Ballistic Thermal Injection: a new mechanism to transfer energy across interfaces and control plasmon absorption published in Nature Nanotechnology – Congrats John Tomko!

Congrats John Tomko for his recent first author paper in Nature Nanotechnology on:

Long-lived modulation of plasmonic absorption by ballistic thermal injection

Current citation until volume and page number are assigned: Tomko, J.A., Runnerstrom, E.L., Wang, YS. et al. Long-lived modulation of plasmonic absorption by ballistic thermal injection. Nat. Nanotechnol. (2020).

In this work, in a collaboration with Penn State (Maria Group), Vanderbilt (Caldwell group), U. Southern California (Prezhdo Group), we demonstrate a new heat transfer mechanism across interfaces in which energy can flow from a metal to a non-metal without the flow of charge. This occurs when the electron energy in the metal is traveling ballistically, and thus injects its heat into the non-metal. We use this new mechanism to control the infrared plasmsonic response of doped CdO, a novel mid-IR plamonic material with strong ENZ mode abosorption.


Light–matter interactions that induce charge and energy transfer across interfaces form the foundation for photocatalysis, energy harvesting and photodetection, among other technologies. One of the most common mechanisms associated with these processes relies on carrier injection. However, the exact role of the energy transport associated with this hot-electron injection remains unclear. Plasmon-assisted photocatalytic efficiencies can improve when intermediate insulation layers are used to inhibit the charge transfer or when off-resonance excitations are employed, which suggests that additional energy transport and thermal effects could play an explicit role even if the charge transfer is inhibited8. This provides an additional interfacial mechanism for the catalytic and plasmonic enhancement at interfaces that moves beyond the traditionally assumed physical charge injection. In this work, we report on a series of ultrafast plasmonic measurements that provide a direct measure of electronic distributions, both spatially and temporally, after the optical excitation of a metal/semiconductor heterostructure. We explicitly demonstrate that in cases of strong non-equilibrium, a novel energy transduction mechanism arises at the metal/semiconductor interface. We find that hot electrons in the metal contact transfer their energy to pre-existing free electrons in the semiconductor, without an equivalent spatiotemporal transfer of charge. Further, we demonstrate that this ballistic thermal injection mechanism can be utilized as a unique means to modulate plasmonic interactions. These experimental results are well-supported by both rigorous multilayer optical modelling and first-principle ab initio calculations.

We acknowledge funding from the US Department of Defense, Multidisciplinary University Research Initiative through the Army Research Office, Grant no. W911NF-16-1-0406. J.R.N. and J.D.C. appreciate support from the Office of Naval Research, Grant no. N00014-18-1-2107.

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