Electrochemical Stability of Low-Density Carboxylic Acid Terminated Monolayers

Using cyclic voltammetry, we studied the reductive desorption of a series of low-density self-assembled monolayers (LD-SAMs) made from mercaptohexadecanoic acid (MHA). Desorption experiments indicate that LD-SAMs are significantly less stable than a full MHA monolayer. All three LD-SAMs investigated presented a broad desorption peak in the region between −1.0 and −0.8 V vs SCE, which is in contrast to the single peak with a narrow distribution at −1.11 V observed for the full MHA monolayer. Upon backfilling the LD-SAM with a shorter-chain thiol (mercaptohexanol), the desorption of the mixed monolayer displayed a single peak, indicative of a well-mixed monolayer. Our results show that LD-SAMs are promising candidates for mixed monolayers and suggest that the broad desorption peak observed for LD-SAMs might arise due to adsorption at different binding sites.