In the scanning capacitance microscope, the capacitance between the probe tip and surface are monitored. SCM is implemented by connecting a capacitance sensor between the probe and surface while scanning (see Figure 4-30). Alternatively, the Kelvin probe technique can be adapted to measure capacitance profiles. The Kelvin probe technique is adapted by monitoring the w2 signal with a lock-in amplifier.

FIGURE 4-30 A capacitance sensor measures the capacitance between the probe and sample. The image is output to an A/D converter.

Although SCM has great promise for applications, especially in the semiconductor industry, there are a few problems. First, the reliability of the data measured is not good because of surface contamination and uncertain probe geometries. Second, data modeling is diffi cult and getting the resolution required for applications such as dopant profiling at the nanometer scale are not possible.

The probe in the AFM can be used for making nanoscale changes to a surface's physical structure or nanoscale chemical composition. There are several methods for making changes in a surface including: voltage induced, mechanically induced, and chemical deposition (see Sections 4.5.1, 4.5.2, and 4.5.3).

FIGURE 4-31 Two methods for writing on a surface with an AFM probe.