Skip to main content

Nature’s Nanotech #7 – Behold the Peacock – Brian Clegg


The final entry in our Nature’s Nanotech series
There is something stunning about the colours of a peacock feather. It’s not just a simple matter of the sort of coloured pigments an artist mixes up on a palette. The colours in the feathers almost glow in their iridescence, changing subtly with angle to catch the eye. To produce this effect, the feather contains a natural nanotechnology that has the potential to transform optics when this remarkable approach is adapted for use in human technology.

Both the iridescence of that peacock’s tail and the swirly, glittering appearance of the semi-precious stone opal are caused by forms of photonic lattices. These are physical structures at the nano level that act on light in a way that is reminiscent of electronics, like the semiconductors that act to switch and control electrons, giving unparalleled manipulation of photons.
The colours of the peacock feather bear no resemblance to those of a pigment. In blue paint, for example, the pigment is a material that tends to absorb most of the spectrum of white light but re-emits primarily blue, so we see anything painted with the pigment as being blue. In the peacock feathers it’s the internal structure of the feather (or to be precise the tiny ‘barbules’ on the feather) that produce the hue.
The colouration is primarily due to internal reflections off the repeated structure of the barbule, similar to the way the lattice arrangement of a crystal can produce enhanced reflection. What happens is that photons reflected from a deeper layer are in phase with those from an outer layer, reinforcing the particular colours of light (or energies of photons) that fit best with the lattice spacing. This is a photonic lattice. These effects depend on the angle at which the light reflects, giving the typical ‘shimmer’ of iridescence.
The practical applications of artificially created photonic crystals can do much more than produce a pretty effect and striking colours. Because a photonic lattice acts on light as semiconductors do on electrons, they are essential components if we are ever to build optical computers.
These theoretical machines would use photons to represent bits, rather than the electrical impulses we currently employ in a conventional computer. This could vastly increase the computing power. Because photons don’t interact with each other, many more can be crammed into a tiny space. What’s more, one of the biggest restrictions in current computer architecture is the complex spaghetti of links joining together different parts of the structure. With photons, those links can flow through each other in a basket of light – unlike wires and circuits, photons can pass through each other without interacting, allowing more complex and faster architectures. Equally, optical switching – and in the end, a computer is just a huge array of switches – could be much faster than the electronic equivalent.
There are significant technical problems to be overcome, but the potential is great. Photonic crystals are already used in special paint and ink systems which change colour depending on the angle at which the paint is viewed, reflection reducing coatings on lenses and high transmission photonic fibre optics.
Another example of nanotechnology having a quantum effect on light is plasmonics. Something remarkable happens, for example, if light is shone on a gold foil peppered with millions of nanoholes. It seems reasonable that only a tiny fraction of the light hitting the foil would pass through these negligible punctures, but in fact in a process known as ‘extraordinary optical transmission’ they act like funnels, channelling all the light that hits the foil through the sub-microscopic apertures. This bizarre phenomenon results from the interaction between the light and plasmons, waves in the two dimensional ocean of electrons in the metal.
The potential applications of plasmonics are remarkable. Not only the more obvious optical ones – near perfect lenses and supplementing the photonic lattices in superfast computers that use light rather than electrons to function – but also in the medical sphere to support diagnostics, by detecting particular molecules, and for drug delivery. Naomi Halas of Rice University in Texas envisions implanting tiny cylinders containing billions of plasmonic spheres, each carrying a minuscule dose of insulin. Infra red light, shone from outside the body, could trigger an exact release of the required dose. ‘Basically, people could wear a pancreas on their arm,’ said Halas.
Over the last seven weeks since the first post, we have explored a wide range of the ways that nanotechnology, given a push in the right direction by nature, is starting to be important in our lives. At the moment we are most likely to come across relatively simple applications like the nanoparticles in sun block or technology making fabrics and electronics water repellent.
As our abilities to construct nanostructures improve we will see increased use of the likes of carbon nanotubes and the nano-optics described in this piece. And eventually? It is entirely possible that we will see Richard Feynman’s 1950s speculation about nanomachines come to fruition, though they are likely to be more like the ‘wet’ machines of nature than a traditional mechanical device.
When nanotechnology appears in the news it is often in a negative light. We might hear that Prince Charles is worrying about the threat of grey goo, or the Soil Association won’t allow artificial nanoparticles in organic products. But the reality is very different. Nanotechnology is both fascinating and immensely valuable in its applications. I, for one, can’t wait to see what comes next.
This series has been sponsored by P2i, a British company that specializes in producing nanoscale water repellent coatings. P2i was founded in 2004 to bring technologies developed at the UK Government’s Defence Science & Technology Laboratory to the commercial market. Applications range from the Aridion coating, applied to mobile technology inside and out after manufacture using a plasma, to protection for filtration media preventing clogging and coatings for trainers that reduce water absorption.

Comments

Popular posts from this blog

UFO Drawings from the National Archives - David Clarke ***

This is a lovely little book that, sadly, not every reader will see the point of. If somebody’s anecdotal account of a presumed alien encounter is obviously a misperception of a mundane occurrence, or else too vague – or too far-fetched – to be taken seriously, then it’s all too easy to dismiss it as worthless. But that’s missing the point. The fact that so many incidents are reported in these terms makes the witnesses’ testimony worthy of serious study – to teach us, not about extraterrestrial civilisations, but about our own culture.

That was the core message of David Clarke’s excellent How UFOs Conquered the World published a couple of years ago. Now Clarke is back with another take on the same basic theme.  His day job is Reader and Principal Lecturer in Journalism at Sheffield Hallam University, but for the last ten years he’s also acted as consultant for the National Archives project to release all of Britain’s official Ministry of Defence (MoD) files on UFOs. Throughout the Cold…

Crashing Heaven (SF) - Al Robertson ****

There's an engaging mix of powerful thriller and science fiction in this impressive novel. After the Earth has been rendered uninhabitable, human life is limited to vast space station. Our central character, Jack, has a symbiotic artificial intelligence, Hugo Fist, designed to destroy other AIs in a mysterious collective that is said to have committed an atrocity - but with a kick in the tail that because of an unbreakable contract, Fist will take over Jack's body in a few weeks' time.

Al Robertson packs remarkable technology concepts into the cyber side of this story, from AI corporations that act as a pantheon of gods to the 'puppet' that is Fist (he usually come across as a virtual cross between Mr Punch and an evil ventriloquist's dummy). Robertson does all the cyber stuff so well that it's easy to miss that this is, in effect, a myth in electronic clothing - you could substitute the myths of 'real' Greek gods and magic for what happens here. Alt…

The Science of Food - Marty Jopson ****

This is a tasty little volume, packed with kitchen-based science. I must admit, when I saw that the author was the One Show's science expert and Marty Jopson's author photo has that 'Hey, I'm a mad scientist, kids!' look, my heart fell - I was sure the book would be the written equivalent of a 'Wow, look, aren't I clever, I can make this go bang!' science show - but, in fact, it's packed full of (appropriately) meaty scientific content.

I was really pleased that Jopson didn't stick purely to the chemistry of cooking, but launched with the working of some familiar kitchen gadgets - there was genuinely fascinating reading to be had about apparently humdrum equipment in the form of the physics and materials science of a knife and chopping board. And Jopson took us into industrial kitchens too, to reveal, for example, the remarkable process required to make puffed wheat.

Inevitably, the chemistry of cooking - how, for example, proteins denature and em…