ZEISS
3 Product and Functional Description | 3.2 Main Components
Info
A specimen can be stored in the airlock when the chamber is in any VP mode (Standard VP,
NanoVP, or XVP).
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In store mode, however, the airlock needs to be re-pumped from time to time. This leads
to an unstable chamber pressure for a few seconds and influences the brightness of im-
ages acquired with the VPSE or C2D detectors.
3.2.2.3 Beam Gas Path Length (BGPL)
When the beamsleeve aperture is inserted and you are working in Nano VP or XVP mode, a pa-
rameter called Beam Gas Path Length (BGPL) is displayed in the
Status Bar
.
The BGPL is the distance from the end of the beamsleeve aperture to the specimen. This means
the BGPL is the distance that the primary beam has to travel through the low vacuum part of the
system. Keeping the distance small means that scattering of the primary electrons on VP gas mol-
ecules is kept small, resulting in good resolution and signal-to-noise ratio.
The BGPL should be not lower than 1 mm, because charge compensation is incomplete in this
case. You will have best results when the BGPL is between 1 and 2 mm.
Info
When working in Nano VP or XVP mode the BGPL is the WD-like parameter which should be
observed carefully not to damage the beamsleeve. The BGPL is calculated by working distance
WD minus length of the beamsleeve, which is 6.17 mm.
NOTICE
Short Beam Gas Path Length (
Risk of damaging the beamsleeve and/or the specimen.
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Do not use a BGPL of less than 1 mm.
Instruction Manual ZEISS GeminiSEM series | en-US | Rev. 2 | 349500-8138-000
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