Seeing things with light
is relatively easy - it just requires good lenses. However, the resolution is ultimately limited by the wavelength
of light; it is difficult to resolve subcellular
structures. One solution is to use electron
s instead, but this too fails at atomic
level (and could only (until relatively recently) be used with dead tissue).
Enter the STM, a device very different from other microscopes in that it 'feels' rather than 'sees'. That is to say, a probe is run across the surface of a sample and the shape is recorded. This is achieved by quantum tunneling between the atoms of the probe tip and the atoms of the sample. The signal is converted into a map of the sample, producing an image of its surface. Similar in principle to an atomic force microscope it also has to be operated at unimaginably low (few kelvin) temperatures. However, it allows accurate visualisation of Ångstrom detail.