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3D Printing of Molecules March 19, 2012

Remember when I wrote about the home-made Scanning Tunneling Microscope (SCM for short) a while back?  Well, an SCM can also act as a 3D printer down at the atomic level, placing one atom at a time and building structures never intended by nature.  Here is one, a graphene-esque deposition of carbon monoxide on a(n infinitely-smooth) copper plate. Besides the fact that this is even possible there are some really extraordinary things about this arrangement of atoms, and what it does to the electons in this configuration: electrons in this structure have graphene-like properties. Unlike ordinary electrons, they appear to have no mass and travel as if they are moving at the speed of light in a vacuum. It seems the carbon monoxide repels the free-flowing electrons on the copper surface, forcing them into a graphene-like honeycomb pattern.

"The behavior of electrons in materials is at the heart of essentially all of today’s technologies," said Hari Manoharan, associate professor of physics at Stanford and a member of SLAC’s Stanford Institute for Materials and Energy Sciences, who led the research. "We’re now able to tune the fundamental properties of electrons so they behave in ways rarely seen in ordinary materials."

In typical deadpan sciencespeak understatement, the modest doctor says "Our new approach is a powerful new test bed for physics. Molecular graphene is just the first in a series of possible designer structures. We expect that our research will ultimately identify new nanoscale materials with useful electronic properties."  Here’s one:

This is a version of molecular graphene where electrons are tuned to respond as if they’re experiencing a very high magnetic field (red areas) when none is present. Scientists from Stanford and SLAC National Accelerator Laboratory calculated the positions where carbon atoms in graphene should be to make its electrons believe they were being exposed to a magnetic field of 60 Tesla, more than 30 percent higher than the strongest continuous magnetic field ever achieved on Earth (a 1 Tesla magnetic field is about 20,000 times stronger than the Earth’s). They put the carbon monoxide molecules (black circles) in those positions and the electrons responded by behaving exactly as expected — as if they were exposed to a real field.

This radically alters the electron’s characteristics: it changes the symmetry of the electron flow. Elsewhere, researchers were able to finely tune the density of electrons on the surface by introducing defects or impurities. By writing complex patterns that mimicked changes in carbon-carbon bond lengths and strengths in graphene, the researchers were able to restore the electrons’ mass in small, selected areas.

Now do you see why I’m excited by 3D printing?  If we can fundamentally alter the behavior of subatomic particles in a repeatable, programmable fashion using computer-controlled STMs, we can make matter have properties we desire, rather than what nature demands.  This high-magnetic field without a magnet, for example could conceivably be used for tiny data storage units, and let’s face it, we’re going to need a lot of that in the future.  That’s just one thing, and I’m not even thinking hard about this (I have real work to do).