Strain and Gain: Moiré Lattice Relaxation and Chemical Intercalation of 2D Heterostructures

Monday, October 17, 2022 from 2:30-3:30 p.m.
Location: 325 Physics South Hall & Zoom
Speaker: Kwabena Bediako, University of California, Berkeley

Abstract: 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 layers. These moiré superlattices result in flat bands that lead to an array of correlated electronic phases. However, complex strain relaxation strongly influences the electronic states of the material. Precise characterization of these materials and their properties is therefore critical to the understanding of the physical and chemical behavior of these moiré materials (and 2D heterostructures in general). The talk will first discuss how spontaneous mechanical relaxation (atomic reconstruction) and resultant intralayer strain fields at moiré superlattices of twisted bilayer graphene and those of transition metal dichalcogenides have been quantitatively imaged using a newly developed technique—4D-STEM Bragg interferometry—and the impact of these mechanical deformations on the electronic band structure. The second part of the talk will discuss superlattices formed by chemically inserting transition metal ions between atomically thin layers as a means of synthesizing few-layer magnetic materials.

Bio: Kwabena was born in Ghana, West Africa. He moved to the US in 2004 for his undergraduate studies in Chemistry at Calvin University, MI, graduating with honors in 2008. In 2009, he began his graduate studies in Inorganic Chemistry with Prof. Daniel Nocera at MIT (and later Harvard University). After receiving his Ph.D. in 2015 from Harvard University, Kwabena began postdoctoral work in Prof. Philip Kim's group in the Department of Physics at Harvard. In July 2018, Kwabena joined the faculty of the UC Berkeley Department of Chemistry.