报告题目:Influence of the Interfacial Coupling Strength on the Growth and Coalescence of 2 Dimensional Materials Revealed by Multiscalein Situ Observations
In the context of large-scale production of 2 dimensional (2D) nanomaterials, the most widely applied method is based on metal-catalyzed CVD growth. To unleash the full potential of 2D nanomaterials and realize a 2D nanomaterials-based technology, consistent control over nucleation, growth and coalescence needs to be achieved. Especially, a seamless coalescence of multiple domains into a continuous single crystalline film would be a noble way of eliminating grain boundaries and produce large single crystal domains. To achieve this, a fine-grained control and/or a complex set of processes is required. Alternatively, if the underlying mechanisms and the role of the substrate are understood, conditions for seamless coalescence and spontaneous formation of single crystalline graphene can be found. Graphene is a prototype 2D nanomaterial, and graphene growth represents a model system for understanding 2D growth processes. Therefore, we use graphene as a candidate to study coalescencebehaviourof 2D nanomaterials.
The present understanding of the coalescence behavior is stagnating because of the limited insights generated on the basis of "state of the art" post growth analysis. Reliable real time data on the growth dynamics under relevant conditions are missing.
Using a combination ofin situexperimental techniques we unravel the growth process under realistic CVD growth conditions. We combinein situenvironmental scanning electron microscopy (ESEM),in situnear ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) andin situscanning tunneling microscopy (STM) to provide a complete picture of graphene coalescence on catalysts presenting different graphene-substrate interactions. With this multi-in situapproach, the detailed atomic-scale information obtained byin situSTM can be embedded in the global picture obtained at lower magnifications byin situESEM and subsequently correlated with the spectroscopic data from NAP-XPS.
In the case of weak graphene-substrate interactions, graphene behaves as a quasi-free-standing layer. This allows micron-sized domains to slightly slide and rotate on the surface under growth conditions, enabling seamless coalescence without the requirement of perfect alignment between adjacent domains. In the case of a strong graphene-substrate interaction, growing domains are pinned to the substrate and show a corrugated Moiré structure. Seamless coalescence thus requiresboth, the alignment between domains and coherence in the respective Moiré corrugation. We reveal how the Moiré corrugation determines the stitching and coalescence behaviour, and show how the strength of the graphene-substrate interaction influences the kink nucleation and growth anisotropy. The unique combination ofin situmethods applied in this work allows to bridge the pressure-gap between UHV- and industrially relevant CVD conditions and provides a general framework for optimizing the large-scale production of single crystals and two-dimensional materials on different substrates.