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Relationship between Ta Oxidation State and Its Local Atomic Coordination Symmetry in a Wide Range of Oxygen Nonstoichiometry Extent of TaOₓ

Kasatikov, S., Filatova, E., Sakhonenkov, S., Konashuk, A., Makarova, A.
Journal of physical chemistry 2019 v.123 no.11 pp. 6849-6860
X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, geometry, ions, oxidation, oxygen, physical chemistry, silicon, spectral analysis
Evolution of electronic and atomic structure of amorphous Ta₂O₅ during sputtering by Ar⁺ ions was investigated by means of X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. XPS Ta 4f spectra were analyzed through spectral decomposition by paying special attention to inelastic scattered electron background subtraction from the Ta 4f spectra. The decomposition revealed the formation of Ta⁴⁺, Ta³⁺, Ta²⁺, Ta⁺, and Ta⁰ chemical states during the sputtering. The dynamics of the Ta chemical states evolution was analyzed and referred to the modification of the local atomic structure revealed by the NEXAFS O K-edge absorption spectra analysis. The transformation of the O K-edge spectra during the sputtering suggests the preservation of a significant part of octahedrons (the structural units of stoichiometric amorphous Ta₂O₅), which serve as a matrix for low-symmetry structural units transformed from the octahedra during the sputtering. Possible mechanisms of the octahedra transformation were discussed based on the O K-edge spectra and orbital correlation diagrams. It is noteworthy that the experiment showed a possibility of complete Ta metallization by Ar⁺ ion bombardment of amorphous Ta₂O₅ on the Si substrate.