The final, optimised etch is shown in Figure . There is no mask undercut, with the pore having the same diameter as the mask. The initial scallops are shorter and more even in shape. The pore walls are almost straight and there is no tapering, with only a 20 nm (or < 6%) variation along the length of the whole pore, as shown in Figure . The bottoms of the pores are flat, which suggests that the etch process could be extended if required.