Researchers from Rice University discovered a way to create Bernal-stacked bi-layer graphene sheets. These kinds of structures (in which every other carbon atom in the six-carbon rings of the top graphene layer sits over the middle of the hexagonal space created by a six-carbon ring of the bottom layer) exhibit a small band gap.

To create these sheets with controlled thickness on copper substrates, the researchers used pressure-tuned CVD chambers, while keeping constant the pressure ratio of hydrogen to methane. The higher the pressure, the thicker the graphene film. They created all sorts of sheets, and the bi-layer ones indeed were Bernal-stacked. They created a transistor and checked the electronic properties to make sure there's a band gap.

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