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Nanohole Arrays Fabricated on Gold Surfaces by Total Wet Nanopatterning through Block Copolymer Masks

Well-ordered nanohole arrays on atomically flat gold (111) surfaces were fabricated by wet etching through block copolymer (BC) masks using ferri/ferrocyanide etchant. Amphiphilic BCs consisting of poly(ethylene oxide) (PEO) and liquid crystalline poly(methacrylate) with azobenzene mesogens [PMA(Az)], PEOm-b-PMA(Az)n, blended with poly(ethylene glycol) monomethylether (EO) form hexagonally arranged ion-transporting nanocylinders of EO-blended PEO microdomains in the BC masks. Atomic force microscopy (AFM) revealed a hexagonally arranged nanohole array on each terrace of the gold surface after the total wet nanopattering including a 5 min etching. The diameter (d) and distance between neighboring nanoholes (D) were controlled by the degree of polymerization of the BC. Two kinds of nanohole arrays with (d, D) = (12 nm, 25 nm) and (20 nm, 41 nm) were obtained in good agreement with the d and D of the EO-blended PEO microdomains of the masks. Scanning tunneling microscopy (STM) indicated that the depth of nanoholes was 3.5 Å, corresponding to the thickness of a single atomic layer of gold, and the flatness of the bottom of the holes was confirmed.