Electron Microscopes A whole new world to be seen

SEM of a plant preparation in cryo conditions, -180 SEM image of a snowflake, color has been added. degrees Celsius. What is an electron microscope? Most microscopes you may have seen are light microscopes, they use a lightbulb to illuminate the specimen. A light microscope is limited to a resolution up to 3 micrometers (magnification up to 1500X). After that, two objects close together do not look separate.

In electron microscopy, high resolution images are the result of using electrons as the source of illumination. The resolution is about 0.01 nanometers (magnification up to 300,000X).

There are two main types of electron microscopes (EM), the scanning EM (SEM), and the transmission EM (TEM).

Scanning Electron Microscope(SEM) The main parts to an SEM are: source of electrons, a column for them to travel with electromagnetic lenses, an electron detector, sample chamber, and a computer and display to view the images.

A high energy beam of electrons is aimed at the sample. As they interact with the sample, secondary electrons and X-rays are produced. Those signals are collected by the detectors and an image is formed on the computer screen.

The image to the below is an SEM of a tardigrade (color has been added). They are a water-dwelling, eight-legged micro- animal. The “water bears” have been found everywhere, from mountains to mud volcanos. They are the most resilient known animals, they have even survived exposure to outer space. To the left is a light microscope image for comparison of the resolution.

The image above is an SEM of a hydrothermal worm. This worm does not have a digestive tract, it can absorb carbon compounds directly.

SEM of 3D Graphene on Nickel Foam Transmission Electron Microscope (TEM)

The TEM is a little different than the SEM. A tungsten filament is used to make an electron beam in a vacuum chamber, then, instead of bouncing off the surface of the sample, the beam passes through it. The sample is a very thin slice of material, less than 100nm. When the electrons pass through, they hit a phosphor screen, CCD or film and an image is made.

TEM can have a resolution of 0.2nm, that is smaller than the size of most atoms. The TEM can show the structural arrangement of atoms in a sample material.

TEM of E. coli

Atomic resolution, demonstrated on a single crystal

High Resolution TEM (HR- TEM) image of a crystal showing the 3.82 Å lattice spacing very clearly. Small defects in the crystal on the atomic scale show up as differences in contrast, sharpness and position of the atoms.

References

Created by Diana Ashby https://www.robin-noorda.com/colored-sem.html https://theydiffer.com/difference-between-a-light-microscope-and-an-electron-microscope/ https://www.umassmed.edu/cemf/whatisem/ https://microbiologyinfo.com/differences-between-light-microscope-and-electron-microscope/ https://www.azonano.com/article.aspx?ArticleID=1723