UC San Diego

Atomically thin transition metal dichalcogenides (TMDCs), such as MoS2 and WS2, are two-dimensional layered semiconductors that exhibit a unique combination of electronic and optical properties, lattice structure, mechanical stability, biocompatibility, and large specific surface area. Because of the large direct bandgap and 2D confinement, charge carriers in TMDCs experience enhanced electrostatic interactions and can respond strongly to incident light despite the materials’ atomically thin form factor. This phenomenon gives TMDCs a range of unusual optical characteristics, such as high absorption, tunable photoluminescence emission, and large refractive indices in the visible spectrum. As promising materials with diverse properties, TMDCs have been integrated into nanoscale platforms to enable unprecedented performance and functionalities unattainable by traditional materials.This dissertation explores the function of few-layer and monolayer TMDCs in nanophotonic and biosensing platforms. In chapter 2, I discuss the light-matter interaction in an atomically thin three-layer WS2 waveguide that enables external control over light propagation direction. Chapters 3 and 4 examine the roles of monolayer MoS2 as an active biosensing element. In chapter 3, I discuss the development of a dual-mode optoelectronic biosensor based on monolayer molybdenum disulfide (MoS2) capable of producing simultaneous electrical and optical readouts of biomolecular signals. The integration of electrical and optical sensors on the same chip can offer flexibility in read-out and improve the accuracy in detection of low concentration targets. Chapter 4 presents a novel monolayer MoS2-based platform as a label-free approach for optical electrophysiology. I discuss how susceptibility of MoS2 excitons to charges can be utilized to convert electrical activity into photoluminescence signals. This first work investigates MoS2’s voltage-tunable photoluminescence, fluorescence imaging capability, photostability and biocompatibility with neuron cultures. Results demonstrate the feasibility of this approach for recording millisecond-scale neuronal action potentials.