Researchers have known that bilayer graphene, consisting of two stacked graphene layers, acts more like a semiconductor when immersed in an electric field.Īccording to NIST researcher Nikolai Zhitenev, the band gap may also form on its own due to variations in the sheets’ electrical potential caused by interactions among the graphene electrons or with the substrate (usually a nonconducting, or insulating material) that the graphene is placed upon. However, the lack of what physicists call a band gap-an energetic threshold that makes it possible to turn a transistor on and off-makes graphene ill-suited for digital electronic applications. Graphene, a single layer of carbon atoms, is prized for its remarkable properties, not the least of which is the way it conducts electrons at high speed. LL(0,+) (1,+) projected on the top layer (ξ = +1) depends on the sign of ΔU.M The eight-fold degenerate N = 0, 1 levels become layer polarized quartets when the graphene layers are subjected to a potential energy asymmetry ΔU. Landau levels are indexed with the orbital and valley index, (N, ξ), and each is two-fold degenerate in spin. d, The formation of bilayer graphene Landau levels in the quantum Hall regime with and without a band gap. Magnetic field B is perpendicular to the sample plane. ΔU equals to the difference between onsite energies for the top (2) and the bottom (1) layers. The disorder potential induced from the substrate is illustrated in color overlaid on the SiO2 surface. The bilayer graphene is placed on a 300 nm SiO2 substrate separating from a back gate electrode (Si). c, Schematic of a gated bilayer graphene device for STM/STS measurement with circuitry showing application of gate voltage Vg and sample bias Vb. The electronic levels form Mexican-hat like energy bands with a potential energy asymmetry ΔU and a band gap of Eg. b, Energy band diagram of bilayer graphene with (solid lines) and without (dashed lines) a band gap. a, Schematic of Bernal-stacked bilayer graphene consisting of a top layer (A2/B2) and bottom layer (A1/B1), with atom A2 directly over B1. Schematics of the bilayer graphene measurements and energy band diagram in the
0 Comments
Leave a Reply. |