- The AFM can work in various modes. Contact mode is used for topography analysis where small change in distance between tip and surface gives large changes in force. Constant height and constant force experiments can be done. It is usually used for hard surfaces. However there is a possibility that the tip may damage the surface of soft/ biological samples.
- Tapping mode lessens the damage as compared to contact mode and is therefore used for biological specimens, poor surface adhesion samples such as nanotubes and thin liquid layers over rigid samples.
- Non-contact mode is also used for biological and soft samples as it prevents the damage of both tip and the sample. It works best under high vacuum and atomic scale resolution is possible.
Atomic Force Microscope operates by scanning the sample surface with an AFM probe made from silicon nitride that consists of a sharp pyramidal or conical tip (4-5 micron height and 100-200 micron long) with a cantilever spring constant ranging from 0.05-50 N/m. The AFM probe or the sample is mounted on a piezoelectric scanner that moves in x,y and z directions and is used to raster scan the probe to obtain 3 dimensional images of the sample surface. As the tip is scanned across the surface, the cantilever deflects based on the tip being repelled or attracted to
the surface due to intermolecular interactions between the atoms of the tip and the surface. The laser beam detector monitors the magnitude of deflection and reflects off the end of the cantilever onto the photodiode.