High-resolution transmission electron microscopic observations were made of  in situ  Ca colloid formation in pure crystals, using low beam-current densities in the [110] orientation. Because the nucleation process was rapid, only already-formed colloids could be monitored. During further irradiation, dislocations and stacking faults appeared in the Ca and CaF2; due to stress relaxation in thin areas of the crystal.

V.S.Teodorescu, L.C.Nistor, J.Van Landuyt: Materials Science Forum, 1997, 239-241, 671-4