Optical microscopes, which use light to view objects, are not very useful for observing or making things at the nano level, since nano-sized things are so tiny that the properties of light itself get in the way and prevent observation. Electron microscopes are able to observe much smaller things than optical microscopes. However, even with a transmission electron microscope (TEM), a type that is able to set its magnification high among electron microscopes, cannot provide the kind of three-dimensional information that is required for engineering at this level.

A new kind of microscope was needed to view the nano world, and so the scanning probe microscope (SPM) was developed.

SPMs are instruments that scan the molecules and atoms on and at the surface of objects to determine the appearance and properties of such surfaces at the nano level. A probe is brought carefully to the surface of the object to be observed, and local physical properties of the surface of the object are measured and then processed by a computer to create an image of the surface.

Various SPMs have been developed, each using different means of creating and measuring local physical properties, including the weak electrical current used by scanning tunneling microscopes (STMs), the forces of interaction between atoms used by atomic force microscopes (AFMs), and near-field light used by scanning near-field optical microscopes (SNOMs). The field of scanning probe microscopy continues to evolve and expand with every passing day.