Hidden Caves in an Aggregate of Single-Wall Carbon Nanohorns Found by Using Gd2O3 Probes

We investigated the inner structure of an aggregate made of single-wall carbon nanohorns (SWNHs). This structure has not been clarified because the thousands of SWNHs are densely packed and difficult to observe directly by electron microscopy. We used Gd2O3 as a probe for the electron microscope, observation: Gd2O3 was confined inside SWNH via the incorporation of Gd acetate inside SWNHs with holes opened (NHox), followed by heat treatment at 1200 degrees C in Ar gas. From microscopic study, we found that Gd2O3 formed clumped crystals with sizes of 7-21 nm around the center of the SWNH aggregates, suggesting that there were 10-20-nm caves near the aggregate's center.