Tuning the Electronic and Chemical Properties of Monolayer MoS$_2$ Adsorbed on Transition Metal Substrates

Using first-principles calculations within density functional theory, we investigate the electronic and chemical properties of a single-layer MoS$_2$ adsorbed on Ir(111), Pd(111), or Ru(0001), three representative transition metal substrates having varying work functions but each with minimal lattice mismatch with the MoS$_2$ overlayer. We find that for each of the metal substrates, the contact nature is of Schottky type, and the dependence of the barrier height on the work function exhibits a partial Fermi-level pinning picture. Using hydrogen adsorption as a testing example, we further demonstrate that the introduction of a metal substrate can substantially alter the chemical reactivity of the adsorbed MoS$_2$ layer. The enhanced binding of hydrogen, by as much as about 0.4 eV, is attributed in part to a stronger H-S coupling enabled by the transferred charge from the substrate to the MoS$_2$ overlayer, and in part to a stronger MoS$_2$-metal interface by the hydrogen adsorption. These findings may prove to be instrumental in future design of MoS$_2$-based electronics, as well as in exploring novel catalysts for hydrogen production and related chemical processes.