July 13, 2007, Riverside, CA--Nanotechnologists at the University of California, Riverside nanotechnologists have succeeded in controlling the color of a solution of very small particles of iron oxide in water simply by applying an external magnetic field to the solution. The spherical iron oxide particles are held by the magnetic field in an photonic-crystal ordered array whose periodic pitch is altered by the change in the magnetic field. Large, inexpensive reflective displays are one potential result of the technology.
Study results appear in Angewandte Chemie International Edition's online edition. The research paper is scheduled to appear in print in issue 34 of the journal. Identified by Angewandte Chemie as a "very important paper," the research will be featured on the inside cover of the print issue.
"The key is to design the structure of iron oxide nanoparticles through chemical synthesis so that these nanoparticles self-assemble into three-dimensionally ordered colloidal crystals in a magnetic field," said Yadong Yin, an assistant professor of chemistry who led the research. "Ours is the first report of a photonic crystal that is fully tunable in the visible range of the electromagnetic spectrum, from violet light to red light."
Iron oxide (Fe3O4) nanoparticles are "superparamagnetic," meaning that they turn magnetic only in the presence of an external magnetic field. In contrast, "ferromagnetic" materials become magnetized in a magnetic field and retain their magnetism when the field is removed. The researchers used the superparamagnetic property of iron oxide particles to tune the spacing between nanoparticles.
"Other reported photonic crystals can only reflect light with a fixed wavelength," Yin said. "Our crystals, on the other hand, show a rapid, wide and fully reversible optical response to the external magnetic field."
Photonic materials such as those used by Yin and his team could help in the fabrication of new optical microelectromechanical systems, as well as reflective color displays. They also have applications in telecommunications (fiber optics), sensors, and lasers.
"What should make the technology commercially attractive is that iron oxide is cheap, nontoxic, and available in plenty," Yin said.
Yin was joined in the research by UC Riverside's Jianping Ge, a postdoctoral researcher, and Yongxing Hu, a first-year graduate student in the Department of Chemistry.
The UCR Office of Technology Commercialization has filed a patent application on the technology.