Atomic Force Microscopes - Tutorial Page

The strongest forces between the probe and surface are mechanical, which are the forces that occur when the atoms on the probe physically interact with the atoms on a surface. However, other forces between the probe and surface can have an impact on an AFM image. These other forces include surface contamination, electrostatic forces, and surface material properties.

Surface contamination
In ambient air all surfaces are covered with a very thin layer, < 50 nm, of contamination. This contamination can be comprised of water and hydrocarbons and depends on the environment the microscope is located in. When the AFM probe comes into contact with the surface contamination, capillary forces can pull the probe towards the surface.

Electrostatic forces
Insulating surfaces can store charges on their surface. These charges can interact with charges on the AFM probe or cantilever. Such forces can be so strong that they "bend" the cantilever when scanning a surface.

Surface material properties
Heterogeneous surfaces can have regions of different hardness and friction. As the probe is scanned across a surface, the interaction of the probe with the surface can change when moving from one region to another. Such changes in forces can give a "contrast" that is useful for differentiating between materials on a heterogeneous surface.