TEM observation of heterogeneous polyhedronization behavior in graphitized carbon nanospheres

Spherical carbon nanoparticles with 200 nm diameter were heat-treated in Ar atmosphere, and their microtexture was characterized with transmission electron microscopy (TEM). According to the observation of carbon 0 0 2 lattice images, pristine sample had a homogeneous, concentric orientation of aromatic layers. Microtexture in the particle began to be separated at 1800 °C, where a sign of polyhedronization started to be seen in the outside region of the particle, while the concentric orientation was still kept in the central region. At 2500 °C and over, the heat-treated particle represented the outside and central texture clearly separated each other: The outside region had well-developed stacking structure of aromatic layers with the obvious feature of polygonization, while the center region consisted of non-graphitic microtexture. From the macroscopic viewpoint, polygonization behavior could be understood by the Cahn's formula indicating the proportional relation between the number of dislocation per area and reciprocal of curvature, while the thickness of outside/central textures was independent of the radius curvature. It is expected that the textural discontinuity can be caused as a result of orientation of aromatic layers originated from the surface of the spherical carbon nanoparticles.