Growth, clustering and morphology of intermetallic alloy core-shell nanodroplets

Sm-Fe-Ta-N core-shell (CS) nanospheroids were fabricated from hot liquefied nanodroplets by 157 nm pulse laser deposition in nitrogen gas. The Sm13.8Fe82.2Ta4.0 intermetallic alloy was used as the target. At low laser energy (20 mJ), spherical CS of 1-35 nm radius were fabricated on a Si/Ta substrate forming uniform films. The small nanodroplets were grown in the plume from the gas phase, and the larger ones (>50 nm radius) from the target's hydrodynamic ejection. The critical radius of the droplets and their surface energy per unit area was found to be 7.5 nm and 3.8 μJ/cm2 respectively. A number of CS solidified in the plume and consist of 2.5-5 nm radius crystalline nucleus surrounded by a <35 nm radius amorphous spherical shell. This structure prevents the oxidization of the crystalline nucleus because oxidization is confined on the surface of the CS. Furthermore, multi-crystalline nanodomains (embryos) were identified in a single CS from both homogeneous and heterogeneous nucleation. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)