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Chemical Approach to Scalable Fabrication of Hybrid Plasmonic Materials in the Strong-Coupling Regime

Periodic Reporting for period 1 - SHINE (Chemical Approach to Scalable Fabrication of Hybrid Plasmonic Materials in the Strong-Coupling Regime)

Reporting period: 2020-04-01 to 2022-03-31

The overall objective of the action is the development of nanostructured materials for the study and exploration of the strong-coupling regime, where light-matter interaction can be used to modify the energy landscape of the system and influence its emission properties and surface chemistry.
The acquired knowledge will serve as a solid base for the development of opto-electronics, opto-mechanics, and catalyst of new-generation, with important implication for society both in energy production and storage, synthesis of new molecules, and more efficient communication systems.

More specifically we aim at preparing ordered plasmonic arrays, where the repeating unit is represented by either a single or a cluster of gold/silver nanoparticles. These type of substrates enable the constructive coupling of the plasmon resonance of each repeating unit exploiting the diffraction of the array, resulting in the generation of lattice plasmon resonances that are characterized by long lives and spatial delocalization, that is translated in sharp features in the extinction profile that can be tuned varying both the nature of the repeating unit (size shape and number of plasmonic nanoparticles) as well as the geometrical parameters of the system (period of the array, illumination angle etc.).

The implementation of these structures inside strong-coupling architecture has been very limited so far. We hypothesized that the use of colloidal bulding blocks in combination with template-assisted self-assembly would enable a level of control over the chemistry of the system never achieved before using standard lithographic methodologies.
During the 8 months of the action we were able to achieve three main objectives.

1) on one side we explored a completely different methodologies for the self-assembly of colloidally synthetized plasmonic building blocks into ordered arrays. More specifically, we adapted the concept of chemical lift-off lithography in order to covalentely link plasmonic nanoparticles to patterned elastomeric molds, ensuring that only the patterned areas were able to lift-off gold nanoparticles from a gold-nanoparticle monolayer. Using this technique we were able to demonstrate the fabrication of linear gratings, chiral patterns, and single nanoparticle manipulation.
This work was published in the peer-reviewed journal "ACS Materials Letters" (expected Q1) with the following DOI: 10.1021/acsmaterialslett.0c00535. Moreover, these results have been presented in 2 different occasions:
- MCAA 2020 Annual Conference (Poster Contribution)
- Invited seminar at the Soft Matter seminar series at the University of Paris Orsay (France).


2) we explore the role of nanoparticle size on the optical properties of plasmonic arrays fabricated by templated self-assembly. We discovered that by reducing the nanoparticle diameter we are able to modulate the near-field and far-field coupling contribution. By maximizing the first (using bigger colloids) one is able to fabricate devices characterize by intense electric field regions that can be use for sensing or photothermal therapy. By maximizing the far-field coupling on the other hand, we demonstrated the fabrication of plasmonic arrays exhibiting lattice resonances with quality factors above 60, among the highest reported in the literature to date.
This work was published in the peer-reviewed journal "Advanced Optical Materials" (Q1) with the following DOI: 10.1002/adom.202100761. Moreover, these results have been presented in 3 different occasions:
- Photonics Online meetings (Poster Contribution)
- "Self-Organization at All Scales" symposium at the nanoGE Spring Meeting 2021(Poster Contribution)
- Conferencia Española de Nanofotónica – CEN2021 (Oral Contribution)

3) the fellow contributed to the exploration of high quality factor plasmonic resonance in copper structures. This contribution was published in the peer-reviewed journal "Nano Letters" (Q1) with the following DOI:10.1021/acs.nanolett.0c04667

Finally, the fellow designed an experimental setup for introducing plasmonics in high-school setups, with the objective of sparking scientific curiosity in the young minds of children and students attending the events. The work resulted in a publication in the Journal of Chemical Education (2020), DOI:10.1021/acs.jchemed.0c01150

The MC fellow set-up a synthetic platform that allowed the group to take advantage of his skills in the preparation of high quality plasmonic colloids. This enable to group to be self-sufficient in the fabrication of the building blocks, and therefore add a new level of control over the optical properties of the prepared devices. On the other hand, the fellow familiarized with all the soft-lithographic techniques that are routinely used within the group, and learnt how to properly and rationally setup an experiment on the optical bench, exploring different types of measurement such as extinction, photoluminescence, or circular dichroism.
The fellow was able to exploit the MC action towards the development of an independent research line, and is now in the process of securing funding for the creation of his own research group.
We were able to demonstrate the highest quality factor reported to date for ordered plasmonic arrays prepared by self-assembly of colloidal building-blocks. Moreover, our findings underline the importance of controlling the internal structure of the repeating unit in order to manipulate light-matter interaction within the array, and generate new interesting optical properties. We already have several ongoing project moving in this direction.

From a socio-economic and societal standpoint, our findings will help identifying a more sustainable and scalable approach for the integration of plasmonics and photonics units into devices and sensors. This moves us one step forward towards achieving full control over light emission processes at the nanoscale, a long sought goals of our society, with important implications in our quest for cleaner energy sources, faster communication systems and an overall more sustainable future. In particular, the possibility of having access to high quality factor resonances using colloidal system can have important implication for the design of novel heterogeneous catalyst, and for interesting optoelectronic and lighting applications such as lasing or photodetection.
Arrays of plasmonic metamolecules made with different Au colloids controlling near field coupling