Fig. 4

Determination of BSE penetration depth. Sections of 50-nm (a, c, e) or 30-nm (b, d, f) thickness of pure Durcupan resin were overlaid on one half of the tissue block (visible on the left half of each image). At 3.0 keV, a significant number of BSEs emanated from beneath the 50- and 30-nm-thick sections (a, b). At 2.0-keV accelerating voltage, almost no signal was observed from below the 50-nm section (c) while some was noted from below a 30-nm-thick section (d). At 1.7 keV, no signal was observed from below a 50-nm section (e), while very little was observed from below a 30-nm-thick section (f). Note that the decrease in signal to noise as the acceleration voltage is lowered