Thermal decomposition of Zn[(C₆H₅)₂PSSe]₂ single-source precursor for the chemical vapour deposition of binary and ternary zinc chalcogenides: a theoretical study

The mechanistic pathways for the formation of zinc selenide, zinc sulphide and ternary zinc selenide sulphide in the gas phase decomposition of Zn[(C₆H₅)₂PSSe]₂ single-source precursor has been explored on the singlet and doublet potential energy surfaces using density functional theory method in order to understand the thermodynamic and kinetic properties. The optimized geometries and the predicted energies were obtained using the M06 functional and a combination of the basis sets LACVP* for Zn and 6-31(d) for light atoms. The rate constants of each elementary reaction have been calculated using the transition state theory. The results indicate that the steps that lead to ternary ZnSe_xS_1−x formation on both the singlet and doublet potential energy surfaces is favoured kinetically and thermodynamically over those that lead to ZnSe and ZnS formation. Density functional theory calculations of the gas phase decomposition of the complex indicate that the deposition of ternary ZnSe_xS_1−x in chemical vapour deposition may involve more than one step but the steps that lead to its formation are consistent with a dominant role for both thermodynamic and kinetic factors. The theoretical study showed important insights as a general tool to anticipate the gas phase decomposition mechanism of a novel precursor when direct experimental measurements are not available.