Abstract
Fe–N clusters were prepared by a plasma-gas-condensation cluster deposition apparatus at various nitrogen gas flow rate RN2, and their crystal structures were investigated by transmission electron microscopy. For RN2>2.2×10−7 mol/s, fcc single-phase FeN clusters are obtained and their lattice parameter is a=0.428 nm, being close to that (a=0.433 nm) of ZnS-type FeN films. When RN2≥7.5×10−7 mol/s, almost all clusters are of a tetrahedron shape with cluster sizes of d=8–25 nm. This reveals that the tetrahedron shape of FeN compound clusters is stable in such small sizes, implying a low (111) surface energy and/or high elastic strain energy and twin boundary energy compared with pure metal clusters with fcc structure.
