It is the most extended imaging mode in ambient air and in a liquid environment. When operating the AFM in this mode, the cantilever is oscillated near the free resonance frequency. Then the sample is approached to the surface until the amplitude of the cantilever is reduced to the set point value. (Tip-sample interaction produces a strong amplitude reduction when the tip-sample gap is in the nanometer range.) The tip is then scanned over the surface while the feedback mechanism measures and keeps the oscillation amplitude constant. In this mode force is less, therefore destruction of the tip and the soft sample is less.