Figure 1: After metal-NP-assisted etching, the random size distribution of Si nanorods on black silicon wafers (BSWs) is averaged. (a) 600 nm-thick nanorods formed on silicon wafer. The orientation of nanorods is normal to the silicon surface, revealing that the anisotropic etching is primarily along . (b) The nanorods built on grains with different crystalline orientations are clearly distinguished. The nanorods have the average length of 1 μm after etched for 3 min. (c) 100 nm-thick nanorods on mc-BSW after 18 s etching.