Imagine you have the world’s best magnifying glass and you could zoom into objects indefinitely, what do you think you would see?

The wonders of the cosmos have captured the imagination of many great thinkers, from Socrates to Galileo and Isaac Newton. Yet, while they may have stared up at the sky and wondered how big the universe is, there is an opposite idea they also pondered: how small are the things that make it up?

While we now know everything is made up of atoms, in order to understand the atomic nature we need a very powerful microscope that allows us to see with atomic resolution. However, this is not possible with a magnifying glass or light microscope due to the nature of light in the visible spectrum, that is the part of light we can actually see, unlike infrared or ultraviolet light which remain invisible to us.

The key to being able to see at the atomic level was thanks to the invention of an electron microscope.

Quantum physics made a stark discovery in the early 1900s, of something called wave-particle duality, whereby electrons which are not only particles, but like light can also behave like a wave! Similar to light as it diffracts forming a colour pattern as it passes through a glass prism (which is the same effect that causes rainbows). These electrons can be accelerated close to the speed of light, and focussed using electricmagnetic lenses onto a object, in a similar way light can be focussed with glass lenses. The electrons scatter off the material, and can be detected to form an image. A diffraction pattern (which shows crystal structure information) can also be obtained due to the wavelike nature of the electrons, and by scanning this beam over your sample you can obtain localised information at the nanoscale, with this technique referred to as scanning transmission electron microscopy, or STEM for short.

There are many different possible ways of collecting an image, but the interpretation of the image is a very important process, with many images full of different artefacts that occur due to the difficult of imaging at such a small scale. Issues such as sample damage due to high energy electrons bombarding the sample are prominent and creates a trade-off between information and damage which can better optimised by imaging at cryogenic temperatures, and the use of cryoSTEM. Other phenomena can also be observed at low temperatures in the electron microscope such as superconductivity!

The electron microscope has revolutionised diverse areas of science, from physics and material science to engineering and biology. The electron microscope remains one of the most important tools for any nanoscientst to probe and see at the nanoscale.

The saying “seeing is believing” has a scientific equivalent of “observation is evidence”. It wasn’t until the invention of the microscope that biological cells were discovered that many breakthroughs in biology occurred. In the same way the invention of the telescope led to the observation of planet and star orbits proving a heliocentric model of the universe that many breakthroughs in astronomy occurred. In science, breakthrough often occur based on new techniques, new experiments, new observations and new ideas, usually in that order, so when we ask ourselves what else is there left to discover about the curious nano world? Only time (or electrons) will tell!

Timothy Lambden

NanoDTC PhD Student, c2021