Growth Anisotropy and Morphology Evolution of Line Defects in Monolayer MoS2: Atomic‐Level Observation, Large‐Scale Statistics, and Mechanism Understanding

Understanding the growth behavior and morphology evolution of defects in 2D transition metal dichalcogenides is significant for the performance tuning of nanoelectronic devices. Here, the low‐voltage aberration‐corrected transmission electron microscopy with an in situ heating holder and a fast frame rate camera to investigate the sulfur vacancy lines in monolayer MoS2 is applied. Vacancy concentration‐dependent growth anisotropy is discovered, displaying first lengthening and then broadening of line defects as the vacancy densifies. With the temperature increase from 20 °C to 800 °C, the defect morphology evolves from a dense triangular network to an ultralong linear structure due to the temperature‐sensitive vacancy migration process. Atomistic dynamics of line defect reconstruction on the millisecond time scale are also captured. Density functional theory calculations, Monte Carlo simulation, and configurational force analysis are implemented to understand the growth and reconstruction mechanisms at relevant time and length scales. Throughout the work, high‐resolution imaging is closely combined with quantitative analysis of images involving thousands of atoms so that the atomic‐level structure and the large‐area statistical rules are obtained simultaneously. The work provides new ideas for balancing the accuracy and universality of discoveries in the TEM study and will be helpful to the controlled sculpture of nanomaterials. The dynamic evolution process of sulfur vacancy lines under different heating temperatures is studied by low‐voltage, in situ scanning transmission electron microscopy (STEM) observations. The anisotropic growth of vacancy lines exhibits both vacancy concentration dependence and temperature dependence, which gives fundamental insights into the similarity between defect structure growth at the atomic scale and 2D material growth at the micrometer scale.