Passivation of CdSe Quantum Dots by Graphene and MoS₂ Monolayer Encapsulation

Abstract

The encapsulation of a monolayer of CdSe quantum dots (QDs) by one-to-three layer graphene and MoS 2 sheets protects the QDs from oxidation. Photoluminescence (PL) from the QD cores shows a much slower decrease in core diameter over time due to slower oxidation in regions where the QDs are covered by van der Waals (vdW) layers than in those where they are not, both for chips stored in the dark and in the presence of light. PL mapping shows that the CdSe QDs under the central part of the vdW sheet age slower than those near its edges, because oxidation of the covered QDs is limited by transport of oxygen from the edges of the vdW sheets and not transport across the vdW layers. The transport of oxygen to the covered QDs is analyzed by coupling the PL results and a model of QD core oxidation.

Physics and chemistry of oxidation of two‐dimensional nanomaterials by molecular oxygen

“…MoS 2 shows good stability in air at room temperature. A few experiments and theoretical calculations have demonstrated that MoS 2 could be used as a passivation or protection layer to prevent oxidation of other materials . Oxidation of MoS 2 occurs at temperature higher than 300°C in air.…”

Tortuosity but not Percolation: Design of Graphene Nanocomposite Coatings for the Extended Corrosion Protection of Aluminum Alloys

“…At these loadings (below percolation as per Fig. 3), 2D sheets of few-layered graphene serve as excellent waterimpermeable 25 and unreactive barriers and greatly reduce the concentration of microscopic defects and pores within the polymeric matrix. As such, the graphene inclusions substantially increase the effective pathlengths for the diffusion of water and aggressive species towards the metal surface.…”

“…[22][23][24] An alternative strand of research has focused on the corrosion protection endowed by graphene nanocomposites wherein few-layered chemically derived graphene flakes are incorporated within a polymeric matrix. As an impermeable 2D material, 25 inclusion of graphene adds substantial tortuosity to pathways for diffusion of species participating in the redox reactions of corrosion. Functionalization of graphene and/or incorporation of graphene in nonconductive polymers results in a considerable enhancement of the tortuosity of ion diffusion pathways and a substantially increased pore transport resistance while preventing direct electrochemical coupling with the substrate.…”

Forming Nanoparticle Monolayers at Liquid–Air Interfaces by Using Miscible Liquids

“…For NPs capped by ligands with nonpolar ends, this means that the upper solvent needs to be more nonpolar and the lower one more polar. (2) The solvents must be immiscible, so they do not mix. (3) The upper solvent must be less dense, so it does not displace the lower solvent.…”