FORMATION AND DEVELOPMENT OF DISORDERED NETWORKS IN SI-BASED CERAMICSUNDER ION-BOMBARDMENT

In the present paper the results of an extended study on the disorderi ng of Si, SIG, Si3N4 and SiO2 by ion bombardment will be reviewed, wit h respect to both long and short range order. It was found that amorph ization 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 occur s. In SiO2, Si3N4 and Si the disordered phase consists of a random net work of [SiX4]-tetrahedrons (X = 0, N, Si), which conserved the chemic al short range order of the crystalline materials. In SIC first a high ly 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 t his network then results in complete destruction of the initial chemic al short range order and the formation of Si-Si and C-C bonds. The res ults are compared with theoretical predictions of the amorphizability of the different compounds and the microstructure of the disordered ph ases. (C) 1998 Elsevier Science B.V. All rights reserved.