The self-assembly of nanoparticles at interfaces

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Ligand-protected metal nanoparticles, which have been identified as a promising class of materials for emerging nanotechnologies, can now be synthesized with a myriad of size- and shape-tunable optical, electronic, and magnetic properties. Metal nanoparticle arrays on surfaces are under intense investigation for their potential in a variety of applications, ranging from nanophotonics to biomolecular sensing devices. A major hindrance to the realisation of these applications is the small number of accessible methods for making arrays with varying complexity and tunable spatial parameters.   Currently, the preparation of nanoparticle arrays faces two major challenges. First, they do not form lattices with long-range order; and secondly, control over nanoparticle spacing is limited to the thickness of the protective ligand shell coating. This research will address these challenges by studying the assembly of nanoparticle monolayers at the interface of water and a hydrophobic medium.  Nanoparticle core size, ligand size and temperature will be systematically explored for their influence on the self-assembly of single and multi-component arrays. Furthermore, the balance of interfacial forces between the nanoparticles and the water and hydrophobic media will be explored by changing the hydrophobicity of the ligand shell and/or the hydrophobic medium (i.e. air vs. oil). Simultaneous measurements of the film's collective optical properties will be used to track the film assembly process.  After transferring these films to solid substrates, electron microscopy and atomic force microscopy will be used to visualise the arrangement of individual nanoparticles within the films.   Elucidating the rules which govern nanoparticle self-assembly has several exciting consequences. The capability to assemble nanoparticle arrays with independent control over the nanoparticle size, shape, and spacing, is currently unprecedented. In doing so, one will gain access to either their individual or collective materials properties, as required by the application.