Atomic-scale information is essential for understanding and designing unique structures and properties of two-dimensional (2D) materials. Recent developments in in situ transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) enable research to provide abundant insights into the growth of nanomaterials. In this study, 2D MoS 2 is synthesized on a suspended graphene substrate inside a TEM column through thermolysis of the ammonium tetrathiomolybdate (NH 4 ) 2 MoS 4 precursor at 500 °C. To avoid misinterpretation of the in situ STEM images, a deep-learning framework, DeepSTEM, is developed. The DeepSTEM framework successfully reconstructs an object function in atomic-resolution STEM imaging for accurate determination of the atomic structure and dynamic analysis. In situ STEM imaging with DeepSTEM enables observation of the edge configuration, formation, and reknitting progress of MoS 2 clusters with the formation of a mirror twin boundary. The synthesized MoS 2 /graphene heterostructure shows various twist angles, as revealed by atomic-resolution TEM. This deep-learning framework-assisted in situ STEM imaging provides atomic information for in-depth studies on the growth and structure of 2D materials and shows the potential use of deep-learning techniques in 2D material research.

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We report the in situ transmission electron microscopy (TEM) experiments to directly observe Ni catalysed CNFs/CNTs growth from alcohol precursor at near atmospheric pressure using a homebuilt bubbler system for the introduction of ethanol vapor. Using real time imaging, we revealed the active state of the Ni catalyst during the temperature-dependent CNFS/CNTS growth (600–800 ℃). We observed the formation of CNFs starting from 600 °C and CNTs were formed at higher temperatures. The lattice parameter measurements pointed to an expansion of the Ni lattice as the temperature was increased, which we attribute to increased carbon solubility. The as-grown CNFs and CNTs were further characterized by XPS, Raman spectroscopy, and EELS, that allowed to have a highly reliable overall view of the structure changes with temperature. Results revealed that the change in structure with temperature was caused by the combined effects of increased carbon solubility and graphitization of the walls of the growing nanostructure. This increased carbon solubility in turn affected carbon diffusion and could be the reason for the change in structure from CNF to CNT at high temperature. We also successfully identified the transition from tip-growth to base-growth in a CNT at 800 ℃.

We report the in situ transmission electron microscopy (TEM) experiments to directly observe Ni catalysed CNFs/CNTs growth from alcohol precursor at near atmospheric pressure using a homebuilt bubbler system for the introduction of ethanol vapor. Using real time imaging, we revealed the active state of the Ni catalyst during the temperature-dependent CNFS/CNTS growth (600–800 ℃). We observed the formation of CNFs starting from 600 °C and CNTs were formed at higher temperatures. The lattice parameter measurements pointed to an expansion of the Ni lattice as the temperature was increased, which we attribute to increased carbon solubility. The as-grown CNFs and CNTs were further characterized by XPS, Raman spectroscopy, and EELS, that allowed to have a highly reliable overall view of the structure changes with temperature. Results revealed that the change in structure with temperature was caused by the combined effects of increased carbon solubility and graphitization of the walls of the growing nanostructure. This increased carbon solubility in turn affected carbon diffusion and could be the reason for the change in structure from CNF to CNT at high temperature. We also successfully identified the transition from tip-growth to base-growth in a CNT at 800 ℃.