Coherent Atomic and Electronic Heterostructures of Single-Layer MoS₂

Abstract

Nanoscale heterostructures with quantum dots, nanowires, and nanosheets have opened up new routes toward advanced functionalities and implementation of novel electronic and photonic devices in reduced dimensions. Coherent and passivated heterointerfaces between electronically dissimilar materials can be typically achieved through composition or doping modulation as in GaAs/AlGaAs and Si/NiSi or heteroepitaxy of lattice matched but chemically distinct compounds. Here we report that single layers of chemically exfoliated MoS(2) consist of electronically dissimilar polymorphs that are lattice matched such that they form chemically homogeneous atomic and electronic heterostructures. High resolution scanning transmission electron microscope (STEM) imaging reveals the coexistence of metallic and semiconducting phases within the chemically homogeneous two-dimensional (2D) MoS(2) nanosheets. These results suggest potential for exploiting molecular scale electronic device designs in atomically thin 2D layers.

Structural phase transitions in two-dimensional Mo- and W-dichalcogenide monolayers

“…1. The 1T 0 phase is observed in WTe 2 under ambient conditions 17 , MoTe 2 at high temperature 39 and as a metastable phase in instances of chemically exfoliated 18 and restacked 38 MX 2 monolayers.…”

“…This polymorphism sets group VI TMD monolayers apart from other 2D materials such as graphene and hexagonal BN [17][18][19] . Intriguingly, one of these structural phases is semiconducting, whereas the others are metallic, unlike in the case of group V TMDs, where electrically activated metal-tometal structural phase transitions have been demonstrated in multilayer TaS 2 (ref.…”

“…It has been suggested that coexistence of metallic and semiconducting regions on a monolithic MX 2 nanosheet can be used to make electronic devices 18 , and metallic regions have been associated with catalytic activity leading to hydrogen evolution 12,16,22 . Moreover, materials with dynamic metal-toinsulator transitions close to ambient conditions are exceedingly rare and worth pursuing because of their nonvolatile information storage potential.…”

“…A process of lithium-based chemical exfoliation of bulk crystals has been shown to be a successful route to obtain a metastable metallic phase of the group VI TMDs 18,[24][25][26] . It is, however, uncertain that this phase would persist under all realistic operating conditions, and reversible switching is not demonstrated in this case.…”

Post‐Graphene 2D Chemistry: The Emerging Field of Molybdenum Disulfide and Black Phosphorus Functionalization

“…As outlined, it has early been observed that the n ‐butyllithium promoted exfoliation of MoS 2 , which involves also an ultrasonication step, leads also to the formation of defects (mainly described as sulfur vacancies) 19, 21b, 31a, 69. This on the other hand provided the basis for one of the initial covalent functionalization approaches for MoS 2 .…”