(3ai) Two-Dimensional Materials at Fluid-Fluid Interfaces

Monolayer two-dimensional (2D) materials such as graphene, hexagonal boron nitride, and molybdenum disulfide (MoS₂) represent the “2D” class of nanomaterials that have (sub-)nanometer-scale thicknesses but colloidal scale (10¹ – 10⁴ nm) lateral dimensions. The 2D nature of these particles is enticing for uses in thin-film technologies, and fluid-fluid interfaces can be used to assemble films of such materials that can ultimately be deposited onto arbitrary substrates. Thus, it is necessary to understand the forces driving 2D materials to self-assemble into a film with a specific morphology to achieve a thin-film device with the desired functional properties. However, it has proven difficult to directly observe these atomically-thin materials at fluid-fluid interfaces, and a lack of a uniform system of 2D particles has stymied progress in modeling their interactions. Our recent work has focused on addressing these two issues using readily available methods: the direct observation of monolayer 2D particles at air-water and oil-water interfaces has been accomplished using interference reflection microscopy (IRM), and systems of uniform, monolayer graphene particles have been created through photolithography. Thus, we now have the experimental means to observe transient phenomena in systems of 2D materials at fluid-fluid interfaces in real time and can begin to understand the dominant interactions between 2D particles that drive self-assembly. These experimental tools have created opportunities to study fundamental phenomena associated with atomic-scale particles at fluid-fluid interfaces, and our results have practical implications in designing future roll-to-roll deposition processes of 2D material films from fluid-fluid interfaces. Trends in this area are towards constructing laterally aggregated films of multiple 2D materials (lateral van der Waals heterostructures) or sequentially stacked films of different 2D materials (vertical van der Waals heterostructures), and in achieving nanoscale resolution of 2D particle dynamics and self-assembled film structure using in situ electron microscopy.

Research Interests

My current and future research interests are in 2D and other nanomaterials, their self- or directed-assembly, and practical thin-film applications of these materials, such as in optoelectronics or (photo)electrochemical catalysis. I am also interested in the broader fields of colloids and soft materials, fluid-fluid interfaces, liquid-phase processing, and in situ characterization techniques.