Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695, USA.
Nanoscale. 2011 Oct 5;3(10):4142-9. doi: 10.1039/c1nr10567a. Epub 2011 Aug 24.
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.
通过化学合成和原子层沉积相结合，制备了具有 4-6nm 直径的 FePt 纳米颗粒（NPs）的热稳定单层膜。FePt NPs 的旋涂单层膜涂覆有 11nm 厚的非晶态 Al(2)O(3)薄层，然后进行退火处理，将 FePt NPs 从合金（A1）转变为金属间化合物 FePt（L1(0)）和 FePt(3)（L1(2)）相。Al(2)O(3)层作为一种阻挡层，可防止在高达 730°C 的温度下退火时 NPs 之间的烧结。电子和 X 射线衍射以及高角度环形暗场扫描透射电子显微镜（HAADF-STEM）表明，合成的 A1 FePt NPs 通过退火转化为 L1(0)和 L1(2)相 NPs。对单个 NPs 的 HAADF-STEM 测量显示出不完全的有序性，并表明 NP 组成决定了获得哪种金属间相。还观察到具有 L1(0)核和 FePt(3) L1(2)壳的混合相 NPs，以及数量较少的未转化的 A1 NPs。这些结果强调了需要改进对 FePt NPs 组成均匀性的控制，以将其用于位图案记录。
