(a) HeIM image of window rims at 31.8 kV, (b) LL-BSE image of a window rim, that does not show any indication for variations in chemical bonding, (c) edge on view of wall, (d) intensity profile to determine wall thickness from peak separation, and (e) intensity profile showing maximum apparent wall thickness due to folding.Due to their wide range of applications, porous polymers obtained from high internal phase emulsions have been widely studied using scanning electron microscopy. However, due to their lack of electrical conductivity, quantitative information of wall thicknesses and surface roughness, which are of particular interest to tissue engineering, has not been obtained. Here, Helium Ion Microscopy is used to examine uncoated polymer foams and some very strong but unexpected contrast is observed, the origin of which is established here. Based on this analysis, a method for the measurement of wall thickness variations and wall roughness measurements has been developed, based on the modeling of Helium ion transmission. The results presented here indicate that within the walls of the void structure there exist small features with height variations of ~30 nm and wall thickness variations from ~100 nm to larger 340 nm in regions surrounding interconnecting windows within the structure. The suggested imaging method is applicable to other porous carbon based structures with wall thicknesses in the range of 40–340 nm.
This paper was originally published in Ultramicroscopy 139 (2014) Pages 13–19.