The test sample is mounted on a mechanical stage below the head. It is held in place by a vacuum from below.
It is then moved below the SPM head. The TV camera is then used to help lower the SPM head until the tip of the cantilever approaches the top surface of the sample.
A final height adjustment is made using the ring electrode at the base of the piezoelectric tube. Depending on the mode of SPM operation, the tip may contact the sample (slightly bending the cantilever) or stop just short of the surface.
