Commercially fabricated probes are now universally used. The best tips may have a radius of curvature of only around 5nm. The need for sharp tips is normally explained in terms of tip convolution . Tip broadening arises when the radius of curvature of the tip is comparable with, or greater than, the size of the feature trying to be imaged. This is what we may call tip convolution.
Compression occurs when the tip is over the feature trying to be imaged.
It should be born in mind that although the force between the tip and sample may only be nN, the pressure may be MPa. However, some changes which may be perceived as being topographical, may be due to a change in force interaction. Forces due to the chemical nature of the tip are probably most important here, and selection of a particular tip for its material can be important. Electron beam deposited tips have been used to image steep-walled features far more faithfully than can be achieved with the common pyramidal tips. The earlier discussion of the way in which the bending of the cantilever is detected considered the use of a laser and a split photo-diode.