Materials processing for future technology
The Science of Electron Microscopy and The Nanoscale
You can learn more about specific aspects of supercritical fluid electrodeposition on our other science pages.
Imagine how small a marble is compared to the size of the Earth. This comparison is the same as comparing a nanometre to a metre. In science the symbol for nanometre is 'nm' and in maths it is written 1x10-9 meaning that it is 1,000,000,000 (i.e. one billion) times smaller than a metre. Scientists refer to these really small dimensions as the 'nanoscale'. If we want to see something that is only a few nanometres in size we need to look at it with something even smaller. Electrons are particles that we can use to do this because they are 1,000,000 (i.e. one million) times smaller than those really small nanometres!
Visit this link to learn more about how small electrons and the nanoscale really are:
Microscopes are pieces of equipment that we use to see things that are too small to see with the our eyes. They add extra lenses, a bit like the ones in our eyes, to magnify whatever we are looking at. Most microscopes magnify the light that reflects from a sample. These are called 'optical microscopes'. A beam of light, however, is too big to show nanoscale details. This is why we make microscopes that use lenses to focus beams of those tiny electrons instead. Such microscopes are called 'electron microscopes'. One of our Research Fellows demonstrates an electron microscope for you in the video below.
For Scientists... diffraction is a property of waves that describes how a wave will start to diverge rapidly if it passes through a gap that is a similar width as its wavelength (left). The same effect is observed if a wave is focused down to these dimensions. The resolution of an optical microscope is therefore limited by diffraction, because beyond the 'diffraction limit' where this becomes a significant effect the microscope cannot accurately manipulate the light.
From this description it is clear that diffraction and thus the resolution of an optical microscope is proportional to the wavelength of the light used. Electron microscopy improves the resolution of images by using the principle of 'wave-particle duality'. This principle states that every particle has an equivalent wavelength and that allows it to exhibit wave-like behaviour. Because electrons have an equivalent wavelength approximately 100,000 times shorter than the wavelength of visible light, a beam of electrons can be focused far more tightly than a beam of light. This enables microscopes that shine electron beams at a sample to view nanoscale detail that a normal optical microscope could not see.
There are different types of electron microscope. Some measure low energy electrons that are back-scattered from the surface of a sample (a 'SEM') and others fire high energy electrons through a sample and measure their properties on the other side (a 'TEM'). As the equivalent wavelength is inversely proportional to the energy of a particle, the high energy TEM will operate at a shorter wavelength than the SEM and therefore be able to see smaller features. It also has the added advantage that as the electrons have passed through and been influenced by the sample, extra information can be determined by analyzing the transmitted electrons.