Ab initio calculations on (SiH 3) 2F +: stability in the gas phase and model for bridging fluorine atom in ion-implanted amorphous silicon

Abstract

Ab initio calculations have been performed on model molecular clusters simulating bridging fluorine configurations in fluorinated amorphous silicon. Optimized geometries, total energies and vibrational frequencies have been computed for (SiH 3) 2F + clusters with the terminal SiH 3 groups eclipsed or staggered. The stable minimum on the potential energy surface corresponds to a linear, but very flexible, Si-F-Si bridging configuration. (SiH 3) 2F + appears to be stable with respect to unimolecular decomposition. The calculated vibrational frequencies include a strongly infrared-active antisymmetric stretch mode at 740 cm −1, similar to the metastable “ Bband” experimentally observed at 750 cm −1 in the ion-implanted samples. These results are compared with calculated geometries and vibrational frequencies of SiH 3F, SiH 3F +, SiH 2F + and Si 2H 5F.