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 C_d 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 d_eff 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 (Δi_p) is only 0.73 ± 0.18 μA cm^?2. EIS experiments show that the phase angle value at 1 Hz Φ_1 Hz, the charge transfer resistance R_ct 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.