Supervisors: Dr Donald McLaren, University of Glasgow and Dr Fumin Huang, Queen's University Belfast

The aim of this project is to explore the potential of ‘bottom-up’ patterning of nanostructured materials for the production of industrially-relevant plasmonic nanostructures. Rather than using conventional ‘top-down’ lithographic patterning to define the geometry of plasmonic elements, this project will explore the self-assembly of nanoparticles to produce complex, even fractal, structures in a cost-efficient manner. The project will involve aspects of synthesis, modelling and characterisation and will be operated in close collaboration with researchers at Laboratoire Aimé Cotton (Orsay, France), who have long-standing interest in exploiting the complex structures formed by nanoparticle self-assembly. A key outcome will be a critical assessment of the performance of self-assembled and fused nanoparticle assemblies for the production of the intense electromagnetic fields required for heat-assisted magnetic recording.

Synthesis and deposition of silver nanoparticle assemblies will be conducted independently in Orsay. The research team of Nouari Kebaili have previously developed protocols for the formation of vapour-phase Ag nanoparticles with well-defined size and geometries [1]. These are then deposited onto graphitic and graphene substrates at low energy, and left to diffuse and aggregate under dispersion forces to form self-assembled complex nanostructures, whose size and form can be controlled. By tailoring the deposition conditions and nature of the substrate, it is possible to produce dendritic, fractal assemblies in a controlled manner [1,2].

The main focus of the project will be physical characterisation of the nanoparticle assemblies, principally by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) [3], which will be conducted in Glasgow. What is interesting is that little is known of the nature of plasmonic resonances in the as-deposited assemblies. For example, although the coupling of one and two nanoparticles has been described, coupling of the plasmonic resonances of a complex assembly is less understood. There are, however, good prospects for the strong scattering of incident radiation from fractal structures to enhance energy transfer and lead to improved device efficiency [4]. The project will be extended to consider the use of patterned substrates to provide discrete, well-defined nucleation sites for nanoparticle aggregation in periodic arrays, using the substantial lithographic and patterning capabilities at both Queen’s and Glasgow Universities. A further avenue of research will be to monitor plasmonic responses while as-deposited nanoparticles are heated and fuse together. There are also prospects to engage with the UK’s national electron microscopy facility, SuperSTEM, to conduct monochromated EELS studies, which are anticipated to be world-leading. All of these studies will be informed by modelling the plasmonic response of prototypical coupled nanoparticles using a variety of theoretical tools.

[1]   Eur. Phys. J. D 16 (2001), 265.

[2]   Phys. Stat. Solidi (b)03 (2014) 251.

[3]   Optics Letters 38 (2013) 13680.

[4]   J Phys: Conf. Ser. 644 (2015) 012005.