Transmission Electron Microscope (TEM)
An electron microscope that fires a broad electron beam through an extremely thin specimen, forming an image from the electrons that pass through — analogous in overall concept to a compound light microscope's transmitted-light imaging, but using electrons to reveal internal ultrastructure at resolutions approaching the atomic scale.
Resolution
~0.1 – 1 nm (near-atomic)
Imaging signal
Transmitted electrons
Specimen requirement
Ultra-thin (typically <100 nm)
Image character
Internal structure, 2D projection
Overview
- A broad, high-energy electron beam is directed through an extremely thin specimen; electrons passing through regions of lower density or lighter atomic mass pass more easily, while electrons encountering denser, heavier-atomic-mass regions are scattered or absorbed more strongly — producing a variation in transmitted electron intensity across the specimen that electromagnetic lenses then magnify and project onto a fluorescent screen, photographic film, or digital detector
- This transmitted-electron imaging principle directly parallels a compound light microscope's transmitted-light brightfield imaging, but because electrons have a vastly shorter effective wavelength than visible light, TEM achieves resolution roughly a thousand times finer, approaching the scale of individual atoms in the best modern instruments
- Because electrons are strongly absorbed and scattered by even modest thicknesses of material, specimens must be prepared extraordinarily thin — typically under 100 nanometers — a specialized and demanding sample preparation process (often involving resin embedding and ultramicrotome sectioning, or ion-beam thinning for materials science samples) that is one of the most challenging aspects of TEM work
- The resulting image is fundamentally a 2D projection of the specimen's internal density variations along the beam's path — revealing internal ultrastructure (organelles, viral particles, crystal lattices, material internal defects) that no surface-imaging technique like SEM can access
Key Features
Near-atomic resolution
The finest resolution of any common microscopy technique, capable in advanced instruments of resolving individual atomic columns in crystalline materials.
Internal ultrastructure imaging
Reveals internal density and structural detail invisible to any surface-imaging technique, from viral capsids to crystal lattice defects.
Demanding ultra-thin sample prep
Specimens must be sectioned to under roughly 100 nm thickness, a specialized preparation process that is often the most time-consuming part of TEM work.
Design and Construction
Electron column
- Electron gun generates and accelerates a broad beam (typically at much higher accelerating voltage than an SEM) toward the specimen; condenser lenses shape the beam before it reaches the specimen
- Objective, intermediate, and projector electromagnetic lenses magnify the transmitted electron pattern in stages, analogous in role to a compound light microscope's objective and eyepiece but with several additional magnifying stages
Sample preparation
- Biological specimens are typically fixed, dehydrated, embedded in resin, and cut into ultra-thin sections with a diamond-knife ultramicrotome
- Materials science specimens are often thinned via ion-beam milling or electropolishing to achieve the required electron-transparent thickness
Applications
Virology & Cell Biology
Virus structure & organelle imaging
The standard tool for directly visualizing viral particle structure and internal cellular organelle detail.
Materials Science
Crystal structure & defect analysis
Used to directly image crystal lattices, dislocations, and internal material defects at near-atomic resolution.
Why choose a TEM
Finest resolution available
Approaches atomic-scale resolution, unmatched by any other common microscopy technique.
True internal structure access
The only technique in this reference that directly reveals a specimen's internal ultrastructure rather than its surface.
Frequently asked questions
Here are some common questions about achromatic lens.
Choose an SEM when the question is about a specimen's surface topography, texture, or external morphology, and when specimen preparation needs to stay comparatively simple (often just a conductive coating). Choose a TEM when the question is about internal structure — what's happening inside a cell, virus, or material at near-atomic resolution — and when the specialized, demanding ultra-thin sample preparation required is justified by the need for that internal detail; note that TEM generally also requires a substantially higher accelerating voltage and a more complex, expensive instrument than a comparable-class SEM.
