to study very small structures inside cells or on cell surfaces. Specimen must be placed in a vacuum chamber and living cells cannot survive this.
transmission electron microscope
electron beam is directed a a very thin slice of specimanstained with metal ions
scanning electron microscope
electron beam is focused on a specimen coated with a very thin layer of metal. SEM shows three dimensional images of cell surfaces.
Scanning tunneling microscope
uses needle like probe to measure differences in voltage caused by electrons that leak, or tunnel from the surface of the object being viewed. Three dimensional and can be used to study living organisms.