The implementation of new technologies harnessing plasmonic effects depends strongly on improving our capacity to reliably and economically produce complex structures from nanoscale metallic building blocks. Unfortunately, the organization of large quantities of nanomaterials via ?bottom-up? strategies that are scalable, cost-effective and that achieve precise structure control is still limited. This project will research a new strategy to assemble complex structures from nanoparticle building blocks by exploiting local steric repulsion and short-ranged attraction. In this new approach, the formation of structured clusters or will be controlled through the use of engineered nanoparticle surfaces containing mixtures of end-grafted polymers to regulate steric repulsion and small functional molecules to induce attraction. Steric repulsion and attractive interactions will be precisely adjusted by altering the surface composition to control particle assembly and to manipulate the morphology of the multi-particle structures. Diverse colloidal clusters with controllable optical and electronic properties will be generated using this robust strategy. Small angle scattering of x-rays and neutrons will be used to selectively probe the nanoparticle configuration (SAXS) and the conformation of the polymers (SANS) in order to develop a complete and self-consistent description of the assembly process. Structural experiments will be complemented by direct comparisons to simulations. The primary goals of the project will be to: 1) Experimentally determine the role of polymer interactions in mediating nanoparticle self-assembly 2) Reduce the structural polydispersity of self-assembled clusters 3) Predict equilibrium cluster structures with Monte Carlo simulations and 4) Increase the structural diversity of colloidal molecules. Achieving these objectives will contribute significantly to the advancement of plasmonic applications that utilize nanoparticle clusters.
Plasmonic technologies exploit the unique interactions between visible light and delocalized electron clouds in small metallic particles. For example, plasmonic effects are used to develop sensors for the rapid identification of trace amounts of chemicals and environmental contaminants in complex samples. They also advance less invasive and more effective medical diagnostic and treatments tools such as photoacoustic imaging and photothermal cancer therapy. Plasmonic approaches are also used to develop advanced solar cells that are more efficient and less expensive than current technologies. Nonetheless, the successful deployment of these and other applications requires significant advances in the scalable fabrication of nanostructures with controllable optical and electronic properties. This project will research a new approach that is suitable to fabricate large numbers of plasmonic nanomaterials while maintaining accurate structure control and with methods that are scalable, robust and versatile.
