Excessive current can heat and destroy the apex of the probe. The value of the current limiting resistor depends on the conductivity of the sample being analyzed. The SHARK electronic unit provides for selection of a current limiting resistor as well as the bias between the probe and sample.

Figure 4-25 is an example of SHARK made on a carbon nanotube that is held perpendicular to a sample's surface.

FIGURE 4-25 Example of SHARK. A carbon nanotube is placed vertically on a conducting substrate and held in place with an insulating matrix. The probe is then scanned over the surface and an electrical conductivity map (left) and a topography map (right) are generated.

Ferroelectric/piezoelectric materials have unique electrical and physical properties that can be measured with an AFM probe. The advantage of the AFM probe for ferroelectric measurements is that the probe has high spatial resolution and localized measurements are possible. There are two primary types of measurements made on ferro/piezo films: electrical properties and spatial displacement.

The electrical properties are measured with a parametric tester and apparatus similar to that described in Section 4.4.1. The probe is placed in contact with the ferro/piezo film and the electrical measurement is made.