Liquid metal catalysts have recently been attracting attention for synthesizing high-quality 2D materials facilitated via the catalysts’ perfectly smooth surface. However, the microscopic catalytic processes occurring at the surface are still largely unclear because liquid metals escape the accessibility of traditional experimental and computational surface science approaches.
An EU-funded collaboration of researchers that included teams from Fritz Haber Institute of the Max Planck Society, The European Synchrotron- ESRF, Technical University of Munich (TUM), Aarhus University, Leiden University and Université Grenoble Alpes used novel in situ and in silico techniques to achieve an atomic-level characterization of the graphene adsorption height above liquid Cu, reaching quantitative agreement within 0.1 Å between experiment and theory.
The experimental results were obtained using in-situ synchrotron X-ray reflectivity at beamline ID10, which needed to work with the curvature of the liquid surface, imposing an additional degree of experimental complexity. To build the computational model, the team trained the ML potentials, specifically, moment tensor potentials, using density functional theory reference data. This helped to obtain large-scale molecular dynamics simulations while leveraging the efficiency of ML algorithms.
The team then determined the adsorption height of monolayer graphene above liquid Cu, known as ‘the gap’, experimentally and computationally. It was found that the experimental value of the gap was 2.2 Å, whereas the computational or theoretical value was 2.119 Å. With a less than 0.1 Å difference, the results demonstrated an almost quantitative agreement between theory and experiment.
The results showed that ML potentials trained with first principles are a powerful approach that can determine the gap with sub-angstrom potential, while being in good agreement with the experimental value. Surprisingly, the computational techniques reveal that the interaction of graphene with solid and liquid Cu is chemically identical, thus adding to the mystery of the superior synthesis from the liquid metal state. These powerful insights can serve for future understanding of a seamless graphene synthesis to develop next-generation electronics.