The reaction is continuously monitored using the signal of backscattered electrons (BSE) or secondary electrons (SE), which are detected inside the SEM column. Obviously, the electrons of the beam can intervene in the reaction directly and indirectly by heating the specimen. the electron beam (e-beam), the manipulator needle is retracted, and the cap of the µReactor is inserted (c). The reaction volume is thus closed and sealed. Overpressure inside the reactor (up to 500 Pa) is assured by the pressurelimiting aperture in the cap viewed by the SEM from the top (white area in (e)). Note that the SEM chamber remains under high vacuum conditions. In-situ SEM imaging is possible through the hole in the aperture (e). The gas inlet is incorporated into the cap. Gas escapes from the µReactor mainly through the aperture. The reactor can be opened/closed inside the SEM chamber without a need for chamber venting, which assures clean sample preparation (by FIB) and sample positioning (by the manipulator EasyLift needle) without exposure to air. The sample deposited on the heating segment of the MEMS chip reacts with the admitted gas or under vacuum at elevated temperatures.