A Helios UC FIB-SEM system (Thermo Fisher Scientific) with the µReactor was used for the in-situ SEM imaging of the growth of nanowhiskers (shown schematically in Figure ). The Reactor is described in detail in Figure . It allows forming of a local overpressure of the processing gas (up to 500 Pa) when placed inside an SEM chamber, while the SEM is operated in a standard high-vacuum mode (with a chamber pressure < 10 2 Pa). The sample heating inside the µReactor is provided by a MEMS-based micro-heating plate allowing maximum temperature up to 1200 °C (Figure ). The temperature of the heating plate is controlled from the SEM user interface. The processed samples were placed manually on the micro-heating plate (Figure ) by tweezers and shifted to the desired position using an EasyLift manipulator needle. Once the sample was placed on the heating plate and aligned under the electron beam, the cap of the µReactor was inserted to seal the reaction volume (Figure ). In-situ imaging was done by an in-lens (TLD) detector collecting signals of secondary (SE) and backscattered (BSE) electrons passing through an aperture hole in the reactor cap (Figure ). Pure hydrogen was flowing into the reaction volume through a capillary connecting the µReactor cap (Figure ) with a gas feedthrough on the SEM chamber. The inlet flow rate was controlled by a mass flow controller placed outside the SEM chamber, between the hydrogen cylinder and the gas feedthrough of the SEM chamber.