Week 7: Counting 602000000000000000000000 Atoms

Share This:

Friday, July 26, 2013


Alec Lindman

On Friday we toured NIST with Alexandra and Dr. John Suehle, her mentor. We visited so many labs that I’ve probably lost track of a few, but these are the highlights. Our first stop was in the electron microscopy suite – though the star of the show wasn’t even an SEM. For what I put down to a lab being reused from some other purpose, the walls of the antechamber and SEM space were covered in anechoic foam; however, it transpired that when people are talking in the space around the microscope, it’s possible to reconstruct the conversation based on the vibration of the sample in the image. After spending quite a while discussing the various samples the first machine could image and why most of their work starts on that one (mostly the larger working volume, as well as the option of a cryogenic stage to hold biological samples), we briefly stopped at another machine that currently holds the world resolution record at half a nanometer. Then we turned a corner and beheld a microscope whose exterior size was at least five times that of the first machine, and which as I mentioned, doesn’t even use electrons: it uses helium ions. It’s capable of imaging many exciting samples, including carbon nanotubes, which by the thinness of their walls barely interact with electrons in the SEM machines. Apparently it’s virtually a one-of-a-kind capability, and the device itself is quite rare – as if SEMs weren’t rare enough in the first place.

NIST is absolutely huge, and much bigger than even its .37 mile long central hallway would indicate: beneath almost the entire footprint of the central buildings are two or three more floors of basements, with the lowest rooms’ footings on the bedrock. This makes sense in the context of our next destination, the coordinate measuring lab.

Here they have two machines with working volumes a meter in length which can make linear, roundness and surface measurements to within 500 nanometers. To enable this accuracy, they’ve air-leveled the floor and the room temperature is maintained within a few millidegrees of 20C. We saw the temperature spike on the screen of the monitor when we walked into the room; even the lights had been designed with temperature control in mind, as the bulbs were located outside the double walls of the room, and the light passed in through waveguides.

One of the efforts underway at NIST – custodian of all measurement standards for the United States – is to find a fundamental definition of the kilogram, the last unit still based on a physical artifact. An approach to this problem is to use Avogadro’s number (the number of particles in a mole, related via carbon to the kilogram) of atoms to construct an object consistent with the fundamental definition. Silicon is the element of choice, and the idea is to grow a perfect crystal, then polish it into a precise sphere. Then, knowing the crystal lattice spacing, one can calculate the number of atoms in the measured sphere.

Next, we visited the NanoFab, where all sorts of ridiculously tiny devices are manufactured on an impressive array of equipment. I must say, however, that seeing a few more multi-million-dollar instruments in cases, class 10 cleanroom notwithstanding, wasn’t much of a shock after all the other incredible tools they have. Finally, we visited a lab attempting to sequence DNA by trapping chemical tags liberated by polymerase in pores in a bilayer membrane. They anticipate bringing the cost to fully sequence a genome down to a few tens of dollars, and the time to a couple of hours. This would significantly alter the paradigm in the medical profession, but there are of course many ethical and privacy concerns to assuage first. Who would have guessed that an organization perhaps more known for complaining about miniscule changes in a lump of platinum-iridium sealed away in a vault would be at the forefront of medicine?

Alec Lindman