We study the plasmonic enhancement of hot electron generation, by measuring the ultrafast
electron spectroscopy and dynamics at Ag nanocluster-decorated graphite and TiO2 surfaces by timeresolved
multiphoton photoemission (mPP) spectroscopy. Deposition of Ag onto the supporting
substrates produces small (5 nm dia., 1 nm high) Ag nanoparticles that support Mie plasmon
resonances of the metal nanoparticle-support system. Excitation of the plasmonic modes greatly
enhances the mPP yields over the bare substrates [1-3]. Analysis of the mPP spectra and hot electron
relaxation rates show that hot electrons are generated directly in the substrates by dephasing of the
plasmon resonances. This is possible because the plasmon resonances are electronically, optically, and
chemically coupled with the substrates. The coupling of molecules with the plasmonic modes causes
modification of the plasmon resonances and the mPP yields. We also find direct coherent photoinduced
electron transfer from Ag nanoclusters to graphite [4]. The probing of ultrafast polarization and hot
electron dynamics reveals the energy and charge coupling at plasmonic heterojunctions.

Tan, S., Argondizzo, A., Wang, C., Cui, X., & Petek, H. Ultrafast Multiphoton Thermionic
Photoemission from Graphite. Phys. Rev. X 7, 011004 (2017).
2 Tan, S., Liu, L., Dai, Y., Ren, J., Zhao, J., & Petek, H. Ultrafast Plasmon-Enhanced Hot
Electron Generation at Ag Nanocluster/Graphite Heterojunctions. J. Am. Chem. Soc. 139,
6160-6168 (2017).
3 Tan, S., Argondizzo, A., Ren, J., Liu, L., Zhao, J., & Petek, H. Plasmonic coupling at a
metal/semiconductor interface. Nature Photon 11, 806-812 (2017).
4 Tan, S., Dai, Y., Zhang, S., Liu, L., Zhao, J., & Petek, H. Photoinduced Coherent Electron
Transfer at Ag/Graphite Heterojunctions. Phys. Rev. Lett. (in press).