First-principles study of charge-transfer-plasmon-enhanced photoemission from a gold-nanoparticle-sodium-atom emitter

The plasmon-enhanced photoemission process significantly improves the quality of electron emission current, making it applicable for next-generation free-electron devices. However, classical descriptions are less suitable for understanding the interactions between plasmonic structures and other materials at the nanoscale. In this study, we investigate the underlying mechanisms and dynamics of a plasmonic emitter composed of a Au nanoparticle and a sodium atom using real-time time-dependent density functional theory. Calculation results reveal three interaction mechanisms, namely, a near-field enhancement effect, orbital hybridization, and chargetransfer plasmon, that strongly affect the emission behavior. Specifically, the presence of the charge-transfer plasmon leads to a substantial deviation of the excitation laser frequency and significantly enhances photoemission currents. The maximum emission current increases by more than twice compared to the excitation at the original resonance frequency of Au nanoparticles. This work provides a guidance for the practical construction and experimentation of plasmon-enhanced photoemission electron sources.