Synthesis and thermal properties of two novel cobalt (II) Schiff's base complexes as precursors for coating cobalt oxide (Co3O4) thin film by a Plasma Enhanced Metallo-Organic Chemical Vapour Deposition

Abstract

Two Schiff's base complexes namely, Co(3,5-di-tertbutyl-salicylaldehydatoethylimine)2 (1) and Co(3,5-di-tertbutyl-salicylaldehydatobutylimine)2 (2) were synthesized by template method and characterized by elemental (C, H & N), FT-IR, DART-MS, TG/DTA and single crystal XRD analysis. Both 1 and 2 were found to crystallize in Orthorhombic crystal system. The complexes 1 and 2 undergoes single step volatilization in an inert N2 atmosphere giving a negligible percentage of residues at 331 °C (1) and 362 °C (2) as observed from thermogravimetry (TG) analysis. The molecular mass (M) of Co-bearing species were found to be 580 and 636 Da for 1 and 2 respectively. The equilibrium vapour pressures (pe) measurement by a TG - based transpiration technique over the temperature range of 489–550 K for 1 and 459–561 K for 2 yielded values of 107.0 (±1.8) and 105.2 (±2.1) kJ mol−1 for 1 and 2 respectively for their standard enthalpies of vapourisation (ΔHovap). Complex 2 was used as precursor for demonstrating the formation of Co3O4 thin film at a substrate temperature of 350 °C in an Ar plasma by using a home-built plasma assisted Chemical Vapour Deposition (CVD) method with a deposition pressure of 0.6–1.0 mbar. The phase identification by XRD showed the preferential growth of cubic Co3O4 in (311) plane. The morphology by SEM confirmed densely agglomerated cauliflower like structure. The particle size (D = 15.6 nm) was calculated using Debye-Scherrer's equation. A band gap value of 2.23 eV was obtained using Kubelka-Munk function.