ZnO Functionalization: Metal–Dithiol Superstructures on ZnO(0001) by Self-Assembly

We present a study of the functionalization of a monocrystalline ZnO surface using aromatic dithiols. The aim is to obtain a sulfur-terminated self-assembled monolayer (SAM), which is then used for creation of further molecular superstructures with intercalated metal atoms. These metal-molecule self-assembled structures are characterized by high-resolution X-ray photoelectron spectroscopy (XPS) and near edge X-ray adsorption fine structure (NEXAFS) measurements. Formation of a 5,5- bis(mercaptomethyl)-2,20- bipyridine (BPD) SAM on ZnO(0001) is demonstrated using a protocol developed by us earlier for dithiol assembly on gold, allowing production of standing-up SAMs with free SH groups. Thereafter the formation of a metal intercalated dithiol super lattice is achieved by first grafting metal atoms (Ag or Ni) and then attaching a second BPD molecular layer. Metal atoms bind to both sulfur and the pyridine nitrogens within the SAM. Clear changes in the valence band region near the Fermi level are observed, and the highest occupied system orbital positions are determined along with work function evolution.