FEI Quanta FEG 250, Руководство пользователя

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System Options: Optional Detectors
9-8
BSE converter plate. A zero voltage potential is applied to the SE
collection grid. When the electrons strike a gas molecule with
enough energy, they ionize it. The two electrons are further
accelerated, causing more collisions. The SE signal is “amplified” in
the gas with gains up to a few thousand resulting in BSE image.
the MIX mode is a combination of a negative potential on the
converter plate and a positive potential on the SE grid, generating
a mixed SE-BSE image.
• Enhanced Contrast adjuster: the GBSD, like other back scattered
electron detectors, works best with high beam currents and
voltages. Since back scattered electron yield is low for light atomic
number elements, using high voltages and high beam currents
may not be a suitable option for these samples. To solve this, an
additional contrast expansion circuit is provided.
Obtaining an images with the GBSD
1. Install the GBSD (if necessary, install the standard insert).
2. Pump down and flush the chamber.
3. In the Detector menu, select GBSD.
Secondary Electrons Mode
4. From the Mode list box select Secondary Electrons . The voltage
changes automatically for SE imaging.
5. Move the sample to a WD of 9.5 to 10.5 mm.
Backscatter Electrons Mode
1. From the Mode list box select Backscatter Electrons . The
voltage changes automatically for BSE imaging.
2. Move the sample to a WD of 8.5 to 9.5 mm. The closer the sample
is to the detector, the stronger the BSE signal is.
Mix Mode
1. Select the Detector menu / Mix mode. Slowly increase the
contrast until an images appears on the screen.
IN COLUMN DETECTOR (ICD)
This solid State detector is ideal for use together with the Beam
Deceleration (see below), when standard off axis secondary electron
(SE) detectors fail. Small diameter diode is integrated with an aperture
holder above the objective lens. Optimum WD should be from 3.5 to
7 mm to achieve maximum detection efficiency.
RETRACTABLE DETECTORS CONTROL
When any retractable optional detector is installed on the system, the
appropriate
Insert / Retract button is added to the Detector Settings
module / Detector: CCD to enable the equipment control while
observing the optical quad.