Self-assembled monolayer formation from decaneselenol on polycrystalline gold as characterized by electrochemical measurements, quartz-crystal microbalance, XPS, and IR spectroscopy

Self-assembled monolayer (SAM) formation from decaneselenol on gold substrate surfaces was studied using electrochemical measurements, reflection-absorption Fourier transform infrared spectroscopy (FT-IRRAS), X-ray photoelectron spectroscopy (XPS), and quartz-crystal microbalance (QCM). The Au substrate modified with the SAMs showed clear IR absorption bands corresponding to the CH stretches while distinct photoemission peaks were observed at C 1s, Se 3d, and Se 3p core levels in its XPS spectrum. Using a quartz-crystal microbalance, the surface coverage by the SAM-forming molecule was determined to be 0.88 nmol cm^-2. Electrochemical impedance measurements revealed frequency-dependent capacitive behavior of the SAM, and the equivalent parameter was determined to be 6.1×10^-6 s^φ Ω^-1 cm^-1 (φ = 0.94). It also showed that the surface coverage of 99.8% can be attained, resulting in the suppression of a heterogeneous electron-transfer rate constant for a redox species dissolved in solution phase. The dielectric constant for the monolayer film was calculated to be 5.0, which was closer to that of alkanethiols than that reported for diphenyl diselenide. Decaneselenol was concluded to adsorb on Au surfaces to form stable monolayers such as alkanethiols.