While bulk MoS in the 2H-phase is known to be an indirect-band gap semiconductor, monolayer MoS has a direct band gap. The layer-dependent optoelectronic properties of MoS have promoted much research in 2-dimensional MoS-based devices. 2D MoS can be produced by exfoliating bulk crystals to produce single-layer to few-layer flakes either through a dry, micromechanical process or through solution processing.
Micromechanical exfoliation, also pragmatically called "Scotch-tape exfoliation", involves using an adhesive material to repeatedly peel apart a layered crystal by overcoming the van der Waals forces. The crystal flakes can then be transferred from the adhesive film to a substrate. This facile method was first used by Konstantin Novoselov and Andre Geim to obtain graphene from graphite crystals. However, it can not be employed for a uniform 1-D layers because of weaker adhesion of MoS to the substrate (either Si, glass or quartz); the aforementioned scheme is good for graphene only. While Scotch tape is generally used as the adhesive tape, PDMS stamps can also satisfactorily cleave MoS if it is important to avoid contaminating the flakes with residual adhesive.
Liquid-phase exfoliation can also be used to produce monolayer to multi-layer MoS in solution. A few methods include lithium intercalation to delaminate the layers and sonication in a high-surface tension solvent.