IMX Colloquium - From Nanoscale Interfaces to Macroscale Devices: Soft Photonics for Large Areas

Modern devices require the tuning of the size, shape and spatial arrangement of nano- objects and their assemblies with nanometre scale precision, over large-area and sometimes soft substrates. Such stringent multi-scale and mechanical requirements are beyond the reach of conventional lithography techniques or simpler self-assembly approaches.

In this talk, at first, we will demonstrate an unprecedented control over the fluid instabilities of thin optical-glass and polymer films as a simple approach for the self-assembly of advanced all-dielectric metasurfaces. We show and model the tailoring of the position, shape, size and inter-particle distance of nano-objects with feature sizes below ten nanometres. This simple and versatile approach can generate optical nanostructures over tens-of-centimetres sized rigid and soft substrates, with better optical performance and a resolution on par with advanced lithography-based processes. By having unprecedented control over the lattice and particle size via a simple nanoimprinting process, we demonstrate sharp Fano resonances with the highest Quality factor of ~300 visible to date. We also observe high-purity structural colors covering an extended gamut of spectra.

In the second part, we will show a recent result from our lab, whereby by tuning the thermal coeeficient of expansion of the substrate and the thin film we obtain large area periodic structures whose optical properties can be tuned dynamically. As a proof of concept we show simple mechnaochromic devices as well as camouflage effect with such materials.

In the third part of the talk I will discuss how by exploiting fluidic interaction of liquid metals and uncured oligomer in soft substrates, we obtained structural colors with Gallium based liquid metal nanospheres, paving the way toward a novel paradigm in soft photonics and large area reflective displays. By tuning and optimizing a range of experimental parameters, and the choice of substrate material we obtain vibrant coloration encompassing a wide range of chromaticity coordinates due to the varying size distribution of controlled Ga nanodroplets.

As a proof-of-principle, we show pallets of structural colors of the films derived from this process. Reflective display technology can benefit greatly by leveraging the advantages of structural colors over its pigmented counterparts. The application of the thus-fabricated device exhibits mechanochromic sensing, which has been characterized to be of high fidelity and reliability, functionalized by exploiting the fluidic properties of Gallium. For at least 1000 cycles of uniaxial stretching and relaxing with a periodicity of 50 seconds, the reflectivity spectrum of the sample for a given strain was unchanged, thus proving the reliable reconfiguration of sample response to the application and removal of mechanical strain. The reversible change in the reflectivity spectrum results in the chromaticity coordinates of the sample, hence a visible change in the sample color. Our results can offer opportunities to dynamically reconfigure thin-film-based functional nanodevices in situ and process technology for high throughput fabrication to achieve the same in a single-step method.
Ref:
1. Das Gupta, T., Martin-Monier, L., Yan, W. et al. Self-assembly of nanostructured glass metasurfaces via templated fluid instabilities. Nat. Nanotechnol. 14, 320–327 (2019). https://doi.org/10.1038/s41565-019-0362-9
2. Sahu, R.R., Ramasamy, A.S., Bhonsle, S. et al. Single-step fabrication of liquid gallium nanoparticles via capillary interaction for dynamic structural colours. Nat. Nanotechnol. 19, 766–774 (2024). https://doi.org/10.1038/s41565-024-01625-1
3. Das Gupta, T., Martin-Monier, L., Butet, J. et al. Second harmonic generation in glass-based metasurfaces using tailored surface lattice resonances. Nanophotonics. 10 (2021). https://doi/10.1515/nanoph-2021-0277
4. Biswas, S., Sahu, R.R., Shinkre, O.D.N. et al. Tailored Thin Films: Modulating Soft Photonics with Dynamically Tunable Large Area Microstructures via Controlled Thermal Processing. Arxiv. (2025). https://doi.org/10.48550/arXiv.2501.05736
5. Sahu, R.R., Das Gupta, T. Real-time tuneable bright bonding plasmonic modes in Ga nanostructures. Arxiv (2025). https://doi.org/10.48550/arXiv.2504.04922

Bio: Tapajyoti Das Gupta obtained his BSc and Btech in Physics and Radio physics respectively from University of Calcutta in 2006 and 2009. He then moved to France where he obtained his MSc in nanoscience from École Polytechnique (l’X) in 2012 and PhD in Condensed Matter Physics lab (PMC) from the same institute in 2015 under Prof. Thierry GACOIN and Alistair ROWE. He then joined prof. Fabien Sorin’s lab of Fiber Optics and Photonics Devices (FIMAP) in École Polytechnique Fédérale de Lausanne (EPFL) during 2015 December-2019 November. He is currently an assistant professor in the Department of Instrumentation and Applied Physics in Indian Institute of Science, Bangalore from July 2020. His research interest includes finding solution to fabricate large area metasurfaces and photonic devices for applications including displays, holography, instrumentation and image processing.