Studies on the effect of electrode pretreatment on the coverage of self-assembled monolayers of dodecanethiol on gold by electrochemical reductive desorption determination

This paper examines the effect of five major pretreatments on the surface coverage Γm of dodecanethiol self-assembled monolayer on polycrystalline gold electrode (C12SH-SAMs-Au). It is based on the electrochemical reductive desorption in the alkaline solution by cyclic voltammetry (CV). The five different pretreatment methods include: aqua regia pretreatment, reductive annealed pretreatment, UV/O3 pretreatment, piranha reagents pretreatment and simple polishing pretreatment, and then all above pretreatments following the same procedure of electrochemistry cleaning. The experimental results show that the surface coverage Γm for C12SH-SAMs-Au by the five pretreatment methods are: aqua regia pretreatment (8.0 × 10−10 mol cm−2) ∼ reductive annealed pretreatment (7.8 × 10−10 mol cm−2) > UV/O3 pretreatment (5.0 × 10−10 mol cm−2) ∼ piranha reagents pretreatment (4.1 × 10−10 mol cm−2) ∼ simple polishing pretreatment (4.0 × 10−10 mol cm−2). This indicates that Au surfaces pretreated by aqua regia and reductive annealing can achieve the best results, and the Γm values obtained are consistent with the theoretical coverage values (Γm ≈ 8.0 × 10−10 mol cm−2); however, the Γm values for other three pretreatment methods (UV/O3, piranha reagents and simple polishing) are not satisfactory, obtaining only almost half of the theoretical Γm value. Thus, we recommend aqua regia and reductive annealed pretreatments as the best methods for self-assembling the alkyl thiol monolayer (CnSH-SAMs-Au), whereas UV/O3, piranha reagents and simple polishing pretreatments are not recommended.