Soft x-ray photoemission spectroscopy of the Ba atomic layer deposition on the ceramic multiferroic BiFeO₃

Highlights: • Ba/BiFeO₃ interface was studied by X-ray synchrotron- photoemission spectroscopy. • Ba adsorption is found to modify the Bi 4f, O 1s and Fe 2p core level spectra. • Ba induced charge transfer causes increasing in Bi-valency and O-ionicity. • Ba adsorption results in increasing the amount of Fe²⁺ ions in the surface region. - Abstract: Electronic structure of the ceramic multiferroic BiFeO₃ and the Ba/BiFeO₃ nanointerface is investigated in situ in an ultrahigh vacuum by synchrotron-based photoemission spectroscopy with the excited photon energy from 120 eV to 900 eV. The Bi 4f, O 1s, Fe 2p, and Ba 5p core-levels spectra are studied. The Ba atomic layer deposition is found to induce a significant change in spectra that is originated from the charge transfer between Ba adatoms and Bi, O surface atoms with increasing the Bi-valency and O-ionicity. The Fe 2p_3/2 core level spectrum for the clean BiFeO₃ is shown to contain both the Fe²⁺ and Fe³⁺ ion components with the atomic ratio of Fe²⁺/Fe³⁺ ∼1. The Ba adsorption is found to increase the ratio up to ∼1.5. This new effect is clearly caused by recharge between Fe³⁺ ↔ Fe²⁺ ions with increasing the amount of Fe²⁺ ions.