Low Vacuum Mode (variable pressure)

Low Vacuum Mode

  • Low vacuum mode can also be known as variable pressure, whereby gas is introduced into the chamber to create a low vacuum and varying pressures can be set. This is similar to the charge compensation mode used in the Crossbeam 550, but on a much larger scale.
  • The gas in the chamber increases the mean free path of the incoming electrons.
  • The gaseous atoms will become ionised to form cations, which neutralises the negatively charged sample surface.
  • The gas can also 'absorb' some of the emitted electrons to reduce charging.
  • This mode is especially effective with biological samples that would otherwise need to be dried and coated.
  • The microscope can be placed into LV mode straight away. This will help preserve the sample and reduce damage from a high vacuum. The vacuum can then be slowly increased to the desired point (or even high vacuum mode), whilst keeping the sample intact.
  • At the PEMC, the low vacuum mode in the JEOL 6610 is combined with the backscattered electron detector.

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