title: Electronic and Magnetic Properties of Encapsulated MoS2 Quantum Dots: The Case of Noble Metal Nanoparticle Dopants.
abstract: With the rise of 2D materials, such as graphene and transition metal dichalcogenides, as viable materials for numerous experimental applications, it becomes more necessary to maintain fine control of their properties. One expedient and efficacious technique to regulate their properties is surface functionalization. In this study, DFT calculations are performed on triangular MoS2 quantum dots (QDs) either partially or completely doped with nanoparticles (NPs) of the noble metals Au, Ag, and Pt. The effects of these dopants on the geometry, electronic properties, magnetic properties, and chemical bonding of the QDs are investigated. The calculations show that the structural stability of the QDs is reduced by Au or Ag dopants, whereas Pt dopants have a contrasting effect. The NPs diminish the metallicity of the QD, the extent of which is contingent on the number of NPs adsorbed on the QD. However, these NPs exert distinctly disparate charge transfer effects-Ag NPs n-dope the QDs, whereas Au and Pt NPs either n- or p-dope. The molecular electrostatic potential maps of the occupied states show that metallic states are removed from the doping sites. Notwithstanding the decrease of magnetization in all three types of hybrid QD, the distribution of spin density in the Pt-doped QD is inherently different from that in the other QDs. Bond analyses using the quantum theory of atoms in molecules and the crystal orbital Hamilton population suggest that bonds between the Pt NPs and the QDs are the most covalent and the strongest, followed by the Au-QD bonds, and then Ag-QD bonds. The versatility of these hybrid QDs is further examined by applying an external electric field in the three orthogonal orientations, and comparing their properties with those in the absence of the electric field. There are two primary observations: 1) dopants at the tail, head and tail, and in the fully encased configuration are most effective in modifying the distribution of metallic states if the electric field is absent, and 2) the metallic states in these aforementioned QDs are generally insensitive to the electric field. Conversely, the asymmetric electric effects on the charge transfer in these QDs have to be carefully monitored to allow finer control of their structural stability. This study aptly demonstrates the value of noble metal dopants for manipulating the properties of MoS2 QDs, and shows the versatility of these hybrid QDs as tunable nanodevices. This notably extends the functionality of these nanostructures for applications such as catalysis and nanoelectronics.
authors.affiliation: Institute of High Performance Computing, 1 Fusionopolis Way, #16-16 Connexis, Singapore, 138632, Singapore. lohgc@ihpc.a-star.edu.sg.
authors.forename: Guan Chee
authors.identifier: http://orcid.org/0000-0002-2040-9511
authors.initials: GC
authors.lastname: Loh
keywords: MoS2; electronic properties; metal doping; noble metals; quantum dots