Chemical bonds studied with functionalized atomic force microscopy tips

Chemically modified atomic force microscopy (AFM) tips were produced by using thiol molecules. A new statistical method which produces information about single chemical bond strength from the retracting part of the force-distance curves in AFM is discussed. Single hydrogen bonds between car☐ylic acid groups on the tip and surface were detected, and the hydrogen bond energy between them was calculated. This measured single hydrogen bond strength shows variation in various liquid media. From the shape of the approaching part of the force-distance curves, we were able to confirm the presence of surface hydrogen bond forces, as well as infer other effects such as hydration shell and electric double-layer repulsion. The experiments represent an important step in rendering the information in AFM chemically specific.