Interaction of Molecular Hydrogen on α-Pu at 300 K: Nucleation of Hydrides and Pu-Catalyzed Carbides

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Abstract
An α-Pu sample was studied in its "as-received" and "sputtered" state by both X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). Analysis of the "as-received" surface indicated significant carbon and oxygen, with oxygen signal pertaining to plutonium dioxide (PuO2) and sesquioxide (Pu2O3). The "sputtered" clean metal surface was then dosed with hydrogen (H2) gas at 300 K and found to nucleate hydride species (PuHx). Interestingly, H2 was observed to be critical for nucleation of carbides (PuxCy) by acting as a catalyst for Pu's reaction with background gases. Because Pu metal has a high affinity for oxygen, reoxidation occurred under UHV, forming PuxOy and disrupting both PuHx and PuxCy growth. Observations from the experiments were modeled for the α-Pu(020) surface, illustrating the ability of H2 to readily dissociate onto sputtered and speciated surfaces at 300 K. The projected density of states from these calculations were compared to experiments, showing good agreement between the Pu 5f, 6d, and 7s states and the H 1s, O 2p, and C 2p valence states. Overall, the above results indicated that the formed hydride layer is unstable at 300 K in UHV conditions.
Funding Information
  • Laboratory Directed Research and Development (20230202DR)

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