Hydrogen implantation defects in MgO

Abstract

Deuterium and hydrogen ions with an energy of 15 keV have been implanted in virgin MgO (1 0 0) single crystals and in single crystals containing helium implantation generated microcavities. Doses were varied from 2´10 15 to 2´10 16 cm À2. The samples were annealed from room temperature to 950 K. The defects produced by hydrogen and the trapping of hydrogen at the defects were monitored by photon absorption and positron beam analysis. With this novel technique a depth distribution of defects can be determined for implantation depths from 0 to 2000 nm. The technique is very sensitive for vacancy and vacancy clusters, i.e. sites with low electron density. After 950 K annealing microcavities were observed for the 2´10 16 cm À2 dose but not for the 10 times lower dose. During annealing up to 750 K point defects are mobile but the defect clusters remain small and ®lled with hydrogen. In samples which contain already microcavities, point defects and deuterium from the deuterium irradiation are accumulated by the microcavities.

Nanocavity formation processes in MgO() by light ion (D, He, Li) and heavy ion (Kr, Cu, Au) implantation

“…No cavities are observed for the light ions D, He and Li. However, in the case of D and He gas bubbles are formed in the implantation zone, which eventually convert into nanocavities when the gas is released from the bubbles: for D and He this transition from bubbles to nanocavities takes place at 950 and 1300 K respectively [2,3]. Lithium forms metallic Li precipitates without a cavity zone.…”

“…Recently, results have been reported of studies where precipitate formation has been tried in two steps. First, cavities are formed by light ion bombardment followed by annealing [2,3]. In a second step, the metal was introduced by bombardment with metal ions followed by Nuclear Instruments and Methods in Physics Research B 191 (2002) 610-615 www.elsevier.com/locate/nimb annealing to diffuse the metal atoms to the preexisting cavities [4,5].…”

Study of radiogenic helium diffusion in the β-thorium phosphate diphosphate ceramic

“…Spectacular examples are given by the external irradiation where the local concentration could form up to micrometrical bubbles (for a fluence of about 10 22 He m À2 in AlSiON at 300 K [15] and 10 20 He m À2 in Al 2 O 3 at 900 K [16]). However, the accumulation of helium could modify first the nanostructure around point defects or dislocation loops by formation of clusters and microcavities [17]. Above all, for polycrystalline material (like b-TPD), these microcavities close to the grain boundaries could generate microcracks which finally modify the macroscopic structure and affect the mechanical properties of the ceramic.…”