Directional Gaseous Analytical Detector (Gad) - FEI Scios 2 User's Operation Manual

Directional Gaseous Analytical Detector (GAD)

This is lens mounted low voltage silicon diode with an active area of approximately 100 mm
at pressures above 10 Pa. It is positioned directly over the sample to obtain maximum detector efficiency.
Directional GAD Diode / Installed in chamber
FIGURE 7-3
The GAD can be used down to a high voltage about 1 kV and works best at a slow scan conditions.
It can be used for HiVac but because it limits the minimum achievable WD, it is disadvantageous for high
resolution imaging. It has a 500 µm PLA cone for the LoVac operation, especially the X-ray analysis. The cone
extends down from the unit to 5.5 mm, which reduces the gas path length for electrons to an efficient 2.5 mm at
the standard WD = 7 mm.
Installing / Removing
When not used, the GAD is placed at the parking position (inside
the chamber at the bottom right side) in the protective aluminium
box to prevent its pollution. The cables are permanently connected
to the feed-through connector board by a FEI authorized service
engineer.
1. With your gloved hand grasp the detector in the protective box.
2. Push the mounting collar gently up to the objective lens cone.
The part with connector cables must face towards the chamber
door rotated about 30° counter clockwise (when viewing from
top) in order not to shadow the ICE detector.
3. Push the sides of the protective box and release the installed
detector.
When removing the detector, proceed in reverse.
Directional GAD detector installation
FIGURE 7-4
1
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C a u t i o n !
The diode is sensitive to a mechanical damage so the active area (shiny diode) should never be touched.
The GAD is mounted close to the (optional) X-ray detector collimator, which must not be touched when changing detectors.
It is advisable to retract the EDX collimator when mounting / removing the detector on / from the objective lens.
7-8
System Options: Optional Detectors
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C O N F I D E N T I A L – FEI Limited Rights Data
, which could be used
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