Dislocation structure formation due to ion implantation

Abstract

A mechanism of dislocation structure formation and its dynamics is presented. Coalescence of the interstitial atoms leads to the formation of dislocation loops. The formed loops grow due to precipitation of the interstitial atoms. Interaction between loops results in their motion deep into material, where loops form a developed dislocation structure. 1. There are many experimental evidence of an influence of ion bombardment on the material structure and properties in the region disposed much deeper than the ion penetration depth. One of this long range effects is the dislocation structure formation at a depth up to about 100 microns.'-4 A number of mechanisms explaining that phenomenon has been suggested. However, a general theory of dislocation structure formation has not been found yet. A mechanism of dislocation structure formation and its dynamics in the implanted specimen is considered in the present paper. It is suggested that the coalescence of the interstitial atoms emerging due to ion bombardment results in the creation of dislocation loops. Then the loops move deep into the specimen because of interaction with each other. Collisions between the loops result in pinning and formation of immobile dislocation structure. 2. Under irradiation a lot of interstitial atoms and vacancies appear in the material. They are created in a narrow region at the ion penetration depth and then diffuse deep into the sample. The diffusion coefficient of interstitial atoms, D, is much greater than that of vacancies, D,. Therefore, at the depth z > (D\ty5 the concentration of interstitial atoms, c, exceeds that of vacancies, c,. This is the condition for the preferable formation of interstitial dislocation loops and their growth. The loops are formed by means of fluctuation. The critical number of atoms in the loop is equal to7