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

Abstract

Self-assembled monolayers of dodecanethiol (C 12SH-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 C d values of the C 12SH-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 (Δ i p) is only 0.69 μA cm −2. From the EIS experiments, we find that the phase angle value at 1 Hz Φ 1 Hz of the C 12SH-SAM prepared under ultrasonic irradiation at 100 W (0.1 W cm −2) for 15 min is 89°, the charge transfer resistance R ct value of this monolayer is 1.40 × 10 6 Ω cm 2 and the surface coverage θ value of this monolayer was calculated to be 99.997% from R ct. These results indicate that the C 12SH-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).