Lectures
The Coalescence Behavior of Two-dimensional Materials Revealed by Multi-scale in situ Imaging during Chemical Vapor Deposition Growth
Posted: 2020-10-19   Author: 秦梦瑶   Views: 234

Subject：The Coalescence Behavior of Two-dimensional Materials Revealed by Multi-scale in situ Imaging during Chemical Vapor Deposition Growth

Speaker：Prof. Zhun-Jun Wang

Emcee：Prof. Qinghong Yuan

Time：10:00 am,20th Oct, 2020 

Place：Optics Building A408

About the Speaker：

Zhu-Jun Wang is an expert on both electron microscopy and heterogeneous catalysis. He has successfully constructed the surface sensitive near-ambient-pressure in-situ scanning electron microscopy (SEM) during his doctoral research. With this technique, the detailed atomic-scale information obtained by in-situ transmission electron microscopy (TEM)/ scanning tunneling microscopy (STM) can be embedded within the global picture obtained at lower magnifications by in-situ SEM and subsequently correlated with the spectroscopic data from near ambient pressure in-situ X-ray photoelectron spectroscopy (NAP-XPS). This multi-scale approach enables to investigate the dynamic nature of catalyst during the ongoing work, bridges the pressure-gap, and links atomistic details to collective processes. One typical work is the analysis of surface dynamics, from the micrometer- to the atomic-scale, at well-controlled experimental environments to obtain a fundamental understanding of the mechanism of graphene and two dimensional (2D) materials growth on metal catalyst.

 

Abstract：

Wafer-scale monocrystalline two-dimensional (2D) materials can theoretically be grown by seamless coalescence of individual domains into a large single-crystal. Here I present a concise study of the coalescence behavior of crystalline 2D films using a combination of complementary in situ methods. Direct observation of overlayer growth from the atomic to the meso-scale and under model- and industrially relevant growth conditions reveals the influence of the film-substrate interaction on the crystallinity of the 2D film. In the case of weakly interacting substrates, the coalescence behavior is dictated by the inherent growth kinetics of the 2D film. It is shown 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. The latter can be traced down to a reduced kink-creation energy at the interface between well-aligned domains. 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. The experimental findings are confirmed by theory based growth simulations and can be generalized to other 2D materials. Based on the gained understanding of the relation between film–substrate interaction, shape evolution and coalescence behavior, a general framework for the optimization of large-scale production of monocrystalline 2D materials is established.