Thin Ti nanocones are deposited on top of the arrays of ZnO
nanopagodas, and the whole structure works as an efficient nanostructured metamaterial
perfect absorber (MPA) without using lithography and dry etching. This figure shows a SEM micrograph of the lithography-free ZnO nano-pagodas. See Lin et al. Opt. Mater. Express 7, 3608-3617 (2017).