FIGURE 4-23 Parametric testing is possible by electrically connecting the parametric tester to a conductive AFM probe.

Although this technique initially seems promising for measuring electrical properties of nanostructures such as nanotubes or quantum dots, there are a few drawbacks. In addition to the problems listed in Section 4.4.0, there is another major drawback. The absolute positioning accuracy of an AFM scanner is limited by thermal drift in the stage. When scanning, it is possible to measure structures with a few nanometer dimensions, although it is very difficult to absolutely position the probe over a feature that has only a few nm in diameter.

The spatial map of the electrical conductivity of a surface is measured with SHARK. The apparatus for making a SHARK map is illustrated in Figure 4-24. A bias is placed between a conductive sample and probe. Then the sample's surface is scanned. Monitoring the current flow between the probe and the surface yields a conductivity map of the surface. A topogram of the surface's 3-d structure is measured at the same time as the conductivity map.

FIGURE 4-24 Electrical conductivity maps are measured by monitoring the current flow between the probe and the surface. The image is displayed with the A/D converter.

Often, a current limiting resistor is necessary to limit the current flow.