Periodic Reporting for period 4 - ATOMICAR (ATOMic Insight Cavity Array Reactor) Reporting period: 2022-08-01 to 2023-01-31 Summary of the context and overall objectives of the project ATOMICAR aims to develop a new paradigm in ultra-sensitive catalytic measurements where it is possible to measure the catalytic turnover of a single nanoparticle under reaction conditions. The ability to measure catalytic turnover on a single nanoparticle combined with the ability to image and perform spectroscopy on said nanoparticle would enable answering the ultimate question in heterogeneous catalysis: How does the activity of a nanoparticle correlate with its size and shape in a specific environment.The application for such capability is the design of new and improved catalysts - in particular for energy storage and transformation processes. ---ATOMICAR is a project to advance the art of catalytic measurements to the point where we can hope to answer the ultimate question in nanoparticle catalysis:"How does the catalytic activity of a specific nanoparticle in a specific reactive environment correlate to its specific composition, size and shape?"If we could answer this question, we could design super-optimized nanoparticles for a given reaction. Such an optimized catalyst would have maximum activity (so that the smallest possible amount of the catalyst is needed which saves precious resources) while ensuring near perfect selectivity (so that only the desired product is made and undesirable bi-products are avoided). The main target application for such technology is energy storage and transformation reactions for a future renewable energy infrastructure. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far At the outset of the project, we had a clear plan for how to achieve the project objectives, but we were otherwise starting from scratch. The first we did was to design and fabricate MEMS chips with large arrays of cavities which were TEM transparent. In parallel, we built up an AFM setup, and a laser interferometry setup for tracking the cavities. Using these tools we could reproduce some literature results on leak-tightness of 2D-chip interfaces towards gas; and going beyond the literature we expanded upon the set of investigated gasses and found the water-solubility of leaking gas to correlate with the leak rates. Beyond that, and using the TEM transparency, we developed a new technique based on EEL-Spectroscopy of the captive gas and used it to perform series of high-temperature leak-rate measurements. This enabled the extraction kinetic parameters of the (Arrhenius-type) leak-rate behavior; and it also enabled the explanation of much of the scatter and inconsistency in the literature. What we did not achieve, within the limited time of ATOMICAR, was the measurement of catalytic turnover of captive nanoparticles, however, this work is currently ongoing in another project which is a direct continuation of the pioneering work done in ATOMICAR.---Since the start of the project we have developed (from scratch) experimental facilities and methodology in order to start catalytic measurements on single, isolated nanoparticles. We have designed and fabricated Cavity Array Reactor (CAR) chips with micron-size cavities, which we seal gas-tight using 2-dimensional "sheets" of material.We study the surface of he 2-dimensional material using Atomic Force Microscopy (AFM) in a custom setup, which we have established as part of the project.We have made such CARs in a special version where the floor of the cavity is only a few tens of nanometers thick which makes it transparent to the electron beam in a Transmission Electron Microscope (TEM). Finally, we have built a laser-setup to study the mechanical properties of the 2-dimensional "sheets". Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) The main results beyond the state of the art is that 1) we have discovered a new regime for how gas behaves in the 2-dimensional sheet/CAR chip interface, and2) we have developed a new spectroscopic technique for measuring the chemical state of the CAR chip in a TEM. These are baby steps towards the larger project goals which include seeking out nanoparticle configurations of extraordinary catalytic activity and the study of non-trival ensemble phenomena such as activity oscillations and sintering kinetics.