New research in an area called plasmonics has raised hopes for all sorts of seemingly implausible inventions, like cancer-killing nanotubes and mobile phones printed into t-shirts. It’s yet another breakthrough we can chalk up to carbon nanotubes and their sister material graphene, which have allowed researchers to replicate the functions of a laser on a much smaller scale than boring old light could ever allow.
One of the biggest problems with using light for industry is that it does not scale. Light of a particular color has a set wavelength, and that wavelength remains static regardless of the size of the generator; the green light of a pocket-sized laser pointer can have the same wavelength as that produced by a building-sized space-laser.
This has the big advantage of providing astronomers with sensible optical information about the rest of the universe, but it also places a hard limit on miniaturization of optical devices. At scales smaller than about half the wavelength of the light being created, it’s impossible to do useful optical work. For reference, visible light runs from about 400 to about 700 nanometers in wavelength, meaning light in that range is dozens of times fatter than the scale of modern transistors.
One proposed solution to this problem is called Surface Plasmon Amplification by Stimulated Emission of Radiation, or a “spaser.” Spasers are generally referred to as nano-scale lasers, though the two technologies seem to have few similarities. Spasers basically trade photons for resonating electrons, sending optical signals called surface plasmons down the a physical substrate (thus, the field is called plasmonics). This differs from electrical conductivity in that when these surface plasmons reach their destination at the other end of the spaser, they behave like photons of light in every way that matters to a computer engineer.
Until now, the only appropriate substrate for a spaser has been bunches of quantum dots or nanoparticles of precious metal. Graphene, however, has the electrical and optical properties needed for a spaser, along with the added bonus of being strong enough for use in the real world. Graphene is an almost theoretically small substance, just a single atom thick in its purest form; this is one of the smallest sorts of computing possible.
This spaser from 2009 uses gold nano particles to create its surface plasmons.
The potential impact of this sort of technology, which is collectively referred to as “nano-photonics,” is enormous. Prior research has shown that carbon nanotubes can be made to grow toward target cells in living tissue — if this nanotube was a hunter-killer spaser, it might be able to blast its target diseased cell to death without disturbing any healthy neighbours. We could weave a nanotube antenna into your clothing, turning you into a walking receiver. It has even been predicted to increase the zoom on optical microscopes by a factor of 10.
This could also be a way around the impending doom of Moore’s Law; so-called optical computing with light instead of electricity is already theorized to allow much higher computing speeds than conventional chips. The former impossibility of doing that kind of work with light on a scale useful for computing, however, has kept the idea from getting the sort of attention it could well deserve.
The gain element for this metaphorical laser is a carbon nanotube element, which was found to very easily pass energy to and from graphene elements. The whole system uses materials that set new records for strength, flexibility, conductivity, and more. Best of all,carbon nanotubes are carbon, life’s primary structural component. This means that graphene spaser-based devices could be biodegradable, too.
This is all a long way off; all that’s been invented here are nano-scale plasmonics made of carbon. It will be up to other researchers to take advantage of all the potential they bring, but there’s already more than enough theory to get started.
