Piezoelectric Scanners

SPM scanners are made from piezoelectric material, which expands and contracts proportionally to an applied voltage. Whether they elongate or contract depends upon the polarity of the voltage applied. With a positive voltage, the material will expand in one axis and contract in the other. With a negative voltage, the opposite occurs.

Many scanners, such as the one located in the Dimension Icon SPM scanner, are constructed by combining independently operated piezo electrodes for X, Y, and Z into a single tube:

The X and Y axes of the tube have conjugate sections on either end of the tube; as one side expands, the other side contracts, causing the tip motion to scan in a direction perpendicular to the vertical axis of the tube. The Z axis is a single element that expands and contracts to move the tip up and down. Each segment can be independently actuated, thus the scanner can manipulate samples and probes with extreme precision in 3 dimensions. In some models (for example, the MultiMode SPM) the scanner tube moves the sample relative to the stationary probe tip. In other models (for example, the Dimension Icon) the sample is stationary while the scanner moves the tip.

In order to generate an image of the sample surface, the probe must interact with as much as the sample surface as possible. It does this by scanning back and forth, line by line, probing the surface and collecting data. AC voltage applied to the X- and Y-axes produce the raster scan pattern:

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