Fig. 5

Electron-penetration depth as a function of probe-beam-landing energy modulated via a decelerating biasing potential. A 30-nm-thick blank plastic section was placed on top of the cerebellum block sample measured in Fig. 4. Images were then collected on the FEI CBS detector with the central ring turned off. The 30-nm section runs diagonally across the middle of the image. Images are inverted, so white shows no backscattering signal. All images were acquired with 3-keV column-electron energy and deceleration appropriate to achieve the electron-landing energy  shown in each panel. At a landing energy between 1.5 and 1 keV, the electron-penetration depth drops below 30 nm