Impact of Quaternary Ammonium Ions on the Properties of 2D MoS2 Synthesized via Electrochemical Exfoliation

Overview & Synopsis

Molybdenum disulfide (MoS2) is a prominent member of the transition metal dichalcogenides (TMDs) family, garnering significant attention for its potential in next-generation semiconducting devices. This study explores the electrochemical exfoliation of MoS2 nanosheets, with a focus on understanding how different quaternary ammonium ions impact the exfoliation efficiency and the resultant electrical properties of the nanosheet networks. Electrochemical exfoliation is a favored cheap and scalable method for producing high-quality MoS2 nanosheets with promising electrical results. 1 However, inconsistency in the process (stemming from the use of various ions, solvents, sonication times, and washing techniques) complicates the reproducibility and optimization of the material’s electronic properties. In this work, we systematically investigate the role of quaternary ammonium ions, specifically analyzing their influence on the exfoliation process and the subsequent electrical performance of MoS2 nanosheets. We utilized Liquid-Liquid Interfacial Deposition (LLID) to accurately transfer the exfoliated nanosheets onto substrates, enabling precise electrical characterization. Our findings indicate that while the exfoliated MoS2 nanosheets exhibit mobility and on-off ratios within expected ranges, they fall short of the highest values reported in the literature. 1-4 Notably, tetraoctylammonium (TOA+) ions emerged as the most effective exfoliation agent, producing nanosheets with superior size metrics, conductivity, mobility, on-off ratio and overall network performance. Furthermore, we observed a trend with the alkyl chain length of the quaternary ammonium ions and the threshold voltage of the resulting transistors. Longer alkyl chains appeared to reduce p-doping or enhance n-doping effects, bringing the threshold voltage closer to zero and, in some cases, slightly above it. In conclusion, this research contributes to the broader understanding of ion-mediated exfoliation processes and presents a pathway for producing 2D MoS2 materials with tailored electrical properties. These insights pave the way for the scalable production of high- performance MoS2-based devices, offering a valuable addition to the field of 2D materials and their applications in advanced electronics.