Tuesday, 18 March 2014

UK facilities: the big science of looking at small stuff

Somewhere in a field in Oxfordshire, there are, side-by-side, two very large scientific instruments. One is housed partly in buildings as large as aircraft hangars, and partly under large mounds of earth; it fires protons onto a huge metal target to produce neutrons and muons. This is ISIS. The other is housed within a ring, looking side-on like the landed saucer section of the starship Enterprise; this machine accelerates electrons, causing them to produce exceedingly bright electromagnetic radiation in the X-ray spectrum. This is Diamond, the UK's synchrotron. These machines are the engines chugging at the heart of research facilities; scientific communities built around central instruments, covering square miles of buildings, employing hundreds of people and providing a scientific 'laboratory-from-home' for thousands more scientists, engineers, technicians, students and collaborators.

ISIS from the air. Image credit: STFC.
Diamond and ISIS are examples of big science that live right here in the UK. Facilities like these and others overseas happen to have become the bread and butter of my own scientific work, but more about that later.

It's a sort of rule* that the smaller the thing you wish to see, the larger a machine you will require to see it: think of CERN, the vast underground ring straddling the borders of countries and accelerating its packets of particles to collide together with the energy of a double decker bus, and all to reveal the tiniest and most fundamental particles in the Universe. We are talking a little bit smaller in terms of facility size, and a little bit bigger in terms of the structures we are looking at. Still we are in impressive territory; the primary ISIS beam line is hundreds of metres long from accelerator to target (and then some, for each instrument), and it's fair to say that the typical length scales probed are measured in nanometres; that is multiples of 0.000000001 metres, or billionths of metres. To use the obligatory reference, that is 100,000 times smaller than the width of a human hair.

I often cite a major turning point in my career as a Ph.D. student as the first time I entered the guide hall of the first Target Station at ISIS. I stepped along the raised metal gangway into that vast edifice of science, crammed with equipment, cranes, and portakabins. Among the concrete shielding blocks was an electric hum and the mechanical breathing of countless fans and compressors. It was a truly inspiring experience - and although on that first visit I had no idea of the difficulties and challenges that lay ahead (the beam is switched on 24 hours a day, 7 days a week for most of the year), I nevertheless had the strong feeling that I had just entered into a new, and special, scientific world.

The experimental hall at Target Station 1, ISIS. Image credit: STFC.

On that first occasion, I was helping out with a neutron reflectivity experiment. Like the bands of colour visible when a thin slick of oil sits on top of the surface of water, seen for example by the side of a road on a rainy day, the reflection of neutrons from a surface is sensitive to extremely thin layers of material and can tell us accurate information about the thickness and the chemical composition of what is deposited there. In this case, we were studying polymer brush layers: single polymer chains tethered at one end to a silicon surface to create a brush-like layer rather like a carpet of seaweed waving about in the water, but only nanometres in height. Such layers have extremely low friction and so are good lubricating coatings; they also hinder proteins from sticking to surfaces and so help to prevent the fouling process which can lead the body to 'reject' foreign objects, and so polymer brushes have uses in medical applications.

In my current work on polymer nanocomposites, we have a material which consists mainly of our host polymer but with mixed with a small proportion of a 'nanofiller', or additive, to change its properties. In our case, our nanofiller is usually some form of graphene (the flat sheets of carbon that have commanded so many column inches since their relatively recent discovery in 2007). We know that the nanofiller is in the composite (it is now a different colour, for example), but how is it distributed? What shape and size are the lumps? What effect, if any, has the nanofiller had upon the polymer chains themselves? From these questions and other, macroscopic experiments, we aim to improve and tailor these materials for use in engineering applications. For my part, we use small-angle neutron scattering, another of the techniques commonly available at facilities such as ISIS (and many others across the world).

That is, we take a beam of neutrons and 'shoot' them at the sample. As they interact with the sample they are scattered, forming a reciprocal-space scattering pattern which we collect on a detector. From that pattern we are able to deduce the shapes and sizes of features in our sample. The inverted nature of scattering is apparent: small features scatter the neutrons through wide angles, and conversely, the larger the feature, the smaller the scattering angle. Thus, even though we are talking about the big science of small stuff, you need a big instrument tens of metres in length that can see very low angles, to look at the bigger end of the small spectrum - objects up to 300 nanometers and beyond! (The smaller the angle the bigger the object you can see - hence the existence of 'ultra-small angle neutron scattering' for even bigger stuff).

These two examples are just a tiny taste of the breadth of science that goes on at facilities like ISIS and Diamond. We are lucky and indeed privileged to have such facilities, and to be able to use their unique powers to dig down and explore the fundamental structures of materials and of life, since a large and growing part of our community is looking at biological systems, such as proteins, DNA and living cells.

An experiment at ISIS or a similar facility can mean a lot of different things to a lot of different people. To me, it usually means a hearty full English breakfast followed by long days and longer nights of measurement, experimentation and investigation: labours in the laboratory and trials on the beamline. Above all other things though, it usually means that unique feeling that you are doing something that you quite simply can't do anywhere else, and that is special every time.

For more information about ISIS click here, and to find out more about Diamond click here.

*Only sort of, because we have very huge telescopes and other instruments that look at very, very huge things that are very, very, very far away, and they are way outside of my knowledge, although well worth getting excited about.

1 comment:

  1. This article was also published as a comment on www.materialstoday.com. You can see it here: http://www.materialstoday.com/characterization/comment/uk-facilities-the-big-science-of-looking-at-small/