Tuning Surface Work Function through Self-Assembled Monolayers of Carborane Isomers

Self-assembled monolayers (SAMs) are useful platforms to probe the fundamental interactions that drive the spontaneous assembly of nanostructures and to directly modify material properties. In this study, we use carborane-based monolayers to alter the electronic structure of the underlying substrate. The carborane cage molecule is advantageous for this purpose as the strength and direction of the dipole moment of the monolayer molecule can be varied based on which carborane isomer is deposited; through this, we can tune the work function of the surface. Previously, we have been able to modulate the work function of gold and silver surfaces using carboranethiol isomers and of germanium surfaces using carborane‑carboxylic acid isomers. This principle can be further extended by using the O4‑carboranethiol isomer, which has a dipole moment almost perfectly parallel to the surface, or the 9,12‑carboranedithiol isomer, which has a dipole moment almost completely perpendicular to the surface. Furthermore, the effect that the carborane cage dipole has on the surface work function can be used to indirectly track the chemical identity of surface bound molecules, for example in the case of when the SAM is used as a platform for a chemical reaction.