Written by Alan Barker, Freelance Writer, British Science Festival
Dr Jessica Boland studies nanomaterials, which have the potential transform ICT, healthcare, security, and energy usage. Delivering the Isambard Kingdom Brunel Award Lecture at this year’s British Science Festival, Jessica took us into a strange world with remarkable physical properties. Alan Barker joined in and tried to keep up.
What would you want from a 21st century device?
Dr Jessica Boland asked us that question early in her Award Lecture at the British Science Association. This was never going to be just a lecture: with a mission to involve her audience and a passion for using British Sign Language in science, Jessica had us participating in her conversation from the very start, both vocally and with our hands. (Check out the sign for ‘laser’. It’s cool.)
Anyway, whatever we want, it will require devices to be smaller, smarter and faster.
If we want smaller, then we’ll have to find new materials. Moore’s law – predicting that the number of components on an integrated circuit doubles roughly every two years – has held good so far; but it’s limited by the material properties of silicon, the base material of electronic circuitry. If we want to go smaller, we need to find a material that transcends those physical limits, and the likely candidates are nanomaterials. Most have dimensions between one and 100 nanometres. Graphene is a good example, with a layer of carbon only 1 atom (~0.3nm) thick.
(Going from one metre to a nanometre is the equivalent of going from the diameter of the sun to the height of a human. Now you know.)
The problem: as you reduce size, you increase processing power but need to increase power consumption – and that increases heat emissions. So, we need to increase energy efficiency and reduce heat.
What about faster? Using volunteers in a demonstration worthy of a Royal Institution Christmas lecture (“And what’s your name?”), Jessica demonstrated that electron mobility is affected both by ‘traps’ – states that retard their ability to move – and crystal defects in a material. In silicon, those features place a fundamental limit on electron speed of about 105 metres per second (the equivalent of running a marathon in half a second).
We need a material that will allow electrons to up their speed.
And smarter? If we want to pack even more functionality into a device, we need to look at how we can exploit switching, electron spin (up or down, which gives a second channel of switching) and light itself as a circuit (after all, nothing travels faster). We need, not an integrated circuit, but an integrated material.
In sum, we need to be able to investigate how electrons perform in nanomaterials.
Which is where terahertz radiation spectroscopy comes in.
Terahertz radiation sits on the electromagnetic spectrum between microwaves and the infrared. It also operates within a usefully wide temperature range. It’s already in use in medical scanning machines – it’s great at detecting tumours and can even be used to treat corneas. Airport scanners will soon use terahertz radiation. It’s even used to analyse the various layers of painting in artworks and the composition of cosmic dust.
Jessica uses it to analyse electrons in nanomaterials.
If you shine terahertz radiation at a nanomaterial, you can look at what’s reflected back and work out how conductive the material is. Jessica needs a camera, of course – a rather big one, taking up a good deal of space in her lab. Not content with being able to investigate nanomaterials in bulk, Jessica wants to investigate individual nanowires. So she also uses a Terahertz SNOM: a very fancy microscope that uses a probe to channel terahertz radiation through materials with an incredibly high degree of resolution. She can even measure how electrons move through different parts of a single nanowire.
The top line message of all this research is that Jessica has found a remarkable candidate to supplant silicon. And that material is known as a topological insulator.
Topological insulators are compounds of heavy materials, like bismuth selenide and telluride. They behave extremely oddly: the bulk of the material is an insulator and the surface is an extremely efficient conductor. That surface conductivity isn’t altered by any defects or non-magnetic impurities. “If you put these in the way of the electrons,” Jessica told us, “they just keep going.” Electrons in these materials act rather like skaters on a rink: they’ll travel in only one direction – close to the speed of light – with less heat and less resistance. Forget a marathon in half a second; in this material, the electrons will manage 100 marathons in the same half-second. Topological insulators, Jessica told us, are the Ferraris of nanomaterials.
Don’t expect any commercial applications for a couple of decades. Among other things, scientists like Jessica need to understand just how the surface of a topological insulator works. At some point, companies will need to be persuaded to ditch silicon – abundant, tried and tested – for these new nanomaterials. And at some point, we shall need to ask ourselves: do we actually want our devices to be smarter, better and faster?
Alan Barker is a writer, trainer and coach specialising in communication skills. He has been working with the British Science Association since 2015. Alan’s webinar, Storytelling for Scientists, is on the 3M YouTube channel.
Banner image credit: Ken-ichi Nomura, University of Southern California.