METAFLEX-Metamaterials on Flexible optically transparent substrate

Metaflex are flexible metamaterials in the optical regime and the EPSRC career acceleration fellowship EP (EP/I004602/1) is named after them. At the reviewing stage, Metaflex was considered a very ambitious and challenging project. Its success has so far been exemplary, as witnessed by several papers in international journals, invited contributions to international conferences and patent applications.

The main key findings follow the milestones and deliverables indicated in the work programme:

- Resonance in the visible: the first milestone, validating the concept of Metaflex, is the demonstration of optical resonance in the visible range, obtained realising metallic nanofeatures on a flexible substrate. This result was achieved in the early stages of the project and generated major impact both in the academic and non-academic community. Thanks to this achievement, Metaflex research received worldwide media coverage.

- Tailored optical response at the nanoscale: while flexibility allows for a post-fabrication modification of the shape of the system, for some applications it is desirable that the optical response would not change with the deformation of the topology. For this purpose we realised a metaflex sample that maintains the same filtering action independently on the direction and polarisation of incident light. The function is realised creating nanofeatures with control at a scale one order of magnitude smaller than the wavelength.

- Mechanical manipulation: we designed, fabricated and characterized a new filtering platform, based on the principle of Guided Mode Resonance on flexible. The filters consist of plasmonic nanofeatures realised on flexible polymer substrates, and work down to the visible range. In the associated publication we also exhibit an example proof-of-concept application by mounting the sample directly onto the end of a collimated fibre output. This progresses research on lab-on-fibre technologies, introducing an alternative to directly fabricating structures on the end of a fibre, and rather produce fibre terminating caps, which can be easily replaced by the end-user on a single fibre.

- Fabrication approach: In the fabrication front we have developed two hybrid approaches, which combine the reliability and accuracy of top down lithographic process with bottom up methods. In particular, we demonstrated the use of electron beam patterned self assembly monolayer as nanostructured mask for electrochemical deposition. This scheme allow fabricating multiple flexible samples starting from one single master, thus reducing the cost of the process. The other approach is based in the transfer and stamping of metallic ink made by silver nanoparticles, with lithographically defined nano-masters. This approach is extremely flexible and powerful, as it allow transferring metallic nano-pattern virtually on any surface with complex geometry and structure.