The tissue is introduced into liquid carbon dioxide which is then brought to its critical point, which is the combination of pressure and temperature at which the fluid and gaseous phases exist together without an interface or meniscus. Thus there is no surface tension. The presence of surface tension during drying is disruptive to a tissue and causes visible distortions. After drying, the surface of the tissue is sputter coated in a vacuum with an electrically conductive layer of gold. The coated dry sample is now placed in a vacuum so that the electron beam can move without interference.
Electricity is passed through the wire and then focused by magnets onto the sample.
When the electrons from the gun strike the surface coating of gold, electrons are reflected back off the specimen to a detector, this is transmitted to a TV screen where the image is viewed and photographed. Depending on the sample, this can vary from 30 minutes for air dried samples eg insects, to 3-4 days if sample has to fixed, dehydrated and critical point dried. See link below for sample procedure.