The maximum obtainable magnification with a conventional optical microscope is approximately 800-1000×, because of the nature of light. For further magnification Scanning Electron Microscopes (SEMs) are used, and among these, the Transmission Electron Microscopes (TEMs) can show single atoms and thus provide the highest possible magnification. Why then do we have the Scanning Probe Microscope, SPM as yet another type of microscope?
One of the reasons is that a sample to be examined in a transmission electron microscope must be sliced thinly and thus becomes ruined. The SPM technique images surface structures with atomic (height) resolution without the necessity of damaging the sample. A further reason is the kind of imaging offered by SPM microscopes, the results are shown as a kind of three-dimensional image (also in cases where only two-dimensional information is evaluated). As this is the case with an optical microscope, it is very difficult to investigate the surface structure of a sample with an electron microscope. In order to measure a surface profile with the highest resolution, it is necessary to slice the sample. Moreover, an SPM operates without vacuum, and unlike to an electron and optical microscopes it can measure other physical effects. This includes electrical properties, such as Kelvin probe force microscopy (KPM / KPFM) or magnetic properties (Magnetic force microscopy, MFM).