FEI Quanta FEG 250, User'S Operation Manual

Page: 88 / 228

Operating Procedures: Detector Types and Usage
5-16
Either diode has an active area of approximately 125 mm
2
per segment
and is positioned directly above the sample to obtain maximum detector
efficiency. Therefore it causes some limitation in the tilt range.
Both detectors are connected to an SSD pre-amplifier input board.
They can be used down to a high voltage about 1 kV and works best
at a slow scan conditions.
The BSED can be used for HiVac mode and for low magnification
imaging in LoVac mode. The GAD can be used for all vacuum modes,
but because it limits the minimum achievable WD, it is
disadvantageous for high resolution imaging in HiVac mode.
Both can be used in parallel with the LFD, which allows simultaneous
use of SE, BSE and X-ray detectors in a gaseous environment. They
should be used at the lower part of a pressure range, obtainable for a
particular detector.
Installing the Diode
Hold the detector by its sides and push up the back of the diode onto
the Standard Insert until it stops. The diode should by oriented so that
its out coming cables side should be faced (and parallel) to the
chamber door.
Detector home position
While the BSED / GAD detector is not used, it could be placed into a
holder which is mounted on the upper edge of the pole piece, saving it
from a mechanical damage and pollutions.
Caution!
The diode is sensitive to a mechanical damage so the active area
(shiny diode) should never be touched.
The BSED / 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 pole piece.
FIGURE 5-4 GAD INSTALLATION AND HOLDER POSITION
Detector Settings
Select the BSED / GAD from the Detector Settings module Detector
list box. Choose the required Mode by ticking the radio button:
• The Z Contrast (A+B) is the normal BSE image with suppressed
topographical contrast and maximum atomic number contrast.
• The Topography (A-B) is the pseudo-topographical image with
suppressed atomic number contrast and maximum topographical
contrast.
• The Segment A / B (Left / Right) uses shadows to create strong
topographical and atomic number contrast.