An EM is a microscope that focuses beams of energetic electrons to examine objects up to nano-scales.
They utilize the same principles behind an optical microscope, but rather than photons or particles of light, concentrate electrons, charged particles located on the outside of atoms, onto an object.
Additional differences include preparation of specimens before being placed in the vacuum chamber, the use of coiled electromagnets instead of glass lenses, the use of a thermionic gun as an electron source and the image or electron micrograph is viewed on a screen rather than an eyepiece.
All EMs use electromagnetic and/or electrostatic lenses, which consist of a coil of wire wrapped around the outside of a tube, commonly referred to as a solenoid.
In addition, EMs use digital displays, computer interfaces, software for image analysis and a low vacuum or variable pressure chamber, which upholds the pressure differential between the high vacuum levels essential to the gun and column area and the low pressure required in the chamber.
All electron microscopy samples must be prepared before placed in the microscope vacuum. Techniques, which vary based on type of specimen and analysis, include:
Cryofixation
Fixation
Dehydration
Embedding
Sectioning
Staining
Freeze-fracture and Freeze-etch
Sputter Coating
Most of these techniques require specialized training and, due to sample manipulation, can result in artifacts or inadvertent changes to the structure of the specimen.
Experienced researchers may be able to differentiate actual sample properties from artifacts, but there is no absolute way to identify all potential artifacts on every single sample.