title: Sinter-free phase conversion and scanning transmission electron microscopy of FePt nanoparticle monolayers.
abstract: Thermally robust monolayers of 4-6 nm diameter FePt nanoparticles (NPs) were fabricated by combining chemical synthesis and atomic layer deposition. Spin-cast monolayers of FePt NPs were coated with thin, 11 nm-thick layers of amorphous Al(2)O(3), followed by annealing to convert the FePt NPs from an alloy (A1) into intermetallic FePt (L1(0)) and FePt(3) (L1(2)) phases. The Al(2)O(3) layer serves as a barrier that prevents sintering between NPs during annealing at temperatures up to 730 °C. Electron and X-ray diffraction in conjunction with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) show that as-synthesized A1 FePt NPs convert into L1(0) and L1(2) phase NPs through annealing. HAADF-STEM measurements of individual NPs reveal imperfect ordering and show that the NP composition determines which intermetallic phase is obtained. Mixed-phase NPs with L1(0) cores and FePt(3) L1(2) shells were also observed, as well as a smaller number of unconverted A1 NPs. These results highlight the need for improved control over the compositional uniformity of FePt NPs for their use in bit-patterned magnetic recording.
authors.affiliation: Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695, USA.
authors.forename: Aaron C
authors.initials: AC
authors.lastname: Johnston-Peck
authors.forename: Giovanna
authors.initials: G
authors.lastname: Scarel
authors.forename: Junwei
authors.initials: J
authors.lastname: Wang
authors.forename: Gregory N
authors.initials: GN
authors.lastname: Parsons
authors.forename: Joseph B
authors.initials: JB
authors.lastname: Tracy
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D008280:Magnetics; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D017348:Microscopy, Electron, Scanning Transmission; D010316:Particle Size; D010984:Platinum / Q000737:chemistry*; D013696:Temperature
chemical_list: D010984:Platinum; D007501:Iron; D000537:Aluminum Oxide