First-principles study of van der Waals interactions and lattice mismatch atMoS2/metalinterfaces

We explore the adsorption of ${\mathrm{MoS}}_{2}$ on a range of metal substrates by means of first-principles density functional theory calculations. Including van der Waals forces in the density functional is essential to capture the interaction between ${\mathrm{MoS}}_{2}$ and a metal surface, and obtain reliable interface potential steps and Schottky barriers. Special care is taken to construct interface structures that have a mismatch between the ${\mathrm{MoS}}_{2}$ and the metal lattices of $<1%$. ${\mathrm{MoS}}_{2}$ is chemisorbed on the early transition metal Ti, which leads to a strong perturbation of its (electronic) structure and a pinning of the Fermi level 0.54 eV below the ${\mathrm{MoS}}_{2}$ conduction band due to interface states. ${\mathrm{MoS}}_{2}$ is physisorbed on Au, where the bonding hardly perturbs the electronic structure. The bonding of ${\mathrm{MoS}}_{2}$ on other metals lies between these two extreme cases, with interface interactions for the late $3d$ transition metals Co, Ni, Cu and the simple metal Mg that are somewhat stronger than for the late $4d/5d$ transition metals Pd, Ag, Pt and the simple metal Al. Even a weak interaction, such as in the case of Al, gives interface states, however, with energies inside the ${\mathrm{MoS}}_{2}$ band gap, which pin the Fermi level below the conduction band.