Anisotropy in the electronic structure of V2 GeC investigated by soft x-ray emission spectroscopy and first-principles theory

Abstract

The anisotropy of the electronic structure of ternary nanolaminate V2 GeC is investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured polarization-dependent emission spectra of V L2,3, CK, Ge M1, and Ge M2,3 in V2 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: V3d-C2p bonding at -3.8 eV, Ge4p-C2p bonding at -6 eV, and Ge4p-C2s interaction mediated via the V3d 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 V3d states. The macroscopic properties of the V2 GeC nanolaminate result from the chemical bonds with the anisotropic pattern as shown in this work. © 2008 The American Physical Society.