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Raster Scanning

SPM relies on raster scanning to probe an area of the sample surface. Raster scanning is performed with actuators whose motion can be incremented in small steps and with high precision. These actuators are usually made of piezoelectric materials shaped into the form of a hollow tube, or they are made of mechanical .exures, or a hybrid of the two.

Raster scanning makes it possible to record the probe-sample interaction point-by-point. For each X,Y coordinate pair, the interaction is recorded as one data point. The collection of these data points is then synthesized into the SPM image, a 3-dimensional map. In other words, the area of the sample surface under study is probed not all at once, but in a time series of measurements that are put together point-by-point, and line-by-line. This is why the instruments are called Scanning Probe Microscopes. In this sense, SPMs are identical to scanning electron microscopes (SEM), except that instead of an electron beam, SPMs use mechanical, opto-mechanical, or electrical probes to interact with and to interrogate the sample surface.

Raster scanning requirement is a major speed bottleneck in SPM. The scanning speeds in SPM have traditionally been slower than in SEM, but this gap is closing fast, and is even projected to be reversing in the near future.

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