AFM is a type of scanned-proximity probe microscopy. It probes the surface of the sample with a sharp tip microfabricated onto the end of a 100-200 micron-long cantilever. Imaging is achieved by raster scanning the tip across the sample using a piezoelectric scanner that can move in the x, y, and z direction. The probe tip is scanned across the sample to sense the intermolecular forces between the probe and surface. As the tip encounters changes in the surface, the cantilever, which acts a flexible spring, deflects accordingly. Changes in the cantilever deflection are usually detected using a laser and compensated for by changing the height of the sample. These positional changes of the sample required to keep the cantilever deflection constant are used to form the image. By controlling the tip-sample separation and/or material properties various different interactions such as van der Waals or electrostatic interactions can be used to build up' the image of the surface. Under certain well controlled conditions this image can show the position of individual atoms on the surface. Often a better understanding of the force interaction and the imaging mechanism are obtained from investigating the distance dependence of the force interactions perpendicular to the surface. This is known as force spectroscopy' and is measured by recording the deflection of the cantilever as it is held at a fixed lateral position over the surface while changing the tip-sample separation.

In our group we use modified MFP-3D AFMs from Asylum Research.