ABSTRACT
The direct measurement of the force interaction between distinct molecules has been a challenge for scientists for many years. Only very recently these forces can be directly measured for single atomic and molecular bonds. Interestingly, the applied technique is surprisingly simple. A spring with a defined elasticity is elongated or compressed due to the weight of the object to be measured. The compression Δz of the spring (with spring constant kcant) is a direct measure of the force F exerted, which in the regime of elastic deformation obeys Hooke’s law:
F = kcant ×Δz (2.1) In atomic force microscopy (AFM) (Binnig et al. 1986), the “spring” is a bendable cantilever with a stiffness between 0.01 and 10 N/m. Since intra-atomic forces are in
the range of some nanonewton, the cantilever will be deflected by 0.01-100 nm. Consequently, the precise detection of the cantilever bending is the key feature of AFM. If a sufficiently sharp tip is directly attached to the cantilever, we could then measure the interacting forces between the last atoms of the tip and the sample through the bending of the cantilever.
