Controlling MoS2 Nanosheet Size and Network Conductivity through Alkylammonium Ion Selection

Abstract

Solution-processed inks of two-dimensional (2D) semiconductors, such as molybdenum disulfide (MoS₂), hold great promise for enabling low-cost, printed electronic devices. To optimize critical performance metrics like network conductivity, large-aspect-ratio (kNS>>100) nanosheets are essential to yield low-resistance flake-to-flake junctions. While electrochemical exfoliation with ammonium salts has emerged as a viable method for producing high-aspect ratio semiconducting nanosheets, the process parameters remain underexplored. In this work, we systematically investigate the role of alkylammonium ion size in the electrochemical exfoliation of MoS₂, demonstrating control over nanosheet lengths (L~1-3µm) and nanosheet thicknesses (tNS~1-4nm), leading to kNS between 400 and 2500. The nanosheet aspect ratio is closely linked to ion size via the energetics of exfoliation. We fabricate networks from these nanosheets and characterize their electrical properties, revealing that higher-aspect ratio nanosheets yield significantly more conductive networks, achieving conductivities up to 6000 Sm⁻¹. Our electrical measurements show that the network conductivity is consistent with a simple model and is limited by inter-nanosheet junctions whose resistance scales inversely with nanosheet area. These findings suggest that ion size determines nanosheet dimensions which in turn determine network conductivity.