Pt-based nanoparticles: Synthesis and imaging by HP-STM

The high-pressure scanning tunneling microscope (HP-STM) allows studying morphological changes of the catalyst during ongoing reactions under realistic conditions (up to 1000 Torr of gas mixture). Studies on (557) and (332) oriented Pt crystals highlight the breaking of the surface steps into 2 nm clusters [1]. To consider the higher complexity of the surface of catalytic clusters, Pt-based nanoparticles were synthesized with narrow size and shape distribution by making use of the concepts of colloidal chemistry [2]. After deposition on flat Au(111) surface or n-doped Si, these nanoparticles were characterized at room temperature by HP-STM. The presence of the organic layer originating from the capping agent induces a loss of resolution: the nanoparticles present an irregular shape and cannot be distinguished from each other. Removal of this layer by post-treatment (UV-ozone, atomic H and O2-plasma) is also discussed.Synthesis of PtCo nanoparticles using oleic acid as stabilizer and O2-plasma as removing treatment seems up to now to be the most efficient way to get rid of the capping agent and to obtain clean monodisperse nanoparticles of 12 nanometer diameter on a flat support (of n-doped Si), separated from each other by 1 to 2 nm.