Dr Kishan Menghrajani
PhD ProjectExcitonics: an organic route to Metamaterials
Many electromagnetic metamaterials are based on metallic elements (meta-atoms) – they make use of the plasmonic modes these elements support. Metals are well suited to this purpose owing to the negative permittivity they possess. The plasmon modes associated with this negative permittivity have the important property that their associated electromagnetic fields are confined to volumes much smaller than the resonant (plasmon) wavelength; one can thus pack many plasmonic elements into a sub-wavelength volume, thereby enabling metamaterials to be made. Other materials may also exhibit negative permittivity – an interesting and little explored class of such materials are excitonic materials such as some dye-doped polymers. Here we will explore the use of such materials as a means to make metamaterials. We have already shown that nanostructures of dye-doped polymers may support localised (excitonic) electromagnetic modes (Nano Lett., 14, 2339 (2014)), enabling optical fields to be confined and enhanced in just the same way that metals afford through the (plasmonic) electromagnetic modes they support. This is a very new area – largely unexplored. We will investigate: how to nanostructure excitonic materials, look at the localised modes supported by these nanostructures, and then explore how these individual structures may be assembled so as to build metamaterials. The properties of these metamaterials will then be investigated, including multilayer structures and arrays of excitonic meta-atoms. In the latter stages of the project we may explore the possibility of assembling them from sustainable materials such as cellulose doped with naturally occurring dyes.