How to measure the radius of curvature of the probe tip of atomic force microscope

For the probe whose scanning morphology is only a few nanometers in radius, it can only be measured by TEM. For probes with hundreds of nanometers or even microns, SEM is used. These are estimated according to the pictures first, and then according to the proportion, which is not accurate. It is said that it is more accurate to calculate the radius of the probe by scanning the carbon nanotubes with the probe and calculating the width change of the carbon nanotubes. The radius of the large probe can also be directly measured by scanning the morphology on the large probe with an extremely accurate probe.