Developing electronic circuits on stretchable substrates would allow renewing numerous industrial sectors, in particular those related to flexible electronics and transports. To this aim, we need to prepare and characterize materials with a low electrical resistivity, a high mechanical strength and significant shaping capacities. Nano-twinned metals have these properties, thanks to numerous and structured interfaces: the twin boundaries. At the Institut P’, we know how to prepare gold nano-twinned single crystals. The project aims at characterizing at the nanoscale these interfaces in thin films, and at anticipating their roles on the mechanical and electrical properties. To reach these goals, we want to develop a microscopy technique applied up to now on model materials: Bragg ptychography. This technique, based on a coherent X-ray beam, should rapidly know significant progress due to the present improvements on synchrotron radiation sources and free electron lasers. Bragg ptychography allows characterizing strain field and crystalline defects at a nanometre scale. It is a three-dimensional and non-invasive method, that does not require any sample preparation, and applicable to films with a thickness between a few nanometres to a few micrometres. I greatly participated to its development on model samples (semi-conductors or bio-crystals) and wish now to enlarge the spectrum to include metals.
Therefore, we want optimizing the deposition technique to prepare single crystalline films with an ideal microstructure in view of the mechanical and electrical properties: nano-twins, with a controlled size and density, and as few as dislocations and impurities as possible. These samples will be characterized with Bragg ptychography, and the results will be confronted to atomistic simulations (molecular dynamics) that will give the intrinsic strain field associated to the desired microstructure. Finally, after a transfer of these films on flexible substrates, tensile tests will be performed, during which we will measure in-situ the electrical resistivity, the stress in the film (thanks to classical X-ray diffraction) and the strain of the substrate.
To sum up, this project aims at giving a push to a method (Bragg ptychography) developed during my post-docs on samples studied in the laboratory where I presently work (metallic thin films on polymeric substrates). It gathers persons belonging to three different teams. Indeed, I asked to experts in various fields to join the project: atomistic simulations (S. Brochard and J. Durinck), mechanical (P.O. Renault) and electrical (S. Hurand) properties at the macro-scale, and physical vapour deposition of thin films (M. Drouet). A transverse group will formalize and make durable these new collaborations. Lastly, this project is seen as a springboard to another project like a PRC or an ERC, during which we want to follow, in-situ and locally, the microstructure evolution of these materials during mechanical tests. We will then have a multi-scale view (atomic scale with molecular dynamics, nanoscopic with Bragg ptychography, macroscopic with classical diffraction and electrical resistivity) of the deformation mechanisms of these promising thin films.
Monsieur Pierre GODARD (Institut P' : Recherche et Ingénierie en Matériaux, Mécanique et Energétique)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
Pprime Institut P' : Recherche et Ingénierie en Matériaux, Mécanique et Energétique
Help of the ANR 229,880 euros
Beginning and duration of the scientific project: January 2020 - 48 Months