Microstructure of Al₂O₃ irradiated with an applied electric field

A thin amorphous film of alumina was irradiated with 2-MeV He⁺ ions at approx.400°C up to a damage level of about 0.01 displacements per atom (dpa). The alumina films were sufficiently thin (approx.1.8 μm) to allow the ion beam to be completely transmitted through the specimen. An electric field of approx.280 V/mm (dc) was applied continuously during the irradiation. Radiation induced electrical degradation (RIED), i.e. a permanent increase in the conductance of the film, was observed in specimens irradiated at temperatures near 400 to 450°C but did not occur in a specimen irradiated above 500°C. An investigation by transmission electron microscopy found no evidence for colloid formation. The observed increase in the conductance of the alumina film may be due to radiation-induced microcracking.