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

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 2p3/2 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.