Multi-wall CNTs (MWCNTs) are a common nano-carbon reinforcement material and are frequently dispersed into a polymer matrix to form composites that can be engineered with specific combinations of desirable properties – electrical, thermal, optical and mechanical, etc. However, this multifunctionality is dependent on the detailed arrangement – dispersion, clustering, networking, etc. – of the MWCNTs within these composites. The primary challenge associated with imaging nanoscale carbon reinforcements embedded within an amorphous carbon matrix (i.e. epoxy resin) is achieving sufficient (< 1 nm) imaging resolution to resolve the nanoscale features of interest while also imaging a large enough volume of material to capture the complex, three-dimensional structure of the material. Typically, thin samples are needed for high-resolution imaging, while much thicker samples are necessary to capture the three-dimensional nature of the structures. Satisfying these conflicting requirements simultaneously demands special sample preparation and innovative microscopy techniques.
High-quality, electron-transparent samples are prepared from carbon nanocomposite materials using a dual-beam focused ion beam (DB-FIB). Energy-filtered TEM (EFTEM) is then used to optimize differences in contrast between the two carbon-containing phases, thus enabling high-resolution images to be obtained from thick samples. Tomography is used to analyze the morphology and distribution of MWCNTs in three dimensions with nanometer resolution.