University of California, Berkeley
New twists on chemistry and physics in atomically layered materials
Atomically thin or two-dimensional (2D) materials can be assembled into bespoke heterostructures to produce some extraordinary physical phenomena. One exciting and relatively recent example is the formation of moiré superlattices from azimuthally misoriented (twisted) layers. These moiré superlattices result in flat bands that lead to an array of correlated electronic phases. Apart from the emergent physics that these systems give access to, moiré materials are also distinctive platforms for exploring fundamental questions of interfacial chemical/electrochemical reactivity. However, in these systems, complex and spontaneous strain relaxation can also strongly influence the fragile electronic states of the material and their interfacial chemical properties. Precise structural characterization of these materials is therefore critical to the understanding of the behavior of these novel moiré materials (and 2D heterostructures in general). In this talk, I will discuss the twist tunable electrochemical behavior we have found in graphene moiré systems and show how spontaneous mechanical deformations (atomic reconstruction) and resultant intralayer strain fields in twisted graphene and metal dichalcogenides have been quantitatively imaged using our new technique of 4D-STEM Bragg interferometry. I will also discuss the impact of these mechanical deformations to the electronic band structure of moiré superlattices, the correlated electronic phases they host, and their interfacial electrochemistry. The talk will then explore how chemical intercalation of van der Waals heterostructures with transition metal ions may be used to design two-dimensional magnetic crystals, and conclude by considering the outlook for combining various chemical/electrochemical approaches with the manifold degrees of freedom that are unique to 2D materials in the search for exotic physics as well as new paradigms of functional materials for energy conversion and low-power electronic devices.