Phase transformation of alumina-coated FePt nanoparticles

Monolayers of FePt nanoparticles (NPs) were coated with 10 nm-thick layers of Al2O3 by pulsed laser deposition (PLD). The Al2O3 coating prevents diffusion and stabilizes the NP monolayer against sintering. Annealing converts the FePt NPs from an alloy phase (A1) into intermetallic phases. Atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) shows that Pt-rich A1 Fe29Pt71 NPs convert into the FePt3 L1(2) intermetallic phase upon annealing and develop faceted morphologies. HAADF-STEM also reveals the presence of structural defects and Pt-rich shells. These results, in conjunction with prior studies of Al2O3 deposition by atomic layer deposition (ALD), demonstrate that coating arrays of FePt NPs with thin Al2O3 films by PLD or ALD imparts thermal stability and provides comparable results. (C) 2012 American Institute of Physics. [doi:10.1063/1.3676419]