3.1.3. Step III
The ZnO nanorods were grown by heating a glass vial containing
precursory solutions with the seed layers at different temperatures
in a box oven for 30 min. The glass vials were loosely capped, such
that only temperature was a variable parameter for the hydrothermal
conditions in the ZnO nanocrystal growths in Step III. Fig. 5 shows the
SEM images of ZnO nanorods developed on the ZnO seed films at different
temperatures starting from 30 to 95 °C with a gap of 5 °C. It is
noticed that the ZnO nanorods start growing on the ZnO seed films
and ZnO flower-like structures on the surface of the ZnO nanorods.
The average size of the ZnO nanorods is ~350 nm in length and
~50 nm in diameter, which is the grain size of the ZnO films grown
in Step II. Therefore, the nanorods must have grown from the top of
the ZnO nanoparticles in the films and kept growing to the c-axis of
the crystals. The cross-section images of the ZnO nanorods and
nanoflowers synthesized by the hydrothermal method on Si substrates
covered with ZnO seed films are presented in Fig. 5 (o and p). The
cross-section images illustrate that the nanoflowers are composed of
numerous petal-like ZnO nanorods which may have grown from a randomly
dispersed nucleation of ZnO on the surface of ZnO nanorods.