Martin Moskovits
Plasmons, Hot Electrons and Artificial Photosynthesis
Surface plasmons – collective conduction electron excitations in nanostructured metals and other good conductors – live for a few femtoseconds. On dephasing, they produce a shower of energetic electrons and holes that equilibrate adiabatically over 10-100 femtoseconds to form a Fermi distribution with electron temperatures of several thousand K. Most of the energy of this hot electron gas is subsequently thermally dissipated over a few picoseconds through electron-phonon interactions. By fabricating nanostructured devices with appropriately constructed interfaces a fraction of these hot carriers can be harvested before they thermalize, and used to carry out light-enabled redox chemistry. To do this efficiently one needs to design and construct materials and systems with appropriate dielectric properties, and bulk and interfacial structures and architectures that permit sufficient charge carriers to be extracted irreversibly in the handful of picoseconds during which they are “hot”. One also needs to adapt (or design anew) an appropriate suite of catalytic materials that willingly collaborate with the plasmonic system and the electrons (and holes) that are produced by them, allowing sunlight to be harvested in this novel way and used to power the photosynthesis of fuels or other valuable compounds. Although the problem seems formidable, remarkable progress has recently been achieved by multiple research labs across the globe, some examples of which will be presented and discussed.