Strategy Optimization of Synthetic Approach Assisted by PeakForce AFM and KPFM

Single-crystal transition metal dichalcogenides (TMDs) and TMD-based heterojunctions are important for a variety of academic and industrial applications. Economic and scalable synthetic approaches have been pursued constantly. In this article, the authors report the development of a facile novel method for direct formation of high-quality, mono- or few-layer MoS₂ crystal. This work is an excellent example about the employment of PeakForce AFM and KPFM techniques to guide the design of synthesis protocol. Briefly, to understand the growth mechanism, the intermediate phases in quenched MoS₂ samples at a sequence of stages were analyzed via PeakForce AFM and KPFM. PeakForce Tapping AFM mode is the benchmark technique for accurately determining the thickness of 2D materials (Shearer et al. Nanotechnology, 2016, 27, 125704). The accuracy in thin film thickness is critical to correlate the as-growth layer(s) with other properties captured by KPFM or other optical techniques. Together with KPFM analysis, the authors could confidently propose a multistep growth model for monolayer MoS₂. In addition, the as-synthesized monolayer is used to build monolayer MoS₂-based ferroelectric programmable Schottky junction devices via local domain patterning. The local poling of this device is through a conductive AFM and the ferroelectric domains were characterized by PFM imaging.