Comparative Photoemission Study of Actinide (Am, Pu, Np and U) Metals, Nitrides, and Hydrides

Abstract

Core-level and valence-band spectra of Pu and the other early actinide compounds show remarkable systematics, which can be understood in the framework of final state screening. We compare the early actinide (U, Np, Pu and Am) metals, nitrides and hydrides and a few other specific compounds (PuSe, PuS, PuC x , PuSi x ) prepared as thin films by sputter deposition. In choosing these systems, we combine inherent 5f band narrowing, due to 5f orbital contraction throughout the actinide series, with variations of the chemical environment in the compounds. Goal of this work was to learn more on the electronic structure of the early actinide systems and to achieve the correct interpretation of their photoemission spectra. The highly correlated nature of the 5f states in systems, which are on the verge to localization, makes this a challenging task, because of the peculiar interplay between ground state DOS and final-state effects. Their influence can be estimated by doing systematic studies on systems with different (5f) bandwidths. We conclude on the basis of such systematic experiments that final-state effects due to strong e-e correlations in narrow 5f-band systems lead to multiplet like structures, analogous to those observed in the case of systems with localized electron states. Such observations in essentially band-like 5f-systems was first surprising, but the astonishing similarity of photoemission spectra of very different chemical systems (e.g. PuSe, Pu 2 C 3 and δ-Pu) points to a common origin, relating them to atomic features rather than material dependent density of states (DOS) features.Mater. Res. Soc. Symp. Proc. Vol. 986

Current understanding of photoelectron spectra in plutonium systems

“…This correlation can also be seen in other case, in which calculations have not been performed yet, as PuSi [4] or PuH 3 [15].…”

Hydrogen in actinides: electronic and lattice properties

“…The comparison to the experimental XPS and BIS [73] in figure 12 indicates that this setting places the uranium 5f states at the correct energies. Moreover, the theory reproduces the shoulder at 0.5 eV BE resolved in UPS [73,95,97], which is the expected 5f 3 → 5f 2 multiplet transition. We were able to prove this assignment by performing a series of calculations with the hybridization between the 5f states and the other electronic states varied from zero (the atomic limit where the multiplet transitions are exact) to the realistic UH 3 strength.…”

“…The magenta spectrum represents the valence band of UH 2 thin film. 5f 3 multiplets, PuH 3 as 5f 4 multiplets, and Am as 5f 5 multiplets, the last two being unresolved [97]. The differences with respect to pure metals are most striking in the case of Pu [97], in which pure metal has most of the emission close to the Fermi level, whereas PuH 3 has very little at E F , reflecting the possible loss of metallicity, and the main emission is in a maximum at 2.5 eV below E F .…”

Electronic properties ofα−UH3stabilized by Zr

“…The calculations performed so far (ours or in Ref. 31) exhibit a certain disagreement with the high-resolution UPS data,50 which show the occupied part of the 5 f band in UH 3 to almost 2 eV binding energy exceeding thus the calculated DOS not reaching more than 1 eV binding energy. More advanced calculations using LDA+U, LDA+Hubbard I or DMFT should determine whether the ground-state DOS is modified if the e-e correlations are treated more explicitely or whether it is actually the f 2 final-state multiplet appearing in the valence-band spectra, as suggested in Ref.…”