Toward a better understanding of bilayer graphene

Oct 26, 2010 By Miranda Marquit feature

(PhysOrg.com) -- "Graphene is a very exciting material with a number of interesting possibilities, including for use in electronic devices," Pablo Jarillo-Herrero tells PhysOrg.com. "However, all graphene systems are electronically different from each other. Single layer graphene has different properties from bilayer graphene, and these have different properties from graphene with more layers. What we want to do is to understand the specific properties of bilayer graphene so that we can learn how to use it for different applications."

Jarillo-Herrero is a scientist at MIT. He worked with Thiti Taychatanapat, at Harvard, to investigate some of the properties of bilayer graphene, and to determine how electronic transport works under certain conditions. Their findings are described in : “Electronic Transport in Dual-Gated Bilayer Graphene at Large Displacement Fields.”

One of the reasons that semiconductors work so well in digital electronics is that they have what is known a band gap. This band gap allows semiconductors to be switched on and off. In order for graphene to work as a viable replacement for these semiconductors, some sort of gap would need to be opened up in the electronic structure.

“It has already been shown that it is possible to open a band gap in bilayer graphene,” Jarillo-Herrero says. “However, the effective electronic transport gap is about 100 times smaller than the theoretical band gap or optical band gap. This difference presents problems. We want to understand the properties of bilayer graphene that make this happen, and how it can be changed.”

Jarillo-Herrero and Taychatanapat offer a systemic look at how the band gap works in bilayer graphene. They found that the band gap is smaller by measuring at low temperatures of less than four degrees Kelvin. “Our studies show that the band gap is still large enough to switch the transistors on and off, but the on/off ratio is only high enough – of order a million – at low temperatures, and we report this for the first time in bilayer graphene,” Jarillo-Herrero says.

However, the main problem is that in order for bilayer graphene to work as a viable semiconductor replacement, it needs to be operable at room temperature. Jarillo-Herrero is hopeful, though. “This is a very important first step that helps us scientifically understand what is happening at low temperatures, and understanding the mechanism that does not permit the electronic transport to work as well at higher temperatures.”

One of the issues, Jarillo-Herrero believes, is that the graphene is usually put on silicon oxide, which introduces electronic disorder. “On silicon oxide, the electrons don’t see their full ,” Jarillo-Herrero explains. “So we try to characterize the disorder and get rid of it. One way to do this is to try putting the graphene on different substrates. When this is done, enormous progress is made. Boron nitride is especially promising, but a number of groups are also trying bilayer graphene on different substrates.”

In the end, Jarillo-Herrero hopes that the information learned from this demonstration will help lead to the use of bilayer graphene in digital electronics. “Our work offers a beginning for learning how bilayer graphene transistors operate, and learning about the mobility of electrons in graphene. Hopefully, as we understand the properties of graphene better, we can work toward future integration with electronics and other applications,” he says.

“This sort of basic science research is very important,” Jarillo-Herrero continues. “Things always have to start at the basic level before we move on, and our work could lead to the use of in electronics.”

Explore further: Thinnest feasible nano-membrane produced

More information: Thiti Taychatanapat and Pablo Jarillo-Herrero, “Electronic Transport in Dual-Gated Bilayer Graphene at Large Displacement Fields,” Physical Review Letters (2010). Available online: link.aps.org/doi/10.1103/PhysRevLett.105.166601

4.6 /5 (7 votes)

Related Stories

Can graphene nanoribbons replace silicon?

Feb 18, 2010

(PhysOrg.com) -- "Graphene has been the subject of intense focus and research for a few years now," Philip Kim tells PhysOrg.com. "There are researchers that feel that it is possible that graphene could replac ...

Physicist wins Packard Fellowship

Oct 16, 2009

(PhysOrg.com) -- MIT physicist Pablo Jarillo-Herrero has won a 2009 David and Lucile Packard Fellowship, an award he will use to study a new class of materials that could have applications in the semiconductor ...

The noise about graphene

Oct 15, 2010

(PhysOrg.com) -- In last week’s announcement of the Nobel Prize in Physics, the Royal Swedish Academy of Sciences lauded graphene’s "exceptional properties that originate from the remarkable world ...

Bilayer graphene gets a bandgap

Jun 10, 2009

Graphene is the two-dimensional crystalline form of carbon, whose extraordinary electron mobility and other unique features hold great promise for nanoscale electronics and photonics. But there's a catch: ...

Recommended for you

Thinnest feasible nano-membrane produced

4 hours ago

A new nano-membrane made out of the 'super material' graphene is extremely light and breathable. Not only can this open the door to a new generation of functional waterproof clothing, but also to ultra-rapid filtration. The ...

Wiring up carbon-based electronics

7 hours ago

Carbon-based nanostructures such as nanotubes, graphene sheets, and nanoribbons are unique building blocks showing versatile nanomechanical and nanoelectronic properties. These materials which are ordered ...

Making 'bucky-balls' in spin-out's sights

Apr 16, 2014

(Phys.org) —A new Oxford spin-out firm is targeting the difficult challenge of manufacturing fullerenes, known as 'bucky-balls' because of their spherical shape, a type of carbon nanomaterial which, like ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

TDK
1 / 5 (13) Oct 27, 2010
the effective electronic transport gap is about 100 times smaller than the theoretical band gap or optical band gap
The probable reason is, graphene sheet is flexible and it distorts in such a way, it forms shortcuts across bilayer, which aren't observable in optical spectrum, but they're still decreasing mobility of electrons a lot.

http://cdn.physor...raph.jpg

More news stories

Thinnest feasible nano-membrane produced

A new nano-membrane made out of the 'super material' graphene is extremely light and breathable. Not only can this open the door to a new generation of functional waterproof clothing, but also to ultra-rapid filtration. The ...

Wiring up carbon-based electronics

Carbon-based nanostructures such as nanotubes, graphene sheets, and nanoribbons are unique building blocks showing versatile nanomechanical and nanoelectronic properties. These materials which are ordered ...

Hackathon team's GoogolPlex gives Siri extra powers

(Phys.org) —Four freshmen at the University of Pennsylvania have taken Apple's personal assistant Siri to behave as a graduate-level executive assistant which, when asked, is capable of adjusting the temperature ...

Better thermal-imaging lens from waste sulfur

Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight, plastic lenses for infrared devices, including night-vision goggles, a University of Arizona-led international team ...