Although the electrical modes are typically relatively simple to implement, getting reliable data is problematic. There are three problems:

Figure 4-22 illustrates a probe in the proximity of a sample's surface and the layers of oxide and contamination that cause uncertainty in AFM electrical measurements. The oxide layers and contamination make it difficult to make an ohmic contact between the probe and surface.

One approach to solving issues b and c is to coat the probe with a conductive diamond coating. The diamond coating is very hard and does not oxidize; however, the coating increases the diameter of the probe significantly. Even when the probe is coated with an inert layer such as diamond, there are still potential problems for contamination.

FIGURE 4-22 Electrical measurements with the AFM require the probe to make electrical contact with the coating.

An electrically conductive probe may be used directly for parametric testing (see Figure 4-23). The parametric tester is attached directly between the conductive AFM probe and the sample.