Size and shape controlled synthesis of magnetic nanocrystals

Abstract

We report solution based approaches toward highly monodisperse maghemite $(\gamma -Fe_2O_3)$ nanospheres and their shape evolutions to novel architectures. We utilized a one step thermolysis method in which $Fe(CO)_5$ molecular precursor is pyrolyzed to form Fe nanoparticles under ambient condition where subsequent air oxidation generates of iron oxide. Modulating the growth parameters- for example, type and amount of capping molecules and also the growth time- can easily vary the sizes and shapes. Resulting structures are diverse including spheres, triangles, diamonds, and hexagons. Spherical nanocrystals easily assemble into the multi-dimensional superlattices, demonstrating the uniformity of these nanocrystals. These large hexagon shaped nanocrystals could be formed through the ripening process with the weakly binding surfactant system such as alkylamine. High-resolution transmission electron microscopic (HRTEM) images, electron diffraction (ED), selected area electron diffraction (SAED), X-ray diffraction (XRD) and X-ray photoelectron microscope (XPS) analyses indicate that both spherical and hexagon-shaped nanocrystals were highly crystalline maghemite $(\gamma -Fe_2O_3)$ and their structures. Core-shell of CoAu nanoparticles were synthesized from redox transmetalation. The Au coated Co nanoparticles have many advantages because of their previous study like surface modification and biological application. Furthermore noble metal has good chemical stability upon corrosion and oxidation. The obtained core-shell nanoparticles are transferred from organic solvent to water by surface modification process and self-assembly of CoAu nanoparticles with in large scale can be formed by DNA template. We can form CoAu-DNA network because CoAu nanoparticles capped with positively charged stabilizer in aqueous solution can attach to negatively charged DNA through coulombic interaction. These results are good example that well established gold chemistry adapt to magnet...