Ordered SMSI Decoration Layer on Rh Nanoparticles Grown on TiO₂(110) Surface

Rh nanoparticles of 20–40 nm lateral size were grown on TiO₂(110) surface by physical vapor deposition and thermal treatments. The top-facet morphology of the Rh nanoparticles and the particle-free support were characterized by scanning tunneling microscopy. The chemical composition of the surface was checked by Auger electron spectrometry. Although most of the particles exhibited complex overlayers, ordered decoration layers were detected only on the top facet of extended hexagonal Rh particles. Several ordered or quasi-ordered encapsulation phases were detected: (1) a “worm-like” overlayer consisting of 1D stripes (width of 0.5 nm and length of 2–3 nm) oriented in the close-packed crystallographic orientations of the Rh nanoparticles and (2) a “wheel-like” hexagonal structure with unit cell vectors of 1.50 (±0.05) nm. The “worm-like” structure is suggested to be an initial stage in the formation of a “wheel-like” structure. It was proved that it is possible to selectively remove the “wheel-like” decoration phase by Ar⁺ sputtering and to recover it by thermal treatment of a few minutes at 1000 K.