Encapsulation of Size-Selected Ru3 Clusters into RF-Deposited TiO2

In this study Ru3 clusters are deposited onto radio frequency-sputter deposited TiO2 (RF-TiO2) substrates by both solution submersion and chemical vapor deposition (CVD) of Ru3(CO)12, as well as cluster source depositions of bare Ru3. TiO2(100) and SiO2 are used as comparison surfaces with differing cluster-surface interactions. Temperature-dependent X-ray photoelectron spectroscopy (XPS), angle-resolved XPS, and temperature-dependent low energy ion scattering (TD-LEIS) are used to probe how the cluster-surface interaction changes due to heat treatment. Results show that bare Ru3 supported on SiO2 remain on the surface layer but agglomerates upon heating. Conversely, when supported on sputter-treated RF-TiO2, bare Ru3 is encapsulated by a layer of titania substrate material as-deposited. Ligated Ru3(CO)12 is also covered by a layer of titania when deposited onto sputter-treated RF-TiO2 but heat treatment is required to remove most of the ligands. TD-LEIS is used to directly measure the encapsulation of CVD Ru3(CO)12 clusters on sputter-treated RF-TiO2 and determine the substrate overlayer thickness. The overlayer was found to be 1-2 monolayers, which is thin enough for catalytic or photocatalytic reactions to occur without Ru being present in the outermost layer.