Browsing by Author "Ras, Robin H.A., Prof., Aalto University, Department of Applied Physics, Finland"

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    Noble Metal Nanoparticles and Clusters - From Basic Concepts to Novel Functionalities
    (Aalto University, 2016) Hassinen, Jukka; Teknillisen fysiikan laitos; Department of Applied Physics; Soft Matter and Wetting; Perustieteiden korkeakoulu; School of Science; Ras, Robin H.A., Prof., Aalto University, Department of Applied Physics, Finland
    Noble metal nanoparticles and clusters are some of the most fascinating materials of contemporary nano-focused science. This thesis focuses on the synthesis and functionalization of three different noble metal nanomaterial systems: atomically precise gold clusters, plasmonic gold nanoparticles, and few-atom silver clusters. In publication I, mixed-monolayer-protected atomically precise Au25 cluster cores having a variable amount of bulky calix[4]arene moieties were synthesized. A mixed ligand feed was used directly in the cluster synthesis to simultaneously facilitate the binding of bulky ligands and the size-focusing of cluster cores. In publication II, thin-layer chromatography (TLC) was established as a feasible method for precise separation of binary mixtures of Au25L18 clusters with different ligands (L), as well as a binary mixture of different cluster sizes, protected with the same ligand. TLC even allowed a separation of mixed-monolayer-protected clusters differing only slightly in their composition. In publication III, a novel method was developed for functionalization of plasmonic gold nanoparticles with positively charged ligands. This two-step phase-transfer method allows rapid cationization of simple citrate-capped gold nanoparticles in the size range 8−20 nm. These cationic gold nanoparticles formed electrostatic self-assemblies with virus particles, thus demonstrating their ability to bind large biomolecules. In publication IV, cationic gold nanoparticles were combined with negatively charged cellulose nanocrystals. This mixture forms colloidal state electrostatic assemblies in which the inherent twist of the nanocrystals leads to chiral positioning of the gold nanoparticles and thus to the emergence of a chiral plasmonic signal. In publication V, the synthesis of silver clusters was demonstrated in a solid polymer thin film by direct laser writing. Direct laser writing with a tightly focused near-infrared femtosecond laser beam produced highly photostable submicrometer-scale fluorescent structures in thin films of silver-containing poly(methacrylic acid). The results of this thesis offer new approaches to the synthesis and functionalization of noble metal clusters and nanoparticles. One of the most significant discoveries was the realization of TLC as an efficient method for separation of gold clusters. In addition, positively charged gold nanoparticles with tunable size were successfully prepared and used in electrostatic self-assemblies that exhibit plasmonic properties. All in all, the findings of this thesis extend the knowledge of previous research and suggest applicability of these nanomaterials at various developing areas.