Scanning Probe Microscopy (SPM) aims at forming images of sample surfaces using a physical probe. To do so, the sample is scanned by a probe, e.g., a sharp tip. During the scan, the probe may be in direct contact with the sample or merely very close to it. This allows to obtain an image of the sample surface. Typically, a raster scan of the sample is carried out, and the probe-surface interaction is recorded as a function of position. The measured values are typically obtained as a two-dimensional grid of data points.
The first SPMs used the tunnelling effect and hence are referred to as scanning tunnelling microscopes (STM). The interaction monitored in STMs is the current tunnelling between a metallic tip brought in very close proximity to a conducting substrate. The quantum mechanical concept of tunnelling allows for electrons to tunnel through a potential barrier. STM was followed by the development of a family of related techniques including Atomic Force Microscopes (AFM). Here, small forces are measured between the tip and the sample. SPM devices may be used for imaging single molecules or atoms, electrical surface characteristics, or nanoscale structures.
