From Mn3O4 thin film towards MnO2: Surface reactivity and the role of O2 and H2O exposures investigated by X-ray Photoelectron Spectroscopy at Near-Ambient Pressure

MnO 2 phase of manganese oxide was identified as the final product of a multiple steps reaction in near ambient pressure-X-ray photoemission (NAP-XPS) chamber. At the first stage of the reaction, an intermediate stable manganese hydroxide film was obtained at ∼ 400 °C in presence of p(O 2 ) and p(H 2 O) and verified by the formation of sizeable hydroxide peak, OH, at binding energy 531.4 (1) eV. The Mn hydroxide film is kept unaltered even when is subsequently exposed to p(O 2 )= 2 mbar at ∼ 450 °C, and it is modified into δ -MnO 2 phase at ∼ 480 °C when p(O 2 ) pressure is suddenly reduced to below 10 −9 mbar. Thus, the OH spectral feature becomes the main signature in O 1s core level spectral regions and a Mn 4 + related feature is identified in Mn 2p energy range. The multiple step reaction follows the proposed mechanism for the MnO 2 formation in electrolytic cell and it is the first observation in a controlled way in NAP-XPS chamber. The findings open new roots for the birnessite manganese oxide phase formation and its manipulation.