Graphite, promising material in electronics

Graphite, a promising material in electronics

9:35 AM, 6th April 2012
Graphite, a promising material in electronics
Matthew Yankowitz, Daniel Cormode and Brian LeRoy (left to right) use a scanning tunneling microscope to make the atomic structures of graphene sheets visible.

ARIZONA, US: Graphite, more commonly known as pencil lead, could become the next big thing in the quest for smaller and less power-hungry electronics. Graphene, a single sheet of graphite, is only one atom thick, making it the world’s thinnest material. Physicists are 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 electronic circuit. Graphene behaves very different than semiconductor material silicon.

Research by University of Arizona physicists cleared the first hurdle by identifying boron nitride, 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. “If you want to make a transistor for example, you need to be able to stop the flow of electrons. But in graphene, the electrons just keep going. It’s difficult to stop them,” said Brian LeRoy, Assistant Professor, University of Arizona. According to LeRoy, 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.

“Normally, when you throw a tennis ball against a wall, it bounces back. 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 per cent of the time,” LeRoy. This strange behaviour 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. The discovery puts the technology a bit closer to someday being able to actually control the flow of electrons through the grapheme.

“The effect depends on the size of the hexagonal pattern resulting from the overlapping sheets. It’s a purely electronic effect brought about by the structure of the two materials and how they sit on top of each other. With our scanning tunneling microscope, we can get an image of each superlattice and measure its size. If the hexagonal pattern is too small, the samples are no good and we throw them out,” explained Matthew Yankowitz, Graduate Student, LeRoy’s lab.

© University of Arizona News



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