The roles which were played by defects in the ion beam-induced amorphization of crystalline material, and the structural relaxation of amorphous material, were investigated. An elementary amorphization process for ion-implanted material was described in terms of molecular dynamics. According to this model, a di-vacancy and a di-interstitial pair which was introduced into the crystalline lattice gave rise to a local atomic arrangement which included 5-membered and 7-membered rings. Raman spectroscopic and positron lifetime data yielded the bond-angle deviations and the vacancy-type defect sizes. During annealing at 450C, the bond-angle deviation decreased appreciably and small vacancies predominated in ion-beam and electron-beam treated material. Large vacancy clusters formed, and the bond-angle deviation was approximately constant, in plasma chemical vapor-deposited material. It was concluded that relaxation processes were suppressed in the latter material. The results suggested that large vacancy-type defects could stabilize amorphous structures.

T.Motooka, Y.Hiroyama, R.Suzuki, T.Ohdaira, Y.Hirano, F.Sato: Nuclear Instruments and Methods in Physics Research B, 1995, 106[1-4], 198-205