The electrospun nanofibrous materials were characterized by SEM with a Versa 3D (Thermo Fischer Scientific) microscope and by scanning transmission electron microscopy (STEM) on an FEI Magellan 400 XHR microscope (Thermo Fischer Scientific). A Helios UC Focused-Ion-Beam (FIB)-SEM system (Thermo Fisher Scientific) was used for the in-situ SEM experiments inthe Reactor and lamella preparation from a W18O49 nanowhisker. For the lamella preparation, W18O49 nanowhiskers were dispersed in isopropyl alcohol, dropcasted on a Si substrate. A Helios 5 FX FIB microscope was used for localization of a specific nanowhisker, micromanipulation and final lamella preparation. A gas injection system (GIS) was utilized for creating of an amorphous carbon protection layer. First deposition step was performed by electron assisted deposition and later ion assisted deposition was used. Chunk thinning and final polishing operations were performed at FIB accelerating voltages ranging from 30 kV to 2 kV and FIB currents ranging from 2 nA to 25 pA.The SEM micrographs were analyzed by the ImageJ software to determine the fiber diameters and the size distribution.