SU Exec Program, Day 2: Nanotech continued

The first part of Merkle's talk was a 40,000-foot flyover. The second part shifted into hyperdrive. Feels like a college term packed into 90 minutes or so.

How do physics change at nanoscale? Merkle ticks off a list. Length scales down linearly. Area scales down by a factor of a 2 - it gets exponentially smaller - and volume by a factor of 3. Frequency gets faster. Time changes (a nanosecond is a sensible interval for a molecular machine). And so on. Interesting points: Speed doesn't change; a walking pace is reasonable for us and for a nanomachine. Gravity disappears Magnetism drops off. Stiff things become floppier and more subject to thermal noise.

From there, we dive into the structure of atoms, with probabilistic electron cloud surrounding a point-mass nucleus (for most practical purposes). Wrap that up with a few basic forces, and you have the basis for modeling atoms and their interactions fairly accurately. And once you can do that, you can think about atoms as building blocks of nanomachines.

So what can you build? A nanotube - a sheet of graphite rolled into a tube, or concentric sheets rolled into concentric tubes. Merkle mentions two concentric tubes, which make a molecular spring; pull one end out, let it go, and it pops back in, courtesy of van der walls force. Unlike a macroscale spring, this nanospring snaps back with the same force no matter how far you pull it out.

These days, though, Merkle is setting his sights much higher. Over the past few years he has put together a theoretical system for building diamond, atom by atom. It involves nine molecular tools and methane/hydrogen feedstock on a diamond substrate. He has analyzed all the side reactions, he says, and shown why they won't throw the process out of kilter. "This is the first effort to define a minimal tool set for positional diamond mechanosynthesis," he says. "It's hard," he says - an understatement - "but it ought to work."