Figure 2.

For a BN sample, the voltage of Lens 2 was decreased from (A) to (E). A) A shadow image, B) a higher magnification shadow image of the area highlighted with the green dashed circle in A, C) an even higher magnification and the start of deflection pattern formation with bright outlines, D) the overfocus deflection pattern , E) beam focused on sample plane and F) the underfocus spot pattern. The scale bar in D is 5 mrad (0.39 cm for a sample to MCP separation of 78.5 cm) and applies to all images. (The green or black crosses mark the approximate beam focal point, i.e., the beam axis). The grid window is 108 µm wide with a grid bar width of 19 µm. Underneath each image is a lens diagram showing the position of the Lens 2 focal point cross over (orange circle), the dashed red line is the sample plane (s) and the dot-dashed black line is the MCP plane (m). The color bar shows the grayscale pixel value recorded in the CCD image.