XPS characterization of transition metal oxalates

Abstract

X-ray photoelectron spectroscopy (XPS) was employed to characterize the surface composition, atoms’ chemical state and electronic structure of oxalates MeC2O4·nH2O (Me = Mn, Fe, Co, Ni, Cu); their structure was characterized by XRD. Core-level Me 2p, Fe 3p, Fe 3s, C 1s, O 1s, X-ray induced Auger Me LMM, O KVV and valence band spectra are presented along with a number of parameters derived from the spectra analysis. A comparative analysis of FeC2O4 and Fe2(C2O4)3 oxalates is performed. The XPS parameters for the oxalates are compared to those for respective oxides. Variation of spin-orbit splitting, multiplet splitting, energy separation and intensity of satellites in the Me 2p spectra across the series of the compounds is considered in terms of changes in the electronic structure and strength of the Me–O bonding. The strong effect of covalency of the ligand (C2O42– vs. O2–) is demonstrated. Auger parameters α′(Me) and α′(O) are determined and used for estimating the initial state effects in photoemission. The surface charging of the oxalates is shown to be mainly dependent on the surface composition and stoichiometric atomic ratios. In the C 1s and O 1s spectra of the oxalates, intense satellites are revealed for the first time.