SELF-ASSEMBLED MONOLAYERS OF THIOALKANOATE ON AG AND AU SURFACES - HYDROLYSIS AND REARRANGEMENT AT THE INTERFACE

Thioalkanoic acids form highly ordered monolayer assemblies upon adsor ption on surfaces of evaporated silver and gold. The thiocarboxyl grou p coordinates through a similar polar covalent bond to the surface as in the case of an alkanethiolate monolayer but exhibits short term sta bility. Hydrolysis of the thiocarboxyl head group proceeds at the inte rface to give the corresponding oxy acid and metal sulfide. On a silve r surface, the resulting carboxylic acids react with surface oxide and transform into a closely packed alkanoate monolayer, while on a gold surface, the acid molecules rearrange to form discrete crystallites of H-bonded dimer, together with some anhydride formation. The alkyl cha ins of the crystallites aligned nearly parallel to the surface. Atomic force microscopy shows that the clusters are of nanometer scale dimen sion.