Synthesis of iron nanoparticles: Size effects, shape control and organisation

Hydrogenation of bis(ditrimethylsilyl)amido iron complex, [Fe{N(SiMe3)2}2], provides iron nanoparticles (NPs) which have been stabilised either by an organic polymer matrix or mixtures of long chain acid and amine ligands leading respectively to spherical nanoparticles of 1.8 nm size or nanocubes with edges of 7.2 or 8.4 nm. The 1.8 nm size NPs are magnetically independent. Their magnetisation is shown to be identical to that of clusters of the same size prepared and measured in UHV conditions, i.e. strongly increased as compared to bulk value. These NPs have been structurally characterised and display an original structure different from the classical bcc and fcc structures encountered in bulk iron. On the reverse iron nanocubes display a bcc structure and magnetic properties similar to those of bulk iron within experimental errors, in agreement with their larger size. These cubes crystallise into 3D superstructures.