Ec epiplan apochromat

Optical micrograph in Fig. 1 was taken using epi-illumination through a 10× objective lens (Zeiss EC Epiplan-Apochromat) using a commercial microscope (Zeiss Axiophot) and camera (Zeiss AxioCamERc5s). Scanning electron micrographs were collected using an FEI Scios FIB/SEM instrument using 30 keV electrons, 6144  $\times$  4376 pixels, a 32  $\mathrm{\mu }$ m aperture, a nominal magnification of 5 k $\times$ and a dwell time of 5  $\mathrm{\mu }$ s, a working distance of 7 mm; the secondary electrons used to create the image were collected using an Everhart–Thornley detector mounted near the column. For each experiment, the two micrographs were aligned with each other by cross correlation to remove drift, cropped to 80  $\mathrm{\mu }$ m wide and binned $4\times$ to create the image for the figure. Beam current was measured using a Faraday cup mounted on the specimen stage. For the trajectory calculations, after drift correction on the complete micrographs, the selected region of the image stack was subdivided into individual 128  $\times$  128  $\times$  2 pixel stacks, and the movement in each was measured by cross correlation. These were then used to generate the vector plots in the figure. Each vector magnitude was multiplied by four to make them easier to see in the plot. Transmission electron micrograph in Fig. 1 was taken using 300 keV electrons on a Gatan K2 direct electron detector operated in super-resolution counting mode in a FEI Titan Krios.