Supplementary Figure 7: Schematic of the load lock system used for positioning the injector capillary close to the interaction region.

In its operating position (a) the capillary tip is located close to the interaction region (x) and can be precisely positioned by an XYZ stage (not shown). The coMESH setup is represented by the yellow block with connecting capillary lines that pass through the 6” (15.24 cm) flange out of vacuum. In order to clean or change the capillary the load lock bellows can be extended and after closing the gate valve on top of the experimental chamber, can be tilted by 90° (b) to allow easy access to the injector capillary. The entire injector assembly is comprised of the feedthrough flange and mounting rod (black), the counter electrode (gray trapezoid) and PEEK holder (brown). The assembly is mounted to a 6” (15.24 cm) flange at the top of the load lock bellows and can be easily swapped for a second injector assembly if necessary. The flange has all the necessary feed-throughs for the liquid lines, high voltage connections and three optical fiber feed-throughs for optional in situ sample illumination.