Secondary Electron (SE)
Definition
Low-energy electron (below 50 eV) ejected from the top few nanometres of the sample when the primary beam knocks a loosely bound electron free. SE detection by an Everhart-Thornley collector gives the topographic image with the deep depth of field that SEM is famous for. The image looks 3D because the SE yield depends on the local angle of the surface.
- Energy range
- Below 50 eV
- Sample depth
- Top 1-10 nanometers
- Detection method
- Everhart-Thornley collector
Common questions
What is a secondary electron in SEM?+
A secondary electron is a low-energy electron (below 50 eV) knocked loose from the top surface layer of a sample when the primary electron beam strikes it. Because these electrons are ejected from very shallow depths (1-10 nanometers), they carry topographic information about the sample's surface.
Why do SEM images look 3D when using secondary electrons?+
The number of secondary electrons released depends on the angle of the surface at each point. Steep surfaces produce more electrons than flat ones. The Everhart-Thornley detector captures these electrons, converting the variable yield into an image where angled areas appear bright and flat areas dim, creating a three-dimensional appearance.
What advantage do secondary electrons give over other SEM signals?+
Secondary electron imaging provides exceptional depth of field and sharp surface detail. Because they come from only the topmost nanometers, they reveal fine surface features and topography with high spatial resolution, making them ideal for examining surface morphology.
Related terms
- ASTM E1588
- ASTM International standard practice for gunshot residue analysis by scanning electron microscopy with energy-dispersive spectrometry. Defines particle classification (characteristic, consistent-with, indicative), morphology...
- Back-Scattered Electron (BSE)
- High-energy electron from the primary beam that has bounced elastically off a nucleus and exited the sample. BSE yield increases with atomic...
- Sputter Coating
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- Characteristic X-Ray
- An X-ray photon emitted when an outer-shell electron drops into an inner-shell vacancy created by ionisation. Energy is set by the difference...
- EDS / EDXRF Detector
- Silicon-drift detector mounted at a fixed take-off angle to the sample that reads characteristic X-rays emitted as the primary beam ionises atoms...
- Energy-Dispersive X-Ray Spectroscopy (EDS)
- An X-ray detection method that simultaneously measures the energies of all characteristic X-ray photons emitted from the interaction volume, identifying all elements...
- Environmental SEM (ESEM)
- Variant of conventional SEM that runs the sample chamber at higher pressure (up to several torr of water vapour) instead of the...
- FIB (Focused Ion Beam)
- A technique using a focused gallium ion beam to mill a specimen at a specific site-selected location, producing a TEM-quality cross-section with...
- Interaction Volume
- The pear-shaped region of specimen material within which the primary electron beam deposits energy and generates signals. At 20 kV in a...
- Lead-Free GSR
- Gunshot residue produced by ammunition using non-lead primer formulations (SINTOX, Diazol, or other variants). Does not contain the conventional Pb-Sb-Ba three-element combination;...
- Silicon Drift Detector (SDD)
- The current standard EDS detector type, using a reverse-biased silicon chip cooled by a Peltier element to achieve high count-rate capability (up...
- Ultramicrotome
- A precision instrument for cutting sections of resin-embedded specimens to 60-100 nm thickness using a diamond knife, enabling TEM examination of the...
Explained in these topics
- Electron Microscopy: SEM, TEM and EDSA low-energy electron (below 50 eV) ejected from the top 1-10 nm of the specimen surface by the primary electron beam. SE yield is topography-dependent, produc...
- Scanning Electron Microscopy (SEM) with EDXRFLow-energy electron (below 50 eV) ejected from the top few nanometres of the sample when the primary beam knocks a loosely bound electron free. SE detection by...