Synthesis and thermal properties of two novel cobalt (II) Schiff's base complexes as precursors for coating cobalt oxide (Co 3 O 4 ) thin film by a Plasma Enhanced Metallo-Organic Chemical Vapour Deposition

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 N 2 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 (ΔH o vap ). Complex 2 was used as precursor for demonstrating the formation of Co 3 O 4 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 Co 3 O 4 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.