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Transmission electron microscope images are greyscale projections of a very thin specimen, and what a given picture shows depends on which imaging mode produced it. A bright-field micrograph, a dark-field micrograph, a diffraction pattern and a lattice image of the same sample look nothing alike. This guide helps you tell the main kinds of TEM picture apart and read each one without over-interpreting it. For how samples are prepared and what limits resolution, see TEM sample preparation and resolution.
What a TEM image actually shows
A TEM image is formed by electrons that pass through the specimen, so the specimen must be very thin: typically less than 200 nm, depending on composition (NC State Analytical Instrumentation Facility). The picture is a two-dimensional projection of a three-dimensional object, which means features at different depths overlap in a single frame. Electron tomography addresses this by collecting hundreds of 2D images over a range of tilt angles (for example -70 to +70 degrees) and reconstructing them by back-projection.
Standard TEM pictures are greyscale because the detector records electrons, not light. Colour in a published TEM picture is added afterwards in software and reflects an interpretation, not the raw signal (Bitesize Bio). When you search for pictures of a transmission electron microscope you may find two different things: photographs of the instrument itself, and micrographs recorded by it. This page is about the second.
Which TEM image type shows what
| Image type | What the picture shows | How it is formed | Typical sample thickness limit |
|---|---|---|---|
| Bright-field image | Overall morphology; heavier or thicker areas look dark | Directly transmitted (direct-beam) electrons | Typically under 200 nm |
| Dark-field image | Only the crystals that diffract into the aperture appear bright; useful for crystal size distribution and defects | Selected diffracted electrons | Typically under 200 nm |
| Diffraction pattern (SAED) | Spots, rings or a diffuse ring that indicate crystallinity | Electron diffraction from the selected area | Typically under 200 nm |
| High-resolution (HRTEM) image | Fine lattice detail | Phase contrast | Normally under 15 nm thick |
| HAADF-STEM image | Contrast that depends on atomic number and thickness (Z contrast) | Incoherently scattered electrons collected at high angles | Not specified |
| EELS / EFTEM map | Elemental mapping using energy windows | Electron energy-loss signal | EELS needs under 50 nm |
| Tomogram | 3D reconstruction of the object | Many tilted 2D images aligned and back-projected | Not specified |
Sources: EPFL CIME, “Imaging modes in TEM”; NC State University Analytical Instrumentation Facility, “TEM description”. Both checked 2026-10-29.
Who uses these images: materials scientists, cell and structural biologists, and the core-facility staff who record and QC the data for them.
Bright-field vs dark-field images
A bright-field image is made by the directly transmitted electrons; a dark-field image is made by selected diffracted electrons. Both are chosen by inserting the objective aperture in the diffraction plane so that it admits either the direct beam or a selected diffracted beam. For dark field there are two set-ups: off-axis (the aperture is shifted onto the diffracted beam) and centred dark field (the incident beam is tilted so the diffracted beam sits on the optic axis).
Mass-thickness contrast
Areas of higher mass or thickness scatter more electrons, more of them are stopped by the aperture, and so those areas appear dark. This applies to crystalline and amorphous material alike.
Diffraction contrast
Strongly diffracting crystals appear dark in bright field. In dark field the situation reverses: only crystals diffracting into the aperture are bright. Contrast also changes when the specimen is tilted. This lets you distinguish crystal phases or orientations and image defects such as dislocations. The EPFL notes give an example from a Ni3Al superalloy where EDX cannot separate the gamma and gamma-prime phases but dark field can.
Diffraction patterns: spots, rings and halos
A diffraction pattern is not a picture of the specimen but a map of how it scatters. The shape tells you the structure class:
- Regular spots: a single crystal.
- Rings: a polycrystalline sample, where each ring corresponds to one set of crystal planes.
- A diffuse ring: an amorphous sample.
Selected-area electron diffraction can be used to identify crystal structures, tell crystallinity and set up conditions for dark-field imaging. Camera length controls how large the pattern is on the detector.
High-resolution (lattice) images
High-resolution TEM works through phase contrast and normally requires very thin samples, under 15 nm. The NC State facility notes that interpretation of HRTEM images is always challenging. Fresnel fringes, bright and dark bands at the edge of a specimen, are a phase-contrast effect, not a feature of the sample (EPFL CIME shows them on molybdenum oxide over holey carbon at 80 kV).
STEM, EFTEM and tomography images
In HAADF-STEM, contrast depends on atomic number and thickness, which is why it is also called “Z contrast”. EFTEM forms elemental maps by selecting energy windows, and EELS needs samples under 50 nm. Tomography turns tilt series into a 3D reconstruction, which is the standard way around the projection problem described above.
Reading a TEM micrograph: checks
- Identify the mode first: bright field, dark field, diffraction, lattice or STEM. The same feature can be dark in one and bright in another.
- Ask whether dark means dense, thick, or strongly diffracting. In bright field it can be any of the three.
- Remember it is a projection: overlapping features at different depths can look like a single structure.
- Check the specimen thickness against the technique limits in the table.
- Check the figure for a scale bar and a legend stating mode and conditions; see figure legend examples and detecting image manipulation in figures.
Common misreadings
- Treating Fresnel fringes at an edge as a real layer or shell.
- Treating colour as measured data when it was added in software.
- Comparing a bright-field and a dark-field image of the same crystal and concluding the material changed.
- Assuming a single frame shows depth. It does not without tilting or tomography.
FAQ
What do TEM microscope images look like?
Mostly greyscale pictures in which denser, thicker or strongly diffracting regions appear dark in bright field. Diffraction patterns look like dot arrays or rings rather than pictures of structure.
Are TEM microscope pictures in colour?
Not as recorded. Colour is added later in software and reflects human interpretation.
How are TEM images different from SEM images?
TEM forms its image from electrons that pass through a very thin specimen, giving an internal projection. See SEM vs TEM for the full comparison.
Why are TEM images greyscale?
The detector records electrons rather than light, so the raw signal has no colour.
Where can I find real transmission electron microscope pictures?
Public archives hold raw data; see the EMPIAR electron microscopy image archive guide.
Sources
- EPFL CIME, “Imaging modes in TEM” (MSE637, Nov 2019): epfl.ch, checked 2026-10-29.
- NC State University Analytical Instrumentation Facility, “TEM description” (2016): aif.ncsu.edu, checked 2026-10-29.
- Bitesize Bio, “Color transmission electron microscopy” (for the greyscale point only): bitesizebio.com, checked 2026-10-29.
