(623f) Direct Observation of the Dynamics of Mono- and Multi-Layer 2D Materials at Fluid-Fluid Interfaces

Two-dimensional (2D) materials have garnered significant interest over the past decade for applications in thin-film (opto)electronic devices because of their nanometer-scale thicknesses and tunable optical and electrical properties. Fluid-fluid interfaces provide a potentially low-cost and high-throughput means to reliably deposit these materials onto arbitrary substrates after trapping and assembling the 2D particles at such interfaces. The formation of functional thin-films with desirable properties is governed by the film morphology, which in turn is dependent on the dynamics of self-assembly. Therefore, it is essential to understand the relevant forces involved in particle self-assembly. However, there are open questions regarding the interactions between nanometer-thick 2D particles pinned to fluid-fluid interfaces as these high aspect ratio particles straddle the nanoscopic (thickness) and microscopic (lateral size) length scales. Using interference reflection microscopy, we have investigated the self-assembly dynamics of CVD-grown mono- and few-layer graphene flakes at an air-water interface. Additionally, in collaboration with the National Renewable Energy Laboratory, we have investigated the interactions between CVD-grown monolayer MoS₂ platelets at air-water and oil-water interfaces. We will present the results from these ongoing studies, and discuss the similarities and differences observed in these two systems regarding the relevant forces leading to their respective interfacial morphologies.