An Optical Approach To Measure Band Energies Of Monolayer MoS₂

About the Seminar 

This talk summarizes recent research results toward quantifying the energetics of monolayer (7 Å thick) molybdenum disulfide (MoS₂).  As a semiconducting 2-dimensional (2D) material, MoS₂ shows promise in energy conversion, nanoelectronics, and sensor applications.  Interestingly, electrostatic gating (i.e. applied voltages) tunes the monolayer MoS₂ band gap.  A central focus of this study is developing an optical method to measure the dynamic band gap of MoS₂.

Interfacial energetics at the semiconductor surface determine the reaction direction and influence the electron transfer rate.  However, existing approaches to quantify interfacial energetics may not work if the band gap is not fixed. Using monolayer MoS₂ as an electrode in a redox environment, we measure the materials’ optical response to different electrostatic gating conditions.  These results, supported by theory, show that band edge movement in monolayer MoS₂ is significant (0.2-0.5 eV) over a narrow range of applied potentials (0.2-0.3 V). Such large band edge shifts could change chemical reaction rates by orders of magnitude.