The nanoparticles are prepared by inert gas condensation in a nanoparticle deposition system that is based on the commercially available "Nanodep 60" (Oxford Applied Research Ltd.). The particles nucleate from a supersaturated vapour provided be DC magnetron sputtering in a noble gas atmosphere (typically Ar with some additions of He at pressures around 1 mbar). They grow by inter-particle collisions and coalescence (sintering) within the nucleation chamber, before they are ejected into high vacuum through two differentially pumped apertures. Here, the particle do no longer collide due to the particles' enhanced mean free path. Prior to their deposition the particle may be subjected to rapid annealing through in-flight optical heating in a home-made light furnace or size fractionated by means of a quadrupole mass filter. Alternatively to soft-landing ain a substrate in the deposition chamber, they may be deposited onto a special transfer holder that allows for a transfer of the particles into an electron microscope without breaking the vacuum or under protective gas atmosphere.
Schematic drawing of the nanoparticle deposition system [E. Mohn, PhD thesis, TU Dresden (2012)].