Electrochemical etching of gold within nanoshaved self-assembled monolayers

Wet etching of metal substrates with patterned self-assembled monolayers (SAMs) is an inexpensive and convenient method to produce metal nanostructures. For this method to be relevant to the fabrication of high precision plasmonic structures, the kinetics of nanoscale etching process, particularly in the lateral direction, must be elucidated and controlled. We herein describe an in situ atomic force microscopy (AFM) study to characterize the etching process within patterned SAMs with nanometer resolution and in real time. The in situ study was enabled by several unique elements, including single crystalline substrates to minimize the variability of facet-dependent etch rate, high-resolution nanoshaved SAM patterns, electrochemical-potential-controlled etching, and AFM kymographs to improve temporal resolution. Our approach has successfully quantified the extent of both lateral etching and vertical etching at different potentials. Our study reveals the presence of an induction period prior to the onset of significant lateral etching, which would be difficult to observe with the limited time resolution and sample-to-sample variation of ex situ studies. By increasing the vertical etch rate during this induction period with higher potentials, gold was etched up to 40 nm in the vertical direction with minimal lateral etching. High-resolution etching was also demonstrated on single crystal gold microplates, which are high quality gold thin films suitable for plasmonics studies.