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3.4.5.1. In-lens detector
The In-lens detector (
1
) is a high efficiency detector for high resolution SE imaging. It is located
above the objective lens (
3
) and detects directly in the beam path (
2
). The detection efficiency of
this detector results from its geometric position in the beam path and from the combination with
the electrostatic/electromagnetic lens.
Fig. 3.6: Schematics of In-lens detector
At an acceleration voltage of maximum 20 kV, the electrons of the primary electron beam are ad-
ditionally accelerated by 8 kV, the so-called beam booster voltage.
To ensure that the electrons reach the specimen surface (
4
) with the energy set as acceleration
voltage, an electrostatic field is generated at the end of the objective lens by 8 kV. This electro-
static field acts as acceleration field to the SE generated on the specimen surface.
At the In-lens detector, the electrons hit a scintillator generating flashlight that is guided out of the
beam path by means of a light guide. The light information is multiplied in a photomultiplier and
output as a signal which can be electronically processed and displayed on the monitor.
IMPORTANT
The In-lens detector can be used up to an acceleration voltage of 20 kV.
At higher acceleration voltages the beam booster and thus the field of the electrostatic lens
are switched off. Therefore, the efficiency of the In-lens detector will be markedly
reduced.
The efficiency of the In-lens detector is mainly determined by the electric field of the electrostatic
lens, which is decreasing exponentially with the distance.
Thus, the working distance (WD) is one of the most important factors affecting the signal-to-noise
ratio of the In-lens detector.
As the tilt angle of the specimen surface affects the emission angle of the electrons, you should
avoid strong specimen tilting.
1
In-lens detector
3
Objective lens
2
Beam path
4
Specimen
1
2
4
3
Содержание AURIGA Compact Crossbeam
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