Electronic Properties Of Graphene Antidot Lattices And MoS₂Nanoribbon

Abstract:Because the material limits and quantum effect limits, the continuation of Moore’s law is facing tough challenges, two-dimensional crystalline materials, as graphene and single-layer MoS2who possess unique physical and chemical properties, are potential candidate for post-silicon electronic devices.. Based on the first-principles calculations, this paper investigated the effects of antidot shape on the bandgap of graphene antidot lattices (GALs) and the effects of edge hydrogenation on the electronic structure of armchair MoS2nanoribbon (AMoS2NR), respectively.GALs is a kind of nanomaterial that obtain by periodically patterning nanoholes on graphene. It has been found that the bandgap of GALs opening or not are depended on the lattice size and symmetry, but it is still unclear whether the antidot shape will affect its bandgap. In the first part, we removed two kinds of three fused benzene rings in a super cell of graphene to construct the model of GALs, and investigated the relationship between the bandgap and lattice parameters on these two GALs, whose antidots are same in size but different in shape. It is shown that these two GALs possess a nonzero bandgap while their lattice parameters are3TV+1and3/V times of graphene’s, where N is an integer. This result implied the bandgap of GALs depends on both the configuration of antidot and the lattice parameter. The bandgap opening or not was interpreted with Clar’s aromatic sextet theory and electron density distribution. It was obtained that, when the GALs do not own a long zigzag edge, the bandgap of open or not can be interpreted by whether the number of Clar sextets exceeds one third of the total number of hexagons in the unit cell. But this rule will be ineffective for GALs that contain a edge of three zigzags or more.AMoS2NRs is semiconductor, whose highest valence band and lowest conductor band are both formed by edge states. This paper studied AMoS2NRs with different edge hydrogenation. It was found that edge hydrogenation make the nanoribbon become more stable, and have a remarkable effect on its electronic properties, making it transit among indirect-gap semiconductor, semi-metal and direct-gap semiconductor. This transition is caused by the change of energy distribution and occupation of the Mo4d orbit on the edge, for they form the bands around fermi level and influenced seriously by the edge modification. Different hydrogen adsorption patterns on each edge induce two kinds of edge state on the nanoribbons, and bands formed by these two kinds of edge state are almost invariant, impling the little effect existing between those edge state. Owing to the edge-induced potential barrier, bandgap of semiconducting AMoS2NRs oscillates with the nanoribbon width. The bandgap of AMoS2NRs terminated with zero or eight hydrogen atoms in each unit cell oscillates in a period of three, while the bandgap changes nonperiodically in those terminated with four hydrogen atoms. In addition, AMoS2NRs terminated with six hydrogen atoms have unpaired electron on the edge, making its groundstate be antiferromagnetic.