First principles study on electronic properties of graphene nanostructures for high current density cathode

Speaker: Prof. Ming-Chieh Lin (Hanyang University)

Date/Time: 2018.07.19/16:30

Abstract:

Graphene is a crystalline allotrope of carbon with two-dimensional properties. Its carbon atoms are densely packed in a nano-scale hexagonal pattern. Graphene has many unusual properties. It is about 200 times stronger than the strongest steel. It can efficiently conduct heat and electricity and is nearly transparent. In this work, we study the electronic properties of graphene nanostructures using first principles or ab initio calculations based on density functional theory (DFT) in order to explore its applications in field emission devices. The work function is a key parameter highly desired for applications in the field emission according to Fowler-Nordheim (FN) equation. The change of work function due to the lattice deformation of graphene is investigated using a supercell including a vacuum layer which is thick enough so that the layer interaction is negligible. It is found that the work function is very sensitive to the lattice size. As the lattice site increases, the work function increases proportionally. However, the work function is reduced doubly while the lattice site is reduced. For realistic applications, the work functions of carbon nanoribbons of different widths terminated with and without edge passivation have been determined. In addition, the local work function of graphene nanostructures has also been calculated for different applied electric fields. This local work function can be used to more accurately predict field emission current from FN equation. Engineering the work function of graphene nanostructures using strain and functional species had been proposed and studied using first principles calculations. The work function of graphene nanostructure can be tuned by strain and edge/surface decorations and this might provide an opportunity to find its applications in high current density field emission cathode.

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