Photogeneration of hot plasmonic electrons with metal nanocrystals: Quantum description and potential applications

Abstract

The paper reviews physical concepts related to the collective dynamics of plasmon excitations in metal nanocrystals with a focus on the photogeneration of energetic carriers. Using quantum linear response theory, we analyze the wave function of a plasmon in nanostructures of different sizes. Energetic carriers are efficiently generated in small nanocrystals due to the non-conservation of momentum of electrons in a confined nanoscale system. On the other hand, large nanocrystals and nanostructures, when driven by light, produce a relatively small number of carriers with large excitation energies. Another important factor is the polarization of the exciting light. Most efficient generation and injection of high-energy carriers can be realized when the optically induced electric current is along the smallest dimension of a nanostructure and also normal to its walls and, for efficient injection, the current should be normal to the collecting barrier. Other important properties and limitations: (1) intra-band transitions are preferable for generation of energetic electrons and dominate the absorption for relatively long wavelengths (approximately >600 nm), (2) inter-band transitions efficiently generate energetic holes and (3) the carrier-generation and absorption spectra can be significantly different. The described physical properties of metal nanocrystals are essential for a variety of potential applications utilizing hot plasmonic electrons including optoelectronic signal processing, photodetection, photocatalysis and solar-energy harvesting.