More information
Description
If current production and waste management trends continue, it is projected that roughly 12 billion metric tons of plastic waste will be in landfills or in the natural environment by 2050. Plastics represent a significant environmental problem: They are for the most part not biodegradable, cause problems for terrestrial and aquatic life, and enter the food chain in the form of microplastics. .
Photonic sensors are ideally suited for material sorting due to the spectroscopy technique, which allows for discrimination between different polymer types by illuminating with near infrared electromagnetic fields and measuring absorption. An important development goal is to make such spectroscopy simple, affordable and energy efficient. The ElastoMETA project aims to design and fabricate functional nanostructured surfaces, known as metasurfaces, to meet these goals. These surfaces contain simple subwavelength nano-structures that can shape light which is transmitted through them. Despite their simplicity, they offer a new paradigm for advanced field manipulation due to unprecedented control of phase, polarization, amplitude and dispersion of the electromagnetic fields. The versatility of this approach is evident by the short time during which numerous realizations have been made: e.g. micro-lenses, filters, couplers, emitters and even holograms. With further development, metasurfaces are expected to have several advantages over existing optical sensor technologies for recycling applications (e.g. diffractive optics), in terms of (i) increased efficiency, (ii) relative ease of fabrication, and (iii) enhanced functionality.
Summary of project results
Responsible consumption and production are imperative tasks for the research community, industry, and governments, as recognized by the United Nation''s Sustainable Development Goals for 2030. The goal of eradicating poverty while the population continues to grow is not sustainable under the current linear economy which generally depletes natural resources and leaves behind negative footprints under “take-make-dispose” production and consumption.
Therefore, there is a growing need for a circular economy, which instead, achieves sustainability through Reducing, Reusing, and Recycling, inspired by the cyclical pattern of nature. An important goal is the efficient recycling of plastics. It was estimated that 6.3 billion metric tons of plastic waste has been generated since large-scale production began in the 1950s, of which only 9% has been recycled.
In this context, photonic sensors have the benefit of long-term use and stability in the detection of plastics. Metasurfaces have recently received significant attention in this field due to their ability to shape transmitted or reflected light arbitrarily. The goal of ElastoMETA was to develop metasurface designs and nanostructuring processes for tuneable and efficient microlenses and Infrared (IR) sources – i.e. the two central components of a spectroscopic sensor.
The project intended to achieve developments at the forefront of photonics and nanotechnology towards commercial sensor applications for a competitive Romanian and Norwegian industry. Therefore, the outputs of the project are:
i. Metasurfaces at industry-relevant cost: low-cost, large-area nano-patterning methodologies (UV-NIL) were used for the realization of metasurfaces with high-precision masks prepared by Electron beam lithography (EBL) compared to EBL methods for the generation of nanostructures of different dimension and orientation;
ii. New principles of active tuning introduced to sensors for plastic detection: These nanostructure surfaces have been embedded in a polymeric matrix for flexible sensors with application in plastic detection. Another supplementary result was using the piezoelectric MEMS technology to assure tunability.
iii. Improvement of efficiency of microsensor components: Metasurface lenses and sources have been investigated towards achieving higher efficiency through reduced diffraction losses and directionality in the emission of IR sources. More information can be found at https://elastometa.ro/.
The ElastoMETA project aimed to bring value to its research field, industry, and society. The project has demonstrated that metasurface concepts can be used for commercialization. The knowledge gained from the project can be considered a competitive advantage for the plastic detection industry towards developing smaller and more cost-effective sensors without compromising performance. With this development, it will be possible to have distributed sensor systems for plastic sorting. This will allow waste sorting on a much larger level, facilitating a circular economy.
For the above purpose, the most significant achievements were: (i) the fabrication of diffraction-limited dielectric metasurface lenses for the near-infrared domain (NIR) using standard industrial high-throughput silicon processing techniques: UV-NIL combined with reactive ion etching (RIE) and pulsed Bosch or cryogenic deep reactive ion etching (DRIE). The resulting metalenses achieved high efficiencies of 50-52% compared to the theoretical limit of around 69% at wavelength λ = 1.55 μm; (ii) the demonstration that metasurfaces can have multiple functionalities using analytical expression and numerical simulations or (iii) that the thermal emittance of a metasurface consisting of an array of rectangular metallic meta-atoms patterned on a layered periodic dielectric structure using standard fabrication methods can be tuned by changing several parameters.
Summary of bilateral results
The bilateral relations were strengthened due to the planned activities. All the partners have interacted with each other. The PP and P1 (Norwegian partner) have worked together to develop the optical set-up in both countries, acquiring the same IR camera, and discussing UV- NIL: resists, masks, stamps, and process parameters. The P1 and P2 have interacted together in terms of the etching procedure, as can be seen from the joint papers. There were multiple meetings between the PP, P1, and P2 in terms of fabrication processes. Also, the P1 and P3 have interacted in terms of simulations and finally, all the partners have interacted especially for the IR thermal emitters. The project was a continuous interaction between the partners. The bilateral relationship is demonstrated by the new Water4all project, involving the PP, P1, and P2 teams. However, the lower funding for Romania excluded the P3 partner. Overall, the project has facilitated equal working conditions for Romanian and Norwegian partners.