One of the most significant developments in the realm of nanotechnolog
y during the 1980s was the invention of the scanning tunnelling micros
cope. This event triggered the evolution of a whole family of scanning
probe microscopes (SPMs), all based on the use of proximal microsenso
rs with very high lateral as well as vertical resolutions, which even
allow atoms to be imaged. The properties sensed range from quantum tun
nelling currents, through interatomic and van der Waals forces, to the
evanescent electromagnetic field. The principal application is imagin
g by the measurement of topography, but for many of the microsensors i
nteraction with the surface is dependent on material properties, thus
allowing a spectroscopic mode of use as well. The principles of severa
l microsensors and associated SPMs are examined. The requirements for
the traceable calibration of SPMs are discussed, and progress towards
the development of calibration artifacts presented.