Kinetics and domain formation in surface reactions by inverted chemical force microscopy and FT-IR spectroscopy

Reaction kinetics of the alkaline hydrolysis of ester groups at the surface of self-assembled monolayers was monitored by a combination of atomic force microscopy (AFM) and FT-IR spectroscopy. In a novel approach, which we termed "inverted" chemical force microscopy (CFM), reactions are studied which take place at the surface of the tip coated with the reactants. The course of the reaction is followed in situ on a scale of less than 100 molecules, corresponding to the contact area between AFM tip and the sample surface at pull-off, by recording force-distance curves. Reactivity differences related to the structure of the monolayers, observed by inverted CFM on the nanometer scale, agree well with average behavior observed by FT-IR. The combined results, together with additional force microscopy data, support the conclusion that for closely packed ester groups, the reaction spreads from defect sites, causing separation of the homogeneous surface into domains of reacted and unreacted molecules.