Researchers at the University of Texas at Austin, Columbia University, and the IBS Center for Multdimensional Carbon Materials at Ulsan have developed a new way to make high-quality Bernal-stacked bilayer graphene an important material for electronics and photonics.
The researchers have studied a way to make bilayer graphene that yields a high percentage of AB stacked material, and were able to produce sub-millimetre single-crystal AB-stacked bilayer graphene domains. In the CVD chamber used to grow their graphene, the researchers intentionally introduced a small amount of oxygen (parts per million concentrations). This oxygen, when combined with the copper foil substrate on which the graphene was grown, dissociates methane molecule precursors into carbon atoms. These atoms then diffuse through the copper foil and help form a second layer of graphene.
When layers of graphene are stacked on top of each other, they organize themselves in one of two main configurations known as Bernal-type and mis-oriented. Bernal stacking occurs when the A-sublattice of one layer sits above the B-sublattice of the underlying layer. This AB-stacked configuration has the lowest possible energy, so under normal circumstances, this is the structure that multilayer graphene likes to adopt.
The resulting material in this study had similar electrical properties to that of exfoliated natural graphite. For example, it has a charge mobility of 60000 cm2V1S1 and a bandgap that can be tuned from 40 meV up to 100 meV. This may be the first time that CVD-grown large-area AB-stacked bilayer graphene samples have been made with such high quality.