Noble metal nanoparticles find use as catalysts in, for example, sensing, energy technology, and environmental clean-up applications. The structural and compositional complexity of such nanosized systems offers many degrees of freedom for tuning their catalytic, as well as other such as mechanical or optical/plasmonic, properties. Nevertheless, structural heterogeneity at the individual particle level is still prevalent in most studies, which commonly use billions of particles at a time. This heterogeneity hampers deeper understanding of how particle size, shape and composition affect their catalytic activity and selectivity, as these parameters directly determine the active sites exposed to the reactants. Revealing such behavior, as well as identifying champion or spectator nanoparticles, requires single nanoparticle-level measurements. To this end, impressive advances have been made in the last years, and a number of approaches now exist that can monitor processes on single nanoparticles, including electrochemical methods, single molecule fluorescence microscopy, plasmonic nanospectroscopy, X-ray microscopy, and surface-enhanced Raman spectroscopy.
However, because of this recent methodological progress, it has also become apparent that one of the major remaining bottlenecks in the development of these and other techniques is the challenge to position the nanoparticles rationally and precisely on the surface. This is the consequence of the fact that – to date – shape- and size-selected nanoparticles are first made by colloidal synthesis in suspensions and then self-assembled, or randomly deposited, onto the substrate surface. On one hand, this provides access to the exquisite chemical control offered by colloidal synthesis, which produces sophisticated nanoparticles in terms of morphology, faceting, and composition, which often express a single-crystal character. On the other hand, and as the key point here, it comes with a significant inherent lack of control during nanoparticle deposition on the substrate once the synthesis is completed.
Hence, recognizing that all existing nanofabrication and synthesis approaches independently have severe limitations, but that they collectively would satisfy all the key requirements necessary for the fabrication of nanocrystal arrays, it was the main aim of this project to develop strategies in which both nanofabrication and colloidal synthesis methods are synergistically combined into a new paradigm. Specifically, the aim was to first use nanolithography to define arrays of relatively simple particles (seeds) on a surface and subsequently transform them through colloidal chemistry into more sophisticated nanostructures. It was also the aim of this project to make these nanostructured surfaces compatible with a plasmonic nanospectroscopy platform to monitor catalytic processes at the single-particle level.
