We have developed a solution based synthesis of epitaxial thin films of neptunium oxide and plutonium oxide. Actinides represent a tremendous challenge to first principle calculations of orbital energies due to the complicating features that arise from f orbital interactions. Theoretical development from first principle calculations relies on predictions of continuous materials with no boundaries. Testing of these theories requires experimental results using high quality single crystals. For actinide oxides the availability of single crystals is quite limited partly because of the recalcitrant nature of the oxides. Experimental work is complicated by the radioactivity that makes typical thin film processes such as CVD challenging from a safety perspective. The challenge of modeling actinide oxides is best represented in Mott insulators such as UO2. Theoretical calculations that worked with transition metals predict UO2 to be a metal as opposed to an insulator with a 2.3 eV band gap. Recent reports predict the same metallic behavior for NpO2. Many theoretical reports have highlighted the need for experimental work on single crystals. In the absence of single crystals they rely on work done on powders as in the case of PuO2. We report here on epitaxial films of PuO2 that are thin enough to measure the optical band gap directly. XRD has been used to determine the alignment of the PuO2 relative to the substrate and EXAFS confirm the stoichiometry.

Aqueous solution route to actinide thin films

251st National Meeting (2016)

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