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 compensationÂ 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.
- 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.
Effective with biological samples
Low vacuum mode is especially effective with biological samples that would otherwise need to be dried and coated, as well as precious samples (e.g. archaeological samples) that are preferentially left uncoated to ensure they are in the same condition coming out of the microscope as they are going in.
Whilst imaging using low vacuum mode is great to analyse samples without being coated, the imaging quality isn't as good as when they are coated. If you would like to see a direct comparison between imaging in high vacuum and imaging in low vacuum, check out our
low vacuum imaging case study.Ìý