Researchers at NIST have discovered that two layers of graphene can exhibit varying electronic properties on a nanometer scale. When two layers of graphene are stacked, the electric charges between them vary across the layers, creating randomly distributed puddles of alternating positive and negative charges. This phenomenon, observed in bilayer graphene, could potentially be manipulated to create a band gap – a key property for digital electronic applications.
The varying charge densities between the two graphene layers are caused by interactions with the insulating substrate material. Pools of electrons and electron holes form in the graphene layers, with deeper pools on the bottom layer due to its proximity to the substrate. This creates a random pattern of alternating charges and spatially varying band gaps.
While the substrate interactions open the door to graphene’s use as a practical electronic material, they also lower the window on electron mobility. However, researchers plan to explore further the role of substrates in creating and controlling band gaps in graphene. If substrate interactions can be reduced sufficiently, the exotic quantum properties of bilayer graphene may be harnessed to create a new quantum field effect transistor.
Source: https://www.nist.gov/news-events/news/2011/04/two-graphene-layers-may-be-better-one
Keywords: graphene, band gap, substrate, electrons, puddles
