X-ray photoemission study ofδ−Pustabilized by 1 wt.% Ga: Electronic structure and sputter-induced surface phase transformation

Photoemission spectra of the core ($4f$) and valence levels of Ar-ion-sputtered, Ga-stabilized $\delta -\mathrm{Pu}$ are similar to those of $\alpha -\mathrm{Pu}$. This disordered $\alpha$- or $\beta$-like surface layer is readily transformed by mild annealing (225 °C) to the $\delta$ allotrope as evidenced by profound changes in $4f$ spectrum. We attribute these changes to a transition from predominantly $f$-like final-state screening in the $\alpha$-like phase to predominantly $d$-like screening in the fcc allotrope. The latter also shows a broadened valence band, presumably resulting from many-body effects associated with incipient localization of the $5f$ electrons.