Rh nanoparticles of 50-100 nm diameter and 20-40 atomic layer thickness with a (111) flat top facet parallel to the support surface were grown on a TiO2(110) surface via physical vapor deposition (PVD) at room temperature (RT) followed by annealing at 1050 K. These nanoparticles were completely encapsulated by an ordered hexagonal pinwheel TiO∼1.2 ultrathin oxide (w-TiO-UTO) film. STM, XPS, and low energy ion scattering (LEIS) methods were used to characterize the postdeposition of gold and the effects of annealing on the Au/w-TiO-UTO/Rh-particle system. The adlayer exhibits 3D growth and Rh-Au bond formation at 500 K. The 3D Au nanoparticles of 2-3 nm diameter and ∼1 nm height are partially covered by TiOx species at RT and sinter via an Ostwald-ripening in the range of 500-800 K. The adparticles are gradually getting free of TiOx decoration, and at around 900 K they exhibit a double layer height with 2D character. Two different arrangements were found for these Au particles: (i) a compressed Au(111)-(1 × 1) and (ii) a reconstructed Au(111)-(2 × 1), both of them pseudomorphic with the Rh lattice underneath. Above 900 K, the thickness of these 2D particles tends to become a single layer, while they spread out and form a continuous gold layer on the Rh nanoparticles. This behavior indicates a thermally activated replacement of the w-TiO-UTO film by an Au ultrathin layer. The gold layer is stable up to 1000 K, where extended 1D interfaces are formed between gold and w-TiO-UTO layers.