A hrem study of neutron-irradiation-induced dislocations in aluminium nitride

Abstract
Aluminium nitride polycrystals have been irradiated to fluences up to 5·2 × 1024 neutrons m-2 (E > 1·0 MeV) in a thermal-fast mixed reactor, the JMTR. Dislocations induced by the neutron irradiation were studied by high-resolution electron microscopy coupled with a multi-slice simulation. Very small interstitial loops, a few nanometres in diameter, lying on the (0001) plane of AIN were observed directly for the specimens irradiated to fluences higher than 2·4 × 1024 neutrons m-2, and it was determined that those loops have a Burgers vector of (c/2)[0001]. The dilation of the c axis by neutron irradiation was greater than that of the a axis, and this anisotropy of the lattice dilation is ascribed to the formation of interstitial loops lying on the basal plane.