What is EM?

Electron microscopes are able to discern fine detail (often called resolving power resolution or resolution) in specimens. The fineness of detail resolved can be many hundreds of times smaller than that achieved by the best light microscopes. In addition, this fine detail can be magnified many thousands of times.

An electron microscope uses accelerated electrons as a source of illumination. Because the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, the electron microscope has a higher resolving power than a light microscope and can reveal the structure of smaller objects. A transmission electron microscope can achieve better than 50 picometre resolution and magnifications of up to about 10,000,000x whereas most light microscopes are limited by diffraction to about 200 nm resolution and useful magnifications below 2000x.

The transmission electron microscope uses electrostatic and electromagnetic lenses to control the electron beam and focus it to form an image. These electron optical lenses are analogous to the glass lenses of an optical light microscope.

An Electron Microscope at work 

FEI Techni Transmission Electron Microscope
FEI Techni Transmission Electron Microscope