Electron energy loss spectra near structural defects in TiN and TiC

In this study, we use first principles multiple scattering calculations on atomic clusters to show how the carbon and nitrogen K-edge fine structures are modified in the vicinity of structural defects in TiN and TiC. Changes in the electron energy loss spectra are due to changes in the atomic structure of the first atomic shells around the absorbing atom. Two different kinds of defects, which both modify the structure of these atomic shells, are investigated here. In a first part, we describe a method which correctly takes into account the statistical spatial distribution of nitrogen vacancies in a TiN cluster. We study the influence of vacancy concentration on the shape of the nitrogen K-edge spectra and we find that vacancies mainly affect the height of the second peak of the spectra. This peak decreases when the number of vacancies in the second nitrogen shell increases. In a second part, we study the carbon K-edge spectrum modification near stacking faults in TiC. Two different stacking faults are studied. These two-dimensional defects are responsible for changes in the position of the carbon as well as titanium atoms of the atomic shells centered on the absorbing carbon atom. The shape of the spectra is strongly modified near the stacking faults and several peaks are affected by these modifications. We show that these fine structure modifications only concern the very first carbon atomic layers near the two-dimensional defects.