Formation and development of disordered networks in Si-based ceramics under ion bombardment

In the present paper the results of an extended study on the disordering of Si, SIG, Si3N4 and SiO2 by ion bombardment will be reviewed, with respect to both long and short range order. It was found that amorphization occurs by nucleation and growth of defect agglomerates in the still crystalline matrix, until a critical damage density is achieved and a transition between the ordered and the disordered networks occurs. In SiO2, Si3N4 and Si the disordered phase consists of a random network of [SiX4]-tetrahedrons (X = 0, N, Si), which conserved the chemical short range order of the crystalline materials. In SIC first a highly disordered network of [SiC4]-tetrahedra forms, which is however not as random as in the other materials, since a correlation between the orientation of neighboring tetrahedra exists. Further bombardment of this network then results in complete destruction of the initial chemical short range order and the formation of Si-Si and C-C bonds. The results are compared with theoretical predictions of the amorphizability of the different compounds and the microstructure of the disordered phases. (C) 1998 Elsevier Science B.V. All rights reserved.