Highly selective etch masks are formed by thin films of a polystyrene-b-poly(ferrocenylisopropylmethylsilane)diblock copolymer, PS-PFiPMS, containing hemicylindrical domains of PFiPMS. These domains, with a period of 35 nm, are readily aligned through mechanical shear. Aligned PS-PFiPMS templates are employed to fabricate high-aspect-ratio nanowire grids from amorphous silicon, which can polarize deep ultraviolet radiation, including 193 nm, at >90% efficiency.