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Research

Nanophotonics

When designing any new technology, component sustainability is a high priority. This is especially true for plasmonic-based technologies, where it is often the case that high laser powers are focused onto relatively small materials. One example of this can be found in near-field transducers (NFTs) used for heat-assisted magnetic recording (HAMR). HAMR is on the cusp of becoming the next magnetic-recording technology, and will allow for higher writing densities. However, the use of HAMR is currently limited by significant heating of the NFT, which results in its deformation and melting. In order to make HAMR a viable option for magnetic recording, it is necessary to understand laser-induced heating and damage of plasmonic materials.

Currently, our work focuses on the effects of cw-laser illumination on Au thin films. Films of different thicknesses are manufactured on different substrates via e-beam evaporation, and their behaviour is investigated using a 488nm cw-laser. It has been found that, even at relatively low laser powers, cw-illumination can cause the formation of delamination fronts in aged Au films. Delamination is a process by which a thin film decouples from its substrate due to poor adhesion. It happens once the stress caused by the mismatch between the substrate and the film becomes greater than the film-substrate interface strength. This has the potential to drastically affect the properties of plasmonic materials, and, even more critically, may affect the long term stability of devices. The delamination fronts increase in size for as long as the area is illuminated. Initial growth speed is power dependant, but settles to a constant speed soon after. The thermal profile of the front can be mapped via the change in reflectivity across the area, and the height profile can be obtained via profilometric measurements.

On the other end, we are also working on obtaining such highly focused spots for technological applications. Plasmonic waveguiding and focusing is used for this purpose. Currently we are working on long range plasmonic modes of metal-insulator-metal (MIM) waveguides tapered down to few tens of nanometres.

Darkfield image of circular delamination fronts induced by cw-laser

Schematic of a MIM waveguide and the taper structure