emission spectra are interpreted with calculated spectra using ab initio density-functional theory including dipole transition matrix elements. Different types of covalent chemical bond regions are revealed: V 3d-C 2p bonding at -3.8 eV, Ge 4p-C 2p bonding at -6 eV, and Ge 4p-C 2s interaction mediated via the V 3d orbitals at -11 eV below the Fermi level. We find that the anisotropic effects are high for the 4p valence states and the shallow 3d core levels of Ge, while relatively small anisotropy is detected for the V 3d states. The macroscopic properties of the V(2)GeC nanolaminate result from the chemical bonds with the anisotropic pattern as shown in this work.