The inherent problem of a zero-band gap in graphene has provided motivation to search for the next-generation electronic materials including transition metal dichalcogenides, such as MoS2. In this study, a triangular MoS2 quantum dot (QD) is investigated to see the effects of passivation, additional layer, and the h-BN substrate on its geometry, energetics, and electronic properties. The results of density functional theory calculations show that the monolayer QD is metallic in nature, mainly due to the coordinatively unsaturated Mo atoms at the edges. This is reaffirmed by the passivation of the S edge atoms, which does not significantly modify its metallic character. Analysis of the chemical topology finds that the Mo−S bonds associated with the edge atoms are predominantly covalent despite the presence of metallic states. A bilayer QD is more stable than its monolayer counterpart, mainly due to stabilization of the dangling bonds of the edge atoms. The degree of the metallic character is also considerably reduced as demonstrated by the I−V characteristics of a bilayer QD. The binding strength of a monolayer QD to the h-BN substrate is predicted to be weak. The substrate-induced modifications in the electronic structure of the quantum dot are therefore not discernible. We find that the metallic character of the QD deposited on the insulating substrate can therefore be exploited to extend the functionality of MoS2-based nanostructures in catalysis and electronics applications at the nanoscale level.
Category: graphene
Switching Behaviors of Graphene- Boron Nitride Nanotube Heterojunctions
High electron mobility of graphene has enabled their application in high-frequency analogue devices but their gapless nature has hindered their use in digital switches. In contrast, the structural analogous, h-BN sheets and BN nanotubes (BNNTs) are wide band gap insulators. Here we show that the growth of electrically insulating BNNTs on graphene can enable the use of graphene as effective digital switches. These graphene-BNNT heterojunctions were characterized at room temperature by four-probe scanning tunneling microscopy (4-probe STM) under real-time monitoring of scanning electron microscopy (SEM). A switching ratio as high as 105 at a turn-on voltage as low as 0.5V were recorded. Simulation by density functional theory (DFT) suggests that mismatch of the density of states (DOS) is responsible for these novel switching behaviors.
First-principles study of strain-induced modulation of energy gaps of graphene/BN and BN bilayers
First-principles calculations based on density functional theory are performed on graphene/BN and BN bilayers to investigate the effect of the strain on their energy gaps. For the graphene/BN bilayer, the bands have characteristic graphenelike features with a small band gap at K. Application of strain modulates the band gap, whose magnitude depends on the strength of interaction between constituent monolayers. For the BN bilayer, on the other hand, a large band gap is predicted, which remains nearly the same for small strains. The increased inhomogeneity in charge density of different carbon sublattices due to a stronger interplanar interaction is the cause of the predicted variation in the band gap with strains applied along the perpendicular direction in the graphene/BN bilayer.