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Active Metamaterials

An overview of the group's research into active metamaterials.

Metamaterials are a new sort of optical material constructed from nano-engineered elements

Nano Engineering StructuresMetamaterials are built from individual elements, designed to mimic the electromagnetic response of atoms. Stacking many nano-engineered elements smaller than the wavelength of light makes new solid materials. Such materials have extremely unusual properties, such as negative refractive indices to focus light much smaller than its wavelength (super-lensing), or electromagnetic cloaking (of an object).

Current Work

R2R      Roll-to-roll (R2R) large-area nano-assembly

We are developing a new R2R kit for large area assembly of active metamaterial nanostructures in a collaboration between the Institute for Manufacturing, Chemistry, and NanoPhotonics.

Self-assembling Scalable Gyroid MetamaterialsSelf-assembling gyroid metamaterials
Scaffolds of block co-polymers built of organic molecules can be induced to separate into nanoscale compartments, creating large-area gold or silver meta- materials. Unit cells are tuned from 30-60nm, and individual struts are 10nm across. A wide variety of optical properties are produced, including enhancing photovoltaics and sensing.

Key papers:
Dolan et al., Adv.Opt.Mat. 3, 12 (2015).
Farah et al., Phys.Rev.App. 2, 044002 (2014).

Optical woodpileOptical woodpile metamaterials
Three dimensional stacked gold nanowires can be produced by stamping grooves into ultrathin plastic layers and coating with metal at an angle. By stacking and rolling multiple layers, new metamaterials can be created over large areas.

Key paper: Ibbotson et al., Sci.Rep. 5, 8313 (2015)

Fexible Elastic Coloured MirrorsFlexible elastic coloured mirrors
By folding sub-micron plastic transparent layers, we create multilayers which selectively reflect specific colours of light. By making these elastic, and pressurising such bubbles, we make balloons with chromatic hearing: they change colour on stretching.

Roll-up Scalable MetamaterialsRoll-up scalable metamaterials
Since metamaterials for visible light require sub-100 nm sized elements, their fabrication has been expensive, time-consuming, and only available in miniscule amounts. Using a new technique in which ultra-thin metal and polymer bi-layers are floated onto the surface  of water and then rolled up, we have made new metamaterials in which light can propagate anisotropically.

Metallo-dielectric StacksMetallo-dielectric stacks
Using the roll-up technique, we fabricate stacks of nm-thick metals that trap light in successive layers. Light is confined in different parts of the structure, and can be flipped by injecting a pulse of light.

Nano-pillar Array Metamaterial FiltersNano-pillar array metamaterial filters
Using arrays of coated silicon or carbon nanotube pillars, optical filters with different properties can be constructed.
StretchDBRFoldingFlexible polymer multilayers
Colours can be produced by absorption from dyes (as in our clothes and possessions) or the selective reflection of specific colours of light inside structures on the same size as the wavelength of light. Multilayers made from alternately stacking two transparent materials around a tenth of a micron thick give this effect, reflecting a band of colours depending on the exact layers dimensions. However such structures cannot be tuned easily.
StretchDBRStretchable colour materials
By using two different transparent rubber polymers that can be precisely coated on top of each other, we make large area sheets of double layers that can then be stacked to form multilayers in a number of ways once they have been floated free onto the surface of water. The double sheets can be cut and stacked, or folded on top of each other, or rolled up into a tube.
StretchDBRHolesBeyond 10 double layers, the films gain a strong colour in reflection. Because the films are elastic, they can be stretched and since this changes the layer thicknesses, the films change colour. We have made red films which can be reversibly extended by >50% tuning right into the blue.

Previous work:

[4] S. Vignolini , N. A. Yufa , P. S. Cunha , S. Guldin , I. Rushkin , M. Stefi k , K. Hur , U. Wiesner , J.J. Baumberg , U. Steiner, Advanced Materials (2011); DOI:10.1002/adma.201103610

[3] G. Kamita, M. Kolle, F. Huang, J. J. Baumberg, U. Steiner, Optics Express 20, 6421 (2012)

[2] N. Gibbons, J. J. Baumberg – Phys. Rev. B 85, 165422 (2012)

[1] “Scalable Cylindrical Metallo-dielectric Metamaterials”, N. Gibbons, J.J. Baumberg, C.L. Bower, M. Kolle, U. Steiner, Advanced Materials 21, 3933 (2009). [pdf]

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