Defect and electronic structure of TiSi2 thin films produced by co-sputterings.: Part II:: Chemical bonding and electron energy-loss near-edge structures

Differences in the bonding mechanisms of amorphous, C49 and C54 TiSi2 have been studied by the combination of experimental Si-L-23 edge electron energy-loss near-edge structures (ELNES) and first-principles calculations using model clusters composed of 48 to 69 atoms. A half-filled core-hole is put into the central Si atom of the cluster in order to include the core-hole effects. Agreement between experiment and theory is quite satisfactory in the first 20 eV; the difference in width of the first peak; between different phases is well reproduced. The width of the first peak can be related to the covalency of the compound. The total covalency of the compounds was quantified using covalent bond density (CBD), defined by the number of bonds and the bond overlap populations computed in this study. The total CBD of the C54 phase is found to be 14% greater than that of the C49 phase. This is consistent with the conclusion reached by analysis of the Si-L-23, edge ELNES. The amorphous phase displayed similar Si-L-23 edge ELNES to that of the C49 phase. This is suggestive of the presence of C49-like bonding structures in the amorphous TiSi2, as exemplified by the presence of Si-Si bonds shorter than 2.5 Angstrom. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd.. All rights reserved.