Retention mechanisms and binding states of deuterium implanted into beryllium

Details Retention mechanisms and binding states of deuterium implanted into beryllium Retention mechanisms and binding states of deuterium implanted into beryllium

Apr 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009njph...11d3023r&link_type=abstract

New Journal of Physics, Volume 11, Issue 4, pp. 043023 (2009).

Physics

7

Scientific paper

The retention of 1 keV D+ ions implanted into clean and oxidized single crystalline Be at room and elevated temperatures is investigated by a combination of in situ analytical techniques including temperature programmed desorption (TPD), nuclear reaction analysis, low-energy ion spectroscopy (LEIS) and x-ray photoelectron spectroscopy. For the first time, the whole temperature regime for deuterium release and the influence of thin oxide films on the release processes are clarified. The cleaned and annealed Be sample has residual oxygen concentration equivalent to 0.2 monolayer (ML) BeO in the near-surface region as the only contamination. LEIS shows that Be from the volume covers thin BeO surface layers above an annealing temperature of 1000 K by segregation, forming a pure Be-terminated surface, which is stable at lower temperatures until again oxidized by residual gas. No deuterium is retained in the sample above 950 K. By analyzing TPD spectra, active retention mechanisms and six energetically different binding states are identified. Activation energies (EA) for the release of D from binding states in Be are obtained by modelling the experimental data. Two ion-induced trap sites with release temperatures between 770 and 840 K (EA= 1.88 and 2.05 eV, respectively) and two trap sites (release between 440 and 470 K) due to supersaturation of the bulk above the steady state fluence of 2×1017 cm-2 are identified. None of the release steps shows a surface recombination limit. A thin BeO surface layer introduces an additional binding state with a release temperature of 680 K. Implantation at elevated temperatures (up to 530 K) changes the retention mechanism above the saturation limit and populates a binding state with a release temperature of 570 K.

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