Active Plasmonics

Actuating nano transducers
Tiny charged particles of gold, are coated with a temperature-responsive polymer (pNIPAM) in the form of a gel. When these 'nano-engines' are heated above  temperature of 32Cwith a laser, they store large amounts of elastic energy in a fraction of a second, as the polymer coatings expel all the water from the gel and collapse. This has the effect of forcing the gold nanoparticles to bind together into tight clusters (dramatically changing their colour). But when the engines are cooled, the polymers instantly absorb water and expand, so the gold nanoparticles are strongly and quickly pushed apart, like a spring. This produces the larges forces yet seen on the nanoscale, which we are looking to harness for building nanomachines.

Key paper: Ding et al., PNAS (2016); DOI:  10.1073/pnas.1524209113 

Studying resistive switches with light
Resistive switching memories (RRAMs) are non-volatile memory cells based on the fact that special types of insulator start to conduct if a high voltage is applied. A very small wire can be formed in the gap between the two electrodes of a cell by a current pulse applied across the electrodes, resulting in a vast reduction of the resistance. How the filament is created and what are the dynamics involved are still open questions. We use plasmon-enhanced light-matter interactions  to studying in real time the movements of individual atoms, and consequently the morphological changes occurring in these novel memory nano-devices.

Key paper: Di Martino et al., Small 12, 1334 (2016)

Biased plasmonics
Plasmonics is based on the oscillation of charges in a metal. We are developing techniques to add and subtract charges by applying an external voltage to metallic nanostructures, exploring the effects this has on the plasmonic behaviour of the system.
 

 Buckling film plasmonic metamaterials
The structural transformation due to buckling instabilities in elastomeric substrates is being exploited to actively control the optical properties of nanostructured gold-polymer hybrid materials. We design patterned environmentally-responsive hydrogel sheets that exhibit a reversible shape transformation via polymer swelling. This provides a novel platform for the active tuning of the surface plasmonic response, which can lead to the fabrication of optomechanic switches or new assembly tools.

stretchable plasmonics
Because plasmons have colours which exquisitely depend on nm-scale distances, combining metals with soft elastic materials allows us to create plasmonic devices which can be deformed to change colours.

quantum plasmonics
When two metal particles approach closer than 1nm, the quantum tunnelling of electrons from one to another starts to change the plasmonics. By developing a new way of measuring the colour of light in such nano-gaps, we show directly how quantum tunneling changes optics.