Colloquium: Ultrafast hot electron generation in graphite and Ag nanocluster/graphite heterojunctions
Electronic heating of cold crystal lattices in nonlinear multiphoton excitation can transiently alter their physical and chemical properties. In semimetal graphite and its derivatives, strong optical absorption, weak screening of the Coulomb interaction, and high cohesive energy enable extreme hot electron generation and thermalization to be realized under femtosecond laser excitation. We study the hot electron generation in clean and Ag nanoparticle decorated graphite surfaces by ultrafast time-resolved multiphoton photoemission. The ineffective screening in clean graphite leads to nearly instantaneous hot electron thermalization that produces hot electron temperatures comparable to the solar photosphere on ~25 fs time scale.1 Decoration of graphite by Ag nanoparticles offers the possibility to further enhance the hot electron generation by excitation of Mie plasmons of Ag/graphite heterojunctions. The plasmonic enhancement is observed, but the charge-transfer doping of graphite by metal nanoparticles leads to some surprising effects.
1. Tan, S.; Argondizzo, A.; Wang, C.; Cui, X.; Petek, H., Phys. Rev. X 2017, 7, 011004.