Azobenzene Adsorption on the MoS2(0001) Surface: A Density Functional Investigation within van der Waals Corrections

The interest in light-sensitive organic molecules, such as azobenzene, has increased because of their ability to functionalize two-dimensional layered systems and engineer their electronic structure. In this work, we explore the azobenzene trans and cis isomer adsorption on a molybdenum disulfide MoS2(0001) layer employing the density functional theory (DFT) within van der Waals (vdW) corrections to the semilocal exchange-correlation functional. We found that the aromatic rings of azobenzene lay parallel to the surface (two in the trans isomer and one in the cis isomer), which contributes to increasing the configuration stability by vdW interactions. Furthermore, we found a relatively large work function change upon adsorption because of the electron density rearrangement, and hence, it might affect the electronic transport properties within the single MoS2(0001) layer. We observed an increase in the relative DFT + vdW total energy among the azobenzene isomers (trans and cis) from 0.51 eV in the gas-phase (trans isomer has the lowest energy) to 0.81 eV for azobenzene supported on the MoS2(0001) surface, which can be explained by the contact of the two rings of the trans isomer directly to the surface. Thus, the binding of azobenzene on the single MoS2(0001) layer affects the isomerization process because of the relative energy increase, and this, in turn, influences the transport properties of the single MoS2(0001) layer because of the changes in the electrostatic potential.