Lab & analytical techniques · Reference
What is electron microscopy?
Electron microscopy uses a focused beam of electrons instead of light to image specimens, achieving far higher resolution and revealing structures down to the near-atomic scale.
Why electrons give higher resolution
Resolution in any microscope is limited by the wavelength of the radiation it uses, as explained under microscopy. Electrons accelerated through a high voltage have a wavelength thousands of times shorter than visible light, so an electron beam can resolve features far smaller than light ever could. Instead of glass lenses, an electron microscope uses electromagnetic lenses — coils that bend the electron beam — and the whole column is held under vacuum so the electrons are not scattered by air. Specimens generally need special preparation to withstand these conditions.
SEM versus TEM
The two principal forms differ in how the beam interacts with the sample. A scanning electron microscope (SEM) sweeps a focused beam across the surface and detects scattered or emitted electrons point by point, producing detailed, three-dimensional-looking images of surfaces.
A transmission electron microscope (TEM) sends electrons through an ultra-thin specimen; variations in how the sample transmits the beam form a high-resolution internal image. SEM excels at surface topography; TEM excels at internal ultrastructure.
Uses in research
Electron microscopy is indispensable in cell biology, virology, materials science, and nanotechnology. Researchers use it to image viruses and cellular organelles, examine the microstructure of metals and semiconductors, and characterise nanomaterials. Advanced cryo-electron microscopy reconstructs the three-dimensional shape of proteins. As with all quantitative imaging, calibrated scale and documented instrument settings are essential so that measurements are accurate and reproducible.
Key facts
At a glance
- Imaging beam: electrons (not visible light)
- Advantage: near-atomic-scale resolution
- Lenses: electromagnetic (coils), not glass
- Environment: high vacuum
- SEM: scans a surface, point by point
- TEM: transmits electrons through a thin sample
Common questions
FAQ
What is the difference between SEM and TEM?+
A scanning electron microscope (SEM) scans a beam across a sample surface to image its topography, while a transmission electron microscope (TEM) passes electrons through a thin specimen to reveal its internal structure at higher resolution.
Why does electron microscopy need a vacuum?+
Electrons are easily scattered by air molecules, which would blur the image. Holding the column under vacuum lets the electron beam travel and focus cleanly, which is also why samples must be prepared to withstand those conditions.
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