Consideration of thiol and carboxylic acid chemisorption on various electrode materials by thermodynamic calculation

Abstract

Thiols and carboxylic acids are important molecules for the anchor of Self-Assemble Monolayer (SAM) on metal surface in organic devices. In order to consider whether carboxylate or thiolate adsorbs on various metals, adsorption energies of methanthiolate and acetate on various metals were thermodynamically calculated using basic quantities of formation enthalpies of metal oxides (H f(M x O y)) and metal sulfide (H f(M xS y)). The calculations were carried out for the adsorption on clean, O adsorbed, and OH adsorbed surface. The results suggested that methanethiolate adsorbs on all clean metals, and on O and OH adsorbed metals except Ti and Al (the high H f(M xO y) metals). On the other hand, acetate adsorbed on all O and OH covered metals, and the clean metals except Au, Ag and Pt (the low H f(M xO y) metals). As the modification of electrodes using SAM is carried out under atmospheric and liquid conditions, it is considered that thiols prefer the adsorption on the low H f(M xO y) metals to the high H f(M xO y) metals, on the contrary, carboxylic acids prefer the adsorption on the high H f(M xO y) metals to the low H f(M xO y) metals.