ZEISS
3 Product and Functional Description | 3.3 Detectors
7
Fluorescent X-rays
Primary Electrons
Primary Electrons (PEs) are electrons forming the scanning beam before hitting the specimen.
Secondary
Electrons
Secondary electrons are emitted from the topmost layer of the specimen.
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Electrons emitted at the point of impact between the beam and the specimen are known as
SE1 type electrons. The amount of electrons emitted at the point of impact is related to the
shape of the specimen.
Secondary electron detectors, such as the InLens SE detector, collect SE1 type electrons from
the surface layer of the specimen and are thus ideal for displaying surface structures.
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The emergence of backscattered electrons from the specimen excites further emission of sec-
ondary electrons. These are known as SE2 type electrons.
Detectors that collect SE2 type electrons are especially suitable where the working distance is
large. Surface detail as the effect of “lateral illumination” emphasizes the topography of the
specimen.
Backscattered
Electrons
All electrons with energy higher than 50 eV are known as backscattered electrons (BSEs). BSEs are
generated by elastic scattering in a much deeper range of the interaction volume (up to 1 µm) and
carry depth information. The backscatter coefficient increases with increasing atomic number of
the elements within the specimen. This allows the BSE detector to generate atomic number con-
trast, or compositional contrast images.
Fig. 14: Backscattered electron coefficient against atomic number
BSE detectors are used to display the materials contrast because the backscatter coefficient is de-
pendent on the mean atomic number of the material under investigation.
Transmitted
Electrons
This comprises primary electrons that are transmitted through an ultrathin specimen and weakly
scattered primary electrons with a small range of angles. Depending on the material, primary elec-
trons are scattered under different angles and can be detected by a STEM detector placed below
the specimen. Unscattered electrons are detected in the center of the STEM detector and give a
bright field image. Electrons scattered under higher angles are detected by outer areas of the
STEM detector and produce dark field images.
Cathodoluminesce
nce
Electrons impacting on luminescent materials cause the emission of photons (Cathodolumines-
cence, CL) which may have wavelengths in the visible spectrum and can be imaged by specialized
detectors.
Instruction Manual ZEISS EVO | en-US | Rev. 10 | 354706-0780-006
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Summary of Contents for EVO
Page 1: ...Instruction Manual ZEISS EVO Scanning Electron Microscope...
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