From Mn[formula omitted]O[formula omitted] thin film towards MnO[formula omitted]: Surface reactivity and the role of O[formula omitted] and H[formula omitted]O 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. [Display omitted] • Reactivity of Mn 3 O 4 under near ambient pressure of H 2 O and O 2. • MnO 2 thin film formation. • Mn oxidation state modification in near ambient pressure reaction. [ABSTRACT FROM AUTHOR]