Enhanced capability in a gas aggregation source for magnetic nanoparticles

We describe the characterization of a high-temperature (2000 K) thermal gas aggregation source that is ultrahigh vacuum compatible and can cleanly deposit transition metal clusters with partial pressures of contaminants in the 10(-11) mbar range allowing codeposition with highly reactive matrices. In particular, we investigate the effect of varying (i) the bath gas pressure and composition on the size distribution and flux of clusters produced and (ii) the position of the crucible within the source. The mass spectra of Fe clusters produced, recorded using a quadrupole filter, show that changing the operating conditions and configuration of the source allow a wide range of cluster sizes-3000-320 000 amu (similar to 50-6000 atoms for Fe or Co) to be produced. We demonstrate the cleanliness of the source by producing uncontaminated Fe clusters in rare-earth matrices.