Abstract 

Atomically thin or two-dimensional (2D) materials can be assembled into bespoke heterostructures to produce some extraordinary physical phenomena. Likewise, these highly tunable materials are useful platforms for exploring fundamental questions of interfacial chemical/electrochemical reactivity. 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. This talk will discuss how the localized electronic states in moiré superlattices also establish these materials as useful platforms for studying and controlling interfacial electrochemical reactions. In addition, in these systems, complex strain relaxation can also strongly influence 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 novel moiré materials (and 2D heterostructures in general). The talk will show how spontaneous mechanical deformations (atomic reconstruction) and resultant intralayer strain fields at moiré superlattices of twisted bilayer graphene have been quantitatively imaged using 4D-STEM Bragg interferometry and the impact of these mechanical deformations on the electronic band structure (with ramifications for both the physics and chemistry of these materials). Finally, the talk will describe new approaches for synthesizing two-dimensional magnetic materials using chemical intercalation.

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). His graduate research focused on structural and mechanistic studies of water splitting electrocatalysis at cobalt and nickel compounds. 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, where he studied ion intercalation and quantum transport in 2D van der Waals heterostructures. In July 2018, Kwabena joined the faculty of the UC Berkeley Department of Chemistry. Kwabena has received awards including Young Investigator Awards from the Office of Naval Research and Air Force Office of Scientific Research, the Department of Energy Early Career Award, and the Gordon and Betty Moore Foundation Synthesis Fellow award.