The ZnO nanoflowers, composed of hexagonal petals as long as
~1 μm and ~500 nm in diameter, began emerging on top of the ZnO
nanorods from 60 °C. Starting from 60 to 85 °C, the shapes of ZnO
nanocrystals stayed clear; however, the nanocrystals started to lose
their structures from 90 °C. Thus, the oven temperature for the
growth of ZnO nanorods was set to 75 °C. Of course, we think that
the low-temperature range of 65–85 °C should be appropriate for
the growth of ZnO nanorods in this system.