Direct observation of the vacancy structure of a (220) platelet in an ion-irradiated platinum--4. 0 at. % gold alloy

A detailed field-ion microscope (FIM) study has been made of the vacancy structure of a (220) platelet created by a single 30 keV W/sup +/ ion in a platinum-4.0 at. percent gold alloy; the specimen was maintained at 40/sup 0/K (below substage II/sub B/) during the in-situ irradiation at approximately 2 x 10/sup -9/ torr. Prior to the pulsed field-evaporation dissection of the specimen at 40/sup 0/K it was warmed isochronally to 100/sup 0/K (above substage II/sub c/). The (220) platelet was found to consist of 31 vacant lattice sites, lying in four (220) planes, and clustered in a disc-shaped region which is approximately 20 A in diameter. If only first nearest-neighbor lattice sites are considered then the distribution of cluster sizes is as follows: (1) two monovacancies; and (2) one jumbo vacancy cluster containing 29 vacancies. The range of the vacancy concentration within the (220) vacancy platelet is approximately 35 to 44 at. percent. Employing the modified Kinchin-Pease equation it was calculated that the displacement efficiency (kappa) for this platelet is 0.12. It is suggested that the prismatic dislocation loops lying on (220) type planes, observed by transmission electron microscopy, in ion or fast-neutron irradiated platinum can form as a result of the direct collapse of (220) type vacancy platelets