Adsorption of Pd onMoS2(1000):Ab initioelectronic-structure calculations

We present ab initio total energy calculations of the adsorption energy of one Pd monolayer on ${\mathrm{MoS}}_2\mathrm{}\left(1000\right).$ We consider four different adsorption sites: the Pd atoms on top of Mo, on top of the hole site, on top of the surface S, and on the bridge position halfway between two adjacent S atoms. The largest adsorption energy obtained corresponds to the hexagonal site on top of Mo. The maximum energy difference between adsorption sites is 0.25 eV. Due to the lattice mismatch, a Pd monolayer should be expanded to grow pseudomorphically on this substrate. Comparing the energy difference between the adsorption sites to the energy involved in the expansion of a Pd monolayer, we conclude that Pd will tend not to grow pseudomorphically, in agreement with the experimental evidence. We have also evaluated the changes in the work function produced by the deposition of the Pd adlayer; we observe a systematic reduction with respect to the clean substrate.