Zeiss GeminiSEM Series, Инструкция по эксплуатации

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3 Product and Functional Description | 3.3 Optional Components and Accessories ZEISS
§ Geological sections
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Complex materials
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Printed circuit boards
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Semiconductors
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Bond pads
Life sciences:
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Mineral deposits in plant structures
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Biological sections
§ Bone structures
The detector has one video output channel. The detector has a relatively large central hole and
therefore has the advantage that it does not limit the field of view of the SEM and does not influ-
ence the electron optical properties of the objective lens. A disadvantage is that especially at low
kV a lot of backscattered electrons are lost in the central hole and cannot be detected.
Function On the surface of the specimen, some of the primary electrons are backscattered. The backscat-
tered electrons then move towards the silicon segments of the BSD detector. If the energy of the
backscattered electrons is high enough, then the electrons pass through the very thin dead layer
of the diode and create electron-hole pairs in the silicon segments.
In each individual segment, the charge separation due to the electron-hole pairs is measured as a
current, which is used as a signal for image generation. Only electrons that have a high enough
energy can create electron-hole pairs and can contribute to image generation. Electrons that have
a lower energy (e.g. secondary electrons) are not detected by the BSD detector.
The emission of backscattered electrons from a specimen is related to the atomic number of the
involved material: Elements with high atomic numbers generate more backscattered electrons (i.e.
the backscatter coefficient is higher). When imaging, regions that contain elements with higher
atomic numbers appear brighter. Regions that contain elements with lower atomic numbers ap-
pear darker.
Since the detector has a limited speed, it is recommended to use scan speed 6 or higher (slower),
especially at small magnifications. The lower the gain is, the faster is the detector.
3.3.1.6 aBSD Detector
Purpose The aBSD detector is a pneumatically retractable annular backscattered electron detector. It is
used for high efficiency and angle selective material characterization even at low-kV applications.
It has six separate diode segments, two inner concentric rings and four outer quadrants. The inner
segments provide mostly material contrast whereas the four outer quadrants provide more topo-
graphical contrast.
Fig. 28: The aBSD detector with two inner concentric segments and four outer quadrants
NOTICE
Motorized specimen stage
Risk of damaging the detector when operating the motorized specimen stage.
4
Retract the detector head completely after you have finished the work with the detector.
52 Instruction Manual ZEISS GeminiSEM series | en-US | Rev. 2 | 349500-8138-000