Investigation of structure and chemical states of self-assembled Au nanoscale particles by angle-resolved X-ray photoelectron spectroscopy

The surface structure of the silane self-assembled monolayer (SAM) prepared by 3-mercaptopropyl-trimethyl-silane (MPTMS) on Si(111) and the chemical states of the self-assembled Au nanoparticles absorbed onto the surface of the silane SAM were studied by angle-resolved X-ray photoelectron spectroscopy. The thickness of the silane SAM was determined as the vertical distance between sulfur atoms on the surface of the silane SAM and the surface of the SiO2 overlayer on the silicon substrate, and had a value of 4.7 Å. In addition, two types of sulfur species were detected in the self-assembled Au nanoparticles at an electron take-off angle of 5°. These species are assigned as bound thiolate and unbound thiol with S 2p binding energies of 162.6 eV and 164.6 eV respectively. The assignments indicate that the gold–thiolate bond was formed when Au nanoparticles were assembled onto the surface of the silicon substrate through MPTMS as a coupling agent.