AFM in Biological Surface Study and Topographic Analysis

AFM generally operates in three different modes contact, noncontact, and tapping mode. In the contact (also called static) mode, the tip is in contact with the sample surface. The force between the tip and the surface is kept constant during scanning by maintaining a constant deflection, which is used as the feedback signal. 

In the noncontact (or dynamic) mode, the probe tip is very close to the sample, but not touching it. The changes to the resonant frequency or amplitude of the 

The tapping mode, also called intermittent contact mode, is a combination of the contact and noncontact modes. The probe tip is closer to the sample than in noncontact mode and intermittently touches or taps the sample surface. While it eliminates the lateral forces, such as dragging (common in contact mode), the tapping mode improves lateral resolution, especially of soft samples by its intermittent tapping. 

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