Due to the nature of light, a traditional optical microscope can be employed to attain a maximum magnification of around 800–1000x. For further magnification, scanning electron microscopes (SEMs) can be used, in this case the transmission electron microscopes (TEMs) can identify single atoms and so provide the highest magnification possible.
Considering this information, why is the scanning probe microscope (SPM) employed as yet another type of microscope? One reason is that a to-be-investigated sample in a transmission electron microscope has to be thinly sliced and so could be damaged.
The SPM technique involves imaging surface structures without ruining the sample at atomic (height) resolution. The type of imaging provided by SPM microscopes is another reason since the outcomes are shown as a type of 3D image (also in instances where only 2D information is examined).