Compared to conventional scanning electron microscopy imaging, FIB-SEM 3D nanotomography adds a “cutting” tool, i.e., a focused ion beam (FIB). Due to its heavier mass, FIB will remove a small amount of material, hence exposing what is underneath. A repetitive FIB milling followed by SEM imaging produces a stack of images, which can be reconstructed into a 3D volume.

FIB can remove material at a nano-meter scale allowing for a completely clean cross sectioned surface to be prepared for SEM imaging. 

Below, a cross section of the polymer membrane of a drug pellet sample was prepared using two methods: conventional freeze cleave and FIB polishing. The resulting cross-sectioned SEM images are dramatically different. Due to mechanical fracturing, residue surface topology remains on the cleaved sample, and obscures the microstructure observation. In comparison, the FIB cross section reveals microporosity accurately, and allows both qualitative assessment and quantification.

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More importantly, the FIB-SEM experiment produces 3D volume at nanometer scale.