Engineering optical properties in materials is an extremely challenging exercise to any materials researcher, and it is particularly so, to those in the business of fine-tuning matter on the nanoscale level.
The whole process involves first the daunting task of identifying the right material for the experiment, fabricating them with suitable methods that are not considered too expensive, later characterizing them for oscillations in electron densities so as to understand how the material responds to the electromagnetic fields, and in the final step, assess above research data carefully to figure out as to what aspects of the structure or the composition of the material we can change that would give the material the property we desire.
Isobel Bicket, a PhD student under Prof. Gianluigi Botton has investigated optical properties of a new kind of material called the 'split ring resonators', which had been previously reported to be 'extremely complex to fabricate'. The Split ring resonators, are basically materials that have been artificially produced to have stronger magnetic coupling than is found in nature. This pronounced magnetic response in such lightweight materials demonstrates an advantage over heavier, naturally occurring materials.
Isobel et al fabricated these materials out of gold (Au) in a 3-dimensional structural model (as opposed to planar forms reported earlier) (see Figure above). For this they had to pay a careful consideration to a number of different factors during the Electron Beam Lithography (EBM) based synthesis.
Although a number of techniques are available to study magnetic responses in such structures (e.g., using photons, electrons etc… to excite the material), Isobel says that the real challenge for them was to be able to capture all the resonant modes during the excitation process (technical known as, Plasmon resonance).
Thanks to the sophisticated instrumentation available at the Canadian Center for Electron Microscopy (Hamilton, Canada) and the AMOLF Institute (Amsterdam), Isobel et al were able to couple both the features of electron-spectroscopy and cathodoluminescence techniques. This allowed them to spatially locate the intensities of different plasmon modes on the 3D structure of the sample. See full details at https://tinyurl.com/y8whj9qk.
With a growing interest in designing such fascinating new materials for a number of applications, the authors think that the analytical methods they have devised can help researchers better understand their optical responses, thus further allowing them to then tailor the material properties to suit the end-user applications.