Theoretical studies on force titration of amino-group-terminated self-assembled monolayers

The structures of (3-aminopropyl)triethoxysilane (APTES), 4-aminothiophenol (4-ATP) and 4-mercaptopyridine (4-MP) self-assembled monolayers (SAMs) are studied by quantum mechanics in order to explain the force titration curves of these amino-group-terminated SAMs. The surface charges and electrostatic surface potentials derived from the ab initio calculations can give satisfactory explanations for the experimental results. We also propose a simple model to simulate the force titration process. The force between the tip and sample can be estimated according to the slope coef®cient of the curve of energy versus distance. This curve can lead to a better understanding of the force titration curves of amino-group-terminated SAMs. q 1998 Elsevier Science B.V. All rights reserved.