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

Bosse, Florian; Gutheil, Christian; Nguyen, D. Thao; Freitag, Matthias; Das, Mowpriya; Tyler, Bonnie J. J.; Adolphs, Thorsten; Schaefer, Andreas H. H.; Arlinghaus, Heinrich F. F.; Glorius, Frank; Ravoo, Bart Jan

Abstract

N-Heterocyclic carbene (NHC)-modified planar gold surfaces (NHC@Au) were found to be more susceptible toward wet chemical etching than undecorated surface areas. Site-selective decoration of NHCs on Au was achieved by microcontact printing (μCP) of the NHC precursors 1,3-bis(diisopropylphenyl)imidazol-3-ium hydrogen carbonate (IPr(H)[HCO3]) or 1,3-dimethylbenzimidazol-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 μCP 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.