Theoretical and experimental study of the forces between different SNOM probes and chemically treated AFM cantilevers

A shear-force mechanism between a chemically etched scanning near-field opt ical microscope tip and different chemically treated atomic force microscop e cantilevers has been experimentally and theoretically investigated as a f unction of the tip-to-sample distance fbr different amplitudes of the tip o scillation. The experimental results show, in agreement with the theoretica l predictions, that as the tip approaches the cantilever the electrostatic force is the most influential in the shear-force mechanism, independently o f the nature of the tip or the sample. As the tip-to-sample distance decrea ses, other forces come into play and the type of interaction depends on the chemical nature of tip and sample surfaces. Thus, for hydrophobic cantilev ers, the decrease in the vibration amplitude is mostly due to the solid fri ction forces resulting from electrostatic interactions. However if the samp le surface is hydrophilic, there is a decrease in the electrostatic force, a water meniscus is formed, and the decrease in the tip amplitude is mostly due to dynamic friction related to capillarity.