Formation Pathways in Intercalated 2D Materials and Heterostructures

The large van der Waals gaps of layered 2D materials enable intercalation of ions, atoms, and molecules into the gaps of the host materials at high concentrations, which lead to high levels of electron doping and lattice strain as well as emergence of new phases. As such, intercalations in 2D transition metal chalcogenides, mostly in the sulfides and selenides, have been studied extensively since the early 70’s to modulate electron-phonon coupling, superconductivity, charge density waves, etc. using bulk crystals of these chalcogenide systems.



Presently, new 2D material systems, nanoscale confinement, construction of heterostructures using dissimilar 2D materials, and twist-angle induced Moiré physics, combined with multi-modal, in situ probes, provide exciting opportunities to revisit the intercalation studies in 2D systems to look for novel effects and to establish mechanistic understandings of the intercalation pathways and formation pathways of intercalation-induced emergent phases.



In this talk, I will discuss electrochemically controlled lithium intercalation into nanoflakes of graphene, MoS₂, WTe₂, and their heterostructures using nanodevice electrochemical cells that allow structural characterization and magneto-transport property measurements as a function of lithium intercalation, in situ. We discover drastic changes in the thermodynamics of lithium staging in graphite due to bending-induced strain; large interfacial effects in the nucleation of the metallic 1T’-MoS₂ from 2H-MoS₂ via lithium intercalation; and a new, insulating phase in semimetallic Td-WTe₂ via lithium intercalation. Our studies present intercalation as an effective post-synthesis design knobs to control and form new 2D materials.