Rapid formation of high-quality self-assembled monolayers of dodecanethiol on polycrystalline gold under ultrasonic irradiation

Self-assembled monolayers of dodecanethiol (C12SH-SAMs) on polycrystalline gold were prepared under ultrasonic irradiation at 100 W (the actual ultrasonic power intensity is about 0.1 W cm−2 including the heat loss) for different time and investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CV experiments show that the differential capacitance Cd values of the C12SH-SAM prepared under ultrasonic irradiation at 100 W (0.1 W cm−2) for 15 min are independent of the scan rate, the thickness d value of this monolayer is 17.5 Å, the tilt angle φ value of the molecules in this monolayer from the gold surface normal was calculated to be 30° and the difference value of the current density at −0.2 and 0.5 V (Δip) is only 0.69 μA cm−2. From the EIS experiments, we find that the phase angle value at 1 Hz Φ1 Hz of the C12SH-SAM prepared under ultrasonic irradiation at 100 W (0.1 W cm−2) for 15 min is 89°, the charge transfer resistance Rct value of this monolayer is 1.40 × 106 Ω cm2 and the surface coverage θ value of this monolayer was calculated to be 99.997% from Rct. These results indicate that the C12SH-SAM of almost defect-free structure and very low ionic permeability can be formed under ultrasonic irradiation at 100 W (0.1 W cm−2) in a short time (15 min).