Scanning electron microscopy (SEM) is extremely popular with materials and life scientists, but it isn’t the only electron beam-based imaging technology available to researchers. There are several different electron microscope configurations.
We have talked extensively about the benefits of SEM—particularly its enhanced resolution and significantly improved magnifying capabilities. However, we haven’t covered other types of electron microscopes like the transmission electron microscope (TEM), the reflection electron microscope (REM), or the scanning tunnelling microscope.
In this article, we aim to compare the principles and performance of TEM and SEM technologies. Hopefully it serves as a good primer for newcomers, while providing insight for anyone looking to buy an electron microscope.
Electron Microscopy—A Quick Introduction
The first thing to know is that both TEM and SEM technologies use focussed electron beams as a source of illumination, which explains their exponentially greater resolution than light-based microscopes. To put that in context: A compound microscope allows us to visualise cells, bacteria, and so on, while electron microscopes let us peer within those structures to observe molecular-scale phenomena. Both provide similar levels of detail despite their different operating principles.
What is Transmission Electron Microscopy?
TEM systems operate by focussing a broad electron beam onto an ultra-thin sample and measuring the transmission of electrons using a fluorescent detection screen placed below it. As the beam completely penetrates the specimen, the 2D image generated can offer invaluable insights into internal structures with unprecedented accuracy. Yet the sample must be thin enough to enable electron transmission, which limits the materials that can be viably imaged while introducing a challenging and potentially costly sample preparation step to the imaging workflow.
What is Scanning Electron Microscopy?
SEM technologies use deflector coils to alter the path of the electron beam so that it scans a sample in a raster pattern. Usually, three detectors are positioned at angles in the sample chamber: an X-ray detector, a back-scattered electron detector, and a secondary electron detector. As none of these depend upon transmission, sample thickness is much less of an issue. Although this means a relative drop in resolution, SEM technologies offer 3D surface mapping compared to the 2D internal imagery provided by TEM.
So, which electron microscope technology should you use? The deciding factor is whether or not you need to visualise internal structures or surface areas. TEMs are ideal for the former while SEM technologies are preferable for the latter. There may be an issue of material applicability with TEM, which can usually be resolved through, admittedly, time-consuming thinning processes. Consequently, SEM technologies are usually considered the faster and more convenient option if internal details are irrelevant.
Interested in learning more about SEM technologies?
Contact a member of the EOI team today if you have any questions about the information in this article. We compare and contrast the remaining types of electron microscopes in future articles, so check back on our blog page to keep up to date with our SEM articles.