X-ray tomography for imaging nanostructures

Structural insight from x-ray tomography allows input from nature into novel materials

We pursue research on various biological and bio-inspired materials in order to obtain a comprehensive insight  into (i) the ultrastructural details of these structures and (ii) on how various processing conditions determine their final assembly. For this, we particularly focus on the structure-function relationship within these materials. The technique of choice is synchrotron scanning coherent diffraction nanotomography, in order to obtain ptychographic nanotomography reconstructions. This X-ray-based technique allows a full 3D insight into the materials and thus exploring, for example, the observation of molecular assembly occurring within the bio-inspired materials. Such insight will ultimately allow us to shed light on the morphological properties that might lead to new generations of bio-inspired technologies or further extending the knowledge on the structure-function relationships within these materials. Refining and developing more accurate algorithms for nanotomography reconstructions, we are able to visualize the complete three-dimensional volume of these bio-materials with a resolution better than 20 nm. Biological structures, e.g. photonic structure encountered in numerous animals and plants, can then be used as a model for bio-inspired applications that aim at increasing their efficiency and usability, as well as accurately controlling their assembly pathways through the understanding of the key chemical-physical factors involved within the assembly process. In fact, within our studies natural structures are used as model structures aiming at a deeper understanding on evolutionary optimized structures. With the help of our coherent diffraction imaging study we were, for instance, able to visualize the three-dimensional chitin network within beetle scales that assembled naturally under ambient conditions. Further insight into this process will enable scientists to adapt assembly pathways from nature and envision novel applications. Our research aims at optimizing the nano-fabrication route of bio-inspired materials in order to achieve the desired morphologies for new generations of bio-technologies.

Using focused ion beam (FIB), we prepare synchrotron-ready pillar-like samples from the biological materials, which allow for optimized computed nanotomography reconstructions. We make use of an advanced and optimized synchrotron setup at the Swiss Light Source (PSI) in order to achieve the highest possible resolution on biological materials without damaging the structure, e.g. due to radiation damage. Furthermore, we develop and implement ad-hoc nanotomography reconstruction algorithms specifically aimed for the extraction of a multitude of structural parameters with as less as possible artifacts while keeping high the resolution. They are optimized to retrieve small low-contrast variations of bio-materials also in the presence of a strong scattering background noise.

These three-dimensional reconstructions are not simply meant for visualization purposes, but are used to as an input for further experiments and simulations. We for example use advanced modelling methods on multi-GPU / CPU clusters that allow to reconstruct the light-matter interaction using the nanotomography reconstructed structures. This allows us to draw conclusions on what structural properties are actually necessary in order to achieve the final function, and in turn how to synthetically replicate and optimize them in the laboratory. We further combine the nanotomography reconstructions on our bio-inspired materials with SEM, TEM and AFM in order to complete our structural study with an onset of techniques that can emphasize the relationship between natural structural properties and artificial technological functionalities.

Our research further aims at developing novel bio-inspired technologies. We expect that our results are transferable to other disciplines, e.g. the material sciences and connected interdisciplinary fields. Our research in fact aims at identifying the most fundamental parameters in order to promote new fabrication pathways and improve our artificially self-assembled replica through a comparative approach between natural and synthetically fabricated nanostructures.

Adolphe Merkle Institute - Chemin des Verdiers 4 - CH-1700 Fribourg - Phone +41 26 300 9254