Image: Variable Pressure SEM  Variable Pressure SEM  Scanning
Electron Microscope (SEM)  Zeiss EVO LS 15 SEM: Variable
Pressure SEM  The Variable pressure SEM allows the examination
of surfaces of almost any specimen, wet or dry, insulating,
uncoated and untreated because the environment around the
specimen no longer has to be at high vacuum. The environment can
be water vapour or other gases in the pressure range from 10 to
3,000 Pa. When the Pressure Limiting Apertures are fitted in the
final aperture of the column, a controllable amount of gas
molecules, usually air, can be introduced into the specimen
chamber whist maintaining a good vacuum in the electron optical
column and the electron gun. Collisions between the high energy
electrons of the beam and the gas molecules will cause the gas
to ionise. The positive ions that are produced will neutralise
the negative charge that has formed on the surface of an
insulating material and will enable disturbance free images of
the specimen to be obtained. The seco