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 Q values of the C12SH-SAM prepared in RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) containing 10 mu L neat C12SH for 24 h (C12SH-SAMS([BMIM]PF6.10 mu L,24h)) are independent of the scan rate, the effective thickness d(eff) value and the average cant angle phi value of this monolayer are 18 +/- 1 angstrom and 27 +/- 4 degrees, respectively. The difference value of the current density at -0.2 and 0.5 V (Delta i(p)) is only 0.73 +/- 0.18 mu A cm(-2). EIS experiments show that the phase angle value at 1 Hz Phi(1 Hz), the charge transfer resistance R-ct value and surface coverage theta value of this C12SH-SAM are 88.2 +/- 0.7 degrees, 3.44 +/- 1.91 M Omega cm(2) 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. (c) 2008 Elsevier B.V. All rights reserved.