The morphology of mass selected ruthenium nanoparticles from a magnetron-sputter gas-aggregation source

We have investigated the morphology of mass selected ruthenium nanoparticles produced with a magnetron-sputter gas-aggregation source. The nanoparticles are mass selected using a quadrupole mass filter, resulting in narrow size distributions and average diameters between 2 and 15 nm. The particles are imaged in situ by scanning electron microscopy and scanning tunneling microscopy (STM) as well as ex-situ using transmission electron microscopy (TEM). For each distribution of mass selected nanoparticles, the height determined by STM and the width determined by TEM are seen to be similar throughout the mass range investigated. The particles are found to have a well-defined morphology for diameters below approximately 6 nm. Larger nanoparticles are less well-defined having rough surfaces, unlike the equilibrium morphology determined from the Wulff construction. The morphology of the particles is, in general, believed to be determined by the conditions inside the gas-aggregation source and the morphology is retained as the particles are soft-landed on the substrate.