Abstract
We report on the atomic and electronic structure of ordered nitrogen vacancies in CrN by using spherical aberration-corrected high-resolution transmission electron microscopy, electron energy-loss spectra, and ab initio calculations. The ordered nitrogen vacancies are identified to be distributed on atomic planes. The vacancy concentrations were evaluated by quantitative high-resolution transmission electron microscopy. A direct consequence of the ordered nitrogen vacancies is a lattice shrinking leading to a reduced lattice constant, displaying a distorted CrN. The experimental measured lattice constant is quantitatively compared to the ab initio calculations. A relationship between the lattice constant and nitrogen vacancy concentration is theoretically and experimentally established, and quantitatively compared. The presence of the ordered N vacancies further induces the electronic changes as reflected in a very small core-level shift as well as a shift of the volume plasmon energy. Moreover, the change of the ionicity in CrN with nitrogen vacancy concentration is revealed. A direct relation between the covalent-ionic level of the bonding and the nitrogen vacancy concentration is shown.
- Received 29 July 2012
DOI:https://doi.org/10.1103/PhysRevB.87.014104
©2013 American Physical Society