What is Bilayer Graphene?

Bilayer graphene is just as it sounds. The material consists of just two atomic layers of graphene. The earliest report of it being successfully isolated goes back to Geim et all in 2004.

They had isolated films containing “just one, two, or three atomic layers” using their now famous “scotch tape” method and invented a whole new class of materials.

Structure

Bilayer graphene is typically in the AB, or Bernal-stacked form meaning that half of the atoms lie centered over a hexagon in the lower graphene sheet.

In the AA form, half of the atoms lie over an atom meaning the layers are exactly aligned.

Twin boundaries are common, transitioning from AB to BA stacking on the same substrate.

Synthesis

Bilayer graphene can be made by exfoliation from graphite or by chemical vapor deposition (CVD). Ruoff et al showed that large single-crystal bilayer graphene could be produced by oxygen-activated chemical vapor deposition in 2016.

Tunable bandgap

Bilayer graphene doesn’t have a bandgap, it functions like a semimetal. Researchers have long predicted that graphene can have a bandgap if an electric field were applied to two layers. The first experimental demonstration of a tunable bandgap in bilayer graphene was in 2009 .