FEI Quanta FEG 250, Руководство пользователя

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System Overview: How Quanta FEG SEM Works
2-2
FIGURE 2-1 SEM SCHEMATIC OVERVIEW
VACUUM SYSTEM
The entire electron path from gun to specimen must be under vacuum
so that the electrons do not collide with air molecules. The Quanta
FEG has 3 operating vacuum modes to deal with different sample
types:
• High Vacuum (HiVac)
• Low Vacuum (LoVac)
• ESEM
™
Various levels of vacuum are necessary, so a Turbo Molecular Pump
(TMP) backed by a rotary pre-vacuum pump (PVP), obtains the
necessary specimen chamber pressure.
In the gaseous modes (LoVac, ESEM) the column is under lower
pressure than the specimen chamber, where the pressure ranges
from 10 to 2600 Pa (0.1 to 20 Torr), with auxiliary gas up to 4000 Pa
(30 Torr). Either mode can use water vapours from a built-in water
reservoir, or an auxiliary gas which is supplied by the user and
connected to a gas inlet provided for this purpose. Observation of
outgassing or highly charging materials can be made using one of
these modes without the need to metal coat the sample, which would
be necessary for conventional HiVac mode.
Specimen exchanges take place through a chamber door which
exposes the specimen stage when opened. Exchange time takes a
few minutes. Software and interlocks protect the system against the
damage and users against the injury.
ELECTRON GUN
CONDENSER
LENS(ES)
SCAN GENERATOR M
FINAL LENS
DEFLECTION
SYSTEM
SCAN UNIT
SPECIMEN
DETECTION UNIT
DE
TE
CT
OR
FILAMENT PINS
EMITTER
SUPPRESSOR
LENS SYSTEM