Quantitative near-atomic-resolution oxidation-state mapping in complex oxide heterostructures by electron energy-loss spectroscopy

Ioannis Iatrakis; Zitao Zhang; Ricardo Egoavil; Emma van der Minne; Christoph Baeumer; Frank de Groot

paper

Quantitative near-atomic-resolution oxidation-state mapping in complex oxide heterostructures by electron energy-loss spectroscopy

arXiv:2610.04797

Abstract

We present a theoretical framework for quantitative oxidation state mapping of transition-metal and rare-earth elements from near-atomic-resolution electron energy-loss spectroscopy (EELS) in complex oxide heterostructures. The total inelastic differential cross section of transition-metal L $_{2, 3}$ and rare-earth M $_{4, 5}$ edges is calculated by combining the relaxed Dirac-Hartree-Fock ionization cross section with ligand-field multiplet theory for the discrete transitions. We apply the approach to two correlated-oxide heterostructures, La $_{0.67}$ Sr $_{0.33}$ MnO $_{3}$ /LaCr $_{0.2}$ Mn $_{0.2}$ Fe $_{0.2}$ Co $_{0.2}$ Ni $_{0.2}$ O $_{3}$ /SrTiO $_{3}$ and NdNiO $_{3}$ /La $_{0.67}$ Sr $_{0.33}$ MnO $_{3}$ /NdGaO $_{3}$ , which include a wide range of transition-metal and rare-earth elements with overlapping features. The method resolves the oxidation states of Cr, Mn, Fe and Co and identifies the Ni contribution within the LaCr $_{0.2}$ Mn $_{0.2}$ Fe $_{0.2}$ Co $_{0.2}$ Ni $_{0.2}$ O $_{3}$ layer at near-atomic resolution. We find predominantly Co $^{2 +}$ together with mixed Mn $^{2 +}$ /Mn $^{3 +}$ /Mn $^{4 +}$ character, indicating site-specific valence redistribution within the layer. We also separate overlapping spectral features, such as La-M $_{4, 5}$ and Ni-L $_{2, 3}$ edges in the NdNiO $_{3}$ /La $_{0.67}$ Sr $_{0.33}$ MnO $_{3}$ /NdGaO $_{3}$ heterostructure, thereby recovering the intrinsic Ni-L $_{2, 3}$ excitation spectrum. We find that the effective Ni valence in NdNiO $_{3}$ deviates from the simple ionic picture. More broadly, this work establishes a generic method for quantitative valence mapping from near-atomic-resolution EELS, applicable to a wide range of experimental conditions for the study of local electronic structure of complex oxides.

arXiv comment14 pages, 15 figures