Tuning the physical properties of MoS2 membranes through organophosphonate interfacial chemistry

Two dimensional, layered van-der Waals materials such as MoS₂ are of fundamental as well as practical interest for use in novel device applications in the areas of electronics, spintronics, optoelectronics, solar energy conversion, and sensing. The properties of such atomistic, thin nanomembranes are strongly influenced by the interaction with their environment and substrate. In particular, the modification of supporting substrates by interfacial chemistry is a critical consideration for many applications. In order to improve the performance of MoS₂-based nanodevices, modulation of interlayer screening effects can be achieved by tuning the electrostatic potential between the substrates and the MoS₂ flakes. We use organophosphonate chemistry as an alternative to siloxane chemistry for the controlled modification of silicon-based support substrates. In particular, two aromatic phosphonic acids, benzylphosphonic acid and 4-nitrobenzylphosphonic acid, were used to fabricate homogeneous organophosphonate self-assembled monolayers (SAMPs) on a silicon oxide support. We find that interaction of single layered MoS₂ with these substrates results in a significant shift of the Raman-active out-of-plane vibration mode A_1g of the twodimensional crystal. This finding points towards a depletion of the intrinsic n-type doping of MoS₂ membranes by aromatic SAMPs and clearly indicate that organophosphonate interfacial chemistry can play an important role in controlling the performance of 2D materials.