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Research: Magnetic materials control light at nanoscale

Posted: 04 Mar 2013 ?? ?Print Version ?Bookmark and Share

Keywords:silicon? nanoparticle? magnetic dipole? optical property?

A team of researchers at the A*STAR Data Storage Institute, Singapore has developed tiny spheres of silicon that can strongly interact with the magnetic field of visible-wavelength light. According to Arseniy Kuznetsov and co?workers, the engineered 'magnetic materials' enable new ways of controlling light at the nanoscale.

Relative permeability is a measure of a substance's ability to support a magnetic field. Most optical materials have a permeability nearly equal to one. A more diverse choice, however, would open the door to a whole host of novel optical devices. Negative permeability, for example, could be used to create high-resolution lenses and even invisibility cloaks. As no such materials exist in nature, scientists have started to develop metamaterials, which are artificial structures engineered to interact with light in a desired way. The team has shown that nanoscale engineering provides a way of tuning the magnetic properties of silicon nanoparticles.

The researchers fired a high-intensity laser at a silicon wafer, which blasted off spheres of silicon with diameters between 100-200nm. The separation between the spheres was large enough that the researchers could see them individually under an optical microscope. They could also see that the nanoparticles scattered light of all colours in the rainbow, from red to violet.

In a theoretical analysis, Kuznetsov and co-workers showed that the optical response resulted from incoming light generating a circular electric field, or displacement current, in the sphere. This, in turn, supported an oscillating magnetic field in the middle of the particleso-called magnetic dipole. "We have experimentally demonstrated that silicon nanoparticles can have strong electric and magnetic dipole resonances in the visible spectrum," noted Kuznetsov. "The advantage of our approach is that it is free of energy loss because the modes are not related to real electron currents."

The properties of the dipole were dependent on the size of the particle, so particles of different sizes scattered light of different colours. The team predicts that more sophisticated fabrication techniques will soon enable greater control over a nanoparticle's size and shape, thus enabling selective tuning of its optical properties. "Our future research will target possible applications of these nanoparticles and the realisation of novel nanodevices for light-on-a-chip integration," concluded Kuznetsov.

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