Non-destructive imaging: helium microscope

09 July 2019

Interview with 

Paul Dastoor

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They say seeing is believing, and the revolution in our understanding of the world and universe around us that came with the invention of the telescope and microscope is hard to over-state. Devices like the electron microscope now mean it’s possible to see what even atoms and molecules look like. But one of the problems with these existing techniques is that you can end up destroying a sample in the course of looking at it. Which is why a new technology being developed at the University of Newcastle in Australia and the University of Cambridge, which uses helium atoms to image things non-destructively looks set to be a game-changer. Naked Scientist Matthew Hall went to see it in action with help from Dr. Paul Dastoor.

Matthew - Imagine you're looking through a microscope, you see something magnificent and decide to zoom in on it, but as you twist the knob you realise you're already at max magnification. This unfortunate circumstance is one of many that plague microscopy, the science of looking at super tiny. In a mission to spread awareness on the varying solutions for these issues, Paul Dastoor from the University of Newcastle in Australia is visiting the UK. Paul is working on a microscope that takes images with helium atoms instead of with light...

Paul - Light can actually damage materials. If we think about what happens to our clothes when we leave them in sunlight for long periods of time, what happens to them? They fade. They fade because the light has enough energy to actually damage the dye molecules in the clothing itself.

Matthew - The reason I made my way into the Cavendish lab was for a new microscopy method - it is called the scanning helium microscope, or SHEM for short, and it operates in a completely different manner to previous microscopes...

Paul - So rather than a charged particle like an electron we are, for the first time, using neutral species - helium atoms.

Matthew - The microscope itself is huge, about the width of a sofa with the main chamber looking like a futuristic barrel to a canon. Lots of little boxes comprise the front of the device as well, allowing for the entire system to be under vacuum. Why is operating in a vacuum so important though?

Paul - In order to create a helium beam, what we have to do is to take helium gas and pump it up to high pressure and allow it to expand through a tiny hole into a vacuum, and that hole is around about 10 microns in size. And when you do that, psst, and you get a beam.

Matthew - That beam then travels to a sample holder where it strikes whatever sample is in its way...

Paul - Its energy is many, many orders of magnitude lower than electrons, even than light, and so there's no chance of the helium atoms damaging the surface at all.

Matthew - The beam then flows through the canon-shaped barrel to a very sensitive helium detector that uses the flux or flow of force from the atoms paired with position data to form an image...

Paul - We pump the helium gas out and then that helium gas can be collected through actually just a large balloon and then recompressed and recycled.

Matthew - Thanks to wave particle duality, a theory in quantum mechanics that says all particles can be represented by wavelengths, helium atoms have their own wavelength. Helium's is absolutely minuscule compared to light's wavelength. This allows for a theoretical maximum resolution of an image taken with helium to be 12,000 times better than the maximum of a light image because the wavelength is 12,000 times smaller than light's.

Paul - We're limited at the moment to a resolution of around about a micron. The next stage of development is to get that now to around about 50 nanometres, and that new instrument is actually being built next door right now.

Matthew - Even with future plans underway to make the resolution much better than it is now, the microscope is still a busy bee in the microscopy community. Up on the screen during my visit were images of a fossilised dinosaur tooth, microscopic glass spheres, and even a live stem cell changing into a different cell type.

Paul - If you want to image them in an electron microscope they are very difficult to image because, of course, electrons are charged, you put them on an insulator, they can't go anywhere. It's like rubbing and balloon on your head, you build up static. So in an electron microscope to image these things you would first have to coat them with gold. You don't actually see what's really there then, you see a coated sample, and for many of these samples they don't want them coated in gold because that means never be able to use them again. And so that's the key point here, we've got a technique that doesn't need to do that and because the helium atoms are electrically neutral, they're not charged.

Matthew - Having the power to image on the nanoscale without damaging a sample has tremendous potential for material and life science research.

Paul - All of science is based on observation. If, when you're actually observing something you change what you look at, how can you be sure of your measurement? The process of measurement should not change what you measure. What we see now here for the first time, I think, is an imaging technique that is guaranteed not to damage what we look at.

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