Transmission Electron Microscopy
Diffraction, Imaging, and Spectrometry
C. Barry Carter · David B. Williams
Since electrons are very small and easily deflected by hydrocarbons or gas molecules, it is necessary to use the electron beam in a vacuum environment. A series of pumps are used to accomplish an adequate vacuum for this purpose. Rotary Pumps are the first in the series. They are also called the "roughing pumps" as they are used to initially lower the pressure within the column through which the electron must travel to 10 -3 mm of Hg range. Diffusion Pumps may achieve higher vacuums (in the 10-5 mm Hg range) but must be backed by the rotary pump. The diffusion pump also maintains pressure. In addition a Turbo, Ion, or Cryo Pumps backed by the preceding pumps may be used when an even greater vacuum is required.