Electron Irradiation Damage in Aluminum in a High Voltage Electron Microscope

Defect clusters are observed to form in aluminum during examination at about 20°C in a high voltage electron microscope operating at 1000 kV with a beam current of 0.1 µA in a 5 µm diameter spot. As the electron dose increased, the clusters grow into resolvable dislocation loops. The defect clusters are identified as vacancy loops of Frank type. When the temperature is raised gradually to 70°C during electron irradiation, defect clusters grow into larger loops and eventually disappear with 70°C irradiation. Furthermore, no electron damage is observed in the specimen irradiated at 70°C without previous 20°C irradiation. In a quenched specimen, production rate of the defect clusters is larger compared with an annealed specimen and large quenched-in loops are found to shrink during 20°C irradiation. The damage rate is discussed in relation to nucleation and growth of the loops under vacancy supersaturated environment.