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What is nanoscale?

Here, we explain how we can use electrons to make microscopes powerful enough to make individual atoms visible.
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How small is small? With sufficient light, the human eye can distinguish two features about a tenth of a mm apart. If they are closer together, we see them merge together as a single point. This distance between points is called resolving power, or resolution. To magnify this distance and separate the points that we
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cannot distinguish with a naked eye, we use light microscopes: an assembly of lenses and a light source. The resolving power of a microscope determines its maximum magnification. A modern light microscope can magnify things by a factor of 1000 or so, and allows us to resolve objects separated by 200 nm, about 500 times smaller than the diameter of a human hair. This resolution is not even sufficient to image a virus. So why can’t we see smaller? What stops us from magnifying objects further? The fundamental limit to how much we can magnify images with visible light, is the wavelength of the light.
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Broadly speaking, the smallest feature that can be resolved by any kind of illumination is about half the length of its wavelength, the distance between a wave crest and trough. For visible light, the wavelength is 700 nm for red, down to 400 nm for blue – so the best we can resolve is around 200 nm. Can we magnify objects even further? It turns out that accelerated electrons in a vacuum behave like waves, just like light. But the electrons’ wavelength is around 100,000 times smaller than that of light. Which means we can use them to see much, much smaller details!
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Very conveniently, accelerated electrons in a vacuum travel in straight lines, but because they are also negatively charged particles, we can move them with electric and magnetic fields. This means that we can build electromagnetic lenses to steer the electrons, similar to the glass lenses of a light microscope. Using these principles, in 1931 German physicist Ernst Ruska built the first electron microscope in Berlin, for which he was awarded the Nobel Prize for Physics in 1986. For his microscope, Ruska used just two magnetic lenses – three years later he added a third lens. The resolution of this microscope was around 100 nm – twice as good as a visible light microscope. He used it to image a thin foil of nickel.
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90 years later, modern electron microscopes have come a long way. They now have multiple optics in their imaging systems, and their resolving power is well over 1000 times better than Ruska’s first microscopes. What is 1000 times better than 100 nm? The resolution of modern microscopes is better than one Angstrom, 10-10 m, around the diameter of a single atom! In other words, with modern electron microscopes, we can examine the details of objects or materials all the way down to the atomic scale, and visualise even single atoms.

What is the smallest object we’re able to see with a microscope? Here, we explain how we can use electrons to make microscopes powerful enough to make individual atoms visible.

You might wonder how we can use particles, such as electrons, to replace the waves of light normally used in a microscope. As Leonardo says in the video, particles can be thought of as having a wavelength. In fact, in some circumstances (such as in our electron microscope) they behave exactly like waves rather than as particles. We can even calculate a particle’s wavelength, (lambda):

[lambda = frac{h}{m_ev}]

Here (h) is planck’s constant – a very small number which sets the scale for the quantum world (6.63 x 10-34 m2kg/s), (m_e) is the mass of the electron, and (v) is the velocity of the electron.

This all sounds very unlikely; how can something be both a wave and a particle? This isn’t what we see at the scale of the everyday world around us. Since this is the only physics we ever experience directly, our brains understand the world in terms of the distinct particles and waves we observe. However, this results from the fact that the world we see around us consists of large numbers of particles carrying a substantial amount of energy. This is the domain of so-called classical physics – the kind we are most familiar with.

At the scale of individual particles there is really no difference between particles and waves. Whether we see an electron behave more like a particle or a wave depends on exactly what it is doing at the time.