Illustration of a plasmon-mediated photocatalytic reaction

How hot are plasmonic hotspots?

Thursday 19 Nov 20
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by Tom Nervil

Contact

Shima Kadkhodazadeh
Senior Researcher
DTU Nanolab
+45 45 25 64 94
Solutions based on renewable sources of energy are urgently needed, not just in the transportation sector but also in the chemical industry, where numerous products we rely on are produced.

In a project newly granted by Villum Experiment senior researcher at DTU Nanolab Shima Kadkhodazadeh addresses, how plasmonic nanoparticles can be the vehicles for efficiently harvesting sunlight to fuel chemical reactions. A perfect example of using sunlight to fuel chemical reactions is the photosynthesis process in plants. The goal in photochemistry is to mimic this with the aid of photocatalysts. 

Challenging the traditional methods

Traditional photocatalysts, such as TiO2, suffer from low efficiency (absorbing only ~ 5% of the solar spectrum) and lack of tunability. Recently, the idea of plasmon-mediated photochemistry has been proposed. Surface plasmon resonances (SPRs) are light-induced coherent motion of conduction electrons in noble metal nanoparticles (NPs), which are capable of confining light to nanometre-scale dimensions (hotspots). Unlike conventional photocatalysts, SPR’s response can be tuned across the entire solar spectrum via NP size, shape, dielectric environment and coupling between neighbouring NPs. As SPRs decay, their energy gets converted into phenomena, such as electron-hole generation or heat, that can promote chemical reactions. 

While encouraging initial results are emerging, questions exist regarding the role of the generated electrons/holes and phonons in reaction pathways and their interplay. These effects are confined to nanoscale spaces and hence, analyzing them requires tools with orders of magnitude better resolution than the size of the hotspots. This precludes optical methods, as they are constrained by the diffraction limit of light (~ 200 nm). 

Finding a new way

“To overcome the limit of light, this project proposes a setup based on a dual electron/photon-beam in a transmission electron microscope (TEM), in which light is used to induce reactions and an Ångström-size electron beam is used to study them,” Shima Kadkhodazadeh says.

Shima Kadkhodazadeh is well aware of the challenge and the opportunities.

“It will tackle the challenge of visualizing and quantifying complex photochemical processes live and on the atomic level, by constituting a TEM as the chamber, where both gases and light can be injected,” she says. 

The DTU Nanolab senior researcher is sure that the results will give unprecedented insight into the role of thermal and non-thermal processes in plasmon-mediated chemical reactions and contribute to the design of structures with optimal photo-reactivity. 

Fact

The project has been granted by Villum Experiment with 2 mio. kr.
The Villum Experiment Programme supports unorthodox ideas in their early phase. It has been created for research projects in technical and natural sciences that challenge the norm and have the potential to change the way we approach important subjects. The applicants are anonymous to the international assessors to increase the focus on the research ideas and to let the researchers think freely.

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