Abstract
The synthesis of high-quality ultrathin overlayers is critically dependent on the surface structure of substrates, especially involving the overlayer-substrate interaction. By using in situ surface measurements, we demonstrate that the overlayer-substrate interaction can be tuned by doping near-surface Ar nanobubbles. The interfacial coupling strength significantly decreases with near-surface Ar nanobubbles, accompanying by an “anisotropic to isotropic” growth transformation. On the substrate containing near-surface Ar, the growth front crosses entire surface atomic steps in both uphill and downhill directions with no difference, and thus, the morphology of the two-dimensional (2D) overlayer exhibits a round-shape. Especially, the round-shaped 2D overlayers coalesce seamlessly with a growth acceleration in the approaching direction, which is barely observed in the synthesis of 2D materials. This can be attributed to the immigration lifetime and diffusion rate of growth species, which depends on the overlayer-substrate interaction and the surface catalysis. Furthermore, the “round to hexagon” morphological transition is achieved by etching-regrowth, revealing the inherent growth kinetics under quasi-freestanding conditions. These findings provide a novel promising way to modulate the growth, coalescence, and etching dynamics of 2D materials on solid surfaces by adjusting the strength of overlayer-substrate interaction, which contributes to optimization of large-scale production of 2D material crystals.
Highlights
The catalytic growth of two-dimensional (2D) materials on metal substrates by chemical vapor deposition (CVD) is the most widely used method to fabricate continuous films and meets the industrial demand for electronic-grade materials [1,2,3,4,5,6]
The quality of overlayers is critically dependent on the overlayer–substrate interaction which can be orthogonally decomposed into the out-of-plane interaction and in-plane interaction [7,8,9]
More than 20 instruments such as photoemission electron microscopy (PEEM)/low-energy electron microscopy (LEEM), scanning tunneling microscopy (STM), Xray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS), are interconnected by ultrahigh vacuum (UHV) tubes where samples can be transferred from one endstation to another one
Summary
The catalytic growth of two-dimensional (2D) materials on metal substrates by chemical vapor deposition (CVD) is the most widely used method to fabricate continuous films and meets the industrial demand for electronic-grade materials [1,2,3,4,5,6]. Our previous reports have indicated that the epitaxial feature of h-BN growth on Ni and Ru substrates depends on the near-surface B species which weakens the out-of-plane coupling strength [22]. In these studies, the near-surface species are from the precursor of 2D materials, and the segregation of near-surface species still contributes to the growth. The neutral near-surface Ar nanobubbles with absence of CVD process, is introduced to systematically investigate the influence of overlayer–substrate interaction on the growth, coalescence, and etching of graphene on Ru(0001) surfaces by tuning out-of-plane coupling strength between overlayers and substrates. These findings provide a novel and promising method to modulate the dynamic processes of 2D materials on surfaces
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