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ZEISS
3 Product and Functional Description | 3.3 Optional Components and Accessories
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.
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.
These semiconductor detectors have a relatively small bandwidth and a high capacitance (rela-
tively long discharge time), and therefore a reduced scan rate is recommended when using them.
The SE detector can initially be used to adjust the electron-optical parameters (focus, stigmation),
then the signal source can be switched to the BSE detector to generate the image.
By selecting and combining different diode segments, it is possible to generate images with both
topographical and compositional information.
The following figure shows an example comparing the compositional contrast (COMPO) and to-
pographic contrast (TOPO) modes when using a BSD.
Fig. 49: COMPO mode image (left) and TOPO mode image (right) acquired with a
The following figures show more examples of shadow mode images created using compositional
contrast and topographic contrast modes with a BSD.
Fig. 50: Compositional contrast image (left) and “Shadow mode” image (right) acquired using a
Instruction Manual ZEISS SIGMA series | en-US | Rev. 7 | 352102-9344-006
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