Stacking on the graphene

Researchers in Japan have found a way to form two materials, each made of three layers of graphene. By stacking graphene differently, researchers were able to develop electrical properties. Their work could lead to novel electronic devices, such as photo sensors that convert light into electrical energy.

In 2004, two scientists realized they had isolated a single layer of carbon atoms on a piece of tape used to clean a graphite crystal. Since then, graphene has captured researchers’ imaginations due to its properties: it is 200x stronger than steel, is flexible, and is an excellent conductor of electricity.

Graphene’s carbon atoms are arranged into hexagons, forming a honeycomb-like lattice. Placing one layer of graphene on top of another leads to the formation of bilayer graphene. The layers can be arranged in one of two positions: the centers of the carbon hexagons of each layer can be organized immediately above one another, called AA-stacking, or they can be displaced forward so that a hexagon center in one layer is above a carbon atom below it, called AB-stacking. By applying an external electric field, AB-stacking two layers of graphene forms a material with semiconducting properties.

Deliberately stacking three layers of graphene has proven difficult but might help researchers study how the physical properties of tri-layered materials change based on how the layers are stacked.

Researchers at Japan’s Tohoku University and Nagoya University heated silicon carbide using two methods. In one experiment, silicon carbide was heated to 1,510°C under pressurized argon. In another, it was heated to 1,300°C in a high vacuum. Both materials were then sprayed with hydrogen gas, breaking the bonds to form single hydrogen atoms. Two types of trilayer graphene formed (see Figure 1). The silicon carbide heated under pressurized argon formed into ABA-stacked graphene, in which the hexagons of the top and bottom layers were aligned exactly while the middle layer was slightly displaced. The silicon carbide heated in a vacuum developed into ABC-stacked graphene, in which each layer was slightly displaced in front of the one below it.

IT IS 200x STRONGER THAN STEEL, IS FLEXIBLE, AND IS AN EXCELLENT CONDUCTOR OF ELECTRICITY.”

The researchers then examined the physical properties of each material and found that their electrons behaved differently.

The ABA graphene was an excellent electrical conductor, similar to monolayer grapheme. However, ABC graphene acted more like AB graphene and had semi-conductor properties.

“The present success in selective fabrication of ABA and ABC trilayer graphene would widen the feasibility of graphene-based nano-electronic devices with variable layer numbers and stacking sequences,” concludes the researchers in their study published in the journal NPG Asia Materials (goo.gl/aazMZG).

http://en.nagoya-u.ac.jp

www.tohoku.ac.jp