Periodic Reporting for period 4 - FLOWTONICS (Solid-state flow as a novel approach for the fabrication of photonic devices)
Reporting period: 2020-08-01 to 2021-07-31
The development of advanced photon-based technologies offers exciting promises in fields of crucial importance for the development of sustainable societies such as energy and food management, security and health care. Innovative photonic devices will however reveal their true potential if we can deploy their functionalities not only on rigid wafers, but also over large-area, flexible and stretchable substrates. Indeed, providing energy harvesting, sensing, or stimulating abilities over windows, screens, food packages, wearable textiles, or even biological tissues will be invaluable technological breakthroughs. Today, however, conventional fabrication approaches remain difficult to scale to large area, and are not well adapted to the mechanical and topological requirements of non-rigid and curved substrates. In FLOWTONICS, we propose innovative materials processing approaches and device architectures to enable the simple and scalable fabrication of nano-structured photonic systems compatible with flexile and stretchable substrates. Our strategy is to direct the flow of optical materials through innovative and so far unexplored exploitation of the solid-state dewetting and thermal drawing processes. Our objectives are three-fold: (1) Study and demonstrate, for the first time, the strong potential of the dewetting of chalcogenide glasses layers for the fabrication of large area photonic devices; (2) Show that dewetting can also be exploited to realize photonic architectures onto engineered, nano-imprinted flexible and stretchable polymer substrates; (3) Demonstrate, for the first time, the use of the thermal drawing process as a novel tool to realize advanced flexible and stretchable photonic ribbons and fibers. These novel approaches can contribute to game-changing scientific and technological advances for the sustainable management of our resources and to meet our growing health care needs, putting Europe at the forefront of innovation in these crucial areas.
In the course of the FLOWTONICS ERC Starting grant project, we have reached all the objectives and milestones that we set in our initial proposal. Here I summarize the achievement following the structure of the proposed work plan:
Part 1: template dewetting of photonic structures
We have demonstrated for the first time the control over fluid instabilities of optical glass thin films to realize state-of-the-art nanophotonic structures over large area, soft and rigid substrates. We could model and experimentally demonstrate the self-assembly of a variety of optical nanostructures with feature sizes down to 10 nm (Figure 1a&b). We demonstrate this process on a variety of Chalcogenide glasses that can be used as optical waveguides, for their non-linear optical properties, their phase change and optoelectronic properties, as well as in sensing and metasurfaces (Figure 1c).
These achievements fulfill the objectives set in Part 1 of the project, and part 2.1. This study has led to one paper in Nature Nanotechnology presenting the science and potential of this novel ano-processing approach. We also published a second paper going more deeply into the fluid dynamic modeling in Physical Review Applied, and one in Nanophotonics demonstrating dewetted structures for nonlinear optics. IP is also being protected for this methodology.
Note that we also went beyond the original objectives of the proposal by applying these principles to liquid metals (Figure 1d&e). Two papers (Adv. Funct. Materials and Science Advances) came out of this approach where thanks to texturing we could control how liquid metal film can self-organize.
Part 2: Large area and flexible photonic nanostructures
The objectives regarding textured and nanowire based electronic and optoelectronic devices were tackled in two projects, that built upon the initial objectives but went beyond with an original fabrication of nanowires:
Sub-micrometer textured fibers:
We proposed a first original concept of combining soft nano-imprinting of thermoplastic plates with their thermal drawing. This work has led to a publication in Advanced Functional Materials (27, 1605935 (2017)) that received a lot of press, and presented in top international conferences. A patent was also submitted.
Nanowire-based optoelectronic fibers:
We have proposed a novel approach to grow nanowires not during thermal drawing but post-drawing. We demonstrated, for the first time, the integration of high quality single crystal semiconducting nanowire-based optoelectronic devices at the tip and along the length of polymer optical fibers.
This work led to a paper in Advanced Materials (29, 1700681 (2017)), and presented at several international conferences such as MRS, Spring Meeting 2017 and CLEO 2018.
Part 3: Nanostructured flexible and stretchable photonic fibers and ribbons
Part 3 proposed to expand the range of materials compatible with the thermal drawing to elastomers. Surprisingly, despite more than 50 years of exploitation of the thermal drawing process, it could never be applied to elastomers. We have been able to alleviate this limitation and demonstrate that some thermoplastic elastomers (TPEs) can be compatible with the multi-material thermal drawing process. We also identified functional materials such as thermoplastics, polymer nano-composites or liquid metals that can be co-drawn within such TPEs matrices in three-dimensional (3D) micro-structured architectures of unprecedented complexity. We showed examples of advanced fibers that can act as highly stretchable (up to 500 % strain) electronic or optical interconnects, or robust pressure or strain sensors, combining high performance and multiple embedded functionalities.
The results we obtained were published in Advanced Materials (30, 1707251 (2018)), which received a lot of press (see for example https://actu.epfl.ch/news/an-elastic-fiber-set-to-revolutionize-smart-clothe/(opens in new window)). Several other papers resulted from this first studies, with novel pressure sensing fibers (Adv. Fucnt. Materials publication, Figure 2a to c)) and the first soft trnasmissionlines for sensing (paper in Nature Electronics, Figure 2 d to h). We also submitted a patent and received an ERC PoC proposal to further investigate the potential commercialization of this novel technology. As we explain in other part of this final report portal, this work has led to a partnership with a company to further exploit these novel fibers.
Part 1: template dewetting of photonic structures
We have demonstrated for the first time the control over fluid instabilities of optical glass thin films to realize state-of-the-art nanophotonic structures over large area, soft and rigid substrates. We could model and experimentally demonstrate the self-assembly of a variety of optical nanostructures with feature sizes down to 10 nm (Figure 1a&b). We demonstrate this process on a variety of Chalcogenide glasses that can be used as optical waveguides, for their non-linear optical properties, their phase change and optoelectronic properties, as well as in sensing and metasurfaces (Figure 1c).
These achievements fulfill the objectives set in Part 1 of the project, and part 2.1. This study has led to one paper in Nature Nanotechnology presenting the science and potential of this novel ano-processing approach. We also published a second paper going more deeply into the fluid dynamic modeling in Physical Review Applied, and one in Nanophotonics demonstrating dewetted structures for nonlinear optics. IP is also being protected for this methodology.
Note that we also went beyond the original objectives of the proposal by applying these principles to liquid metals (Figure 1d&e). Two papers (Adv. Funct. Materials and Science Advances) came out of this approach where thanks to texturing we could control how liquid metal film can self-organize.
Part 2: Large area and flexible photonic nanostructures
The objectives regarding textured and nanowire based electronic and optoelectronic devices were tackled in two projects, that built upon the initial objectives but went beyond with an original fabrication of nanowires:
Sub-micrometer textured fibers:
We proposed a first original concept of combining soft nano-imprinting of thermoplastic plates with their thermal drawing. This work has led to a publication in Advanced Functional Materials (27, 1605935 (2017)) that received a lot of press, and presented in top international conferences. A patent was also submitted.
Nanowire-based optoelectronic fibers:
We have proposed a novel approach to grow nanowires not during thermal drawing but post-drawing. We demonstrated, for the first time, the integration of high quality single crystal semiconducting nanowire-based optoelectronic devices at the tip and along the length of polymer optical fibers.
This work led to a paper in Advanced Materials (29, 1700681 (2017)), and presented at several international conferences such as MRS, Spring Meeting 2017 and CLEO 2018.
Part 3: Nanostructured flexible and stretchable photonic fibers and ribbons
Part 3 proposed to expand the range of materials compatible with the thermal drawing to elastomers. Surprisingly, despite more than 50 years of exploitation of the thermal drawing process, it could never be applied to elastomers. We have been able to alleviate this limitation and demonstrate that some thermoplastic elastomers (TPEs) can be compatible with the multi-material thermal drawing process. We also identified functional materials such as thermoplastics, polymer nano-composites or liquid metals that can be co-drawn within such TPEs matrices in three-dimensional (3D) micro-structured architectures of unprecedented complexity. We showed examples of advanced fibers that can act as highly stretchable (up to 500 % strain) electronic or optical interconnects, or robust pressure or strain sensors, combining high performance and multiple embedded functionalities.
The results we obtained were published in Advanced Materials (30, 1707251 (2018)), which received a lot of press (see for example https://actu.epfl.ch/news/an-elastic-fiber-set-to-revolutionize-smart-clothe/(opens in new window)). Several other papers resulted from this first studies, with novel pressure sensing fibers (Adv. Fucnt. Materials publication, Figure 2a to c)) and the first soft trnasmissionlines for sensing (paper in Nature Electronics, Figure 2 d to h). We also submitted a patent and received an ERC PoC proposal to further investigate the potential commercialization of this novel technology. As we explain in other part of this final report portal, this work has led to a partnership with a company to further exploit these novel fibers.
The major results we presented above are all going significantly beyond state of the art. All the results discussed in the part above, and in the other parts on the portal were obtained during the project and already have publications and patents applications associated to them. The one thing to mention here is that just at the end of the project, we tackled the last remaining objective, the proposed scheme to combine dewetting and thermal drawing to generate micro and nanowires in-fiber at prescribed positions. Based on our improved understanding of dewetting, we tackled this objective 2.3 from the action plan and are writing a manuscript. The results we obtain go significantly beyond state-of-the-art by integrating complex nanowire based device via a dynamic self-assembly process during fiber drawing. This will generate optoelectronic fibers with performance on par with their 2D counterparts. The integration of such fibers into smart fabrics will be a natural conitunation of this achievement.