Investigation of the crystallization behaviors in a sub-micron space using carbon nanocones

Up to now, there have been many research studies that have revealed the unique phenomena of various materials encapsulated in a confined nano-sized space, such as in the interior of carbon nanotubes (CNTs). Confined in such a space several nanometers in size, these materials showed many different and interesting properties. However, the morphology and behaviors of these materials encapsulated in a comparatively bigger space, i.e., from tens of nanometers to microns, have been little investigated. In this work, carbon nanocones (CNCs), which are multilayered graphene-like nanomaterials with a hollow conical structure and an inner size varying continuously from several nanometers to micrometers, were used as the workhorse to investigate the nano-confinement effects on different scales. Gd acetate was adopted to be incorporated into the conical inner space of the CNCs. The corresponding Gd oxide, formed upon heating, showed a unique morphology and crystallization behavior in this sub-micron space. The confined Gd oxide was conical in shape, perfectly fitting the interior of the CNCs. Several crystallization orientations were often presented in the Gd oxide cone structure, and single crystallization was also observed located close to the apex of the CNCs. The crystal size of Gd oxide was over 100 nm, implying the effective scale of the confinement phenomenon between the CNCs and Gd oxide. Moreover, we further found that the Gd oxide cone retained its structure, instead of forming a spherical particle when it moved outward from the CNC driven by a high temperature, indicating the high stability of the conical Gd oxide nanocrystals.