Non-uniform size variation of smaller pits on the same substrate indicates that the formation of such pits may occur throughout the etching along with the growth of previously formed smaller pits. The micro-dimensional etching and the consequent evolution in surface roughness can be explained as follows: As the masked Au NPs are weakly bound to the surface, they are dislodged and during etching the particles move closer to form a chain-like assembly and further form larger aggregates. This is visible in the SEM images shown in Figure . These larger aggregates act as the mask for a larger area and provide more contact points to initiate the micro-dimensional etching. The transport of these aggregates along with the etchant on the surface might be responsible for the formation of the long array of pits on the surface. This also explains why such arrays of elongated pits are not seen in the case of bare silica etching. The schematic shown in Figure explains how HF reacts with Au NP-coated silica resulting in different surface structures.