Ion bombardment of H.C.P. and F.C.C. cobalt in the electron microscope

Visible defects having diameters ranging from 15 to 80 Å were produced in h.c.p. and f.c.c. cobalt during bombardment at about 20 °K with 100 keV O− ions in the electron microscope. The principal component of the strain field was along 〈111〉 for the majority of the defects in the f.c.c. regions and along 〈2023〉 for many of the defects in the h.c.p. regions. The strain fields are consistent with that expected for dislocation loops lying on {111} planes and having 1/3 〈111〉 Burgers vectors in the f.c.c. case and dislocation loops lying on the (0001) plane and having 1/6〈2023〉 Burgers vectors in the h.c.p. case. It is not possible, however, to differentiate between a single dislocation loop and an assembly of small narrowly spaced loops all having the same Burgers vector and the same loop habit plane. Stereo analysis of the defects produced during ion bombardment at about 20 °K was performed at 300 °K. The analysis showed that vacancy like defects were involved. It is proposed that the defects represent depleted regions formed directly in the collision cascade.