Electron displacement damage in copper and aluminium in a high voltage electron microscope

Defect clusters are observed to form in copper and aluminium during examination at ∼20°C in a high voltage electron microscope when the voltage is greater than ∼500 kv and the beam current is high (0·1–0·4 μamps in a 5 μ spot). Experimental and theoretical considerations show that the damage is the result of the direct displacement of lattice atoms by the electron beam, resulting in the homogeneous nucleation of point defect clusters. In annealed copper the threshold electron energy required to produce the effect is orientation dependent, and the effective displacement energy Ed' is ≥ ∼30 ev in the 〈100〉 and 〈110〉 directions, and ≤26 ev in directions away from the corners of the unit triangle. Complex effects are observed in copper previously neutron irradiated and partially annealed, quenched, or cold worked. The results are interpreted in terms of the nucleation of interstitial loops and the formation of sub-microscopic vacancy clusters.