Imaging Methods in Atomic Force Microscopy

One can easily distinguish between two general modes of operation of the atomic force microscope (AFM) depending on absence or presence in the instrumentation of an additional device that forces the cantilever to oscillate in the proximity of its resonant frequency. The first case is usually called static mode, or DC mode, because it records the static deflection of the cantilever, whereas the second takes a variety of names (some patented) among which we may point out the resonant or AC mode. In this case, the feedback loop will try to keep at a set value not the deflection but the amplitude of the oscillation of the cantilever while scanning the surface. To do this, additional electronics are necessary in the detection circuit, such as a lock-in or a phase-locked loop amplifier, and also in the cantilever holder to induce the oscillatory excitation.