Metal Contacts on Physical Vapor Deposited Monolayer MoS₂

The understanding of the metal and transition metal dichalcogenide (TMD) interface is critical for future electronic device technologies based on this new class of two-dimensional semiconductors. Here, we investigate the initial growth of nanometer-thick Pd, Au, and Ag films on monolayer MoS₂. Distinct growth morphologies are identified by atomic force microscopy: Pd forms a uniform contact, Au clusters into nanostructures, and Ag forms randomly distributed islands on MoS₂. The formation of these different interfaces is elucidated by large-scale spin-polarized density functional theory calculations. Using Raman spectroscopy, we find that the interface homogeneity shows characteristic Raman shifts in E_2g¹ and A_1g modes. Interestingly, we show that insertion of graphene between metal and MoS₂ can effectively decouple MoS₂ from the perturbations imparted by metal contacts (<i>e.g.</i>, strain), while maintaining an effective electronic coupling between metal contact and MoS₂, suggesting that graphene can act as a conductive buffer layer in TMD electronics