FEI Quanta FEG 250, User'S Operation Manual

Page: 87 / 228

Operating Procedures: Detector Types and Usage
5-15
DETECTOR CONNECTION
Detectors are connected to the feed-through connector panel.
Connectors have engraved names and they are used to connect
following detectors:
• The STEM connector:
STEM I (Scanning Transmitted Electron Microscopy, Wet STEM),
STEM II (Annular STEM)
• The GAD connector: GAD, GSED / GAD, ICD
• The BSD connector: BSED, Quad BSED, vCD, CBS
EVERHART THORNLEY DETECTOR (ETD)
It is a scintillator photo-multiplier type detector monitoring electrons
generated by the primary beam interaction with the specimen surface.
It is permanently mounted in the chamber above and to one side of
the sample. It works in two
Mode s:
• Secondary Electrons (SE)
• Backscattered Electrons (BSE).
The ETD Settings
The Detector Settings / Mode list box enables to choose a
Secondary Electrons / Back Scatter Electrons mode (the Grid
Voltage is set to +250 V / -150 V) / Custom mode (the Grid Voltage
could be set by the adjuster in a range from -240 to + 260 V). When
the voltage is negative (use a range of -50 to - 240 V), SE are repelled
from the ETD detector and only BSE are detected.
BACKSCATTERED ELECTRONS (BSED)
AND GASEOUS ANALYTICAL (GAD - optional)
DETECTORS
These are two-segment low-voltage diodes. The BSED is designated
for a HiVac large field of view. The GAD (optional) has a 500 µm PLA
cone for the Low Vacuum and ESEM modes, especially for the X-ray
analysis. The cone extends down from the unit to 8.5 mm, which
reduces the gas path length for electrons to an efficient 1.5 mm at the
standard 10 mm analytical WD.
FIGURE 5-3 BSED / GAD DIODE UNITS