Cobalt and manganese carboxylates for metal oxide thin film deposition by applying the atmospheric pressure combustion chemical vapour deposition process

Abstract

Coordination complexes [M(O₂CCH₂OC₂H₄OMe)₂] (M = Co, 4; M = Mn, 5) are accessible by the anion exchange reaction between the corresponding metal acetates [M(OAc)₂(H₂O)₄] (M = Co, 1; M = Mn, 2) and the carboxylic acid HO₂CCH₂OC₂H₄OMe (3). IR spectroscopy confirms the chelating or μ-bridging binding mode of the carboxylato ligands to M(II). The molecular structure of 5 in the solid state confirms a distorted octahedral arrangement at Mn(II), setup by the two carboxylato ligands including their α-ether oxygen atoms, resulting in an overall two-dimensional coordination network. The thermal decomposition behavior of 4 and 5 was studied by TG-MS, revealing that decarboxylation occurs initially giving [M(CH₂OC₂H₄OMe)₂], which further decomposes by M–C, C–O and C–C bond cleavages. Complexes 4 and 5 were used as CCVD (combustion chemical vapour deposition) precursors for the deposition of Co₃O₄, crystalline Mn₃O₄ and amorphous Mn₂O₃ thin films on silicon and glass substrates. The deposition experiments were carried out using three different precursor solutions (0.4, 0.6 and 0.8 M) at 400 °C. Depending on the precursor concentration, particulated layers were obtained as evidenced by SEM. The layer thicknesses range from 32 to 170 nm. The rms roughness of the respective films was determined by AFM, displaying that the higher the precursor concentration, the rougher the Co₃O₄ surface is (17.4–43.8 nm), while the manganese oxide films are almost similar (6.2–9.8 nm).