AFM is a surface sensitive technique permitting to obtain a microscopic image of the topography of a material surface. Typical lateral image sizes are within a range of only a few Nanometers to several 10 Micrometers, whereas height changes of less than a Nanometer may be resolved.
A fine tip attached to a cantilever is scanned across the material surface and enables to measure height changes via a laser that is reflected from the rear side of the cantilever onto a segmented photodiode. The position of a laser spot on the photodiode permits to track height changes as, e.g. due to a nano-particle on the surface or an atomic terrace of a single crystal surface. A feedback loop controls the tip-surface distance and therefore ensures stable imaging conditions.
Different operation modes like contact or non-contact mode can be used to optimize the imaging conditions with highest lateral resolution on one hand and least sample interaction on the other hand.
Additional surface properties may be obtained for each point of the scan like friction force by lateral force imaging and magnetization properties by magnetic force imaging. Elasticity maps of heterogeneous sample surfaces can be obtained by non-contact phase imaging utilizing the phase shift arising from the local penetration behavior of the tip into the surface.