Periodic Reporting for period 3 - PrISMoID (Photonic Structural Materials with Controlled Disorder)
Periodo di rendicontazione: 2022-09-01 al 2024-02-29
The way colour arises from materials is seemingly well known. In the vast majority of cases (natural as well as manufactured), pigments absorb part of the optical spectrum. In nature, so called “structural colour” is also wide-spread. Rather than absorbing part of the visual optical spectrum, light interference from 100-nm-scale structures separates different optical dispersion in transmission and reflection. While this is qualitatively known for more the 100 years, there is still a controversy about the requirements for these structures. Perfectly regular periodic transparent structures have a well defined, brilliant colour signature (“optical band gap”), while disordered morphologies randomise the light paths though the material, giving rise to the “colour” white.
Surprisingly, many organisms, e.g. many birds, produce a brilliant colour response from seeming disordered morphologies made from transparent materials. From a physics point of view, these colours must also arise from a certain level of interference of the light waves within the material, which requires structural correlations. In other words, there must be an interplay of order and disorder in the bird-feather structures to account for their coloured appearance.
It is the purpose of PrISMoID to discover the rules that underly this order-disorder interplay, provide a theoretical description for the phenomenon, and develop manufacturing approaches to create coloured materials that make use of the discovered structural “blue-print”.
The PrISMoID project will provide a new way to create colour. One approach that is being pursued is to create “photonic pigments”. These are small spheres that have an internal structure that are coloured though the oder-disorder mechanisms described above. Since these can be made from any transparent material, they can replace brightly coloured “traditional” pigments, which are often toxic or give rise to adverse health conditions.
The main objectives of PrISMoID are subdivided into four phases. The first phase consists of the establishment of the experimental and theoretical techniques required for the PrISMoID. This includes in particular the acquisition and analysis of 3D data on the sub-100 nm length scale. In the second phase these techniques are employed in analysis ordered and disordered photonic morphologies in various biological specimens, both in animals and plants.
Surprisingly, many organisms, e.g. many birds, produce a brilliant colour response from seeming disordered morphologies made from transparent materials. From a physics point of view, these colours must also arise from a certain level of interference of the light waves within the material, which requires structural correlations. In other words, there must be an interplay of order and disorder in the bird-feather structures to account for their coloured appearance.
It is the purpose of PrISMoID to discover the rules that underly this order-disorder interplay, provide a theoretical description for the phenomenon, and develop manufacturing approaches to create coloured materials that make use of the discovered structural “blue-print”.
The PrISMoID project will provide a new way to create colour. One approach that is being pursued is to create “photonic pigments”. These are small spheres that have an internal structure that are coloured though the oder-disorder mechanisms described above. Since these can be made from any transparent material, they can replace brightly coloured “traditional” pigments, which are often toxic or give rise to adverse health conditions.
The main objectives of PrISMoID are subdivided into four phases. The first phase consists of the establishment of the experimental and theoretical techniques required for the PrISMoID. This includes in particular the acquisition and analysis of 3D data on the sub-100 nm length scale. In the second phase these techniques are employed in analysis ordered and disordered photonic morphologies in various biological specimens, both in animals and plants.
The project has proceeded according to plan.
The first phase of the project focussed on two aspects.
1. Two techniques focussing on the acquisition and analysis of 3D morphologies were established. This involved the optimising the "slice-and-view" methodology of the focussed-ion-beam – scanning electron microscopy technique (FIB-SEM). One particular challenge that needed to be overcome is the fragile nature of photonic chitin and carotin morphologies of the studied biological and the fact that this morphologies a porous, which makes the faithful reconstruction of the specimen difficult. This was addressed by using a gas-injection depositing PT into the pores, stabilising it and substantially enhancing the fidelity of the FIB-SM reconstruction.
2. To make progress with the scientific questions of the PrISMoID project during the establishment of the FIB-SEM method, first experimental studies focussed on beetles that have differently coloured scales. In the studied organisms, differently coloured scales feature ordered, partially ordered disordered morphologies within them. These studies allowed first qualitative conclusions about the role of disorder in the scales and their colour response.
The second phase of the PrISMoID project employed the developed FIB/SEM methodology to study organisms with different photonic morphologies. These results are currently on the descriptive level.
Employing the developed 3D imaging techniques, two types of organisms were studied, one type with a 3D co-continuous network and the other with a colloid-like packing.
Work on WP2has also commenced, but was somewhat delayed through Covid lock-downs during the past two years. Work in the WP is seasonal, and required the cultivation of flowering plants, which is carried out by the botanical gardens in Fribourg.
In terms of manufacture (WP3), work has started on the creation of "photonic pigments", which are a promising approach towards the scalable implementation of the results of the ERC-funded project. The initial phase is making use of ordered structures (as a proof-of-principle). First disordered photonic pigments have also been created.
Concerning WP4, the students have even trained in the numerical modelling and the comparison of its result with optical experiments. This is now routinely employed in all projects.
The first phase of the project focussed on two aspects.
1. Two techniques focussing on the acquisition and analysis of 3D morphologies were established. This involved the optimising the "slice-and-view" methodology of the focussed-ion-beam – scanning electron microscopy technique (FIB-SEM). One particular challenge that needed to be overcome is the fragile nature of photonic chitin and carotin morphologies of the studied biological and the fact that this morphologies a porous, which makes the faithful reconstruction of the specimen difficult. This was addressed by using a gas-injection depositing PT into the pores, stabilising it and substantially enhancing the fidelity of the FIB-SM reconstruction.
2. To make progress with the scientific questions of the PrISMoID project during the establishment of the FIB-SEM method, first experimental studies focussed on beetles that have differently coloured scales. In the studied organisms, differently coloured scales feature ordered, partially ordered disordered morphologies within them. These studies allowed first qualitative conclusions about the role of disorder in the scales and their colour response.
The second phase of the PrISMoID project employed the developed FIB/SEM methodology to study organisms with different photonic morphologies. These results are currently on the descriptive level.
Employing the developed 3D imaging techniques, two types of organisms were studied, one type with a 3D co-continuous network and the other with a colloid-like packing.
Work on WP2has also commenced, but was somewhat delayed through Covid lock-downs during the past two years. Work in the WP is seasonal, and required the cultivation of flowering plants, which is carried out by the botanical gardens in Fribourg.
In terms of manufacture (WP3), work has started on the creation of "photonic pigments", which are a promising approach towards the scalable implementation of the results of the ERC-funded project. The initial phase is making use of ordered structures (as a proof-of-principle). First disordered photonic pigments have also been created.
Concerning WP4, the students have even trained in the numerical modelling and the comparison of its result with optical experiments. This is now routinely employed in all projects.
Significant progress has been made since the beginning go the project, both along the lines of the proposal and in the wider field of the project. Technologically, the development of a robust slice-and-view method of the acquisition of 3 D datasets of biological specimens with a voxel resolution down to 10 nm was an essential break-through, on which the entire project hinges. A publication of this work has been uploaded onto a preprint server. First results on the interplay of order and disorder have been achieved and published. An important first qualitative result is a structural motive that has been found in all so-far studied biological photonic specimen featuring network-like morphologies: nodes within the network exhibit a connectivity to 4 neighbours (i.e. a diamond-like local structure). This is, on the one hand surprising, since such a connectivity is difficult to achieve though self-assembly and self-organisation processes. It is on the other hand interesting, since diamond morphologies are predicted to exhibit a full (angular-independent) photonic band-gap. While we in the process of further analysing these results, we speculate that the morphologies are highly effective in creating a strong photonic response.
Further results include a new paradigm on the interplay of pigments absorption and structural colour in biological specimen. In terms of manufacture (WP3), a first result is a fully colour tunable photonic pigment (one publication, one in preparation). Interestingly it is possible to vary between order and disorder in these photonic spheres, which lies within the scope of WP3, and is a very promising first result.
Plans of the reminder of the project include:
WP1: With the acquisition of first 3D datasets, focus will now shift on the analysis and modelling of these data, as anticipated in WP1. More 3D data will be acquired, to test the universally of the models.
WP2: With first preliminary results in place, the upcoming flowering season will be employed for intensive data acquisition and analysis.
The main push of the project will concern WP3, the manufacture of disordered photonic systems. Two approaches will be pursued. (1) We will explore the creation of photonic structures via self-organisation in micro-emulsions. This approach is highly bio-inspired and attempts to mimic the biological processes that give rise to photonic morphologies in butterfly scales. (2) Disordered colloidal assemblies will be manufactured that exhibit a 4-fold connectivity, i.e. a morphology that is similar to the on discovered in WP1, and which does not form through a random packing process.
Further results include a new paradigm on the interplay of pigments absorption and structural colour in biological specimen. In terms of manufacture (WP3), a first result is a fully colour tunable photonic pigment (one publication, one in preparation). Interestingly it is possible to vary between order and disorder in these photonic spheres, which lies within the scope of WP3, and is a very promising first result.
Plans of the reminder of the project include:
WP1: With the acquisition of first 3D datasets, focus will now shift on the analysis and modelling of these data, as anticipated in WP1. More 3D data will be acquired, to test the universally of the models.
WP2: With first preliminary results in place, the upcoming flowering season will be employed for intensive data acquisition and analysis.
The main push of the project will concern WP3, the manufacture of disordered photonic systems. Two approaches will be pursued. (1) We will explore the creation of photonic structures via self-organisation in micro-emulsions. This approach is highly bio-inspired and attempts to mimic the biological processes that give rise to photonic morphologies in butterfly scales. (2) Disordered colloidal assemblies will be manufactured that exhibit a 4-fold connectivity, i.e. a morphology that is similar to the on discovered in WP1, and which does not form through a random packing process.