Spatial positioning and control

Spatial positioning and control of the SPM probe with respect to the surface need to be considered in three contexts  

Coarse lateral movement is required in order to locate promising regions of the surface within the dynamic range of the field of view this may be done manually, or with a stepper motor under software control, or with a mechanical lead-screw/lever arrangement, or with a so-called inchworm linear drive, or with a combination of these. 

Coarse and fine movements of tip with respect to the surface in the r-direction are required in order to bring the probe into the dynamic range of the gap control loop (the tip approach sequence). The coarse movement may be implemented, as above, with an inchworm and/or lead-screw drive. The trend for modem instruments is to have the approach sequence fully automated and under computer control. 

The piezoelectric building biocks-beam, tube and bimorph-are illustrated in Fig. 9. The displacement. Av. as a function of applied voltage, V, of the respective configuration will be 

Function Device type Dynamic range Resolution 

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