Theoretical studies of the decomposition of Zn[(iPr)2PSSe]2 single-source precursor in the gas phase for the chemical vapor deposition of binary and ternary zinc chalcogenides

The reaction pathway analysis of phosphoric acid with the active radicals: a new insight of the fire-extinguishing mechanism of ABC dry powder

Dry powder fire-extinguishing agent is one of Halon substitutes due to its superior fire-extinguishing performance, non-toxicity, and environmental friendliness. As one of the most widely used dry powders, ABC dry powder has attracted wide attention. Understanding its reaction mechanism is important to the design of more efficient compound dry powder based on it. When ABC dry powder was applied to the flame, ammonium dihydrogen phosphate (the main fire-extinguishing component of ABC dry powder) would rapidly decompose into phosphoric acid (H₃PO₄) and ammonia. Therefore, in order to figure out the chemical reaction mechanism of ABC dry powder and active radicals, the main focus of this paper is on the H₃PO₄. Analysis of the electrostatic potential on van der Waals surface of H₃PO₄ was carried out. Besides, detailed theoretical investigation has been performed on the mechanism, kinetics, and thermochemistry of the reactions of H₃PO₄ with H, OH, and CH₃ radicals and further decomposition of H₃PO₄ using M06-2X/6-311G(d,p)//CCSD(T)/cc-pVTZ level of theory. Mayer bond order for all intrinsic reaction coordinate points was also calculated. Finally, it is theoretically proved that ABC dry powder extinguishes the fire mainly by chemical inhibition on H and OH radicals. Grapical Abstract .

A comprehensive understanding of the chemical vapour deposition of cadmium chalcogenides using Cd[(C6H5)2PSSe]2 single-source precursor: a density functional theory approach

Background

The phosphinato complexes of group IIB are of great interest for their potential toward technological applications. A gas phase mechanistic investigation of the chemical vapour deposition of cadmium chalcogenides from the decomposition of Cd[(C₆H₅)₂PSSe]₂, as a single source precursor is carried out and reported herein within the framework of density functional theory at the M06/LACVP* level of theory.

Results

The results reveal that the activation barriers and the product stabilities on the singlet potential energy surface (PES) favour CdS decomposition pathways, respectively. However, on the doublet PES, the activation barriers favour CdS while the product stabilities favour CdSe decomposition pathways, respectively. Contrary to the previously reported theoretical result for Cd[(ⁱPr)₂PSSe]₂, CdSe decomposition pathways were found to be the major pathways on both the singlet and the doublet PESs, respectively.

Conclusion

Exploration of the complex gas phase mechanism and a detailed identification of the reaction intermediates enable us to understand and optimise selective growth process that occur in a chemical vapour deposition.Graphical abstract

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 ZnSexS1-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 ZnSexS1-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.