An antireflection structure was fabricated using vertically synthesized iron oxide nanowires as an initial structure. Iron oxide nanowires can be synthesized by simply annealing a thin Fe film in air. The authors propose a process for transforming these nanowires into an array of cone: An additional thin Cr film is deposited onto the nanowires and then etched by reactive ion etching. As a result of the redeposition of Cr, the vertical nanowires were successfully transformed into conical structures. This antireflection nanostructure is replicated onto a polymer surface by thermal nanoimprinting, and the replicated surface exhibited low reflectivity at all visible wavelengths. (C) 2010 American Vacuum Society. [DOI:10.1116/1.3467506]