electron  microscope   It uses the de Broglie wave characteristic of an electron instead of visible light. Electrons with kinetic energy  100  keV  have  wave length 3.7´ 10^-3 nm, five orders of magnitude smaller than the wavelength of visible light (~ 500 nm) used  in  optical microscope. Due to this electron microscope can resolve structural details as small as 0.25 fm.

They   are  of  two  main  types  :  (1)  Transmission  Electron Microscope (TEM), (2) Scanning Electron Microscope (SEM).

Fig.   e4  shows  schematically    a  Transmission  Electron Microscope.  A part of the electron beam is diffracted by the sample,  while  the  other part is transmitted. The crystalline irregularities  cause  a  variation in the fraction of the electron beam diffracted leading to variation of illumination in the image on  the fluorescent screen on which the image is seen.

In  Scanning Electron Microscope the electron beam (~1 fm in diameter) repeatedly scans  the surface of the sample producing secondary electrons. This secondary electron signal is displayed on a TV screen revealing the surface topography. In addition characteristic  X-rays  are  produced that identify the elemental composition of the material under study.