Jen Dionne 2012-2013 Seminar Series
March 6, 2013
Metallic nanoparticles support strong, localized oscillations of conduction electrons – surface plasmons – that have recently enabled significant improvements in photovoltaic and photocatalytic cell efficiencies. While considerable research has investigated the potential for somewhat larger plasmonic particles (>20 nm) to enhance solar energy conversion, most catalytic reactions rely on the high catalytic activity of very small metallic particles. In this presentation, we explore the plasmonic and catalytic properties of such small metallic nanoparticles, with the aim of using plasmons to both monitor and enhance catalytic reactions. We first investigate the plasmon resonances of individual nanoparticles as their sizes are reduced from 20 nm down to less than 2 nm. We find that plasmon resonances are influenced by quantum confinement effects for particles smaller than 5 nm. Then, we study the photocatalytic activity of individual metal nanoparticles coated with titania. Shifts of the plasmon resonance probe addition or removal of electrons during a redox reaction, providing insight into charge-separation mechanisms. Finally, we explore the potential to achieve broadband solar absorption in photocatalytic and photovoltaic systems using upconversion. Calculations indicate that upconverting materials can significantly improve cell efficiencies, and we develop the experimental techniques to realize high-efficiency upconversion by tailoring the optical density of states via plasmonics and the electronic density of states via pressure measurements. Our single-particle measurements unravel the interplay of particle structure and function, and provide a platform for enhancing future photocatalytic and photovoltaic systems.