Dislocation loop formation under various irradiations of laser and/or electron beams

A high-voltage electron microscope (HVEM) equipped with a laser head (laser-HVEM) was developed at Hokkaido University and is used to investigate the surface modification of semiconductors and the behaviour of lattice point defects in metals under various irradiations of laser (photon) and/or electron beams. In the present study, the annealing effect of pulsed laser irradiation on a face-centred-cubic metal was experimentally investigated and theoretically calculated. The systematic assessment of dislocation loop evolution under laser-electron sequential irradiation and laser-electron dual-beam irradiation was performed. Our results show that the rapid heating and quenching that occurred during pulsed laser irradiation caused vacancies to be introduced at the surface of the specimen and to diffuse to the interior, which led to the formation and growth of vacancy-type (V-type) dislocation loops. These loops gradually shrank and finally disappeared during the subsequent electron irradiation of the sample. During laser-electron simultaneous dual-beam irradiation, the type of loop formed, interstitial-type (I-type) or V-type loops, is determined by the relative intensities of the laser beam and electron beam, which indicates that the loop type can be controlled by changing the relative intensities of the beams. Accordingly, models of dislocation loop formation during various irradiations were proposed. The newly developed laser-HVEM instrument is expected to be employed in the exploration of mechanisms in material science, as well as in other scientific fields.