Controlling Bimetallic Composition at Individual Nanoparticle Level
Problem statement: Self-assembled magnetic arrays of FePt nanoparticles are candidate structures for ultra-high areal storage density. Compositional variation between individual FePt nanoparticles can lead to wide distributions in the magnetic properties and performance of these nanoparticles
Solution: Through extracting nanoaprticles at various stages of chemical synthesis, we have learned how FePt nanoparticles nucleate and grow. Subsequently, we have discovered that simultaneous decomposition/reduction of Fe-based and Pt-based precursors results in wide compositional distributions. Alternatively, the initial formation of Pt-rich seeds followed by the subsequent incorporation of Fe significantly narrows the compositional distribution (see Srivastava et al. JAP 102 (2007) p. 104310). We have tailored the surfactant chemistry of a previous method that exhibited wide compositional variation into a 2-step nucleation and growth process. The corresponding compositional histograms show a significant narrowing of the composition, demonstrating that the nucleation sequence (not precursor choice) is critical in controlling the nanoscale composition in these bimetallic nanoparticles.