Figure 4.

SEM micrographs show pore expansion. (a) The nanopore before thermal process. The initial diameter of nanopore was ~350 nm and thickness of the oxide membrane was ~300 nm. (b) The nanopore after processing at 1150°C for 15 min. The diameter increased to 650 nm. (c) The nanopore further expanded to 1.5 μm after 50 min heating at 1150°C.