Figure 3.

SEM images of porous silicon etched for different time periods. The Si substrate was immersed in piranha solution prior to spin-coating of the gold nanoparticles and was plasma-treated prior to metal-assisted etching. (A) Etching time, 1 min; (B) etching time, 10 min; and (C) etching time, 60 min. Insets show cross-sectional images of the corresponding samples.