Figure 2. Experiments with time-varying temperature for quartzes with nominal initial resonant frequency 3.579 MHz and equimolar 5 mM concentration of zinc nitrate and HMTA.

(a) f_R and temperature when the Pyrex container is cyclically moved from hot bath (92°C) to cold bath (25°C for 30 minutes) and vice versa. (b) Identification of the threshold temperature (between 60°C and 65°C); the growth rate is not significantly changed until the temperature stays above the threshold. (c) SEM images of nanostructures grown with alternating stop-and-go phases that degrade their single-crystal nature, as evident from the lines of interrupted growth and from the conversion of single nanorods into many entangled ZnO nanostructures. (d) f_R and temperature during growth with time-dependent temperature (10°C steps from 50°C to 90°C); the growth rate is not significantly modified by increases of temperature above the threshold.