Molecular Orbital Studies of Zinc Oxide Chemical Vapor Deposition:  Gas-Phase Hydrolysis of Diethyl Zinc, Elimination Reactions, and Formation of Dimers and Tetramers

The chemical vapor deposition of zinc oxide thin films can be carried out with diethyl zinc and water vapor. The present study uses molecular orbital methods to examine complexes of one and two molecules of H2O with Zn(C2H5)2, and the subsequent hydrolysis, elimination, and oligomerization reactions which may occur in the gas phase. Geometry optimizations were carried out at the B3LYP/6-311G(d) level of theory. Hydrolysis of Zn(C2H5)2 by a single water has an enthalpy barrier of 19 kcal/mol relative to separated reactants, which is reduced to 4 kcal/mol by the presence of a second water. Further hydrolysis of Zn(C2H5)OH to Zn(OH)2 is facile, but elimination of C2H6 or H2O to form ZnO is very endothermic. Zn(C2H5)OH and Zn(OH)2 form very stable dimers and tetramers. Elimination of C2H6 and H2O from the dimers and tetramers is also endothermic and leads to ring opening.