This rough appearance is the beginning of the pore walls etching away. This becomes apparent as pore widening in nanopores with a diameter of 320 nm or less, which causes inconsistencies across the photonic crystal. This can greatly reduce the reflectivity of the photonic crystal and cause large shifts of the photonic band gap across the crystal. In structures with a small pitch, which is required for photonic crystal devices operating in the telecommunications range, pore widening can even cause the breakdown of the walls between the nanopores, effectively destroying the structures, as was observed by Grishina et al. IV) The initial etch process also exhibits significant positive tapering, narrowing of the bottom of the nanopores as shown in Figure . This creates inconsistencies and a reduction in quality of the optical properties, similar to pore widening.