Roughening and Long-Range Nanopatterning of Au(111) through Potential Cycling in Aqueous Acidic Media

Electrochemical treatment of Au(111) in aqueous H2SO4 solution by repetitive application of oxide formation–reduction cycles (OFRC) generates nanopatterned surfaces with long-range order. The pattern development depends on the lower and upper potential limits (E L, E U), the number (n) of OFRCs, and the potential scan rate (s). Surface patterning of Au(111) initially (n = 1–2) generates small islands and holes that are one atomic step in height. As n increases to 5, the number of islands decreases and the holes become larger; after n = 10 OFRCs, the islands become inexistent and large, randomly distributed holes are observed. Increase of OFRCs to n = 20 generates surface structures that reside within three atomic layers and resemble phase separation through a spinodal decomposition mechanism. As the number of OFRCs rises to n = 50, a network of interconnected islands and holes emerges; the islands and holes are two-three atomic steps in height, and are located within topmost five monolayers. Further increase of the number of OFRCs to n = 100 creates a network of interconnected trigonal pyramids that are pointed in the same direction. The size of the pyramids depends on the electrolyte composition and the number of OFRCs. In the case of n = 100, the pyramids are 12–25 nm in base length and 0.4–1.6 nm in height in 0.1 M aqueous H2SO4, and 20–50 nm in base length and 0.8–1.6 nm in height in 0.1 M aqueous HNO3. The number of OFRCs and scan rate play an important role in patterning of Au(111), and complete nanopattern development requires a large number of OFRCs and low scan rates.