Contact

In this mode, the cantilever tip is brought into mechanical contact with the sample surface. A feedback mechanism measures and keeps the cantilever deflection (tip-surface normal force) constant while the tip is scanned over the surface. The image is formed by recording the voltage applied to the piezoelectric actuator in order to maintain the deflection at a fixed set point value. This mode is suitable for hard samples with sharp tips.

Non Contact

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.

Tapping Mode

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.

Force Spectroscopy

Atomic Force Microscope (AFM) Spectroscopy is an AFM based technique to measure, and sometimes control the polarity and strength of the interaction between the AFM tip and the sample. Although the tip-sample interaction may be studied in terms of the energy, the quantity that is measured first is always the tip-sample force, and thus the nomenclature: force spectroscopy. Unlike imaging, force spectroscopy is performed mostly when the servo feedback loop is deactivated. In force spectroscopy, the cantilever-tip assembly acts as a force sensor.

Force spectroscopy is widely used in air, liquids, and different controlled environment. Force spectroscopy provides the necessary sensitivity to characterize biomolecular interactions such as the unfolding forces of single proteins or forces of a single chemical bond.