Hierarchical nanoporous films obtained by surface cracking on Cu-Au and ethanethiol on Au(001)

Nanoporous gold (npg) produced by dealloying of Au alloys has been recently proposed for many different applications from catalysis to bio-sensors. Furthermore, Au alloys constitute an important model system in the context of corrosion, dealloying, and stress corrosion cracking. Adsorbed self-assembled monolayers of thiol molecules inhibit the dealloying reaction. On thiol-modified Cu-Au alloys dealloying finally proceeds in a localized reaction instead of a homogeneous process. Using ethanethiols as an example, we show here that thiols can be effectively removed by application of anodic oxidation. Homogeneous porosity forms then after an oxidation step. In-situ X-ray diffraction and crystal truncation rod analysis of ethanethiol-modified Au (001) confirms that a bare Au surface is recovered after a similar oxidation step. In consequence, a multi-step dealloying process including complete initial thiol-layers as well as partially or fully re-cleaned surfaces can produce different micro-cracks, providing larger scale openings, and homogeneous nanoporous Au in between. Such hierarchically structured surfaces may show superior applicability for reactions where mass transport into the porous layer plays a decisive role for the reaction rate or detection probability.