Comparison of diazonium salt derived and thiol derived nitrobenzene layers on gold

The reduction of diazonium salts to produce aryl films on surfaces has expanded in application from carbon electrodes to a variety of conducting materials. The increasing interest in this method for modifying gold surfaces has motivated us to directly compare the structure and stability of nitrobenzene films derived from diazonium salts with monolayers formed from the corresponding thiol. We employ spectroscopic and microscopic techniques to characterize the structure and thickness of the as-formed layers. As a means of assessing stability, the nitrobenzene films were subjected to rigorous sonication, refluxing solvents, and chemical displacement by octadecanethiol. Infrared reflection-absorption spectroscopy and electrochemical blocking were used to assess the stabilities of the films generated by the two methods. Sonication and refluxing both remove more material from the diazonium-derived film relative to the thiol monolayer. However, a significant amount of each layer remains bonded to the surface following these treatments. Immersion in octadecanethiol solution results in complete displacement of the thiol derived nitrobenzene monolayer. Importantly, a significant fraction of the diazonium derived films cannot be displaced by octadecanethiol. These findings show that under certain conditions aryl films formed from the reduction of diazonium salts are more strongly bonded to gold surfaces compared to the thiol analogue.