First Principles Study on Electronic Properties of Graphene for High Current Density Cathode
Nan Zhao,Liangliang Xu, Ming-Chieh Lin1*
1Electrical and Biomedical Engineering, Hanyang University, seoul, Korea
* Presenter:Nan Zhao,Liangliang Xu, Ming-Chieh Lin
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 using first principles or ab initio calculations based on density functional theory in order to explore its applications in field emission devices. The electronic structure and density of states of graphene are calculated using both CPMD and VASP codes for comparison. 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. Recently, an individual single-layer graphene has been considered for use as a field emission electron source. The work function of graphene has been determined to be ~4.6 eV, close to that of graphite and the local work function of graphene has also been analyzed for studying the local field enhancement effect. With an introduction of some foreign atoms into the graphene lattice as well as a substrate effect, we could significantly improve the field emission characteristics for industrial applications.

Keywords: graphene, field emission, density function theory, VASP