In the construction of the stage it is important that mechanical loop, that is all the mechanical components between the probe and surface, be very rigid. If the mechanical loop is not rigid, the probe will tend to vibrate relative to the sample and introduce unwanted noise into the images. In general, if the microscope stage is smaller, it will be less susceptible to external vibrations. Creating a rigid mechanical loop becomes more difficult the large the sample size is. The highest resolution AFMs tend to be very small so that the mechanical loop is rigid, and the microscope stage is not susceptible to external environmental vibrations (or noise).

In an AFM stage the motion control mechanisms capable of moving several millimeters or greater are designated X,Y, and Z. The motion control mechanisms that are used for moving small distances are designated x,y, and z. This nomenclature is used throughout this document.

It is possible to construct an AFM with two different configurations, as illustrated in Figure 2-7. In the first configuration the sample is scanned and the force sensor is held in one place. In the second configuration, the sample is held fixed and the probe is scanned. The advantage of the probe scanning microscope is that it can be used on any size of sample. However, the construction of a probe scanning microscope is much more difficult.

FIGURE 2-7 Left: In a "sample scanning" AFM the sample is mounted on an xyz scanner and the force sensor remains fixed. Right: In the "tip scanning" AFM the sample remains fixed and the probe is scanned. The advantage of a "tip scanning" AFM is that it can scan many sample sizes.