Growth of Ag and Au Nanoparticles on Reduced and Oxidized Rutile TiO2(110) Surfaces

Abstract

The nucleation and growth of Au and Ag nanoparticles on rutile TiO2(110)–(1 × 1) surfaces in different oxidation states is studied by means of photoelectron spectroscopy (PES) and scanning tunneling microscopy (STM). Au and Ag nanoparticles were found to bind much more strongly to oxidized TiO2(110) model supports than to reduced TiO2(110) surfaces, as directly revealed by STM. Detailed PES studies addressing small Au and Ag particles complete this picture and show that the PES core level spectra acquired on Au/TiO2(110) and Ag/TiO2(110) can be best described by fitting with two binding energy (BE) components. Particularly for coverages in the sub-monolayer regime and for depositions at low temperatures (100 K) the PES core level spectra must be fitted with at least two BE components. The higher BE component is attributed to atoms at the interface between the metal clusters and the TiO2(110) support. For Au/TiO2(110), the two BE components were evident in the core level spectra for higher coverage than for Ag/TiO2(110), consistent with different growth modes for Au (initially 2D) and Ag (3D) on TiO2(110). Finally, strong evidence for charge transfer from Ag nanoparticles to the TiO2(110) support is presented, whereas the charge transfer between Au nanoparticles and the TiO2(110) support is very small.