1 February 2012

Data deconstructed

How researchers use powerful magnets to learn about materials.


Every year, more than 1,000 scientists use the lab's magnets to explore new, exotic materials – and what they discover could just change the way we live.

One of the most promising materials MagLab scientists are studying is graphene, a substance found right in the flakes of your lead pencil. Some say graphene might one day be used to make everything from computer screens to airplanes.

Scientists want to know how graphene – a one-atom thick, honeycomb array of carbon atoms so thin it's virtually see-through – reacts to light and different magnetic fields. To find out, they put a sample of graphene inside a powerful magnet. Then they observe what happens when the graphene is subjected to different forces: electric currents, magnetic-field strengths and wavelengths of light.

Chun Ning "Jeanie" Lau, an associate physics professor at the University of California at Riverside, travels more than 2,000 miles to do graphene research at the Magnet Lab.

"Graphene is such a beautiful and unique material," Lau says. "It's stronger than steel yet softer than silk. It's transparent like plastic, but conducts heat and electricity better than copper. It's the thinnest single-atomic-layer elastic membrane that's also a conductor and in which electrons 'lose' their mass. It's a Nobel-winning material but is produced by every school kid every day."

Other MagLab scientists are fascinated with graphene, too, including condensed matter physicists Dimitry Smirnov and Zhiqianq "Jason" Li, and postdoctoral associate Jean-Marie Poumirol.

"A lot of companies are trying to do research to make graphene commercial," Li says. "One of the first applications could be a large area display … television, computer, maybe billboard."

That's one reason scientists want to know how this material interacts with different kinds of light. One way to discover that is to shoot laser beams at a graphene sample.

Researchers also want to find out how the electrons in graphene behave in the presence of magnetic fields. To generate a magnetic field, scientists send an electric current through a wire coil, then observe the variations of the graphene's resistance.

Curious to see what a graphene experiment at the lab actually looks like? Here's a photo tour of an experiment that was carried out in Lab 3 of the Resistive Magnet Wing. Lab 3 has a special magnet that allows scientists to shoot laser beams at their sample.

1. The sample

The sampleThe sample. This graphene sample is so tiny, it's invisible to the eye. It's been mounted on a computer chip – that's the long triangular part. The chip is carefully attached to the probe.

2. The probe

The probeThe probe.

A probe is a long, stick-like device with a test sample (in this case, graphene) mounted on it. The probe must be slowly lowered into the center of the magnet. In this picture, the graphene chip is attached at the right end of the probe.

3. Readying the experiment

Readying the experimentLowering the probe into the magnet.

Scientist Jean-Marie Poumirol is now ready to insert the probe (with the graphene sample attached to it) into the magnet's bore (the space inside the magnet where the experiment takes place). The bore is at the very center of the magnet, where the magnetic field strength is strongest. In this photo, Poumirol is about to begin to insert the probe into the magnet, which is actually on the floor below him. He's opening a valve that will allow him to very slowly lower the probe into the magnet.

4. The magnet

The magnetThe magnet.

This is where all the action takes place: inside the magnet. This magnet rises through an opening cut through the first-floor ceiling, which allows scientists to access it. The magnet is inside the shiny barrel-shaped container, so you can't actually see it. Directly below the magnet, polarizers – optical devices that cause light to vibrate in a particular direction – have been lined up. Scientists shoot a laser beam through the polarizers, which direct the light into the sample of graphene inside the magnet.

5. Optical close-up

Optical close-upClose-up of polarizers. This is a close-up of the polarizers lined up under the magnet. Three of the polarizing devices are vertically aligned; below them, a silver mirror, tilted at a 45 degree angle, redirects the laser beam through the three polarizers and into the sample of graphene inside the magnet's bore. The cement blocks (to the left of the polarizers) are there to prevent accidental injuries. Laser beams can burn your skin and permanently injure your eyesight. The blocks absorb any miscalculated laser beams; you can see the burn marks left behind from some slightly misdirected laser beams.

6. Watching the data compile

Data compileChecking the data from the experiment.

Putting the probe into the magnet's experimental space and making sure everything is in place can take a half-day – sometimes longer. The experiment itself can last a week or more. But once everything is ready and the experiment is running, Poumirol checks the data being collected using a computer and other equipment. When the experiment is finally completed, researchers may spend months analyzing their findings before determining what to tackle next.

This story was originally published in Issue 8 of flux magazine, a discontinued publication of the National High Magnetic Field Laboratory.