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What happens to electrons in a metal when they are illuminated? This fundamental problem is a driving force in shaping modern physics since the discovery of the photo-electric effect. In recent years, this problem resurfaced from a new angle, owing to developments in the field of nano-plasmonics, where metallic nanostructures give rise to resonantly enhanced local electromagnetic fields (surface plasmons). Presumably, these plasmons can transfer their energy to the electrons in the metal very efficiently, creating “hot electrons”, i.e. energetic electrons out of equilibrium. In a series of high-impact papers, such energetic electrons have been experimentally demonstrated to be useful in a variety of ways, most recently in catalysis of chemical reactions.
Or have they?
In this talk we argue that what appears to be hot-electron-mediated photo-catalysis is really a simple heating effect. We present a theory for plasmonic hot-electron generation, which takes into account non-equilibrium as well as thermal effects, thus going well beyond the limit of existing theories. Calculating the efficiency of hot-electron generation, we find that it is extremely small, and most power goes into heating. We use this theory to re-interpret data from central experiments claiming hot-electron generation, and show that the data fits remarkably well (and with minimal number of fit parameters) a simple theory of heating. Invoking Occam’s razor, this implies that these highly-cited papers were wrong in their interpretation of the data. We underline a series of (sometimes horrific) experimental errors that are responsible for this misinterpretation, and suggest control experiments to further test our conclusions.
[1] Y. Sivan, J. Baraban, I. W. Un & Y. Dubi, Comment on "Quantifying hit carrier and thermal contributions in plasmonic photocatalysis", Science 364, eaaw9367 (2019).
[2] Y. Dubi & Y. Sivan, "Hot" electrons in metallic nanostructures - no -thermal carriers or heating? Nature Light: Science & Applications 8, 89 (2019)
[3] Y. Sivan, I. W. Un & Y. Dubi, Thermal effects - an alternative mechanism for plasmonic-assisted photo-catalysis, Chem. Sci., 2020, 11, 5017-5027
[4] Y. Sivan, J. Baraban & Y. Dubi, Eppur si riscalda -- and yet, it (just) heats up: Further Comments on "Quantifying hot carrier and thermal contributions in plasmonic photocatalysis", OSA Continuum 3, pp. 483-497 (2020).
[5] Y. Dubi & Y. Sivan, Assistance of metal nanoparticles to photo-catalysis - nothing more than a classical heat source, Faraday Discussions 2019, 10.1039/C8FD00147B.
