Graphene shows unusual thermoelectric response to light

Oct 07, 2011 by David L. Chandler
Photo: Len Rubenstein

Graphene, an exotic form of carbon consisting of sheets a single atom thick, exhibits a novel reaction to light, MIT researchers have found: Sparked by light’s energy, the material can produce electric current in unusual ways. The finding could lead to improvements in photodetectors and night-vision systems, and possibly to a new approach to generating electricity from sunlight.

This current-generating effect had been observed before, but researchers had incorrectly assumed it was due to a photovoltaic effect, says Pablo Jarillo-Herrero, an assistant professor of physics at MIT and senior author of a new paper published in the journal Science. The paper’s lead author is postdoc Nathaniel Gabor; co-authors include four MIT students, MIT physics professor Leonid Levitov and two researchers at the National Institute for Materials Science in Tsukuba, Japan.

Instead, the MIT researchers found that shining light on a sheet of , treated so that it had two regions with different electrical properties, creates a temperature difference that, in turn, generates a current. Graphene heats inconsistently when illuminated by a laser, Jarillo-Herrero and his colleagues found: The material’s electrons, which carry current, are heated by the light, but the lattice of carbon nuclei that forms graphene’s backbone remains cool. It’s this difference in temperature within the material that produces the flow of electricity. This mechanism, dubbed a “hot-carrier” response, “is very unusual,” Jarillo-Herrero says.

Such differential heating has been observed before, but only under very special circumstances: either at ultralow temperatures (measured in thousandths of a degree above absolute zero), or when materials are blasted with intense energy from a high-power laser. This response in graphene, by contrast, occurs across a broad range of temperatures all the way up to room temperature, and with light no more intense than ordinary sunlight.

The reason for this unusual thermal response, Jarillo-Herrero says, is that graphene is, pound for pound, the strongest material known. In most materials, superheated electrons would transfer energy to the lattice around them. In the case of graphene, however, that’s exceedingly hard to do, since the material’s strength means it takes very high energy to vibrate its lattice of carbon nuclei — so very little of the electrons’ heat is transferred to that lattice.

Because this phenomenon is so new, Jarillo-Herrero says it is hard to know what its ultimate applications might be. “Our work is mostly fundamental physics,” he says, but adds that “many people believe that graphene could be used for a whole variety of applications.”

But there are already some suggestions, he says: Graphene “could be a good photodetector” because it produces current in a different way than other materials used to detect light. It also “can detect over a very wide energy range,” Jarillo-Herrero says. For example, it works very well in infrared light, which can be difficult for other detectors to handle. That could make it an important component of devices from night-vision systems to advanced detectors for new astronomical telescopes.

The new work suggests graphene could also find uses in detection of biologically important molecules, such as toxins, disease vectors or food contaminants, many of which give off infrared light when illuminated. And graphene, made of pure and abundant carbon, could be a much cheaper detector material than presently used semiconductors that often include rare, expensive elements.

The research also suggests graphene could be a very effective material for collecting solar energy, Jarillo-Herrero says, because it responds to a broad range of wavelengths; typical photovoltaic materials are limited to specific frequencies, or colors, of light. But more research will be needed, he says, adding, “It is still unclear if it could be used for efficient energy generation. It’s too early to tell.”

“This is the absolute infancy of graphene photodetectors,” Jarillo-Herrero says. “There are many factors that could make it better or faster,” which will now be the subject of further research.

Philip Kim, an associate professor of physics at Columbia University who was not involved in this research, says the work represents “extremely important progress toward optoelectric and energy-harvesting applications” based on graphene. He adds that because of this team’s work, “we now have better understanding of photo-generated hot electrons in graphene, excited by .”

This story is republished courtesy of MIT News (, a popular site that covers news about MIT research, innovation and teaching.

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5 / 5 (8) Oct 07, 2011
50 years from now:
"Man, do you remember back when we had stuff that wasn't made of graphene?"

3 / 5 (2) Oct 07, 2011
That could make it an important component of devices from night-vision systems to advanced detectors for new astronomical telescopes.

This is similar to an article from almost a year ago about optical antennae from Carbon Nanotubes.

Back then, I suggested the multi-phasic optical array detector at the nano scale for cameras and science instruments. It would seem to offer near-infinite resolution, if you follow a design similar to multi-phasic radar devices.

This phenomenon with the graphene seems to be perfect for just that sort of application.

Perhaps by using oriented strips or circular, triangular, square, etc, shaped detectors you may even be able to tweak it for determining polarization and other properties of light besides color.

Imagine a single camera on a telescope capable of taking a one multi-spectral exposure of a distant galaxy, simultaneously serving as spectrometer, infrared, and visible telescope in one analog frame, instead of digital composite.
5 / 5 (1) Oct 07, 2011
It never ends, I love you graphene.
1 / 5 (1) Oct 07, 2011
When you peel off the single graphene layer from graphite, the surface/volume ratio increases significantly. The movable electrons of graphite are suddenly constrained into very small volume, which results into strong mutual repulsive forces between them. Such highly compressed electrons are moving chaotically, because their repulsive interactions are compensating mutually from many directions at the same moment. The geometric constrains, which are keeping electrons in body centric lattice vanish and electrons are moving in waves, powered with quantum noise of vacuum. A similar effect occurs with electrons around holes within superconductors, but in graphene it manifests itself even at room temperature, just in weaker way.
1 / 5 (1) Oct 07, 2011
The electron waves are moving with relativistic speed, so they could be described with Dirac's equation. Because electrons aren't interacting with neighbouring electrons too much, they remain hot after excitation with photons long time and they're propagating ballistically through other electrons like unguided missile.

As a real life analogy of Dirac electrons could serve the people under (social) stress. Such people are acting confusedly, impulsively and they often don't follow rational motivations of their neighbours. When they're excited, their reaction can have devastating consequences.

1 / 5 (1) Oct 07, 2011
Graphene, an exotic form of carbon consisting of sheets a single atom thick, exhibits a novel reaction to light, and the material can produce electric current in unusual ways. So my question is, can we use the unique properties of graphene for the purposes of producing a controlled, magnetotoroidic type effect for the purposes of magnetic based propulsion and is such research being conducted? This effect is shown to exhibit itself by applying curled electric fields on physical properties of stress-free BiFeO3 dots being under open-circuit electrical boundary conditions and since these fields can lead to a control of not only the magnitude but also the direction of the magnetization and if this is the case, I am curious to the possibilities of how these fields can applied as a means of propulsion? The benefits of this would be obvious and as the means to create an electric field with Graphene involve light; it would seem an area of research worth pursuing.
5 / 5 (2) Oct 07, 2011
Soylent Graphene is people!
1 / 5 (1) Oct 07, 2011
magnetotoroidic type effect for the purposes of magnetic based propulsion
There is no connection of magnetotoroidic effect to propulsion. You probably mean gravitomagnetic effect revealed with Podkletnov and Tajmar. IMO the graphene wouldn't play a significant role in it, the superconductors can. The graphene layers are too brittle and they need a support, which eliminates their properties. Whereas inside of superconductors the electrons are constrained not into layers, but into stripes, where the places of repulsive forces between electrons alternate with attractive forces of atoms outside of stripes. Such structure can exert a much higher pressure to electrons.

After all, this is a reason, why sodium never becomes superconductor, even under high pressure. Its orbitals are full of electrons, but they're of spherical shape - there are no binding sites. Whereas the niobium has both spherical orbitals, both elongated orbitals, which are serving like hooks binding atoms together.
1 / 5 (1) Oct 07, 2011
The more we compress electrons together, the higher speed they will get. In my opinion, the fast moving charged particles interact strongly with density fluctuations of vacuum, so that the empty space serves for superconductive pad like the air for wing of plane. In his fundamental experiments Mr. Podkletnov revealed, that the electric impulse introduced into superconductive electrodes generates a pulse, which propagates like tractor beam along the direction of electrons, which were moved with EM pulse. This pulse propagates through massive objects and it exerts a force impulse to small pendulums, hanging in its path. The reactive force could serve as a for "no-propellant" propulsion: the vacuum itself would serve as a thin atmosphere for such drive.

The symptomatic for contemporary physics is, these effects are of extremely low grant support and their research stagnates in the same way, like the research of cold fusion. The mainstream physicists are really scared with them.
1 / 5 (2) Oct 08, 2011
This is alien tech.The guy who theorized about it was in the year of Roswell crash :p
not rated yet Oct 08, 2011

For example, it works very well in infrared light, which can be difficult for other detectors to handle. That could make it an important component of devices from night-vision systems to advanced detectors for new astronomical telescopes.

LMAO .. This discovery has just made the $5bn James Web Telescope obselete even before it's launched.
2.5 / 5 (2) Oct 08, 2011
LMAO .. This discovery has just made the $5bn James Web Telescope obselete even before it's launched.

Not entirely, but basically you're right.

If you made an array of telescopes based on these effect, you'd get very good results.

If you put an telescope or an array of such telescopes in space, you'd still want to put it in a heavily shaded location to minimize any background energy pollution from the Sun.

You have to figure they still need to build test instruments and do enough testing and researching to learn how to calibrate devices made with this technology, and what can and can't be done reliably. That would probably take 5 to 10 years research to get quality worthy of a NASA telescope.

Then you need a computer that is powerful enough with the hardware, firmware, and software to receive and interpret the inputs. Somebody has to learn to program those systems.
5 / 5 (1) Oct 09, 2011
PhysOrg -- Come for the Graphene, stay for the neutron repulsion whackos.
1 / 5 (1) Oct 09, 2011
neutron repulsion whackos?, there's only one whacko, Dr Oliver Manuel. I wish there was a latin expression which equated to "bat-shit insane", because that's what Oliver is. His madness has also, unfortunately, taken its toll on his children too:
1 / 5 (1) Oct 09, 2011
This article led me to wonder, is there a Silicon analogue of graphene?
1 / 5 (1) Oct 09, 2011
This is efficient for IR so couldnt this serve as a thermoelectric source? Conduction/radiation?
Back then, I suggested the multi-phasic optical array detector at the nano scale for cameras and science instruments...Not entirely, but basically you're right.
-And your opinions carry much authority because you have spent many years of hard work and study to become a physmatist, learning to use words like phasic with, uh, authority.

not rated yet Oct 09, 2011
It's called application and extrapolation, you unqualified moron.

Unlike you, I can think for my own damn self, instead of only being able to quote some authority.
4 / 5 (1) Oct 09, 2011
Soylent Graphene is people!
- Says the carbon-based life form...
not rated yet Oct 09, 2011
This article led me to wonder, is there a Silicon analogue of graphene?

Not in mass production yet. Graphene is the DOH! of our generation. It's been there right under our noses all this time and we are still learning a lot about what it's capable of. For some more info see: http://dailyrecko...silicon/

What I'd love to see is a graphine mass production plant hooked up to the exhaust of industrial/commercial carbon-based fuel burning power plants. Talk about carbon capture...
1 / 5 (1) Oct 10, 2011
I am not edu-macated enough to truly understand the visionaries. I would like a graphene couch because it seems like it would last a really long time, and with all those hot electron thingys zooming back and forth I'm thinking it might provide that tingly sensation that us couch potatoes have only achieved with a Homedics massage pad. If we lack the technology to make a graphene couch, how about a graphene hammock? Will graphene leave pencil marks all over my clothes? Would I be susceptible to attack by pencil sharpeners? Research is clearly required and I am not the one to do it.