Water Dispersible FePt Nanoparticles Self-Assemble into Cubic Arrays of Particles

Janis Mabry, Christopher J. Thode, Xiangcheng Sun, Mohammad Shamsuzzoha, J. W. Harrell and David E. Nikles

A high school chemistry teacher spent the summer of 2003 in our laboratories as a part of our NSF research experiences for teachers (RET) program. She prepared water dispersible FePt nanoparticles by exchanging the oleylamine and oleic acid ligands with 11-mercaptoundecanoic acid. A dispersion of FePt nanoparticles, having the oleylamine and oleic acid ligands, in hexane was mixed with a solution of 11-mercaptoundecanoic acid in either cyclohexanone or acetone. After mixing and standing, as the 11-mercaptoundecoic acid replaced the oleyl amine and oleic acid ligands, the particles precipitated and were isolated by centrifuging. The particles were dispersed in basic water, made basic with either sodium hydroxide or ammonium hydroxide. The dispersion was dropped onto a carbon-coated copper TEM grid and after drying the particle formed a highly ordered square array of FePt nanoparticles, Fig. 1.

Films containing FePt nanoparticles are under serious consideration as future high-density magnetic disk drive media, with capacities beyond one terabit per square inch. Our MRSEC seeks to solve the fundamental materials science problems thereby enabling these materials to be used in these devices. The ability to replace the ligands on FePt magnetic nanoparticles proves an important means of controlling the self-assembly. Self-assembly of FePt nanoparticles, having oleyl-amine and oleic acid ligands gave films consisting of close-packed arrays of particles.

This research was sponsored by the NSF Research Experiences for Teachers award in the Department of Chemistry and the NSF Materials Research Science and Engineering Center.