By Cameron Chai
A team of researchers from the University of California, Riverside have established that the electrical properties of graphene can be altered by adopting a technique called Bernal trilayer stacking.
In Bernal-stacked trilayer (ABA), the top (third) sheet is exactly on top of the lowest sheet. In rhombohedral-stacked (ABC) trilayer, the top sheet is shifted by the distance of an atom, so that the top (third) sheet and the lowest sheet form a Bernal stacking as well. Credit: Lau lab, UC Riverside.
Graphene is made up of carbon atoms that are arranged in the shape of hexagonal rings and has high electrical and thermal conductivity, thus making it the ideal material to be used in semiconductors and computers.
Graphene sheets can easily be stacked upon one another through Bernal stacking due to its planar structure. Under regular Bernal stacking the corner of the hexagon formation of the second sheet is placed in the middle of the bottom sheet. Researchers adopted a new method of stacking called the Bernal trilayer stacking where three sheets of graphene were arranged in such a manner that the top sheet is directly below the lowest sheet. It was discovered that devices that had graphene sheets arranged in this way displayed electricity conductivity while the other devices displayed insulation.
However, if the arrangement was slightly shifted, the sheets displayed insulation. The researchers used Raman spectroscopy to analyze the devices that had the desired stacking order. The research team also plans to analyze the gap that arises due to the stacking arrangement as it will help in the engineering of band gaps in graphene electronics. This study was sponsored by grants from the Office of Naval Research, the Focus Centre for Functional Engineered Nano Architectonics and the National Science Foundation.