Page "Transmission electron microscopy" Paragraph 13

where, h is Planck's constant, m < sub > 0 </ sub > is the rest mass of an electron and E is the energy of the accelerated electron.

Electrons are usually generated in an electron microscope by a process known as thermionic emission from a filament, usually tungsten, in the same manner as a light bulb, or alternatively by field electron emission.

The electrons are then accelerated by an electric potential ( measured in volts ) and focused by electrostatic and electromagnetic lenses onto the sample.

The transmitted beam contains information about electron density, phase and periodicity ; this beam is used to form an image.