Room-temperature ionic liquid as a new solvent to prepare high-quality dodecanethiol self-assembled monolayers on polycrystalline gold

This paper reports a new solvent, room-temperature ionic liquid (RTIL), for the preparation of dodecanethiol self-assembled monolayers (C12SH-SAMs) on polycrystalline gold. The quality of C12SH-SAMs was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). From CV experiments, we find that the differential capacitance Cd values of the C12SH-SAM prepared in RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) containing 10 μL neat C12SH for 24 h (C12SH-SAMs[BMIM]PF6,10 μL,24 h) are independent of the scan rate, the effective thickness deff value and the average cant angle φ value of this monolayer are 18 ± 1 Å and 27 ± 4°, respectively. The difference value of the current density at −0.2 and 0.5 V (Δip) is only 0.73 ± 0.18 μA cm−2. EIS experiments show that the phase angle value at 1 Hz Φ1 Hz, the charge transfer resistance Rct value and surface coverage θ value of this C12SH-SAM are 88.2 ± 0.7°, 3.44 ± 1.91 MΩ cm2 and 99.998 ± 0.001%, respectively. These results indicate that high-quality C12SH-SAMs can be formed in [BMIM]PF6. In addition, the rate of formations of high-quality C12SH-SAMs in RTIL can be substantially improved by ultrasound.