Selective Removal of Gold: N-Heterocyclic Carbenes as Positive Etch Resists on Planar Gold Surfaces

N-Heterocyclic carbene (NHC)-modified planar gold surfaces (NHC@Au) were found to be more susceptible toward wet chemical etching than undecorated surface areas. Siteselective decoration of NHCs on Au was achieved by microcontact printing (mu CP) of the NHC precursors 1,3-bis(diisopropylphenyl)imidazol-3-ium hydrogen carbonate (IPr(H)[HCO3]) or 1,3dimethylbenzimidazol- 3-ium hydrogen carbonate (BIMe(H)[HCO3]). Strikingly, BIMe@Au showed concentration-dependent etching behavior, tunable from a positive resist to a negative resist. Surface patterning was verified by time-of-flight secondary-ion mass spectrometry and Kelvin probe force microscopy. Moreover, orthogonal mu CP enabled the patterned functionalization of planar Au with both IPr and 1-eicosanethiol and the subsequent formation of three-dimensional structures with a single etching step. The selective removal of Au by functionalization with a surface ligand is unprecedented and enables novel applications of NHCs in materials chemistry and nanofabrication.