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Atomic force microscopy works by the principle of force acting upon a tip (probe) at close distance and is therefore a scanning probe microscopy (SPM). The nature of the acting force can vary. Typically, van der Waals, electrostatic or magnetic forces are measured. For this technique a very fine tip with a curvature in the nanometre range is brought in close proximity of the sample surface. The tip is attached to a bendable cantilever. When the tip gets close enough to feel the attractive interactions the cantilever deflects. This deflection is measured by a laser beam that is focused on the back side of the cantilever just above the tip. The laser beam is reflected onto a position sensitive photodiode. If the cantilever deflects the photodiode can measure the deflection. The sample is fixed on a motorised stage and moved in X and Y direction. The tip deflection changes depending on the underlying sample surface and a 3D image can be constructed. AFM offers a resolution in the few nanometre range under ambient conditions making it a very feasible and fast analytical technique.

When operated in contact mode the tip is approached till a certain repulsive force is matched. The tip has real contact to the surface. In this mode the tip distance is regulated to maintain the same level of repulsive force. Thereby the height level of the samples surface is measured.As modification of the contact mode a conductive tip can be used to measure the electronic nature the sample surface. This technique is then called scanning voltage microscopy (SVM).
In the non-contact mode, the cantilever is oscillated with a high frequency (50-600 kHz) and an amplitude in the nano to micrometre range. Once attractive forces act upon the tip, the amplitude is dampened. This dampening can then be calculated to the height of the sample surface.
A variation of the non-contact mode can be the magnetic force microscopy (MFM), where by using a magnetized tip the magnetic force of the sample is additionally measured.
To measure the electrostatic force the sample is scanned once normally and then with a fixed distance to the sample scanned again. During the second scan a constant voltage is applied to the sample. The technique is then called electrostatic force microscopy (EFM).

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