Detectors
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MIRA3 FEG-SEM
6
Detectors
The detection system may contain a set of detectors designed for detecting various signals
resulting from electron beam interaction with the sample surface. The microscope is always
delivered with the SE detector.
Switching on
In the case of adjustment of the required detector, select the appropriate one from
the list box in the SEM Detectors & Mixer panel (see Figure 8). This procedure is valid
for all detectors except the LVSTD, where further procedures are needed (see
chapter 6.3). In the case of the InBeam detector, check the item InBeam Mode in the
main SEM menu first.
6.1
SE Detector
The detector works in high vacuum only.
Secondary electrons enhance topographic contrast as opposed to material contrast of back-
scattered electrons (BSE). The secondary electron (SE) detector is a basic standard detector
always present in the microscope.
The SE detector is of an Everhart-Thornley type. The grid on the front part of the detector
has positive potential. This attracts and accelerates the low-energy secondary electrons
arising on the specimen surface and focuses them onto the scintillator. The light flashes,
which result from the impingement of the electrons on the scintillator, are transferred
through the light guide to the photo-multiplier outside the chamber of the microscope.
6.2
In-Beam SE Detector
The detector works in high vacuum only.
The so-called In-Beam detector is located in the objective lens and detects secondary
electrons. It attracts electrons emanating from the sample surface into the objective lens and
catches them there. This type of detection is sometimes called “in-lens“ or “through-the-
lens“ in the literature.
This allows for the observation of specimens at very short working distances (WD) and thus
with improved resolution. The standard SE detector at a short WD would not have a good
signal because the path of secondary electrons from the specimen to the standard SE
detector would be shielded by the column. Moreover, the combined electrostatic-magnetic
lens gives further improvement of microscope performance.
In-Beam technology works in its own mode of the column (the item InBeam Mode in the
main SEM menu is checked). Therefore, objective centering and stigmator parameters are
different from the condition of disabled InBeam mode. The software automatically
remembers the set of parameters when switching between these two. All optical modes are
available in the In-Beam regime (RESOLUTION, DEPTH, FIELD, WIDE FIELD, and CHANNELING)
and all detectors may be used (InBeam, SE, BSE and others). We recommend working with
InBeam mode enabled all the time.
Images taken by the SE detector and the In-Beam detector may differ because the In-Beam
detector observes a specimen from the top whereas the SE detector from the side. The
resolution is better at a short WD using the In-Beam detector. The signal also varies with
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