Modeling radiation induced structural evolution in nonmetallic compounds

To interpret and moreover to predict whether the structure of the near surf ace region of an ion bombarded crystalline system will be able to withstand irradiation, or it will undergo radiation induced amorphization is a diffi cult problem. The atomistic segregation charge transfer model is adopted he re to interpret the stage of nucleation of a crystalline, or an amorphous s tructure in binary films of covalently bonded materials, ion bombarded unde r conditions favoring the formation of dense collision cascades. A nonequil ibrium compositional profile is supposed to develop at the cascade-matrix i nterface, following bombardment induced interface segregation of one of the film constituents. Such a local stoichiometry change is associated with th e development of a nonequilibrium electronic density profile. Interatomic i nteractions leading to the formation of amorphous, or crystalline nuclei ar e treated by local charge transfer reactions. Qualitative differences are f ound both concerning the energetics of charge transfer reactions and the bo nding features of the nuclei, with a set of 14 compounds undergoing amorphi zation and 12 compounds remaining crystalline upon ion bombardment. (C) 199 9 American Institute of Physics. [S0021-8979(99)00803-8].