Cross-sectional structural analysis of C60 nanowhiskers by transmission electron microscopy

Cross-sectional observations of C60 nanowhiskers (C60NWs) were successfully conducted using the focused ion beam (FIB) method. The C60NWs were observed to possess the core-shell structures with porous cores and dense surface thin layers. The size and number of pores decreased from the center to the surface, showing that the densification of C60NWs proceeds from the surface to the center upon drying. A cross-sectional high-resolution transmission electron microscopy (HRTEM) image of a C60NW showed a disordered structure comprising the domains with sizes on the order of 10 nm. The most frequently observed cross-sections were hexagons, reflecting the solvated hexagonal crystal structures of as-grown C60NWs. From the observation of various cross-sectional shapes of C60NWs with different diameters and crystallographic surface analysis, it is suggested that C60NWs grow longer above a critical diameter Dc with the development of low-energy crystal surfaces.

Research Highlights
► C60 nanowhiskers have a core-shell structure with dense surface thin layers and porous inner cores.
► The most frequently observed cross-section of C60 nanowhisker was hexagonal. A C60 nanowhisker was observed to be surrounded by crystal surfaces with low Miller indices of the hexagonal crystal system.
► The cross-sections of C60 nanowhiskers became rounded with decreasing whisker diameter, suggesting the isotropic growth of C60 nanowhiskers during their initial nucleation and growth stage.