In this video, we're going to begin our lesson on the scanning electron microscope, or the SEM. The scanning electron microscope is commonly abbreviated as the SEM, and this microscope forms a 3-dimensional image. Unlike the TEM, the transmission electron microscope, which only forms 2-dimensional images. The SEM forms 3-dimensional images from a beam of electrons scattering off of a specimen surface. There are a variety of sample preparations that may be used for a scanning electron microscope, mainly used for visualizing external cell structures on the surface of the specimen.
Take a look at the image below, showing you a diagram of the scanning electron microscope or the SEM. Notice over here on the left-hand side, we're showing an actual image of a scanning electron microscope, a very complex and expensive instrument that is hooked up to a computer. We’re also showing a diagram of the scanning electron microscope where an electron gun at the top creates an electron beam (represented by the pink lines). The electron beam passes through electromagnetic lenses and ultimately hits the specimen. Notice the specimen's placement is different from that of the transmission electron microscope. The electrons scatter off the surface of the specimen, detected by an electron collector, with an amplifier in place that projects the image onto a viewing screen.
These are some of the images that can be captured by a scanning electron microscope, important for visualizing external cell structures instead of internal cell structures like the transmission electron microscope. Here’s an image of some melting ice, prairie hollyhock pollen, algae and bacterial cells, and the surface of a butterfly wing. Note that all these images are three-dimensional and focus on observing external cell structures.
This concludes our brief introduction to the scanning electron microscope or the SEM. We'll be able to get some practice applying these concepts as we move forward. So, I'll see you all in our next video.