Optical spectroscopy study of modifications induced in cerium dioxide by electron and ion irradiations

ABSTRACT

UV-visible absorption spectroscopy and Raman spectroscopy were used to study damage production in cerium dioxide epitaxial films and polycrystalline sintered samples after irradiation with electrons for three energies to span the threshold displacement energies of cerium and oxygen atoms, and 2.4-MeV Cu ions. Neither amorphization nor specific colour-centre bands were detected. Evolutions of the refractive index were derived from the interference fringes in the optical transmission spectra of epilayers after irradiation. No significant change of the refractive index occurred for the 1.0-MeV electron irradiation, whereas a maximum decrease by 28 ± 8% was deduced for the 1.4-MeV and 2.5-MeV energies. These modifications are consistent with ballistic damage on the cerium sublattice for high electron energies producing Ce³⁺ ions. However, no significant change of refractive index was found for the Cu ion irradiation. This likely stems from the high rate of Frenkel pair recombination in the collision cascades induced by more energetic recoils than for the electron irradiations, combined with electronic excitations and hole capture on Ce³⁺ ions. This study reveals modifications of the electronic structure upon irradiation that could take place in other non-amorphizable oxide systems.

KEYWORDS:

• Cerium dioxide
• electron irradiation
• heavy ion irradiation
• UV-visible absorption spectroscopy
• Raman spectroscopy

• PACS Codes: 76.30.Kg
• 78.30.-j
• 78.40.-q

Acknowledgments

We thank the French EMIR network for supporting this research programme. The authors are also indebted to Bruno Boizot and Olivier Cavani (École Polytechnique, Palaiseau, France) for their help during the electron irradiations. One of the authors (W. J. W.) was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Science & Engineering Division. This work was also supported by JSPS KAKENHI with a grant number of JP16K06961. The CeO₂ thin films were grown at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. Ion irradiation was performed under the Join Research Program at RIAM of Kyushu University.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

William J. Weber http://orcid.org/0000-0002-9017-7365

Additional information

Funding

This work was also supported by JSPS (Japan Society for the Promotion of Science) KAKENHI with a grant number of JP16K06961.