Force titration of self-assembled monolayer using chemical force microscopy

The concept of force titration was firstly proposed based on the technique of Chemical Force Microscopy (CFM). Self-Assembled Monolayer (SAM) on substrate surface can be titrated with buffer solutions at a nanometer scale by measuring the adhesion force between the SAM-modified substrate and probe tip. The plot of adhesion force vs pH value was termed as force titration curve. As an example, the titration behavior of ω-mercaptoundecanoic acid monolayer on gold has been studied. It was found that there is a big hump around pH 5 ∼ 6 in its force titration curve. Taking the contact angle titration result together, an interaction model for the monolayer was suggested from the chemical hysteresis point of view.