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Towards nanoscale reality in plasmonic hot-carrier generation

Periodic Reporting for period 1 - RealNanoPlasmon (Towards nanoscale reality in plasmonic hot-carrier generation)

Reporting period: 2019-04-01 to 2021-03-31

The development of renewable energy technologies is crucial for the goal of a global sustainable society. For reaching this goal, solar energy technologies that rely on the efficient utilization of abundant sunlight play an important role. To this end, plasmon-enhanced processes enabled by metal nanoparticles provide particularly promising avenues for harvesting sunlight.

Plasmon-enhanced technologies are based on metal nanoparticles that support localized surface plasmon resonances. Thanks to these resonances, metal nanoparticles exhibit large photoabsorption cross-sections, which makes them efficient light absorbers. Upon light absorption, the absorbed energy is confined in the nanometer-scale volume of the nanoparticle, and a particularly attractive approach for utilizing this energy is through plasmonic catalysis. In this process, the plasmon resonance decays on a femtosecond timescale, creating high-energy electrons and holes, so-called hot carriers. These plasmon-generated hot carriers could trigger chemical reactions in molecules adsorbed on the nanoparticle surface, turning metal nanoparticles into solar-to-chemical energy converters.

Detailed understanding of plasmonic hot-carrier generation at the atomic scale is highly important for plasmonic catalysis as chemical reactions take place at this size scale. In this spirit, the main objectives of this project were to develop computational first-principles methods for addressing plasmonic hot-carrier generation with atomistic resolution and to gain understanding of the atomic-scale effects on plasmonic hot-carrier generation by utilizing the developed methods. These aims were achieved in the project and the developed understanding and methods form a basis for further explorations of atomic-scale contributions.
In the project, computational first-principles methods and tools were developed for analyzing the atomic-scale distribution of plasmon-generated hot carriers. The results obtained with the developed tools suggest that the distribution of hot-carriers can vary significantly at the atomic scale. In the analyzed prototypical noble metal nanoparticles, surface sites exhibit enhanced hot-electron generation in comparison to the nanoparticle as a whole, which is emphasized for high-energy hot electrons as their energetic distributions vary substantially between different atomic sites.

Multicomponent systems that combine plasmonic metals with catalytic materials are of particular interest for applications in plasmonic catalysis. The plasmonic responses of such multicomponent nanosystems were analyzed in collaborative projects from two different viewpoints. First, a multiscale approach was applied for large nanoparticles allowing comparing calculated results with experimental data. Second, an atomic-level description was applied for atomic clusters providing estimates for the effect of individual atoms on the response of clusters. Together, these results form a strong foundation for analyzing plasmonic hot-carrier generation in realistic multicomponent nanoparticles.

To approach plasmonic catalysis, hybrid systems composed of metal nanoparticles and molecules adsorbed on them were analyzed. When the plasmon resonance in the nanoparticle and the molecular excitation overlap and couple strongly, the hybrid system exhibits distinct polaritonic excitations. Such strong plasmon-molecule coupling was modeled during the project, demonstrating the description of the formation of strongly coupled excitations through first-principles calculations. Direct hot-carrier generation on an adsorbate molecule was also analyzed within the supervision training activities of the project.

The research was carried out according to FAIR principles. The results of the project are published in high-profile scientific journals and are openly accessible. The generated data are also publicly available as open-access data sets. The developed codes for performing the analysis and reproducing the data have also been released as open-source software. The results were also presented in international conferences, but the COVID-19 pandemic changed many of the initial conference plans.
The project produced results beyond the state of the art in the field of plasmonic catalysis by analyzing the importance of atomic-scale effects on plasmonic hot-carrier generation. These results have potential impact for optimizing plasmonic catalytic processes for utilizing renewable solar energy or improving industrial catalytic processes. The potential impact of the project is amplified by the open-source publication of the developed methods and tools, accelerating their subsequent application to further in-depth explorations of atomic-scale effects on plasmonic hot-carrier generation beyond the scope and duration of this project. In addition, the openness of the performed research has a general societal impact by contributing to equal opportunities for practising science and utilizing scientific results.