Microprocessors from pencil lead

Mar 30, 2012 By Daniel Stolte
Microprocessors from pencil lead
When a sheet of graphene sits atop a sheet of boron nitride at an angle, a secondary hexagonal pattern emerges that determines how electrons flow across the sample. Credit: Brian LeRoy

(PhysOrg.com) -- University of Arizona physicists are making discoveries that may advance electronic circuit technology.

Graphite, more commonly known as pencil lead, could become the next big thing in the quest for smaller and less power-hungry electronics.

Resembling chicken wire on a , graphene – single sheets of – is only one atom thick, making it the world's thinnest material. Two million graphene sheets stacked up would not be as thick as a credit card.

The tricky part have yet to figure out how to control the flow of electrons through the material, a necessary prerequisite for putting it to work in any type of . Graphene behaves very different than silicon, the material currently used in semiconductors.

Last year, a research team led by UA physicists cleared the first hurdle by identifying , a structurally identical but non-conducting material, as a suitable mounting surface for single-atom sheets of graphene. The team also showed that in addition to providing mechanical support, boron nitride improves the electronic properties of graphene by smoothening out fluctuations in the electronic charges.

Now the team found that boron nitride also influences how the electrons travel through the graphene. Published in Nature Physics, the results open up new ways of controlling the electron flow through graphene.

"If you want to make a transistor for example, you need to be able to stop the flow of electrons," said Brian LeRoy, an assistant professor in the University of Arizona's department of physics. "But in graphene, the electrons just keep going. It's difficult to stop them."

LeRoy said relativistic quantum mechanical effects that come into play at atomic scales cause electrons to behave in ways that go against our everyday experiences of how objects should behave.

Take tennis balls, for example.

Lab members Matthew Yankowitz, Daniel Cormode and Brian LeRoy (left to right) use a scanning tunneling microscope to make the atomic structures of graphene sheets visible. Credit: Beatriz Verdugo/UANews

"Normally, when you throw a tennis ball against a wall, it bounces back," LeRoy said. "Now think of the electrons as tennis balls. With quantum mechanical effects, there is a chance the ball would go through and end up on the other side. In graphene, the ball goes through 100 percent of the time."

This strange behavior makes it difficult to control where electrons are going in graphene. However, as LeRoy's group has now discovered, mounting graphene on boron nitride prevents some of the electrons from passing to the other side, a first step toward a more controlled electron flow.

The group achieved this feat by placing graphene sheets onto boron nitride at certain angles, resulting in the hexagonal structures in both materials to overlap in such a way that secondary, larger hexagonal patterns are created. The researchers call this structure a superlattice.

If the angle is just right, they found, a point is reached where almost no electrons go through.

"You could say we created holes in the wall," LeRoy said, "and as soon as the wall has holes in it, we find that some of the tennis balls no longer go through. It's the opposite of what you would expect. That shows you how weird this is. It's all due to those relativistic quantum effects."

The discovery puts the technology a bit closer to someday being able to actually control the flow of through the graphene, the authors of the paper said.

"The effect depends on the size of the hexagonal pattern resulting from the overlapping sheets," explained Matthew Yankowitz, a first-year graduate student in LeRoy's lab and the study's lead author.

The pattern, he explained, creates a periodic modulation of the potential – picture a ball rolling across an egg carton.

"It's a purely electronic effect brought about by the structure of the two materials and how they sit on top of each other," Yankowitz said. "It's similar to the Moiré pattern you see when someone wears a striped shirt on TV."

As of now, the researchers are not yet able to control how the graphene and boron nitride end up oriented relative to each other when they combine the two materials. Therefore, they make many samples and check the structure of each one under an electron microscope.

"With our scanning tunneling microscope, we can get an image of each superlattice and measure its size," Yankowitz said. "We take a picture and see what the pattern looks like. If the hexagonal pattern is too small, the samples are no good and we throw them out."

Yankowitz said about 10 to 20 percent of samples showed the desired effect.

If it becomes possible to someday automate this process, graphene-based microelectronics might be well on their way to propel us from the silicon age to the graphene age.

The research study is a collaboration among LeRoy's lab and researchers at MIT in Cambridge, Mass., the National Institute for Materials Science in Tsukuba, Japan and the University of Geneva, Switzerland. The UA portion of the project was funded by grants from the U.S. Army Research Office and the National Science Foundation.

Explore further: New absorber will lead to better biosensors

Related Stories

Probing atomic chicken wire

Mar 01, 2011

(PhysOrg.com) -- Graphene, the material that makes up pencil "lead," could someday make electronic devices smaller, faster and more energy-efficient. Providing the first detailed analysis of graphene on boron ...

Graphene's 'Big Mac' creates next generation of chips

Oct 09, 2011

The world's thinnest, strongest and most conductive material, discovered in 2004 at the University of Manchester by Professor Andre Geim and Professor Kostya Novoselov, has the potential to revolutionize material ...

Two graphene layers may be better than one

Apr 27, 2011

(PhysOrg.com) -- Researchers at the National Institute of Standards and Technology have shown that the electronic properties of two layers of graphene vary on the nanometer scale. The surprising new results ...

Recommended for you

New absorber will lead to better biosensors

20 hours ago

Biological sensors, or biosensors, are like technological canaries in the coalmine. By converting a biological response into an optical or electrical signal, they can alert us to dangers in our external and internal environments. ...

Ultrafast remote switching of light emission

Sep 30, 2014

Researchers from Eindhoven University of Technology can now for the first time remotely control a miniature light source at timescales of 200 trillionth of a second. They published the results on Sept. 2014 ...

Nanotube cathode beats large, pricey laser

Sep 30, 2014

Scientists are a step closer to building an intense electron beam source without a laser. Using the High-Brightness Electron Source Lab at DOE's Fermi National Accelerator Laboratory, a team led by scientist ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Shifty0x88
not rated yet Apr 02, 2012
Graphene is amazing!

This is just one step closer to the reality of Graphene-based CPUs and GPUs.

When we figure this stuff out, it will make what we use feel like a Commodore 64!