What is inside carbon nanohorn aggregates?

Carbon nanohorn (CNH) aggregates are spherical with a diameter of ∼80 nm. There are thousands of protruding nanohorns at the periphery of each CNH aggregate. However, the interior structure of CNH aggregates remains a question. In this work, we used focused ion beam (FIB) to cut CNH aggregates followed by electron microscopy observations. It was revealed that the interior consists of disordered single-layered graphene sheets with a lateral size of up to 10 nm and an interlayer distance of approximately 4–5 Å. The growth mechanism of CNH aggregates was discussed on the basis of this new finding.