fig2
Figure 2. Surface SEM and pore-size distributions of the (A) control, (B) PU-L, (C) control-S, and (D) PUS-L precursor films; (E) Schematic illustration of the proposed pore-formation process in the precursor film. SEM: Scanning electron microscopy; PU-L: Pb(NO3)2 precursor film containing 0.3 mg/mL urea; PUS-L: the corresponding PU-L precursor film after additional heat treatment at 150 °C for 20 min.
