DFT Study on the Gas-Phase Potential Energy Surface Crossing Mechanism of ZnO Formation from Diethylzinc and Triplet Oxygen during Metal-Organic Chemical Vapor Deposition

摘要

Metal-organic chemical vapor deposition of zinc oxide (ZnO) using diethylzinc (DEZn) and triplet oxygen (3O2) is investigated at density functional theory level. The structures of reactants, transition states, intermediates, products, and the possible spin conversion points where singlet and triplet potential energy surfaces (PES) crossing have been determined at B3LYP/6-311G (d) level of theory. The Zn-C bonds are generally considered as the weakest bonds in DEZn, however, the first dissociated bond of DEZn during the oxidation by triplet oxygen is calculated to be the C-H bonds of methyl groups. The reaction is proposed to occur on the triplet PES through a spin conversion points, and to generate zinc hydroxides on the singlet PES. Consequently, the zinc hydroxide tends to organize in oligomers and then dehydrate to generate ZnO clusters. This study could provide theoretical insights for the gas-phase oxidation mechanism of DEZn by ~3O2. We provide the evidence theoretically that the initial reaction inferred from the present computational results is inconsistent with that proposed by the experiment, which includes a coordination of oxygen to the metal atom and shift of an ethyl group from metal to oxygen.