Contact mode is the most basic mode of Atomic Force Microscopy for measuring topography. In this mode, the cantilever scans while applying a constant force onto the surface of the sample. As the tip approaches close to the sample, the tip eventually contacts the surface. Once engaged, the cantilever bends upwards proportional to the amount of applied imaging force. As the tip passes over higher sample features, the cantilever will bend and deflect. The deflected laser spot on the position sensitive photo detector will move due to the change in contact force. The feedback loop responds by moving the Z scanner to restore the initial cantilever deflection to keep the applied imaging force constant. By tracking the displacement of the Z scanner, you can ultimately determine the surface topography of the sample.

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