Plasmonic Hot Carriers—Materials and Devices

Highly absorbing, plasmonic metal nanostructures offer a promising route to relax the challenging constraints imposed on semiconducting photocatalysts by both light-absorption and band-alignment conditions. In fact, it has been recently demonstrated that plasmon non radiative decay generates highly energetic hot carriers that can be transferred to either an adjacent semiconductor (sensitization) or an adsorbed molecule, in the latter case altering the chemical reaction pathway. Hence plasmonic hot carriers turn metallic nanostructures into novel photocatalysts and can have a dramatic impact for solar fuel applications [1]. To adequately harness these energetic, non-equilibrium carriers, fundamental knowledge of their energy distributions, dynamics and associated lifetimes is necessary.<br/>In this talk I will show how the synergistic combination of experiments and theory is critical to correctly unravel the fundamental mechanisms occurring in non-equilibrium devices while guiding the choice of materials and the design of the devices. Indeed, while measurement of plasmonic devices give access to integral quantities, theory provides the otherwise missing microscopic picture. For example, to-date experimental studies of hot carrier devices have focused almost entirely on the exploitation of hot electrons to produce a photocurrent or initiate a chemical reaction. In contrast, there have been very few realizations of hot-hole based plasmonic devices and the dynamics of hot holes in metal nanostructures have remained largely unknown, despite the favorable energetics of hot holes predicted by ab-initio calculations.<br/>First, I will report the construction, optoelectronic and photoelectrochemical characterization of plasmon-driven photocathodes based on a metal/p-type gallium nitride (p-GaN) heterostructure that operate within the visible regime via hot-hole injection. In particular I will discuss how the metal band structure and hot carrier properties determine their collection efficiency [1,2] demonstrating the peculiarities of d-band metals, such as gold and copper, under visible illumination. Importantly, I will show that the performance of hot electron and hot hole devices is fundamentally limited by different processes [2]. Subsequently, I will show how plasmonic hot carriers can alter the selectivity of solar-to-fuel energy conversion via plasmonic hot-carriers [3,4] using either gold or copper nanoparticles. In order to unravel the complex mechanisms at play in these photoelectrochemical devices, I will present ultrafast transient absorption spectroscopy data that demonstrate the occurrence of ultra-fast hot-hole injection across the metal/semiconductor interface and an unexpected prominent effect of hot-hole removal onto the thermalization dynamics of hot-electrons in the metal [5]. This first part will thus provide a perspective of the impact of plasmonic nanostructures for solar fuel generation, in particular CO2 reduction.<br/>Next, I will highlight some emerging opportunities for plasmonic hot carriers from both the material and application perspectives [6].<br/>References<br/>[1] G Tagliabue, AS Jermyn, R Sundararaman, AJ Welch, JS DuChene, R Pala, AR Davoyan, P Narang, HA Atwater, Nature Comm. 9 (1), 3394<br/>[2] G Tagliabue, JS DuChene, A Habib, R Sundararaman, HA Atwater ACS Nano 2020, 14, 5, 5788–5797<br/>[3] JS DuChene*, G Tagliabue*, AJ Welch, WH Cheng, HA Atwater, Hot Hole Nano letters 18 (4), 2545-2550<br/>[4] JS DuChene, G Tagliabue, AJ Welch, X Li, WH Cheng, HA Atwater, Nano Lett. 2020, 20, 4, 2348–2358<br/>[5] G. Tagliabue*, JS. DuChene*, M. Abdellah*, A. Habib, Y.Hattori, K.Zheng, SE Canton, DJ Gosztola, W.H Cheng, R. Sundararaman, J Sá, HA Atwater, Nature Materials volume 19, pages1312–1318(2020)<br/>[6] E. Cortés, L.V. Besteiro, A.Alabastri, A.Baldi, G. Tagliabue, A. Demetriadou, P. Narang ACS Nano 2020, 14, 12, 16202–16219<br/>[7] F. Kiani, G. Tagliabue*, submitted.