EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Wafer-scale monocrystalline two-dimensional (2D) materials can theoretically be grown on the basis of seamless coalescence of individual domains into a large single-crystal. However, the coalescence behavior of 2D materials is not sufficiently understood to be controlled and utilized in industrial production.
Building on our in situ studies of graphene and hexagonal boron nitride growth [1,2,3], we recently conducted a concise study of the coalescence behavior of crystalline 2D films using a combination of complementary in situ methods. Direct observation of growth dynamics from the atomic to the mm-scale and under model- and industrially relevant growth conditions reveals how the strength of the film-substrate interaction determines the growth and coalescence behavior.
For the case of weak film-substrat interactios, we found that the merging of co-aligned domains leads to a distinct modification of the growth dynamics through the formation of fast-growing high-energy edges (see Figure 1). In the case of strongly interacting substrates, the lattice mismatch between film and substrate induces a pronounced Moiré corrugation that determines the growth and coalescence behavior. It furthermore imposes additional criteria for seamless coalescence and determines the structure of grain boundaries. It is demonstrated that the findings obtained for the case of graphene and hexagonal boron nitride growth can be generalized to other 2D materials. Based on the gained understanding of the link between film-substrate interaction, shape evolution and coalescence behavior, a general framework for optimizing the large-scale production of monocrystalline 2D materials is established.