A new approach toward high quality epitaxial actinide thin films

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The illustration depicts the formation of different phases of epitaxial UOx thin films (middle region) by atoms in the plasma (purple oval) generated during the laser ablation on single crystal substrates (bottom).

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Technique benefits fundamental understanding and theoretical modeling of nuclear materials

For the first time ever, Los Alamos researchers working in collaboration with external researchers have synthesized high-quality epitaxial UO₂, U₃O_8, and UO₃ thin films using pulsed laser deposition (PLD). Once fabricated, the films’ functional properties were explored via a variety of spectroscopy techniques.

Uranium oxides have been considered as the most interesting actinide oxides because of their intriguing physical properties and technological significance in nuclear energy applications. In particular, advancing the growth processes of uranium oxides will open new routes to develop novel correlated materials for future energy, sensing, and other applications. Given this technological significance and the rich physical and chemical properties of the UO_x material system, exploring the growth of high quality epitaxial UO_x films with desired crystal structures and polymorphic phases is imperative.

In work appearing in ACS Applied Materials and Interfaces, the researchers describe the successful use of PLD to grow three different types of UO_x thin films and explore the structural and optical properties. This production capability opens new avenues to explore applications and properties of a variety of actinide thin films.

The team systematically optimized the processing conditions for the epitaxial growth of the films with a high degree of control over both the phase and the structure. The crystal structures and chemical valance states of the UO_x films were confirmed by Raman spectroscopy and x-ray photoelectron spectroscopy. The optical properties of these films are investigated by ultraviolet-visible spectroscopy. Additionally, the lattice vibrational modes of epitaxial UO_x films from Raman spectra were in good agreement with the density functional theory calculations.

The work leverages the Laboratory’s capabilities and expertise in thin film growth and characterization and materials modeling and simulation.

The work, which supports the Lab’s Energy Security mission and its Materials for the Future science pillar, was performed in part at CINT, a DOE Office of Science Basic Energy Sciences user facility jointly operated by Los Alamos and Sandia national laboratories. The Los Alamos portion of the work was funded by the Laboratory Directed Research and Development (LDRD) program, with partial support from the Lab’s G.T. Seaborg Institute.

Researchers: Aiping Chen, Erik Enriquez, Yogesh Sharma, Ibrahim Sarpkaya, Nicholas Winner, Paul Dowden, Han Htoon (Center for Integrated Nanotechnologies, MPA-CINT); Gaoxue Wang, Ping Yang, Enrique Batista (Physics and Chemistry of Materials, T-1); John Dunwoody, Joshua White, Andrew Nelson (Materials Science in Radiation and Dynamics Extremes, MST-8); and Hongwu Xu (Earth System Observations, EES-14).

Reference: “Structural and optical properties of phase-pure UO₂, α‑U₃O₈, and α‑UO₃ epitaxial thin films grown by pulsed laser deposition,” ACS Appl. Mater. Interfaces 12, 35232−35241 (2020). https://doi.org/10.1021/acsami.0c08635

Technical contact: Aiping Chen

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(Left) Photographs of epitaxial thin films grown by the PLD. (Right) Transmittance spectrum for epitaxial thin films.