Electromagnetic Materials Group Opportunities
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Detailed study of zigzag metal gratings
An EPSRC-funded project supporting TWO PhD studentships from Summer 2009
Supervisors:  Prof. Roy Sambles and Dr. Alastair Hibbins

There have been many recent and exciting advances in photonics demonstrating that metallic structures can be patterned on the subwavelength scale to exhibit novel electromagnetic properties not found naturally.  While the term “metamaterial” has only recently been coined to describe these structures, perhaps the simplest example of a metamaterial is a metallic diffraction grating.  In these two EPSRC funded projects we wish to study for the first time zigzag gratings. These present an entirely new, and as yet completely overlooked type of metamaterial, the study of which will draw together the highly topical and active research areas of plasmonics and metamaterials.  This work will keep our team at the cutting edge of research in this area.

The research focus in the Electromagnetic Materials Group is on the interaction between light and matter, where we have a particularly strong interest in the fundamental study of electromagnetic materials that incorporate structure from the nanometre to centimetre scale.  Recent activities include, creating patterned metallic surfaces for control of surface waves, controlling the optical properties of molecules (including application to organic LEDs and lasers), understanding natural photonic materials (biomimetics), exploring bistable liquid crystals, plasmonics, probing ultrafast spin dynamics in nanomagnets, developing magnonics, exploring THz photonics (including carbon-based materials), and investigating other sub-wavelength structured metamaterials that exhibit novel electromagnetic properties.  We are interested in exploring the physics underlying new phenomena, and in developing ways to control these phenomena for applications.  Over the past twenty years, we have pioneered a wide range of novel surface plasmon studies at visible wavelengths, publishing nearly 100 scientific papers in this area.  We have also developed a collimated beam microwave apparatus, and have been exploring bound surface waves at microwave frequencies observing some extraordinary resonant phenomena, including designs for ultra-thin resonant absorbers.

PhD studentship 1. The use of Focussed Ion Beam fabrication and the development of fast modelling codes to study surface plasmons supported by zigzag gratings of silver and gold films.
PhD studentship 2.  The exploration of ‘designer’ surface plasmons on zigzag gratings in the microwave regime These gratings on the millimetre scale will be fabricated using three-dimensional printing technologies and metallising techniques.

The first studentship will use zigzag gratings to provide a mechanism for visible radiation to couple to the surface modes (surface plasmons) that exist on silver and gold films. However, at microwave frequencies, where metals are almost perfect conductors, no bound surface waves exist.  Therefore in the second project, we will rely on the perturbation of the surface itself to induce the necessary boundary conditions so that localised surface modes may now be supported.  Coupling to both traditional surface plasmons, and the microwave equivalent, will allow for an exploration of the modes' propagation and dispersion on surfaces with novel symmetries not previously considered, including those with chiral properties.  We therefore expect to observe an interesting polarisation response, with the surface able to couple both transverse magnetic and transverse electric radiation into surface modes, and potentially strong polarisation conversion from blazed gratings. We have already produced a theoretical treatment for the interaction of electromagnetic radiation with such a structure, and a vital part of the project will therefore be to develop this theory into a computer code.  This will not only allow for a comparison to the experimental data, but also an opportunity to discover the most interesting phenomena by quickly modelling the whole of parameter space associated with these exciting structures.  We will also utilise commercial numerical modelling software, which while much slower, will enable the researchers to optimise and study the structures from the outset.
The results from this study will help develop our understanding of surface waves, and it will open up potential for new optical and low frequency devices.  The possibility of designing a new type of structured metal surfaces with strongly resonant characteristics may lead to dichroic structures, optical filters, absorbers, resonant field enhanced structures and non-linear optics studies. In addition the metamaterial studies in the microwave domain will be of direct relevance to our colleagues at QinetiQ, BAE Systems and Dstl.

samples

(left) Three simple zigzag grating structures: (a) symmetric zigzag; (b) ‘blazed’ zigzag; and (c) oblique ‘blazed’ zigzag.

These two studentships are funded by the EPSRC and each offer tuition fees and a maintenance grant in accordance with Research Council eligibility criteria, and they are available from Spring/Summer 2009. The project offers tuition fees and a maintenance grant in accordance with Research Council eligibility criteria. Please contact Prof Roy Sambles or Dr Alastair Hibbins for more information. Applications should be made using the online procedure, and should include a CV, publications list and contact details for two professional referees. Please also send a copy of your cover letter to Dr Alastair Hibbins (a.p.hibbins@ex.ac.uk), School of Physics, University of Exeter, Exeter, EX4 4QL. UK