The Atomic force microscope reference article from the English Wikipedia on 24-Apr-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Atomic force microscope

The atomic force microscope (AFM) consists of a cantilever with a sharp tip at its end. The tip is brought into close proximity of a sample surface. The force between the tip and the sample leads to a deflection of the cantilever according to Hooke's law. Typically, the deflection is measured using a laser interferometer.

If the tip were scanned at constant height, there would be a risk that the tip would collide with the surface, causing damage. Hence, in most cases a feedback mechanism is employed to adjust the tip-to-sample distance to keep the force between the tip and the sample constant. This can be achieved by mounting the sample on a piezoelectric crystal.

The tip is then scanned across the sample surface and the vertical displacement s necessary to maintain a constant force on the tip is recorded. The resulting map of s(x,y) represents the topography of the sample.

In general, there are two imaging modes. The first one is contact mode, in which the force between the tip and the surface is kept constant during scanning. It usually gives good resolution. The second mode, tapping mode, is less harmful for the sample. The cantilever oscillates close to its resonance frequency and therefore it interacts only a short time with the surface during each oscillation period. From the amplitude of the oscillation the feedback adjusts the distance between the surface and the tip.

See also: scanning tunneling microscope

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