Energy and Momentum Distribution of Surface Plasmon-Induced Hot Carriers Isolated via Spatiotemporal Separation

• Published in: ACS nano Vol. 15; no. 12; pp. 19559 - 19569
• Main Authors: Hartelt, Michael, Terekhin, Pavel N., Eul, Tobias, Mahro, Anna-Katharina, Frisch, Benjamin, Prinz, Eva, Rethfeld, Baerbel, Stadtmüller, Benjamin, Aeschlimann, Martin
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 28.12.2021
• Subjects: 2-photon photoemission; PEEM; plasmon-induced hot carriers; momentum microscopy; surface plasmon polariton
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/acsnano.1c06586

Understanding the differences between photon-induced and plasmon-induced hot electrons is essential for the construction of devices for plasmonic energy conversion. The mechanism of the plasmonic enhancement in photochemistry, photocatalysis, and light-harvesting and especially the role of hot carriers is still heavily discussed. The question remains, if plasmon-induced and photon-induced hot carriers are fundamentally different or if plasmonic enhancement is only an effect of field concentration producing these carriers in greater numbers. For the bulk plasmon resonance, a fundamental difference is known, yet for the technologically important surface plasmons, this is far from being settled. The direct imaging of surface plasmon-induced hot carriers could provide essential insight, but the separation of the influence of driving laser, field-enhancement, and fundamental plasmon decay has proven to be difficult. Here, we present an approach using a two-color femtosecond pump–probe scheme in time-resolved 2-photon-photoemission (tr-2PPE), supported by a theoretical analysis of the light and plasmon energy flow. We separate the energy and momentum distribution of the plasmon-induced hot electrons from that of photoexcited electrons by following the spatial evolution of photoemitted electrons with energy-resolved photoemission electron microscopy (PEEM) and momentum microscopy during the propagation of a surface plasmon polariton (SPP) pulse along a gold surface. With this scheme, we realize a direct experimental access to plasmon-induced hot electrons. We find a plasmonic enhancement toward high excitation energies and small in-plane momenta, which suggests a fundamentally different mechanism of hot electron generation, as previously unknown for surface plasmons.