The shear plane structure of tungsten suboxides is well-documented. The rearrangement of the corner-shared [WO6] octahedra array in WO3 (Figure ) produces uniform crystal planes with edge-sharing [WO6] octahedra. In the case of the W18O49 nanowhiskers, a unique pattern of pentagonal columns consisting of a [WO7] central cluster is surrounded by five [WO6] octahedra forming hexagonal channels (Figure ). Experiment No. 2 in the Reactor showed the growth of W18O49 nanowhiskers from the-WO3/a-SiO2 nanofibers under vacuum (1.10 4 Pa) at 900 °C (see Supplementary Discussion 2). The same MEMS chip used in the Reactor can be also used for in-situ TEM experiments utilizing the NanoEx-i/v holder. Therefore, the in-situ TEM (under high vacuum In-situ observations revealed discrepancies and misalignments in the shear planes during the growth, suggesting the complex structure of the W18O49 nanowhiskers. As a result, a crosssectioned lamella of a W18O49 nanowhisker was produced using focused ion beam lift-out procedure. This cross-section underwent analysis with high-resolution scanning transmission electron microscopy in high-angle annular dark field (HRSTEM-HAADF) mode, as displayed in Fig. -d and Fig. (which offers a comprehensive view of the lamella). Notably, the nanowhisker's structure was heterogeneous, encompassing multiple phases.