Quantized adhesion detected with the atomic force microscope

The atomic force microscope (AFM) is rapidly becoming a powerful tool for investigating surface chemistry and adhesion. Current efforts with this new instrument are guided by the pioneering research of Israelachvili and his colleagues, whose work with the surface force apparatus has laid the foundation for investigating interactions near and between surfaces. The AFM is capable of measuring forces of less than 10^(-11) N with high spatial resolution, thus making possible the study of very weak interactions and local surface chemistry. Here we report the first (to our knowledge) observation of discrete adhesive interactions with measured forces of 1 x 10^(-11) N. Two mechanisms for this effect are proposed: individual hydrogen bonds between the tip and surface are resolved or ordered water layers create different force minima near the surface