AFM Tapping Mode Advantages

AFM Tapping Mode

• There are two main modes of AFM. The first mode is known as contact mode and in this configuration the tip is physically dragged across the sample surface. As the tip moves up and down in response to the features on the surface, the height is detected via a laser beam reflected off the cantilever surface. In tapping mode, the tip does not make contact with the surface, but instead oscillates up and down at a constant height above the surface. As the tip laterally scans across the sample surface, the force between the tip and the sample leads to a change in the oscillation amplitude which is detected by a laser beam reflected off the cantilever surface.

Tip Preservation

• Contact mode involves the dragging of the tip across the sample surface. Although contact mode tips are hard, they can inevitably be damaged if the sample features are abrupt, and tips have to be replaced quite frequently. Tapping mode tips should, in principle, never make contact with the surface, and this means that the tip has a longer lifetime than the contact mode equivalents. Since AFM tips are expensive, tapping mode is the most cost-effective means to carry out studies.

Sample Preservation

• Contact mode is very invasive since the tip makes physical contact with the sample. This can lead to damage of the sample surface, and often part of the tip material will be deposited onto the sample surface. Tapping mode does not make contact with the sample, and the sample surface should remain clean.

Magnetic Force Microscopy

• Sometimes it is necessary to map out the magnetic properties of a sample. When a magnetic tip makes contact with the sample, it can be difficult to resolve the forces on the tip resulting from magnetism, and those just from the topology of the sample. Since magnetism is a long-range force, whereas topological forces are short range, tapping mode, taking place at a constant height above the sample surface, allows height and magnetic information to be separated.