The initial stages of point defect cluster formation on the {111} habit planes of Si crystals were investigated during  in situ  electron irradiation in a high-resolution electron microscope. It was observed that <110> interstitial chains, located on {111} planes at regular intervals, were formed by the agglomeration of self-interstitial atoms to the core of vacancy or interstitial Frank partial dislocation loops and by the insertion of interstitial chains between 2 perfect {111} planes. On the basis of experimental and calculated high-resolution electron microscopic images, a structural model was proposed, for the {111} defect, which included a regular sequence of double 5-membered and single 8-membered rings in which no dangling bonds were involved. A dependence of the displacement vector of the {111} defect upon the formation mechanism was observed. An isolated {111} defect was characterized by a fully relaxed atomic structure with a displacement vector of (a/5)<111>. The aggregation of self-interstitials within the core of Frank partial dislocations resulted in a relaxation of the strongly deformed crystal lattice by decreasing the displacement vector of the initial defects.

L.Fedina, A.Gutakovskii, A.Aseev, J.Van Landuyt, J.Vanhellemont: Philosophical Magazine A, 1998, 77[2], 423-35