Wang, Mengjing Kim, Jung Han Han, Sang Sub Je, Minyeong Gil, Jaeyoung Noh, Chanwoo Ko, Tae-Jun Lee, Kyu Seung Son, Dong Ick Bae, Tae-Sung Ryu, Hyeon Ih Oh, Kyu Hwan Jung, YounJoon Choi, Heechae Chung, Hee-Suk Jung, Yeonwoong 2024-01-19T18:34:43Z 2024-01-19T18:34:43Z 2021-09-05 2019-11-14 1932-7447 https://pubs.kist.re.kr/handle/201004/119328 Benefiting from a large density of layer edges exposed on the surface, vertically aligned two-dimensional (2D) molybdenum disulfide (MoS2) layers have recently harvested excellent performances in the field of electrochemical catalysis and chemical sensing. With their increasing versatility for high-temperature, demanding applications, it is vital to identify their thermally driven structural and chemical stability, as well as to clarify its underlying principle. Despite various ex situ and in situ characterizations on horizontally aligned 2D MoS2 layers, the direct in situ heating of vertically aligned 2D MoS2 layers and the real-time observation of their near-atomic-scale dynamics have never been approached, leaving their thermal stability poorly understood. Moreover, the geometrical advantage of the surface-exposed vertically aligned 2D MoS2 layers is anticipated to unveil the structural dynamics of interlayer van der Waals (vdW) gaps and its correlation with thermal energy, unattainable with 2D MoS2 layers in any other geometry. Herein, we report a comprehensive in situ heating TEM study on cleanly transferred, vertically aligned 2D MoS2 layers up to 1000 degrees C. Several striking phenomena were newly observed in the course of heating: (1) formation and propagation of voids between the domains of vertical 2D MoS2 layers with distinct grain orientations starting at similar to 875 degrees C; (2) subsequent decompositions of the 2D MoS2 layers accompanying a formation of Mo nanoparticles at similar to 950 degrees C, a temperature much lower than the melting temperature of their bulk counterpart; and (3) initiation of decomposition from the surface-exposed 2D layer vertical edge sites, congruently supported by molecular dynamics (MD) simulation. These new findings will offer critical insights into better understanding the thermodynamic principle that governs the structural stability of general vdW 2D crystals as well as providing useful technological guidance for materials design and optimization in their potential high-temperature applications. English American Chemical Society GENERALIZED GRADIENT APPROXIMATION MONOLAYER MOS2 MELTING-POINT SIZE NANOSTRUCTURES TRANSITION REDUCTION GROWTH TEM Structural Evolutions of Vertically Aligned Two-Dimensional MoS2 Layers Revealed by in Situ Heating Transmission Electron Microscopy Article 10.1021/acs.jpcc.9b06899 1 The Journal of Physical Chemistry C, v.123, no.45, pp.27843 - 27853 The Journal of Physical Chemistry C 123 45 27843 27853 scie scopus 000497260100062 Chemistry, Physical Nanoscience & Nanotechnology Materials Science, Multidisciplinary Chemistry Science & Technology - Other Topics Materials Science Article GENERALIZED GRADIENT APPROXIMATION MONOLAYER MOS2 MELTING-POINT SIZE NANOSTRUCTURES TRANSITION REDUCTION GROWTH TEM Two-Dimensional MoS2 Transmission Electron Microscopy Vertically