Metal deposition onto a thiol-covered gold surface: A new approach

In this study, we report on details of a new technique for depositing metal on top of a self-assembled monolayer (SAM). The experiments were performed with 4,4′-dithiodipyridine (4-PySSPy) SAMs on Au(1 1 1) electrodes, which were immersed without potential control into a Pd(II)-containing solution, where Pd(II) adsorbs on the surface by forming a complex with the pyridine nitrogen. The complexed Pd(II) ions were reduced electrochemically to Pd(0) after transferring the electrode to a Pd ion-free solution. Upon reduction, monoatomic high Pd islands were observed in STM. From cyclic voltammetry, in situ STM and ex situ angle-resolved XPS we conclude that these islands reside on top of the SAM, not underneath. It is shown that palladium complexation and deposition on self-assembled monolayers of 2-mercaptopyridine is not possible.