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Kwabena Bediako: New Twists on Chemistry and Physics in Moiré Superlattices

March 31 @ 10:00 am - 11:00 am

Meeting ID: 684 7017 3961

Passcode: 113399

Speaker: Kwabena Bediako, Assistant Professor at UC Berkeley, Dept. of Chemistry

Title: New twists on chemistry and physics in moiré superlattices    

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. However, in these systems, complex strain relaxation can also strongly influence the fragile electronic states of the material. Precise characterization of these materials and their properties 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 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. I will also discuss the impact of these mechanical deformations to the electronic band structure of these moiré superlattices and the correlated electronic phases they host. The talk will then explore how various degrees of freedom that are unique to 2D materials may be used to tailor interfacial chemistry at well-defined mesoscopic electrodes and the outlook for new paradigms of functional materials for energy conversion and low-power electronic devices.

Bio: Kwabena was born in Ghana, West Africa. He moved to the US in 2004 for his undergraduate studies in Chemistry at Calvin College, MI, graduating with honors in 2008. After a year working at UOP Honeywell in IL where he researched new catalysts for the petrochemical and gas processing industries, he traveled from the Midwest to the East Coast to begin 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. Awards received include: AFOSR Young Investigator award, ONR Young investigator award, DOE Early Career Award, Gordon and Betty Moore Materials Synthesis Fellow, and CIFAR–Azrieli Global Scholar.