Structural Identification of 2D TMDs for Energy Applications using Cross-sectional TEM

Transmission Electron Microscopy (TEM) has been considered as a powerful technique to investigate the structural, chemical, and electronic properties of two-dimensional transition metal dichalcogenides (2D-TMDs). Especially, the advanced scanning TEM (STEM) equipped with a spherical aberration corrector was introduced and actively used for uncovering the atomic-scale structure and chemical composition of 2D TMDs in a sub-?? level. Recently, ultrathin layers of metallic TMDs such as 1T-MoS2, NbS2, TaS2, and VS2 have been extensively studied as catalytic materials for the application of hydrogen evolution reaction (HER). In the real catalytic systems, revealing the exact physical and chemical structures found at the surface and edges as well as bulk areas is so crucial for improving the performance. In this case, the cross-sectional TEM analysis combined well-prepared TEM samples is useful and effective. In this presentation, I will present cross-sectional STEM works which were performed using a Cs corrected STEM combined with a focused ion beam (FIB) sample preparation technique. Metallic 2H and 3R phase of niobium disulfide (Nb1+XS2) with additional niobium atoms for potential hydrogen revolution reaction (HER) catalysts is clearly visualized via cross-sectional scanning TEM (STEM) images. It is demonstrated that Nb terminated surface of Nb1+XS2 phase with additional niobium atoms is attributed to the enhanced HER performance by STEM image and theoretical calculation