Probing the surface forces of monolayer films with an atomic-force microscope

Using an atomic force microscope (AFM), we have studied the attractive and adhesive forces between a cantilever tip and sample surfaces as a function of sample surface energy. The measured forces systematically increased with surface energy. The AFM is very sensitive; changes in the surface forces (i.e., attraction and adhesion) of monolayer covered samples could be clearly discerned when only the surface group of the monolayer film was changed from -${\mathrm{CH}}_3$ to -${\mathrm{CF}}_3$.