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

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Abstract
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+ ion in a platinum-4·0 at. % gold alloy; the specimen was maintained at 40 K (below substage IIB) during the in situ irradiation at ∼ 2 × 10−9 torr. Prior to the pulsed field-evaporation dissection of the specimen at 40 K it was warmed isochronally to 100 K (above substage IIC). 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 ∼ 20 Å in diameter. If only first nearest-neighbour 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 ∼35 to 44 at. %. Employing the modified Kinchin-Pease equation it was calculated that the displacement efficiency (k) 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.