3.5.4 Other modes
The investigation of new scanning modes for the AFM has been something of a playground for researchers: think of any interaction between materials in which a force plays a part and you have a potential scanning mode. Coating the probe with a magnetic material, appropriately magnetised, enables samples to be scanned in magnetic-force mode. An obvious industrial use for this technique is the investigation of the structure of magnetic storage media. Electrostatic forces too have been used. Using an insulating probe tip and applying a charge to it, it is possible to map the distribution of charge on surfaces. This has uses in areas of research ranging from polymer science to semiconductors.
The field is large and ever-growing. Even the diagram in Figure 9 does not give a complete picture of the multitude of ways in which this simple cantilever-tip system is being applied.
The STM and AFM turn surface properties ultimately into a current, a voltage or a frequency. State which of these quantities are used to encode the surface properties in an AFM and an STM.
The AFM detects shifts in frequency or voltage and the STM measures changes in a current.