The reaction directions are all from left to right for Eqs.
(3)–(6) when they are performed in a high water
concentration. The role of H2O in the deposition process
is multifold. Firstly, it suppresses the pyrolysis reaction of
BZA (Eq. (2)) since BZA is consumed by the decarboxylation
reaction (Eq. (3)). In fact, the pyrolysis reaction of
BZA (Eq. (2)) can be negligible in a high H2O concentration.
This leads to the formation of crystalline films.
Secondly, it acts partly as the oxygen source to produce
stoichiometric ZnO (Eq. (6)). The deposition rate of
crystalline films thus increases. Thirdly, the adsorbed H
resulted from the hydrolysis reaction (Eq. (4)) combines
with the organic fragments producing CH3COOH vapor
(Eq. (5)), which is exhausted outside and so reduces the film
contamination. In addition, the presence of water in the
ambient can also effectively enhance the (0 0 2) orientation
of ZnO films.We have applied another growth condition to
obtain ZnO by dissolving ZA in methanol or alcohol, and
the results showed that there was no (0 0 2) preferential film
obtained in this condition. In contrast to that, ZnO films
with good (0 0 2) preferential orientation could be obtained
by dissolving ZA in water. Therefore, the presence of H2O
during the film growth is expected to improve the
perfection and physical properties of the ZnO crystals.