SEM images of ZnO films deposited using different source temperature profiles. (a1-e1) SEMs (top view), (a2-e2) SEMs (edge-on view), and (a3-e3) source temperature profiles of ZnO nanocrystalline films deposited with saw-toothed temperature profiles that have resident times of (a3) 135 s, (b3) 290 s, and (c3) 445 s above the melting point of zinc (420°C). The corresponding nominal thicknesses are (a2) 25 nm, (b2) 70 nm, and (c2) 108 nm. (d) and (e) show the SEM images of ZnO films deposited using saw-toothed temperature profile similar to (a) but with longer times - (d3) 5 s and (e3) 75 s - at the peak temperature of 570°C. The thicknesses of films hence deposited are (d2) 22 nm and (e2) 57 nm. Scale bar = 100 nm.