Microscopic
probing reveals the structure of the sample.
Conventional optical microscope employs visible light as the probing
agent. For electron microscopes such as transmission electron microscopes and scanning tunneling microscopes, the probing agent is
electrons. Electron microscopes
operating with electrons have shorter corresponding wavelength than visible
light. As the resolution of the Rayleigh criterion is proportional to the
wavelength, the minimum resolvable dimension of an electron microscope is
smaller than that of an optical microscope. The resolution of optical
microscope is about 200 nm while that in electron microscopes can go down to
0.1 nm resolution.