Improved blocking properties of short-chain alkanethiol monolayers self-assembled on gold

Blocking of gold surfaces by self-assembled monolayers (SAMs) of n-octanethiol (OT) was investigated. Short-chain alkanethiols such as OT are known to form loosely-packed SAMs with abundant defects and pinholes, exhibiting poor blocking of the gold surface. Hence, gold substrates subjected to 20 h OT adsorption manifested excessive electrochemical penetrability, low contact angles with a large hysteresis, and extensive exchange of functional disulfide molecules into the OT SAM. It is shown that a single electrochemical cycle in H₂SO₄ solution after 1 h OT adsorption, followed by another 20 h adsorption, results in a dramatic improvement of the coverage and blocking properties of the SAM, showing considerably lower electrochemical penetrability, improved contact angles, and sluggish exchange of the functional molecules into the OT SAM. Insertion of the latter molecules into the monolayer was monitored by their ability to coordinatively attach ligand-substituted gold nanoparticles.