Trickster figures are a feature in mythologies around the world. They’re always mischievous, tricking humans and other beings into doing things they shouldn’t.

Tricksters can be good and/or villainous. For example, Raven in the Pacific Northwest gave us the sun, moon, and stars but stole them in the first place from someone else.

I don’t think the researchers at the University of Maryland have done anything comparable (i.e., stealing) with their graphene discovery but the analogy does amuse me. From the June 3, 2012 news release by Lee Tune,

Researchers at the Center for Nanophysics and Advanced Materials of the University of Maryland have developed a new type of hot electron bolometer a sensitive detector of infrared light, that can be used in a huge range of applications from detection of chemical and biochemical weapons from a distance and use in security imaging technologies such as airport body scanners, to chemical analysis in the laboratory and studying the structure of the universe through new telescopes. [emphasis mine]

Before launching into why I highlighted the part about the universe and the telescopes, here’s the problem the researchers were solving (from the news release),

Most photon detectors are based on semiconductors. Semiconductors are materials which have a range of energies that their electrons are forbidden to occupy, called a “band gap”. The electrons in a semiconductor can absorb photons of light having energies greater than the band gap energy, and this property forms the basis of devices such as photovoltaic cells.

Graphene, a single atom-thick plane of graphite, is unique in that is has a bandgap of exactly zero energy; graphene can therefore absorb photons of any energy. This property makes graphene particularly attractive for absorbing very low energy photons (terahertz and infrared) which pass through most semiconductors. Graphene has another attractive property as a photon absorber: the electrons which absorb the energy are able to retain it efficiently, rather than losing energy to vibrations of the atoms of the material. This same property also leads to extremely low electrical resistance in graphene.

University of Maryland researchers exploited these two properties to devise the hot electron bolometer. It works by measuring the change in the resistance that results from the heating of the electrons as they absorb light.

Normally, graphene’s resistance is almost independent of temperature, unsuitable for a bolometer.

Here’s how the researchers solved the problem (from the news release),

So the Maryland researchers used a special trick: when bilayer graphene is exposed to an electric field it has a small band gap, large enough that its resistance becomes strongly temperature dependent, but small enough to maintain its ability to absorb low energy infrared photons.

The researchers found that their bilayer graphene hot electron bolometer operating at a temperature of 5 Kelvin had comparable sensitivity to existing bolometers operating at similar temperatures, but was more than a thousand times faster.  They extrapolated the performance of the graphene bolometer to lower temperature and found that it may beat all existing technologies.

As usual, there is more work to be done (from the news release),

Some challenges remain. The bilayer graphene bolometer has a higher electrical resistance than similar devices using other materials which may make it difficult to use at high frequencies. Additionally, bilayer graphene absorbs only a few percent of incident light.  But the Maryland researchers are working on ways to get around these difficulties with new device designs, and are confident that a graphene has a bright future as a photo-detecting material.

As for why I highlighted the passage about telescopes and the structure of the universe, our local particle physics laboratory (TRIUMF located in Vancouver, Canada) is hosting the Physics at the Large Hadron Collider (PLHC) conference this week. This is a big deal, from the 7th annual PLHC conference home page (Note: I have removed some links),

PLHC2012 is the seventh conference in the series. The previous conferences in this series were held in Prague (2003), Vienna (2004), Cracow (2006), Split (2008), Hamburg (2010) and Perugia (2011). The conference consists of invited and contributed talks, as well as posters, covering experiment and theory.

Topics at the conference

• Beauty Physics
• Heavy Ion Physics
• Standard Model & Beyond
• Supersymmetry
• Higgs Boson

There was a June 3, 2012 public event (mentioned in my May 15, 2012 posting) featuring Rolf Heuer, Director General of CERN (European Particle Physics Laboratory) which houses the Large Hadron Collider and experiments where they are attempting to discern the structure of the universe. (I did attend Heuer’s talk and I think one needs to be more of a physics aficionado than I am.  Thankfully I had watched the Perimeter Institute’s webcast  (What the Higgs is going on?) when the big Higgs Boson announcement was made in December 2012 (mentioned in my Dec. 14, 2012 posting) and that helped.

There is of course an alternate view of the universe and its structure as presented by the story of Raven (from the Wikipedia essay [Note: I have removed a link]),

Raven steals the sun

This is an ancient story told on the Queen Charlotte Islands and includes how Raven helped to bring the Sun, Moon, Stars, Fresh Water, and Fire to the world.

Long ago, near the beginning of the world, Gray Eagle was the guardian of the Sun, Moon and Stars, of fresh water, and of fire. Gray Eagle hated people so much that he kept these things hidden. People lived in darkness, without fire and without fresh water.

Gray Eagle had a beautiful daughter, and Raven fell in love with her. In the beginning, Raven was a snow-white bird, and as a such, he pleased Gray Eagle’s daughter. She invited him to her father’s longhouse.

When Raven saw the Sun, Moon and stars, and fresh water hanging on the sides of Eagle’s lodge, he knew what he should do. He watched for his chance to seize them when no one was looking. He stole all of them, and a brand of fire also, and flew out of the longhouse through the smoke hole. As soon as Raven got outside he hung the Sun up in the sky. It made so much light that he was able to fly far out to an island in the middle of the ocean. When the Sun set, he fastened the Moon up in the sky and hung the stars around in different places. By this new light he kept on flying, carrying with him the fresh water and the brand of fire he had stolen.

He flew back over the land. When he had reached the right place, he dropped all the water he had stolen. It fell to the ground and there became the source of all the fresh-water streams and lakes in the world. Then Raven flew on, holding the brand of fire in his bill. The smoke from the fire blew back over his white feathers and made them black. When his bill began to burn, he had to drop the firebrand. It struck rocks and hid itself within them. That is why, if you strike two stones together, sparks of fire will drop out.

Raven’s feathers never became white again after they were blackened by the smoke from the firebrand. That is why Raven is now a black bird.

While it’s less poetic in tone, there is an image from the University of Maryland illustrating their graphene photodetector,

Electrons in bilayer graphene are heated by a beam of light. Illustration by Loretta Kuo and Michelle Groce, University of Maryland .