Liquid phase acoustic wave exfoliation of layered MoS2: critical impact of electric field in efficiency

Liquid phase exfoliation techniques of layered crystals establish the basis for high yield production of two-dimensional (2D) flakes suspension. However, such techniques generally require a long processing time. The recent demonstration of the piezoelectric phenomenon in noncentrosymmetric layered transition metal dichalcogenides, such as molybdenum disulfide (MoS2), leads to new opportunities for fast and efficient exfoliation processes. Here we use concomitant electric field and mechanical shear force for producing a suspension of MoS2 nanoflakes from exfoliation of their layered bulk powder particles. The electrical and mechanical fields are applied by a surface acoustic wave (SAW) microcentrifugation device. We show that the overall yield per unit of time of 3.816%/h can be achieved, which is at least an order of magnitude larger than previously reported liquid phase exfoliation methods. Simultaneously, the impressive monolayer yield is 58% in an excellent agreement with the computational estimation based on electric field assisted density functional theory calculations. The work therefore reports two major advancements. We show efficient exfoliation of layered MoS2. More importantly, we demonstrate the importance of the electric field in increasing the efficiency of liquid phase exfoliation. It is thus expected that these outcomes to fundamentally impact research activities focused on the exfoliation of piezoelectric 2D materials.