Array of perfect nanometer-scale spheres that can control the flow of visible light may find use in invisibility cloaks

Jan 29, 2014
An artificial material with depth
Meta-atoms comprising a metal nanosphere with a precisely etched trench have the electric (D) and magnetic (B) properties that allow them to interact with both components of visible light. Credit: A*STAR Data Storage Institute

The optical properties of a material are predominantly determined by its constituent atoms and electrons and the way that these respond to electromagnetic waves. In natural materials, the diversity of possible optical characteristics is limited, and so metamaterials—artificial structures engineered to control the propagation of light—offer hope for a plethora of novel optical applications.

Arseniy Kuznetsov and Boris Luk'yanchuk at the A*STAR Data Storage Institute, Singapore, and their co‐workers, have now created a novel type of three-dimensional metamaterial that can influence both the electric and magnetic parts of visible . Their approach provides a simple route to constructing unusual devices such as optical cloaks, which enable 'invisibility', and hyperlenses that offer super-resolution.

Metamaterials are arrays of subwavelength metallic structures called meta-atoms, which have been engineered to mimic atoms and their interaction with light. "Metamaterials provide a new route to controlling light at the nanoscale," explains Luk'yanchuk. "They pave the way for novel optical elements with unique functionalities that cannot be achieved with ."

A common approach taken by researchers of optical metamaterials is to construct meta-atoms from rings of metal that each contains a small break. These so-called split-ring resonators need to be a few hundred nanometers or less in size to work with , and any physical imperfections severely limit their performance.

Designing a split-ring resonator with both the electric and magnetic properties required to interact with these two different components of has also proved a challenge. "Magnetic resonance at visible frequencies could not be achieved with standard, flat split-ring resonator designs," says Luk'yanchuk.

Now, Kuznetsov and Luk'yanchuk's team have shown that a three-dimensional version of this structure—the split-ball resonator—could lead to nearly flawless metamaterials with a strong electric and magnetic response.

Using standard nanofabrication techniques, the researchers first created an array of gold or silver disks on a substrate. They then fired a high-power laser at each disk so that it melted to form a liquid droplet, which solidified into a perfect sphere, thus eliminating flaws. Finally, the team used a beam of helium ions to etch a trench into each nanosphere (see image).

The researchers confirmed that their split-ball resonators displayed a within the visible spectrum, demonstrating a strengthened ability to 'tune' the optical responses of metamaterials.

In the future, the researchers could use the same method to pattern more complicated three-dimensional features on the meta-atoms, which would enable even more complex ways of manipulating light.

Explore further: 'Nanoimprinting' technique makes it possible to fabricate visible-light-bending metamaterials at unprecedented scales

More information: Kuznetsov, A. I., Miroshnichenko, A. E., Fu, Y. H., Viswanathan, V., Rahmani, M. et al. Split-ball resonator as a three-dimensional analogue of planar split-rings. Nature Communications 5, 3104 (2014). dx.doi.org/10.1038/ncomms4104

add to favorites email to friend print save as pdf

Related Stories

Engineered materials: Custom-made magnets

May 24, 2012

A novel approach to designing artificial materials could enable magnetic devices with a wider range of properties than those now available. An international team of researchers have now extended the properties ...

Recommended for you

First direct observations of excitons in motion achieved

Apr 16, 2014

A quasiparticle called an exciton—responsible for the transfer of energy within devices such as solar cells, LEDs, and semiconductor circuits—has been understood theoretically for decades. But exciton ...

User comments : 0

More news stories

Thinnest feasible nano-membrane produced

A new nano-membrane made out of the 'super material' graphene is extremely light and breathable. Not only can this open the door to a new generation of functional waterproof clothing, but also to ultra-rapid filtration. The ...

Wiring up carbon-based electronics

Carbon-based nanostructures such as nanotubes, graphene sheets, and nanoribbons are unique building blocks showing versatile nanomechanical and nanoelectronic properties. These materials which are ordered ...

Hackathon team's GoogolPlex gives Siri extra powers

(Phys.org) —Four freshmen at the University of Pennsylvania have taken Apple's personal assistant Siri to behave as a graduate-level executive assistant which, when asked, is capable of adjusting the temperature ...

Better thermal-imaging lens from waste sulfur

Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight, plastic lenses for infrared devices, including night-vision goggles, a University of Arizona-led international team ...