Impedance differences found with n-alkanethiol monolayers prepared by contact printing and solution adsorption

Defects in self-assembled n-alkanethiol monolayers are readily apparent in the impedance spectroscopy of the modified interface. Self-assembled monolayers (SAMs) of n-octadecanethiol, n-dodecanethiol and n-pentanethiol formed by contact printing and solution adsorption are characterized by electrochemical impedance spectroscopy (EIS). Impedance measurements show that monolayers prepared by contact printing are on the order of 5 times less resistive to charge transfer and have greater defect density than monolayers prepared by solution adsorption. Modeling of the average defect size and density show that the size of monolayer defects stays relatively constant independent of the monolayer preparation conditions; however, the density of defects decreases with increasing concentration for the contact printed monolayers. The impedance data also show that monolayers prepared by solution adsorption have fewer defects than those prepared by contact printing.