Schrödinger's Kitten

Irreverent Science for Everyone

Thursday 10 April 2008

Nanotech for the Enthusiastic Amateur

  • micro
  • opensource
  • nanotech

While I was looking for a diagram to put in my recent research project (to illustrate atomic force microscopy, because I couldn't face drawing it), I found The Open Source Handbook of Nanoscience and Nanotechnology. This is great! Not only for us students who cannot manage to stay awake in our nanotech lectures (sorry Prof. Petrashov...) and who are prepared to chance our coursework on internet hearsay; but also for everyone else who doesn't want to pay £3000 (or more?) per year of education, but does want to know about the tech we're building the future out of.

Why should you care?

Because nanotech is going to be that important. If some of the irons currently in the fire come to fruition, we're looking at a reduction in our use of resources, increased efficiency for those we do use, and hopefully a new paradigm to supersede some of the tech that's been around since the industrial revolution. But nanotechnology requires a very different approach to the technology we're used to dealing with, and if you want to have a clue, whether babbling in the pub, protecting your lungs from nanotubes, avoiding replicating nanobots or choosing self-cleaning windows, I recommend reading up.


Most things you use in your day to day life can be perfectly satisfactorily explained by Newtonian laws and a bit of thermal physics, unless you're an early-adopting gadget freak or a nuclear technician. But to 'get' nanotech, you need a fundamental basis in at least molecular physics, and quantum physics is quite helpful too. (I am actually doubtful about whether it is possible to teach yourself quantum and really understand it. I mean, I read A Brief History of Time when I was a kid and thought I understood it, but when it comes to deep understanding, as best the puny human mind can, you really need to hack through the maths.)

The online WikiTextbook mentioned above will get you off to a good start, though, because nanotech isn't as complicated as pure quantum - listen carefully and you can hear a thousand nanotech researchers shout indignantly at their screens - because nanoscales involve ensembles of quantum states, leading to a more easily disgested interpretation of quantum probability. Basically, instead of assuming that one atom is simultaneously in a number of states before you collapse it, you can just interpret it as half the atoms in the group being in one state, and half in another. Much happier.

Projects for Madboys

So, theory is all very nice and all, but we really want to get our hands dirty peering into the private lives of atoms. Scanning tunnelling microscopes (STMs) are pretty cool: they can show you the contours of a conducting or semi-conducting surface down to atomic level. I cannot believe people are making STMs at home, but they are. Your basic STM consists of a probe with a tip one atom wide (in the lowest-tech case, you make this by cutting wire at a jaunty angle and hoping it is sufficiently pointy) which is moved towards the surface of the sample very slowly and precisely by piezoelectric motors.

Atomic res image of graphite that I took. Graphite consists of 2-D hexagonal structures like chickenwire laying on top of each other — in places they reinforce giving bright spots: in places you can 'see' through to the layer below giving dark spots. I've superimposed the atomic structure on top in white.

When the gap between the surface and the probe is sufficiently small, quantum comes into play. Classically, the electrons are not allowed to escape the sample or the tip into the air gap, because they'd be leaving a nice low energy conductor for the high energy states of an insulator. But if you look at this in quantum terms, the electrons are represented by wavefunctions which can extend into 'forbidden zones'. If the forbidden zone is a very thin gap, the wavefunction can actually appear on the other side — and, because of the magic of the uncertainty principle and never knowing exactly where anything is, there is a possibility that the electron will be on the other side too. Putting this back into the real world, the practical upshot is that the electrons can move through the apparently insurmountable air gap between the probe and the same, but whether or not they do so depends on the width of the gap.

STMs exploit this by moving the probe close to the sample until electrons tunnel across the gap, causing a current. Then, by advancing and retracting the probe, a constant current (indicating that the probe is a constant distance from the surface) can be maintained while the tip moves across the sample. And if you record how the probe has been moved to keep it a constant distance from the surface, you know the relative contours of the surface, et voilá! By scanning more 1-D lines a 2-D picture is built up.

Warning! Do not panic when the atoms don't look like the billiard balls/balls on sticks they showed us in school. Looking at STM images makes it painfully obvious that those were simplifications, and in reality (whatever that is nowadays) you're actually seeing combinations of waves.

To buy a basic STM like Nanosurf's EasyScan will set you back a couple of grand (that's in real money, ie. pounds sterling). But...if you make your own, an STM with no output mechanism can be as little as $100. It's a rough and ready version, but it's hella cheap and could definitely get you to nanoscales, no problem. You'll also see atomic force microscopes (AFMs) for sale - these are kind of similar to STMs, but rely on keeping the force on a probe constant instead of the current. The good thing about AFMs is that you can use them on insulators, so you can get pictures of biological structures and organic chemicals. And both STMs and AFMs can be used not only to observe atomic and molecular scale structures, but to make them: individually placing the fundamental blocks of nature.

These projects do eat your time and attention, and are not for most people. But I can't help dreaming of a world where instead of doing painstakingly precise needlepoint, housewives pour their energy into assembling atomic cars...

Content: Scary Boots — Design: Canis Lupus