Radiation Damage in Cobalt

Metal irradiated with ions (in the following examples Au -ion with energies of some 10 kV) will be heavily damaged; besides lots of Frenkel pairs, small vacancy type dislocation loops usually form some 10 nm below the surface.

This kind of research was important for nuclear materials science and for ion implantation techniques in general.

The loops are far too small to be seen as loops in conventional imaging; at best they appear as black dots. However, if imaged with dynamical bright-field conditions, they give rise to so-called black-white contrasts with peculiar geometries.

The following picture shows black-white contrasts of dislocation loops imaged with a {1,1,-2,0} type of diffraction vector in a specimen with a {0001} orientation. Six distinctly different kinds of contrast are observed. Two calculated contrast profiles for a particular set of Burgers vector and normal vector of the loop are also included. The size of the black-white contrasts is about 20 nm.

Same as before, but for a {1122} type specimen orientation. The observed contrasts match closely the calculated profiles for the types of dislocation loops assumed.

With frame

6.3.2 Examples and Case Studies for Dislocations

6.3.3 Stacking Faults and Other Defects