What’s the Difference Between SEM and TEM?

Within cells lies an intricate, microscopic world that remains invisible to the human eye. To visualize cellular details, scientists rely on the power of electron microscopes. With unparalleled spatial resolution and the ability to reveal fine structural details, electron microscopy has become an indispensable tool for studying biological samples.

Among the various types of electron microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are the most common. While both techniques harness the power of electrons to generate images, they differ in how they capture images of these microscopic worlds. The choice of imaging method largely depends on the resolution or field of view required for the project.

SEM: Scattered Electrons Offer a Surface-Level View

With SEM, a high-energy electron beam is directed through a series of lenses and coils that focus and guide it in a raster pattern across the surface of a sample. As the focused beam interacts with the sample, it generates backscattered and secondary electrons, which are captured by detectors and recorded pixel by pixel.

This process creates detailed, high-resolution 3D images of a sample's surface. Compared to TEM, SEM offers the advantages of a larger field of view and the ability to analyze thicker samples, simplifying sample preparation.

TEM: More than a Passing Activity

TEM involves imaging beyond the surface of the sample, providing a glimpse into the intricate internal structures. In TEM, a wide, static electron beam passes through a series of lenses that guide it to the sample. Unlike SEM, where electrons bounce off the surface, in TEM, the beam travels through the sample and continues through additional lenses that magnify and project the image onto a viewing device, such as a camera, at the base of the instrument. This process creates highly detailed, two-dimensional images.

Because electrons are easily deflected by matter, TEM requires samples to be extremely thin—typically just a few hundred nanometers thick—a challenging preparation step. While TEM offers a smaller field of view and is limited to thin samples, it outshines SEM in magnification and spatial resolution, offering unparalleled insights into the microstructures inside cells and other fine details at the nanoscale.

In the rapidly evolving field of electron microscopy, both TEM and SEM continue to push the boundaries of discovery, with advanced modalities enabling electron microscopy to reveal ever more intricate details of the microscopic world.¹