Abstract:
Thin films of zinc oxide have been deposited on Pyrex glass substrate by using
sol gel process and characterized by means of different charactcrizatioll
techniques including optical microscopy, X-ray diffractometry (XRD),
thermogravimetry and spectrophotometry. The sol has been prepared by reacting
zinc acetate and ethylene glycol and dissolving the resultant solution in npropanol.
Glycerol was added to the sol to increase its stability. A proton
acceptor like diethyl amille was added to assist hydrolysis of zinc acetate. Thin
films of zinc oxide were cast on the substrate by dip coating method and gelled in
humid air. The as deposited film was annealed at various temperatures ranging
from 150 C to 450 C for 15 minutes at each set temperature. It has been found
that the cleanliness of the glass substrate, the humidity during the gelation of the
film as well as the time and temperature of the heal treatment affect the
appearance and the morphology of the film. Cleaning of the glass substrate for
the successful deposition of the film was achieved by the use of deionized water,
acetic acid and absolute ethanol. Relative humidity less than 50% during the
deposition of the film on to the glass substrate was found to be favorable for
yielding good transparent film. It has been found that annealing of the film
pyrolyzes gelled film to zinc oxide, drives out moistures and other volatiles and
at higher temperatures decomposes the metalorganic complexes. The amorphous
as-deposited film transforms to polycrystalline as a result of annealing above 275
C and the XRD peaks become sharper and more intense with the increase in
annealing temperature, The films annealed at higher temperature, especially those
annealed above 400 C, are denser and less porous and annealing leads to the
increase in the size of the ZnO crystallites in them. The thin films of ZnO formed
are randomly oriented without showing any preferred orientation. The ZnO
crystallites have the hexagonal wurtdte structure, with e = 5.271 A and a =
3.285 A. The average thickness of the films from thermogravimetric analyses has
been found to be about I ,.un after annealing at 450 C for 15 minutes and the film
and the film exhibited about 80% transmission.
