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

TL;DR

This study combines soft x-ray emission spectroscopy and first-principles calculations to analyze the anisotropic electronic structure of V2GeC, revealing specific covalent bonding regions and their influence on material properties.

Contribution

It provides a detailed experimental and theoretical investigation of electronic anisotropy in V2GeC, highlighting the role of covalent bonds and their directional dependence.

Findings

High anisotropy in Ge 4p valence states and shallow 3d core levels

Small anisotropy detected in V 3d states

Identification of covalent bonding regions and their energy levels

Abstract

The anisotropy of the electronic structure of ternary nanolaminate V2GeC is investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured polarization-dependent emission spectra of V L2,3, C K, Ge M1 and Ge M2,3 in V2GeC are compared to 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 V2GeC nanolaminate result from the chemical bonds with the anisotropic pattern as shown in this work.